{
  "abstract": "Background Triple-negative breast cancer (TNBC) has the highest recurrence and relapse rates among breast cancer subtypes. While chemotherapy, alone or in combination with immune checkpoint inhibitors, is the standard care, many patients remain unresponsive. mRNA-lipid nanoparticle (LNP) vaccines targeting tumor neoantigens provide a personalized approach to stimulate antitumor T cell responses, yet improved preclinical models are essential to optimize vaccine design and enhance clinical outcomes. Here, we established a humanized patient-derived xenograft (hu-PDX) model of TNBC that captures human immune-tumor interactions to evaluate the efficacy of mRNA-LNP vaccines in vivo.Methods hu-PDX mice were generated by intravenous injection of CD34+ hematopoietic stem cells (HSCs) from HLA-A2+ cord blood donors into sublethally γ-irradiated female NSG-HLA-A2/HHD mice (The Jackson Laboratory). Human immune engraftment was assessed 12 weeks post-transplantation by flow cytometry analysis of human CD45+ cells in peripheral blood (PB). Successfully engrafted mice were implanted orthotopically with a TNBC PDX (MC1) into the mammary fat pad. Once tumors were established, hu-PDX mice received intramuscular injections of an mRNA-LNP vaccine encoding 20 HLA-A2-restricted neoantigens identified in the MC1 tumor (Neo20). Mice were treated with Neo20 vaccine (10 µg mRNA/mouse) or control (vehicle/empty LNPs) twice per week for 3 weeks and euthanized 10 days after the final dose. Tumor volumes were measured twice weekly to assess therapeutic efficacy. Neo20 immunogenicity was evaluated on splenocytes collected at endpoint.Results Immunophenotyping of PB, spleen, and bone marrow (BM) from humanized NSG-HLA-A2/HHD mice at 12 weeks post-HSCs transplantation demonstrated robust human immune reconstitution, including T, B, NK, and myeloid cells. CD4+ and CD8+ T cell differentiation was confirmed, with CD8+ subsets comprising naïve, central memory, effector memory, and terminally differentiated cells in the recipient spleen. Upon concanavalin A stimulation, CD8+ T cells produced IFN-γ and granzymes A and B, indicating functional cytotoxic capacity. Myeloid profiling of the BM revealed development of human antigen-presenting cells, including dendritic cell subsets, supporting the utility of this model for studying acquired immunity following vaccination. Consistently, MC1 tumor-bearing humanized mice (hu-PDX) treated with Neo20 vaccine exhibited neoantigen-specific T cell immunity, evidenced by ex vivo IFN-γ production from splenocytes stimulated with vaccine peptides. Notably, these mice showed a significant reduction in tumor volume compared to the control group, demonstrating the antitumor efficacy of the Neo20 vaccine.Conclusions The hu-PDX model developed in this study recapitulates a functional human immune system and represents a powerful tool to preclinically validate mRNA-based vaccines candidates for TNBC.Ethics Approval This study was approved by Houston Methodist Research Institute’s Institutional Animal Care and Use Committee (IACUC); approved protocols: IS00007220, IS00008399.",
  "authors": [
    {
      "affiliations": [
        "Houston Methodist Research Institute, Houston, TX, USA"
      ],
      "name": "Maria F Chervo"
    },
    {
      "affiliations": [
        "Houston Methodist Research Institute, Houston, TX, USA"
      ],
      "name": "Chiara Mancino"
    },
    {
      "affiliations": [
        "Houston Methodist Research Institute, Houston, TX, USA"
      ],
      "name": "Raghav Shroff"
    },
    {
      "affiliations": [
        "Houston Methodist Research Institute, Houston, TX, USA"
      ],
      "name": "Wei Qian"
    },
    {
      "affiliations": [
        "Houston Methodist Research Institute, Houston, TX, USA"
      ],
      "name": "Jenying Deng"
    },
    {
      "affiliations": [
        "Houston Methodist Research Institute, Houston, TX, USA"
      ],
      "name": "Karina A Ortega Martinez"
    },
    {
      "affiliations": [
        "Houston Methodist Research Institute, Houston, TX, USA"
      ],
      "name": "Jianying Zhou"
    },
    {
      "affiliations": [
        "Houston Methodist Research Institute, Houston, TX, USA"
      ],
      "name": "Fotis Nikolos"
    },
    {
      "affiliations": [
        "Houston Methodist Research Institute, Houston, TX, USA"
      ],
      "name": "Francesca Taraballi"
    },
    {
      "affiliations": [
        "Houston Methodist Research Institute, Houston, TX, USA"
      ],
      "name": "Keith Syson Chan"
    },
    {
      "affiliations": [
        "Houston Methodist Research Institute, Houston, TX, USA"
      ],
      "name": "John P Cooke"
    },
    {
      "affiliations": [
        "Houston Methodist Research Institute, Houston, TX, USA"
      ],
      "name": "Jimmy D Gollihar"
    },
    {
      "affiliations": [
        "Houston Methodist Research Institute, Houston, TX, USA"
      ],
      "name": "Jenny C Chang"
    }
  ],
  "title": "925 Personalized mRNA vaccine induces antitumor T cell immunity in humanized patient-derived xenograft mouse models of triple-negative breast cancer",
  "uid": "92f0dc28-ab41-5ebb-8f49-797fe642c18d"
}