{
  "abstract": "Background Colorectal cancer (CRC) is the second leading cause of cancer-related death worldwide. KRAS mutations are among the most prevalent genetic alterations in CRC, frequently occurring at defined hotspot codons. These mutations are well known for driving tumor progression and reshaping the immune landscape. However, the mechanisms by which distinct KRAS mutations alter the immune microenvironment remain poorly understood.Methods Tumor and matched normal tissues were collected from patients with colorectal cancer (CRC) and classified based on KRAS mutation status. Tumor-infiltrating lymphocytes (TILs) were analyzed by multicolor flow cytometry to evaluate phenotypes of CD8 + T cells and regulatory T (Treg) cells. Bulk RNA sequencing was performed on tumor samples to identify KRAS-mutation associated gene expression signatures within tumor microenvironment. Public transcriptomic datasets were analyzed for validation. IL-33 protein expression was assessed by immunohistochemistry. Functional assays, including IL33-induced Treg differentiation and Treg-mediated suppression assays, were performed using ex vivo cultured TILs to elucidate the mechanisms of Treg induction and their immunosuppressive activity.Results We compared the phenotypic characteristics of CD8 + and CD4+ T cells in tumor and matched normal tissues. Tumors exhibited higher frequencies of tumor-specific PD-1+CD39+ CD8+ T cells and immunosuppressive FOXP3+CD25+CD127– regulatory T (Treg) cells compared to normal tissues. In a cohort of 121 patients who underwent curative resection for colorectal cancer, a high Treg-to-tumor-specific CD8+ T cell ratio was significantly associated with worse disease-free survival. Multivariate analysis further identified this ratio as an independent prognostic factor, underscoring the clinical relevance of immunosuppressive FOXP3+CD25+CD127– Treg cells in colorectal cancer.KRAS-mutated colorectal cancer (CRC) tumors exhibited significantly higher frequencies of both PD-1+CD39+CD8+ T cells and Treg cells compared to KRAS wild-type tumors. Notably, among the hotspot mutations, KRAS G12D was associated with a markedly increased frequency of Treg cells within CD4+ TILs, along with elevated expression of immunosuppressive molecules such as CD39 and TIGIT.To elucidate the mechanism underlying Treg enrichment in KRAS G12D-mutant tumors, we analyzed tumor transcriptomic profiles and identified selective overexpression of IL33, a cytokine known to promote Treg expansion. IL33 expression correlated strongly with intratumoral Treg density at both the RNA and protein levels. Ex vivo analyses further demonstrated that IL-33 stimulation enhanced the proliferation and suppressive activity of tumor-infiltrating Tregs, leading to dampened CD8+ T cell responses.Conclusions These findings demonstrate that KRAS G12D-mutant CRC orchestrates an immunosuppressive microenvironment through IL-33-driven Treg activation, suggesting a mechanistic basis for poor immunotherapy efficacy and highlighting IL-33 as a potential therapeutic targetEthics Approval This study was approved by the Institutional Review Boards of Severance Hospital (IRB Number: 4-2014-0054).",
  "authors": [
    {
      "affiliations": [
        "CHA University School of Medicim, Republic of Korea"
      ],
      "name": "Jae Hyung Jung"
    },
    {
      "affiliations": [
        "Korea Advanced Institute of Science and Tne, Seongnam, Republic of Korea"
      ],
      "name": "Chang Gon Kim"
    },
    {
      "affiliations": [
        "Korea Advanced Institute of Science and Tne, Seongnam, Republic of Korea"
      ],
      "name": "Byung Soh Min"
    },
    {
      "affiliations": [
        "Yonsei University College of Medicine, Seoul, Republic of Korea"
      ],
      "name": "YongJoon Lee"
    },
    {
      "affiliations": [
        "CHA Bundang Medical Center, Seongnaechnology, Daejeon, Republic of Korea"
      ],
      "name": "Eui-cheol Shin"
    }
  ],
  "title": "737 IL-33 drives KRAS G12D-specific expansion of regulatory T cells in colorectal cancer",
  "uid": "c2ce4b78-4002-52ce-852a-81ca008c1f8d"
}