A monoclonal Trd chain supports the development of the complete set of functional ?d T cell lineages

The clonal selection theory describes the key features of adaptive immune responses of B and T cells. For aß T cells and B cells antigen recognition and selection principles are known at a detailed molecular level. The precise role of the antigen receptor in ?d T cells remains less well understood. To better understand the role of the ?d T cell receptor (TCR), in particular its specificity for thymic selection of ?d T cells and for ?d T cell biology in general, we generated a novel orthotopic TCRd transgenic mouse model. We demonstrate a multi-layered functionality of ?d TCRs and diverse roles of CDR3d-mediated selection during ?d T cell development. Whereas epithelial populations using V?5 or V?7 chains are affected to only minor extend in their biology in the presence of a single TCRd chain, pairing with V?1 positively selects subpopulations of ?d T cells with distinct programs in several organs, thereby distorting the repertoire. In conclusion, our data support dictation of developmental tropism together with adaptive-like recognition principles in a single antigen receptor. Overall design: Murine ?d T cells were isolated from the spleen via Fluorescence-activated cell sorting (FACS) according to the presence of CD3 and ?dTCR and the absence of aßTCR, B220 and CD11c, and analyzed using scRNAseq for transcriptome and V(D)J repertoire analysis.