{
  "abstract": "Background Whilst cancer immunotherapy with immune checkpoint inhibitors (ICIs) has revolutionized the treatment of patients with certain malignancies, clinical trials in prostate cancer have shown ICIs to have very limited efficacy. To understand the role that the tumour microenvironment (TME) and in particular innate immunity plays in determining the responsiveness of prostate tumours to ICI we used the immune-stimulating properties of oncolytic virotherapy to transform the TME of prostate cancer, exploring the innate effectors essential for effective anti-tumour immunity and the benefit of combination therapy with IL-15 to enhance ICI responsiveness and anti-tumour activity.Methods FVB/NJ mice carrying subcutaneous Myc-CaP tumours were divided into eight groups (n=20/group) and treated with single agent (reovirus (i.t.), Il-15 (i.p.) or anti-PD1 (i.p.)), dual agents or triple combination therapy. Control mice received injections of PBS. Tumour growth rate and overall survival was measured for each treatment group to compare treatment efficacies. 10 mice from each treatment group were sacrificed following the last reovirus treatment and their tumours harvested, and formalin fixed paraffin embedded for subsequent multispectral imaging (Akoya Biosciences) of immune infiltrates and Nanostring GeoMx digital spatial profiling (DSP).Results No tumour control was observed using single agents alone. Reovirus monotherapy or dual therapy with IL-15 or anti-PD-1 partially controlled tumour growth, however optimal tumour control was seen from combined treatment with reovirus therapy, recombinant IL-15 and anti-PD-1 antibody therapy. Complete tumour regressions were predominantly observed in animals treated with the triple combination therapy (n=7/10 mice) all of which did not develop tumours upon subsequent tumour re-challenge. Multispectral imaging revealed a significant immune infiltration in the combination treated tumours, in particular of macrophages. GeoMx DSP profiling and differential gene expression analysis of macrophage-enriched areas showed a significant upregulation of genes indicative of M1 macrophage polarization including chemokine genes (e.g. CCL5) involved in recruiting and modulating macrophage function as well as chemokines (CXCL9, CXCL10) produced by macrophages and known to play a crucial role in immune responses in tumours. Another notable finding was the significant upregulation of the gene, GBP5, a known marker of the M1-phenotype and good predictor of treatment response to ICIs being positively correlated with immune score.Conclusions The TME analyses revealed that our combination immunotherapy remodelled the immunosuppressive microenvironment in prostate tumours, characterized by increased infiltration and polarization of M1 macrophages, key players in their recruitment of other immune effectors supported by IL-15 and resulting in the success of immunotherapy.Acknowledgements This work was supported by Prostate Cancer UK through a [Major Awards: Immunology and Immunotherapy] ([MA-IMM19-001] and from The Prostate Project (https://prostate-project.org.uk/)Ethics Approval All animal procedures in this study were conducted in accordance with ethical standards and were approved by the University of Surrey’s Animal Welfare and Ethical Review Body, as well as the UK Home Office under project licence number PP7099312.",
  "authors": [
    {
      "affiliations": [
        "University of Surrey, Guildford, Surrey, UK"
      ],
      "name": "Guy Simpson"
    },
    {
      "affiliations": [
        "University of Surrey, Guildford, Surrey, UK"
      ],
      "name": "Einthavy Arunachalam"
    },
    {
      "affiliations": [
        "University of Surrey, Guildford, Surrey, UK"
      ],
      "name": "James R Thetford"
    },
    {
      "affiliations": [
        "University of Surrey, Guildford, Surrey, UK"
      ],
      "name": "Sunny Sunshine"
    },
    {
      "affiliations": [
        "University of Surrey, Guildford, Surrey, UK"
      ],
      "name": "Irena Norman"
    },
    {
      "affiliations": [
        "University of Surrey, Guildford, Surrey, UK"
      ],
      "name": "Diyendra Withana"
    },
    {
      "affiliations": [
        "University of Surrey, Guildford, Surrey, UK"
      ],
      "name": "Hardev S Pandha"
    },
    {
      "affiliations": [
        "University of Surrey, Guildford, Surrey, UK"
      ],
      "name": "Nicola E Annels"
    }
  ],
  "title": "654 Oncolytic viral therapy macrophage reprogramming is critical for establishing the immune infiltrate which supported by IL-15 reverses immune checkpoint inhibitor unresponsiveness of prostate cancer",
  "uid": "a17f750f-522b-55e0-b3e8-4ada636ea249"
}