Comparative investigation of the role of tumor-infiltrating and peripheral blood γδ T cells in melanoma rejection under checkpoint therapy

01.06.2022 bis 31.05.2025

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 flow cytometry and single cell 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 high-dimensional tissue imaging 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.