{
  "abstract": "Background The local effect of radiotherapy (RT) is enhanced by CD8 + T-cell responses elicited through dendritic cell (DC)-mediated cross-presentation of tumor antigens, facilitated by RT-induced damage-associated molecular patterns. The abscopal effect—regression of non-irradiated tumors—has been observed clinically, particularly in combination with immune checkpoint blockade, although it remains uncommon. To better understand how to enhance this effect, we investigated two RT/α-programmed death 1 (PD-1)-based triple combinations incorporating either α-cytotoxic T lymphocyte-associated protein 4 (CTLA-4) or CD122-targeted interleukin (IL)-2 complexes (IL-2c).Methods We tested these regimens in B16 melanoma and C51 colon carcinoma models in mice with one irradiated and one non-irradiated tumor on opposite flanks.Results In both models, RT/αPD-1/αCTLA-4 elicited a stronger abscopal response than RT/αPD-1/IL-2c. In the C51 model, RT/αPD-1/αCTLA-4 achieved a 61.5% abscopal cure rate, dependent on both CD8 + and CD4+ T cells. In contrast, the less effective RT/αPD-1/IL-2c response required only CD8+ T cells. The enhanced abscopal effect with RT/αPD-1/αCTLA-4 was associated with increased numbers, effector function, and reduced exhaustion of tumor-specific CD8+ tumor-infiltrating lymphocytes (TILs) and of CD4+ TILs, along with elevated CD80+CD86+ DCs in abscopal tumors, as shown by flow cytometry; immunofluorescence confirmed increased T-cell infiltration. CD4+ T-cell depletion during RT/αPD-1/αCTLA-4 treatment impaired abscopal but not irradiated tumor control, reducing infiltration of tumor-specific CD8+ T cells and conventional (c) DC1s, and diminishing cDC1-mediated cross-presentation in abscopal tumors. Activated CD4+ T cells upregulated CD80/CD86 on cDC1s and enhanced cross-presentation, partly via interferon-γ and tumor necrosis factor. Adoptively transferred tumor-specific CD8+ T cells from tumor-irradiated donors localized to unirradiated tumors and draining lymph nodes in αPD-1/αCTLA-4-treated recipients, but not in untreated or CD4+ T cell-depleted mice.Conclusions These results demonstrate that an RT-based combination therapy that robustly induces CD4 + T cells alongside CD8+ T cells can elicit a strong abscopal response and suggest that CD4+ effector T cells act at abscopal sites by promoting DC-mediated cross-presentation of tumor antigens to CD8+ T cells originating from the irradiated tumor.",
  "authors": [
    {
      "affiliations": [
        "Department of Radiation Oncology, Faculty of Medicine, University of Freiburg, Freiburg, Germany",
        "German Cancer Consortium (DKTK), Partner Site Freiburg, a partnership between DKFZ and Medical Center-University of Freiburg, Freiburg, Germany"
      ],
      "name": "Xi Rao"
    },
    {
      "affiliations": [
        "Department of Urology, Emory University School of Medicine, Atlanta, Georgia, USA"
      ],
      "name": "Kateryna Onyshchenko"
    },
    {
      "affiliations": [
        "Department of Radiation Oncology, Faculty of Medicine, University of Freiburg, Freiburg, Germany",
        "Faculty of Biology, University of Freiburg, Freiburg, Germany"
      ],
      "name": "Meidan Wang"
    },
    {
      "affiliations": [
        "Department of Thoracic Oncology Ward, Cancer Center and State Key Laboratory of Biotherapy, Sichuan University West China Hospital, Chengdu, Sichuan, China"
      ],
      "name": "Ren Luo"
    },
    {
      "affiliations": [
        "Department of Thoracic Oncology Ward, Cancer Center and State Key Laboratory of Biotherapy, Sichuan University West China Hospital, Chengdu, Sichuan, China"
      ],
      "name": "Xuanwei Zhang"
    },
    {
      "affiliations": [
        "Department of Radiation Oncology, Harbin Medical University Cancer Hospital, Harbin, Heilongjiang, China"
      ],
      "name": "Liqun Wang"
    },
    {
      "affiliations": [
        "Department of Radiation Oncology, Faculty of Medicine, University of Freiburg, Freiburg, Germany"
      ],
      "name": "Siegmar Kuhn"
    },
    {
      "affiliations": [
        "Department of Radiation Oncology, Faculty of Medicine, University of Freiburg, Freiburg, Germany"
      ],
      "name": "Yizhou Yang"
    },
    {
      "affiliations": [
        "Department of Radiation Oncology, Faculty of Medicine, University of Freiburg, Freiburg, Germany"
      ],
      "name": "Simone Gaedicke"
    },
    {
      "affiliations": [
        "Department of Radiation Oncology, Faculty of Medicine, University of Freiburg, Freiburg, Germany",
        "German Cancer Consortium (DKTK), Partner Site Freiburg, a partnership between DKFZ and Medical Center-University of Freiburg, Freiburg, Germany"
      ],
      "name": "Anca-Ligia Grosu"
    },
    {
      "affiliations": [
        "Department of Radiation Oncology, Faculty of Medicine, University of Freiburg, Freiburg, Germany"
      ],
      "name": "Elke Firat"
    },
    {
      "affiliations": [
        "Department of Radiation Oncology, Faculty of Medicine, University of Freiburg, Freiburg, Germany",
        "German Cancer Consortium (DKTK), Partner Site Freiburg, a partnership between DKFZ and Medical Center-University of Freiburg, Freiburg, Germany"
      ],
      "name": "Gabriele Niedermann"
    }
  ],
  "title": "CD4+ T cells facilitate the RT-induced abscopal effect by promoting antigen cross-presentation to CD8+ T cells at unirradiated tumor sites",
  "uid": "3243b515-0aa0-5543-ac0d-1cb4455a052b"
}