Post-Transplant Cyclophosphamide-Based Prophylaxis and Its Impact on Infectious Complications and Immune Reconstitution According to Donor Type.

This study evaluated infectious complications and immune reconstitution in 253 adults undergoing peripheral blood allogeneic hematopoietic cell transplantation (allo-HCT) with post-transplant cyclophosphamide (PTCY)-based GVHD prophylaxis. Patients received grafts from HLA-matched donors (47.4%), mismatched unrelated donors (MMUD, 33.2%), or haploidentical donors (19.4%). The estimated 2-year non-relapse mortality (NRM) was 11.8%, 26.4%, and 22.4%, respectively ( = 0.0528). The cumulative incidence (Cum.Inc) of acute and chronic GVHD, immunosuppression duration, and post-transplant outcomes were similar across donor types. The day +30 Cum.Inc of bacterial bloodstream infections (BSI) tended to be higher in HLA-matched transplants (49.2%, = 0.073), while HHV-6 reactivation showed a trend toward higher frequency in haploidentical transplants (22.4%, = 0.068). Cytomegalovirus (CMV) reactivation occurred between days +30 and +100, with the highest Cum.Inc in MMUD (59.5%, = 0.033). BK virus-associated hemorrhagic cystitis showed a trend toward higher incidence in MMUD (22.3%, = 0.056). Respiratory and fungal infections were most frequent in the first 100 days, with comparable rates across donor types. By day +180, most patients achieved immune reconstitution, with normalization of CD4+ T cells, CD8+ T cells, and IgG levels, independent of donor type. Patients undergoing allo-HCT with PTCY-based prophylaxis experience a high infectious density rate early post-transplant, which decreases after 6 months as immune reconstitution progresses, regardless of donor type.