Characterization of T and B cell repertoire diversity in patients with RAG deficiency

Abstract

Recombination-activating genes 1 and 2 (<i>RAG1</i> and <i>RAG2</i>) play a critical role in T and B cell development by initiating the recombination process that controls the expression of T cell receptor (TCR) and immunoglobulin genes. Mutations in the <i>RAG1</i> and <i>RAG2</i> genes in humans cause a broad spectrum of phenotypes, including severe combined immunodeficiency (SCID) with lack of T and B cells, Omenn syndrome, leaky SCID, and combined immunodeficiency with granulomas or autoimmunity (CID-G/AI). Using next-generation sequencing, we analyzed the TCR and B cell receptor (BCR) repertoire in 12 patients with <i>RAG</i> mutations presenting with Omenn syndrome (<i>n</i> = 5), leaky SCID (<i>n</i> = 3), or CID-G/AI (<i>n</i> = 4). Restriction of repertoire diversity skewed usage of variable (V), diversity (D), and joining (J) segment genes, and abnormalities of CDR3 length distribution were progressively more prominent in patients with a more severe phenotype. Skewed usage of V, D, and J segment genes was present also within unique sequences, indicating a primary restriction of repertoire. Patients with Omenn syndrome had a high proportion of class-switched immunoglobulin heavy chain transcripts and increased somatic hypermutation rate, suggesting in vivo activation of these B cells. These data provide a framework to better understand the phenotypic heterogeneity of RAG deficiency.