{
  "abstract": "Background Immune checkpoint inhibitors (ICIs, e.g., anti-PD1 therapy) have shown significant success against melanoma and lung cancer, yet their efficacy in breast cancer has been more limited. 1–4 Tumor infiltration of co-stimulatory receptor-positive (ICOS+) regulatory T cells (Tregs) can suppress the cytotoxic function of CD8+ T cells and natural killer (NK) cells by upregulating PD-1 expression, a potential cause of the limited efficacy of immunotherapy. Therefore, blocking ICOS receptor, which is required for Treg cell activity, could be an effective strategy to reverse the cytotoxic immune cell functions in the tumor microenvironment.5 6 The current study evaluates the benefits of therapeutic targeting of the ICOS in treating primary and metastatic disease burden using preclinical mammary tumor models.Methods Orthotopic syngeneic mammary tumor models (EO771.LMB; hormone-receptor negative) were established using ICOS -/- C57BL/6 female mice to understand ICOS-driven immunosuppressive mechanisms in breast tumors. The therapeutic efficacy of blocking the ICOS receptor was evaluated using monoclonal antibodies in EO771.LMB and hormone-receptor positive 67NR models targeting ICOS receptor in combination with ICIs (anti-PD1). Flow cytometry and single-cell RNA sequencing (scRNA-seq) analysis were used to identify the affected immune cell populations and their activity. Multiplex immunohistochemistry (mIHC) and a spatial transcriptomic platform were employed on clinical specimens to understand the cellular and molecular interactions of ICOS+ Tregs in the tumor microenvironment.Results Systemic deletion of ICOS resulted in a significant reduction in mammary tumor growth, associated with decreased Treg activation and function, and increased infiltration of CD8+ T and NK cells and activity ( figure 1A). Moreover, the combination treatment (anti-ICOS + anti-PD-1) demonstrated a substantial reduction in mammary tumor burden in both EO771.LMB and 67NR models, indicating synergistic anti-tumor activity through simultaneous depletion of ICOS+ Treg cells and reinvigoration of exhausted cytotoxic cells (figure 1B). Additionally, combination immunotherapy demonstrated improved metastasis-free survival in both neoadjuvant and adjuvant treatment settings (figure 2A). Spatial-omics data provide a detailed map of ICOS+ Treg enrichment in the tumor core, forming immunosuppressive niches with ICOS-Ligand+ cancer cells and exhausted CD8+ T cells (figure 2B).Conclusions Pharmacological blockade of the ICOS receptor can suppress Treg cell-induced immunosuppression, sensitizing breast cancer cells to immunotherapy-driven anti-tumor responses. Hence, an anti-ICOS and anti-PD1 combination may provide a promising therapeutic approach for patients with early-stage or advanced breast cancer. Additionally, the integration of ICOS + Tregs into Tumor Infiltrating Lymphocytes (TILs) scoring systems would aid in stratifying breast cancer patients for future ICOS-targeted immunotherapy trials.Acknowledgements This work was supported by grants from the Victorian Cancer Agency (VCA), Australia (MCRF21002, B.P.), the Australian National Breast Cancer Foundation (NBCF, IIRS-23-016), and Tour de Cure (RSP-239-FY2023).References Onkar SS, Carleton NM, Lucas PC, Bruno TC, Lee AV, Vignali DA, Oesterreich S. The great immune escape: understanding the divergent immune response in breast cancer subtypes. Cancer Discov. 2023;13(1):23-40.Debien V, De Caluwé A, Wang X, Piccart-Gebhart M, Tuohy VK, Romano E, Buisseret L. Immunotherapy in breast cancer: an overview of current strategies and perspectives. NPJ Breast Cancer 2023;9(1):7.Denkert C, von Minckwitz G, Darb-Esfahani S, Lederer B, Heppner BI, Weber KE, Budczies J, Huober J, Klauschen F, Furlanetto J, Schmitt WD. Tumour-infiltrating lymphocytes and prognosis in different subtypes of breast cancer: a pooled analysis of 3771 patients treated with neoadjuvant therapy. Lancet Oncol. 