SEC Form 3

FORM 3

UNITED STATES SECURITIES AND EXCHANGE COMMISSION Washington, D.C. 20549 INITIAL STATEMENT OF BENEFICIAL OWNERSHIP OF SECURITIES Filed pursuant to Section 16(a) of the Securities Exchange Act of 1934 or Section 30(h) of the Investment Company Act of 1940

OMB APPROVAL OMB Number: 3235-0104 Estimated average burden hours per response: 0.5

1. Name and Address of Reporting Person* ZIFF ASSET MANAGEMENT LP (Last) (First) (Middle) 283 GREENWICH AVE (Street) GREENWICH CT 06830 (City) (State) (Zip)	2. Date of Event Requiring Statement (Month/Day/Year) 06/20/2008	3. Issuer Name and Ticker or Trading Symbol IMMUNOGEN INC [ IMGN ]
		4. Relationship of Reporting Person(s) to Issuer (Check all applicable) Director X 10% Owner Officer (give title below) Other (specify below)	5. If Amendment, Date of Original Filed (Month/Day/Year)
			6. Individual or Joint/Group Filing (Check Applicable Line) Form filed by One Reporting Person X Form filed by More than One Reporting Person

Table I - Non-Derivative Securities Beneficially Owned
1. Title of Security (Instr. 4)	2. Amount of Securities Beneficially Owned (Instr. 4)	3. Ownership Form: Direct (D) or Indirect (I) (Instr. 5)	4. Nature of Indirect Beneficial Ownership (Instr. 5)
Common Stock	9,046,200	D(1)(2)

Table II - Derivative Securities Beneficially Owned (e.g., puts, calls, warrants, options, convertible securities)
1. Title of Derivative Security (Instr. 4)	2. Date Exercisable and Expiration Date (Month/Day/Year)		3. Title and Amount of Securities Underlying Derivative Security (Instr. 4)		4. Conversion or Exercise Price of Derivative Security	5. Ownership Form: Direct (D) or Indirect (I) (Instr. 5)	6. Nature of Indirect Beneficial Ownership (Instr. 5)
	Date Exercisable	Expiration Date	Title	Amount or Number of Shares

1. Name and Address of Reporting Person* ZIFF ASSET MANAGEMENT LP (Last) (First) (Middle) 283 GREENWICH AVE (Street) GREENWICH CT 06830 (City) (State) (Zip)

1. Name and Address of Reporting Person* PBK HOLDINGS INC (Last) (First) (Middle) 283 GREENWICH AVE (Street) GREENWICH CT 06830 (City) (State) (Zip)

1. Name and Address of Reporting Person* KORSANT PHILIP B (Last) (First) (Middle) 283 GREENWICH AVE (Street) GREENWICH CT 06830 (City) (State) (Zip)

1. Name and Address of Reporting Person* ZBI Equities, L.L.C. (Last) (First) (Middle) 283 GREENWICH AVE (Street) GREENWICH CT 06830 (City) (State) (Zip)

Explanation of Responses:

1. This statement is being filed by Ziff Asset Management, L.P. ("Ziff Asset Management"), PBK Holdings, Inc. ("PBK Holdings"), Philip B. Korsant ("Korsant") and ZBI Equities, L.L.C. ("ZBI Equities" and collectively with Ziff Asset Management, PBK Holdings and Korsant, the "Reporting Persons."). PBK Holdings is the general partner of Ziff Asset Management, Korsant is the sole shareholder of PBK Holdings and ZBI Equities assists in the management of certain assets held by Ziff Asset Management.

2. Ziff Asset Management is the record owner of all of the 9,046,200 shares of common stock, par value $.01 per share of ImmunoGen, Inc. (the "Common Stock") reported herein. The Reporting Persons do not have or share voting or investment power over 1,233,700 shares of the Common Stock reported herein and each of the Reporting Persons disclaims beneficial ownership of such 1,233,700 shares, except to the extent of its respective pecuniary interests, if any, in such shares. PBK Holdings, Korsant and ZBI Equities may each be deemed to have or share voting or investment power over the remaining 7,812,500 shares of Common Stock reported herein. Each of the Reporting Persons disclaims beneficial ownership of such 7,812,500 shares of Common Stock, except to the extent of its respective pecuniary interest, if any, in such 7,812,500 shares.

	/s/ David Gray, Vice President of PBK Holdings, Inc., the general partner of Ziff Asset Management, L.P.	06/30/2008
	/s/ David Gray, Vice President of PBK Holdings, Inc.	06/30/2008
	/s/ Philip B. Korsant	06/30/2008
	/s/ David Gray, Vice President of PBK Holdings, Inc., sole member of ZBI Equities, L.L.C.	06/30/2008
	** Signature of Reporting Person	Date
Reminder: Report on a separate line for each class of securities beneficially owned directly or indirectly.
* If the form is filed by more than one reporting person, see Instruction 5 (b)(v).
** Intentional misstatements or omissions of facts constitute Federal Criminal Violations See 18 U.S.C. 1001 and 15 U.S.C. 78ff(a).
Note: File three copies of this Form, one of which must be manually signed. If space is insufficient, see Instruction 6 for procedure.
Persons who respond to the collection of information contained in this form are not required to respond unless the form displays a currently valid OMB Number.