The increase in tumor treatment efficacy that results from engineered expression of IL-12 by tumor-specific T cells appears to be due in part to IL-12-mediated effects on bone marrow-derived tumor stromal cells and induction of the Fas death receptor.32 33 In the present study in which IL-12 is localized to the T-cell membrane, it is not known which cells IL-12 may influence. This evidence concerns the gene FAS and neoplasm.