A novel immunodeficiency associated with hypomorphic RAG1 mutations and CMV infection

Abstract

Amorphic mutations in the recombination activating genes RAG1 and RAG2 have been reported to cause T- B- SCID, whereas hypomorphic mutations led to the expansion of a few autoimmune T cell clones responsible for the Omenn syndrome phenotype. We report here a novel clinical and immunological phenotype associated with recessive RAG1 hypomorphic mutations in 4 patients from 4 different families. The immunological phenotype consists of the oligoclonal expansion of TCR gammadelta T cells combined with TCR alphabeta T cell lymphopenia. The clinical phenotype consists of severe, disseminated CMV infection and autoimmune blood cell manifestations. Repertoire studies suggest that CMV infection, in the setting of this particular T cell immunodeficiency, may have driven the TCR gammadelta T cell clonal expansion. This observation extends the range of clinical and immunological phenotypes associated with RAG mutations, emphasizing the role of the genetic background and microbial environment in determining disease phenotype.

Figure 1

TCRVB usage by patients’ T lymphocytes. (A) VB repertoire was determined either using available specific mAb in immunofluorescence assay in P2 and P4 or using real-time PCR analysis assay in P3. In this latter patient, similar results were obtained by PCR analysis and using available specific mAb in immunofluorescence assay (data not shown). The x axis indicates VB families; the y axis indicates relative frequency of usage (%) within the TCRαβ T cells. Controls values shown in rectangles represent mean ± 2 SDs. Gray bars indicate abnormal VB usage. *Not done. (B) Profiles of the fluorescent Vβ-Cβ runoff products obtained with mononuclear cells. The x axis indicates CDR3 length.

Figure 2

TCRVγ and -Vδ usage by patients’ T lymphocytes. Vδ (A) and Vγ (C) repertoire was determined either using available specific mAb in immunofluorescence assay in P1 or using real-time PCR analysis in P2, P3, and P4. The x axis indicates Vδ family usage by TCRγδ cells; the y axis indicates relative frequency (%) within the TCRγδ T cells. Controls values shown in rectangles represent mean ± 2 SDs. Similar results were obtained using available specific mAb in immunofluorescence assay (data not shown). *Not done. Profiles of the fluorescent Vδ-Cδ (B) and Vγ-Cγ (D) runoff products obtained with mononuclear cells. The x axis indicates CDR3 length.

Figure 3

Schematic representation of the RAG1 gene mutations. Mutations are represented and placed on the overall schematic primary structure of the RAG1 protein. Horizontal bars represent the expected truncated products as compared with the wild-type RAG1 protein. fs, frameshift.