Immune checkpoint blockade (ICB) in metastatic melanoma (MM) was the first successful immunotherapy in solid cancers. Meanwhile, ICB utilizing antagonistic antibodies to the checkpoint molecules PD-1±CTLA-4 on the surface of effector T cells are standard of care for a steadily increasing list of advanced solid cancers. However, despite the groundbreaking success of ICB over the past decade, still only 50% of MM patients respond durably, but many nonetheless suffer side effects. Thus, there is the urgent need to improve today´s ICB strategies.
γδ T cells are “unconventional” T cells with MHC-unrestricted cytotoxicity, which are a direct target of ICBs. The studies proposed here aim at a better understanding of the contribution of γδ T cells to cancer immunosurveillance under ICB and of their (impaired) role in MM rejection. This may lead to the identification of potential means of modulating these cells to reinvigorate/boost their anti-cancer functionality. In our previous FOR2799 project, we showed that i) peripheral blood (PB) Vδ1 T cell frequencies are a predictive biomarker for successful ICB, ii) patients with a poor outcome exhibit an accumulation of terminally differentiated, potentially exhausted PB Vδ1 T cells that might be dominated by a few expanded clones, iii) γδ T cell functionality is impaired in MM before and during ICB, relative to healthy donors. We also have preliminary evidence for the trafficking of γδ T cell clones between tumor and PB.
Here, we propose an in-depth analysis of ICB-associated, tumor-infiltrating γδ T cells to investigate their phenotype and function utilizing high-dimensional single cell proteomic and transcriptomic analyses approaches, in correlation with respective clinical data. This analysis will compare the impact of ICB on PB Vδ1 T cell signatures in MM patients with the most extreme terminally differentiated phenotype (poor prognosis under ICB) with patients exhibiting a more effector cell-dominated profile with a better prognosis. Both PB and tumor samples will be studied in parallel, including the TCR repertoire, functional properties and high dimensional phenotyping. These studies will also include spatial multiplexed in-situ proteomic analyses to gain insight into the orientation of γδ T cells in the tumor microenvironment. Finally, γδ T cell cytotoxicity and potential translational strategies to boost it will be studied in our recently established in vitro melanoma model testing novel agents, for example a new bispecific antibody.
From this project, we expect to generate new insights into the contribution of γδ T cells to MM rejection that will allow us to formulate new hypotheses for future exploitation of these unconventional T cells in strategies both including and independent of ICB.