Monday, May 1, 2000

Immunex and Genentech Moving Forward with Preclinical Development Program of TRAIL/Apo2L

South San Francisco, Calif. and Seattle -- May 1, 2000 --

Immunex (Nasdaq: IMNX) and Genentech (NYSE: DNA) today reiterated the intention of the two companies to move forward in their collaborative preclinical study of TRAIL/Apo2L in cancer research.

Published experiments, including in vitro and in vivo preclinical models, demonstrates that the TRAIL/Apo2L molecule has the ability to kill a broad cross section of human tumor cell types without significantly affecting the survival of normal human cells (NATURE MEDICINE, Volume 5, Number 2, February 1999). Based on these results, the two companies moved forward in 1999 with a joint preclinical research collaboration involving TRAIL/Apo2L.

Recently, the journal NATURE MEDICINE published a paper from the University of Pittsburgh regarding a version of TRAIL/Apo2L made at the University of Pittsburgh, material different from that used by scientists at Genentech and Immunex. The paper describes an experiment regarding the affects the University of Pittsburgh molecule has on isolated human hepatocytes (human liver cells) in culture, concluding that this particular form of the molecule induced the death of isolated human hepatocytes in culture.

Previous experiments by scientists at Immunex and Genentech have shown that different forms of the TRAIL/Apo2L molecule can demonstrate very different biological properties. Scientists at the companies are collaborating with the senior author of the experiment, Dr. Stephen Strom, Ph.D., of the University of Pittsburgh, to compare the University of Pittsburgh TRAIL material with the Immunex/Genentech TRAIL/Apo2L material.

In collaboration with Dr. Strom, scientists at the companies are focused on determining whether the TRAIL/Apo2L material being produced and studied by Genentech/Immunex will have similar properties on isolated human hepatocytes in culture to those observed with the University of Pittsburgh TRAIL molecule.

As planned, the future development of TRAIL/Apo2L will be based on the results of numerous toxicology and other pre-clinical experiments, including the results of the collaborative studies with Dr. Strom.

Genentech, Inc. is a leading biotechnology company that discovers, develops, manufactures, and markets human pharmaceuticals for significant unmet medical needs. Thirteen of the currently approved biotechnology products stem from Genentech science. Genentech markets seven biotechnology products directly in the United States. The company has headquarters in South San Francisco, California, and is traded on the New York Stock Exchange under the symbol DNA.

Immunex Corporation is a biopharmaceutical company dedicated to improving lives through immune system science innovations.

AHP owns a majority interest in Immunex. AHP is one of the world's largest research-based pharmaceutical and health care products companies. It is a leader in the discovery, development, manufacturing and marketing of prescription drugs, including biotechnological and vaccine products, animal health care products and over-the-counter medications.

NOTE: This news release contains forward-looking statements that involve risks and uncertainties, including risks associated with clinical development, regulatory approvals, patent litigation, product commercialization, and other risks described from time to time in the SEC reports filed by Immunex and Genentech, including their most recently filed Form 10-Ks and Form 10-Qs. For more information, please refer to www.immunex.com.

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