Mismatched Related Donor Versus Matched Unrelated Donor Stem Cell Transplantation for Children, Adolescents, and Young Adults With Acute Leukemia or Myelodysplastic Syndrome

PRIMARY OBJECTIVE: I. To compare the 1-year cumulative incidence of severe Graft Versus Host Disease (GVHD) (from day of HCT) defined as grade III-IV acute GVHD (aGVHD) and/or chronic GVHD (cGVHD) that requires systemic immunosuppression and to compare the disease free survival (DFS) (from time of randomization) in children and young adults (AYA) with acute myeloid leukemia (AML), acute lymphoid leukemia (ALL), mixed phenotype acute leukemia (MPAL), and myelodysplastic syndrome (MDS) who are randomly assigned to haploHCT or to an 8/8 adult MUD-HCT. SECONDARY OBJECTIVES: I. To compare overall survival (OS) between children and AYA with AML/ALL/MPAL/MDS randomly assigned to haploHCT and MUD HCT. II. To compare differences in health-related quality of life (HRQOL) between haploHCT and MUD HCT from baseline (pre-transplant), at 6 months, 1 year and 2 years post-transplant. EXPLORATORY OBJECTIVES: I. To compare the median time to engraftment and cumulative incidences of neutrophil engraftment at 30 and 100 days post transplant and platelet engraftment at 60 and 100 days post transplant, primary graft failure by 60 days, secondary graft failure at 1 year post transplant, Grade II-IV and III-IV acute graft versus host disease (aGVHD) requiring systemic immunosuppression at 100 days and 6 months, and cumulative incidences of transplant-related mortality (TRM), relapse, and moderate and severe chronic graft versus host disease (cGVHD) at 6 months, 1 and 2 years after haploHCT and MUD HCT. II. To estimate 1 year, 18-month and 2-year cumulative incidence of graft-versus-host disease (GVHD)-free relapse-free survival (GRFS) with events defined as occurrence of any of the following from Day 0 of HCT: Grade III-IV acute GVHD, chronic GVHD requiring systemic immunosuppressive treatment, disease relapse or progression, and death from any cause. IIa. To compare "chronic GVHD" (GRFS) after haploHCT and MUD HCT using landmark definitions. IIb. To compare "current" GRFS is defined as the time to onset of any of the following events from Day 0 of HCT: Grade III-IV acute GVHD, chronic GVHD that is STILL requiring systemic immunosuppressive treatment, disease relapse or progression, death from any cause at 18 months and 2 years. III. To evaluate the influence of key clinical variables: age (\<13 years and 13-21.99 years), disease (ALL/MPAL versus \[vs.\] AML/MDS), haploHCT approach (TCR alpha beta + T cell depletion vs. post-transplant cyclophosphamide \[PTCy\]); donor age (by ten-year increments), donor sex (maternal vs. paternal for parental donation), pre-HCT minimal residual disease status (MRD + vs MRD -); pediatric disease risk index (low, intermediate, and high, impact on OS and DFS only), conditioning regimen (chemotherapy based versus total-body irradiation \[TBI\] based), immunosuppressive regimen (anti-thymocyte globulin \[ATG\] exposure according to the weight and absolute lymphocyte count \[ALC\] dependent dosing approach vs no ATG exposure) time to transplant (interval between diagnosis/relapse and date of stem cell infusion) graft cell dose, use of relapse prevention therapy (yes or no) and weight on engraftment, OS, DFS, GRFS, relapse, transplant related mortality (TRM), aGvHD and cGvHD at 1 and 2 years after haplo and MUD HCT by performing stratified and multivariate analyses. IV. To compare other important transplant related outcomes after haplo and MUD HCT, such as: IVa. Incidence of any significant fungal infections (defined as proven or probable fungal infection) through 1 year post HCT; IVb. Incidence of viremia with or without end organ disease (i.e. cytomegalovirus \[CMV\], adenovirus, Epstein-Barr virus \[EBV\], human herpesvirus 6 \[HHV-6\], BK) requiring hospitalization and/or systemic