Abstract
Abstract Patients with Lynch Syndrome, an inherited mismatch repair deficiency, have an increased risk for developing microsatellite unstable (MSI-H) cancers. Our team recently identified shared immunogenic frameshift peptides in patient tumors that can be targets of T cell surveillance and preventative MSI-H cancer vaccines. We hypothesize that in Lynch Syndrome some premalignant lesions are capable of evading immune surveillance from cytotoxic T lymphocytes due to immune checkpoint expression and immunosuppression from tumor, myeloid and stromal cell populations. Immune checkpoint blockade (ICB) showed promising results in the treatment of MSI-H tumors and are being evaluated in the adjuvant setting of patients with Lynch syndrome post surgical resection. However, a significant percentage of advanced MSI-H tumors resist ICB suggesting evolving mechanisms of immune resistance. We will use a MSI-H in vivo mouse model and additionally develop 3D spheroids cocultured with immune cells to characterize the underlying immune resistance mechanisms. The MSI-H mouse model will first be applied to identify shared frameshifts in MSI-H tumors by WES to develop vaccination approaches preventing tumor growth. Then, we will quantify MSI-H tumor growth and immune infiltration in the MSI-H mouse model, with or without ICB. We will analyze the presence of immunosuppressive pathways and myeloid subsets in high growth resisting tumors by immunohistochemistry, scRNAseq, spatial transcriptomics and flow cytometry. In addition, we will perform short-term in vitro spheroid-splenic cell co-cultures to better characterize the early immune resistance mechanisms. We will also perform these spheroid-immune cell co-cultures using the immune cells taken from mice after vaccination or ICB to identify the early myeloid immune resistance mechanisms. Overall, the identification of shared immune frameshifts in MSI-H tumors will allow developing peptide vaccination approaches to prevent tumor growth. Further, the identification of myeloid resistance pathways will guide therapeutic strategies against tumor resisting to ICB and/or vaccination. Citation Format: Guillaume Mestrallet. Overcoming immune resistance in DNA mismatch repair deficient tumors [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2023; Part 1 (Regular and Invited Abstracts); 2023 Apr 14-19; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2023;83(7_Suppl):Abstract nr 6652.
Published Version
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