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                                 UNITED STATES
                       SECURITIES AND EXCHANGE COMMISSION
                             WASHINGTON, D.C. 20549
 
                                   FORM 10-K
 
[X] ANNUAL REPORT PURSUANT TO SECTION 13 OR 15(D) OF THE SECURITIES EXCHANGE ACT
    OF 1934
 
                       FOR THE FISCAL YEAR ENDED JUNE 30, 1996
 
                                       OR
 
[  ] TRANSITION REPORT PURSUANT TO SECTION 13 OR 15(D) OF THE SECURITIES
     EXCHANGE ACT OF 1934
 
                         COMMISSION FILE NUMBER 0-17999
 
                                IMMUNOGEN, INC.
             (EXACT NAME OF REGISTRANT AS SPECIFIED IN ITS CHARTER)
 

<TABLE>
<S>                                                <C>
                   MASSACHUSETTS                                       04-2726691
          (STATE OR OTHER JURISDICTION OF                           (I.R.S. EMPLOYER
          INCORPORATION OR ORGANIZATION)                           IDENTIFICATION NO.)
</TABLE>

 
                     148 SIDNEY STREET, CAMBRIDGE, MA 02139
          (ADDRESS OF PRINCIPAL EXECUTIVE OFFICES, INCLUDING ZIP CODE)
 
                                 (617) 661-9312
              (REGISTRANT'S TELEPHONE NUMBER, INCLUDING AREA CODE)
 
          SECURITIES REGISTERED PURSUANT TO SECTION 12(B) OF THE ACT:
                                      NONE
 
          SECURITIES REGISTERED PURSUANT TO SECTION 12(G) OF THE ACT:
                          COMMON STOCK, $.01 PAR VALUE
                                (TITLE OF CLASS)
 
     Indicate by check mark whether the registrant (1) has filed all reports
required to be filed by Section 13 or 15(d) of the Securities Exchange Act of
1934 during the preceding 12 months (or for such shorter period that the
registrant was required to file such reports,) and (2) has been subject to such
filing requirements for the past 90 days. Yes X No  _
 
     Aggregate market value, based upon the closing sale price of the shares as
reported by the Nasdaq National Market, of voting stock held by non-affiliates
at September 9, 1996: $61,230,984 (excludes shares held by Executive Officers,
Directors, and beneficial owners of more than 10% of the Company's Common
Stock). Exclusion of shares held by any person should not be construed to
indicate that such person possesses the power, direct or indirect, to direct or
cause the direction of management or policies of the registrant, or that such
person is controlled by or under common control with the registrant. Common
Stock outstanding at September 9, 1996: 16,959,827 shares.
 
     Indicate by check mark if disclosure of delinquent filers pursuant to Item
405 of Regulation S-K is not contained herein, and will not be contained, to the
best of registrant's knowledge, in definitive proxy or information statements
incorporated by reference in Part III of this Form 10-K or any amendment to this
Form 10-K. [X]
 
                      DOCUMENTS INCORPORATED BY REFERENCE
 
     Portions of the registrant's Definitive Proxy Statement for its 1996 Annual
Meeting of Shareholders are incorporated by reference into Part III of this
Report.
 
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                                     PART 1
 

ITEM 1.  BUSINESS
 
THE COMPANY
 
     ImmunoGen, Inc. ("ImmunoGen" or the "Company") develops pharmaceuticals,
primarily for the treatment of cancer. The Company's first technology
platform -- immunoconjugate technology -- uses highly potent, proprietary toxins
or drugs coupled to proprietary monoclonal antibodies for the targeted
eradication of tumor cells. The Company's lead product candidate, Oncolysin B,
is based on its blocked-ricin immunoconjugate technology and is now in a
pivotal, large-scale Phase III clinical trial. The Company also has developed a
new class of immunoconjugates using small-molecule drugs. Three small-drug
immunoconjugate product candidates are now in research and preclinical
development.
 
     Through its majority-owned subsidiary, Apoptosis Technology, Inc. ("ATI"),
the Company is developing additional technology platforms based on the
regulation of programmed cell death, or apoptosis. ATI is applying its
understanding of how apoptotic pathways are triggered in cells to identify
product candidates for the treatment of cancer and viral infections, two targets
where inhibition of apoptosis is recognized as an essential element of the
disease. ATI has identified several key proteins which play a role in the
regulation of apoptosis in cancer cells and viruses and, using these, has
developed proprietary screens with which to identify leads for drug development.
 
     The Company was organized in 1981 as a Massachusetts corporation.
 
OVERVIEW OF CANCER TREATMENT
 
     Cancer is a set of different diseases, each of which is characterized by
aberrations in cell growth, cell differentiation, apoptosis and chromosome
stability. The establishment and spread, or metastasis, of a malignant growth,
or tumor, is a function of its growth characteristics and its ability to
suppress or evade the body's normal defenses, including activation of the
cell-death program in transformed cells and surveillance and elimination of
these cells by the immune system. Eradication of malignant cells which can
metastasize to vital organs, leading to death, is central to the effective
treatment of cancer.
 
     Despite recent advances in diagnosis and treatment, cures in many cancers
continue to be elusive. A significant drawback to conventional anti-cancer
therapy is that hidden (occult) or residual disease often remains, which can
lead to relapse. Surgery may be used to remove primary masses of some solid
tumors; however, it cannot be used to remove occult disease, which may spread.
Conventional treatment with combination chemotherapy and radiation may not be
capable of eradicating disease because of inadequate potency at the tumor site,
the result of drug doses that must be limited because of side-effects to healthy
tissues. These agents attack cells nonspecifically, during cell division, and
their use damages other dividing cells such as bone marrow and epithelial cells
(e.g., hair follicles and the gastrointestinal lining). Further, exposure to
chemotherapy or radiation may trigger mechanisms within tumor cells which render
them multi-drug resistant, making repeat courses of therapy ineffective.
 
     Because of the non-specific toxicities, limited potency and resistance
associated with conventional anti-cancer therapies, a great need exists for new
therapeutic products. One way in which the Company is addressing this
therapeutic void is through applications of its immunoconjugate technology. By
using the targeting ability of a monoclonal antibody to direct cell-killing
agents to the tumor, more potent cytotoxic agents may be used, tumor-killing
activity increased and side-effects minimized. Further, use in immunoconjugates
of a cytotoxic agent with a mechanism of action different from any of the
conventional chemotherapeutic agents may help overcome tumor-cell resistance,
thereby improving the effectiveness of repeat courses of chemotherapy. The
Company believes that apoptosis technology being developed at its subsidiary,
ATI, offers a second potential approach to the creation of innovative
anti-cancer products. That technology may be used in the development of
anti-cancer agents that restore apoptotic function to tumor cells, triggering
cancer cells, in essence, to commit suicide.
 
                                        1

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IMMUNOCONJUGATE TECHNOLOGY
 
     Each of the Company's immunoconjugates consists of a monoclonal antibody
coupled to a cytotoxic (cell-killing) agent, known as an effector molecule. The
specificity of an antibody forms the basis for its use to deliver effector
molecules to disease sites. Antibodies are proteins produced by the immune
system in response to the presence of foreign substances in the body. A
particular antibody detects and binds to only one specific antigen, or marker.
Since cancer cells may have unique antigens on their surfaces, an antibody with
the correct specificity for those cells may be used as a targeting agent. When
such an antibody is coupled to a highly potent cytotoxic agent, forming an
immunoconjugate, tumor cells are killed while normal cells, even those in close
association with the tumor, can be spared.
 
     The Company believes its immunoconjugates possess the following potential
attributes which make them attractive as anti-cancer agents:
 
     Potency.  Highly potent effector molecules are linked to a targeting agent
and their high potency may thereby be harnessed for specific elimination of the
tumor;
 
     Specificity.  The targeting vehicle may be capable of differentiating
between cancerous tissue and normal tissue;
 
     Tolerable Side-Effects.  The specific delivery of highly potent effector
molecules to a tumor at low concentrations may yield a tolerable side-effect
profile and, consequently, a minimal disturbance of patients' quality of life
during treatment;
 
     Distinct Mechanism of Action.  An effector molecule which kills cells via a
different mechanism -- one not shared by conventional agents -- may provide a
complementary and additive cell-killing effect when used in conjunction with
conventional agents;
 
     Modular Components.  By varying targeting agents, each directed to a
different tumor type, and using different effector molecules, each with a
different mechanism of cell killing, the Company's immunoconjugate technology
platform can provide an entire family of products, each member of which is
designed to target a different type of cancer or to treat a different stage of
disease.
 
     The Company, in conjunction with researchers at the University of Bath in
the United Kingdom, has developed a proprietary method, called resurfacing,
which it uses to humanize the monoclonal antibodies used in its small-drug
immunoconjugates. Using the resurfacing technique, antibodies originally derived
from mice are engineered to appear human to the immune system. They therefore
are expected to be nonimmunogenic, allowing repeat dosing. The Company has
successfully humanized several monoclonal antibodies using resurfacing as well
as another antibody humanization technique, CDR grafting. In February 1995, the
Company entered into an agreement with Oxford Molecular Ltd. ("OML"), a research
and development firm which provides computer software for modeling protein
structure. Under the agreement, the Company may use OML's molecular modeling
software and OML receives rights to utilize the Company's antibody resurfacing
technology. See " -- Licenses -- Oxford Molecular Ltd."
 
     ImmunoGen has identified five monoclonal antibodies which it believes
possess the requisite characteristics for use in immunoconjugates. Each targets
a different type of tumor: B-cell cancers (certain lymphomas and leukemias),
small-cell lung cancer, myelogenous leukemias, T-cell cancers and colorectal
cancer. The Company also has developed two classes of effector
molecules -- blocked ricin and small-molecule drugs -- whose high potency and
other distinct characteristics have yielded products it believes are uniquely
suited to the treatment of different stages of cancer.
 
     The Company's blocked-ricin immunoconjugates are being developed to prevent
or substantially delay relapses of disease. Blocked-ricin immunoconjugates are
comprised of nonhuman proteins, however, and also may cause an immune response
in patients which limits the effectiveness of repeat doses. The Company
therefore is developing its small-drug immunoconjugates, which are not expected
to be immunogenic, for broad use as initial therapy and for long-term treatment
of cancer. The Company believes that use of its small-drug immunoconjugates will
be complementary to that of its blocked-ricin immunoconjugates.
 
                                        2

<PAGE>   4
 
               STATUS OF IMMUNOGEN'S PRODUCTS UNDER DEVELOPMENT:
              ONGOING CLINICAL AND PRECLINICAL DEVELOPMENT ONLY(1)
 

<TABLE>
<CAPTION>
           PRODUCT/APPLICATION                     CLINICAL SETTING              STATUS(2)
- -----------------------------------------    -----------------------------    ----------------
<S>                                          <C>                              <C>
Oncolysin Immunoconjugates:
Oncolysin B
  B-Cell Lymphomas                           After Autologous Bone Marrow     Phase III(3)
     and Leukemias                           Transplantation
                                             AIDS-Related Lymphoma            Phase I/II
                                             Synergy with Chemotherapy        Phase I/II
Small-Drug Immunoconjugates(4):
huC242-DM1
  Colorectal Cancer                          Tumor Debulking                  Research
huAnti-B4-DC1
  B-Cell Lymphomas                           Tumor Debulking                  IND Accepted(5)
huN901-DC1
  Small-Cell Lung Cancer                     Tumor Debulking                  Preclinical
</TABLE>

 
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(1) As part of a December 1994 restructuring, the Company focused its clinical
    resources on clinical trials of its first product, Oncolysin B, and stopped
    development of three other product candidates then in clinical trials:
    Oncolysin S, Oncolysin M and Oncolysin CD6. There will be no further
    development of these three products unless the Company enters into
    agreements with third parties to support their commercialization.
 
(2) For a description of Phase I-III clinical trials, see "-- Regulatory
    Issues -- Clinical Trials Process." Preclinical denotes work to refine
    product performance characteristics and studies relating to product
    composition, stability, scale-up, toxicity and efficacy to create a
    prototype formulation in preparation for submission of an Investigational
    New Drug Application ("IND") to the U.S. Food and Drug Administration
    ("FDA") to begin human clinical studies. Research denotes work up to and
    including bench-scale production of a formulation which meets the basic
    product performance characteristics established for the product.
 
(3) Pivotal study to support the Company's first Product License Application
    ("PLA").
 
(4) The Company's small-drug immunoconjugates will not enter human clinical
    trials until the Company secures collaboration funding from a third party or
    sufficient equity financing. The Company is actively seeking such funding or
    financing.
 
(5) In 1994, FDA accepted the Company's IND to begin human clinical testing of a
    product candidate comprising the original, mouse-derived antibody, anti-B4,
    linked to DC1. The Company intends to use its recently developed humanized
    version of the anti-B4 antibody in this product, which will require
    additional preclinical testing and the submission and acceptance of a new
    IND.
 
THE ONCOLYSINS
 
     Each of the Company's first product candidates, the Oncolysins, comprises
blocked ricin (a derivative of ricin, a potent, naturally occurring plant toxin
readily available from castor beans) linked to a monoclonal antibody to form an
immunoconjugate. The Company has conducted in vitro tests which compare the
potency of blocked-ricin immunoconjugates to the most commonly used conventional
chemotherapeutic agents, including adriamycin, methotrexate, actinomycin D,
vinblastine and mitomycin C. In these tests, the Company has demonstrated that
the same proportion of tumor cells is killed by antibody immunoconjugates of
blocked ricin at concentrations 1,000-times lower than those of the
chemotherapeutic drugs tested. Thus, due to the potency and specificity of the
immunotoxin, blocked-ricin immunoconjugates have the potential for greater tumor
destruction before reaching dose levels which cause unacceptable side-effects in
the patient.
 
                                        3

<PAGE>   5
 
     In addition to their high potency and specificity, the Company's
blocked-ricin immunoconjugates kill cells by a mechanism not shared by
conventional anti-cancer agents -- disruption of protein synthesis. This
complementary mechanism of action of blocked-ricin immunoconjugates makes them
particularly attractive agents for the treatment of the subclinical
(undetectable) residual disease which frequently remains after initial
chemotherapy. Residual disease may be resistant to conventional agents and often
regrows, causing relapsed disease. The Company believes that applications of the
Oncolysin products, to prevent or substantially delay cancer relapse, will be
complementary to those of its small-drug immunoconjugates, which are being
developed for use as initial therapy and for long-term treatment of cancer.
 
     ImmunoGen believes it is the only company with a proprietary position in an
effective derivative of intact ricin. Two United States patents relating to
blocked ricin and its use in antibody conjugates have issued to Dana-Farber
Cancer Institute ("Dana-Farber") and ImmunoGen has an exclusive worldwide
license for all applications of these patents. See "-- Patents, Trade Secrets
and Trademarks."
 
     Oncolysin B.  Oncolysin B, the Company's lead product candidate, is being
evaluated as a treatment for non-Hodgkin's B-cell lymphoma and B-cell leukemias.
Non-Hodgkin's lymphoma affects an estimated 45,000 new patients every year in
the United States; over 36,000 suffer from the B-cell variant. There are
approximately 19,000 deaths each year among B-cell lymphoma patients. There are
also approximately 12,500 new cases of acute and chronic lymphocytic leukemia in
the United States each year. Approximately 5,700 persons die of these B-cell
leukemias annually. Oncolysin B uses an antibody, anti-B4, to target blocked
ricin specifically to a marker, CD19, found on these B-cell malignancies.
 
     The Company currently is conducting clinical efficacy studies of Oncolysin
B in lymphoma patients following autologous bone marrow transplantation
("ABMT"), in patients with AIDS-related lymphoma and in other B-cell cancer
patients in combination with conventional chemotherapy. Based on the results of
clinical trials in which over 600 patients were treated in a wide range of
studies using Oncolysin B in different clinical settings, the Company believes
that the drug has an acceptable side-effect profile.
 
     Pivotal Phase III Trial in B-cell Lymphoma Subsequent to ABMT.  Based on
encouraging data from Phase I and Phase II studies in patients with minimal
residual disease, described below, the Company began enrollment of patients in a
pivotal, multicenter Phase III clinical trial of Oncolysin B in July 1993. This
clinical trial is measuring the effectiveness of the drug in preventing relapses
in lymphoma patients subsequent to ABMT. In the ABMT procedure, a portion of the
patient's bone marrow is removed and stored and a remission is then induced with
high-dose chemotherapy, with or without radiation. This intensive chemotherapy
and radiation obliterate the remaining bone marrow and the patient is then
salvaged by reinfusion of the previously stored marrow. Even if these patients
have no clinical evidence of disease subsequent to ABMT (minimal residual
disease), only 30-50% are expected to remain disease-free for two years because
of regrowth of occult, residual tumor.
 
     In contrast to the expected two-year rate of disease-free survival, the
disease-free survival rate at two years for the twelve patients in the Company's
Phase I trial of Oncolysin B after ABMT was over 90%. Further, as of July 1996,
with a median follow-up time of the patients in remission after transplant of
over four years, seven of twelve patients treated in that trial, or 58%, have
remained disease-free. In the Phase II trial of Oncolysin B after ABMT, the
two-year disease-free survival rate was over 60%. Thirty-one of 50 patients, or
62%, remain disease-free as of July 1996, with a median follow-up time of the
patients in post-transplant remission of over three years.
 
     The Company believes that the ABMT setting serves as a model for all B-cell
malignancy patients in remission. The Phase III trial measures the time to
relapse of patients in complete remission who receive Oncolysin B subsequent to
ABMT versus results for those who do not receive the drug subsequent to ABMT. It
is being conducted in conjunction with the Cancer and Leukemia Group B and the
Eastern Cooperative Oncology Group, both cooperative groups of the National
Cancer Institute ("NCI") of the National Institutes of Health. Currently, the
clinical trial is open to enrollment at 46 sites in the United States and
Canada. In June 1996, the Company and the NCI agreed that NCI will be
responsible for patient monitoring and generation of data for the clinical
trial.
 
                                        4

<PAGE>   6
 
     Enrollment in the Oncolysin B Phase III trial has been slower than
anticipated. The Company expects enrollment in the trial to continue into 1997
and does not expect to complete data analysis for submission to FDA for at least
18-24 months following the completion of enrollment. A number of factors make
the time to completion of the Phase III trial difficult to predict. These
include the rate of enrollment of patients into the trial, the number of
patients who are declared ineligible or who voluntarily drop out prior to
randomization (the time when patients are divided into two groups -- treatment
with Oncolysin B versus observation) and their time to relapse subsequent to
randomization.
 
     AIDS-related Lymphoma.  The Company has completed the treatment phase of a
Phase I clinical trial and a Phase I/II clinical trial of Oncolysin B as a
treatment for AIDS-related lymphoma. This is a devastating disease where
conventional chemotherapy has limited effectiveness and relapsed disease usually
is refractory to additional chemotherapy. A further problem in the treatment of
AIDS-related lymphoma is that the aggressive chemotherapy normally undertaken
for lymphoma patients may not be tolerated by patients with AIDS. Because
Oncolysin B does not suppress the bone marrow, the Company believes that AIDS
patients with compromised bone marrow function may tolerate Oncolysin B better
than they tolerate the myelosuppressive agents normally used to treat lymphoma.
 
