Abstract 4679: Rectal cancer-infiltrating T cells show clonal expansion associated with spatially restricted tolerogenic phenotypes

Abstract

Abstract T cell infiltration correlates with prognosis and outcome in colorectal cancer regardless of the tumor stage. However, data on clonal expansion, phenotypes, functions, and spatial distribution of tumor-infiltrating T cells (TILs) are limited. We hypothesized that subsets of clonally expanded rectal cancer-associated T cells are specifically recruited into the tumor and show characteristic phenotypes and functions. Paired TILs and T cells from adjacent unaffected mucosa were isolated from five treatment-naïve rectal cancer patients. Although T cell immune phenotypes were heterogeneous, the frequencies of CD38+, PD-1+, and TIM-3+ cells were significantly higher in CD8+ TILs when compared to T cells from unaffected mucosa (p < 0.05). To track clonal expansion and phenotypes at the single cell level, we combined 13-parameter FACS single cell index sorting with next generation T cell receptor (TCR) and phenotype sequencing. Paired TCRαβ sequences were obtained from 1237 TILs (on average 412 TILs per patient) and 1257 T cells infiltrating the unaffected mucosa (on average 419 T cells per patient) from three selected patients. Clonal T cell expansion was not restricted to TILs and occurred predominantly in CD8+ T cells (p < 0.05). Expanded TIL clones were more frequently TIM-3+, PD-1+, and CD38+ (p < 0.05) and occupied characteristic phenotype compartments when compared to T cells from unaffected mucosa with t-stochastic neighbor embedding (t-SNE) visualization. FOXP3 expression was enriched in non-expanded TILs (p < 0.05). Only 11 out of 179 TIL clones were also detectable in unaffected mucosa of the same patients and these overlapping clones were exclusively PD-1- TIM-3-. In conclusion, rectal cancer is infiltrated by oligoclonal T cells. Selected clones were exclusively detected in TILs suggesting their expansion and recruitment driven by tumor-associated cues. Tolerance was induced i) in an antigen-specific manner by the expression of immune checkpoint molecules predominantly on clonally expanded TILs, and ii) in an antigen-independent manner by infiltrating polyclonal FOXP3+ regulatory T cells. Citation Format: Livius Penter, Kerstin Dietze, Felix Aigner, Lars Bullinger, Thomas Blankenstein, Leo Hansmann. Rectal cancer-infiltrating T cells show clonal expansion associated with spatially restricted tolerogenic phenotypes [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2018; 2018 Apr 14-18; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2018;78(13 Suppl):Abstract nr 4679.