Gammadelta T Cells Are Required for CD8+ T Cell Response to Vaccinia Viral Infection

Vaccinia virus (VV) is the most studied member of the poxvirus family, is responsible for the successful elimination of smallpox worldwide, and has been developed as a vaccine vehicle for infectious diseases and cancer immunotherapy. We have previously shown that the unique potency of VV in the activation of CD8+ T cell response is dependent on efficient activation of the innate immune system through Toll-like receptor (TLR)-dependent and -independent pathways. However, it remains incompletely defined what regulate CD8+ T cell response to VV infection. In this study, we showed that gammadelta T cells play an important role in promoting CD8+ T cell response to VV infection. We found that gammadelta T cells can directly present viral antigens in the context MHC-I for CD8+ T cell activation to VV in vivo, and we further demonstrated that cell-intrinsic MyD88 signaling in gammadelta T cells is required for activation of gammadelta T cells and CD8+ T cells. These results illustrate a critical role for gammadelta T cells in the regulation of adaptive T cell response to viral infection and may shed light on the design of more effective vaccine strategies based on manipulation of gammadelta T cells.

838 Phenotypic and functional signatures of peripheral and tumor-resident γδ T cells are informative for outcome of checkpoint blockade in melanoma

BackgroundImmune checkpoint blockade (ICB) set a milestone in cancer immunotherapy, but still only a fraction of patients responds. Thus, there is an urgent need for biomarkers predicting outcome, and also for understanding the responsible mechanisms. γδ T cells constitute a numerically minor subset of 1-10% of the peripheral T cell compartment in healthy people and have a major role in defense against multiple microbial and non-microbial challenges. Unlike the majority of T cells, γδ T cells bind their ligands in an MHC-independent manner. We previously studied γδ T cells, that also express checkpoint molecules, in patients in the pre-checkpoint blockade era and thereafter, and identified correlations between subset frequencies of these unconventional T cells and patients‘ overall survival (OS). Here, we present a detailed phenotyping and functional investigation of tumor-resident as well as peripheral γδ T cells.MethodsPhenotyping was performed in stage IV melanoma patients before and under PD-1+/-CTLA-4 blockade using as basis our published OMIP-20 protocol.1 Cytokine expression patterns and proliferative capacities were determined as described according to our established protocols.2 Primary flow cytometry data analysis was performed using FlowJo (BD) and correlations with clinical meta data were determined using Prism (GraphPad) and SPSS (IBM).ResultsWe found previously that low frequencies of peripheral Vδ1 γδ T cells were associated with prolonged OS. Here, we investigated functional aspects and abundance of γδ T cells within the tumor as well as in the blood. The peripheral Vδ1 but not the Vδ2 differentiation signature revealed significantly lower proportions of naive and effector cells as well as an accumulation of late differentiated cells in patients with high Vδ1 frequencies. The cytokine expression pattern (IFNγ, TNF and IL-17) and the degranulation marker CD107a were different in patients with high versus low peripheral Vδ1 frequencies. The proliferative capabilities of Vδ1 cells in melanoma were limited in comparison to healthy subjects. Both Vδ1 and Vδ2 cells were found in tumor tissues, and these analyses are ongoing, including analyses of replicative senescence through CD57 expression.ConclusionsOur data provide novel insights into the role of γδ T cells in cancer rejection. The previously found negative correlation of Vδ1 T cells with OS is likely due to an accumulation of mal-functioning, probably exhausted Vδ1 T cells in patients with poor outcome of ICB. Thus, we suggest that Vδ1 T cells are promising candidates for future exploitation in novel ICB-approaches.Ethics ApprovalThis study was approved by K. Wistuba-Hamprecht´s Ethics Committee (approval nos. 490/2014BO1 and 792/2016BO2).ReferencesWistuba-Hamprecht K, Pawelec G, Derhovanessian E. OMIP-020: Phenotypic characterization of human gammadelta T-cells by multicolor flow cytometry. Cytometry A 2014;85:522–524. doi:10.1002/cyto.a.22470Beucke N, et al. Pitfalls in the characterization of circulating and tissue-resident human gammadelta T cells. J Leukoc Biol 2020. doi:10.1002/JLB.5MA1219-296R

A gene expression signature of TREM2hi macrophages and γδ T cells predicts immunotherapy response

Identifying factors underlying resistance to immune checkpoint therapy (ICT) is still challenging. Most cancer patients do not respond to ICT and the availability of the predictive biomarkers is limited. Here, we re-analyze a publicly available single-cell RNA sequencing (scRNA-seq) dataset of melanoma samples of patients subjected to ICT and identify a subset of macrophages overexpressing TREM2 and a subset of gammadelta T cells that are both overrepresented in the non-responding tumors. In addition, the percentage of a B cell subset is significantly lower in the non-responders. The presence of these immune cell subtypes is corroborated in other publicly available scRNA-seq datasets. The analyses of bulk RNA-seq datasets of the melanoma samples identify and validate a signature - ImmuneCells.Sig - enriched with the genes characteristic of the above immune cell subsets to predict response to immunotherapy. ImmuneCells.Sig could represent a valuable tool for clinical decision making in patients receiving immunotherapy.