SEATTLE, Nov. 13, 1995 -- A U.S. Food and Drug Administration (FDA) advisory committee today recommended approval of Immunex Corporation's (Nasdaq: IMNX) white blood cell stimulant, Leukine(R) (sargramostim), for use in peripheral blood stem cell (PBSC) mobilization and subsequent myeloid reconstitution in patients undergoing PBSC transplantation. The committee's recommendation, although not binding, will be considered by the FDA in completing its review of the company's application to obtain expanded use for Leukine.

Immunex filed a product license application supplement with the FDA seeking approval to market Leukine for use in PBSC mobilization and transplantation in February of this year.

"We are pleased the committee has recommended approval of Leukine for mobilization of stem cells and after transplantation of the PBSC recognizing it as a standard of care for this important therapeutic use," said Peggy V. Phillips, Immunex senior vice president, pharmaceutical development. "This recommendation is a significant step forward in expanding our labelling for Leukine."

The FDA Biological Response Modifiers Advisory Committee is composed of independent experts from the fields of oncology, hematology, gene therapy, transplantation and immunology and is convened by the FDA to provide independent expertise and technical assistance related to the review of biologic therapeutics. At the conclusion of the meetings, which are open to the public, the panel typically makes a non-binding recommendation to the FDA concerning any issues or questions presented to the committee by FDA staff.

Background on PBSC Mobilization for Transplantation

Stem cells are the fundamental cells from which all other cells of the blood and immune system arise. Stem cells are vital in helping patients recover after chemotherapy and radiotherapy -- two treatments for a variety of cancers. Bone marrow harvesting has been the procedure traditionally used to obtain stem cells from the bone marrow. These same stem cells are present in small quantities in the peripheral blood and can be collected from peripheral blood through a procedure called apheresis. By giving a growth factor, such as Leukine, before apheresis, the number of stem cells in peripheral blood can be enhanced.

During apheresis, a patient's stem cells are collected, saved and reinjected after radiotherapy or chemotherapy treatment, to help repopulate the bone marrow and lead to a quicker recovery of circulating blood cells which fight infections and promote blood clotting. Apheresis is less painful than bone marrow harvesting and requires no anesthesia. Therefore, using PBSC to repopulate the marrow following chemotherapy and radiotherapy is replacing the use of bone marrow stem cells in many settings.

Other Leukine Indications

Leukine, a white blood cell stimulant, is a yeast-derived granulocyte-macrophage colony stimulating factor. It was originally licensed by the FDA in 1991 for use following autologous bone marrow transplantation (BMT) and to prevent death following BMT engraftment delay or failure. It has subsequently been licensed to reduce the duration of neutropenia and prevent early death from infection following induction chemotherapy for older patients suffering from acute myelogenous leukemia. Leukine also has been shown to reduce infection following treatment of acute myelogenous leukemia and has been shown to reduce infection, antibiotic use and hospital stays following autologous bone marrow transplantation in the treatment of certain cancers.

Immunex is a biopharmaceutical company dedicated to developing immune system science to protect human health.

American Home Products Company (NYSE: AHP) owns a majority interest in Immunex. AHP is one of the world's largest research-based pharmaceutical and health care products companies and is a leading developer, manufacturer and marketer of prescription drugs and over-the-counter medications. It is also a leader in vaccines, generic pharmaceuticals, biotechnology, agricultural products, animal health care, medical devices and food products.

CONTACT: Robin Shapiro of Immunex, 206-587-0430 (IMNX AHP)