PDCD1 and acute myeloid leukemia: In a very elegant study comparing bone marrow-infiltrating T cells from HSCT recipients displaying relapse of acute myeloid leukemia after transplantation and from patients maintaining complete remission, Noviello et al. (7) recently reported higher proportions of T cells expressing inhibitory receptors, including PD-1, in relapsing patients than in patients maintaining complete remission.