scRNA-seq reveals functionally distinct gd T cells in human colorectal tumors.

Colorectal cancer is the third most common malignancy worldwide, with increasing numbers due to the spreading obesity epidemic and Western diet. Colorectal tumors are subclassed by mutational burden, caused by microsatellite instability (MSI). MSI-high tumors tend to induce robust T-cell responses and respond well to immunotherapy. However, microsatellite-stable (MSS) tumors lack high mutational burden and conventional T-cell recognition. While these tumors have therefore been considered immunologically “cold,”, MSS tumors are infiltrated by innate lymphocytes, including gd T cells, natural killer (NK) cells, and mucosal associated invariant T (MAIT) cells. We therefore focused on the innate antitumor response in these patients. Colon tumor and uninvolved tissue were sampled from 6 patients undergoing surgical resection for MSS tumors. Using the 10x genomics platform, single-cell RNAseq was performed on isolated populations of gd T cells, NK cells, MAIT cells, and conventional T cells. Single-cell analysis of these tumors revealed significant heterogeneity in all cell subsets analyzed, revealing phenotypic and functional changes not previously observed in bulk sequencing data. A subset of gdT cells adopted a wound healing phenotype in all colorectal cancer samples. These soluble factors are involved in the tissue repair response and barrier integrity, providing mitogenic signals to epithelial cells. In addition, they are associated with immune suppression and induction of regulatory T cells. In humans, this phenotype can be induced in Vd1 T cells in response to proinflammatory cytokine stimulation. In the murine gut, resident gd T cells adopt this phenotype basally and increase production in response to inflammatory cytokine production. The combination of pro-tissue growth and immune suppression, by gd T cells, likely contributes to the poor immunogenicity of MSS tumors. Depleting or converting these cells represents a novel immunotherapeutic target in colorectal cancer. Citation Format: Cathal Harmon, Alex Zaborowski, Harry Kane, Stephen Cunningham, Leandro Agudelo, Manolis Kellis, Des Winter, Lydia Lynch. scRNA-seq reveals functionally distinct gd T cells in human colorectal tumors [abstract]. In: Proceedings of the AACR Special Conference on Tumor Immunology and Immunotherapy; 2019 Nov 17-20; Boston, MA. Philadelphia (PA): AACR; Cancer Immunol Res 2020;8(3 Suppl):Abstract nr A47.