Abstract 3458: Antagonism between tumors and lymphocytes drives coevolutionary processes throughout metastasis

Abstract The development of metastatic disease is a conserved feature across most solid organ malignancies and accounts for the majority of cancer-related deaths. While adaptations within the local immune microenvironment of primary tumors are well-appreciated hallmarks of tumor progression, there remains much unknown about the specific impact of metastasis on both local and systemic immune responses. Here, we present an analysis of changes in the adaptive immune response to tumors during metastasis and clonal selection. Our group previously developed a syngeneic melanoma mouse model of spontaneous lymph node metastasis, performing nine generations of in vivo serial passaging to select for metastatic phenotypes. As previous work suggests, we find that tumors undergo clonal selection during metastasis using lentivirus integration mapping to measure clonality. Even amidst reduced genomic diversity, we find that metastases exhibit comparable or increased transcriptomic diversity when compared to primary tumors. In light of this discordance between genomic and transcriptomic diversity, we ask whether the immune response, especially T cells, exhibit similar dynamics. Performing both bulk and single cell T cell receptor (TCR) sequencing, we find that T cell clonality mirrors the reduced clonal diversity of metastatic tumors both in the total T cell compartment and specifically in regulatory T cells. Through paired investigation of evolution of tumors and the responding immune cells, we develop a model of tumor-immune coevolution in which reduced tumor clonality selects for narrower T cell repertoires; yet, diverse tumor transcriptional profiles support the differentiation of a variety of T cell subsets that are advantageous for tumors including regulatory T cells and exhausted CD8+ T cells. We further perturb this dynamic by evolving new metastatic cell lines in the absence of T cell pressure, finding unique evolution of metastatic pathways when the immune system is altered, impairing metastasis when reimplanted into immunocompetent mice. This model of tumor-immune coevolution establishes the importance of ongoing, dynamic communication between the host and tumors throughout metastatic progression. Citation Format: Cort B. Breuer, Marcos Labrado, Nathan E. Reticker-Flynn. Antagonism between tumors and lymphocytes drives coevolutionary processes throughout metastasis [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 3458.