     A total of 52 patients were treated in the Phase I trial and the Phase I/II
trial of Oncolysin B in AIDS-related lymphoma. The Company currently is
analyzing data from these trials. Preliminary results indicate that it may be
given safely with conventional chemotherapy to these patients. Observations from
the Phase I trial conducted by the NCI also suggest that Oncolysin B may cause
significant tumor shrinkage in relapsed patients.
 
     Oncolysin B Combined with Chemotherapy.  Encouraging laboratory and
preclinical results also led the Company to begin a Phase I/II trial of
Oncolysin B using the drug in combination with conventional chemotherapeutic
agents. Studies by the Company in mice which had been given B-cell tumors were
published in May 1996 in the medical journal, Blood. The data show that
combining Oncolysin B with the conventional chemotherapeutics adriamycin or
vincristine produced additive, or synergistic, anti-tumor effects -- superior to
those seen with Oncolysin B or the conventional agents alone. In addition, 50%
of mice given Oncolysin B followed by a combination of cyclophosphamide,
cisplatin and etoposide remained tumor-free for over 180 days and were
considered cured. Furthermore, ImmunoGen scientists observed enhanced cell
killing using Oncolysin B in combination with conventional agents on tumors
which were resistant to conventional drugs.
 
     The Phase I/II study testing the additive, or synergistic, effect of
Oncolysin B in combination with conventional chemotherapy began in September
1994 in lymphoma patients and enrollment is ongoing. Fourteen patients have been
treated as of July 1996. The Company believes that observations from this trial
demonstrate that Oncolysin B may be used safely in combination with
chemotherapy. Further, clinical responses have been seen in the trial; the
Company is now evaluating the efficacy of this combination approach.
 
     Other Oncolysin Product Candidates.  The Company has brought three other
blocked-ricin immunoconjugates into human clinical trials: Oncolysin S, an
immunoconjugate using the antibody, N901, which targets small-cell lung cancer;
Oncolysin M, designed to treat patients with acute myelogenous leukemia; and
Oncolysin CD6, for the treatment of T-cell malignancies and potentially for
acute organ transplant rejection.
 
     As part of its December 1994 restructuring, the Company focused its
clinical resources on studies of its first product, Oncolysin B, and stopped
development of these other product candidates. At the time, Oncolysin S had
entered Phase II testing and Oncolysin M and Oncolysin CD6 were in Phase I
studies. There will be no further development of these three products unless the
Company enters into agreements with third parties to support their
commercialization.
 
SMALL-MOLECULE DRUG IMMUNOCONJUGATES
 
     The Company has also developed a new class of immunoconjugates consisting
of monoclonal antibodies linked to highly potent small-molecule drugs that are
over 100 times more potent than existing chemothera-
 
                                        5

<PAGE>   7
 
peutic agents. The Company has conducted in vitro tests that it believes
demonstrate that immunoconjugates containing either of the small drugs, DC1 or
DM1, are more effective than current anti-cancer drugs at killing tumor cells.
The Company has developed derivatives of these drugs which allow them to be
attached to antibodies to target tumor cells and allow for their release at the
target site in a fully active form. In animal tumor models using immunodeficient
mice, the Company's small-drug immunoconjugates have shown therapeutic efficacy
and, in the case of DM1 immunoconjugates, complete cures at doses which do not
produce toxicity in normal tissues.
 
     The first compound, DC1, is one of a class of agents called DNA
groove-binding compounds. After binding to DNA, these agents attach covalently,
thereby interfering with cellular function and inducing the death of cells.
ImmunoGen has incorporated DC1 into several immunoconjugates. In June 1995, the
Company received a $750,000 Phase II Small Business Innovation Research ("SBIR")
grant from the NCI to help fund development of DC1-based immunoconjugates. The
award is for $375,000 annually for two years beginning June 1, 1995. In December
1995, the Company received a United States patent covering the use of DC1 in
immunoconjugates.
 
     The second small-drug compound, DM1, is a potent inhibitor of cell
division. It is derived from maytansine, a natural product. The Company has
obtained an exclusive license for use of maytansine in conjugated form and has
received two patents covering the use in conjugated form of small-drug
immunoconjugates derived from maytansine. See "-- Licenses -- Takeda Chemical
Industries, Ltd."
 
     The Company has conducted in vitro tests that it believes demonstrate that
immunoconjugates containing either DC1 or DM1 are more effective than current
anti-cancer drugs at killing tumor cells. This high degree of killing power is
important in debulking tumor masses. In animal tumor models using
immunodeficient mice, the Company's small-drug immunoconjugates have shown
therapeutic efficacy and, in the case of DM1 immunoconjugates, complete cures at
doses with no toxicity to normal tissues. Based on these data, the Company
believes its small-drug immunoconjugates may be a successful first-line cancer
therapy.
 
     The Company has humanized the antibodies it uses in its small-drug
immunoconjugates which target B-cell cancers and small-cell lung cancer using
two techniques: its proprietary resurfacing technology and CDR grafting.
Laboratory experiments have demonstrated that these humanized antibodies
maintain the same level of high-affinity binding as the original, mouse-derived
antibodies. In addition to these, the Company intends to humanize other
antibodies, including those which target solid tumors.
 
     huC242-DM1.  The Company has been testing an antibody, C242, provided by a
major pharmaceutical company, which targets colorectal cancer cells. The Company
believes this antibody possesses the requisite specificity which would make it a
useful targeting agent in a small-drug immunoconjugate: the antibody binds
strongly to 70% of colorectal cancers and has minimal cross-reactivity with
normal human tissues. The Company has linked C242 to its small-molecule drug,
DM1. Because DM1 is a small-molecule, nonprotein drug, it is not expected to be
immunogenic, which should allow for the administration of repeat courses of
therapy. The immunoconjugate therefore may be a suitable agent for tumor
debulking.
 
     In August 1996, the Company published the results of its in vitro and
animal studies of its C242-DM1 in the journal, Proceedings of the National
Academy of Sciences USA. These tests were done with the original, mouse-derived
C242 antibody linked to DM1. In the Company's studies, C242-DM1 completely
eradicated human colon tumors grown in mice at doses well below those which
produce toxic side-effects and the mice remained free of tumor and were
considered cured at 200 days. Significantly, the mice did not lose weight,
indicating the absence of toxic side-effects when treated with the drug.
 
     The Company also compared the effect on larger tumors of C242-DM1 with that
of 5-fluorouracil ("5-FU"), the chemotherapeutic most commonly used against
colorectal cancer. While C242-DM1-treated mice were cured, remaining tumor free
after 200 days, administration of 5-FU at its maximum tolerated dose only
slightly delayed tumor growth (for five days). The Company also compared the
effectiveness of C242-DM1 to that of 5-FU in mice which had been injected with
other types of colon tumors, those which express the protein recognized by the
C242 antibody on only 20-30% of their cells, as opposed to on all of their
 
                                        6

<PAGE>   8
 
cells, as in the previous experiments. There were complete tumor regressions of
five weeks in all of the animals treated with C242-DM1 and administration of a
second course of C242-DM1 extended the tumor-free period to nine weeks without
toxic side-effects, suggesting that use of multiple cycles of the Company's
immunoconjugate for treatment of colorectal cancer may be a feasible clinical
regimen. In contrast, these tumors grew large rapidly in the animals treated
with 5-FU.
 
     Upon the successful execution of a licensing agreement to obtain commercial
rights to the antibody, the Company expects to begin preclinical studies with a
humanized version conjugated to DM1. The Company will require additional funding
to complete preclinical development and clinical trials of this product. The
Company is actively seeking additional funding for this program; clinical
testing will not begin until such funding is secured.
 
     huAnti-B4-DC1.  This small-drug immunoconjugate consists of the same
antibody as in Oncolysin B (anti-B4) linked to the potent small-drug effector
molecule, DC1. The antibody has been humanized successfully, and the Company has
expressed it in cells at sufficiently high levels to be suitable for
manufacturing scale up. DC1 is a synthetic drug and, like DM1, is not expected
to be immunogenic. This should allow for the administration of repeat courses of
therapy. The immunoconjugate therefore may be a suitable agent for tumor
debulking.
 
     In September 1995, the Company published the results of its in vitro and
animal studies of this product candidate in the medical journal, Cancer
Research. These tests were done with the original, mouse-derived anti-B4
antibody linked to DC1. Anti-B4-DC1 increased mean survival time of mice given
human lymphoma tumors to 62 days as compared with 22-26 days if left untreated.
At their maximum doses, conventional chemotherapeutic drugs known to be
effective against this type of lymphoma tumor had only a modest effect on
survival, with mean survival times of 44 days for cyclophosphamide, 37 days for
vincristine, 32 days for etoposide and 28 days for doxorubicin. Further, over
60% of animals treated with Anti-B4-DC1 two to three days after being injected
with tumor cells survived long-term and were considered cured at 120 days.
 
     The Company submitted an IND to test Anti-B4-DC1 in relapsed lymphoma
patients in April 1994 and FDA accepted its application. The Company intends to
use a humanized version of the anti-B4 antibody in this product, however, which
will require additional preclinical testing and the submission and acceptance of
a new IND. The Company will require additional funding to complete preclinical
development and clinical trials of this product. The Company is actively seeking
additional funding for this program; clinical testing will not begin until such
financing is secured.
 
     huN901-DC1.  This product consists of a humanized version of the antibody
in Oncolysin S (N901), conjugated to DC1. This antibody also has been humanized
successfully, and the Company has expressed it in cells at sufficiently high
levels to be suitable for manufacturing scale up. As with the Company's other
small-drug immunoconjugates, huN901-DC1 is not expected to be immunogenic, which
should allow for the administration of repeat courses of therapy. The Company
does not intend to begin clinical testing of huN901-DC1 unless a corporate
partner is found to support further development and commercialization. The
Company expects to test huN901-DC1 as a tumor debulking agent in small-cell lung
cancer.
 
APOPTOSIS TECHNOLOGY
 
     Recent research has shown that human cells have an intrinsic "suicide
program" called apoptosis, one function of which is to destroy certain cells in
order to protect the body against disease. Defects in this program may allow
cancerous cells to proliferate or viruses to reproduce and spread. Inappropriate
signaling of apoptosis or the blocking of apoptotic signals also have emerged as
key factors in immunological, neurodegenerative, cardiovascular and other
diseases.
 
     Based on the belief that pharmacologic manipulation of apoptosis offers a
promising, novel approach to the treatment of disease, in January 1993 the
Company established ATI as a majority-owned subsidiary to pursue development of
therapeutics based on the regulation of apoptosis. Further, because cancer and
viral infections are two targets where inhibition of apoptosis is recognized as
an essential element of the disease, ATI is focusing its research in these two
areas. ATI has identified several key proteins which regulate
 
                                        7

<PAGE>   9
 
apoptosis in cancer cells and viruses and, using these, has developed
proprietary screens with which to identify leads for drug development.
 
     ATI's strategy has been to leverage existing knowledge in the field of
apoptosis by establishing, at the discovery stage, a series of key research
collaborations with academic scientists. To this end, ATI has established
collaborative ties with leading scientists at academic centers to complement its
own internal research team. ATI also intends to collaborate with pharmaceutical
companies both to use its screens with their libraries of existing therapeutic
compounds and to jointly develop small-molecule drugs based on the molecular
targets for apoptosis regulation that ATI has identified.
 
REGULATION OF APOPTOSIS AND CANCER
 
     In normal, healthy tissue, cell proliferation and cell death are intimately
linked, providing an efficient means for organisms to control unwanted or excess
cellular proliferation. Cancer cells have accumulated mutations, however, that
circumvent the normal regulation of proliferation and cell death through
apoptosis, leading to excess and uncontrolled cell growth. Tumor cells escape
apoptosis through the active suppression, or blockage, of stimuli which
otherwise would directly induce cell death. The Company believes that the
restoration of apoptosis in these cells by interference with such blockage of
the cell-death pathway therefore constitutes a promising approach to the
eradication of cancer.
 
     It is now well accepted that two key, distinct mechanisms that block
apoptosis in cancer cells are (i) the activation of "anti-death" genes, and (ii)
regulation of cellular survival signals. Some types of cancer cells may survive
due to the activation of anti-death genes while others may survive due to the
activation of specific survival signals.
 
     Activation of "anti-death" genes.  Bcl-2, the product of one of these
anti-death genes, is a member of a family of proteins that has been shown to
regulate apoptosis. Some of these proteins actively suppress apoptosis while
others trigger it. Interactions between those members of the Bcl-2 family which
promote apoptosis, and those which suppress it, regulate the cell-death program.
The Bcl-2 protein has been shown to block apoptosis in tumors and also to make
tumors resistant to chemotherapy. ATI believes that inhibition of the function
of Bcl-2 and other Bcl-2 family cell-death suppressors may restore a tumor
cell's susceptibility to apoptosis and will provide an innovative approach to
the development of anti-cancer therapeutics.
 
     ATI has discovered and characterized several proteins of the Bcl-2 family
that are potent promoters of cell death but whose function in tumor cells is
disrupted by cell-death suppressors such as Bcl-2. The first of these is the Bak
protein. Laboratory experiments published by ATI in the journal, Nature, in
April 1995 have shown that expression of Bak induces rapid and extensive
apoptosis, raising the possibility that it is directly involved in triggering
the cell-death program. The cloning and analysis of a second cell-death
promoter, Bik, discovered and characterized in collaboration with an ATI
consultant at St. Louis University Medical Center, were published in November
1995 in the journal, Oncogene. ATI also has discovered a third promoter of cell
death, Bbk. Each of these three promoters of apoptosis is the subject of a
separate application by ATI for a United States patent.
 
     Importantly, ATI scientists also have identified BH3, a domain present in
all three of these promoters of cell death, as well as in other proteins of the
Bcl-2 family. The Company believes that BH3 is both necessary and sufficient for
the triggering of cell death. ATI believes that the reason apoptosis is blocked
in tumor cells is due to the binding of Bcl-2 or other related cell-death
suppressor proteins to BH3. Identification of the BH3 domain therefore gives ATI
molecular information with which it can design screens for drugs which
counteract the influence of Bcl-2 and related suppressors of cell death, thereby
restoring apoptosis in tumor cells. The identification of BH3 was published by
ATI researchers in November 1995 in the European Molecular Biology Organization
Journal.
 
     Regulation of survival signals.  Cells also may suppress the cell-death
program through survival signals provided by growth factors such as insulin-like
growth factor 1 ("IGF-1"). Research by collaborators at the Imperial Cancer
Research Fund ("ICRF"), a leading cancer research foundation in the United
Kingdom, has shown that survival signals provided by IGF-1 help prevent cancer
cells from undergoing apoptosis. ATI has
 
                                        8

<PAGE>   10
 
established a research program with ICRF to elucidate the role of IGF-1 and
other survival factors in the cell-death pathway and to identify drugs that
mimic or disrupt the survival signal of IGF-1 in cells. See "--
Licenses -- Imperial Cancer Research Fund." The IGF-1 receptor ("IGF-1R") is
overexpressed on cells of many tumor types, such as breast and small-cell lung
carcinoma, and may be a critical requirement for the survival of tumor cells.
ATI therefore believes that the suppression of survival signals may induce
apoptosis in a great number of tumor types.
 
     In addition to ICRF, ATI also is collaborating in this area with
researchers at Thomas Jefferson University, Philadelphia, Pennsylvania, who have
shown that IGF-1R is required for cells to become cancerous and that blocking
IGF-1R expression can trigger apoptosis. In a collaboration with Thomas
Jefferson University, ATI has identified a domain on IGF-1R which is essential
for the transmission of the survival signal, thereby providing a molecular
target for drug design. Using this target, ATI and Thomas Jefferson University
are collaborating to design screens with which to identify therapeutic agents
that will induce apoptosis in tumor cells by blocking IGF-1R-mediated survival.
 
REGULATION OF APOPTOSIS AND VIRAL DISEASE
 
     Viral infection involves the binding of virus to host cells, viral entry
into those cells and, ultimately, the commandeering of the host cells'
reproductive machinery, which permits replication of the viral genome and the
generation of new virus particles. It is now generally recognized that host
cells use their ability to undergo apoptosis as an effective means of stopping
virus propagation: in many viruses, genes have evolved whose action is to block
apoptosis in the host cell and so permit viral replication. In vitro experiments
with several viruses have demonstrated that suppression of their anti-apoptotic
mechanisms may effectively limit viral infection.
 
     Certain viruses which infect human tissue carry genes whose products act as
functional homologs of Bcl-2. These genes have evolved in order to prevent
apoptosis in the host cell and so allow for viral replication. ATI, with
collaborators at St. Louis University Medical Center, has discovered novel
anti-death genes through study of these viruses. The Bcl-2-related protein, Bik,
for example, interacts with the products of some of these viral genes,
suggesting that one mechanism by which viruses survive is through crippling the
activity of Bik. ATI is using this information to search for antiviral drugs
which block the activity of cell-death suppressors, thereby restoring the
natural function of Bik and preventing viral replication.
 
     ATI, in collaboration with St. Louis University Medical Center, is also
focusing on the identification of the anti-apoptotic genes of human
cytomegalovirus (CMV), a herpes virus which often infects immunocompromised
individuals and which is life threatening in those afflicted with AIDS. CMV also
is a common post-transplantation complication. ATI is developing screens based
on anti-apoptotic CMV genes that will permit the identification of compounds
effective against the propagation of CMV.
 
     ATI has entered into an agreement giving it an option to a royalty-bearing
exclusive license to technology arising from its collaboration with St. Louis
University Medical Center.
 
BUSINESS STRATEGY
 
     ImmunoGen's objective is to be a leader in the development of novel
pharmaceuticals for the treatment of cancer and other human diseases. The
Company has developed a four-point business strategy to meet this objective:
 
     - ImmunoGen will focus its current clinical resources on studies of its
       first product, Oncolysin B. No further development of other Oncolysin
       products will occur unless the Company enters into agreements with third
       parties to support their commercialization;
 
     - ImmunoGen will continue the preclinical development of its small-drug
       immunoconjugates. The Company will aggressively pursue corporate partners
       and equity financing to support further clinical development and
       commercialization of its small-drug immunoconjugates;
 
                                        9

<PAGE>   11
 
     - ATI will leverage its existing knowledge in the field of apoptosis
       through its collaborations with academic scientists. The Company will
       continue to seek pharmaceutical partners to use ATI's screens with their
       own libraries of existing drugs and to jointly develop small-molecule
       drugs based on the molecular targets for the regulation of apoptosis that
       ATI has identified; and
 
     - The Company will seek to enter into marketing agreements for the sales
       and distribution of its products outside the United States. In many
       cases, the marketing of products within the United States may also be
       optimized by entering into such agreements with other companies and in
       these cases the Company will attempt to do so. It is anticipated that
       these marketing agreements will very likely be linked to the development
       agreements described above.
 
