Patients with T+/low NK+ IL-2 receptor γ chain deficiency have differentially-impaired cytokine signaling resulting in severe combined immunodeficiency

Abstract

X-linked severe combined immunodeficiency (X-SCID) leads to a T-NK-B+ immunophenotype and is caused by mutations in the gene encoding the IL-2 receptor γ-chain (IL2RG). IL2RGR222C leads to atypical SCID with a severe early onset phenotype despite largely normal NK- and T-cell numbers. To address this discrepancy, we performed a detailed analysis of T, B, and NK cells, including quantitative STAT phosphorylation and functional responses to the cytokines IL-2, IL-4, IL-15, and IL-21 in a patient with the IL2RGR222C mutation. Moreover, we identified nine additional unpublished patients with the same mutations, all with a full SCID phenotype, and confirmed selected immunological observations. T-cell development was variably affected, but led to borderline T-cell receptor excision circle (TREC) levels and a normal repertoire. T cells showed moderately reduced proliferation, failing enhancement by IL-2. While NK-cell development was normal, IL-2 enhancement of NK-cell degranulation and IL-15-induced cytokine production were absent. IL-2 or IL-21 failed to enhance B-cell proliferation and plasmablast differentiation. These functional alterations were reflected by a differential impact of IL2RGR222C on cytokine signal transduction, with a gradient IL-4