Activity of CTLs. (A) IFNG genotype associates with TGF-β–mediated inhibition of CTL activity. PBLs were cultured with HLA-A/-B–matched LCLs in the absence or presence of 10 ng/mL TGF-β for 5 days. Viable cells were washed 3 times to remove any exogenous TGF-β and CTL activity assessed using standard lysis assays as described in “Materials and methods.” Data are shown as percent control lysis of PBLs cultured with LCLs in the absence of TGF-β. For each donor, multiple effector-to-target ratios were tested in triplicate, and LUs determined from the linear portions of the curves. The percent inhibition was calculated using LUs from control versus TGF-β–treated cultures. The results shown are the mean and SD for the triplicates from representative experiments for each donor. When analyzed by the t test, the CTL activity in A/A and T/A PBLs restimulated in the presence of TGF-β is significantly different from either control CTL activity or the CTL activity in T/T PBLs after culture with TGF-β (P = .015). (B) The ability of CTLs to prevent matched LCL growth is inhibited by CTL restimulation in the presence of TGF-β. CTLs were restimulated in the presence or absence of 10 ng/mL TGF-β. At the end of 5 days, CTL activity was assessed by standard CTL assays as in panel A. In addition, a portion of the restimulated cells (10⁴/well) were cultured with titrated numbers of HLA-A/-B–matched or mismatched LCLs for 2 weeks. Data are shown as the mean percent LCL growth ± SD in wells containing both CTLs and LCLs compared to growth in wells containing only LCLs as determined by Alamar blue. Data are combined for 3 donors of each genotype at an 8: 1 effector-to-target ratio; ▪, control CTLs restimulated in the absence of TGF-β; □, CTLs restimulated in the presence of TGF-β.