Curative allogeneic hematopoietic stem cell transplantation following reduced toxicity conditioning in adults with primary immunodeficiency.

Primary immunodeficiencies (PID) are heterogeneous inborn errors of the immune system. Allogeneic hematopoietic stem cell transplantation (allo-HSCT) is curative and safe at the pediatric age but remains underperformed in adults. We report our experience on 32 consecutive adult patients with various PID including 17 (53%) with a combined immune deficiency, six (19%) with a disease of immune dysregulation and nine (28%) with a chronic granulomatous disease (CGD) who underwent an allo-HSCT between 2011 and 2020. The median age at transplant was 27 years (17-41). All assessable patients engrafted. The majority of patients received a fludarabine-Busulfan (FB) based regimen (FB2-3 in 16, FB4 in 12). Overall survival (OS) was 80.4% (100% for CGD and 74% for other PID patients) at 9 months and beyond (median follow-up 51.6 months). Six patients died, all in the first-year post-transplant. Cumulative incidences of grade II-IV acute GVHD/chronic GVHD were 18%/22%. Stem cell source, GVHD prophylaxis and conditioning intensity had no impact on OS. All surviving patients had over 90% donor chimerism, immune reconstitution, no sign of active PID related complications and were clinically improved. Allo-HSCT is effective in young adults PID patients with an acceptable toxicity and should be discussed in case of life-threatening PID.