CTLA4 and acute lymphoblastic leukemia: When patients' ALL blasts were used as target cells, proliferation of T cells could be significantly increased under PD-1 blockade or under combined blockade of PD-1 and CTLA-4 (Figure 5A): CD3+ T-cell proliferation was 19.8%±14.9 after stimulation of PBMC with irradiated ALL blast cells and 1ng/ml Blinatumomab (n=13) and was increased to a mean CD3+ T-cell proliferation of 24.4%±15 after addition of PD-1 blocking antibody and of 31.1%±15.1 after PD-1 and CTLA-4 antibody blockade.