Long-term outcomes of fludarabine, melphalan and antithymocyte globulin as reduced-intensity conditioning regimen for allogeneic hematopoietic stem cell transplantation in children with primary immunodeficiency disorders: a prospective single center study

Reduced-intensity conditioning (RIC) has offered many primary immunodeficiency disorder (PID) patients who are ineligible for myeloablative regimens a chance of cure. However, the beneficial role of RIC was questioned following reports suggesting higher chance of rejection and lower symptom resolution rate in mixed chimerism settings. Forty-five children affected by PIDs with a median age of 21 months underwent allogeneic hematopoietic stem cell transplantation in our institute from 2007 to 2013. All patients received an identical RIC regimen. Forty-one patients had successful primary engraftment (91%). Of the successful engraftments, 80% (n = 33) had stable full donor chimerism at last contact. Overall, eleven transplant-related mortalities were reported including five patients due to sepsis, three children due to grade IV acute GvHD, two due to chronic GvHD and one patient due to sepsis after primary graft failure. The median post-transplantation follow-up of deceased patients was 55 days. Five-year overall survival and disease-free survival was 75.6% and 68.89%, respectively. All surviving patients with successful engraftment became disease free, regardless of having full or mixed chimerism. Our study suggests that RIC regimen provides satisfactory rates of successful engraftment and full chimerism. Furthermore, patients with mixed chimerism were stable in long-term follow-up and this chimerism status offered the potential to resolve symptoms of immunodeficiency.