Gads is differentially required for the thymic development of conventional and innate-like T cells

The adaptor Gads bridges a TCR-inducible interaction between the adaptors SLP-76 and LAT. Thymocyte development absolutely depends on SLP-76 and LAT; but is only moderately impaired in Gads-deficient mice, which accumulate non-naive peripheral T cells. We developed a model for tamoxifen-induced ablation of Gads (GadsiKO), accompanied by the expression of tdTomato. Using this model, we compared the fate of GadsiKO (Tom+) and Gads+ (Tom-) thymocytes within the same mice. Compared to Gads+ DN thymocytes, GadsiKO DNs were less likely to undergo β-selection; yet their ability to develop into γδ or NKT cells was not impaired. The progression of GadsiKO thymocytes into the DP and SP compartments was reduced, compared to Gads+ thymocytes. Among the GadsiKO DP and SP thymocytes, a large proportion were TCRβlo/neg and failed to upregulate CD5, a TCR-induced marker that is normally expressed upon β-selection and further increases upon positive selection. These observations suggest that a TCR-independent, innate-like thymic developmental pathway may be unmasked in the absence of Gads. Among the CD5+ GadsiKO CD4 SP thymocytes, a large proportion exhibited the non-naive phenotype CD44hiCD62Llo and expressed NK1.1. In contrast, developmentally normal peripheral T cells that were rendered GadsiKO maintained a naive CD44loCD62Lhi phenotype for up to five weeks. Our results suggest that Gads is dispensable for peripheral quiescence, but regulates thymic development, by promoting conventional αβ T cell development, while suppressing innate-like developmental fates.