Multiple reversions of an IL2RG mutation restore T cell function in an X-linked severe combined immunodeficiency patient.

Reversion mosaicism is increasingly being reported in primary immunodeficiency diseases, but there have been few cases with clinically improved immune function. Here, a case is reported of X-linked severe combined immunodeficiency (SCID-X1) with multiple somatic reversions in T cells, which restored sufficient cell-mediated immunity to overcome viral infection. Lineage-specific analysis revealed multiple reversions in T cell receptor (TCR) αβ+ and TCRγδ+ T cells. Diversity of the TCRVβ repertoire was comparable to normal and, furthermore, mitogen-induced proliferation of the patient's T cells was minimally impaired compared to healthy controls. In vivo and in vitro varicella antigen-specific T cell responses were comparable to those of healthy controls, although a reduced level of T cell receptor excision circles suggested that recent thymic output was low. During long-term evaluation of the patient's immunologic status, both the number of CD4+ and CD8+ T cells and T cell proliferation responses were stable and the patient remained healthy. This case demonstrates that multiple but restricted somatic reversions in T cell progenitors can improve the clinical phenotype of SCID-X1.