Immune reconstitution in children after haploidentical haematopoietic stem cell transplantation.

Introduction: Immune reconstitution (IR) kinetics of paediatric patients underwent haploidentical haematopoietic stem cell transplantation (HSCT) with post‐transplant cyclophosphamide (PTCy) have not been extensively studied. We compared IR patterns of children receiving HSCT from haploidentical (n = 92) and HLA‐matched donors (n = 36), and analysed risk factors for viral infection in these patients. Methods: We prospectively measured lymphocyte subset numbers before HSCT and at 1, 3, 6 and 12 months after HSCT. Blood cytomegalovirus (CMV), Epstein–Barr virus, adenovirus, BK virus (BKV) and urine adenovirus and BKV viral loads were measured at designated time points. Results: The median numbers of total T and T helper cells at 1 month were significantly lower in the haploidentical group compared with the HLA‐matched group. Haploidentical HSCT recipients had significantly lower median numbers of several T cell subsets and B cells for 1 year after HSCT. The median NK cell count of the haploidentical group was lower at 1 month. BKV haemorrhagic cystitis, blood CMV and urine adenovirus reactivation were more frequently found in the haploidentical group. Post‐haploidentical HSCT patients receiving anti‐T lymphocyte globulin (ATG) had significantly lower median numbers of total T cells (at 1 month) and T helper cells (at 6 and 12 months) and higher rate of blood BKV reactivation compared with those without ATG. Conclusion: Paediatric patients who undergo haploidentical HSCT with PTCy are likely to have delayed IR and an increased risk of viral reactivation/infection compared with HLA‐matched HSCT. The addition of ATG to PTCy delayed T cell recovery and increased risk of BKV reactivation. [ABSTRACT FROM AUTHOR]