Human peripheral invariant natural killer T are adaptive lymphocytes, whose TCR CDR3β regulates their antigen specificity and reactivity to avoid harmful autoimmune responses (BA8P.124)

Human invariant natural killer T (iNKT) cells carry a sole variable element, complementarity determining region 3β (CDR3β) in their T cell receptors (TCRs). It has been widely accepted that iNKT cells recognize foreign and self-ligands via CD1d in a pattern recognition-like innate-type manner. Here, we have created a thymically unselected human iNKT Vβ11 TCR repertoire and isolated a series of iNKT TCRs with ultra-high to low autoreactivity. We have found three distinctive CDR3β sequence motifs that dictate high iNKT TCR autoreactivity. In vitro and in vivo studies demonstrated that highly autoreactive iNKT cells carry innate-type TCRs, recognize CD1d molecules in a ligand-independent manner and evoke severe systemic autoimmune responses within a few hours upon adoptive transfer. In contrast, iNKT cells with intermediate to low autoreactivity express adaptive-type TCRs, which selectively recognize self-ligands and induce tissue-specific moderate autoimmune responses in vivo. High throughput CDR3β sequencing revealed that the frequency of highly autoreactive human iNKT cells positive for all 3 motifs was significantly reduced among iNKT cells in the periphery compared to the thymus. We conclude that intermediately and lowly autoreactive iNKT cells which prevail in the human periphery are adaptive lymphocytes and that the sole adaptive CDR3β sequences regulate the antigen specificity and reactivity of iNKT cells to avoid harmful autoimmune responses.