Abstract A033: Pro-inflammatory tumor cells drive CD4+ T cell localization within heterogeneous tumors

Abstract Immunotherapies such as immune checkpoint inhibitors (ICIs) have greatly improved patient outcomes in multiple tumor types, but ICIs have failed to achieve responses in many patients. Meta-analyses of patient cohorts treated with ICIs have observed that worse clinical outcomes are strongly correlated with high levels of intratumoral genetic heterogeneity (ITH). ITH occurs when tumor cells mutate as they divide, typically due to oxidative stress or DNA damage from rapid proliferation and continued carcinogenic insults, generating tumor subclones. However, the mechanisms by which ITH impairs the anti-tumor immune response are not fully understood. We propose a novel mechanism for how ITH in highly T cell-infiltrated inflamed tumors can adversely affect T cell behavior. We hypothesize that strongly pro-inflammatory tumor subclones secreting robust pro-inflammatory chemokine profiles can dominate T cell trafficking within the tumor, resulting in a weakened immune response against other tumor subclones. Using a murine squamous cell skin carcinoma (SCC) model, we have demonstrated that in immune-inflamed tumors, the spatial distribution and behavior of tumor-infiltrating T cells is influenced by ITH. A strongly pro-inflammatory tumor line expressing an endogenous RFP fluorophore was mixed with a weakly pro-inflammatory tumor line expressing an endogenous YFP fluorophore at a 1:1 ratio. The resulting tumors contained distinct RFP+ and YFP+ regions. These were analyzed by immunofluorescence (IF) and by manually dissecting the tumors and analyzing each region by flow cytometry. Flow cytometry analysis determined that the strongly pro-inflammatory RFP+ regions contained significantly more total T cells and CD4+ T cells than YFP+ regions. Furthermore, FoxP3- “conventional” CD4+ T cells were significantly more likely to be “terminal effector-like” CD44+CD62L- in RFP+ regions, and significantly more likely to be “naïve-like” CD62L+CD44- in YFP+ regions. IF analysis confirmed the preferential distribution of CD4+ T cells in RFP+ regions, and observed that this spatial pattern was evident as early as 11 days after subcutaneous injection. Notably, this localization trend did not occur with CD8+ T cells, which were evenly dispersed throughout the tumors. ELISA analysis of lysates of both tumor cell lines determined that the pro-inflammatory RFP+ cell line secretes significantly higher levels of the chemokine CCL5, which has been observed by other studies to selectively mediate CD4+ T cell chemotaxis. These results demonstrate that intratumoral CD4+ trafficking is shaped by the spatial distribution of specific tumor subclones, and suggest tumor cell chemokine signaling may directly mediate T cell spatial localization and behavior within tumors. Citation Format: Robert Letchworth, Savannah Hughes, Abigail Keku, Melissa Reeves. Pro-inflammatory tumor cells drive CD4+ T cell localization within heterogeneous tumors [abstract]. In: Proceedings of the AACR Special Conference in Cancer Research: Tumor Immunology and Immunotherapy; 2024 Oct 18-21; Boston, MA. Philadelphia (PA): AACR; Cancer Immunol Res 2024;12(10 Suppl):Abstract nr A033.