Abstract 5166: Increasing translatability of syngeneic mouse models of cancer through the application of human-validated, clinically relevant gene expression-based measurements of the tumor immune microenvironment

Abstract Background: Syngeneic mouse models serve as invaluable tools in preclinical research. Implanting cancer cells into immunocompetent mice allows immunotherapy responses to be assessed in a physiologically relevant setting. To further improve the translatability of syngeneic models, we (1) characterized the immune landscape of different syngeneic models using human-validated immune gene expression (iGEX)-based measurements of the tumor immune microenvironment and (2) investigated the feasibility and utility of using these measurements to differentiate variable responses to treatment in mice. Methods: Our study analyzed tumor fragments from 15 models covering 10 cancers. Tumor fragments were taken from treatment naïve tumors of representative mice from each model and subjected to whole-transcriptome RNA-seq. Non-implanted cell lines from each model were also subjected to RNA-seq for comparison to tumor fragments. Data for immune-related genes were extracted and normalized to gene expression ranks for analysis. Previously validated iGEX signatures for monitoring the tumor immune microenvironment were calculated including tumor immunogenicity (TIGS), cellular proliferation (CP), and cancer testis antigen burden (CTAB) signatures. RNA-seq and tumor growth data from 1,839 mice treated with 1 of 8 treatments were paired to observe iGEX-based tumor growth differences among treatment conditions. Results: Tumor fragments and cell lines had distinct iGEX profiles with tumor fragments being highly enriched for genes involved in immune activity. Measures of iGEX in mouse tumor fragments recapitulated values in human patient tumors, providing confidence in the translatability of our results. Various associations were detected between iGEX signatures and response to treatment, most notably TIGS and CP. When testing mouse orthologs of 64 clinically relevant immune genes, almost all were associated with variable responses to therapy in at least one treatment condition. Robust positive associations were seen for Gm5751 (ortholog of SSX1/2 genes in humans), where high-expressing models had slower tumor growth overall and better responses to TNF receptor-based agonists (anti-CD137, -GITR, -OX40) and anti-CTLA4. Conclusions: We characterized the immune landscape of different syngeneic models using human-validated iGEX-based measurements. We detected variable responses to treatment in mice treated with various immunotherapies and radiation based on the high or low expression of these measurements. Our work shows that human-validated iGEX-based measurements can be implemented in syngeneic models, which enhances the translatability of syngeneic models in pre-clinical research and reiterates their important role in informing therapeutic strategies. Citation Format: Zachary D. Wallen, Kyle C. Strickland, Sheri Barnes, Sarabjot Pabla, Simon Brooks, Taylor J. Jensen, Brian Caveney, Marcia Eisenberg, Eric A. Severson, Scott C. Wise, Shakti Ramkissoon. Increasing translatability of syngeneic mouse models of cancer through the application of human-validated, clinically relevant gene expression-based measurements of the tumor immune microenvironment [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 5166.