{
  "abstract": "Background Cancer vaccines have been tested in multiple cancer types without significant clinical success. 1 2 However, cancer vaccine interest has resurfaced due to an improved understanding of the tumor microenvironment (TME).3–6 The TME is comprised of immune suppressive myeloid-derived suppressor cells (MDSCs) and a paucity of antigen (Ag)-specific CD8+ T cells.7–10 Both features hinder immunotherapeutic efficacy, including immune checkpoint inhibitors (ICIs), such as anti-PD-1.11 To overcome the obstacle of MDSCs, our laboratory developed a novel approach to mitigate MDSC suppressive function, through dihydroorotate dehydrogenase (DHODH) inhibition, sensitizing solid tumors to immune checkpoint blockade.12 Furthermore, to increase low frequencies of Ag-specific CD8+ T cells, we turned to the concept of cancer vaccines.13 We developed a multi-modal platform to boost ICI response by mitigating MDSCs and incorporating a novel peptide-based vaccine to prime and expand endogenous Ag-specific CD8+ T cells.Methods To develop an optimal triple therapy platform, we tested several treatment regimens encompassing a DHODH inhibitor, anti-PD-1, and a novel peptide vaccine. Mice were implanted with ICI-refractory 4T1 triple negative breast cancer (TNBC) cells in which tumor growth was monitored over time. At endpoint, immune cell phenotyping through flow cytometry was conducted to analyze intra-tumoral T cell subsets. To further demonstrate the potency of the tri-therapy, we developed an ‘add-back’ approach. Specifically, splenic T cells from treated 4T1 tumor-bearing groups were adoptively transferred to untreated 4T1-bearing mice. Additionally, RNA-sequencing, reverse transcription-quantitative polymerase chain reaction (RT-qPCR), and other tumor models were used to assess the antitumor response of the optimized tri-therapy regimen.Results In multiple preclinical models, our optimal tri-therapy regimen elicited a significant antitumor response. Immunophenotyping revealed that strong antitumor responses correlated with a significant increase in intra-tumoral Ag-specific CD8 + T cells, based on tetramer staining (figure 1). Intra-tumoral tri-therapy T cells also expressed an increase in markers associated with a central memory T cell phenotype and a reduction in T cell exhaustion markers. In some cases, we observed nearly complete tumor regression. Additionally, in the ‘add-back’ experiment, T cells generated in response to the tri-therapy reduced tumor growth significantly more than T cells derived from vehicle or the double combination cohorts. RNA-sequencing and RT-qPCR revealed increased gene expression associated with antitumor function.Conclusions Altogether, our results suggest that a novel multimodal strategy that concurrently reduces MDSCs, overcomes T cell exhaustion, and expands tumor-reactive CD8 + T cells have important implications to improve outcomes against ICI-refractory solid tumors.References Saxena M, van der Burg SH, Melief CJM, Bhardwaj N. Therapeutic cancer vaccines. Nat Rev Cancer 2021;21:360-378.Tay BQ, et al. Evolution of cancer vaccines-challenges, achievements, and future directions. Vaccines. 2021;9:535.Liu J, et al. Cancer vaccines as promising immuno-therapeutics: platforms and current progress. J Hematol Oncol. 2022;15:28.Blass E, Ott PA. Advances in the development of personalized neoantigen-based therapeutic cancer vaccines. Nat Rev Clin Oncol. 2021;18:215-229.Barbier AJ, Jiang AY, Zhang P, Wooster R, Anderson DG. The clinical progress of mRNA vaccines and immunotherapies. Nat Biotechnol. 2022;40:840-854.Hollingsworth RE, Jansen K. Turning the corner on therapeutic cancer vaccines. npj Vaccines. 2019;4:7.Kumar V, Patel S, Tcyganov E, Gabrilovich DI. The nature of myeloid-derived suppressor cells in the tumor microenvironment. Trends Immunol. 2016;37:208-220.Gabrilovich DI, Nagaraj S. Myeloid-derived suppressor cells as regulators of the immune system. Nat Rev Immunol. 2009;9:162-174.Gabrilovich DI. Myeloid-derived suppressor cells. Cancer Immunol Res. 2017;5:3-8.Gabrilovich DI, Ostrand-Rosenberg S, Bronte V. Coordinated regulation of myeloid cells by tumours. Nat Rev Immunol. 2012;12:253-268.Waldman AD, Fritz JM, Lenardo MJ. A guide to cancer immunotherapy: from T cell basic science to clinical practice. Nat Rev Immunol. 2020;20:651-668.Colligan SH, et al. Inhibiting the biogenesis of myeloid-derived suppressor cells enhances immunotherapy efficacy against mammary tumor progression. JCI. 2022;132:23.Lin MJ, et al. Cancer vaccines: the next immunotherapy frontier. Nat Cancer. 2022;3:911-926.Ethics Approval The animal care facilities and programs of Roswell Park meet the requirements of the law and NIH regulations. Roswell Park is accredited by the American Association of Laboratory Animal Care (AALAC). Animal welfare assurance number A-3143-01. All experiments conducted with murine models have been previously approved (#1108M, effective 11/23/22; and #1117M, effective 03/15/23) by the Roswell Park Institutional Animal Care and Use Committee (IACUC).Abstract 693 Figure 1(A) 4T1 tumor growth in mice treated with vehicle, BRQ (4 mg/kg) combined with αPD-1 (200 μg/injection), and/or the triple combination of BRQ, αPD-1, and cancer vaccine (5µg AH1). (B) Percentage of tetramer positive CD8+ T cells from the tumor",
  "authors": [
    {
      "affiliations": [
        "Roswell Park Comprehensive Cancer Center, Buffalo, NY, USA"
      ],
      "name": "Brian G Morreale"
    },
    {
      "affiliations": [
        "Roswell Park Comprehensive Cancer Center, Buffalo, NY, USA"
      ],
      "name": "Andrea M Monell"
    },
    {
      "affiliations": [
        "Roswell Park Comprehensive Cancer Center, Buffalo, NY, USA"
      ],
      "name": "Han Yu"
    },
    {
      "affiliations": [
        "Massachusetts General Hospital, Boston, MA, USA"
      ],
      "name": "David B Sykes"
    },
    {
      "affiliations": [
        "University at Buffalo, Buffalo, NY, USA"
      ],
      "name": "Jonathan F Lovell"
    },
    {
      "affiliations": [
        "Roswell Park Comprehensive Cancer Center, Buffalo, NY, USA"
      ],
      "name": "Michael J Nemeth"
    },
    {
      "affiliations": [
        "Roswell Park Comprehensive Cancer Center, Buffalo, NY, USA"
      ],
      "name": "Scott I Abrams"
    }
  ],
  "title": "693 A novel tri-therapy overcoming immune suppression, immune exhaustion, and low antigen-specific T cell infiltration elicits robust antitumor responses",
  "uid": "36f4cdbc-3331-5c25-9f04-2a873bcfe71f"
}