Open-label, Single Ascending Dose Study of QUAIL-100 in Pediatric and Young Adult Participants With High-Risk Hematologic Malignancies Who Have Received a 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 immunological disease that could compromise safe participation * Known allergies, hypersensitivity or intolerance to both amoxicillin and gentamycin * Implanted medical devices with high potential for bacterial seeding, including pacemakers, artificial cardiac valves, prosthetic joints, orthopedic plates or screws, atrial appendage or inferior vena cava devices for thrombosis prevention * Planned anti-leukemic therapy within 21 days of planned dosing * Use of TNFa or PI3K inhibitors within 60 days of screening * Any prior investigational Listeria product including QUAIL-100 * Live, attenuated vaccine within 4 weeks of first dose