Abstract 3529: T-cell trafficking and extravasation is suppressed in distal tumors during gastrointestinal tract dysbiosis

Abstract The crosstalk between the microbiota and the host is crucial to maintaining immune homeostasis. A growing body of evidence shows that microbial imbalance affects cancer susceptibility and progression. A common significant influence on the microbiota in the gastrointestinal (GI) tract is the use of antibiotics. Oral antibiotics severely alter the bacteria in the GI tract by destroying beneficial bacteria alongside pathogenic ones — producing a state of microbial imbalance called dysbiosis. The overall use of antibiotics has increased by more than 30% in recent years, and moreover, many cancer patients are prescribed antibiotics during treatment, as infection is frequently a complication. We hypothesized that antibiotic-induced dysbiosis of the gut microbiota would suppress cytokine profiles in the host, thereby causing stromal immune surveillance suppression. We found that antibiotics as well as tumorigenesis caused changes in the bacterial abundance, composition, or diversity in the GI tract. On the host side, we found that antibiotic-induced dysbiosis caused the small intestine and cecum to enlarge and elongate, yet the colon was not affected. Moreover, B16-F10 melanoma and Lewis Lung carcinoma progressed more quickly during dysbiosis. Mechanistically, tumor progression was mediated by suppressed TNF-α levels, both locally and systemically. In contrast, IFN-γ and VEGF did not change significantly during dysbiosis. The suppressed levels of TNF-α, a pleiotropic regulator of intercellular adhesion molecule-1 (ICAM-1), resulted in reduced expression of tumor endothelial cell associated ICAM-1, and a subsequent decrease in the number of activated and effector CD8+ T-cells in the tumor. However, suppression of ICAM-1 or its binding site, the alpha subunit of lymphocyte function-associated antigen-1 (LFA-1), was not seen in established vasculature during dysbiosis as assessed in the spleen or the thymus. While dysbiosis enhanced tumor growth in ICAM-1+/+ and immunocompetent mice, it did not affect tumor growth in ICAM-1-/- or T-cell deficient mice, highlighting the influence and impact of dysbiosis on T-cell trafficking and extravasation. TNF-α supplementation in dysbiotic mice was able to overcome the dysbiosis-induced suppression as evident by increased ICAM-1 expression, leukocyte trafficking and tumor growth inhibition. Overall, these results demonstrate the importance of commensal bacteria in supporting immune surveillance and expand our understanding of the crosstalk between the gut microbiome and the stroma in distal non-GI tract tumors. Moreover, this knowledge has the potential to influence clinical decision-making when treating patients for solid cancers with dysbiosis-inducing antibiotics and may further inform concurrent and (neo-)adjuvant treatments to overcome the adverse effects of the antibiotics. Citation Format: Samir V. Jenkins, Michael S. Robeson, Eric R. Siegel, Charles M. Quick, Robert J. Griffin, Martin J. Cannon, Kieng B. Vang, Ruud P. Dings. T-cell trafficking and extravasation is suppressed in distal tumors during gastrointestinal tract dysbiosis [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 3529.