LAUSR

Allogeneic hematopoietic cell transplantation (HCT) from HLA‐haploidentical donors with post‐transplantation high‐dose cyclophosphamide (PT/Cy‐haplo) now predominates worldwide. However, to our knowledge, no prospective study has compared immune reconstitution after PT/Cy‐haplo with that after conventional HCT. The mechanism by which chronic graft‐versus‐host disease (GVHD) is inhibited by PT/Cy‐haplo also remains unknown. We prospectively compared immune recovery patterns of lymphocyte subsets among four groups of adult patients with hematological disease who received HCT from either HLA‐matched related or HLA‐matched unrelated donors, cord blood transplantation, or reduced‐dose PT/Cy‐haplo. Counts of CD4+ T‐cell subsets, CD8+ T‐cell subsets, and NK cells on days 30 and 60 were often lower in PT/Cy‐haplo than those in HLA‐matched related HCT. The immune recovery pace in PT/Cy‐haplo subsequently caught up with that of the other grafts. The regulatory T cells (Tregs) to conventional CD4+ T‐cell (Tcon) ratio was significantly higher until day 90 in PT/Cy‐haplo. In multivariate analysis, a higher Tregs‐to‐Tcon ratio on day 60 was significantly associated with a lower incidence of chronic GVHD (P < 0.01). The preservation of Tregs by PT/Cy in the early phase might have resulted in a lower incidence of chronic GVHD.