Impact of methotrexate‐dosing regimens for GVHD prophylaxis on clinical outcomes of HLA ‐matched allogeneic HSCT

Summary Severe graft‐versus‐host disease (GVHD) remains a major complication of allogeneic haematopoietic stem cell transplantation (allo‐HSCT), necessitating optimal immunosuppressive strategies. This retrospective study used data from the Japanese Transplant Registry Unified Management Program to compare three methotrexate (MTX)‐dosing regimens for GVHD prophylaxis in patients undergoing human leucocyte antigen (HLA)‐matched allo‐HSCT: a low‐dose 3‐day regimen (Ld3:10 mg/m 2 on day 1, 7 mg/m 2 on days 3 and 6), a low‐dose 4‐day regimen (Ld4: Ld3 with an additional 7 mg/m 2 on day 11) and an original‐dose 3‐day regimen (Od3: 15 mg/m 2 on day 1, 10 mg/m 2 on days 3 and 6). Among 2537 analysed patients, Ld3 was the most commonly used regimen. Multivariate analyses showed no significant differences in the cumulative incidence of grade II–IV acute GVHD among regimens. However, Od3 was associated with an increased risk of grade III–IV acute GVHD, and Ld4 was linked to delayed neutrophil engraftment. This study is the first large‐scale retrospective analysis of the impact of different MTX‐dosing regimens on the outcomes of HLA‐matched allo‐HSCT, providing valuable insights into optimal MTX‐dosing strategies in clinical practice.