Letermovir improves the outcome of allogenic stem cell transplantation with anti-thymocyte globulin against acute leukemia and myelodysplastic syndromes.

Graft versus host disease (GVHD) is a serious side effect of allogenic stem cell transplantation (allo-SCT). Anti-thymocyte globulin (ATG) reduces GVHD but raises the risk of infections following allo-SCT. Preventive therapy is recommended for cytomegalovirus (CMV), which is a major pathogen. Prophylactic administration of letermovir has shown a significant reduction in CMV reactivation. We hypothesized letermovir could reduce CMV reactivation and affect the outcome of allo-SCT. We retrospectively studied 88 patients who received allo-SCT with ATG for acute leukemia or myelodysplastic syndromes (MDS) from 2014 to 2022. The patients were divided into letermovir (n = 34) and non-letermovir (n = 54) groups. 3-year overall survival rates were 85% (95%Confidence interval [CI]: 67%-93%) and 47% (95%CI: 33%-60%) in the letermovir and non-letermovir groups, respectively (p < 0.01). Non-relapse mortality rate was equivalent, and the relapse rate was 21% (95%CI: 9.0%-36%) vs. 47% (95%CI: 33%-60%) and significantly lower in the letermovir group (p = 0.015). The cumulative CMV reactivation incidence rates at day 100 were 5.9% (95%CI: 1.0%-17%) and 43% (29%-55%) in the letermovir and non-letermovir groups (p = 0.012). These findings suggest letermovir helped the suppression of CMV reactivation and improved the outcome of allo-SCT with ATG by lowering relapse.