A mechanism for expansion of the regulatory T cell repertoire and its role in enforcing self-tolerance

To investigate the influence of CNS3, a cis-regulatory element in the Foxp3 locus, on the selection of T cell antigen receptor (TCR) repertoire of regulator CD4+ T cells (Treg), we crossed Foxp3ΔCNS3-gfp or control Foxp3gfp mice to DO11.10 TCRβ transgene and Tcra-/+ background. We isolated Treg and conventional CD4+T cells from thymus, spleen and lymph nodes of Foxp3ΔCNS3-gfp DO11.10 TCRβ Tcra-/+ or Foxp3gfp DO11.10 TCRβ Tcra-/+ male littermates, and sequenced the TCRα chains. Analysis of the diversity of Complementary Determining Region 3 (CDR3) of TCRα showed a distinct clustering of CNS3-deficient Treg cells from the CNS3-sufficient ones. DO11.10 TCRβ transgene inhibits the recombination of endogenous Tcrb loci thus restricting TCR repertoire to TCRα chains expressed by T cells. Further limitation of the TCR repertoire was achieved by the presence of one functional Tcra gene. With restricted TCR repertoire, mRNA of TCRα was extracted from Treg and conventional CD4+ T cells for library preparation and high throughput sequencing.