Inclusion Criteria: 1. Men and women ≥ 18 years of age, at the time of signing the ICD (Informed Consent Document). 2. Subject must understand and voluntarily sign an ICD prior to any study-related assessments/procedures being conducted. 3. Relapsed or refractory AML (Acute Myeloid Leukemia) (Parts A and B) or relapsed or refractory (R/R) higher-risk MDS (Myelodysplastic Syndrome) (HR-MDS) (Part B only) as defined by World Health Organization criteria who are not suitable for other established therapies. 1. In Part A, R/R AML 2. In Part B, R/R AML including - Relapsed after allogeneic HSCT or - In second or later relapse or - Refractory to initial induction or re-induction treatment or - Refractory or relapse after HMA treatment (HMA failure defined as primary progression or lack of clinical benefit after a minimum of 6 cycles or unable to tolerate HMA due to toxicity) or - Refractory within 1 year of initial treatment (excluding those with favorable risk based on cytogenetics) 3. In Part B, R/R HR-MDS (Revised International Prognostic Scoring System score (IPSS-R) > 3.5 points, IPSS-R calculated during screening period): - IPSS-R intermediate risk (in combination with more than 10% bone marrow blasts or poor or very poor IPSS-R cytogenetic risk) or - IPSS-R high or - IPSS-R very high risk 4. Eastern Cooperative Oncology Group Performance Status (ECOG PS) of 0 to 2. 5. At least 4 weeks (from first dose) has elapsed from donor lymphocyte infusion (DLI) without conditioning. 6. Subjects must have the following screening laboratory values: - Corrected serum Ca or free (ionized) serum Ca within normal limits (WNL). o Corrected Ca (mg/dL) = Total Ca (mg/dL) - 0.8 (albumin [g/dL] - 4) - Total White Blood Cell count (WBC) < 25 x 10^9/L prior to first infusion. Prior or concurrent treatment with hydroxyurea to achieve this level is allowed. - Potassium and magnesium within normal limits or correctable with supplements. - Aspartate aminotransferase/serum glutamic oxaloacetic transaminase (AST/SGOT) or alanine aminotransferase/serum glutamate pyruvic transaminase (ALT/SGPT) ≤ 2.5 x Upper Limit of Normal (ULN). - Uric acid ≤ 7.5 mg/dL (446 μmol/L). Prior and/or concurrent treatment with hypouricemic agents (eg, allopurinol, rasburicase) are allowed. - Selected electrolytes within normal limits or correctable with supplements. - Serum bilirubin ≤ 1.5 x ULN (upper limit of normal). - Estimated serum creatinine clearance of ≥ 60 mL/min using the Cockcroft-Gault equation. Measured creatinine clearance from a 24-hour urine collection is acceptable if clinically indicated. - International normalized ratio (INR) < 1.5 x ULN and Partial thromboplastin time (PTT) < 1.5 x ULN. Exclusion Criteria: 1. Subjects with acute promyelocytic leukemia (APL) 2. Subjects with clinical symptoms suggesting active central nervous system (CNS) leukemia or known CNS leukemia. Evaluation of cerebrospinal fluid is only required if there is clinical suspicion of CNS involvement by leukemia during screening. 3. Patients with prior autologous hematopoietic stem cell transplant who, in the investigator's judgment, have not fully recovered from the effects of the last transplant (e.g., transplant related side effects). 4. Prior allogeneic hematopoietic stem cell transplant (HSCT) with either standard or reduced intensity conditioning ≤ 6 months prior to starting CC-90009. 5. Subjects on systemic immunosuppressive therapy post HSCT at the time of screening, or with clinically significant graft-versus-host disease (GVHD). 6. Prior systemic cancer-directed treatments or investigational modalities ≤ 5 half lives or 4 weeks prior to starting CC-90009, whichever is shorter. Hydroxyurea is allowed to control peripheral leukemia blasts. 7. Leukapheresis ≤ 2 weeks prior to starting CC-90009.