Outcomes following matched sibling donor transplantation for severe combined immunodeficiency: a report from the PIDTC

The Primary Immune Deficiency Treatment Consortium performed a retrospective analysis of 133 patients with severe combined immunodeficiency (SCID) receiving matched sibling donor (MSD) hematopoietic cell transplantation (HCT) between 1980 and 2023 at 30 North American institutions. In this largest cohort of MSD outcomes in patients with SCID to date, we examined the impact of conditioning regimen and graft-versus-host disease (GVHD) prophylaxis on survival and immune recovery. Outcomes after MSD HCT for SCID were excellent. Patients without an active infection or failure to thrive (FTT) at the time of HCT had 5-year overall survival superior to those with infection or FTT. Acute and chronic GVHD outcomes were independent of GVHD prophylaxis, conditioning regimen, SCID type, or presence of maternal engraftment. Patients without active infection at the time of HCT had superior chronic GVHD-free event-free survival vs those with infection. T-cell reconstitution at 6 months was less likely achieved with use of GVHD prophylaxis or serotherapy, and in patients with leaky SCID or Omenn syndrome. At 6 months, 1 year, and 2-5 years, T-cell reconstitution was less likely with ADA, DCLRE1C, or RAG genotype. B-cell reconstitution at 1 year and 2-5 years was negatively affected by development of grade 2 to 4 or 3 to 4 acute GVHD. Conditioning did not affect T- or B-cell reconstitution. Our data suggest omitting conditioning and GVHD prophylaxis for patients with typical SCID did not negatively affect 5-year outcomes after MSD HCT, but the data are insufficient to recommend this approach for best long-term outcomes. This trial was registered at www.clinicaltrials.gov as #NCT01186913 and #NCT01346150.