Involvement of Fas/FasL in tumor-induced apoptosis of T cells.

(A) Inhibition of tumor-mediated apoptosis of Jurkat cells by anti-FasL Ab. [³H]TdR-labeled Jurkat cells were treated for 2 hours with anti-FasL Ab (4H9) or with a hamster IgG control at various concentrations, as indicated. Target cell death was determined at 16 hours by measuring fragmentation of ³H-labeled DNA. The error bars represent the SEM of 8 replicates. (B) Reduced sensitivity of Fas-resistant Jurkat cells to PCI-13–mediated apoptosis. Fas-resistant Jurkat cells were obtained as described in “Materials and methods.” [³H]TdR-labeled Fas-sensitive and [³H]TdR-labeled Fas-resistant Jurkat cells were coincubated with PCI-13 cells (tumor-to-Jurkat ratio, 80:1) or anti-Fas (CH-11) Ab for 16 hours, and tested for apoptosis by JAM assay.