{
  "abstract": "Background Metastasis is the primary cause of melanoma death. The mechanistic basis for why metastatic disease occurs mainly in elderly patients (>65 years of age) is a critical gap in knowledge, in part, because most studies employ young mouse models (8-weeks old, equivalent to 20 human years) to investigate mechanisms of metastasis. Moreover, most studies have focused exclusively on lung metastasis, despite melanoma commonly metastasizing to sites such as the liver, which is significantly more resistant to checkpoint inhibitors (ICIs).Methods Using syngeneic melanoma cells, we optimized intravenous (IV) injections to model lung colonization and developed a novel liver colonization model using hydrodynamic tail vein injections. Tumor cells were injected into young (8 weeks) and aged (12–16 months) male C57BL/6 mice. Spleen, lungs, and liver were harvested to assess immune infiltration of lymphocyte and myeloid populations via flow cytometry. Hematoxylin and eosin (H&E) and immunohistochemistry (IHC) staining were used to quantify metastases and examine spatial immune cell locations. Upon observation that regulatory T cells (Tregs) increased consistently in aged mice, we treated additional aged cohorts with either anti-mouse CD25 antibody, which we show decreased Tregs while not changing CD3, 4 or 8 cell infiltration, vs an IgG control (200 μg/mouse, intraperitoneally) to evaluate the role of Tregs and in metastasis.Results Aging significantly increased melanoma colonization in both the lungs and liver compared to young mice. Analysis of common changes in the immune microenvironment of both the lung and the liver revealed elevated Treg infiltration in both metastatic sites of aged mice. Notably, Tregs were not elevated in the pre-metastatic niche, suggesting an age- and tumor-specific mechanism of immune suppression. Depletion of Tregs in aged mice using anti-CD25 antibody significantly reduced liver metastases compared to IgG controls.Conclusions Age-associated increases in Treg infiltration play a key role in promoting metastatic outgrowth in the lung and liver. Targeting Tregs may represent a promising strategy to mitigate age-related metastatic progression in melanoma.Ethics Approval This study followed the tenets of the Declaration of Helsinki and was approved by our institutional research ethics committee (Fox Chase Cancer Center, Philadelphia, USA; protocols #23-05; OLAW #D16-00184).",
  "authors": [
    {
      "affiliations": [
        "Fox Chase Cancer Center, Philadelphia, PA, USA"
      ],
      "name": "Anastasiia Burtseva"
    },
    {
      "affiliations": [
        "Fox Chase Cancer Center, Philadelphia, PA, USA"
      ],
      "name": "Kelly Coutant"
    },
    {
      "affiliations": [
        "Fox Chase Cancer Center, Philadelphia, PA, USA"
      ],
      "name": "Christopher Price"
    },
    {
      "affiliations": [
        "Temple University, Philadelphia, PA, USA"
      ],
      "name": "Jhon Pasamonte"
    },
    {
      "affiliations": [
        "Fox Chase Cancer Center, Philadelphia, PA, USA"
      ],
      "name": "Mitchell Fane"
    }
  ],
  "title": "816 Aged induced increases in tissue infiltrating tregs promote melanoma liver and lung metastasis",
  "uid": "f58dc27c-7796-5b54-a84a-9749247ce187"
}