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CAMBRIDGE, Mass., Aug 08, 2002 /PRNewsire-FirstCall via Comtex/ -- ImmunoGen, Inc. (Nasdaq: IMGN) and British Biotech plc (LSE: BBG, Nasdaq: BBIOY) announced today that patient treatment has begun in the planned second Phase I study of huN901-DM1/BB- 10901, a novel anti-cancer agent targeted at small-cell lung cancer that uses a humanized monoclonal antibody to deliver a highly potent chemotherapeutic agent specifically to the site of the tumor.

This study will assess daily dosing of the product and complements a weekly dosing Phase I study currently underway in the United States. It is being conducted in the United Kingdom at the Christie Hospital in Manchester, under the direction of Dr. Paul Lorigan and Dr. Malcolm Ranson of the Department of Medical Oncology, and at the Nottingham City Hospital, under the direction of leading cancer expert Professor James Carmichael and Dr. Penella Woll.

This open-label, dose-escalation study will assess the safety, tolerability, and pharmacokinetics of increasing doses of huN901-DM1/BB-10901; evidence of biological activity will also be determined. The drug will be administered daily for three successive days followed by an eighteen-day follow-up period. As in the U.S. Phase I study, eligible patients have relapsed or refractory small-cell lung cancer, or other tumors that express the CD56 antigen targeted by the drug's antibody component. Dosage will be increased in each new cohort of patients until dose-limiting toxicity occurs and the maximum tolerated dose is established.

The study is expected to be completed by mid-2003, with results available later in the year, although timing is dependent on the rate of patient recruitment and the extent of dose escalation.

Commenting on the study, Dr. Elliot Goldstein, Chief Executive Officer of British Biotech, said, "We have made good progress in the U.S. with our trial of this novel agent. In this study we aim to find out whether a more frequent dosing regimen can be safely employed. We expect that the data from these two Phase I studies will provide the information needed to select the optimum dosing regimen to take forward into Phase II anti-tumor efficacy studies."

Mitchel Sayare, Ph.D., Chairman and Chief Executive Officer of ImmunoGen, said, "We are pleased with the progress being made by British Biotech. The data from the U.S. Phase I study with huN901-DM1/BB-10901 are encouraging and, combined with the data this study is expected to yield, should establish the appropriate dosing schedule for future studies with the product. This study also marks the first clinical trial to be conducted with an ImmunoGen Tumor- Activated Prodrug product in Europe."

Earlier this year, data from the ongoing U.S. Phase I study of huN901- DM1/BB-10901 were presented at the 2002 Annual Meeting of the American Society of Clinical Oncology (ASCO). The presentation included data on the product's pharmacokinetics and tolerability; initial evidence of biological activity was also presented. Patients in this study are now being dosed at 75 mg/m2.

British Biotech acquired rights to develop and commercialize huN901- DM1/BB-10901 for Europe and Japan under an agreement with ImmunoGen in May 2000. ImmunoGen retained commercialization rights for the U.S. and the rest of the world.

About ImmunoGen, Inc.

ImmunoGen, Inc. develops innovative biopharmaceuticals for the treatment of cancer. The Company's Tumor-Activated Prodrug (TAP) technology couples highly potent cytotoxic agents with tumor-targeting antibodies to create effective new treatments for cancer with minimal damage to normal tissue. Two TAP products developed by ImmunoGen are in clinical trials - huN901-DM1/BB- 10901 and cantuzumab mertansine; the latter is licensed to GlaxoSmithKline. Several companies are developing TAP products comprised of ImmunoGen's TAP technology and the their own antibody - Genentech (Trastuzumab-DM1), Millennium (MLN591DM1) and Boehringer Ingelheim (bivatuzumab mertansine). ImmunoGen also has multi-target agreements with Genentech, Abgenix, and Millennium that can potentially yield multiple additional TAP products.

About British Biotech plc

British Biotech is a research and development stage pharmaceuticals company aiming to develop and commercialize specialist drugs for serious illnesses, principally cancer. It currently has four diverse products in or near to patient trials, supplemented by focused drug discovery research programs.

For ImmunoGen, Inc.

This press release includes forward-looking statements based on management's current expectations. Factors that could cause future results to differ materially from such expectations include, but are not limited to: the success of the Company's research strategy; the applicability of the discoveries made therein; the difficulties inherent in the development of pharmaceuticals, including uncertainties as to the timing and results of preclinical studies; delayed achievements of milestones; reliance on collaborators; uncertainty as to whether the Company's potential products will succeed in entering human clinical trials and uncertainty as to the results of such trials; uncertainty as to whether adequate reimbursement for these products will exist from the government, private healthcare insurers and third-party payors; the uncertainties as to the extent of future government regulation of the pharmaceutical business; and other factors described in ImmunoGen's periodic filings with the Securities and Exchange Commission.

For British Biotech

This news release contains forward-looking statements that reflect the Company's current expectations regarding future events. Forward-looking statements involve risks and uncertainties. Actual events could differ materially from those projected herein and depend on a number of factors including the success of the Company's research strategies, the applicability of the discoveries made therein, the successful and timely completion of clinical studies and the uncertainties related to the regulatory process.

CONTACT:
Carol Hausner, Senior Director, Investor Relations and Corporate Communications for ImmunoGen, Inc., +1-617-995-2500, info@immunogen.com; or Pete Holmberg of Rx Communications Group, LLC, +1-917-322-2164, pholmberg@rxir.com; or Dr. Elliot Goldstein, Chief Executive Officer, or Tony Weir, Finance Director, (U.K.) 01865 781166, both for British Biotech plc; or Duke Coffey of GA Kraut +1-212-696-5600; or Georgina Briscoe of Hogarth Partnership, (U.K.) 020-7357-9477 /Company News On-Call: http://www.prnewswire.com/comp/420425.htm