Immune checkpoint ligands expressed on cells in the AML microenvironment interact with receptors including programmed death receptor 1 (PD-1), cytotoxic T-lymphocyte associated protein 4 (CTLA-4), lymphocyte-activation gene 3 (LAG3), and T cell immunoglobulin and mucin-containing-3 (TIM3) on T cells, leading to T cell exhaustion (34, 36, 37). Here, CTLA4 is linked to acute myeloid leukemia.