PDCD1 and acute myeloid leukemia: In our in vitro co-culture experiments we observed cytotoxic activity from CAR T-cells challenged with either PD-L1neg or PD-L1+ AML blasts, although it is possible that in the in vivo milieu, this mechanism could contribute to increased T-cell apoptosis for binding the respective receptor on T-cells, as PD-1+ CD8 T-cells were found to increase in AML metastatic site in vivo [35].