2018;19(1):40-50.Nelson MA, Ngamcherdtrakul W, Luoh SW, Yantasee W. Prognostic and therapeutic role of tumor-infiltrating lymphocyte subtypes in breast cancer. Cancer and Metastasis Rev. 2021;40(2):519-536.Wang P, Zhang Q, Zhang H, Shao J, Zhang H, Wang Z. Molecular and clinical characterization of ICOS expression in breast cancer through large-scale transcriptome data. Plos One. 2023;18(12):e0293469.Diamantopoulos N, Li J, Bouchard A, Joumier L, Mohammaei S, Panneton V, Chang J, Malleshaiah M, Suh WK. ICOS-expressing regulatory T cells influence the composition of antitumor CTL populations. J Immunol. 2024;213(5):753-762.Ethics Approval Animal Studies - Animal-related studies were approved by the Austin Health Animal Ethics Committee - Application number A2021_05727. Human Sample Collection - Human Sample collection protocols were approved by the Austin Ethics Committee and ONJCRI Ethics Committee.Abstract 692 Figure 1Orthotopic mammary tumor models to study the effect of systemic ICOS deletion and blockade by monoclonal antibodiesAbstract 692 Figure 2Effect of anti-ICOS treatment on breast cancer metastasis and spatial omic distribution of ICOS+ Tregs in clinical specimens",
  "authors": [
    {
      "affiliations": [
        "Olivia Newton-John Cancer Research Institute, Heidelberg, VIC, Australia",
        "School of Cancer Medicine, La Trobe University, Bundoora, VIC, Australia"
      ],
      "name": "Chamikara Liyanage"
    },
    {
      "affiliations": [
        "Olivia Newton-John Cancer Research Institute, Heidelberg, VIC, Australia",
        "School of Cancer Medicine, La Trobe University, Bundoora, VIC, Australia"
      ],
      "name": "Shalini Guleria"
    },
    {
      "affiliations": [
        "The Walter and Eliza Hall Institute of Medical Research, Parkville, VIC, Australia"
      ],
      "name": "William Hutchison"
    },
    {
      "affiliations": [
        "Olivia Newton-John Cancer Research Institute, Heidelberg, VIC, Australia",
        "School of Cancer Medicine, La Trobe University, Bundoora, VIC, Australia"
      ],
      "name": "Liam Neil"
    },
    {
      "affiliations": [
        "Olivia Newton-John Cancer Research Institute, Heidelberg, VIC, Australia",
        "School of Cancer Medicine, La Trobe University, Bundoora, VIC, Australia"
      ],
      "name": "Caroline Bell"
    },
    {
      "affiliations": [
        "The Walter and Eliza Hall Institute of Medical Research, Parkville, VIC, Australia",
        "The University of Melbourne, Parkville, VIC, Australia"
      ],
      "name": "Raymond Yip"
    },
    {
      "affiliations": [
        "Olivia Newton-John Cancer Research Institute, Heidelberg, VIC, Australia",
        "School of Cancer Medicine, La Trobe University, Bundoora, VIC, Australia"
      ],
      "name": "John Mariadason"
    },
    {
      "affiliations": [
        "The University of Melbourne, Parkville, VIC, Australia",
        "The Peter Doherty Institute for Infection and Immunity, Melbourne, VIC, Australia"
      ],
      "name": "Axel Kallies"
    },
    {
      "affiliations": [
        "School of Cancer Medicine, La Trobe University, Bundoora, VIC, Australia"
      ],
      "name": "Ajith Vasanthakumar"
    },
    {
      "affiliations": [
        "Austin Health, Heidelberg, VIC, Australia"
      ],
      "name": "Belinda Yeo"
    },
    {
      "affiliations": [
        "Olivia Newton-John Cancer Research Institute, Heidelberg, VIC, Australia",
        "School of Cancer Medicine, La Trobe University, Bundoora, VIC, Australia"
      ],
      "name": "Robin Anderson"
    },
    {
      "affiliations": [
        "The Walter and Eliza Hall Institute of Medical Research, Parkville, VIC, Australia",
        "South Australian immunoGENomics Cancer Institute, Adelaide, SA, Australia"
      ],
      "name": "Stefano Mangiola"
    },
    {
      "affiliations": [
        "Olivia Newton-John Cancer Research Institute, Heidelberg, VIC, Australia",
        "School of Cancer Medicine, La Trobe University, Bundoora, VIC, Australia"
      ],
      "name": "Bhupinder Pal"
    }
  ],
  "title": "692 Targeting ICOS receptor to improve breast cancer immunotherapy",
  "uid": "14c272c5-aba1-5bc8-99b2-3879fb0516ae"
}