Comparison of Viral Infection Rates after T-cell Depletion in Pediatric HCT: Alemtuzumab Vs Post-Transplant Cyclophosphamide

Alemtuzumab and Post-Transplant Cyclophosphamide (PTCy) are T-cell depletion approaches utilized in pediatric allogeneic hematopoietic cell transplants (HCT). These strategies carry a risk of viral reactivations and infections. Direct comparative studies between alemtuzumab and PTCy in children are limited. This study evaluates the incidence of viral infections within one year following HCT for each strategy. We performed a retrospective review of pediatric patients who underwent allogeneic HCT at Mayo Clinic (Rochester, MN) between 6/1/2018 – 9/30/2024, receiving either alemtuzumab or PTCy for in vivo T-cell depletion at first transplant. Collected data included patient and transplant characteristics, pre-transplant serologies, antiviral prophylaxis, and post-transplant viral infections. Viral infections were defined as detectable viral RNA/DNA in blood or tissue, excluding results below the limit of quantification. Follow-up extended to one year post-HCT or until subsequent cytotoxic therapy, transfer, or death. The primary endpoint was total viral infection incidence at one year; secondary endpoints included individual viral infections. BlueSky was used for statistical analysis. Twenty-eight patients met inclusion criteria (20 alemtuzumab, 8 PTCy). The alemtuzumab group was younger (median 7.7 vs 13.9 years) and, as expected, primarily received MUD transplants (85%), while the PTCy group mainly received haploidentical transplants (63%); letermovir use was similar between groups (Table 1). At one year, the total viral infection incidence did not differ significantly (alemtuzumab 65% vs PTCy 50%; p=0.67), nor did incidences of specific viral infections (Figures 1 and 2). Among CMV-seropositive patients in the whole cohort, CMV reactivation was numerically lower with letermovir as compared to no prophylaxis (36% vs 67%; p=0.37). In this pediatric HCT cohort, viral infection rates were comparable between alemtuzumab and PTCy. Despite the small sample size, both T-cell depletion approaches appear to pose comparable infectious risks, supporting tailored platform choice based on donor and clinical factors.