Eligible subjects must meet all of the following criteria: 1. Subject must have confirmation of diagnosis of AML (except for acute promyelocytic leukemia [APL]) or MDS per 2016 World Health Organization (WHO) criteria. 2. For AML (except for APL) cohort: 1. Previously treated relapsed/refractory AML subjects 2. Treatment-naïve AML subjects should be: ≥60 years of age OR ≥18 years and <60 years will be eligible if the subject has at least one of the following co-morbidities, which make the subject unfit for intensive chemotherapy 3. For MDS cohort: Adult TN MDS and R/R MDS: revised International Prognostic Scoring System (IPSS-R) score > 3 and bone marrow blasts ≥ 5%. 4. Subject must have a projected life expectancy of at least 12 weeks. 5. Subject must have adequate renal function as demonstrated by a creatinine clearance ≥ 30 mL/min; determined via urine collection for 24-hour creatinine clearance or by the Cockcroft-Gault formula. 6. Subject must have adequate liver function

1. R/R AML or R/R MDS with no response or intolerance to post azacitidine or BCL-2i. 2. Subject has acute promyelocytic leukemia (French-American-British Class M3 AML) . 3. Subject has known central nervous system (CNS) leukemia. 4. Suggest patients with active hepatitis B or C virus infection 5. History of immunodeficiency, including a positive human immunodeficiency virus (HIV) antibody test. 6. Subjects have another active malignancy within the past 2 years before study entry, except for curatively treated.