LICENSES
 
     The Company and ATI each have entered into license agreements with third
parties in order to acquire rights to materials and techniques which strengthen
their technology base, usually in exchange for a royalty on sales of products
which incorporate such materials and techniques. The principal licenses are:
 
  Licenses -- ImmunoGen, Inc.
 
     Dana-Farber.  Under a Research and License Agreement with Dana-Farber,
entered into in May 1981, the Company has provided funds for research projects
conducted by Dana-Farber involving the development of monoclonal antibodies,
toxins and drugs for conjugation and use as cancer therapeutics. Dana-Farber
retains ownership of the technology developed through such research and has
granted the Company a worldwide exclusive license to use such technology in the
Company's products, including the right to sublicense to others. Oncolysin B,
Oncolysin M, Oncolysin S, Oncolysin CD6 and several of the Company's other
products under development use Dana-Farber technology which has been licensed to
the Company under this agreement. In return for these rights, the Company agreed
to pay Dana-Farber royalties on product sales by ImmunoGen and its sublicensees.
 
     As of June 1996, the Company has satisfied all past and present funding
obligations under the Research and License Agreement. The Company has no further
funding obligations to Dana-Farber except for payment of royalties on future
sales of products which incorporate Dana-Farber technology.
 
     Oxford Molecular Ltd.  In March 1995, the Company entered into an agreement
with OML under which the two companies cross-licensed technology for the design
of monoclonal antibodies. Under the agreement, the Company has the right to use
OML's molecular modeling software in exchange for granting OML the right to use
the Company's proprietary resurfacing technology in the development of
monoclonal antibodies outside of the field of oncology and case-by-case rights
within oncology areas not under development at the Company. OML also will pay
the Company a percentage of the gross revenues it derives from the use of
resurfacing.
 
     Takeda Chemical Industries, Ltd.  A licensing agreement with Takeda
Chemical Industries, Ltd. ("Takeda"), executed in April 1994, gives the Company
a worldwide license to make, use and market immunoconjugate products containing
maytansine or its analogs. Under the agreement, Takeda will receive a royalty of
4% of ImmunoGen's annual net sales of such products and will have a right of
first refusal to market such products in most Asian and certain Middle Eastern
countries.
 
     In addition, Takeda will furnish to ImmunoGen, free of charge, up to 40
grams of maytansine for research and development during the term of the license
agreement. Subsequent supplies will either be furnished by Takeda on a cost plus
15% basis or produced by ImmunoGen with royalties payable to Takeda equal to 15%
of ImmunoGen's cost.
 
  Licenses -- Apoptosis Technology, Inc.
 
     Dana-Farber.  In January 1993, ATI and Dana-Farber entered into a licensing
agreement in the field of apoptosis under which ATI was granted an exclusive,
worldwide license, with full right to enter into sublicense agreements, for all
therapeutic applications and certain diagnostic applications arising from
existing inventions
 
                                       10

<PAGE>   12
 
and an option to license future inventions made in specified laboratories at
Dana-Farber. In consideration for this license, Dana-Farber received a minority
equity share in ATI, an initial license fee and a commitment by ATI to fund the
research activities of those laboratories at Dana-Farber from which ATI is to
derive rights under the agreement.
 
     In June 1996, ATI made its final payment under the license agreement. As of
June 1996, the Company has satisfied all past and present obligations under the
agreement. The Company has no further funding obligations to Dana-Farber except
for payment of royalties on future sales of products which incorporate
Dana-Farber technology.
 
     Imperial Cancer Research Fund and Imperial Cancer Research Technology
Ltd.  In July 1994, ATI entered into a three-year research and development
collaboration agreement in the field of apoptosis and cell proliferation with
the Imperial Cancer Research Fund ("ICRF") and the Imperial Cancer Research
Technology Ltd ("ICRT"), ICRF's technology transfer arm, under which ATI was
granted an exclusive, worldwide license, with full right to enter into
sublicense agreements, for all therapeutic and diagnostic applications arising
from existing inventions and an option to license future inventions within the
scope of the collaboration made in specified laboratories at ICRF. In
consideration for this license, ICRT received a minority equity interest in ATI
in addition to a commitment by ATI to fund ongoing research in those ICRF
laboratories from which ATI will derive rights under the agreement. ATI also
will give ICRT royalty payments on the sale of any products which incorporate
licensed ICRF technology. As of August 1996, no milestone or royalty payments
have been made under this agreement.
 
PATENTS, TRADEMARKS AND TRADE SECRETS
 
     ImmunoGen seeks patent protection for its proprietary technology and
products both in the United States and abroad. Nine patents have been issued to
Dana-Farber in the United States covering technology exclusively licensed by
ImmunoGen, along with several patents in Canada, Europe and Japan. Five of these
patents claim a variety of acid-labile and photo-labile conjugation technologies
as inventions; one claims a toxin immunoconjugate as an invention; one claims a
monoclonal antibody specific to small-cell lung carcinoma cells as an invention;
and two claim the use of blocked ricin in immunoconjugates. The Company has
received two United States patents on the use of maytansinoids in conjugated
form and one covering use of DC1 in immunoconjugates. In July 1996, the Company
also received a Notice of Allowance of a second United States patent on the use
of DC1 in immunoconjugates.
 
     Additional patent applications covering proprietary toxins, small-drug
derivatives, immunoconjugates and use of certain of these products for indicated
diseases have been submitted in the United States, Canada, various European
countries and Japan and are pending or awaiting examination. Work leading to
other patent applications is being performed by Company employees. In all such
cases, the Company will either be the assignee or owner of such patents or have
an exclusive license to the technology covered by the patents. No assurance can
be given, however, that the patent applications will issue as patents or that
any patents, if issued, will provide ImmunoGen with adequate protection against
competitors with respect to the covered products, technology or processes.
 
     Many of the processes and much of the know-how of importance to the
Company's technology are dependent upon the skills, knowledge and experience of
certain of the Company's key scientific and technical personnel, which skills,
knowledge and experience are not patentable. To protect its rights in these
areas, the Company requires all employees and most consultants, advisors and
collaborators to enter into confidentiality agreements with ImmunoGen. There can
be no assurance, however, that these agreements will provide meaningful
protection for the Company's trade secrets, know-how or other proprietary
information in the event of any unauthorized use or disclosure of such trade
secrets, know-how or proprietary information. Further, in the absence of patent
protection, the Company may be exposed to competitors who independently develop
substantially equivalent technology or otherwise gain access to the Company's
trade secrets, know-how or other proprietary information.
 
                                       11

<PAGE>   13
 
     The Company has exclusive rights to a large number of antibodies, most of
which are covered by Dana-Farber patents or patent applications in the United
States and abroad. In many cases, the underlying antigens also are patented.
 
COMPETITION
 
     The areas of product development on which the Company has focused are
highly competitive. ImmunoGen's competitors include major pharmaceutical and
chemical companies, specialized biotechnology firms, universities and research
institutions, many of which have greater resources than the Company. In
addition, many specialized biotechnology firms have formed collaborations with
large, established companies to support research, development and
commercialization of products that may be competitive with those of the Company.
Competitive factors within the cancer therapeutic market include the safety and
efficacy of products, the timing of regulatory approval and commercial
introduction, special regulatory designation of products, such as Orphan Drug
status, and the effectiveness of marketing and sales efforts.
 
     The Company's competitive position also depends on its ability to attract
and retain qualified personnel, develop effective proprietary products,
implement production and marketing plans, obtain patent protection and secure
sufficient capital resources.
 
     Competitors have developed products which currently are in clinical trials
for the treatment of B-cell lymphoma, a disease for which the Company has
designed Oncolysin B, its first product. The Company does not believe that any
of these products are being developed for the treatment of patients with
residual disease, to prevent or substantially delay relapse. Competitors have
initiated clinical trials of modified monoclonal antibodies for the treatment of
acute myelogenous leukemia, the disease for which Oncolysin M has been designed.
Competitors also have begun clinical trials of monoclonal antibody-based
products for the treatment of small-cell lung cancer which could compete with
Oncolysin S, although none are known by the Company to be directed at the
treatment of residual disease. The Company also is aware of competitors
developing monoclonal-antibody based products to purge cancer cells ex vivo,
which may compete with the ex vivo use of Oncolysin B or Oncolysin M.
 
     Technologies other than those involving monoclonal antibodies can be
applied to the treatment of cancer. The application of recombinant DNA
technology to develop potential products made of proteins that occur normally in
the body in small amounts has been underway for some time. Included in this
group are Interleukin-2, the interferons, tumor necrosis factor, colony
stimulating factors and a number of other biological response modifiers. The
Company believes that these products offer only limited competition for
ImmunoGen's anti-cancer products.
 
     Continuing development of conventional chemotherapeutics by large
pharmaceutical companies carries with it the potential for discovery of an agent
active against resistant forms of non-Hodgkin's lymphoma, acute and chronic
lymphocytic leukemia, acute myelogenous leukemia, small-cell lung cancer and
colorectal cancer -- the markets upon which the Company has focused. The Company
is not aware of the development of any experimental agents which are targeted
specifically for these markets, although many companies do not publish or
otherwise distribute information about their products under development.
 
     The technology of the Company's subsidiary, ATI, also is highly
competitive. Over the past several years, many companies and research
institutions, including academic laboratories, biotechnology companies and large
pharmaceutical firms have dedicated resources to apoptosis research. ATI is
expected to face competition from other biotechnological approaches as well as
more traditional, drug-based approaches to cancer and viral diseases. ATI will
experience competition from fully integrated pharmaceutical companies with
expertise in research and development, manufacturing and product
commercialization, and which have greater resources in these areas than ATI. The
Company also is aware of numerous development-stage companies that are exploring
new therapies for the same disease targets as ATI.
 
                                       12

<PAGE>   14
 
REGULATORY ISSUES
 
     ImmunoGen's products are regulated in the United States by FDA in
accordance with the Federal Food, Drug, and Cosmetic Act as well as the Public
Health Service Act. Parenteral monoclonal antibody products are most often
considered biologicals and therefore subject to regulation by the Center for
Biologics Evaluation and Research within FDA. Thus, human clinical trials of a
new product are conducted after submission of an IND application acceptable to
FDA and commercial marketing of that product may occur only after approval of a
PLA and an Establishment License Application ("ELA"). For biologicals such as
the Company's products, the PLA/ELA may be combined into a single Biologic
Application requesting product marketing approval. Manufacturing must be
performed in accordance with Good Manufacturing Practices ("GMPs").
 
     The regulatory issues that have potential impact on future marketing of
ImmunoGen products are summarized in the following paragraphs:
 
     Clinical Trials Process.  Before a pharmaceutical product may be sold in
the United States and other countries, clinical trials of the product must be
conducted and the results submitted to the appropriate regulatory agencies for
approval.
 
     In the United States, these clinical trial programs generally involve a
three-phase process. Typically, Phase I trials are conducted in healthy
volunteers to determine the early side-effect profile and the pattern of drug
distribution and metabolism. In Phase II, trials are conducted in groups of
patients afflicted with the target disease to determine preliminary efficacy and
optimal dosages and to expand the safety profile. In Phase III, large-scale
comparative trials are conducted in patients with the target disease to provide
sufficient data for the proof of efficacy and safety required by federal
regulatory agencies. In the case of drugs for cancer and other life-threatening
diseases, Phase I human testing often is performed in patients with advanced
disease rather than in healthy volunteers. Because these patients are already
afflicted with the target disease, it is possible for such studies to provide
results traditionally obtained in Phase II trials and they often are referred to
as Phase I/II studies.
 
     The Company also will be subject to widely varying foreign regulations
governing clinical trials and pharmaceutical sales. Whether or not FDA approval
has been obtained, approval of a product by the comparable regulatory
authorities of foreign countries must be obtained prior to the commencement of
marketing of the product in those countries. The approval process varies from
country to country and the time may be longer or shorter than that required for
FDA approval. The Company intends to rely on foreign licensees to obtain
regulatory approvals to market ImmunoGen products in foreign countries.
 
     Regulatory approval often takes a number of years and involves the
expenditure of substantial resources. Approval times also depend on a number of
factors, including the severity of the disease in question, the availability of
alternative treatments and the risks and benefits demonstrated in clinical
trials.
 
     Orphan Drug Designation.  The Orphan Drug Act of 1983 generally provides
incentives to manufacturers to undertake development and marketing of products
to treat relatively rare diseases or diseases affecting fewer than 200,000
persons in the United States at the time of application for Orphan Drug
designation. Orphan Drug designation has been granted for Oncolysin B, Oncolysin
S, Oncolysin M and Oncolysin CD6.
 
     ImmunoGen will continue to pursue this designation with respect to all of
its products intended for qualifying patient populations. A drug that receives
Orphan Drug designation and is the first product to receive FDA marketing
approval for its product claim is entitled to a seven-year exclusive marketing
period in the United States for that product claim. However, a drug that is
considered by FDA to be different from a particular Orphan Drug is not barred
from sale in the United States during such seven-year exclusive marketing
period.
 
     Treatment IND Status.  ImmunoGen may file for Treatment IND status for some
indications under provisions of the IND regulations revised in 1987. These
regulations apply to products for patients with serious or life-threatening
diseases and are intended to facilitate the availability of new products to
desperately ill patients after clinical trials have shown convincing evidence of
efficacy, but before general marketing approval
 
                                       13

<PAGE>   15
 
has been granted by FDA. Under these regulations, the Company anticipates that
it will be in a position to recover some of the costs of research, development
and manufacture of its products before marketing begins.
 
     Drugs for Life-Threatening Illnesses.  FDA regulations issued in October
1988 are intended to speed the availability of new therapies to desperately ill
patients. These procedures permit early consultation and commitment from FDA
regarding preclinical and clinical studies necessary to gain marketing approval.
Additional FDA regulations issued in December 1992 define opportunities for
accelerated review and approval of therapies for serious or life-threatening
illnesses. Guidelines for FDA accelerated review, articulated in November 1991
by the President's Council on Competitiveness, state that by 1994 such reviews
should be made within six months. The Company believes that certain applications
for its products qualify for accelerated review.
 
     Further, in March 1996, the President and the FDA Commissioner announced
four initiatives intended to provide cancer patients with faster access to new
cancer therapies. One of these initiatives states that the initial basis for
approval of anti-cancer agents to treat refractory, hard-to-treat cancer may be
objective evidence of response, rather than statistically improved disease-free
and/or overall survival, as has been common practice. The sponsor of a product
approved under this accelerated mechanism would be required to follow up with
further studies on clinical safety and effectiveness in larger groups of
patients.
 
     ImmunoGen believes that the opportunity may exist under this initiative to
obtain marketing approval for Oncolysin B prior to the completion of the Phase
III trial now under way.
 
RESEARCH AND DEVELOPMENT SPENDING
 
     During each of the three years ended June 30, 1994, 1995 and 1996 the
Company spent approximately $19.9 million, $16.8 million and $9.6 million,
respectively, on research and development activities. Most of these expenditures
were for Company-sponsored research and development.
 
EMPLOYEES
 
     As of June 30, 1996, the Company had 66 full-time employees, of whom 20
hold Ph.D. or M.D. degrees. The Company considers its relations with its
employees to be good. None of the Company's employees is covered by a collective
bargaining agreement. The Company has entered into confidentiality agreements
with all of its employees, members of the Scientific Advisory Board and other
consultants.
 
SCIENTIFIC ADVISORY BOARDS
 
  ImmunoGen, Inc.
 
     At June 30, 1996 the members of the Company's Scientific Advisory Board
were as follows:
 
     Baruj Benacerraf, M.D. Chairman of the Scientific Advisory Board;
President, Dana-Farber, Inc. and Fabyan Professor of Comparative Pathology,
Emeritus, Harvard University Medical School; 1980 Nobel Prize in Physiology or
Medicine.
 
     Emil Frei, M.D. Physician-in-Chief, Emeritus, and Chief, Division of Cancer
Pharmacology, Dana-Farber Cancer Institute and Richard and Susan Smith Professor
of Medicine, Harvard University Medical School; 1983 Kettering Prize.
 
     Stuart F. Schlossman, M.D. Professor of Medicine, Harvard University
Medical School; member of the National Academy of Sciences; Head of the Division
of Tumor Immunology of Dana-Farber Cancer Institute.
 
  Apoptosis Technology, Inc.
 
     Paul J. Anderson, M.D., Ph.D. Assistant Professor of Medicine, Harvard
University Medical School; Associate Rheumatologist, Brigham & Women's Hospital;
associated with Dana-Farber Cancer Institute since 1986. Dr. Anderson has
received numerous awards for excellence in research, and is a member of the
American Association of Immunologists and a Fellow of the American College of
Rheumatology.
 
                                       14

<PAGE>   16
 
     Walter A. Blattler, Ph.D. Senior Vice President, Research and Development,
ATI and Chairman of the ATI Scientific Advisory Board. Dr. Blattler received his
Ph.D. from the Swiss Federal Institute of Technology (ETH) in Zurich in 1978. He
was the founding scientist of ImmunoGen, Inc. and currently serves as
ImmunoGen's Senior Vice President for Research.
 
     Gerard Evan, Ph.D. Royal Society Napier Research Professor, Department of
Biochemistry, University College, London, and Principal Scientist and Head of
Biochemistry of the Cell Nucleus Laboratory, Imperial Cancer Research Fund,
London. Dr. Evan received his Ph.D. from the University of Cambridge and MRC
Laboratory of Molecular Biology and is an authority on the control of cellular
proliferation and programmed cell death in mammalian cells.
 
     Elliott D. Kieff, M.D., Ph.D. Professor of Medicine and Professor of
Microbiology and Molecular Genetics, Harvard University Medical School; Director
of Infectious Diseases, Brigham & Women's Hospital; Chairman of Virology at
Harvard University and an authority on herpes viruses.
 
     Stuart F. Schlossman, M.D. Professor of Medicine, Harvard University
Medical School; member of the National Academy of Sciences; Head of the Division
of Tumor Immunology of Dana-Farber Cancer Institute.
 

I
TEM 2.  PROPERTIES
 
     ImmunoGen leases approximately 52,700 square feet of laboratory and office
space at two locations in Cambridge, Massachusetts, of which approximately
30,800 square feet has been subleased by the Company since September 1, 1995.
This subleased space will increase to 37,700 square feet on or about October 1,
1996. The Company also leases 27,500 square feet of space in Norwood,
Massachusetts, which is currently the Company's pilot manufacturing facility.
The Company had also leased 47,000 square feet of space in Canton, Massachusetts
until January 1, 1996 when it assigned the lease on that facility to another
biotechnology company. The Canton facility had been idle since the Company
implemented its restructuring plan in December 1994. The Company believes that
the manufacturing portion of the Norwood facility, although not yet inspected by
FDA, complies with all applicable FDA Good Manufacturing Practice Regulations.
 

ITEM 3.  LEGAL PROCEEDINGS
 
     Not applicable.
 

ITEM 4.  SUBMISSION OF MATTERS TO A VOTE OF SECURITY HOLDERS
 
     A Special Meeting of Shareholders was held by the Company on June 6, 1996.
At the meeting, the following matter was voted upon:
 
        The proposal to amend and restate the Company's Restated Articles of
        Organization to increase the number of authorized shares of the
        Company's Common Stock from 20,000,000 to 30,000,000 shares was approved
        by a vote of 12,583,631 shares FOR the amendment and 458,336 shares
        AGAINST, 12,512 shares ABSTAINING, and 2,475,876 shares were NOT VOTED.
 
