Reduced-intensity post-cyclophosphamide-based graft-versus-host disease prophylaxis for umbilical cord blood transplantation: a single-center pilot study.

BACKGROUND: Post-cyclophosphamide (PTCy)-based GVHD prophylaxis has shown significant success in haploidentical transplants. The potential of PTCy in adult umbilical blood transplantation (UCBT) remains unclear due to concerns about engraftment, given the limited number of CD34+ cells. This study aimed to explore the preliminary safety and efficacy of a reduced-intensity PTCy (RI-PTCy) in single-unit UCBT in adults. METHODS: A total of 52 adult patients who underwent a single-unit UCBT were included in this pilot study. Patients were divided into three groups based on GVHD prophylaxis regimens: No PTCy (n=30), 100 mg RI-PTCy (n=15), and 400 mg RI-PTCy (n=7). Safety and efficacy were investigated post-transplantation. RESULTS: The median times for neutrophil engraftment were 15 days (range, 12-27 days) in the No PTCy group, 16 days (range, 13-25 days) in the 100 mg RI-PTCy group, and 18 days (range, 15-24 days) in the 400 mg RI-PTCy group. Platelet engraftment occurred at 30 days (range, 21-77 days), 32 days (range, 18-40 days), and 31 days (range, 25-42 days), respectively. By day +100, the RI-PTCy groups had a significantly lower cumulative incidence of grade II-IV aGVHD than the No PTCy group. The cumulative incidence of grade II-IV aGVHD was 30.0% (95% CI, 13.6%-46.4%) in the No PTCy group, compared with 6.7% (95% CI, 0%-19.3%) in the RI-PTCy 100 mg group and 0% in the RI-PTCy 400 mg group (P = .044). Notably, the 400 mg RI-PTCy group presents a higher incidence of 28-day bloodstream infection. Moreover, the estimated 1-year GRFS were 53.3% (95% CI, 34.3%-69.1%), 71.1% (95% CI, 39.4%-88.3%), and 100.0% in the No PTCy group, the 100 mg and 400 mg RI-PTCy groups (P = .059). CONCLUSIONS: RI-PTCy appears promising as a GVHD prophylaxis strategy in this exploratory pilot cohort; these hypothesis-generating findings warrant validation in larger prospective studies.