News Release

Immunex's TRAIL Molecule Shows Potential As Anti-Tumor Agent

Peer-Reviewed Publication

Immunex Corporation

SEATTLE, WA -- A preclinical study published in the journal Nature Medicine today demonstrated that TRAIL (TNF-related apoptosis-inducing ligand) suppresses tumor growth, and in some instances caused complete remission of tumors, by a direct and specific mechanism. The work described in the journal was conducted in mice by scientists at Immunex Corporation (NASDAQ:IMNX).

In the study, groups of mice were injected with tumor cells from a human breast cancer, or either of two different colon cancers. Following two weeks of daily injections with TRAIL, complete remission of all tumors was observed in a high proportion (70%-100%) of the treated mice. In contrast, the tumors of the untreated control mice grew progressively. Importantly, because of TRAIL's apparent specificity in targeting tumor cells, normal tissues showed no observable adverse effects.

"TRAIL is the first of a new generation of novel molecules that directly and selectively induce apoptosis of tumor cells and may have potential in the treatment of a wide variety of cancers," said David Lynch, Ph.D., senior staff scientist and senior author of the manuscript. "We are particularly excited by the apparent lack of toxicity shown in mouse studies with TRAIL to date."

Unlike most traditional chemotherapeutics, TRAIL is a naturally occurring immune system protein that is a member of the tumor necrosis factor (TNF) family. TRAIL binds to at least four distinct receptors found on many tumor cells and signals these cells to destroy themselves via a process known as apoptosis. Immunex scientists constructed a soluble form of TRAIL that was found to stimulate tumor cell destruction.

"We are very pleased about the results of the study and have promoted TRAIL to a high priority pre-development product," said Doug Williams, senior vice president, discovery research. "We will continue to study TRAIL as an anti-tumor agent in a variety of cancers."

In June of 1998, the U.S. Patent and Trademark Office issued to Immunex a gene patent that covers DNA encoding of TRAIL. Immunex has filed additional patent applications worldwide.

Immunex is a biopharmaceutical company dedicated to developing immune system science to protect human health. The company's products offer hope to patients with cancer, inflammatory and infectious diseases.

American Home Products 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 and over-the-counter medications. It is also a global leader in vaccines, biotechnology, agricultural products, and animal health care.

NOTE: This news release contains forward-looking statements that involve risks and uncertainties, including risks associated with clinical development, regulatory approvals, product commercialization and other risks described from time to time in the SEC reports filed by Immunex, including the most recently filed Form 10K and 10-Q.

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This news release, as well as additional information about Immunex of interest to investors, customers, prospective employees and patients, is available on the Immunex web site at http://www.immunex.com.



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