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Filed Pursuant to Rule 424(b)(3)
REGISTRATION NO. 333-07661
PROSPECTUS SUPPLEMENT NO. 3 DATED FEBRUARY 29, 2000
TO THE PROSPECTUS DATED JULY 12, 1996 OF IMMUNOGEN, INC.
This Prospectus Supplement No. 3 amends the information in the section
entitled "Selling Stockholders" in the Prospectus dated July 12, 1996 and as
amended by Prospectus Supplement No. 1 dated July 23, 1996 and Prospectus
Supplement No. 2 dated February 21, 1997. Hawthorne Capital Corporation Money
Purchase Pension Plan ("Hawthorne") has sold to Harry Leopold (Roth IRA Bear
Stearns Sec. Corp. Cust.) ("Harry Leopold") Hawthorne Warrants to purchase
250,000 shares of ImmunoGen, Inc. Common Stock, $.01 par value per share,
("Common Stock"). In order to reflect Harry Leopold as a Selling Stockholder
hereunder, and assuming for such purposes that the Warrants to purchase 250,000
shares are exercised, the Selling Stockholder table is amended by deleting the
information as to Hawthorne as Selling Stockholder with respect to 250,000
shares of Common Stock and substituting therefor the following information:
<TABLE>
<CAPTION>
Shares Owned Prior Shares Owned After
to Offering(1) Offering (2)
-------------- Number of Shares ------------
Selling Stockholder Number Percent Being Offered Number Percent
- ------------------- ------ ------- ---------------- ------ -------
<S> <C> <C> <C> <C> <C>
Harry Leopold 250,000 * 250,000 0 --
</TABLE>
- -------------
*Less than 1%.
(1) Based on 32,835,562 shares of Common Stock outstanding on February 28, 2000.
Assumes the transfer of the Hawthorne Warrants to Harry Leopold and adjusted
to reflect the exercise of the Warrants by Harry Leopold into 250,000 shares
of Common Stock.
(2) Assumes the sale of all shares offered hereby to unaffiliated third parties.
This Prospectus Supplement No. 3 should be read in conjunction with the
Prospectus dated July 12, 1996 and the Prospectus Supplements Nos. 1 and 2 dated
July 23, 1996 and February 21, 1996, respectively.
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