                                       15

<PAGE>   17
 

                                    PART II
 

ITEM 5.  MARKET FOR REGISTRANT'S COMMON EQUITY AND RELATED STOCKHOLDER MATTERS
 
     ImmunoGen's Common Stock is traded in the over-the-counter market and is
quoted on the Nasdaq National Market under the symbol IMGN. The table below sets
forth the high and low sale prices for ImmunoGen Common Stock for each of the
quarters indicated during the Company's last two fiscal years.
 

<TABLE>
<CAPTION>
                                                                             HIGH     LOW
                                                                             ----     ---
    <S>                                                                      <C>      <C>
    Fiscal Year 1996
      First Quarter........................................................  5 5/8    3 1/4
      Second Quarter.......................................................  3 7/16   1 5/16
      Third Quarter........................................................  3 13/16  2 1/16
      Fourth Quarter.......................................................  5 11/16  2 1/4
    Fiscal Year 1995
      First Quarter........................................................  5 1/8    2 5/8
      Second Quarter.......................................................  5        1 7/8
      Third Quarter........................................................  2 23/32  1 3/4
      Fourth Quarter.......................................................  4        1 3/4
</TABLE>

 
     As of August 27, 1996, there were approximately 799 holders of record of
the Company's Common Stock and, according to the Company's estimates,
approximately 10,000 beneficial owners of the Company's Common Stock.
 
     The Company has not paid any cash dividends on its Common Stock since its
inception and does not intend to pay any cash dividends in the foreseeable
future.
 

ITEM 6.  SELECTED FINANCIAL DATA


<TABLE>
     The following table sets forth consolidated financial data with respect to
the Company for each of the five years in the period ended June 30, 1996. The
information set forth below should be read in conjunction with "Management's
Discussion and Analysis of Financial Condition and Results of Operations" and
the consolidated financial statements and related notes included elsewhere in
this Form 10-K report.
 
<CAPTION>
                                                             YEAR ENDED JUNE 30,
                                        -------------------------------------------------------------
                                          1992         1993         1994         1995         1996
                                        ---------   ----------   ----------   ----------   ----------
                                                    (IN THOUSANDS, EXCEPT PER SHARE DATA)
<S>                                     <C>         <C>          <C>          <C>          <C>
Total revenues.......................   $   2,770   $    1,658   $      926   $      512   $      568
Total expenses.......................      18,074       20,274       24,606       20,363       17,111
Net loss.............................     (15,344)     (18,634)     (23,690)     (19,857)     (16,544)
Loss per share of common stock.......       (1.58)       (1.76)       (2.09)       (1.58)       (1.15)
Total assets.........................      62,036       46,458       38,384       17,046        8,506
Capital lease obligations,
  less current portion...............         551        1,212        3,338        2,331           37
Stockholders' equity.................      59,080       40,540       29,960       10,123        2,715
Weighted average shares
  outstanding........................   9,702,988   10,617,109   11,332,194   12,571,134   14,379,064
</TABLE>

 

ITEM 7.  MANAGEMENT'S DISCUSSION AND ANALYSIS OF FINANCIAL CONDITION AND RESULTS
OF OPERATIONS
 
OVERVIEW
 
     Since inception, ImmunoGen has been primarily engaged in research and
development of immunoconjugate products which the Company believes have
significant commercial potential as human therapeutics. The major sources of the
Company's working capital have been the proceeds of equity and convertible debt
financings, license fees and income earned on investment of those funds. The
Company expects no revenues to be derived from product sales for the foreseeable
future.
 
                                       16

<PAGE>   18
 
     In the past two fiscal years the Company has successfully reduced its
operating costs and obtained additional funds for working capital purposes. The
following is a summary of management actions taken during this period to reduce
operating costs. In December 1994, the Company implemented a restructuring plan,
which included halting operations at two of its facilities, reducing or
eliminating certain areas of research and focusing its clinical efforts on its
lead product. In addition, effective September 1, 1995, the Company subleased
approximately 82% of one of its Cambridge, Massachusetts facilities and leased
certain related equipment for a term which initially was to expire in February
1998. In July 1996, the Company signed an amendment to this sublease agreement,
increasing the subleased space from 82% to 100% of the facility and extending
the term of the sublease to February 1999 with options to further extend the
sublease term to February 2000. This amendment is expected to become effective
on or about October 1, 1996. Total net receipts under the amended sublease
agreement, which are credited to reduce operating expenses, are expected to
total approximately $2.3 million through February 1999, of which approximately
$498,000 was received by the Company in fiscal 1996.
 
     In a further cost reduction effort, the Company assigned its facility and
equipment leases related to one of its production facilities, located in Canton,
Massachusetts, to another biotechnology company, effective January 1, 1996. The
Company estimates its savings in monthly operating expenses from this
transaction to be approximately $140,000.
 
     The Company has been unprofitable since inception and expects to incur net
losses over the next several years, if it is able to raise sufficient working
capital to continue operations. The Company's cash resources at June 30, 1996
were approximately $2.8 million, and the Company continues actively to seek
additional capital. While the Company remains hopeful that it will be able to
consummate an additional financing transaction in the near term, no assurance
can be given that such financing will be available to the Company on acceptable
terms, if at all. If the Company is unable to obtain financing on acceptable
terms in order to maintain operations through the fiscal year, it could be
forced to curtail or discontinue its operations.
 
RESULTS OF OPERATIONS
 
     Revenues in fiscal 1994 and 1995 were derived principally from interest
income on the proceeds of the Company's equity offerings, with smaller amounts
of development revenues received under the Small Business Innovation Research
Program of the National Institutes of Health ("SBIR Program"). In 1996, revenues
were derived principally under the SBIR Program, with smaller amounts received
as interest income and as licensing fees pursuant to two licensing agreements.
In addition, in all three years revenues included a gain on sale of assets which
resulted from a sale/leaseback agreement for equipment at the Canton facility
executed in fiscal 1994 which had been deferred and recorded as other income
through December 1995.
 
     Interest income decreased 45% from approximately $840,000 in fiscal 1994 to
approximately $460,000 in fiscal 1995 and then decreased 73% to approximately
$124,000 in fiscal 1996. These decreases are attributable to the lower cash
balances available for investment between these periods. In fiscal 1996, the
decrease in interest earned on cash available for investment was partially
offset by interest earned on amounts due from the assignee of its Canton
production facility.
 
     The Company's total expenses decreased 17% from approximately $24.6 million
in fiscal 1994 to approximately $20.4 million in fiscal 1995 and then decreased
16% to approximately $17.1 million in fiscal 1996. Exclusive of the one-time
charge to dispose of the Canton assets (approximately $2.0 million) and the
financing costs associated with the issuances of debt securities which were
charged to interest expense (approximately $3.5 million), the decrease between
fiscal 1995 and 1996 operating expenses would have been substantially greater.
 
     Research and development costs constituted the primary component of the
Company's total expenses (81%, 83% and 56% in fiscal 1994, 1995 and 1996,
respectively), decreasing from approximately $19.9 million in fiscal 1994 to
approximately $16.9 million in fiscal 1995, and then decreasing to approximately
$9.6 million in fiscal 1996. The 16% decrease between fiscal 1994 and fiscal
1995 is the result of the Company's restructuring plan implemented in December
1994, offset in part by increased costs associated with the Company's 72%-owned
subsidiary, Apoptosis Technology, Inc. ("ATI"), and increased non-cash
depreciation
 
                                       17

<PAGE>   19
 
and amortization charges associated with the capital expenditures made in prior
periods. A planned substantial reduction in raw materials purchases in fiscal
1995 also contributed to the decrease in expenses. The 43% decrease between
fiscal 1995 and 1996 is a consequence of the Company's continuing cost reduction
efforts begun in calendar year 1994.
 
     General and administrative expenses decreased 33% from approximately $4.5
million in fiscal 1994 to approximately $3.0 million in fiscal 1995, and then
decreased 42% to approximately $1.8 million in fiscal 1996. The decrease from
fiscal 1994 to fiscal 1995 represented savings associated with the restructuring
plan and reductions in management and administrative staff in the second and
third quarters of calendar 1994, offset in part by the restructuring charges
incurred. The decrease from fiscal 1995 to fiscal 1996 is a result of the
Company's continuing cost reduction efforts begun in calendar year 1994.
 
     Interest expense increased 193% from approximately $174,000 in fiscal 1994
to approximately $510,000 in fiscal 1995, and then increased 629% to
approximately $3.7 million in fiscal 1996. The increase between fiscal 1994 and
1995 was due to the utilization of capital lease arrangements to finance certain
equipment and leasehold improvements at its Canton production facility. The
increase between fiscal 1995 and fiscal 1996 was due primarily to the
substantial costs incurred in conjunction with the issuances of convertible
debentures, including a non-cash charge to interest of approximately $2.7
million related to warrants issued in connection with the Company's fiscal 1996
issuance of convertible debentures, as well as $511,000 of cash fees paid to
third parties in connection with its debenture financings.
 
LIQUIDITY AND CAPITAL RESOURCES
 
     Since July 1, 1993, the Company has financed its operating deficit of
approximately $60.1 million from various sources, including proceeds from its
fiscal 1994 public offering, issuances in fiscal 1996 of convertible debentures,
amounts received pursuant to its fiscal 1996 assignment of leases and from the
exercise of stock options.
 
     In February 1994, the Company sold in a public offering 2,012,500 shares of
its Common Stock. Net proceeds to the Company amounted to $13.2 million. In
March 1994, the Company executed a sale/leaseback agreement to finance
approximately $4.0 million of equipment at the Canton facility. At June 30,
1994, all monies under this agreement had been received. The transaction
included warrants to purchase 26,738 shares of common stock which expire in
April 1999.
 
     Effective January 1, 1996, the Company assigned its facility and equipment
leases on one of its production facilities, located in Canton, Massachusetts, to
another biotechnology company. Under the terms of the agreements, the assignee
has assumed all payment obligations under the leases and, in addition, will make
cash payments to the Company totaling approximately $2.4 million at various
dates to July 1999, of which approximately $786,000 had been received through
June 30, 1996.
 
     In August 1995, the Company issued $3.6 million of 7% subordinated
convertible debentures in a private placement to a small number of overseas
investors. As of March 31, 1996, all of these debentures plus accrued interest
thereon had been converted into 2,753,269 shares of the Company's Common Stock.
 
     In March 1996, the Company issued $5.0 million of 9% convertible debentures
to a single investor in a private placement. This amount was received by the
Company in two installments -- $2.5 million was received in March 1996 and the
remaining $2.5 million was received in June 1996. As of June 30, 1996, the first
installment, together with accrued interest thereon, was converted into
1,018,000 shares of the Company's $.01 par value per share Common Stock. In
connection with that conversion, warrants to purchase 509,000 and 500,000 shares
of the Company's Common Stock were issued to the debenture holder. These
warrants have exercise prices of $4.00 and $6.00, respectively, and expire in
2001. Also in connection with the issuance of the 9% convertible debentures, the
Company issued warrants to purchase a total of 250,000 shares of the Company's
Common Stock to a third party as a finder's fee. These warrants have an exercise
price of $3.105 and expire in 2003.
 
     On June 28, 1996, ImmunoGen and its subsidiary, ATI, satisfied obligations
to Dana-Farber Cancer Institute ("Dana-Farber") totaling approximately $1.3
million by issuing to Dana-Farber a convertible
 
                                       18

<PAGE>   20
 
debenture (see Note E to the Consolidated Financial Statements). Pursuant to the
settlement agreement, the Company issued to Dana-Farber an 11.5% $1,312,943
debenture convertible into shares of ImmunoGen Common Stock at a conversion
price based on the market price for the Company's Common Stock at the time of
conversion. Shortly thereafter, the Company filed a registration statement under
the Securities Act of 1933 to register the resale by Dana-Farber of the Common
Stock issuable upon conversion of the debenture, and in July 1996 the debenture
and accrued interest thereon were converted into 351,662 shares of the Company's
Common Stock.
 
     Although in the period since July 1, 1993 approximately $8.1 million was
expended on property and equipment, no significant amounts were expended on
property and equipment in fiscal 1996 or are expected to be expended on property
and equipment in fiscal 1997.
 
     ImmunoGen was committed under its agreements with ATI to provide ATI with
$3.0 million in research and development services and $2.0 million in cash
equity contributions over a three-year period. At June 30, 1995 these
obligations had been fulfilled by the Company. ImmunoGen has also agreed to
obtain or furnish an additional $3.0 million in equity for ATI on such terms and
conditions as may be mutually agreed to by ATI and the providers of such equity.
As of June 30, 1996, amounts owed by ATI to ImmunoGen approximated $10.0
million. The Company intends to convert a majority of this amount into equity of
ATI, thereby satisfying the agreement to provide an additional $3.0 million in
equity. The Company anticipates that approximately $452,000 of additional
funding will be required by ATI during fiscal year 1997 to satisfy certain
existing contractual obligations.
 
     The Company anticipates that its existing capital resources will enable it
to maintain its current and planned operations through October 1996. Because of
its continuing losses from operations, the Company will be required to obtain
additional capital to satisfy its ongoing capital needs and to continue its
operations. Although management continues to pursue additional funding
arrangements, no assurance can be given that such financing will in fact be
available to the Company. If the Company is unable to obtain financing on
acceptable terms in order to maintain operations through the fiscal year, it
could be forced to curtail or discontinue its operations.
 
CERTAIN FACTS THAT MAY AFFECT FUTURE RESULTS OF OPERATIONS
 
     This report contains certain forward-looking statements as that term is
defined in the Private Securities Litigation Reform Act of 1995. Such statements
are based on management's current expectations and are subject to a number of
factors and uncertainties which could cause actual results to differ materially
from those described in the forward-looking statements. The Company cautions
investors that there can be no assurance that actual results or business
conditions will not differ materially from those projected or suggested in such
forward-looking statements as a result of various factors, including, but not
limited to, the following: the early stage of the Company's initial product
development and lack of product revenues; the Company's history of operating
losses and accumulated deficit; the Company's limited financial resources and
uncertainty as to the availability of additional capital to fund its development
on acceptable terms, if at all; the Company's lack of commercial manufacturing
experience and commercial sales, distribution and marketing capabilities;
reliance on suppliers of ricin and antibodies necessary for production of the
products and technologies; the potential development by competitors of competing
products and technologies; the Company's dependence on potential collaborative
partners, and the lack of assurance that the Company will receive any funding
under such relationships to develop and maintain strategic alliances; the lack
of assurance regarding patent and other protection for the Company's proprietary
technology; governmental regulation of the Company's activities, facilities,
products and personnel; the dependence on key personnel; uncertainties as to the
extent of reimbursement for the costs of the Company's potential products and
related treatment by government and private health insurers and other
organizations; the potential adverse impact of government-directed health care
reform; the risk of product liability claims; and general economic conditions.
As a result, the Company's future development efforts involve a high degree of
risk. For further information, refer to the more specific risks and
uncertainties discussed throughout this Annual Report on Form 10-K.
 
                                       19

<PAGE>   21
 

I
TEM 8.  FINANCIAL STATEMENTS
 
                   INDEX TO CONSOLIDATED FINANCIAL STATEMENTS
 

<TABLE>
<CAPTION>
                                                                                        PAGE
                                                                                        ----
<S>                                                                                     <C>
Report of Independent Accountants.....................................................    21
Consolidated Financial Statements:
  Consolidated Balance Sheets at June 30, 1995 and 1996...............................    22
  Consolidated Statements of Operations for the Years
     Ended June 30, 1994, 1995 and 1996...............................................    23
  Consolidated Statements of Stockholders' Equity
     for the Years Ended June 30 1994, 1995 and 1996..................................    24
  Consolidated Statements of Cash Flows for the Years
     Ended June 30 1994, 1995 and 1996................................................    25
  Notes to Consolidated Financial Statements..........................................    26

</TABLE>

 
                                       20

<PAGE>   22
 

                       REPORT OF INDEPENDENT ACCOUNTANTS
 
To the Board of Directors and Shareholders of ImmunoGen, Inc.:
 
     We have audited the accompanying consolidated balance sheets of ImmunoGen,
Inc. as of June 30, 1995 and 1996, and the related consolidated statements of
operations, stockholders' equity and cash flows for each of the three years in
the period ended June 30, 1996. These financial statements are the
responsibility of the Company's management. Our responsibility is to express an
opinion on these financial statements based on our audits.
 
     We conducted our audits in accordance with generally accepted auditing
standards. These standards require that we plan and perform the audit to obtain
reasonable assurance about whether the financial statements are free of material
misstatement. An audit includes examining, on a test basis, evidence supporting
the amounts and disclosures in the financial statements. An audit also includes
assessing the accounting principles used and significant estimates made by
management, as well as evaluating the overall financial statement presentation.
We believe that our audits provide a reasonable basis for our opinion.
 
     In our opinion, the financial statements referred to above present fairly,
in all material respects, the consolidated financial position of ImmunoGen, Inc.
as of June 30, 1995 and 1996 and the consolidated results of its operations and
its cash flows for each of the three years in the period ended June 30, 1996, in
conformity with generally accepted accounting principles.
 
     The accompanying financial statements have been prepared assuming that the
Company will continue as a going concern. As discussed in Note A, the Company
has suffered recurring losses from operations, at June 30, 1996 the Company has
cash resources of $2.8 million, which management anticipates is sufficient to
maintain current and planned operations only through October 1996 and,
therefore, requires significant additional financing. These factors raise
substantial doubt about the Company's ability to continue as a going concern.
Management's plans in regard to these matters are also described in Note A. The
financial statements do not include any adjustments that might result from the
outcome of this uncertainty.
 
                                                        COOPERS & LYBRAND L.L.P.
 
Boston, Massachusetts
 
August 28, 1996

 
                                       21

<PAGE>   23
 
                                IMMUNOGEN, INC.
 
