Experience with post-transplant cyclophosphamide (PTCy) for GVHD prophylaxis in HLA-matched related donor HSCT in pediatric and adult patients. evidence of real-life outcomes from a Latin American transplant center.

Abstract Introduction: Post-transplant cyclophosphamide based prophylaxis against graft-versus-host disease (GVHD) has been widely used in the haploidentical transplant setting. Recent studies have demonstrated its efficacy in allogeneic transplants from HLA-matched related donors as well. This study presents the experience of a transplant center in Mexico using PTCy as GVHD prophylaxis in both pediatric and adult patients undergoing HLA-matched related donor allogeneic hematopoietic stem cell transplantation. Objective: To describe the outcomes of PTCy prophylaxis in patients undergoing HLA-matched related donor allogeneic hematopoietic stem cell transplantation in hospital IMSS UMAE 25 Monterrey Mexico. Materials and methods: Pediatric and adult patients who underwent MRD HSCT between 2023 and 2025 were included. Descriptive analyses were performed using measures of central tendency and percentages. Outcomes analyzed included overall survival (OS), relapse-free survival (RFS), non-relapse mortality (NRM), and the cumulative incidence of GVHD, using the Kaplan–Meier method. Results: A total of 43 patients were included (22 male, 21 female), with a median age of 18 years (range: 0.5–56 years). The most common diagnosis was acute lymphoblastic leukemia (ALL, 58%), followed by acute myeloid leukemia (AML, 11%), immunodeficiencies (9%), myelodysplastic syndrome (MDS, 5%), aplastic anemia (AA, 5%), and other diagnoses (12%). Myeloablative conditioning (MAC) was used in 93% of cases, and reduced-intensity conditioning (RIC) in 7%. GVHD prophylaxis was based on PTCy/tacrolimus ± MMF, PTCy doses of 35-40 mg/kg were used in 11 patients (25%). Donors were brothers in 44% and sisters in 56% of cases. The median CD34⁺ cell dose was 12.7 × 10⁶/kg (range: 4.0–57.2), all obtained from peripheral blood stem cells (PBSC). Median neutrophil engraftment occurred at 14.5 days (range: 11–22), and platelet engraftment at 15 days (range: 10–48). Median donor chimerism on day 30 was 99% (range: 20–100). Primary graft failure occurred in 2 % of patients. The median follow-up was 280 days (range: 17–1350). One- and two-year OS rates were 69% and 62%, respectively; RFS rates were 71% and 54%. GVHD occurred in 27% of patients. The 2-year overall survival (OS) was 75% in recipients with a male donor and 53% with a female donor; however, the difference was not statistically significant (log-rank p = 0.49). The cumulative incidence of GVHD was 31% at 1 year and 36% at 2 years. The cumulative incidence of grade 3–4 acute GVHD was 10%, and chronic GVHD at 2 years was 24% (with moderate-to-severe was 15%). The 2-year incidence of GVHD was 14% in recipients with a brother donor and 49% in those with a sister donor (log-rank p = 0.06). The incidence of GVHD was analyzed in relation to donor age. The incidence was 41% in recipients with donors older than 30 years, compared to 14% in those with donors younger than 30 years (log-rank p = 0.019). Non-relapse mortality (NRM) was 9% (4 patients died due to: pneumonia , Sinusoidal Obstruction Syndrome / Veno-Occlusive Disease (SOS/VOD), graft failure, and severe GVHD). Infectious complications occurred in 23% of patients ( one patient with severe COVID-19 and 3 patients with severe pneumonia requiring invasive mechanical ventilation). The CMV reactivación ocurred in 26 %, without evidence of clinical disease. BK virus reactivation was observed in 4% of patients, and hemorrhagic cystitis ocurred in 9% of cases. Conclusions: GVHD prophylaxis with post-transplant cyclophosphamide in HLA-matched related donor transplants proved effective in this Mexican patient cohort, showing early engraftment, low NRM, and a low incidence of severe acute and chronic GVHD; particularly when the donor was a male under 30 years of age.