A, PBMC from a healthy human donor were activated with PHA for 72 hours and subsequently stained with antagonist anti-CTLA4 mAb L3D10 or Ipilimumab. Human melanoma C8161 cells were stained for PDL1 expression (29E.2A3 mAb). B, PHA-treated CTLA4+ T cells were co-cultured with PDL1+ C8161 human melanoma cells in the presence or absence of CD80-Fc, Ipilimumab, control recombinant protein TROY-Fc, antagonist CTLA4 mAb L3D10, or irrelevant isotype antibody. After three days of culture T cell activation was assessed by measuring IFNγ in the supernatants. Top panel shows one of three independent experiments; bottom panel shows the average of three independent experiments. Error bars indicate SD. Bars with * are statistically different from all other values and are not statistically different from each other at p < 0.05.