Protective factors, management and prognosis of mixed chimerism after allogeneic hematopoietic stem cell transplantation for severe aplastic anemia in children.

Mixed chimerism (MC) frequently arises in children with severe aplastic anemia (SAA) after allogeneic hematopoietic stem cell transplantation (allo-HSCT). Nonetheless, there is a paucity of research regarding potential predictors and effective interventions. This retrospective study, performed on 150 pediatric patients with SAA who underwent allo-HSCT between December 2015 and June 2022, explored the characteristics, risk factors, treatment, and prognosis of MC. A total of 29 patients (19.3%) developed MC following allo-HSCT, with two individuals experiencing MC twice. The CTX + ATG regimen was associated with the development of MC. Peripheral blood (PB) + bone marrow (BM) stem cell graft and a high number of CD34⁺ cells were identified as independent protective factors for MC. The cumulative incidence of grade II-IV acute graft-versus-host disease was significantly elevated in donor chimerism (DC) relative to MC. Among MC patients with cytopenia, only two patients who received increased immunosuppression alone were effective. Complete DC was achieved in all four patients who received the second transplantation. In conclusion, we emphasize that prompt second transplantation is essential when cellular therapy and enhanced immunosuppression fail for MC patients with cytopenia.