Graft CD8+ T cells for improving event-free survival after T cell-replete haploidentical stem cell transplantation in children with hematological malignancies.

T cell-replete haploidentical hematopoietic stem cell transplantation (TCR-haplo-HSCT) is a potentially curative therapy for pediatric intractable hematological malignancies due to its graft-versus-leukemia efficacy. This single-center cohort study examined the effects of graft composition (T cell type and dose) on pediatric TCR-haplo-HSCT outcomes in 32 children with relapsed/intractable hematological malignancies. Graft T cell composition was classified using flow cytometry. High graft CD8⁺ T cell doses reduced disease relapse and improved overall survival and event-free survival, but did not increase transplant-related mortality and the incidence of grade III/IV acute graft-versus-host disease. Doses of grafted CD3⁺, CD4⁺, and CD34⁺ T cells did not affect patient outcomes. Children with differing event-free survival times were divided by a graft CD8⁺ T cell dose cut-off of 2.03 × 10⁸ kg^-1. These findings revealed that grafted CD8⁺ T cells improved the graft-versus-leukemia effect of pediatric TCR-haplo-HSCT without increasing the risk of transplant-related mortality.