Abstract 66: A new mechanism of tumor immune escape: TCF19 promotes the development of novel terminally exhausted T cells through E2F and MYC transcription family
Authors: Wang Fuhui , Dong Nan , Zhang Changhua 
Published: March 2024

Abstract
Introduction: ICB (immune checkpoint blocking) has been a promising therapy in cancer treatment, but there are still some patients do not response to this therapy. And it is well known that the majority cells reactivated to ICB are TCF1+ precursor exhausted T cells. Thus, studying the formation and heterogeneity of exhausted T cells are very necessary for improving the efficacy of ICB therapy. In this research, we identified a new population as TCF19+PD1+TIM3+ exhausted CD8+ T cells, which blocked the responds to ICB therapy.
Methods: We collected single cell sequencing data, including colorectal cancer, gastric cancer, melanoma, and lung cancer, and drew tumor immune cells map through cluster analysis. Then using bioinformatics tools CytoTRACE. T and CCAT. A to calculate the differentiation of exhausted T cell populations, which discovered a new subset of highly proliferative and poorly differentiated terminal exhausted T cells. Subsequently, the existence of this group of cells was verified through in vitro experiments, and their formation mechanism and correlation with immunotherapy were further studied.
Results: We utilized CytoTRACE.T and CCAT.A to predict differentiation states of terminally exhausted T cells. Then GEO and KEGG pathway gene set enrichment analysis were used. After analyzing, we found out that there was a subset of cells in terminally exhausted T cells defined as TCF19+PD1+TIM3+ Tex cells, which presented low differentiated and high proliferative potential.Then we performed multiple immunofluorescence staining and flow cytometry to verified the existence of TCF19+PD1+TIM3+ Tex cells in vitro. Clarifing the generation of these cell subset through regulating the expression of E2F and MYC transcription factor families.By collecting pathological sections of patients with immunotherapy information, we found that the amount of TCF19+PD1+TIM3+ Tex cells was inversely proportional to the efficacy of ICB, through immunofluorescence staining and immunohistochemical analysis as well as organoid models cocultured with T cells.
Conclusion: In this research, we found a new subpopulation of terminal Tex cells, which showed high proliferation and low differentiation. For cells, TCF19 mediated the generation of stemness terminal Tex cells may through regulating the expression of E2F and MYC. Finally, we discovered that the existence of TCF19+PD1+TIM3+ Tex cells can predict the efficacy of ICB, that the more TCF19+PD1+TIM3+ Tex cells contained, the less efficacy of ICB in patients.This finding may provide a new research direction for immunotherapy. Thus, more attention should be paid to this new cell subset.
Citation Format: Fuhui Wang, Nan Dong, Changhua Zhang. A new mechanism of tumor immune escape: TCF19 promotes the development of novel terminally exhausted T cells through E2F and MYC transcription family [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2024; Part 1 (Regular Abstracts); 2024 Apr 5-10; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2024;84(6_Suppl):Abstract nr 66.