An Open-label, First-in-Human, Single Ascending Dose Study of QUAIL-100 in Pediatric and Young Adult Subjects With High-Risk Acute Leukemias and Myelodysplastic Syndrome Who Have Received a TCR αβ+ T Cell/CD-19+ B Cell-Depleted Hematopoietic Stem Cell Transplantation

Inclusion Criteria: * Weight \>/= 10 kg * Have received HLA-partially matched related or unrelated donor ab-depleted hematopoietic stem cell transplant (HSCT) for high-risk malignant disease and has achieved myeloid and platelet engraftment * Lanksy/Karnofsky score \> 60 * Participants of childbearing potential must agree to use contraception to prevent pregnancy Exclusion Criteria: * Active Grade II acute graft versus host disease (aGVHD) requiring \> 0.5 mg/kg methylprednisolone or any diagnosis of Grade III/IV aGVHD * Significant cardiac, pulmonary, renal, hepatic, GI, neurological or im…