                          CONSOLIDATED BALANCE SHEETS
                          AS OF JUNE 30, 1995 AND 1996
 

<TABLE>
<CAPTION>
                                                                           JUNE 30,
                                                                -------------------------------
                                                                    1995              1996
                                                                -------------     -------------
<S>                                                             <C>               <C>
ASSETS
Cash and cash equivalents.....................................  $   3,047,236     $   2,796,636
Prepaids and other current assets.............................        293,852           163,280
                                                                -------------     -------------
     Total current assets.....................................      3,341,088         2,959,916
                                                                -------------     -------------
Property and equipment, net of accumulated depreciation.......     13,621,383         4,163,416
Note receivable...............................................       --               1,338,929
Other assets..................................................         83,700            43,700
                                                                -------------     -------------
          Total assets........................................  $  17,046,171     $   8,505,961
                                                                 ============      ============
LIABILITIES AND STOCKHOLDERS' EQUITY
Accounts payable..............................................      2,229,003           733,446
Accrued compensation..........................................        397,153           233,515
Other accrued liabilities.....................................        898,073           832,573
Current portion of capital lease obligations..................        942,749           141,533
                                                                -------------     -------------
     Total current liabilities................................      4,466,978         1,941,067
                                                                -------------     -------------
Capital lease obligations.....................................      2,330,680            37,068
Convertible debentures........................................       --               3,812,943
Other non-current liabilities.................................        125,354          --
Commitments (Notes H and I)
Redeemable convertible preferred stock, $.01 par value;
  authorized 277,080 shares; none issued......................       --                --
Stockholders' equity:
  Common stock, $.01 par value; authorized 20,000,000 and
  30,000,000 as of June 30, 1995 and 1996, respectively;
  issued and outstanding 12,578,606 and 16,599,855 shares as
  of June 30, 1995 and 1996, respectively.....................        125,786           165,999
  Additional paid-in capital..................................    118,988,736       128,084,708
                                                                -------------     -------------
                                                                  119,114,522       128,250,707
  Accumulated deficit.........................................   (108,991,363)     (125,535,824)
                                                                -------------     -------------
     Total stockholders' equity...............................     10,123,159         2,714,883
                                                                -------------     -------------
          Total liabilities and stockholders' equity..........  $  17,046,171     $   8,505,961
                                                                 ============      ============
</TABLE>

 
    The accompanying notes are an integral part of the financial statements.
 
                                       22

<PAGE>   24
 
                                IMMUNOGEN, INC.
 
                     CONSOLIDATED STATEMENTS OF OPERATIONS
                FOR THE YEARS ENDED JUNE 30, 1994, 1995 AND 1996
 

<TABLE>
<CAPTION>
                                                                      JUNE 30,
                                                   ----------------------------------------------
                                                       1994             1995             1996
                                                   ------------     ------------     ------------
<S>                                                <C>              <C>              <C>
Revenues:
  Development fees...............................  $     74,700                      $    398,289
  Interest.......................................       839,005     $    459,293          124,208
  Licensing......................................       --               --                18,070
  Other..........................................        12,504           52,571           27,856
                                                   ------------     ------------     ------------
          Total revenues.........................       926,209          511,864          568,423
                                                   ------------     ------------     ------------
Expenses:
  Research and development.......................    19,929,474       16,819,082        9,622,132
  General and administrative.....................     4,502,259        3,034,087        1,769,414
  Interest.......................................       173,867          509,700        3,718,218
  Loss on disposal of assets.....................       --               --             2,001,480
                                                   ------------     ------------     ------------
          Total expenses.........................    24,605,600       20,362,869       17,111,244
                                                   ------------     ------------     ------------
Loss before income taxes.........................   (23,679,391)     (19,851,005)     (16,542,821)
Income tax expense...............................        11,075            6,063            1,640
                                                   ------------     ------------     ------------
Net loss.........................................  $(23,690,466)    $(19,857,068)    $(16,544,461)
                                                    ===========      ===========      ===========
Loss per common share............................  $      (2.09)    $      (1.58)    $      (1.15)
                                                    ===========      ===========      ===========
Shares used in computing loss per share
  amounts........................................    11,332,194       12,571,134       14,379,064
                                                    ===========      ===========      ===========
</TABLE>

 
    The accompanying notes are an integral part of the financial statements.
 
                                       23

<PAGE>   25
 
                                IMMUNOGEN, INC.
 
                CONSOLIDATED STATEMENTS OF STOCKHOLDERS' EQUITY
                FOR THE YEARS ENDED JUNE 30, 1994, 1995 AND 1996
 

<TABLE>
<CAPTION>
                                                 COMMON STOCK
                                   ----------------------------------------
                                                                ADDITIONAL                           TOTAL
                                                                 PAID-IN         ACCUMULATED      STOCKHOLDERS'
                                     SHARES        AMOUNT        CAPITAL           DEFICIT           EQUITY
                                   -----------    --------     ------------     -------------     ------------
<S>                                <C>            <C>          <C>              <C>               <C>
Balance at June 30, 1993.........   10,498,793    $104,988     $105,878,986     $ (65,443,829)    $ 40,540,145
                                    ----------    --------     ------------     -------------     ------------
  Issuance of common stock.......    2,055,938      20,559       13,012,864          --             13,033,423
  Issuance of common stock
    warrants.....................      --            --              76,738          --                 76,738
  Net loss.......................      --            --             --            (23,690,466)     (23,690,466)
                                    ----------    --------     ------------     -------------     ------------
Balance at June 30, 1994.........   12,554,731     125,547      118,968,588       (89,134,295)      29,959,840
                                    ----------    --------     ------------     -------------     ------------
  Stock options excercised.......       23,875         239           20,148          --                 20,387
  Net loss.......................      --            --             --            (19,857,068)     (19,857,068)
                                    ----------    --------     ------------     -------------     ------------
Balance at June 30, 1995.........   12,578,606     125,786      118,988,736      (108,991,363)    $ 10,123,159
                                    ----------    --------     ------------     -------------     ------------
  Stock options excercised.......      168,500       1,685          120,900          --                122,585
  Conversion of convertible
    debentures...................    3,852,749      38,528        6,281,587          --              6,320,115
  Issuance of common stock
    warrants.....................      --            --           2,693,485          --              2,693,485
  Net loss.......................      --            --             --            (16,544,461)     (16,544,461)
                                    ----------    --------     ------------     -------------     ------------
Balance at June 30, 1996.........   16,599,855    $165,999     $128,084,708     $(125,535,824)    $  2,714,883
                                    ==========    ========     ============     =============     ============
</TABLE>

 
    The accompanying notes are an integral part of the financial statements.
 
                                       24

<PAGE>   26
 
                                IMMUNOGEN, INC.
 
                     CONSOLIDATED STATEMENTS OF CASH FLOWS
                FOR THE YEARS ENDED JUNE 30, 1994, 1995 AND 1996
 

<TABLE>
<CAPTION>
                                                                                  JUNE 30,
                                                                 ------------------------------------------
                                                                     1994           1995           1996
                                                                 ------------   ------------   ------------
<S>                                                              <C>            <C>            <C>
Cash flows from operating activities:
  Net loss.....................................................  $(23,690,466)  $(19,857,068)  $(16,544,461)
  Adjustments to reconcile net loss to net cash
    used for operating activities:
    Depreciation and amortization..............................     2,031,477      3,350,685      2,516,231
    Loss on disposal of facility...............................         4,888        (15,630)     2,001,480
    Amortization of discount on convertible
      debentures charged to interest expense...................       --             --           3,019,676
    Amortization of debt issuance costs........................       --             --             511,000
    Other......................................................       --             --              25,674
    Change in operating assets and liabilities:
      Other current assets.....................................        18,988        335,957        267,168
      Note receivable..........................................       --             --             (48,395)
      Other assets.............................................       392,015        --             --
      Accounts payable.........................................      (566,100)        19,852       (288,690)
      Accrued compensation.....................................       531,073       (619,941)      (163,638)
      Accrued construction costs...............................      (616,816)       --             --
      Other accrued liabilities................................       176,728         48,275         98,777
      Other non-current liabilities............................       250,709        --             (27,856)
                                                                 ------------   ------------   ------------
    Net cash used for operating activities.....................   (21,467,504)   (16,737,870)    (8,633,034)
                                                                 ------------   ------------   ------------
Cash flows from investing activities:
  Purchase of property and equipment...........................    (7,628,278)      (477,288)       (23,608)
  Proceeds from sale/maturity of marketable securities.........    40,967,462     30,505,763        --
  Purchase of marketable securities............................   (35,685,475)   (10,925,635)       --
                                                                 ------------   ------------   ------------
    Net cash (used for) provided by investing activities.......    (2,346,291)    19,102,840        (23,608)
                                                                 ------------   ------------   ------------
Cash flows from financing activities:
  Proceeds from convertible debentures.........................       --             --           8,600,000
  Debt issuance costs..........................................       --             --            (511,000)
  Stock issuances, net.........................................    13,033,423         20,387        122,585
  Proceeds from sale/leaseback transactions....................     4,015,330        --             --
  Principal payments on capital lease obligations..............    (1,197,999)      (910,510)      (455,543)
  Proceeds from assignment of lease............................       --             --             650,000
                                                                 ------------   ------------   ------------
    Net cash provided by (used for) financing activities.......    15,850,754       (890,123)     8,406,042
                                                                 ------------   ------------   ------------
Net change in cash and cash equivalents........................    (7,963,041)     1,474,847       (250,600)
                                                                 ------------   ------------   ------------
Cash and cash equivalents, beginning balance...................     9,535,430      1,572,389      3,047,236
                                                                 ------------   ------------   ------------
Cash and cash equivalents, ending balance......................  $  1,572,389   $  3,047,236   $  2,796,636
                                                                 ============   ============   ============
Supplemental disclosure of cash flow information:
  Cash paid for interest.......................................  $    156,669   $    513,635   $    684,325
                                                                 ============   ============   ============
  Cash paid (refunded) for income taxes........................  $     12,310   $     (4,390)  $      5,000
                                                                 ============   ============   ============
Supplemental disclosure of noncash financing activities:
  Conversion of convertible debentures.........................  $    --        $    --        $  6,212,164
                                                                 ============   ============   ============
  Conversion of accounts payable to 11.5% convertible
    debenture..................................................  $    --        $    --        $  1,312,943
                                                                 ============   ============   ============
  Assignment of capital lease obligations......................  $    --        $    --        $  2,639,285
                                                                 ============   ============   ============
  Note receivable issued in relation to assignment of lease....  $    --        $    --        $  1,338,929
                                                                 ============   ============   ============
</TABLE>

 
    The accompanying notes are an integral part of the financial statements.
 
                                       25

<PAGE>   27
 
                                IMMUNOGEN, INC.
 
                   NOTES TO CONSOLIDATED FINANCIAL STATEMENTS
 
A. NATURE OF BUSINESS AND PLAN OF OPERATION:
 
     ImmunoGen, Inc. ("the Company") was incorporated in Massachusetts on March
27, 1981. The Company was formed to develop, produce and market commercial
cancer and other pharmaceuticals based on molecular immunology. The Company
continues research and development of its various products, and expects no
revenues to be derived from product sales for the foreseeable future.
 
     The Company has been unprofitable since inception and expects to incur net
losses over the next several years. The Company's cash resources at June 30,
1996 were approximately $2.8 million, and the Company continues actively to seek
additional capital by pursuing one or more financing transactions and/or
strategic partnering arrangements.
 
     In the past two fiscal years the Company has successfully reduced its
operating costs and obtained additional funds for working capital purposes. The
following is a summary of management actions during this period. In December
1994 the Company implemented a restructuring plan, which included halting
operations at two of its facilities, reducing or eliminating certain areas of
research and focusing its clinical efforts on its lead product. In addition,
effective September 1, 1995, the Company subleased approximately 82% of one of
its Cambridge, Massachusetts facilities and leased certain related equipment for
a term which initially was to expire in February 1998. In July 1996, the Company
signed an amendment to this sublease agreement, increasing the subleased space
from 82% to 100% of the facility and extending the term of the sublease to
February 1999 with options to further extend the sublease term to February 2000.
This amendment is expected to become effective on or about October 1, 1996.
Total net receipts under the amended sublease agreement, which are credited to
operating expenses, are expected to total approximately $2.3 million through
February 1999, of which approximately $498,000 was received by the Company in
fiscal 1996.
 
     In addition, effective January 1, 1996 the Company assigned its leases on
its Canton, Massachusetts ("Canton") facility and equipment to another
biotechnology company (see Note D).
 
     In August 1995 the Company issued $3.6 million of 7% subordinated
convertible debentures in a private placement to a small number of overseas
investors. As of March 31, 1996, all of these debentures plus accrued interest
thereon had been converted to 2,753,269 shares of the Company's Common Stock. In
addition, 81,480 shares of the Company's Common Stock were issued to a third
party as a finder's fee in connection with the issuance of the debentures.
 
     In March 1996 the Company sold $5.0 million of 9% convertible debentures in
a private placement. This amount was received by the Company in two installments
of $2.5 million in March 1996 and $2.5 million in June 1996. As of June 30,
1996, the first installment, together with accrued interest thereon, was
converted into 1,018,000 shares of the Company's Common Stock. In conjunction
with that conversion, warrants to purchase 509,000 shares and 500,000 shares of
the Company's Common Stock were issued to the debenture holder. These warrants
have exercise prices of $4.00 and $6.00, respectively, and expire in 2001. Also
in connection with the issuance of the 9% convertible debentures, the Company
issued warrants to purchase a total of 250,000 shares of the Company's Common
Stock to a third party as a finder's fee. These warrants have an exercise price
of $3.105 and expire in 2003.
 
     On June 28, 1996, ImmunoGen and its subsidiary, Apoptosis Technology, Inc.
("ATI"), satisfied obligations to Dana-Farber Cancer Institute ("Dana-Farber")
totaling approximately $1.3 million by issuing to Dana-Farber a convertible
debenture (see Note E). Pursuant to the settlement agreement, on June 28, 1996
the Company issued to Dana-Farber an 11.5% $1,312,943 debenture convertible into
shares of ImmunoGen Common Stock at a conversion price based on the market price
for the Common Stock at the time of conversion. Shortly thereafter, the Company
filed a registration statement under the Securities Act of 1933 to register the
resale by Dana-Farber of the Common Stock issuable upon conversion of the
debenture, and in July 1996 the debenture and accrued interest thereon,
aggregating $1,318,734, were converted into 351,662 shares of the Company's
Common Stock.
 
                                       26

<PAGE>   28
 
                                IMMUNOGEN, INC.
 
           NOTES TO CONSOLIDATED FINANCIAL STATEMENTS -- (CONTINUED)
 
     The Company anticipates that its existing capital resources will enable it
to maintain its current and planned operations through October 1996. Because of
its continuing losses from operations, the Company will be required to obtain
additional capital in the short term to satisfy its ongoing capital needs and to
continue its operations. Although, as noted above, management continues to
pursue additional funding arrangements and/or strategic partners, no assurance
can be given that such financing will in fact be available to the Company. If
the Company is unable to obtain financing on acceptable terms in order to
maintain operations, it could be forced to curtail or discontinue its
operations. The financial statements do not include any adjustments that might
result from the outcome of this uncertainty.
 
B. BASIS OF PRESENTATION AND SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES:
 
  Principles of Consolidation
 
     The consolidated financial statements include the accounts of the Company
and its wholly owned subsidiary, ImmunoGen Securities Corp. (established in
December 1989), and its 72%-owned subsidiary, ATI (established in January 1993)
(see Note E). All intercompany transactions and balances have been eliminated.
 
     Certain reclassifications have been made to the prior year financial
statements to conform to the 1996 presentation.
 
  Use of Estimates
 
     The preparation of financial statements in conformity with generally
accepted accounting principles requires management to make estimates and
assumptions that affect the reported amounts of assets and liabilities and
disclosure of contingent assets and liabilities at the date of the financial
statements and the reported amounts of revenues and expenses during the
reporting period. Actual results could differ from those estimates.
 
  Research and Development Costs
 
     Research and development costs are expensed as incurred.
 
  Cash, Cash Equivalents and Marketable Securities
 
     The Company considers all investments purchased with maturity dates of
three months or less from the date of acquisition to be cash equivalents.
 
     Cash and cash equivalents include, at cost plus accrued interest which
approximates market value, $3,047,236 and $2,796,636 of money market funds,
demand notes and repurchase agreements at June 30, 1995 and 1996, respectively.
 
  Financial Instruments and Concentration of Credit Risk
 
     The Company has outstanding convertible debentures with maturities of one
to four years; however, management believes the carrying amount of these
convertible debentures is a reasonable estimate of the fair value because of the
historically short holding period prior to conversion of the Company's
convertible debentures.
 
     The Company has a note receivable from a biotechnology company with
payments due at various dates to July 1999. Management believes the carrying
amount of this note receivable (on a discounted basis) is a reasonable estimate
of the fair value based on the current rates offered to the Company for debt
with similar maturities.
 
                                       27

<PAGE>   29
 
                                IMMUNOGEN, INC.
 
           NOTES TO CONSOLIDATED FINANCIAL STATEMENTS -- (CONTINUED)
 
     The Company minimizes the risk associated with concentration of credit by
utilizing the services of more than one custodian for its cash and assuring that
financial instruments purchased by its cash managers include only high-grade,
low-risk investments. At June 30, 1995 and 1996, those investments included
various U.S. Government securities, money market investments with major
financial institutions and cash on deposit with major banks.
 
  Property and Equipment
 
     Property and equipment are stated at cost. The Company provides for
depreciation based upon expected useful lives using the straight-line method
over the following estimated useful lives:
 

<TABLE>
        <S>                                                    <C>
        Machinery and equipment..............................  3-5 years
        Computer hardware and software.......................  5 years
        Furniture and fixtures...............................  5 years
        Leasehold improvements...............................  Shorter of lease term or
                                                               estimated useful life
</TABLE>

 
     Maintenance and repairs are charged to expense as incurred. Upon retirement
or sale, the cost of disposed assets and the related accumulated depreciation
are removed from the accounts and any resulting gain or loss is credited or
charged to operations. Gains recorded under sale/leaseback arrangements are
deferred and amortized to operations over the life of the lease.
 
  Income Taxes
 
     The Company uses the liability method whereby the deferred tax liabilities
and assets are recognized based on temporary differences between the financial
statement and tax basis of assets and liabilities using current statutory tax
rates. A valuation allowance against net deferred tax assets is recorded if,
based on the available evidence, it is more likely than not that some or all of
the deferred tax assets will not be realized.
 
     Management evaluates on a quarterly basis the recoverability of the
deferred tax assets and the level of the valuation allowance. At such time as it
is determined that it is more likely than not that deferred tax assets are
realizable, the valuation allowance will be appropriately reduced.
 
  Impairment of Long-Lived Assets
 
     In fiscal year 1996, the Company adopted Statement of Financial Accounting
Standards (SFAS) No. 121, "Accounting for Impairment of Long-Lived Assets to Be
Disposed Of" which requires the evaluation of recoverability in the event that
facts and circumstances indicate that the cost of a long-lived asset may be
impaired. Adoption of the Standard had no effect on the 1996 financial
statements.
 
     The Company periodically evaluates the potential impairment of its
long-lived assets whenever events or changes in circumstances indicate that the
carrying amount of an asset may not be recoverable. At the occurrence of a
certain event or change in circumstances, the Company evaluates the potential
impairment of an asset based on estimated future undiscounted cash flows. In the
event impairment exists, the Company will measure the amount of such impairment
based on the present value of estimated expected future cash flows using a
discount rate commensurate with the risks involved. Based on management's
assessment as of June 30, 1996, the Company has determined that no impairment of
long-lived assets exists.
 
  Recent Accounting Pronouncements
 
     In October 1995, the Financial Accounting Standards Board issued SFAS No.
123, "Accounting for Stock-Based Compensation" ("SFAS No. 123"), which
encourages companies to recognize compensation expense in the income statement
based on the fair value of the underlying common stock at the date the
 
                                       28

<PAGE>   30
 
                                IMMUNOGEN, INC.
 
