To reach a clinically detectable size, neoplasms must be able to suppress or evade a host immune response. Activated T cells may enter apoptosis in the presence of Fas ligand (FasL) (1), and tissue expression of FasL has been shown to contribute to immune privilege in the eye and testis (2, 3). We have demonstrated that all human lung carcinoma cell lines tested (16 of 16) express a Mr 38,000 protein consistent with FasL by immunoblotting, whereas the majority of resected tumors (23 of 28) show positive staining for FasL by immunohistochemistry. DNA sequencing of reverse transcription-PCR products from lung cancer cells and resected lung tumors confirms the presence of human FasL mRNA in these neoplastic tissues. Furthermore, lung carcinoma cells are capable of killing a Fassensitive human T cell line (Jurkat) in coculture experiments; this killing was inhibited by a recombinant form of the soluble portion of the Fas receptor (FasFc). FasL expression by neoplastic cells represents a potential mechanism for peripheral deletion of tumor-reactive T-cell clones.

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Supported by a Research Advisory Group grant from the Department of Veterans Affairs (to R. A. K.) and Grant GM2735 (to D. R. G.) from the NIH, Bethesda, MD. T. B. is a fellow of the Swiss Foundation for Medical-Biological Fellowships.

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