Clinical and immunological analysis of letermovir for preventing cytomegalovirus infection in children after hematopoietic stem cell transplantation

Objective: The present study aimed to analyze the efficacy and safety of letermovir for preventing cytomegalovirus (CMV) infection and its impact on immune reconstitution in children after allogeneic hematopoietic stem cell transplantation (allo-HSCT). Methods: The retrospective analysis included 83 patients who underwent allo-HSCT at Shanghai Children's Hospital between January 2022 and June 2025 and survived ≥100 days post-transplantation. Forty patients received letermovir as primary CMV prophylaxis (letermovir group), and 43 patients did not receive prophylaxis (control group). The primary outcomes were the post-transplantation incidence of CMV infection and CMV disease. Secondary outcomes included the effects of letermovir on acute graft-versus-host disease (aGVHD), hematopoietic reconstitution (time to neutrophil and platelet engraftment), liver function, incidences of Epstein-Barr virus (EBV) and BK virus (BKV) infections, and cellular immune reconstitution. Results: T cell counts were significantly increased 1 year post-transplantation compared to pre-transplantation (p=0.027). Conclusion: Letermovir is safe and effective at reducing the risk of CMV infection in children after allo-HSCT, significantly delaying the onset of infection and shortening its duration. Although letermovir may impact early lymphocyte subset reconstitution, immune function can recover to pre-transplantation levels by 1 year post-transplantation.