           NOTES TO CONSOLIDATED FINANCIAL STATEMENTS -- (CONTINUED)
 
awards are granted. However, it will permit continued accounting under
Accounting Principles Board Opinion No. 25, "Accounting for Stock Issued to
Employees" ("APB Opinion 25"), accompanied by a disclosure in the footnotes to
the financial statements of the pro forma effects on net income and earnings per
share had the new accounting rules been applied. The statement is effective for
fiscal year 1997. The Company has determined to continue accounting for
stock-based compensation under APB Opinion 25, and thus will adopt the
disclosure-only alternative permitted under SFAS 123. The Company has not
determined the impact of the pro forma adjustments on its net loss or loss per
share.
 
C. LOSS PER COMMON SHARE:
 
     Net loss per common share is based on the weighted average number of common
shares outstanding during the periods. Common share equivalents have not been
included because their effect would be anti-dilutive. Fully diluted earnings per
share are the same as primary earnings per share.
 
     If the conversions of convertible debentures into common shares of the
Company which occurred during 1996 (see Note A) had occurred at the beginning of
the fiscal year, then the weighted average number of shares outstanding used to
calculate the loss per share would have been 16,485,630 and the loss per share
would have been $1.00.
 
     If the above conversions described above plus the conversion in July 1996
(see Note A) had occurred at the beginning of the fiscal year, the weighted
average number of shares outstanding used to calculate the loss per share would
have been 16,837,292 and the loss per share would have been $0.98.
 
D. NOTE RECEIVABLE:
 
     Effective January 1, 1996, the Company assigned its leases on its Canton
facility and equipment to another biotechnology company. Under the terms of the
agreements, the assignee has assumed all payment obligations under the leases,
which amount to approximately $116,000 per month and, in addition, will make
cash payments to the Company totaling approximately $2.4 million at various
dates to July 1999, of which approximately $786,000 has been received through
June 30, 1996. Amounts due the Company from the assignee under these agreements
were discounted to their present value using a risk adjusted discount rate of
9%. The Company is accreting interest income over the life of the note and,
accordingly, the note receivable balance in the Company's consolidated balance
sheets as of June 30, 1996 reflects the original discounted present value of
$1,291,000 plus accreted interest of approximately $48,000.
 
E. AGREEMENTS:
 
  ImmunoGen/Dana-Farber Agreement
 
     The Company has a long-standing research and license agreement with
Dana-Farber, a Massachusetts not-for-profit corporation. As part of the research
and license agreement, the Company has agreed to fund certain research and
development projects conducted by Dana-Farber in relation to the development and
eventual commercialization of certain biologicals to be used in the treatment of
certain forms of cancer. In fiscal years 1994, 1995 and 1996 the Company
incurred research and development expenses of approximately $567,000, $225,000
and $40,000, respectively, in connection with that agreement. To the extent that
any invention develops at Dana-Farber which derived its principal support and
funding from the Company, the Company has the exclusive right to use such
invention. Also as part of the arrangement, the Company is required to pay to
Dana-Farber, when product sales commence, certain royalties based on a formula
stipulated in the agreement. The Company owed Dana-Farber approximately $1.2
million and $0.9 million at June 30, 1995 and June 28, 1996, respectively, for
work performed under the agreement. Of the balance due under this agreement as
of June 28, 1996, the Company accrued interest of approximately $106,000 (which
includes interest retroactive to 1993 on ImmunoGen's obligation to Dana-Farber
plus interest on ATI's $335,100
 
                                       29

<PAGE>   31
 
                                IMMUNOGEN, INC.
 
           NOTES TO CONSOLIDATED FINANCIAL STATEMENTS -- (CONTINUED)
 
obligation to DFCI), and issued a $1.3 million 11.5% convertible debenture as
described in Note A to these financial statements in payment thereof.
 
  ATI/Dana-Farber Agreements
 
     ATI is a joint venture between ImmunoGen and Dana-Farber established to
develop therapeutics based on apoptosis technology developed at Dana-Farber. In
January 1993, the Company purchased 7,000 shares of Class A Preferred Stock of
ATI. The Preferred Stock is voting stock and carries a liquidation preference
over the common stock. The Company's investment represents 72% of the currently
authorized equity of ATI and, accordingly, is consolidated. In addition, the
Company has a right of first refusal to purchase any ATI shares which may be
offered for sale by the other current stockholders of ATI. If ATI has not
concluded a public offering of its stock for at least $5.0 million prior to
January 11, 1998, the other stockholders (currently representing 2,765 shares of
common stock) of ATI can require ImmunoGen to purchase, or ImmunoGen can require
such stockholders to sell, their shares in ATI at a predetermined price. At
ImmunoGen's option, the shares of common stock of ATI can be paid for in cash or
by delivery of shares of ImmunoGen Common Stock.
 
     ImmunoGen was committed to provide ATI with $3.0 million in research and
development services and $2.0 million in cash equity contributions over a
three-year period. At June 30, 1995, these obligations had been fulfilled by the
Company. ImmunoGen has also agreed to obtain or furnish an additional $3.0
million in equity for ATI on such terms and conditions as may be mutually agreed
to by ATI and the providers of such additional equity. As of June 30, 1996,
amounts owed by ATI to ImmunoGen approximated $10.0 million. The Company intends
to convert a majority of this amount into equity of ATI, thereby satisfying the
agreement to provide an additional $3.0 million in equity.
 
     Under agreements between ATI and Dana-Farber, ATI was the licensee of
Dana-Farber's apoptosis technology and ImmunoGen possessed the exclusive right
to license products developed by ATI, including those based on Dana-Farber's
apoptosis technology. These agreements were terminated as of January 1, 1996. A
portion of the Company's research and development expenses was incurred in
connection with an agreement between ATI and Dana-Farber, under which ATI had
agreed to fund certain research projects conducted at Dana-Farber. In fiscal
1994, 1995 and 1996, these expenses amounted to $530,000, $670,000 and $327,000,
respectively. The balance due Dana-Farber under this agreement of approximately
$350,000 was included in the June 28, 1996 debenture issued by the Company to
Dana-Farber as described in Note A. Under the terms of the termination
agreement, the Company satisfied all past and present obligations under the
license agreement and ATI retains any rights to technology developed prior to
January 1, 1996.
 
  Other
 
     Development revenues of approximately $75,000 and $398,000 in fiscal 1994
and 1996, respectively, represent income earned under the Small Business
Innovation Research Program of the National Institutes of Health and, in fiscal
1996, amounts received pursuant to licensing agreements of the Company and its
subsidiary, ATI.
 
                                       30

<PAGE>   32
 
                                IMMUNOGEN, INC.
 
           NOTES TO CONSOLIDATED FINANCIAL STATEMENTS -- (CONTINUED)
 
F. PROPERTY AND EQUIPMENT:


<TABLE>
     Property and equipment consisted of the following at June 30, 1995 and
1996:
 
<CAPTION>
                                                                          JUNE 30,
                                                                  -------------------------
                                                                     1995          1996
                                                                  -----------   -----------
    <S>                                                           <C>           <C>
    Machinery and equipment.....................................  $ 6,760,500   $ 5,235,339
    Computer hardware and software..............................    1,063,883     1,054,586
    Furniture and fixtures......................................      136,722       133,964
    Leasehold improvements......................................   15,889,963     8,131,394
                                                                  -----------   -----------
                                                                   23,851,068    14,555,283
    Less accumulated depreciation and amortization..............   10,229,685    10,391,867
                                                                  -----------   -----------
                                                                  $13,621,383   $ 4,163,416
                                                                  ===========   ===========
</TABLE>

 
     Depreciation and amortization expense was $2,043,537, $3,284,583 and
$2,507,704 for the years ended June 30, 1994, 1995 and 1996, respectively.
 
     Maintenance and repair expense was approximately $229,000, $173,000 and
$120,000 for fiscal years 1994, 1995 and 1996, respectively.
 
     In connection with the Company's assignment of its equipment leases at its
Canton facility, as described in Note D, the Company wrote off approximately
$9.3 million of assets, with a corresponding reduction in accumulated
depreciation of approximately $2.3 million. This disposition of the Company's
Canton assets includes recognition of a net loss on its equipment lease at the
Canton facility of approximately $2.0 million for the year ended June 30, 1996.
 
     The Company's policy is to depreciate property and equipment over its
remaining useful life, generally three to five years, and to evaluate the
remaining life and recoverability of such property and equipment in light of
current conditions as discussed in Note A. Since there is substantial doubt
about the Company's ability to continue as a going concern, it is reasonably
possible that the Company's estimate that it will recover the carrying amount of
its property and equipment from future operations will change in the near term;
however, management believes the fair value of its property and equipment
exceeds its net book value at June 30, 1996.
 
G. INCOME TAXES:
 
     No income tax provision or benefit has been provided for U.S. federal
income tax purposes as the Company has incurred losses since inception. As of
June 30, 1996 net deferred tax assets totaled approximately $43.0 million,
consisting of federal net operating loss carryforwards of approximately $110.0
million and approximately $4.0 million of research and experimentation credit
carryforwards. These net operating loss and credit carryforwards will expire at
various dates between 1997 and 2011 and may be subject to limitation when used
due to certain changes in ownership of the Company's capital stock. Due to the
uncertainty surrounding the realization of these favorable tax attributes in
future tax returns, the net deferred tax assets of approximately $40.0 million
and $43.0 million at June 30, 1995 and 1996, respectively, have been fully
offset by a valuation allowance. Income tax expense consists primarily of state
income taxes levied on the interest income of the Company's wholly owned
subsidiary, ImmunoGen Securities Corp., at a rate of 1.32%.
 
                                       31

<PAGE>   33
 
                                IMMUNOGEN, INC.
 
           NOTES TO CONSOLIDATED FINANCIAL STATEMENTS -- (CONTINUED)
 
H. CAPITAL STOCK:
 
  Common Stock
 
     In August 1995, the Company issued $3.6 million of 7% subordinated
convertible debentures to a small number of overseas investors. Net proceeds to
the Company amounted to approximately $3.3 million. As of June 30, 1996, all of
these debentures plus accrued interest thereon had been converted into shares of
the Company's Common Stock. In total, 2,753,269 shares were issued to the
holders of the $3.6 million 7% subordinated convertible debentures for both
principal and interest. In addition, 81,480 shares of the Company's Common Stock
were issued to a third party as a finder's fee in connection with the issuance
of the debentures. The value of the shares, approximately $108,000, was charged
to interest expense.
 
     In March 1996, the Company sold a $5.0 million 9% convertible debenture in
a private placement. Net proceeds to the Company amounted to approximately $4.75
million. As of June 30, 1996, a $2.5 million principal amount debenture plus
accrued interest thereon had been converted into 1,018,000 shares of the
Company's Common Stock based upon a predetermined formula discounted from the
market price of the Company's Common Stock. The remaining $2.5 million principal
amount debenture still outstanding at June 30, 1996, due in 2000, and any
accrued interest thereon can be converted into shares of the Company's Common
Stock at any time according to a predetermined formula providing for a discount
from the market price of the Common Stock.
 
     In June 1996 the Company satisfied its own and ATI's obligations to
Dana-Farber, totaling approximately $1.3 million, by issuing an 11.5%
convertible debenture in that amount. On July 12, 1996, the 11.5% debenture and
accrued interest thereon, aggregating $1,318,734, was converted into 351,662
shares of the Company's Common Stock.
 
  Stock Options
 
     Under the Company's Restated Stock Option Plan (the "Plan") originally
adopted by the Board of Directors on February 13, 1986, and subsequently amended
and restated, employees, consultants and directors may be granted options to
purchase up to 2,400,000 shares of Common Stock of the Company. Prior to June 7,
1994, 1,700,000 shares of Common Stock were reserved for the grant of options
under the Plan. On June 7, 1994, the Board of Directors authorized, and the
shareholders subsequently approved, an amendment to the Plan to increase the
number of shares reserved for the grant of options to 2,400,000 shares of Common
Stock.
 
                                       32

<PAGE>   34
 
                                IMMUNOGEN, INC.
 
           NOTES TO CONSOLIDATED FINANCIAL STATEMENTS -- (CONTINUED)
 
     Information related to stock option activity under the Plan during fiscal
years 1994, 1995 and 1996 is as follows:
 

<TABLE>
<CAPTION>
                                                                                  OPTION
                                                                   SHARES          PRICE
                                                                  ---------     -----------
    <S>                                                           <C>           <C>
    Outstanding at June 30, 1993................................  1,248,620     $0.67-14.75
                                                                  ---------     -----------
    Granted.....................................................    582,200      4.50-10.50
    Exercised...................................................     41,438      0.90- 2.00
    Canceled....................................................    205,869      2.00-14.75
                                                                  ---------     -----------
    Outstanding at June 30, 1994................................  1,583,513      0.67-14.75
                                                                  ---------     -----------
    Granted.....................................................    338,300      1.94- 4.38
    Exercised...................................................     10,875      0.90- 2.00
    Canceled....................................................    623,572      0.90-14.75
                                                                  ---------     -----------
    Outstanding at June 30, 1995................................  1,287,366      0.67-14.75
                                                                  ---------     -----------
    Granted.....................................................    613,900      1.44- 5.00
    Exercised...................................................    108,500      0.67- 3.38
    Canceled....................................................    118,904      2.00-14.75
                                                                  ---------     -----------
    Outstanding at June 30, 1996................................  1,673,862     $0.90-14.75
                                                                  =========     ===========
</TABLE>

 
     In addition to options granted under the Plan, the Board previously has
approved the granting of other, non-qualified options. In July 1987 and February
1988, the Company granted non-qualified options for the purchase of 115,500 and
15,000 shares of Common Stock at exercise prices of $0.67 and $0.90 per share,
respectively. During 1994, 1995 and 1996, options for 2,000, 13,000 and 60,000
shares were exercised at a price of $0.67 per share. As of June 30, 1996,
options for 19,687 of these shares had been cancelled, 92,813 had been exercised
and 18,000 were outstanding and exercisable.
 
     The Company has granted options at the fair market value of the Common
Stock at the date of such grant. There were a total of 1,095,810 stock options
exercisable under the Company's stock option plans as of June 30, 1996.
 
     Options vest at various rates over periods up to four years and may be
exercised within ten years from the date of grant.
 
  Common Stock Reserved
 
     Shares of authorized Common Stock have been reserved for the exercise of
all options and warrants outstanding.
 
  Warrants
 
     In connection with a capital lease financing in March 1994, the Company
issued warrants to purchase 26,738 shares of Common Stock at an exercise price
of $7.48 per share expiring in April 1999. The value of these warrants,
approximating $77,000, was recognized as interest expense over the life of the
lease.
 
     In connection with the 9% $5.0 million principal amount debenture financing
in March 1996, the Company issued warrants to purchase 509,000 and 500,000
shares of Common stock at exercise prices of $4.00 and $6.00 per share,
respectively, expiring in 2001. The value of these warrants, approximating $2.2
million, was recognized as interest expense at the time of issuance.
 
     Of the original $5.0 million principal amount debentures, $2.5 million had
been converted into shares of the Company's Common Stock as of June 30, 1996. If
the remaining $2.5 million principal amount and
 
                                       33

<PAGE>   35
 
                                IMMUNOGEN, INC.
 
           NOTES TO CONSOLIDATED FINANCIAL STATEMENTS -- (CONTINUED)
 
accrued interest are converted into shares of the Company's Common Stock, the
holder will receive warrants to purchase additional shares of the Company's
Common Stock equal to one-half the number issued upon conversion of the
debenture. These warrants will carry an exercise price of $4.00 per share and be
exercisable for a period of five years from date of issuance. Because issuance
of these warrants is based upon future events, no value has been ascribed to
this potential issuance of warrants at June 30, 1996. Also in connection with
the issuance of the 9% debentures, the Company issued warrants to purchase a
total of 250,000 shares of the Company's Common Stock to a third party as a
finder's fee. These warrants have an exercise price of $3.105, expire in 2003,
and their value, totaling approximately $461,000, was charged to interest
expense at the time of issuance of the warrants.
 
I. COMMITMENTS:
 
  Operating Leases
 
     At June 30, 1996, the Company is leasing facilities in Norwood and
Cambridge, Massachusetts. The lease term on the Norwood facilities expires in
June 1997 (with a three-year extension option). The Cambridge facilities are
rented under two separate lease arrangements, expiring in 1997 and 2003. The
latter of these facilities is subject to the sublease agreement discussed in
Note A, with a current sublease term expiring in February 1999. The Company is
required to pay all operating expenses for the leased premises subject to
escalation charges for certain expense increases over a base amount. Rent
expense for leased facilities and equipment was approximately $1,186,000,
$913,000 and $382,000 (net of sublease income of $500,000) during fiscal years
1994, 1995 and 1996, respectively.


<TABLE>
     The minimum rental commitments, including real estate taxes, for the next
five years under the lease agreements are as follows:
 
<CAPTION>
                     FISCAL YEAR                  COMMITMENTS     SUBLEASE INCOME        NET
                     -----------                  -----------     ---------------        ---
        <S>                                       <C>             <C>                 <C>
        1997..................................     $ 921,230         $ 751,447        $ 169,783
        1998..................................       566,469           792,306         (225,837)
        1999..................................       524,804           561,298          (36,494)
        2000..................................       447,382                --          447,382
        2001..................................       447,382                --          447,382
</TABLE>

 
     In January 1996, the Company assigned the lease on its Canton facility to a
third party (see Note D).
 
  Capital Leases
 
     In fiscal year 1988, the Company, as part of one of its lease agreements,
arranged financing for $989,975 of improvements to one of its leased facilities
through the lessor. The lessor obtained a five-year promissory note with a bank
specifically to finance the improvements to the facility. The promissory note
was amortized over a ten-year period. At the end of the first five years, the
lessor refinanced the unamortized principal due the bank. Interest expense on
the new note is incurred at the rate of 7.50% per annum.
 
     In March 1994, the Company executed a sale/leaseback agreement to finance
approximately $4.0 million of equipment at its Canton facility. As of June 30,
1994, all funds available under this agreement had been received. In January
1996, all obligations under this lease agreement were assigned to another
biotechnology company, along with the Canton facility (see Note D).
 
                                       34

<PAGE>   36
 
                                IMMUNOGEN, INC.
 
