Study of Tagraxofusp for Post-Transplant Maintenance for Patients With CD 123+ AML, MF and CMML (HSCT 002)

Inclusion Criteria:

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

2. The patient has a life expectancy of >6 months.

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

4. The patient has adequate baseline organ function, including cardiac, renal, andhepatic function within 28 days of start of therapy:

• Left ventricular ejection fraction (LVEF) ≥ 50% as measured by multigatedacquisition scan (MUGA) or 2-dimensional (2-D) echocardiogram (ECHO) and noclinically 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 theupper 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 toenable eligibility)

5. Patient meets the 2016 WHO diagnostic criteria for MF, is CD 123+, and has anIPSS/DIPSS/DIPSS-plus intermediate-1 with anemia (Hb < 10g/dl), splenomegaly (> 12cm), 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/Lfor at least 3 months, with other causes excluded, and monocytes ≥10% of WBC inperipheral blood, no criteria and no previous history of CML, ET, PV, and acutepromyelocytic 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

6. Receipt of first allogeneic stem cell transplant (related, unrelated, haploidenticalor cord blood) 60-120 days prior to study registration

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

8. Provision of signed and dated informed consent form

9. Stated willingness to comply with all study procedures and availability for theduration of the study

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

11. For males of reproductive potential: use of condoms or other methods to ensureeffective contraception with partner. Other (non-study) medications may requireparticipants to use adequate contraception for longer.

12. Agreement to adhere to Lifestyle Considerations throughout study duration

Exclusion Criteria:

1. Treatment with any disease-related therapy, including radiation therapy orinvestigational agent, within 14 days of study entry

2. Previous treatment with tagraxofusp or known hypersensitivity to any components ofthe drug product

3. Active malignancy and/or cancer history (excluding myeloproliferative disorders andconcomitant myeloid malignancies as specified in the inclusion criteria) that canconfound the assessment of the study endpoints. Patients with a past cancer history (within 2 years of entry) and/or ongoing active malignancy or substantial potentialfor recurrence must be discussed with the Sponsor before study entry. Patients withthe following neoplastic diagnoses are eligible: non-melanoma skin cancer, carcinomain situ (including superficial bladder cancer), cervical intraepithelial neoplasia,or organ-confined prostate cancer with no evidence of progressive disease.

4. Known active or suspected disease involvement of the central nervous system (CNS)

5. Receiving > 10 mg prednisone daily for GVHD

6. Overall Grade 2 or greater acute GVHD (per Magic criteria) at time of registration

7. Pregnant or breast feeding

8. Requirement of supplemental oxygen

9. Clinically significant cardiovascular disease (e.g., uncontrolled or any New YorkHeart Association Class 3 or 4 congestive heart failure, uncontrolled angina,history of myocardial infarction or stroke within 6 months of study entry,uncontrolled hypertension or clinically significant arrhythmias not controlled bymedication)

10. Uncontrolled, clinically significant pulmonary disease (e.g., chronic obstructivepulmonary disease, pulmonary hypertension) that in the opinion of the Investigatorwould put the patient at significant risk for pulmonary complications during thestudy

11. Uncontrolled intercurrent illness including, but not limited to, uncontrolledinfection, disseminated intravascular coagulation, or psychiatric illness/socialsituations that would limit compliance with study requirements

12. Known positive status for human immunodeficiency virus or active or chronicHepatitis B or Hepatitis C

13. Receiving treatment for known or suspected fungal infection (prophylaxis isacceptable)

14. Known positive SARS-COV-2 test within 3 weeks of study entry. Exception: Tests thatreflect past, resolved infection where the patient is determined to NOT beinfectious, according to an infectious disease specialist, do not exclude thepatient from participation.

15. Pedal edema ≥ grade 2