In vivo modeling of human γδ T cell ontogeny reveals terminal deoxynucleotidyl transferase as a key regulator of type 3 Vδ2 T cell development

Profound differences in T cell receptor (TCR) repertoire and functional profiles between human and murine γδ T cells pose significant challenges for translational γδ T cell research. Therefore, we generated humanized immune system (HIS) NBSGW (NOD,B6.Prkdc^scidIl2rγ^-/-Kit^W41/W41) mice reconstituted with human fetal liver CD34⁺ hematopoietic stem and progenitor cells (HSPCs) enabling evaluation of human γδ T cells in vivo. The HIS mice accurately recapitulate the TCR-associated thymic programming of human γδ T cells-alongside αβ T cell development-and their peripheral effector functions, including the generation of phosphoantigen-reactive Vγ9Vδ2 T cells uniquely found in humans. Moreover, terminal deoxynucleotidyl transferase (TdT) is identified as a key regulator of type 3 Vδ2 T cell development. These findings demonstrate that HIS mice are a powerful model to screen human γδ T cell-targeting immunotherapies and to obtain mechanistic insights into human γδ T cell biology.