News Release

Immunex Advances CD40 Ligand To Phase II Clinical Trial In People With Metastatic Kidney Cancer

Peer-Reviewed Publication

Immunex Corporation

CD40L Moved Forward Based On Outcomes Of Multi-Dose Safety Trial

SEATTLE - Immunex Corporation (Nasdaq: IMNX) announced today that it has launched a Phase II trial of the investigational agent CD40 Ligand (CD40L) in the most common form of kidney cancer, renal cell carcinoma. The company is continuing the development of CD40L based on results of a multi-dose Phase I trial of the drug in advanced cancer patients.

The Phase I study, which evaluated escalating doses of CD40L in patients with recurrent solid tumors and lymphoma, has been completed and the objectives of the study were met. The results of this multi-dose study will be presented at a future medical meeting. Several pre-clinical studies on the anti-tumor effect of CD40L will be presented next week at the 35th Annual Meeting of the American Society of Clinical Oncology (ASCO). In these studies, conducted in both mice and fresh human tumor samples, CD40L inhibited tumor growth in multiple solid tumor types, such as breast, lung, ovarian and colon.

"Based on the results of these safety trials, Immunex is moving forward with a Phase II trial of CD40L in metastatic renal cell carcinoma," said Ann Hayes, M.D., senior vice president, medical development, Immunex. "Patients with this disease currently have limited treatment options. Treatment with CD40L represents a novel approach to treating cancer, by potentially having a direct effect on tumor cells and by stimulating the immune system to recognize and seek out cancer cells for destruction."

The study, being conducted in three cancer treatment centers across the United States, will evaluate the safety and efficacy of the drug in metastatic renal cell carcinoma.

Approximately 30,000 new cases of kidney cancer will be diagnosed this year in the United States and about 11,900 people will die from this disease. It is the 8th most common cancer in men and the 10th most common in women. Renal cell carcinoma (renal is the Latin word for kidney) accounts for about 85% of all kidney tumors. Men are diagnosed with renal cell carcinoma almost twice as often as women are and it usually occurs between the ages of 50-70 years.

CD40L is a protein primarily expressed on the surface of activated CD4+ T cells. Its receptor, CD40, is expressed on B cells, antigen presenting cells such as dendritic cells, macrophages and on some other normal and tumor cells. Engagement of CD40 on antigen presenting cells by CD40L plays a key role in activating the immune system. Pre-clinical research has shown that CD40L can stop tumor growth and actually kill many tumor cell types. It does this in two ways. The first way is by direct binding to its CD40 partner present on many tumor cell types generating a signal for the tumor cell to either stop growing or self destruct (apoptose). The second way is by stimulating specific immune responses to the tumor.

Immunex plans to conduct a second Phase II trial of CD40L in a separate solid tumor type. Pre-clinical studies have also suggested potential for the compound in HIV and other immunodeficiency diseases. Immunex holds the exclusive global rights CD40L.

Immunex Corporation 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 leader in vaccines, biotechnology, agricultural products, and animal health care.

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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, including the most recently filed form 10-K and form 10-Q. For more information, please refer to www.immunex.com.

An electronic version of this news release - as well as additional information about Immunex of interest to investors, customers, future employees and patients - is available on the Immunex home page at www.immunex.com.



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