Importance: Patients requiring allogeneic hematopoietic cell transplantation have variable likelihoods of identifying an 8/8 HLA-matched unrelated donor. A Search Prognosis calculator can estimate the likelihood. Objective: To determine if using a search algorithm based on donor search prognosis can result in similar incidence of transplant between patients Very Likely (>90%) vs Very Unlikely (<10%) to have a matched unrelated donor. Design: This interventional trial utilized a Search Prognosis-based biologic assignment algorithm to guide donor selection. Trial enrollment from June 13, 2019-May 13, 2022; analysis of data as of September 7, 2023 with median follow-up post-evaluability of 14.5 months. Settings: National multi-center Blood and Marrow Transplantation Clinical Trials Network 1702 study of US participating transplant centers. Participants: Acute myeloid and lymphoid leukemias, myelodysplastic syndrome, Hodgkins and non-Hodgkins lymphomas, severe aplastic anemia, and sickle cell disease patients referred to participating transplant centers were invited to participate. 2225 patients were enrolled and 1751 were declared evaluable for this study. Patients were declared evaluable once it was determined no suitable HLA-matched related donor was available. Intervention: Patients assigned to the Very Likely arm were to proceed with matched unrelated donor, while Very Unlikely were to utilize alternative donors. A third stratum, Less Likely (~25%) to find a matched unrelated donor, were observed under standard center practices, but were not part of the primary objective. Main Outcome: Cumulative incidence of transplantation by Search Prognosis arm Results: Evaluable patients included 1751 of which 413 (24%) were from racial/ethnic minorities. Search prognosis was 958 (55%) Very Likely, 517 (30%) Less Likely and 276 (16%) Very Unlikely. 1171 (67%) received HCT, 384 (22%) died without HCT, and 196 (11%) remained alive without HCT. Among the 1,234 patients, the adjusted cumulative incidence (95% CI) of HCT at 6-months was 59.8% (56.7-62.8) in the Very Likely group versus 52.3% (46.1-58.5) in the Very Unlikely (P=0.113). Conclusions: A prospective Search Prognosis-based algorithm can be effectively implemented in a national multicenter clinical trial. This approach resulted in rapid alternative donor identification and comparable rates of HCT in patients Very Likely and Very Unlikely to find a matched unrelated donor. Trial Registration: NCT#03904134

S.J.L- Board of Directors, nmdp (uncompensated) A.S.-Consulting Fees: Sanofi and Therakos

NCT03904134

Support for this study was provided by grants #U10HL069294 and #U24HL138660 to the Blood and Marrow Transplant Clinical Trials Network from the National Heart, Lung, and Blood Institute and the National Cancer Institute. The CIBMTR registry is supported primarily by the U24-CA76518 from the National Cancer Institute, the National Heart, Lung, and Blood Institute, and the National Institute of Allergy and Infectious Diseases and from HHSH234200637015C (HRSA/DHHS) to the Center for International Blood and Marrow Transplant Research.

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The IRB of NMDP gave ethnical approval for this work.

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Data will be submitted by the Blood and Marrow Transplant Clinical Trials Network (BMT CTN) to the National Heart, Lung, and Blood Institute (NHLBI) Data Repository within a month of peer-reviewed primary study results publication and will be accessible via standard Repository processes.

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