Mounting evidence supports synergistic roles for the gut microbiome in cancer progression. Yet, the interplay between the gut microbiome and immune responses in cancer is still poorly understood. We recently showed that gut microbiome changes are closely associated with development of Kras-mutant lung adenocarcinoma (KM-LUAD) in a human-relevant, tobacco-associated mouse model (Gprc5a-/-; G). Knockout of the antimicrobial protein Lcn2 in these mice (Gprc5a-/-/Lcn2-/-; GL) further reduced microbial diversity while enhancing inflammation and tumor development. We thus hypothesized that microbial dysbiosis in the gut, such as that incurred by loss of Lcn2, may exacerbate LUAD development. Here, we investigated the effects of gut microbiome modulation on LUAD pathogenesis using fecal microbiota transfer (FMT) in both syngeneic and tobacco carcinogenesis models. Syngeneic G mice (transplant of G LUAD cells) that received FMT from GL donors (G < GL) exhibited significantly increased tumor growth relative to littermates with FMT from G mice (G < G). These effects were recapitulated in an independent syngeneic model (KrasG12D LKR13 cells in wild type mice). Tobacco carcinogen-exposed G < GL mice also exhibited increased lung tumor development compared with similarly exposed G < G littermates. 16S rDNA-Seq analysis of fecal pellets revealed significant differences in gut beta diversity between syngeneic G < G and G < GL mice. G < GL mice additionally displayed elevated relative abundance of tumor-promoting Alistipes, while Ruminoccocus and Akkermansia, taxa associated with favorable response to immunotherapy, were reduced. We next performed single-cell RNA-sequencing to comprehensively probe the tumor immune microenvironment (TIME) and the immune milieu near the gut of tumors and mesenteric lymph nodes (MLNs), respectively. The TIME in G < GL mice displayed an overall enhanced immunosuppressive phenotype evidenced by prominently increased fractions of T regulatory and Cd4+ Izumo1r+ exhausted T cells and, conversely, reduced levels of activated Isg15+ Cd8a+ T cells. MLNs from G < GL mice showed markedly increased fractions of memory B cells expressing the immunosuppressor Bank1 and reduced levels of follicular B cells and Cd8a+ Clec9a+ class 1 dendritic cells (cDC1). Flow cytometry further showed enhanced immunosuppression in G < GL relative to G < G mice, including increased fractions of myeloid-derived suppressor cells in the TIME of the former group. Our findings show that gut microbiome dysbiosis fosters lung cancer development by promoting immunosuppression, perhaps via a local and systemic gut microbiota-immune system crosstalk. Modulating the gut microbiome may be a promising strategy for interception or early treatment of lung cancer.

Citation Format: Zahraa Rahal, Fuduan Peng, Yuejiang Liu, Matthew C. Ross, Ansam Sinjab, Ke Liang, Jiping Feng, Chidera O. Chukwuocha, Manvi Sharma, Elizabeth Tang, Camille Abaya, Joseph Petrosino, Junya Fujimoto, Seyed Javad Moghaddam, Linghua Wang, Kristi L. Hoffman, Humam Kadara. Gut microbiome dysbiosis promotes immune suppression and lung cancer development [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 2883.