Abstract 5246: Chromosomal instability promotes colorectal cancer progression through manipulation of gamma delta T cells

Abstract Colorectal cancer (CRC) can be divided into 2 genetically different subtypes: Microsatellite instable CRC (MSI-CRC; ∼15% of CRC), and microsatellite stable (MSS-CRC; ∼85%). While MSI-CRC develops point mutations that increase neoantigen burden and enhanced response to immunotherapy, MSS-CRC develops chromosomal instability (CIN) and resistance to immunotherapy. Current mouse models do not recapitulate the key genetic defect of MSS-CRC: CIN. This limits our understanding of CIN‘s role in regulating tumor immunity in CRC, and therefore our capacity to generate new immunotherapies for MSS-CRC. To address this gap, we developed the first genetically engineered mouse model of MSS-CRC with human-like CIN. To recapitulate human CIN caused by telomere erosion, we incorporated the conditional null Apc and Trp53, and inducible Lox-Stop-Lox (LSL) mouse telomerase reverse transcriptase (mTert) alleles, referred to as iTAP. Due to LSL-mTert, mice lack mTert expression and therefore telomerase activity, which leads to telomere erosion upon successive generational intercrosses, evolving from G0 mice (LSL-mTert+/-) that have no CIN (CIN- iTAP) to G3 mice after 3 breeding generations with the mTert+/+ allele that develop CIN (CIN+ iTAP). Colonoscopy-guided submucosal administration of 4-OHT activates Villin-driven Cre-ER in colonocytes leading to Apc and Trp53 deletion and deletion of the stop cassette of LSL-mTert causing activation of telomerase in cancer cells. Oncogenesis in cells with telomere erosion leads to CIN. Consistent with worse OS in human MSS CINhigh, CIN+ iTAP tumors were more aggressive than CIN- iTAP. Single-cell RNA sequencing (scRNA-seq) confirmed that CIN+ iTAP tumors developed more copy number variations. Subclustering of the infiltrating immune populations revealed that γδ T cells expanded and changed their phenotype in CIN+ iTAP tumors, which was confirmed by flow cytometry. Treatment with a blocking antibody towards γδ TCR in mice with established tumors lead to increased survival in CIN+ iTAP mice but not in CIN- iTAP mice. ScRNA-seq of primary tumors of patients with MSS-CRC revealed that γδ T cells also exhibit phenotypic changes upon different levels of CIN in human MSS CRC. Citation Format: Paulino Tallón de Lara, Aviad Ben-Shmuel, Wen-Hao Hsu, Chaohao Li, Kyle Labella, Chi Wut Wong, Yonghong Liu, Shan Jiang, Xiaoying Shang, Scott Kopetz, Ronald DePinho. Chromosomal instability promotes colorectal cancer progression through manipulation of gamma delta T cells [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2025; Part 1 (Regular Abstracts); 2025 Apr 25-30; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2025;85(8_Suppl_1):Abstract nr 5246.