Hypomorphic RAG deficiency: impact of disease burden on survival and thymic recovery argues for early diagnosis and HSCT.

Patients with hypomorphic mutations in RAG1 and RAG2 genes present as either Omenn syndrome or atypical combined immunodeficiency (CID) with a wide phenotypic range. Hematopoietic stem cell transplantation (HSCT) is potentially curative, but data are scarce. We report on a worldwide cohort of 60 patients with hypomorphic RAG variants who underwent HSCT, 78% of whom experienced infections (29% active at HSCT), 72% autoimmunity and 18% granulomas pre-transplant. These complications were frequently associated with organ damage. Eight individuals (13%) were diagnosed by newborn screening or family history. HSCT was performed at a median of 3.4 years (range 0.3 - 42.9 years) from matched unrelated donors, matched sibling or matched family donors or mismatched donors (MMFD) in 48%, 22% and 30% of the patients, respectively. Grafts were T-cell depleted in 15 cases (25%). Overall survival at 1 and 4 years was 77.5 and 67.5% (median follow-up 39 months). Infection was the main cause of death. In univariable analysis, active infection, organ damage pre-HSCT, T-cell depletion of the graft and transplant from a MMFD were predictive of worse outcome, while organ damage and T-cell depletion remained significant in multivariable analysis (HR=6.01, HR=8.46, respectively). All patients diagnosed by newborn screening or family history survived. Cumulative incidences (CI) of acute and chronic GvHD were 35% and 22% respectively. CI of new-onset autoimmunity was 15%. Immune reconstitution, particularly recovery of naïve CD4+ T-cells was faster and more robust in patients transplanted before 3.5 years and without organ damage. These findings support the indication for early transplantation.