Abstracts: Fifth AACR-IASLC International Joint Conference: Lung Cancer Translational Science from the Bench to the Clinic; January 8-11, 2018; San Diego, CAWe recently conducted the first comprehensive characterization of the lung cancer microbiome, utilizing 16S rRNA gene sequencing of lung tissue from controls and cancer cases, with validation by metagenomics analysis of RNA-seq unmapped reads from lung cancer samples in The Cancer Genome Atlas. Evidence from 16S rRNA and metagenomics analysis indicated that specific bacteria are associated with the development of lung cancer in humans. However, the functional role of bacteria in the inflammatory microenvironment of the lung and the incidence and progression of lung cancer is unknown. Cigarette smoke, the primary risk factor in lung cancer, reduces epithelial barrier integrity and increases susceptibility to infections. We hypothesized that lung colonization with selected bacterial strains will affect the immune microenvironment and accelerate the rate of tumor development in an autochthonous mouse model of lung cancer. Specifically, we focused on Acidovorax, a taxon we found to be enriched in lung squamous cell carcinoma (SCC) from smokers and with TP53 mutations. KrasLSL-G12D/+ and Trp53LSL-R172H/+ mice (KPC mouse model), conditionally expressing oncogenic Kras and a gain-of-function mutant p53 (a combination of mutations commonly found in human lung cancer), were exposed to Acidovorax temperans via intranasal delivery. Two weeks after exposure to 5 x 106 PFU Ad-Cre (specifically activating the conditional alleles in the lungs), mice were randomly assigned to treatment groups. A biweekly intranasal instillation of 109 CFU Acidovorax temperans (ATCC #49666) was administered in PBS and compared with a sham treatment (PBS alone) for a total of six instillations. One week after the last bacteria instillation (13 weeks after Ad-Cre treatment), mice were subjected to magnetic resonance imaging (MRI). We found a significant increase in tumor volume in animals inoculated with Acidovorax temperans as compared to sham-treated animals (p=0.03), and increased lung weight as a percent of total body weight.To delineate the interactions between the bacteria and the immune system of the host, we co-cultured Acidovorax temperans with human primary macrophages. Our findings show that when Acidovorax temperans is engulfed by M2-like macrophages, the phagocytotic activity of the macrophages is attenuated. In addition, when T cells were co-cultured with M2 macrophages pre-exposed to Acidovorax temperans, their cytotoxicity was inhibited. This inhibition was governed by the CD47-SIRPα “Don’t eat me” signal. These preliminary data indicate that Acidovorax temperans contributes to lung tumorigenesis in the presence of activated Kras and mutant p53. We are conducting additional experiments to investigate the specificity of this observation with respect to Acidovorax temperans and to better understand the role of the microbiota in cancer initiation and progression.This abstract is also being presented as Poster B19.Citation Format: Ana I. Robles, Tomer Cooks, Eleazar Vega-Valle, Marie Vetizou, Uriel Rose, Akihiko Miyanaga, Akriti Trehan, Takahiro Oike, Brid M. Ryan, Shurjo Sen, Leigh Greathouse, Giorgio Trinchieri, Curtis C. Harris. Role of the microbiota in inflammation and lung cancer [abstract]. In: Proceedings of the Fifth AACR-IASLC International Joint Conference: Lung Cancer Translational Science from the Bench to the Clinic; Jan 8-11, 2018; San Diego, CA. Philadelphia (PA): AACR; Clin Cancer Res 2018;24(17_Suppl):Abstract nr PR07.