(045) Comparison of Graft-Versus-Host Disease- and Relapse-Free Survival of Haploidentical Versus Matched Unrelated Donor Allogeneic Stem Cell Transplants

Poster Abstract:

Background:
Allogeneic hematopoietic stem cell transplantation (allo-HSCT) is a potential cure for acute myeloid leukemia (AML), acute lymphoblastic leukemia (ALL), chronic myeloid leukemia (CML), and myelodysplastic syndromes (MDS). Disease relapse and graft-versus-host disease (GVHD) are the principal causes of morbidity and mortality after allo-HSCT. Human leukocyte antigen (HLA) -mismatch is the most crucial risk factor for developing GVHD. Matched-related donor (MRD) is preferred but not always available. Without MRD, a matched-unrelated donor (MUD) is the next preferred option, followed by other alternatives, including haploidentical donors. Haploidentical donors may allow faster transplants, with decreased costs and logistic hurdles, though historically, with a higher GVHD risk. Haploidentical donor use has increased with post-transplant cyclophosphamide (PTCy)-based GVHD prophylaxis regimens. Recent studies suggested comparable GVHD rates between haploidentical and MUD transplants. However, no trials are comparing GVHD risk and relapse. Graft-versus-host disease-free and relapse-free survival (GRFS) recognizes the immunosuppression balance needed for GVHD prevention while conserving the graft-versus-leukemia effect for disease relapse prevention. While GRFS is a clinically meaningful outcome used in recent trials, it is unknown whether it is comparable between haploidentical and MUD transplants.

Objective:
This study aimed to determine if GRFS of haploidentical allo-HSCT is non-inferior to MUD allo-HSCT.

Methods:
This was a single-center, non-inferiority, retrospective cohort study. Included patients who received haploidentical or MUD transplants at The Ohio State University Comprehensive Cancer Center – James Cancer Hospital between January 2017 and January 2023. Included patients 18 to 89 years old with myelofibrosis, AML, ALL, CML, or MDS who received haploidentical peripheral blood stem cell transplant (PBSCT) with PTCy, tacrolimus, and mycophenolate or MUD PBSCT with methotrexate and tacrolimus for GVHD prophylaxis. Reduced-intensity conditioning and myeloablative preparatory regimens were included. Patient characteristics, GVHD rates, and infection complications were compared between study groups. The primary outcome was GRFS at 1-year post-transplant. Secondary outcomes included non-relapse mortality, overall survival, disease-free survival, time to platelet and neutrophil engraftments, and infection complications. The GRFS between the study groups were estimated using a multivariable Cox progression model adjusted for covariates, including age, Disease Risk Index, regimen, donor type, and GVHD prophylaxis.

Results:
The results of this study will be presented at the 2024 Hematology/Oncology Pharmacy Association Annual Conference.

Conclusions:
These results will demonstrate whether haploidentical is non-inferior to MUD allo-PBSCT. Non-inferiority would allow for less expensive and more readily available transplants. If non-inferiority cannot be established, it would support keeping MUD as the preferred transplant source.

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