antiviral therapy and/or cell therapy through 1 year post HCT; IVc. Incidence of sinusoidal obstruction syndrome (SOS) through 100 days post HCT; IVd. As defined by the Cairo criteria; IVe. To compare the incidence and outcome of SOS when different criteria are used (European Bone Marrow Transplant \[EBMT\], Cairo, Baltimore, and modified Seattle criteria); IVf. Incidence of transplant-associated thrombotic microangiopathy (TA-TMA) through 100 days post HCT. V. To compare immune recovery after haplo PTCy, haplo alpha-beta T cell depletion, and MUD HCT via: Va. Pace of reconstitution of T, B, and natural killer (NK) cells and immunoglobulins at 30 days, 60 days, 100 days, 180 days and 365 days after HCT; Vb. Response to vaccinations as determined by vaccination-specific antibody titers at 12-18 months post hematopoietic stem cell transplant (HSCT); Vc. Biobanking blood or marrow to analyze the impact of graft composition on GvHD, relapse and viremia; Vd. Biobanking whole blood and serum to compare immune recovery using extended immune phenotyping and immune functional assessments. VI. Biobanking whole blood or serum to measure rabbit antithymocyte globulin (rATG) exposure when dosed according to weight and absolute lymphocyte count (ALC) using established pharmacokinetic and pharmacodynamics assays (after last infusion, Day -4, Day 0, Day +7). VII. To compare resource utilization after haplo and MUD HCT. VIIa. Length of HCT hospital stay from Day 0 and readmissions within the first 100 days (number of readmissions, duration, and reason). VIIb. Inpatient costs within the first 100 days and at 2 years post HCT. VIII. To describe and compare outcomes (neutrophil and platelet engraftment, graft failure, OS, DFS, GRFS, NRM, relapse, GvHD and health-related quality of life \[HRQOL\] post HCT) by recipient race/ethnicity, annual household income, primary spoken language and conserved transcriptional response to adversity (CTRA). IX. To describe HRQoL outcomes in racial/ethnic minorities and compare HRQoL outcomes between White patients receiving haploHCT and racial/ethnic minority patients receiving haploHCT. X. To assess the feasibility of incorporating total body irradiation (TBI) delivered with volumetric modulated arc therapy (VMAT) or tomotherapy into a multi-institutional study, to describe the toxicities and oncologic outcomes (relapse, DFS, OS, and TRM) of the subgroup of patients treated with this approach, and to compare these outcomes to those of patients treated with conventional TBI. OUTLINE: Patients who have both a MUD and haplo donor are randomized to Arm A or Arm B. Patients who only have a haplo donor are nonrandomly assigned to Arm C. ARM A: Patients receive a haplo HCT following a TBI- based or chemotherapy-based myeloablative conditioning regimen with PTCy or alpha beta T cell depletion (center's choice). When PTCy is used, it Is administered on days 3 and 4 after HCT and additional immunsouppression is started on day 5 after SCT. ARM B: Patients receive a MUD HCT following a TBI-based or chemotherapy-based myeloablative conditioning regimen between days -9 and -2 Patients then receive GVHD prophylaxis on days 1-11. ARM C: Patients receive a haploHCT following a TBI-based or chemotherapy-based myeloablative conditioning regimen with PTCy or alpha beta T cell depletion (center's choice). When PTCy is used, it Is administered on days 3 and 4 after HCT and additional immunsouppression is started on day 5 after SCT. Patients in all arms undergo standard HCT screening prior to transplant including disease evaluation (lumbar puncture, bone marrow aspiration), and organ function evaluation including but not limited to echocardiogram (ECHO) or multigated acquisition scan (MUGA), PFTS, and bloodwork.Patients also undergo collection of blood throughout the trial. After completion of study treatment, patients are followed periodically for up to 5 years from HCT.