Impact of particulate matter 2.5 on a mouse model of lung adenocarcinoma

Over the years, lung cancer incidence in never-smokers has been rising. Air pollution is a non-smoking-related factor that promotes lung cancer progression. Particulate matter 2.5 (PM2.5) is a component of air pollution that is associated with a type 2 immune response mediated by group 2 innate lymphoid cells (ILC2) and T helper 2 (Th2) cells. Furthermore, PM2.5 can activate fibroblasts, induce the secretion of collagen, and contribute to the development of lung fibrosis. Although type 2 immune response and lung fibrosis are described as pro-tumorigenic in lung cancer, whether PM2.5-driven type 2 immune response and/or lung fibrosis promote lung cancer tumorigenesis in mouse models of lung cancer remains unclear. This study investigated the impact of PM2.5 on the type 2 immune response, lung fibrosis, and lung cancer tumorigenesis in vivo. We treated EGFR and KRAS/Trp53 mouse models of LUAD intranasally with PM2.5, analyzed lung tumor burden and lung fibrosis by histology, and changes in type 2 immune cell (ILC2, Th2) and CAF markers by flow cytometry. Different durations of PM2.5 treatment (3-week short-term vs. 6-week long-term), experimental time points (10 weeks vs. 15 weeks), and intervals between the onset of EGFR and KRAS/Trp53 mutations and first exposure to PM2.5 (3 days vs. 4 weeks delayed) were assessed. Unpaired t-test and One-way ANOVA statistical tests were utilized. We found that PM2.5 did not significantly impact lung tumor burden in EGFR and KRAS/Trp53 mouse models of LUAD. Notably, PM2.5 did not significantly affect the type 2 immune response mediated by ILC2 and Th2 cells. However, long-term exposure to PM2.5 or delayed treatment with PM2.5 significantly increased the abundance of CD90.2+ CAFs in lung cancer without impacting lung cancer burden. In summary, while PM2.5 did not significantly impact EGFR and KRAS/Trp53 lung tumor burden or the type 2 immune response, long-term or delayed exposure to PM2.5 promoted CD90.2+ CAFs in vivo. This study demonstrates that preclinical modeling of PM2.5-driven LUAD requires further validation and consideration of confounding variables to reflect air pollution-associated LUAD observed in humans.