           NOTES TO CONSOLIDATED FINANCIAL STATEMENTS -- (CONTINUED)

<TABLE>
     Assets recorded under capital leases as of June 30, 1995 and 1996 are
included in property and equipment as follows:
 
<CAPTION>
                                                                           JUNE 30,
                                                                   ------------------------
                                                                      1995          1996
                                                                   ----------     ---------
    <S>                                                            <C>            <C>
    Machinery and equipment......................................  $1,590,510     $ 989,975
    Leasehold improvements.......................................   3,413,490            --
    Less accumulated depreciation................................   1,727,403       866,230
                                                                   ----------      --------
    Net book value...............................................  $3,276,597     $ 123,745
                                                                   ==========      ========
</TABLE>

 
The future minimum lease payments are as follows:
 

<TABLE>
<CAPTION>

     FISCAL YEAR                                                                 AMOUNT
     -----------                                                                 ------
    <S>                                                                         <C>
    1997....................................................................    $ 150,129
    1998....................................................................       37,532
                                                                                 --------
    Total future minimum lease payments.....................................      187,661
    Less amount representing interest.......................................        9,060
                                                                                 --------
    Present value of minimum lease payments.................................      178,601
    Less current portion....................................................      141,533
                                                                                 --------
    Noncurrent portion, minimum lease payments..............................    $  37,068
                                                                                 ========
</TABLE>

 
J. EMPLOYEE BENEFIT PLANS:
 
     Effective September 1, 1990, the Company implemented a deferred
compensation plan under Section 401(k) of the Internal Revenue Code (the
"Plan"). Under the Plan, eligible employees are permitted to contribute, subject
to certain limitations, up to 15% of their gross salary. The Company makes a
matching contribution which currently totals 20% of the employee's contribution,
up to a maximum amount equal to 1% of the employee's gross salary. In fiscal
1994, 1995 and 1996, the Company's contributions to the Plan amounted to
$62,000, $51,000 and $31,000, respectively.
 

I
TEM 9.  CHANGES IN AND DISAGREEMENTS WITH ACCOUNTANTS ON ACCOUNTING AND
FINANCIAL DISCLOSURE
 
     None
 
                                       35

<PAGE>   37
 

                                    PART III
 

ITEM 10.  DIRECTORS AND EXECUTIVE OFFICERS
 
DIRECTORS
 
     The section entitled "Election of Directors" in the Company's definitive
proxy statement for its 1996 Annual Meeting of Shareholders, which the Company
intends to file with the Securities and Exchange Commission on or about October
1, 1996, is hereby incorporated by reference.
 
EXECUTIVE OFFICERS


<TABLE>
     The following is a list of the executive officers of the Company and their
positions with the Company. Each individual officer serves at the pleasure of
the Board of Directors.
 
<CAPTION>
                NAME                   AGE           POSITIONS WITH THE COMPANY
                ----                   ---     ---------------------------------------
<S>                                    <C>     <C>
Mitchel Sayare, Ph.D.................  48      Chairman of the Board of Directors and
                                               Chief Executive Officer
Frank J. Pocher......................  55      Vice President, Chief Financial Officer
                                               and Treasurer
Walter A. Blattler, Ph.D.............  47      Senior Vice President, Research and
                                               Development
Dixie-Lee W. Esseltine,..............  49      Vice President, Medical Affairs
  M.D., FRCPC
Carol A. Gloff, Ph.D.................  44      Vice President, Chief Regulatory
                                               Officer
</TABLE>

 
     The background of these executive officers is as follows:
 
     Mitchel Sayare, Chief Executive Officer and a Director since 1986, joined
the Company in 1986. He served as President from 1986 to July 1992. From 1982 to
1985, Mr. Sayare was an executive at Xenogen, Inc., a biotechnology company
specializing in monoclonal antibody-based diagnostic systems for cancer. As Vice
President for Development at Xenogen, Mr. Sayare was responsible for the
development of several diagnostic kits which were licensed to major
pharmaceutical companies. From 1977 to 1982, Mr. Sayare was Assistant Professor
of Biophysics and Biochemistry at the University of Connecticut. He holds a
Ph.D. in Biochemistry from Temple University School of Medicine.
 
     Frank J. Pocher, Vice President, Chief Financial Officer and Treasurer, and
a Director since 1995, joined the Company in November 1988. Prior to joining
ImmunoGen, Mr. Pocher was the Executive Vice President and Chief Financial
Officer of Seragen, Inc., a biotechnology company developing recombinant
products for cancer and transplantation rejection. From 1980 to 1984, Mr. Pocher
served as Chief Financial Officer and then President and Chief Executive Officer
of Aviation Simulation Technology, Inc. Prior to that time, he held a variety of
senior financial positions at General Electric Company and Honeywell, Inc. He
holds an MBA from Rutgers University.
 
     Walter A. Blattler, Ph.D., Senior Vice President, Research and Development,
and a Director since 1995, joined the Company in October 1987. From 1981 to
1987, Dr. Blattler was chief scientist for the ImmunoGen-supported research
program at Dana-Farber Cancer Institute, where he managed the work of fourteen
other scientists. Dr. Blattler received his Ph.D. from the Swiss Federal
Institute of Technology in Zurich in 1978.
 
     Dixie-Lee W. Esseltine, M.D., FRCPC, Vice President, Medical Affairs,
joined the Company in 1992 as Director of Oncology. In 1995 she was promoted to
Vice President, Medical Affairs. From 1990 to 1992, Dr. Esseltine was employed
by Ortho-McNeil (Johnson & Johnson) Canada as an Associate Director responsible
for the Hematology/Oncology, Immunology and Psychiatry therapeutic areas. Prior
to joining industry, Dr. Esseltine was Assistant Director of Hematology at the
Montreal Childrens' Hospital and Associate Professor of Pediatrics, McGill
University from 1978 to 1990.
 
                                       36

<PAGE>   38
 
     Carol A. Gloff, Ph.D., Vice President, Chief Regulatory Officer, joined the
Company in November 1993. Prior to joining ImmunoGen, Dr. Gloff held various
positions at Alkermes, Inc., a neuropharmaceutical company developing CNS
therapeutics and diagnostics, including Director of Product Development and most
recently Vice President of Regulatory Affairs. From 1984 to 1990, Dr. Gloff held
a variety of positions at Triton Biosciences, Inc., a biotechnology firm
specializing in recombinant DNA and monoclonal antibody-derived technologies
applied to cancer diagnosis and therapy, most recently as Manager of
Toxicology/Pharmacology. Prior to that time, Dr. Gloff held positions at
Pennwalt Pharmaceuticals and the University of Rochester Medical Center. Dr.
Gloff holds a Ph.D. in Pharmaceutical Chemistry from the University of
California San Francisco.
 
     The section entitled "Section 16(a) Beneficial Ownership Reporting
Compliance" in the Company's definitive proxy statement for its 1996 Annual
Meeting of Shareholders is hereby incorporated by reference.
 

ITEM 11.  EXECUTIVE COMPENSATION
 
     The reports entitled "Summary Compensation Table," "Option Grants in Last
Fiscal Year," "Employment Contracts, Termination of Employment and Change in
Control Agreements" and "Aggregated Option Exercises in Last Fiscal Year and
Fiscal Year-End Values" in the Company's definitive proxy statement for its 1996
Annual Meeting of Shareholders are hereby incorporated by reference.
 

ITEM 12.  SECURITIES OWNERSHIP OF CERTAIN BENEFICIAL OWNERS AND MANAGEMENT
 
     The section entitled "Principal Shareholders" in the Company's definitive
proxy statement for its 1996 Annual Meeting of Shareholders is hereby
incorporated by reference.
 

ITEM 13.  CERTAIN RELATIONSHIPS AND RELATED TRANSACTIONS
 
     The section entitled "Certain Transactions" in the Company's definitive
proxy statement for its 1996 Annual Meeting of Shareholders is hereby
incorporated by reference.
 
                                       37

<PAGE>   39
 

                                    PART IV
 

ITEM 14.  EXHIBITS, FINANCIAL STATEMENT SCHEDULES AND REPORTS ON FORM 8-K
 
     (a) Financial Statements
 
     (1) and (2) See "Index to Consolidated Financial Statements and
Supplemental Schedules" at Item 8 of this Annual Report on Form 10-K. Schedules
not included herein are omitted because they are not applicable or the required
information appears in the Consolidated Financial Statements or Notes thereto.
 
     (3) Exhibits
 

<TABLE>

<CAPTION>

EXHIBIT NO.                                      DESCRIPTION
- -----------                                      -----------
<S>           <C>
  (3.1)       Restated Articles of Organization+
  (3.2)       By-Laws, as amended#
  (3.3)       Articles of Amendment to Restated Articles of Organization
  (4.1)       Article 4 of the Restated Articles of Organization (See Exhibit 3.1)+
  (4.2)       Form of Common Stock Certificate*
 (10.1)       Research and License Agreement dated as of May 22, 1981 by and between the
              Registrant and Sidney Farber Cancer Institute, Inc. (now Dana-Farber Cancer
              Institute, Inc.) with addenda dated as of August 13, and August 22, 1989*
 (10.3)       Amended and Restated Registration Rights Agreement dated as of December 23, 1988
              by and among the Registrant and various beneficial owners of the Registrant's
              securities*
 (10.4)x      Restated Stock Option Plan##
 (10.6)x      Letter Agreement Regarding Employment dated as of October 14, 1988 between the
              Registrant and Mr. Frank J. Pocher*
 (10.7)x      Letter Agreement Regarding Employment dated as of October 1, 1987 between the
              Registrant and Dr. Walter A. Blattler*
 (10.8a)x     Letter Agreement Regarding Employment Termination of Dr. Carol L. Epstein, dated
              April 16, 1994 as amended May 25 and June 6, 1994###
 (10.9)       Lease dated June 30, 1987 by and between Edward S. Stimpson, III and Harry F.
              Stimpson, III, as trustees, lessor, and the Registrant, lessee(1)
 (10.10)      Lease dated as of January 13, 1989 by and between FAR IV Limited Partnership,
              lessor, and the Registrant, lessee(2)
 (10.10a)     First Amendment to Lease dated as of February 1, 1990 by and between 60 Hamilton
              Street Limited Partnership, lessor, and Registrant, lessee(3)
 (10.11)      Leases dated as of December 1, 1986 and June 21, 1988 by and between James H.
              Mitchell, Trustee of New Providence Realty Trust, lessor, and Charles River
              Biotechnical Services, Inc. ("Lessee") together with Assignment of Leases dated
              June 29, 1989 between Lessee and the Registrant(4)
 (10.11a)     First Amendment, dated as of May 9, 1991, to Lease dated as of June 21, 1988 by
              and between James A. Mitchell, Trustee of New Providence Realty Trust, lessor,
              and the Registrant(5)
 (10.13c)x    Letter Agreement Regarding Compensation of Mitchel Sayare, dated April 29,
              1994###
 (10.14a)x    Transition Agreement Regarding Employment Termination of Dr. Donald J. McCarren,
              dated May 20, 1994###
 (10.15)      Lease dated as of July 1, 1992 by and between AEW#1 Corporation, lessor, and the
              Registrant, lessee++
 (10.16)      Lease dated as of December 23, 1992 by and between Massachusetts Institute of
              Technology, lessor, and the Registrant, lessee##
</TABLE>

 
                                       38

<PAGE>   40
 

<TABLE>

<CAPTION>

EXHIBIT NO.                                      DESCRIPTION
- -----------                                      -----------
<S>           <C>
 (10.18)      Option Agreement dated April 5, 1990 by and between the Registrant and Takeda
              Chemical Industries, Ltd.(6)
 (10.19a)x    Separation Agreement regarding employment termination of Robert E. Tellis dated
              June 14, 1994 and as amended June 21, 1994###
 (10.21)x     Letter Agreement Regarding Employment dated September 15, 1993 between the
              Registrant and Carol A. Gloff###
 (10.22)      Capital Lease Agreement dated March 31, 1994 by and between the Registrant and
              Aberlyn Capital Management Limited Partnership###
 (10.23)      Sublease dated as of August 31, 1995 by and between the Registrant, as landlord,
              and Astra Research Center Boston, Inc., as tenant+++
 (10.24)      Equipment Use and Services Agreement dated as of August 31, 1995 by and between
              the Registrant, as landlord, and Astra Research Center Boston, Inc., as tenant+++
 (10.25)      Consent to Sublease and Agreement dated as of August 31, 1995 by and between
              Massachusetts Institute of Technology, as lessor, the Registrant, as sublessor,
              and Astra Research Center Boston, Inc., as sublessee+++
 (10.26)      Amendment to Lease dated August 31, 1995 between Massachusetts Institute of
              Technology, as lessor, and the Registrant, as lessee+++
 (10.27)      Form of 7% Subordinated Convertible Debenture Due July 31,1996 and Schedule of
              Debenture Holders+++
 (10.28)      Form of Offshore Securities Subscription Agreement between the Registrant and
              Purchasers of the Debentures+++
 (10.29)      Securities Purchase Agreement, including the Form of Convertible Debenture and
              The Form of Stock Purchase Warrant, dated as of March 15, 1996 by and among the
              Registrant and Capital Ventures International(7)
 (10.30)      Registration Rights Agreement dated as of March 15, 1996 by and among the
              Registrant and Capital Ventures International(8)
 (10.31)      Letter Agreement dated as of March 21, 1996 by and among the Registrant and
              Capital Ventures International regarding the Securities Purchase Agreement dated
              as of March 15, 1996(9)
 (10.32)      Letter Agreement dated as of June 6, 1996 by and among the Registrant and Capital
              Ventures International regarding an amendment to their agreement dated March 15,
              1996(10)
 (10.33)      First Amendment to Sublease dated August 31, 1995 by and between the Registrant,
              as landlord, and Astra Research Center Boston, Inc., as tenant
(21)          Subsidiaries of the Registrant
(23)          Consent of Coopers & Lybrand
</TABLE>

 
- ---------------
    * Previously filed with the Commission as Exhibits to, and incorporated
      herein by reference from, the Registrant's Registration Statement on Form
      S-1, File No. 33-31219.
 
   + Previously filed with the Commission as Exhibits to, and incorporated
     herein by reference from, the Registrant's Registration Statement on Form
     S-1, File No. 33-38883.
 
 ++ Previously filed with the Commission as Exhibits to, and incorporated herein
    by reference from, the Registrant's annual report on Form 10-K for the
    fiscal year ended June 30, 1992.
 
+++ Previously filed with the Commission as Exhibits to, and incorporated herein
    by reference from, the Registrant's annual report on Form 10-K for the
    fiscal year ended June 30, 1995.
 
   # Previously filed with the Commission as Exhibits to, and incorporated
     herein by reference from, the Registrant's annual report on Form 10-K for
     the fiscal year ended June 30, 1990.
 
                                       39

<PAGE>   41
 
 ## Previously filed with the Commission as Exhibits to, and incorporated herein
    by reference from, the Registrant's quarterly report on Form 10-Q for the
    quarter ended December 31, 1992.
 
### Previously filed with the Commission as Exhibits to, and incorporated herein
    by reference from the registrant's annual report on Form 10-K in the fiscal
    year ended June 30, 1994.
 
 (1) Previously filed with the Commission as Exhibit No. 10.8 to, and
     incorporated herein by reference from, the Registrant's Registration
     Statement on Form S-1, File No. 33-31219.
 
 (2) Previously filed with the Commission as Exhibit No. 10.9 to, and
     incorporated herein by reference from, the Registrant's Registration
     Statement on Form S-1, File No. 33-31219.
 
 (3) Previously filed with the Commission as Exhibit No. 10.9a to, and
     incorporated herein by reference from, the Registrant's Registration
     Statement on Form S-1, File No. 33-38883.
 
 (4) Previously filed with the Commission as Exhibit No. 10.10 to, and
     incorporated herein by reference from, the Registrant's Registration
     Statement on Form S-1, File No. 33-31219.
 
 (5) Previously filed with the Commission as Exhibit No. 10.10a to, and
     incorporated herein by reference from, the Registrant's Registration
     Statement on Form S-1, File No. 33-43725, as amended.
 
 (6) Previously filed with the Commission as Exhibit No. 10.15 to, and
     incorporated herein by reference from, the Registrant's Registration
     Statement on Form S-1, File No. 33-38883.
 
 (7) Previously filed as Exhibit 99.2 to the Registrant's Current Report on Form
     8-K for the March 25, 1996 event, and incorporated herein by reference.
 
 (8) Previously filed as Exhibit 99.3 to the Registrant's Current Report on Form
     8-K for the March 25, 1996 event, and incorporated herein by reference.
 
 (9) Previously filed as Exhibit 99.4 to the Registrant's Current Report on Form
     8-K for the March 21, 1996 event, and incorporated herein by reference.
 
 (10) Previously filed as Exhibit 10.29 to the Registrant's Current Report on
      Form 8-K for the June 6, 1996 event, and incorporated herein by reference.
 
 (x) Exhibit is a management contract or compensatory plan, contract or
     arrangement required to be filed as an exhibit to Form 10-K.
 
     (b) The Company filed a report on Form 8-K on June 6, 1996 reporting the
signing of a Letter Agreement dated as of June 6, 1996 by and among the
Registrant and Capital Ventures International regarding an Amendment to their
agreement dated March 15, 1996.
 
                                       40

<PAGE>   42
 

                                   SIGNATURES
 
     Pursuant to the requirements of Section 13 or 15(d) of the Securities and
Exchange Act of 1934, the Registrant has duly caused this report to be signed on
its behalf by the undersigned, thereunto duly authorized.
 
                                          IMMUNOGEN, INC.
 
                                          By: /s/       MITCHEL SAYARE
 
                                            ------------------------------------
                                            Mitchel Sayare
                                            Chairman of the Board and
                                            Chief Executive Officer
 
                                          Dated: September 12, 1996
 
     Pursuant to the requirements of the Securities and Exchange Act of 1934,
this report has been signed below by the following persons on behalf of the
Registrant in the capacities and on the dates indicated.
 

<TABLE>
<CAPTION>
                SIGNATURE                               TITLE                      DATE
- ------------------------------------------  ------------------------------  -------------------
<C>                                         <S>                             <C>

                                            Chairman of the Board of        September 12, 1996
          /s/ MITCHEL SAYARE                  Directors and Chief
- ------------------------------------------    Executive Officer (principal
              Mitchel Sayare                  executive officer)

                                            Vice President, Chief           September 12, 1996
          /s/ FRANK J. POCHER                 Financial Officer, Treasurer
- ------------------------------------------    (principal financial officer
             Frank J. Pocher                  and principal accounting
                                              officer) and Director

                                            
         /s/ WALTER A. BLATTLER             Senior Vice President,          September 12, 1996  
- ------------------------------------------    Research and Development,
            Walter A. Blattler                and Director

                                            
           /s/ MICHAEL EISENSON             Director                        September 12, 1996
- ------------------------------------------
             Michael Eisenson

           /s/ STUART F. FEINER             Director                        September 12, 1996
- ------------------------------------------
             Stuart F. Feiner

          /s/ DONALD E. O'NEILL             Director                        September 12, 1996
- ------------------------------------------
            Donald E. O'Neill
</TABLE>

 
                                       41

<PAGE>   43
 

                               INDEX TO EXHIBITS
 

<TABLE>

<CAPTION>

EXHIBIT
  NO.                                          DESCRIPTION                                   PAGE
- -------                                        -----------                                   ----
<C>       <C>   <S>                                                                          <C>
   3.3      --  Articles of Amendment to Restated Articles of Organization
 10.33      --  First Amendment to Sublease dated August 31, 1995 by and between the
                Registrant, as landlord, and Astra Research Center Boston, Inc., as
                tenant
    21      --  Subsidiaries of the Registrant
    23      --  Consent of Coopers & Lybrand
</TABLE>






<PAGE>   1
                                                                     Exhibit 3.3

                   [COMMONWEALTH OF MASSACHUSETTS LETTERHEAD]


                                                          FEDERAL IDENTIFICATION
                                                          No. 04 2726691


                             ARTICLES OF AMENDMENT       
                     GENERAL LAWS, CHAPTER 156B, SECTION 72

We  Mitchel Sayare,                                        President and
    Jonathan L. Kravetz                                    Clerk/of

                                ImmunocGen, Inc.
- -------------------------------------------------------------------------------
                          (EXACT Name of Corporation)

located at: 128 Sidney Street, Cambridge, MA 02139
            -------------------------------------------------------------------
                     (MASSACHUSETTS Address of Corporation)

do hereby certify that these ARTICLES OF AMENDMENT affecting Articles NUMBERED:
                                       3
- -------------------------------------------------------------------------------
      (Number those articles 1, 2, 3, 4, 5 and/or 6 being amended hereby)

of the Articles of Organization were duly adopted at a meeting held on June 6,
1996, by vote of:

12,583,631 shares of       Common          out of 15,530,355 shares outstanding,
- ----------           ---------------------        ----------
                     type, class & series, 
                           (if any)

           shares of                       out of            shares outstanding,
- ----------           ---------------------       -----------
                     type, class & series, 
                           (if any)

           shares of                       out of            shares outstanding,
- ----------           ---------------------        ----------
                     type, class & series, 
                           (if any)

CROSS OUT  being at least a majority of each type, class or series outstanding
INAPPLI-   and entitled to vote thereon-
CABLE      
CLAUSE


 C   / /
 P   / / 
 M   / /    1  For amendments adopted pursuant to Chapter 156B, Section 70.
R.A. / /    2  For amendments adopted pursuant to Chapter 156B, Section 71.
             
