Female donor to male recipient transplantation is associated with altered immune reconstitution and increased risk of chronic graft-versus-host disease: a single-center cohort study

Background Donor–recipient sex mismatch, particularly female-to-male (F-to-M) transplantation, has been associated with an increased risk of chronic graft-vs.-host disease (cGVHD) after allogeneic hematopoietic stem cell transplantation (allo-HSCT), but its relationship with early immune reconstitution remains incompletely characterized. Methods In this single-center retrospective cohort of 294 patients transplanted between 2016 and 2025, patients were classified by donor–recipient sex combination (F-to-M, M-to-F, M-to-M, F-to-F). Multivariable regression was used for cGVHD and survival analyses, and lymphocyte subsets were measured by flow cytometry at months 1–3 in 170 patients. Results The F-to-M group had the highest cGVHD incidence (51.1%) and was independently associated with cGVHD relative to M-to-M [odds ratio (OR) 2.62, 95% CI: 1.23–5.58; p = 0.013], which remained significant after adjustment for acute GVHD (OR: 2.48, 95% CI: 1.15–5.33; p = 0.020); in a sensitivity analysis restricted to patients with available pre-transplant measurable residual disease (MRD) data ( n = 199), the estimate was similar in magnitude but did not reach statistical significance after MRD adjustment (OR: 2.58, 95% CI: 0.95–6.99; p = 0.062). Overall survival differed marginally among the four groups (log-rank p = 0.049), with the lowest 3-year OS in the F-to-M group (58.0%, 95% CI: 35.4–77.1, vs. 83.3–89.5%); however, F-to-M transplantation was not independently associated with OS in the multivariable model [hazard ratio (HR) 2.01, 95% CI: 0.94–4.29; p = 0.071]. Cumulative non-relapse mortality was higher in F-to-M recipients (Gray's test p = 0.016), whereas relapse did not differ (Gray's test p = 0.536). F-to-M recipients showed a persistently higher CD4+/CD8+ ratio during months 1–3, mainly reflecting delayed CD8+ T-cell recovery. Within this subgroup, a lower 3-month NKT-like cell count was associated with cGVHD; an exploratory threshold of ≤14 cells/µL yielded an apparent area under the curve of 0.814 (95% CI: 0.618–0.965; bootstrap-corrected 0.810), and the F-to-M × log(NKT-like) interaction was significant ( p = 0.046). Conclusions These findings suggest that F-to-M transplantation may be associated with a higher burden of cGVHD and with higher non-relapse mortality, accompanied by a characteristic early immune-reconstitution pattern, whereas its association with overall survival was not statistically significant after adjustment. Low 3-month NKT-like cell counts may serve as an exploratory candidate marker for cGVHD risk stratification, but require validation in larger prospective cohorts.