γ9δ2 T-Cell Expansion and Phenotypic Profile Are Reflected in the CDR3δ Repertoire of Healthy Adults

gamma 9 delta 2T cells fill a distinct niche in human immunity due to the unique physiology of the phosphoantigen-reactive gamma 9 delta 2TCR. Here, we highlight reproducible TCR delta complementarity-determining region 3 (CDR3 delta) repertoire patterns associated with gamma 9 delta 2T cell proliferation and phenotype, thus providing evidence for the role of the CDR3 delta in modulating in vivo T-cell responses. Features that determine gamma 9 delta 2TCR binding affinity and reactivity to the phosphoantigen-induced ligand in vitro appear to similarly underpin in vivo clonotypic expansion and differentiation. Likewise, we identify a CDR3 delta bias in the gamma 9 delta 2T cell natural killer receptor (NKR) landscape. While expression of the inhibitory receptor CD94/NKG2A is skewed toward cells bearing putative high-affinity TCRs, the activating receptor NKG2D is expressed independently of the phosphoantigen-sensing determinants, suggesting a higher net NKR activating signal in T cells with TCRs of low affinity. This study establishes consistent repertoire-phenotype associations and justifies stratification for the T-cell phenotype in future research on gamma 9 delta 2TCR repertoire dynamics.