Inclusion Criteria:

Patients ≧ 18 years of age with persistence or relapse/progression AML, MDS, or MDS/MPN, 1. following allogeneic stem cell transplantation.

• - grade 1 overall GVHD at time of inclusion with stable immune suppression for at least 2 weeks pre infusion on study and planned stable immune suppression dose for at least 8 weeks (the safety evaluation period) 2.

Calculated creatinine clearance ≥ 60ml/min as estimated by Cockcroft Gault and not dialysis dependent. 3. AST, ALT <3 x ULN unless documented due to medications (ie azole or other common therapy for such patients). Total bilirubin ≤3.0 mg/dl unless there is a history of Gilbert's syndrome in which case the T bili hould be < 5.0 mg/dl. 4. Females cannot be pregnant or breast-feeding from time of enrollment till 16 weeks post final agent exposure on this study. 5. Immune suppression not greater than 20mg prednisone daily or equivalent dosing of alternative GVHD prophylaxis/therapy. 6. Patients are at least 30 days from most recent allogeneic stem cell infusion. 7. Patients may have had other therapy post alloBMT and other donor lymphocyte infusions but they must be at least 60 days from the last infusion of cell therapy products. 8. Patients must have other anti-leukemia therapies stopped 2 weeks prior to infusion on this study. Hydrea or pheresis ARE allowed prior to this study and may continue until 14 days following the first infusion on this study if deemed to be needed to assist in count control.

Exclusion Criteria:

1. Patients with progressive infections at time of first infusion (patients with treated infections documented as controlled by the treating team are eligible). 2. Known active CNS disease at time of enrollment. 3. Patients with other cancers treated within 3 years. 4. Known history of immunogenicity or hypersensitivity to a CD25 antibody or a component of ADCT-301. 5. Major surgery, chemotherapy, systemic therapy (excluding hydroxyurea, steroids, and any targeted small molecules or biologics), or radiotherapy within 14 days or 5 half-lives (whichever is shorter) prior to Cycle 1, Day 1 treatment, except if approved by Dr. Rizzieri. 6. Patients with proven, progressive severe autoimmune disease such as multiple sclerosis, active Guillain Barré syndrome, poliomyelitis, sjogren's are not eligible. Given the immediate, life threatening nature of the relapsed cancer in this patient population, those with other stable and non-immediate non-threatening autoimmune disorders such as thyroid disease or diabetes and others are eligible. 7. Patients with a known infection/reactivation of any of the following within 28 days of the first dose of this agent on study are not eligible: HSV1, HSV2, VZV, EBV, CMV, measles, influenza A, Zika, Chikungunya, mycoplasma pneumonia, Campylobacter jejuni, enterovirus B68, or SARS-CoV-2. Patients will have evaluation for HSV1, HSV2, VZV, EBV, CMV as part of screening studies. Patients will have SARS-CoV-2 screening performed if at all possible during the screening process. If screening is not available, then screening based on symptoms will be documented. Additionally, screening based on clinical concern and/or symptoms will be conducted for measles, influenza A, Zika, Chikungunya, mycoplasma pneumonia, Campylobacter jejuni, enterovirus B68.

Arms

Experimental: ADCT-301 Infusion

Patients will receive ADCT-301 37.5 ug/kg infused day 1,8, and 15 of a q3week cycle. Patients will have up to 2 cycles to assess response and safety to therapy and if they are not progressing may continue for up to 6 cycles.

Interventions

Drug: - ADCT-301

Patients will receive ADCT-301 37.5 ug/kg infused day 1,8, and 15 of a q3week cycle. Patients will have up to 2 cycles to assess response and safety to therapy and if they are not progressing may continue for up to 6 cycles.