Expression of immune checkpoint molecules PD-1, CTLA-4, T-cell immunoglobulin and mucin domain-containing protein 3 (TIM-3), and T cell immunoglobulin and ITIM domains (TIGIT) on T cells from patients with MDS or AML suggest that T cells in these patient populations are exhausted.19 Here, PDCD1 is linked to acute myeloid leukemia.