Posttransplantation cyclophosphamide mediates effective reconstitution of memory B cells after allogeneic hematopoietic cell transplantation.

Objectives: Impaired B‐cell reconstitution after allogeneic hematopoietic cell transplantation (allo‐HCT) contributes to the pathogenesis of chronic graft‐versus‐host disease (cGVHD). Therefore, methods to consistently achieve effective B cell lymphogenesis are required. We assessed the long‐term effects of posttransplantation cyclophosphamide (PTCy) use on immune reconstitution in clinical settings, an emerging strategy to suppress allogeneic immunological inflammation early after allo‐HCT and prevent subsequent GVHD. Methods: We comprehensively analyzed peripheral immune cell subsets and measured serum immunoglobulin G (IgG) or cytokine levels in 39 patients who survived for >1 year after allo‐HCT. Results: The absolute counts of B1 and IgM memory B cells were significantly lower in patients with severe cGVHD than in those without. The absolute count and percentage (among total CD19+ B cells) of switched memory B cells and serum IgG levels were significantly higher in patients transplanted with PTCy than in those transplanted with conventional GVHD prophylaxis. Interestingly, increased percentages of switched memory B cells and serum IgG levels were observed only in patients transplanted with PTCy and not in those transplanted with umbilical cord blood. Conclusions: PTCy administration can mediate favorable memory B‐cell reconstitution long after allo‐HCT and may therefore suppress cGVHD. [ABSTRACT FROM AUTHOR]