Background Obesity is a significant health concern and cancer risk factor linked to chronic low-grade inflammation and immune dysfunction, including T cell exhaustion and up-regulation of inhibitory immune checkpoint molecules.¹ Recent studies have highlighted the detrimental effects of obesity on anti-tumor immunity in the tumor microenvironment (TME).² Foxp3+ Regulatory T cells (Tregs), a major source of immune suppression, are known to obstruct anti-tumor immunity and contribute to poor disease outcomes in non-small cell lung cancer.³ Treg function is known to be sensitive to environmental and metabolic factors,^4–7 and obesity is associated with sweeping changes in metabolism at cellular and organismal levels.⁸ However, the specific effects of obesity on Tregs in distinct tissues such as the lung and lung tumors remain incompletely understood. Here we tested the hypothesis that obesity-associated immune dysfunction arises in part from an enhanced Treg pool in lung cancer.

Methods Mice were subjected to a 14-week high-fat diet (60% fat) or normal diet (10% fat) prior to challenge with Lewis Lung Carcinoma (LLC) and mutant Kras-driven tumor models. Treg phenotypes in lungs and spleens were evaluated via flow cytometry and functional assays. Similar assessments were conducted on bronchoalveolar lavage (BAL) samples from lung cancer patients of normal and high Body Mass Index (BMI). Integrated transcriptomic and metabolite analyses were also carried out on the lungs and tumors of obese and control mice.

Results We observed significantly increased Treg frequencies in obese mice compared to controls, particularly in lung tissues, where these Tregs showed markers of an activated, effector-like phenotype and strong suppressive function ex vivo. Similar findings were seen in BAL samples from high BMI lung cancer patients compared to normal weight individuals. Furthermore, obese mice exhibited enhanced tumor burden across models, accompanied by heightened Treg activation and suppressed anti-tumor immune responses. Importantly, Treg depletion reversed the accelerated LLC tumor growth in obese mice. Lastly, integrated transcriptomic and metabolite analysis revealed several distinct metabolic pathways accompanying obesity-mediated enhancement of Tregs previously implicated as key for immune response control and anti-cancer immunotherapy response.

Conclusions Our findings deepen our understanding of how obesity influences immune regulation through tissue-specific modulation of the Treg pool. These effects and the associated changes in immunometabolism triggered under obese conditions may present new avenues for identifying therapeutic targets to undermine immune suppression and enhance cancer treatment and prevention measures.

Acknowledgements We acknowledge the valuable work of core facilities at Roswell park as well as grant support: NIH R25 GM095459, an American Lung Association Lung Cancer Discovery Award, 1R01 CA255515-01A1, and institutional support grant P30-CA016056.

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Ethics Approval This study was approved by the Roswell Park IRB and IACUC.