Use of Post-Transplant Cyclophosphamide in One-Antigen Mismatched Unrelated Donor Transplantation Results in Similar Transplant Outcomes Than Haploidentical Hransplantation: A Retrospective Study on Behalf of the Acute Leukemia Working Party of the EBMT

Introduction. In the absence of an HLA-identical sibling or a matched unrelated donor, whether to prefer a Haploidentical (Haplo) or a one antigen mismatched unrelated donor (MMUD) for allogeneic hematopoietic cell transplantation (HCT) remains an unanswered question. Implementation of graft-versus-host disease (GVHD) prophylaxis with post-transplant cyclophosphamide (PTCY) was initially pioneered in the Haplo and then also extended to MMUD setting, resulting in low rates of GVHD. Methods. This was a retrospective study from the EBMT registry. Included were adults undergoing either Haplo- or MMUD-HCT for acute myeloid leukemia during the period 2010-2018 and who were in first or second complete remission at allo-HCT. Only patients receiving unmanipulated grafts with PTCY as GVHD prophylaxis were included. Ex vivo and in vivo T-cell depletion were exclusion criteria. Comparisons were made among three groups: MMUD-HCT with peripheral blood as stem cell source (PBSC; n=124); Haplo-HCT with bone marrow (Haplo-BM; n=560); Haplo-HCT with PBSC (Haplo-PB; n=769). Results. Patients in Haplo-PB were older (median age of 55 years versus (vs) 52 and 51 years in MMUD-HCT and Haplo-BM, respectively; p Conclusion. According to our results, use of MMUD is associated to significantly higher LFS. However, our results highlight that both MMUD- and Haplo-HCT are valid options for transplant candidates, with no differences in GRFS. On the other hand, when choosing Haplo over MMUD, one should consider BM as stem cell source in order to better prevent GVHD. Further strategies to better prevent NRM are needed, particularly in Haplo-HCT. Disclosures Labopin: Jazz Pharmaceuticals: Honoraria. Blaise: Jazz Pharmaceuticals: Honoraria. Sica: F. Hoffmann-La Roche Ltd: Other: All authors received support for third-party writing assistance, furnished by Scott Battle, PhD, provided by F. Hoffmann-La Roche, Basel, Switzerland., Research Funding. Pane: Amgen: Consultancy, Other: Travel Expenses, Speakers Bureau; AbbVie: Consultancy, Other: Travel Expenses, Speakers Bureau; Daiichi Sankyo: Consultancy, Other: Travel Expenses; Jazz Pharmaceuticals: Consultancy, Other: travel expenses, Speakers Bureau; Novartis pharma SAS: Consultancy, Other: Travel Expenses, Research Funding, Speakers Bureau; Janssen: Other: Travel Expenses; Bristol Myers Squibb: Membership on an entity's Board of Directors or advisory committees, Speakers Bureau; Celgene: Membership on an entity's Board of Directors or advisory committees, Speakers Bureau. Mohty: BMS: Consultancy, Honoraria, Research Funding, Speakers Bureau; Takeda: Consultancy, Honoraria, Research Funding, Speakers Bureau; Novartis: Consultancy, Honoraria, Research Funding, Speakers Bureau; Amgen: Consultancy, Honoraria, Research Funding, Speakers Bureau; Jazz Pharmaceuticals: Consultancy, Honoraria, Research Funding, Speakers Bureau; Sanofi: Consultancy, Honoraria, Research Funding, Speakers Bureau; Celgene: Consultancy, Honoraria, Research Funding, Speakers Bureau; Stemline: Consultancy, Honoraria, Research Funding, Speakers Bureau; GSK: Consultancy, Honoraria, Research Funding, Speakers Bureau; Janssen: Consultancy, Honoraria, Research Funding, Speakers Bureau.