MOLECULAR MECHANISMS OF IMMUNE-MEDIATED LYSIS OF MURINE RENAL-CANCER - DIFFERENTIAL CONTRIBUTIONS OF PERFORIN-DEPENDENT VERSUS FAS-MEDIATEDPATHWAYS IN LYSIS BY NK AND T-CELLS

Mice bearing the experimental murine renal cancer Renca can be success fully treated with some forms of immunotherapy, In the present study, we have investigated the molecular pathways used by NK and T cells to lyse Renca cells, Renca cells normally express low levels of Fas that can be substantially enhanced by either IFN-gamma or TNF-alpha, and th e combination of IFN-gamma + TNF-alpha synergistically enhances cell-s urface Fas expression. In addition, cells pretreated with IFN-gamma an d TNF-alpha are sensitive to lysis mediated by Fas ligand (FasL)-expre ssing hybridomas (dllS), cross-linking of anti-Fas Abs or soluble Fas (FasL), Lysis via Fas occurs by apoptosis, since Renca shows all the t ypical characteristics of apoptosis, No changes in levels of bcl-2 wer e observed after cytokine treatments. We also examined cell-mediated c ytotoxic effects using activated NK cells and T cells from gld FasL-de ficient mice, and perforin-deficient mice, as well as wild-type C57BL/ 6 and BALB/c mice. Interestingly, the granule-mediated pathway predomi nated in killing of Renca by activated NK cells, while the Fas/FasL pa thway contributed significantly to cell-mediated killing of Renca by a ctivated T cells. These results suggest that killing of Renca tumor ce lls by immune effector cells can occur by both granule and Fas-mediate d cytotoxicity. However, for the Fas-mediated pathway to function, cel l surface levels of Fas need to be increased beyond a critical thresho ld level by proinflammatory cytokines such as IFN-gamma and TNF-alpha.