Checkpoint receptors in circulating γδ T cells can discern the outcome of cancer immunotherapy

Gamma delta ({gamma}{delta}) T cells are innate-like lymphocytes that in humans can be broadly classified into two main subtypes based on their unique TCR{delta} chain, V{delta}1 and V{delta}2. Both subsets have potent anti-tumor properties and the presence of V{delta}1 cells in the tumor is often associated with positive prognosis. Herein, we investigated the molecular interplay between immune checkpoint receptors (ICRs), IC blockade (ICB) therapy and {gamma}{delta} T cells. We show that ICRs display differential expression and regulation by the JAK-STAT pathway in circulating V{delta}1 and V{delta}2 cells and identify constitutive (e.g. TIGIT, PD-1) and inducible (e.g. TIM-3, LAG-3, CTLA-4) ICRs. In melanoma, V{delta}1 cells, especially in patients who did not respond to ICB or required combination therapy, expressed high levels of ICR, TOX and inhibitory killer Ig-like receptors (KIR) transcripts, reminiscent of an exhaustion transcriptional signature. At the same time all {gamma}{delta} T cells had a prominent downregulation in AP-1 transcription factors. Patient derived cells were functionally competent, although induction of LAG-3 and CTLA-4 was impaired. In the context of anti-PD-1 monotherapy, V{delta}1 cells specifically bound high levels of therapeutic antibody but only in patients who responded to treatment, revealing a potential new prognostic marker for evaluating the efficacy of ICB therapy. Finally, expression of KIR genes in V{delta}1 cells was downregulated in response to successful ICB therapy. Collectively, our data indicate an intricate relationship between ICRs, putatively also KIRs, and {gamma}{delta} T cells and reveal novel approaches by which these cells can be harnessed in order to discern or improve cancer immunotherapy.