{
  "abstract": "Background Stromal-rich CMS4 colorectal cancer (CRC), is associated with high stromal burden, poor immune cell infiltration, poor response to anti-cancer therapies leading to poor prognosis. 1 Immune checkpoint inhibitors (ICIs) have limited impact on this tumor, highlighting the need for new therapy. Emerging studies have highlighted that stromal cells in stromal-rich tumors, including CRC, are highly sialylated and immunosuppressive.2 3 This study investigates the effect of targeting stromal cells sialylation in modulating macrophage phenotype and function in CRC.Methods Sialic acid and Siglec-7/9/10 ligand expression on tumor-conditioned MSCs and CAFs were evaluated using lectins (SNA-I, MAL-II) and Siglec-7/9/10 fc chimera, and Siglec-7/9/10 were measured on immune cells, all by flow cytometry. Ex vivo human monocyte derived and murine bone marrow-derived macrophage were co-culture with stromal cells, macrophage polarisation and phagocytosis were measured by flow cytometry and Incucyte. In vivo syngeneic immunogenic subcutaneous CT26 mouse tumor model with co-injection of MSCs were performed and the changes in macrophage macrophage phenotype within the tumor, draining lymph nodes (DLNs), and spleen were evaluated using flow cytometry.Results We observed that MSC TCS and CAF in CRC tumors are highly sialylated and significantly overexpressed Siglec-10 ligand compared to cancer cells. In co-culture experiments, MSCTCS and CAFs induced Siglec-10 expression on macrophages and suppressed phagocytic function. This immunosuppressive effect was reversed bwith sialic acid removal by E610 Sialidase. In the in vivo study, co-injection of MSCTCS with CT26 tumor cells promoted tumor growth and pre-treatment of MSCTCS with Sialidase significantly attenuated this tumor progression. Immune cells analysis demonstrated that MSCs drove immunosuppressive macrophage phenotype, characterized by high expression of CD206, PD-L1, and Siglec-G. Partial reversal of this phenotype was observed with stromal desialylation, most notably evidenced by a significant increase in the frequency of activated CD80+ macrophages within the tumor. While immunosuppressive markers on tumor-associated macrophages (TAMs) were not reduced, their expression, particularly Siglec-G, was significantly decreased on macrophages in both the spleen and draining lymph nodes, suggesting a broader, systemic modulation of the anti-tumor immune response.Conclusions Our findings demonstrate that targeting sialylation on cancer-associated stromal cells reverses their immunosuppressive effects on macrophages and enhances anti-tumour immunity. This is achieved by promoting activated macrophages in the TME and reducing systemic immunosuppression, resulting in attenuated tumour growth. These findings identify the stromal sialic acid-Siglec axis as a key immunosuppressive pathway in CRC and suggest stromal desialylation as a promising therapeutic strategy to overcome immune exclusion and enhance immunotherapy efficacy.References Mouillet-Richard S, Cazelles A, Sroussi M, Gallois C, Taieb J, Laurent-Puig P. Clinical challenges of consensus molecular subtype CMS4 colon cancer in the era of precision medicine. Clin Cancer Res. 2024;30(11):2351–8. 2.Egan H, Treacy O, Lynch K, Leonard NA, O’Malley G, Reidy E, et al. Targeting stromal cell sialylation reverses T cell-mediated immunosuppression in the tumor microenvironment. Cell Rep. 2023:112475. 3.Boelaars K, Rodriguez E, Huinen ZR, Liu C, Wang D, Springer BO, et al. Pancreatic cancer-associated fibroblasts modulate macrophage differentiation via sialic acid Siglec interactions. Commun Biol. 2024;7(1):430.",
  "authors": [
    {
      "affiliations": [
        "University of Galway, Galway, Ireland"
      ],
      "name": "Norashikin Zakaria"
    },
    {
      "affiliations": [
        "Discipline of Pharmacology and Therapeutics, School of Medicine, College of Medicine, Nursing and Health Sciences, University of Galway, Galway, Ireland"
      ],
      "name": "Aoise O’neill"
    },
    {
      "affiliations": [
        "University of Galway, Galway, Ireland"
      ],
      "name": "Lei Lei"
    },
    {
      "affiliations": [
        "University of Galway, Galway, Ireland"
      ],
      "name": "Anastasija Walsh"
    },
    {
      "affiliations": [
        "Palleon Pharmaceuticals, Waltham, MA, USA"
      ],
      "name": "Jenny Chee"
    },
    {
      "affiliations": [
        "Palleon Pharmaceuticals, Waltham, MA, USA"
      ],
      "name": "Li Peng"
    },
    {
      "affiliations": [
        "Palleon Pharmaceuticals, Waltham, MA, USA"
      ],
      "name": "Lizhi Cao"
    },
    {
      "affiliations": [
        "Division of Anatomical Pathology, Galway University Hospital, Galway, Ireland, Galway, Co. Galway, Ireland"
      ],
      "name": "Sean O Hynes"
    },
    {
      "affiliations": [
        "Department of Colorectal Surgery, Galway University Hospital, Galway, Ireland, Galway, Co. Galway, Ireland"
      ],
      "name": "Aisling M Hogan"
    },
    {
      "affiliations": [
        "Discipline of Pharmacology and Therapeutics, School of Medicine, College of Medicine, Nursing and Health Sciences, University of Galway, Galway, Ireland"
      ],
      "name": "Oliver Treacy"
    },
    {
      "affiliations": [
        "University of Galway, Galway, Ireland",
        "CÚRAM, SFI Research Centre for Medical Devices, Galway, Ireland",
        "Regenerative Medicine Institute (REMEDI), School of Medicine, College of Medicine, Nursing and Health Sciences, Galway, Ireland"
      ],
      "name": "Aideen E Ryan"
    }
  ],
  "title": "1276 Targeting sialic acid on cancer-associated stromal cells modulates macrophage phenotype and phagocytosis in colorectal cancer",
  "uid": "b6d97032-c14c-55dd-851f-83f55559fde7"
}