Tagraxofusp (SL-401) in Participants With Chronic Myelomonocytic Leukemia (CMML) and Myelofibrosis (MF)

Key Inclusion Criteria

All Participants - Participants meeting all the following criteria were considered for enrollment:

• The participant had a life expectancy of > 6 months.
• The participant had an Eastern Cooperative Oncology Group performance status of 0-2.
• The participant had adequate baseline organ function, including cardiac, renal, and hepatic function:
• Left ventricular ejection fraction 2: institutional lower limit of normal as measured by multigated acquisition scan or 2-dimensional echocardiogram within 28 days prior to the start of therapy and no clinically significant abnormalities on a 12-lead electrocardiogram.
• Serum creatinine ≤ 1.5 milligrams/deciliter (dL).
• Serum albumin ≥ 3.2 grams (g)/dL (or 32 g/liter [L]) in the absence of receipt of intravenous albumin within the previous 72 hours.
• Aspartate transaminase and alanine transaminase ≤ 2.5 times the upper limit of normal (ULN).
• Creatine phosphokinase ≤ 2.5 times the ULN.
• Absolute neutrophil count ≥ 0.5×10^9/L.
• If a woman of child-bearing potential, the participant had a negative serum or urine pregnancy test within 1 week prior to tagraxofusp treatment (intervals shorter than 1 week are acceptable, if required by institutional guidelines).
• The participant (either male or female) agrees to use acceptable contraceptive methods for the duration of time in the study, and to continue to use acceptable contraceptive methods for 1 week after the last tagraxofusp infusion.
• The participant can adhere to the study visit schedule and other protocol requirements, including follow-up for response assessments.

Myelofibrosis (Stage 2) - Participants with MF meeting all of the following criteria, in addition to those specified for all participants, above, are eligible for enrollment in Stage 2:

• Participant meets the 2016 World Health Organization (WHO) diagnostic criteria for MF and has an International Prognostic Scoring System/Dynamic International Prognostic Scoring System (IPSS/DIPSS)/DIPSS-plus intermediate-2 or high-risk disease. Participants with IPSS/DIPSS/DIPSS-plus low or intermediate-1 risk disease who have at least 1 of the following symptoms are also eligible: MF-related anemia (hemoglobin 10 centimeters), leukocytosis (white blood cell count [WBC] > 25×10^9/L), marked thrombocytosis (platelet count > 1,000×10^9/L), or constitutional symptoms (weight loss > 10%, during prior 6 months or fever [> 37.5 degrees Celsius or drenching night sweats for > 6 weeks]), as recommended by the European LeukemiaNet/International Working Group (ELN/IWG) 2018 criteria.
• Participant was approved JAK therapy (JAK1/JAK2 or JAK2) resistant/refractory or intolerant, in accordance with the ELN/IWG 2018 criteria, and at least 4 weeks have elapsed between the last dose of any MF-directed drug treatments, excluding HU, and study enrollment (first dose). HU can be continued until 2 weeks prior to study enrollment.
• Participant was not eligible for an immediate allogeneic-stem cell transplantation.

CMML (Stage 3A):

• Participant had a 2016 WHO-defined diagnosis of CMML (persistent monocytosis ≥ 1×10^9/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 CMML, essential thrombocythemia, polycythemia vera, and acute promyelocytic leukemia; if eosinophilic, neither platelet-derived growth factor receptor A, platelet-derived growth factor receptor beta, fibroblast growth factor receptor 1 rearrangements nor pericentriolar material 1-JAK2 translocation; 1 following criteria: dysplasia in > 1 myeloid lineage, acquired clonal cytogenetic or molecular abnormality in hematopoietic cells).
• Participant had 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).
• Participant was refractory/resistant/intolerant, as defined f