The purpose of this study is to improve upon the TINI study treatment. The study will test the ability of a type of immunotherapy called blinatumomab to clear persistent leukemia. Blinatumomab targets CD19 which is located on the leukemia cells outer membrane.

Inclusion Criteria:

• Patient is ≤ 365 days of age at the time of diagnosis.
• Patient has newly diagnosed CD19 positive acute lymphoblastic leukemia (ALL) or acute undifferentiated leukemia. Subjects with bilineage or biphenotypic acute leukemia are eligible provided they express CD19. Patients with CD19 positive mature B-cell ALL who carry a KMT2A rearrangement are eligible.
• Limited prior therapy, including hydroxyurea for 72 hours or less, systemic glucocorticoids for one week or less, cytarabine for 72 hours or less, one dose of vincristine, and one dose of intrathecal chemotherapy.
• Written informed consent following Institutional Review Board, NCI, FDA, and OHRP Guidelines.

Exclusion Criteria:

• Patients with prior therapy, other than therapy specified in inclusion criteria.
• Patients with mature B-cell ALL that do not have a KMT2A rearrangement or patients with acute myelogenous (AML) or T-cell ALL.
• Patients with Down syndrome.
• Inability or unwillingness of legal guardian/representative to give written informed consent