• The patient is ≥18 years old and ≤ 75 years old.

• The patient has a life expectancy of \>6 months.

• The patient has an Eastern Cooperative Oncology Group (ECOG) performance status (PS) of 0-2.

• The patient has adequate baseline organ function, including cardiac, renal, and hepatic function within 28 days of start of therapy:

‣ Left ventricular ejection fraction (LVEF) ≥ 50% as measured by multigated acquisition scan (MUGA) or 2-dimensional (2-D) echocardiogram (ECHO) and no clinically significant abnormalities on a 12-lead electrocardiogram (ECG)

⁃ Serum Creatinine ≤ 1.5 mg/dL

⁃ Bilirubin ≤1.5 mg/dL

⁃ Aspartate transaminase (AST) and alanine transaminase (ALT) ≤2.5 times the upper limit of normal (ULN)

⁃ Absolute neutrophil count (ANC) ≥0.5 × 10⁹/L

⁃ Platelets ≥ 80,000/mm\^3

⁃ Serum albumin ≥3.2 (note that albumin infusions are not permitted in order to enable eligibility)

• Patient meets the 2016 WHO diagnostic criteria for MF, is CD 123+, and has an IPSS/DIPSS/DIPSS-plus intermediate-1 with anemia (Hb \< 10g/dl), splenomegaly (\> 12 cm), leukocytosis (WBC \> 25K) intermediate-2 or high-risk disease pre transplant.

• Or

• Patient has a 2016 WHO-defined diagnosis of CMML (persistent monocytosis ≥1 × 10⁹/L for at least 3 months, with other causes excluded, and monocytes ≥10% of WBC in peripheral blood, no criteria and no previous history of CML, ET, PV, and acute promyelocytic leukemia) pre transplant and is CD123+

• Or

• Patient has 2016 WHO-defined CMML-1 (2-4% blasts in peripheral blood and/or 5-9% blasts in bone marrow) and CMML-2 (5-19% blasts in peripheral blood and/or 10-19% blasts in bone marrow, and/or presence of Auer rods) pre transplant and is CD 123+

• Or

• Patient has CD 123+ AML in morphologic remission pre transplant

• Or

• Patient has Intermediate or high risk MDS by IPSS-R or moderate or high risk by IPSS-M pre transplant and has had no morphologic progression of disease post-transplant.

• Receipt of first allogeneic stem cell transplant (related, unrelated, haploidentical or cord blood) 60-120 days prior to study registration

• Patient is in morphologic remission according to bone marrow biopsy completed within 30 days prior to planned start of study treatment

• Provision of signed and dated informed consent form

• Stated willingness to comply with all study procedures and availability for the duration of the study

• For females and males of reproductive potential: agreement to use adequate contraception for at least one month prior to screening, during study participation and for an additional one week after the end of study drug administration. Other (non-study) medications may require participants to use adequate contraception for longer.

⁃ For males of reproductive potential: use of condoms or other methods to ensure effective contraception with partner. Other (non-study) medications may require participants to use adequate contraception for longer.

⁃ Agreement to adhere to Lifestyle Considerations throughout study duration