            Note: if the space provided under any Amendment or item on this form
            is insufficient, additions shall be set forth on separate 8-1/2 x 11
            sheets of paper leaving a left-hand
 margin of at least 1 inch for
            binding. Additions to more than one Amendment may be continued on a
            single sheet so long as each Amendment requiring each such addition
            is clearly indicated.



<PAGE>   2
To CHANGE the number of shares and the par value (if any) of any type, class or
series of stock which the corporation is authorized to issue, fill in the 
following:

The total presently authorized is:

                            WITHOUT PAR VALUE STOCKS


<TABLE>
<CAPTION>
TYPE                                         NUMBER OF SHARES
<S>                                          <C>
COMMON:.....................................  
PREFERRED:..................................  
</TABLE>


                             WITH PAR VALUE STOCKS


<TABLE>
<CAPTION>
TYPE                                         NUMBER OF SHARES          PAR VALUE
<S>                                          <C>                       <C>
COMMON:.....................................    20,000,000                $.01
PREFERRED: Series A.........................          None                
           Series B.........................          None
           Series C.........................       122,555                $.01
           Series D.........................       154,525                $.01
</TABLE>


CHANGE the total authorized to:

                             WITHOUT PAR VALUE STOCKS


<TABLE>
<CAPTION>
TYPE                                         NUMBER OF SHARES
<S>                                          <C>
COMMON:.....................................  
PREFERRED:..................................  
</TABLE>

 
                             WITH PAR VALUE STOCKS


<TABLE>
<CAPTION>
TYPE                                         NUMBER OF SHARES          PAR VALUE
<S>                                          <C>                       <C>
COMMON:.....................................    30,000,000                $.01
PREFERRED: Series A.........................          None                
           Series B.........................          None
           Series C.........................       122,555                $.01
           Series D.........................       154,525                $.01
</TABLE>


<PAGE>   3
The foregoing amendment will become effective when these articles of amendment
are filed in accordance with Chapter 156B, Section 6 of The General Laws unless
these articles specify, in accordance with the vote adopting the amendment, a
later effective date not more than thirty days after such filing, in which
event the amendment will become effective on such later date.

                              LATER EFFECTIVE DATE: _________________________


IN WITNESS WHEREOF AND UNDER THE PENALTIES OF PERJURY, we have hereunto signed
our names this    sixth    day of June    , in the year 1996.


          /s/  Mitchel Sayare                             President
_________________________________________________________
               Mitchel Sayare


          /s/  Jonathan L. Kravetz                        Clerk
_________________________________________________________
               Jonathan L. Kravetz
  
                    

<PAGE>   4

                         THE COMMONWEALTH OF MASSACHUSETTS


                                ARTICLES OF AMENDMENT
                       GENERAL LAWS, CHAPTER 156B, SECTION 72
                       ______________________________________
                       ______________________________________


                       I hereby approve the within articles of
                       amendment and, the filing fee in the
                       amount of $______ having been paid, said
                       articles are deemed to have been filed
                       with me this ____ day of _____________,
                       19__.



                                 MICHAEL J. CONNOLLY
                                 Secretary of State








                      To be filled in by Corporation

                      PHOTOCOPY OF ARTICLES OF AMENDMENT TO BE SENT




                 TO:    Anne T. Leland, Legal Assistant
                     ______________________________________________________
                          
                        Mintz, Levin, Cohn, Ferris, Glovsky and Popeo, P.C.
                     ______________________________________________________

                        One Financial Center, Boston, MA 02111
                     ______________________________________________________
     
                                       617 542 6000
                     Telephone: ___________________________________



<PAGE>   1
     FIRST AMENDMENT TO SUBLEASE

Dated:    July      , 1996

     WHEREAS, by a Sublease (the "Sublease") dated as of August 31, 1995,
IMMUNOGEN, INC. ("Landlord") sublet unto ASTRA RESEARCH CENTER BOSTON, INC. a
Massachusetts corporation ("Tenant"), certain Premises (more particularly
defined in the Sublease), on the terms and conditions set forth therein. The
Premises demised under the Sublease comprise a portion of the building known as
and numbered 128 Sidney Street, Cambridge, Massachusetts (the "Building"), which
portion contains approximately 30,778 rentable square feet (consisting of 30,309
square of office and laboratory space and 469 square feet of shipping area), and
constitutes the entire Building other than the portion shown on Exhibit A to the
Main Lease, which portion (the "Retained Portion") was retained by Landlord for
its use; and

     WHEREAS, Landlord and Tenant now desire to amend the Sublease by, among
other things, expanding the Premises by approximately 6,453 square feet (the
"Additional Space"), so as to comprise the entire Building and Land (as defined
in the Sublease), other than certain loading and office areas, which will
continue to be reserved to the Landlord's use, and amending the right of Tenant
to extend the term of the
 Sublease.

     NOW, therefore, in consideration of the foregoing, and for other good and
valuable consideration, each to the other paid, Landlord and Tenant agree that
the Sublease be amended as follows:

     1.   Effective as of the date (the "Effective Date") on which Landlord
          tenders possession of the Additional Space to Tenant, the description
          of the Premises, as set forth in Section 1.0 of the Sublease shall be
          amended to read as follows:

          "The entire building known as and numbered 128 Sidney Street,
          Cambridge, Massachusetts (the "Building"), which contains
          approximately 37,700 rentable square feet; excepting, however, and
          reserving to Landlord (i) that portion of the loading area of the
          Building shown on Exhibit A-1, which portion contains approximately
          469 square feet of space, thus leaving the Tenant 37,231 square feet
          of space, and (ii) a portion of office area. The Building is located
          on the parcel of land (the "Land") shown on the plan attached hereto
          as Exhibit B, together with the portion(s) of the parking area located
          on the Land as are hereafter designated by Landlord and Tenant
          pursuant to Section 9.1 below (collectively, the "Leased Land") (such
          portion of the Building being sometimes hereinafter referred to as the
          "Premises")."

     2.   (a) Effective as of the date hereof, Landlord and Tenant confirm that
          Tenant has duly exercised its options to extend the term of the
          Sublease, as described in Section 2.2 thereof, for both the First
          Extended Term and the Second Extended Term, such that the term of the
          Sublease will expire on February 28, 1999. In addition to the First
          and Second Extended Terms, and provided that, at the time of each such
          exercise, (i) there exists no Event of Default under the Sublease;
          (ii) the Sublease is still in full force and effect; and (iii) Tenant
          shall not have assigned the Sublease or sublet any or all of the
          Premises, Landlord agrees that Tenant shall have the right to further
          extend the term of the Sublease for two additional 



<PAGE>   2

          extended terms (the "Third Extended Term" and the "Fourth Extended
          Term," respectively) of six (6) months each. The Third Extended Term
          shall commence on March 1, 1999, and shall end on August 31, 1999, and
          the Fourth Extended Term shall commence on September 1, 1999, and
          shall end on February 28, 2000. Tenant shall exercise each such option
          by giving Landlord notice of its desire to do so, not later than (i)
          August 31, 1997 with respect to the Third Extended Term, and (ii)
          February 28, 1998 with respect to the Fourth Extended Term, it being
          agreed that time shall be of the essence with respect to the giving of
          each such notice. The giving of any such notice shall automatically
          extend the term of this Sublease for the applicable Extended Term, and
          no instrument of renewal need be executed. In the event that Tenant
          fails to give such notice to Landlord, the term of this Lease shall
          automatically terminate at the end of the term then in effect, and
          Tenant shall have no further right or option to extend the term of
          this Sublease. Each Extended Term shall be on all the terms and
          conditions of this Lease, except that the Rent for each Extended Term
          shall be determined in accordance with Section 3 below.

     3.   (a) Tenant shall continue to pay Rent on the existing portion of the
          Premises as outlined in the Sublease, which is currently $19.50 per
          square foot. In addition, commencing on the Effective Date, Tenant
          shall pay rent on the Additional Space at the rate of $6.55 per square
          foot per annum. For example, for the period commencing on the
          Effective Date and expiring on the last day of the Initial Term, Rent
          shall be $642,438.15 ($19.50 x 30,778 square feet contained in the
          existing Premises, plus $6.55 x 6,453 square feet of Additional Space)
          per annum. Thereafter, the Rent for each portion of the Premises shall
          be separately adjusted as provided in the Sublease, as amended hereby,
          and the sum of the adjusted rents shall be payable.

          (b) The Rent for the Third Extended Term shall be an annualized rate
          equal to the product of (x) the annual Rent payable with respect to
          the Second Extended Term, multiplied by (y) a fraction, the numerator
          of which is the point at which the Index stood at the last day of the
          Second Extended Term, and the denominator of which is the point at
          which the Index stood at the first day of the Second Extended Term.
          The Rent for the Fourth Extended Term shall be an annualized rate
          equal to the product of (x) the annual Rent payable with respect to
          the Third Extended Term, multiplied by (y) a fraction, the numerator
          of which is the point at which the Index stood at the last day of the
          Third Extended Term, and the denominator of which is the point at
          which the Index stood at the first day of the Third Extended Term.

          (c) From and after the Effective Date, pursuant to Section 3.1 of the
          Sublease, Landlord hereby designates the following address as the
          place to which all payments shall be made to Landlord:

                    Immunogen, Inc.
                    333 Providence Highway
                    Norwood, MA 02062
                    Attn: Mr. Frank Pocher

     4.   (a) Effective as of the Effective Date, and notwithstanding the
          provisions of Section 5.1 of the Sublease to the contrary, Tenant
          shall be responsible for, and pay as provided therein, 100% of all
          taxes, special or general assessments, water rents, betterments, rates
          and charges, sewer rents and other impositions and charges described
          therein, and the definition of "Tenant's Tax Share" shall be amended
          to be "100%."



<PAGE>   3

          (b) For purposes of Section 5.3 of the Sublease, it shall be deemed
          that Landlord will not apply for any abatement of Taxes, unless
          Landlord gives Tenant notice that Landlord will do so, which notice is
          given not less than seven (7) days prior to the date on which
          applications are due.

     5.   Effective as of the Effective Date, and notwithstanding the provisions
          of Section 6.0 of the Sublease to the contrary, Tenant shall be
          responsible for, and pay as provided therein, 100% of all utilities
          described therein, including without limitation water and sewer
          charges." In addition, effective as of the Effective Date, and
          notwithstanding the provisions of Section 7.2 of the Sublease to the
          contrary, Tenant shall be responsible for, and pay as provided
          therein, 100% of all insurance premiums incurred by Landlord for the
          coverages described in such Section.

     6.   Landlord presently intends to deliver the Additional Space on or about
          September 1, 1996, but Landlord shall have no liability for failure to
          so deliver the Additional Space on such date. The Additional Space
          shall be delivered to Tenant "broom clean," and free of Landlord's
          equipment. Landlord warrants to Tenant that the HVAC equipment in the
          Additional Space is currently in good working order and condition. In
          all other respects, the Additional Space is to be delivered in its
          then AS IS condition, without representation or warranty by Landlord.
          Landlord shall not be required to perform any work in or to the
          Additional Space, or pay any allowance, to make the same ready for
          Tenant's occupancy. As to the portion of the Premises that will
          continue to be used by Landlord, Landlord and Tenant shall in good
          faith cooperate with each other to develop working procedures such
          that each party can have useful and regular access to its portion of
          such portion as it is entitled to use.

     7.   Tenant shall promptly deliver to Landlord and Overlandlord an amended
          Certificate of Insurance reflecting the increase of the size of the
          Premises pursuant to the provisions of this Amendment.

     8.   From and after the Effective Date, Landlord hereby designates the
          following address as the place to which all notices to Landlord shall
          be sent:

                    Immunogen, Inc.
                    333 Providence Highway
                    Norwood, MA 02062
                    Attn: Mr. Frank J.Pocher

     9.   From and after the Effective Date, and notwithstanding the provisions
          of Section 18.3 of the Lease to contrary, Tenant agrees that it shall
          be responsible for 100% of all amounts paid by Landlord to
          Overlandlord in respect of services provided by Overlandlord under the
          Main Lease.

     10.  Any holding over by Tenant in the Premises beyond the expiration of
          the Third or Fourth Extended Terms shall be treated under clause (x)
          of Section 21.0 of the Sublease.

     11.  Tenant hereby represents and warrants to Landlord that: (i) the
          Sublease is in full force and effect; (ii) there currently exists no
          default (or claim on which a default could be based) on the part of
          Landlord under the Sublease; (iii) the individual(s) executing this
          Amendment on behalf of Tenant is (are) acting according to direction
          of the Board of Directors of Tenant, and has (have) been duly
          authorized 



<PAGE>   4

          and directed to execute and deliver this Amendment; and (iv) no
          approval or consent of any third party or parties (other than
          Overlandlord) is required in order for Tenant to be bound by the terms
          and conditions hereof.

     12.  Any capitalized terms not defined herein shall have the meanings
          ascribed in the Sublease or the Main Lease.

     13.  Effective from and after the Effective Date, the Sublease shall be
          amended by deleting Exhibit A thereto, and substituting therefor
          Exhibit A-1 annexed hereto.

     14.  Reference is made to that certain Equipment Use and Services
          Agreement, between Landlord and Tenant, of even date with the Sublease
          (the "Equipment Agreement"). For purposes of clarification, the
          provisions of Section 2.0 of the Equipment Agreement shall be deemed
          to refer to the term of the Sublease, as affected by this Amendment.
          If the term of the Sublease is extended beyond February 28, 1999,
          Tenant will pay Rent under the Equipment Agreement as follows: The
          Basic Rent for the Third Extended Term shall be an annualized rate
          equal to the product of (x) the annual Rent payable with respect to
          the Second Extended Term, multiplied by (y) a fraction, the numerator
          of which is the point at which the Index stood at the last day of the
          Second Extended Term, and the denominator of which is the point at
          which the Index stood at the first day of the Second Extended Term.
          The Rent for the Fourth Extended Term shall be an annualized rate
          equal to the product of (x) the annual Rent payable with respect to
          the Third Extended Term, multiplied by (y) a fraction, the numerator
          of which is the point at which the Index stood at the last day of the
          Third Extended Term, and the denominator of which is the point at
          which the Index stood at the first day of the Third Extended Term.

     15.  Except as herein specifically amended, the Sublease and the Equipment
          Agreement are ratified and confirmed.



<PAGE>   5


     WITNESS the execution hereof in multiple counterparts under seal the day
     and year first above written.

     Landlord:                     IMMUNOGEN, INC.


                                   By:
                                      Name:
                                      Title:
                                      Hereunto duly authorized

                                      Date:



     Tenant:                       ASTRA RESEARCH CENTER BOSTON, INC.

                                   By:
                                      Name:
                                      Title:
                                      Hereunto duly authorized

                                      Date:


APPROVED:


MASSACHUSETTS INSTITUTE OF TECHNOLOGY


By:
Name:
Title:




<PAGE>   1
 
                                                                      EXHIBIT 21
 
                                IMMUNOGEN, INC.
 
                         SUBSIDIARIES OF THE REGISTRANT
 
ImmunoGen Securities Corp.
Apoptosis Technology, Inc.





<PAGE>   1
 
                                                                      EXHIBIT 23
 
                                IMMUNOGEN, INC.
 
                       CONSENT OF INDEPENDENT ACCOUNTANTS
 
     We consent to the incorporation by reference in the registration statements
of ImmunoGen, Inc. on Form S-8 (File Nos. 33-41534 and 33-73544) of our report,
which includes any explanatory paragraph concerning uncertainties surrounding
the Company's ability to continue as a going concern, dated August 28, 1996, on
our audits of the consolidated financial statements of ImmunoGen, Inc. as of
June 30, 1996 and 1995, and for each of the three years in the period ended June
30, 1996, which reports are included in this Annual Report on Form 10-K.
 
                                          COOPERS & LYBRAND L.L.P.
 
Boston, Massachusetts
September 12, 1996





<TABLE> <S> <C>

<ARTICLE> 5
       
<S>                             <C>
<PERIOD-TYPE>                   12-MOS
<FISCAL-YEAR-END>                          JUN-30-1996
<PERIOD-END>                               JUN-30-1996
<CASH>                                       2,796,636
<SECURITIES>                                         0
<RECEIVABLES>                                        0
<ALLOWANCES>                                         0
<INVENTORY>                                          0
<CURRENT-ASSETS>                             2,959,916
<PP&E>                                      14,555,284
<DEPRECIATION>                              10,391,868
<TOTAL-ASSETS>                               8,505,961
<CURRENT-LIABILITIES>                        1,941,067
<BONDS>                                              0
<PREFERRED-MANDATORY>                                0
<PREFERRED>                                          0
<COMMON>                                   128,250,707
<OTHER-SE>                                           0
<TOTAL-LIABILITY-AND-EQUITY>                 8,505,961
<SALES>                                              0
<TOTAL-REVENUES>                               568,423
<CGS>                                                0
<TOTAL-COSTS>                                        0
<OTHER-EXPENSES>                            13,393,026
<LOSS-PROVISION>                                     0
<INTEREST-EXPENSE>                           3,718,218
<INCOME-PRETAX>                           (16,542,821)
<INCOME-TAX>                                     1,640
<INCOME-CONTINUING>                                  0
<DISCONTINUED>                                       0
<EXTRAORDINARY>                                      0
<CHANGES>                                            0
<NET-INCOME>                              (16,544,461)
<EPS-PRIMARY>                                   (1.15)
<EPS-DILUTED>                                   (1.15)
        

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