The distinct MHC-unrestricted immunobiology of innate-like and adaptive-like human γδ T cell subsets-Nature's CAR-T cells.

Willcox, Carrie R; Mohammed, Fiyaz; Willcox, Benjamin E

Distinct innate-like and adaptive-like immunobiological paradigms are emerging for human γδ T cells, supported by a combination of immunophenotypic, T cell receptor (TCR) repertoire, functional, and transcriptomic data. Evidence of the γδ TCR/ligand recognition modalities that respective human subsets utilize is accumulating. Although many questions remain unanswered, one superantigen-like modality features interactions of germline-encoded regions of particular TCR Vγ regions with specific BTN/BTNL family members and apparently aligns with an innate-like biology, albeit with some scope for clonal amplification. A second involves CDR3-mediated γδ TCR interaction with diverse ligands and aligns with an adaptive-like biology. Importantly, these unconventional modalities provide γδ T cells with unique recognition capabilities relative to αβ T cells, B cells, and NK cells, allowing immunosurveillance for signatures of "altered self" on target cells, via a membrane-linked γδ TCR recognizing intact non-MHC proteins on the opposing cell surface. In doing so, they permit cellular responses in diverse situations including where MHC expression is compromised, or where conventional adaptive and/or NK cell-mediated immunity is suppressed. γδ T cells may therefore utilize their TCR like a cell-surface Fab repertoire, somewhat analogous to engineered chimeric antigen receptor T cells, but additionally integrating TCR signaling with parallel signals from other surface immunoreceptors, making them multimolecular sensors of cellular stress.