Abstract 1519: Effect of obesity on CD4+ T cells in the tumor immune microenvironment of colorectal cancer

Abstract Background: The number of new cases and deaths from colorectal cancer (CRC) is increasing rapidly, and obesity is considered one of the risk factors. Obesity-associated cancers are related to the overproduction of hormones, induction of reactive oxygen species (ROS) production by free fatty acids, and changes in the gut microbiome. Obesity also promotes immune cell dysfunction in the tumor immune microenvironment (TIME). The increase of fatty acid levels due to obesity causes metabolic reprogramming and decreases the cytotoxic activity of natural killer (NK) cells and CD8+ T cells, which accelerate tumor progression. However, the impact of obesity on CD4+ T cells in the TIME remains unclear. Therefore, this study aimed to clarify how obesity affected the number and the anti-tumor activity of CD4+ T cells in CRC using mouse models. Methods: Seven-week-old male C57BL/6J mice were randomly divided into two groups and fed the control diet (CD) or high-fat diet (HFD) for nine weeks. Blood samples were collected from the buccal vein of the mice every four weeks after feeding for analysis. MC38 CRC cells of 4 × 106 were subcutaneously inoculated in the middle of the backs of mice to analyze tumor progression. Three weeks after tumor cell inoculation, the mice were sacrificed, and the immune cells of the tumor, blood, and various organs were analyzed. Results: After nine weeks of feeding, the HFD-fed mice had a significantly increased body weight compared to CD-fed mice. Flow cytometry results revealed that the number and frequency of CD4+ T cells in the blood were significantly reduced in HFD-fed mice compared to those in CD-fed mice, and the expression of programmed death-1 (PD-1) in CD4+ T cells in HFD-fed mice was significantly higher than that in CD-fed mice at eight weeks. Three weeks after tumor inoculation, HFD feeding accelerated tumor growth and decreased the survival rate. The number of CD4+ T cells in the tumors was significantly reduced in HFD-fed mice compared to that in CD-fed mice (55. 9 vs 18. 2 cells/mg; 95% CI 14. 9-60. 3 cells/mg; P = 0. 006). The number of CD8+ T cells in the tumors was also reduced, which was more pronounced for CD4+ T cells than for CD8+ T cells. In addition, the production of cytokines such as IFN-γ and TNF-α was significantly reduced in CD4+ T cells and CD8+ T cells of HFD-fed mice. In a depletion analysis of CD4+ T cells, the feeding-dependent acceleration of tumor growth was not observed in each group. This result indicated that CD4+ T cells were involved in accelerating tumor growth due to HFD-induced obesity. Conclusion: We showed that the reduced number and dysfunction of CD4+ T cells due to obesity led to a decreased anti-tumor response of both CD4+ and CD8+ T cells, ultimately accelerating the progression of colorectal cancer. Our findings may elucidate the pathogenesis for poor outcomes of colorectal cancer associated with obesity. Citation Format: Masayuki Ando, Kota Yamada, Masafumi Saito, Kimihiro Yamashita, Takao Tsuneki, Yuri Adachi, Tomoki Abe, Tomosuke Mukoyama, Ryuichiro Sawada, Yasufumi Koterazawa, Hitoshi Harada, Naoki Urakawa, Hironobu Goto, Hiroshi Hasegawa, Shingo Kanaji, Takeru Matsuda, Yoshihiro Kakeji. Effect of obesity on CD4+ T cells in the tumor immune microenvironment of colorectal cancer abstract. In: Proceedings of the American Association for Cancer Research Annual Meeting 2024; Part 1 (Regular Abstracts) ; 2024 Apr 5-10; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2024;84 (6Suppl): Abstract nr 1519.