This is a research study to find out if a drug called blinatumomab is effective for treating patients with relapsed or refractory (R/R) or measurable residual disease (MRD) CD19-positive mixed phenotypic acute leukemia (MPAL). Measurable Residual Disease (MRD) means that there are a small number of cancer cells remaining after treatment

This is a multicenter, non-randomized, open-label, phase II study evaluating the efficacy of blinatumomab to achieve the following objectives:

1. The best morphologic response after the first two cycles of therapy in subjects with morphologic R/R CD19-positive MPAL
2. MRD-negativity in subjects with CD19-positive MPAL in CR, or CRh, or CRi or CRp after receiving at least one chemotherapy block of standard ALL or AML treatment with MRD-positivity at a level of ≥ 0.1% using an assay with a minimum sensitivity of 0.01%

The trial consists two groups (Group A and B) and three phases ( induction, consolidation and maintenance) of therapy. Subject will receive study drug blinatumomab by continuous IV infusion (CIV). Each treatment cycle consists of 28 days of blinatumomab CIV followed by a 14±3 days treatment-free interval for induction, 28±3 days treatment-free interval for consolidation, and 56±3 days treatment-free interval for maintenance

Blinatumomab is approved by Food and Drug Administration [FDA] and European Medicines Agency [EMA] for use in people with another type of acute leukemia called acute lymphoblastic leukemia (ALL) but not MPAL.

Inclusion Criteria:

• Subjects must have histologically or cytologically confirmed R/R CD19-positive MPAL based on the WHO criteria, OR CD19-positive MPAL in CR/CRh/CRi/CRp after at least one chemotherapy block of standard ALL or AML therapy with detectable MRD ≥ 0.1%. Primary refractory MPAL is defined by absence of CR/CRh/CRi/CRp after at least one cycle of standard AML/ALL induction therapy. A patient has relapsed MPAL if they achieved a CR/CRh/CRi/CRp after induction therapy (CR1) and has then relapsed during, or after continuation of therapy.

• Age 18 years and older

• Subjects who have undergone allo-HSCT are eligible if they are ≥ 4 weeks post stem cell infusion, have no evidence of GVHD > Grade 2, and are at least ≥ 1 week off all immunosuppressive therapy

• Previous cytotoxic chemotherapy (except for hydroxyurea) must have been completed at least 2 weeks prior to day 1 of treatment on the study. Subjects with hematologic malignancies are expected to have hematologic abnormalities at study entry.

• ECOG performance status < 3

• Subjects must have organ function as below:

  • Direct bilirubin ≤ 2.5 mg/dL
  • AST/ALT/Alkaline phosphatase ≤ 5 X institutional upper limit of normal
  • Serum creatinine ≤ 3 mg/dL

• Subjects with a history of CNS leukemia must be clinically stable with a flow cytometric clear CSF in the 2 weeks prior to day 1 of blinatumomab administration. Subjects with history of CNS leukemia in Cohort A should have received one dose of intrathecal chemotherapy in the 4 weeks prior to day 1 of blinatumomab administration. Subject can receive subsequent prophylactic intrathecal chemotherapy.

• Female subjects of childbearing potential must have a negative pregnancy test

• Ability to understand and willingness to sign a written informed consent document

• Agree to comply with the study requirements and agree to come to the clinic/hospital for required study visits

Exclusion Criteria:

• Subjects receiving any other investigational agents, or concurrent chemotherapy, radiation therapy, or immunotherapy not including corticosteroids or hydroxyurea

• Subjects with acute leukemia with any of the following cytogenetic abnormalities:

  t(15;17)(q24;q21) PML/RARA, t(8;21)(q22;q22) RUNX1/RUNX1T1, inv(16)(p13q22)/t(16;16)(p13;q22) CBFB-MYH11

• A history or presence of clinically relevant CNS pathology (e.g., as epilepsy, paresis, aphasia, stroke, severe brain injuries, dementia, cerebellar disease, psychosis)

• Hyperleukocytosis with > 50,000 blasts/µL. Hydroxyurea for blast count control is permitted before starting treatment and up to maximum of 10 days after starting treatment on the study. The WBC need not reach 50,000/µL to start hydroxyurea during protocol; the decision to start hydroxyurea during this time is at the discretion of the treating physician

• Active, uncontrolled infection; subjects with infection under active treatment and controlled with antimicrobials are eligible

• Pregnant women

• Uncontrolled undercurrent illness including, but not limited to, symptomatic congestive heart failure, unstable angina pectoris, uncontrolled active seizure disorder, or psychiatric illness/social situations that per site Principal Investigator's judgment would limit compliance with study requirements