Abstract 2164: Chromosomal instability as a mediator of anti-tumor immunity in pancreatic cancer
Authors: Bronder Daniel , Sriram Roshan K. , Bakhoum Samuel F. 
Published: June 2022

Abstract
Chromosomal instability (CIN) is a hallmark of solid cancers and an established driver of dis-ease progression, therapy resistance, metastasis and on the whole poor patient outcome. Pancreatic cancer, in particular, is defined by dismal survival rates with many patients presenting with metastatic disease upon diagnosis and 5-year survival only reaching ~10%. Recent efforts to improve prognosis for pancreatic cancer patients involved immunotherapies alone and in combination with other therapeutics, however, progress remains limited. Despite CIN’s established role as a driver of disease progression, we have made the paradoxical observation that chromosomally unstable, murine pancreatic cancer cells elicit an anti-tumor immune response. CIN was induced in a chromosomally stable, metastatic model using piggyBac mutagenesis to increase chromosome segregation errors and simultaneously express the diphtheria toxin receptor, thymidine kinase, firefly luciferase and blue fluorescence protein transgenes. Modeling metastatic dissemination by injection of cells into the tail vein of mice led to robust tumor formation in the lungs where CINlow cells formed many small lesions while CINhigh cells formed fewer but larger tumors. We investigated if the tumors were infiltrated differentially by immune cells by immunofluorescence and found that CINhigh tumors were more readily infiltrated by effector T-cells. This observation motivated us to test immunotherapy response in CINlow and CINhigh tumors. Subcutaneously implanted tumor cells were treated with an immune checkpoint inhibitor and isotype control antibody which revealed that CINhigh cells responded to immunotherapy while CINlow cells did not. However, this response could easily be explained by the expression of ectopic antigens in CINhigh cells as a result of the piggyBac mutagenesis, therefore, we derived isogenic single cell clones from the CINhigh population and probed chromosome segregation fidelity and anti-tumor immunity in a more controlled system. Indeed, we were able to isolate CINlow and CINhigh subclones and found that these displayed similar lung engraftment to original CINlow and CINhigh cells as demonstrated by in vivo bioluminescence imaging. Importantly, this difference in engraftment efficiency was alleviated in immunocompromised mice supporting our notion that CIN mediates an anti-tumor immune response in this setting. In summary, our data implicates CIN as a determinant of therapeutic and genetic anti-tumor immunity in a preclinical model of pancreatic cancer. The utility of this model is illustrated by the isogenic nature of cells that only differ in CIN levels and their expression of in vitro and in vivo selection markers. Currently, we are determining the mechanistic underpinnings of our observation using a combination of transcriptomics and genetic manipulations by CRISPR/Cas9.
Citation Format: Daniel Bronder, Roshan K. Sriram, Samuel F. Bakhoum. Chromosomal instability as a mediator of anti-tumor immunity in pancreatic cancer [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2022; 2022 Apr 8-13. Philadelphia (PA): AACR; Cancer Res 2022;82(12_Suppl):Abstract nr 2164.