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Hypomorphic Rag1 mutations alter the preimmune repertoire at early stages of lymphoid development

L. M. Ott de Bruin, M. Bosticardo, A. Barbieri, S. G. Lin, J. H. Rowe, P. L. Poliani, K. Ching, D. Eriksson, N. Landegren, O. Kämpe, J. P. Manis and L. D. Notarangelo

Key Points

  • Mice with hypomorphic mutations in the Rag1 C-terminal domain are a model of leaky combined immunodeficiency with autoantibodies.

  • Hypomorphic C-terminal domain Rag1 mutations cause repertoire skewing at the earliest stages of B- and T-cell development.

Abstract

Hypomorphic RAG1 mutations allowing residual T- and B-cell development have been found in patients presenting with delayed-onset combined immune deficiency with granulomas and/or autoimmunity (CID-G/AI) and abnormalities of the peripheral T- and B-cell repertoire. To examine how hypomorphic Rag1 mutations affect the earliest stages of lymphocyte development, we used CRISPR/Cas9 to generate mouse models with mutations equivalent to those found in patients with CID-G/AI. Immunological characterization showed partial development of T and B lymphocytes, with persistence of naïve cells and preserved serum immunoglobulin but impaired antibody responses and presence of autoantibodies, thereby recapitulating the phenotype seen in patients with CID-G/AI. By using high-throughput sequencing, we identified marked skewing of Igh V and Trb V gene usage in early progenitors, with a bias for productive Igh and Trb rearrangements after selection occurred and increased apoptosis of B-cell progenitors. Rearrangement at the Igk locus was impaired, and polyreactive immunoglobulin M antibodies were detected. This study provides novel insights into how hypomorphic Rag1 mutations alter the primary repertoire of T and B cells, setting the stage for immune dysregulation frequently seen in patients.

  • Submitted December 9, 2017.
  • Accepted April 30, 2018.
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