CTL-mediated killing of DA1-3b/d365 persistent leukemic cells and in vitro blocking experiments. (A) Incubation of CTL/d35 and DA1-3b/d365 cells with blocking antibodies against B7-H1, B7.1, B7-H1+B7.1, PD1, or control isotype. (B) Incubation of CTL/d365 and DA1-3b/d365 cells with the same antibodies. (C) Incubation of CTL/d35 and DA1-3b/d365 cells with blocking or activating antibodies against CTLA-4, soluble CTLA-4-Ig, anti-B7-H1 plus activating antibodies against CTLA-4, or control isotype. (D) Incubation of CTL/d35 and DA1-3b/d365 cells with blocking or activating antibodies against CD28, anti-B7-H1 plus blocking antibody against CD28, or with a control isotype. All experiments were performed in quadruplicate and repeated at least 3 times. Error bars indicate standard deviation.