Can Posttransplant Cyclophosphamide Reduce the Risk of Graft-Versus-Host Disease for Pediatric Fully Matched Nonrelated Stem Cell Transplant?

Objectives: Allogeneic stem cell transplant is the only curative strategy for a variety of pediatric malignant/nonmalignant diseases. The introduction of posttransplant cyclophosphamide therapy as prophylaxis for graft-versus-host disease in haploi-dentical bone marrow transplant setting has been a game changer and is also being investigated for its benefits in matched hematopoietic stem cell transplants. The effect of posttransplant cyclophosphamide therapy for prophylaxis of graft-versus-host disease for fully matched hematopoietic stem cell transplants remains unclear for pediatric patients. As a part of conditioning regimen, antithymocyte globulin allows in vivo T-cell depletion for graft-versus-host disease prophylaxis and is known to reduce graft-versus-host disease incidence without increasing relapse. We investigated whether posttransplant cyclophosphamide therapy has an additive effect with antithymocyte globulin to reduce acute graft-versus-host disease and chronic graft-versus-host disease in pediatric cases of peripheral blood stem cell transplant. Materials and Methods: We conducted a retrospective clinical study of 110 pediatric patients who underwent pediatric blood stem cell transplant from matched unrelated donors. Fifty randomly selected patients received 50 mg/kg/d cyclophosphamide on post- transplant days 3 and 4 (group 1); the remaining 60 patients (group 2) did not receive cyclophosphamide. All patients were given a regimen of standard immunosuppression as graft-versus-host disease prophylaxis. Results: Patients were followed for a median of 2 years. The incidence of grade 2-4 and grade 3-4 acute graft-versus-host disease was 28% and 18%, respectively, in group 2, and 20% and 10%, respectively, in group 1. The incidence of chronic graft-versus-host disease was 8.3% in group 2 and 4% in group 1. Differences between groups were not significant. Conclusions: Our findings suggested no effect of post-transplant cyclophosphamide therapy for pediatric patients undergoing blood stem cell transplant with matched unrelated donors. Larger studies are needed to investigate the reasons for differences between pediatric and adult patients.