Scientists at Immunex Corp. have identified a new cytokine, designatedInterleukin-15 (IL-15), which they believe may have potential as ananti-cancer agent and a therapy for infectious diseases. The findings ofthe Seattle, Wash. company were reported in the May 13 issue ofScience.The scientists reported that IL-15 stimulates proliferation of T-lymphocytes _ cells which kill tumor cells and host cells infected withvirus, and which recognize and reject foreign tissue. It shares theseproperties with Interleukin-2 (IL-2) but also exhibits some differences.The Immunex team is still trying to determine the exact differences."IL-2 stimulates T-cell activity but it is extremely toxic," said KennethGrabstein, the director of the company's department of celllularimmunology and one of the authors of the study. "One possibility isthat IL-15 has the anti-tumor activity of IL-2 without its toxicproperties."Grabstein said IL-15 was discovered while testing a simian kidneyepithelial cell line, CV-1/EBNA, for cytokine activity more than a yearago. The cell line was purified and cloned. The human clone has alsobeen isolated and the molecule is already undergoing testing in mousemodels.Grabstein said IL-15 has a molecular structure similar to that of helicalcytokines. However, he noted, "It is made by cells that don't makeother cytokines we know of. The tissue distribution is unusual, and wedon't know what its significance may be. We have found the presenceof the messenger RNA, and presumably of the protein as well, in thetissue of the muscle, kidney, liver and placenta as well as the heart andlung."IL-15 uses the chains of the IL-2 receptors, and may share itsbiological activity through these receptors. What this means is still tobe determined.The scientists demonstrated that IL-15 uses components of the IL-2receptor and can function in the absence of IL-2. "This suggests thatIL-15 does not act by inducing IL-2 activity, as we originallytheorized," Grabstein said. "It interacts itself with IL-2 receptors, notby inducing IL-2 activity."Immunex shares closed at $13.25, up 25 cents, boosted by the IL-15discovery and by news that it will develop anti-cancer drugs based onpaclitaxel. (See a related story, p. 4)

-- Philippa Maister

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