• Histologically or cytologically confirmed diagnosis of AML, MDS, or MDS/MPN that is at high risk for post-transplant relapse and that has measurable disease prior to transplant, except for patients with TP 53 mutated disease who are eligible regardless of measurable residual disease. Patients at high risk for post-transplant relapse include:

‣ De novo AML diagnosed at or after age 60, except CBF AML

⁃ De novo AML in CR1 AND MRD+ by Hematologics Inc. flow cytometry pretransplant (this would be on the most recent pre-transplant bone marrow)

⁃ Secondary AML

⁃ Any AML transplanted in CR2 or greater

⁃ TP53-mutated MDS or AML

⁃ Therapy-related MDS or AML

⁃ MDS with monosomy 7

⁃ MDS with \>= 10% blasts at the time of transplant

⁃ MDS/MPN or CMML

• Adequate organ function within 2 weeks of NK cell infusion as defined below (should correspond with admission for SCT):

‣ Total bilirubin: ≤1.5 x institutional upper limit of normal (ULN) (except Gilbert's or disease related hemolysis, then \< 3 x ULN)

⁃ AST(SGOT)/ALT(SGPT): ≤3 x institutional ULN

⁃ Serum creatinine \</= 2.0mg/dL

⁃ O2 saturation: ≥90% on room air

⁃ LVEF \>40%. If there is no clinical evidence of a change in cardiovascular function from the time of pre-transplantation ECHO (per FACT standards should be performed within 6 weeks of stem cell infusion), then there is no need to repeat it. Otherwise, an ECHO will need to be repeated.

• Adult patients (age ≥ 18) eligible for and planned to undergo a standard-of-care reduced intensity conditioning (RIC) HLA-matched related or related haploidentical allogeneic stem cell transplant using PTCY-based GVHD prophylaxis. All eligibility criteria and workups for undergoing SOC allogeneic SCT for the recipient and donor will be based on institutional standards and SOPs.

• For patients with AML, the disease must meet criteria for CR/Cri according to 2017 ELN guidelines. For patients with MDS and MDS/MPN patients, the blast percentage on the bone marrow aspirate and biopsy must be less than 10%.

• The same related donor is available to provide a non-mobilized apheresis product after the stem-cell donation.

• ECOG performance status \<= 2 (Karnofsky \>= 60%, see Appendix C).

• Negative pregnancy test for women of childbearing age

• The effects of CIML NK cells combined with IL-2 on the developing human fetus are unknown. For this reason, women of child-bearing potential and men must agree to use adequate contraception (hormonal or barrier method of birth control; abstinence) prior to study entry and for the duration of study participation. Should a woman become pregnant or suspect she is pregnant while she or her partner is participating in this study, she should inform her treating physician immediately. Men treated or enrolled on this protocol must also agree to use adequate contraception prior to the study, for the duration of study participation, and 4 months after IL-2 dose administration.

• No laboratory evidence of ongoing hemolysis in opinion of investigator

• Adequate organ function within 24 hours of NK cell infusion as defined below:

‣ Total bilirubin: ≤1.5 x institutional upper limit of normal (ULN) (except Gilbert's or disease-related hemolysis, then \< 3 x ULN)

⁃ AST(SGOT)/ALT(SGPT): ≤3 x institutional ULN

⁃ Grade ≥3 non-hematologic toxicities of cyclophosphamide and fludarabine conditioning (except for Grade 3 nausea, vomiting, diarrhea, or constipation).

• No significant change in clinical status that would, in the opinion of the investigator, increase the risk of adverse events associated with CIML NK infusion, (e.g., symptomatic congestive heart failure, unstable angina, cardiac arrhythmia)

• No evidence of ongoing hemolysis in opinion of investigator