Pembrolizumab, Decitabine +/- Venetoclax

This phase Ib trial studies the side effects and best dose of pembrolizumab and how well it works in combination with decitabine with or without venetoclax in treating patients with acute myeloid leukemia or myelodysplastic syndrome that is newly-diagnosed, has come back (recurrent), or does not respond to treatment (refractory). Immunotherapy with monoclonal antibodies, such as pembrolizumab, may help the body's immune system attack the cancer, and may interfere with the ability of tumor cells to grow and spread. Decitabine is in a class of medications called hypomethylation agents. It works by helping the bone marrow produce normal blood cells and by killing abnormal cells in the bone marrow. Venetoclax is in a class of medications called B-cell lymphoma-2 (BCL-2) inhibitors. It may stop the growth of cancer cells by blocking Bcl-2, a protein needed for cancer cell survival. This trial may help doctors find the best dose of pembrolizumab that can be safely given in combination with decitabine with or without venetoclax, and to determine what side effects are seen with this treatment.