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

Gamma delta (γδ) T cells are innate-like lymphocytes that in humans can be broadly classified into two main subtypes based on their unique TCRδ chain, Vδ1 and Vδ2. Both subsets have potent anti-tumor properties and the presence of Vδ1 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 γδ T cells. We show that ICRs display differential expression and regulation by the JAK-STAT pathway in circulating Vδ1 and Vδ2 cells and identify constitutive (e.g. TIGIT, PD-1) and inducible (e.g. TIM-3, LAG-3, CTLA-4) ICRs. In melanoma, Vδ1 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 γδ 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, Vδ1 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 Vδ1 cells was downregulated in response to successful ICB therapy. Collectively, our data indicate an intricate relationship between ICRs, putatively also KIRs, and γδ T cells and reveal novel approaches by which these cells can be harnessed in order to discern or improve cancer immunotherapy.