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Dendritic cell (DC)–based vaccines have shown promise for treating high-grade glioma (HGG), but efficacy has been limited by antigenic heterogeneity of the tumors. Now, Garg et al. combine DC vaccines with hypericin-based photodynamic therapy–induced immunogenic cell death (ICD) to treat HGG in an animal model. They found that ICD-based DC vaccines improved survival, and that this effect was dependent on the cell-associated reactive oxygen species and release of damage-associated molecular patterns (DAMPs) acting as danger signals. These ICD-based DC vaccines synergized with standard-of-care therapy to further improve survival in HGG-bearing mice and shifted the tumor immune signature from regulatory to TH1/TH17, which is associated with positive outcome in patients.
The promise of dendritic cell (DC)–based immunotherapy has been established by two decades of translational research. Of the four malignancies most targeted with clinical DC immunotherapy, high-grade glioma (HGG) has shown the highest susceptibility. HGG-induced immunosuppression is a roadblock to immunotherapy, but may be overcome by the application of T helper 1 (TH1) immunity–biased, next-generation, DC immunotherapy. To this end, we combined DC immunotherapy with immunogenic cell death (ICD; a modality shown to induce TH1 immunity) induced by hypericin-based photodynamic therapy. In an orthotopic HGG mouse model involving prophylactic/curative setups, both biologically and clinically relevant versions of ICD-based DC vaccines provided strong anti-HGG survival benefit. We found that the ability of DC vaccines to elicit HGG rejection was significantly blunted if cancer cell–associated reactive oxygen species and emanating danger signals were blocked either singly or concomitantly, showing hierarchical effect on immunogenicity, or if DCs, DC-associated MyD88 signal, or the adaptive immune system (especially CD8+ T cells) were depleted. In a curative setting, ICD-based DC vaccines synergized with standard-of-care chemotherapy (temozolomide) to increase survival of HGG-bearing mice by ~300%, resulting in ~50% long-term survivors. Additionally, DC vaccines also induced an immunostimulatory shift in the brain immune contexture from regulatory T cells to TH1/cytotoxic T lymphocyte/TH17 cells. Analysis of the The Cancer Genome Atlas glioblastoma cohort confirmed that increased intratumor prevalence of TH1/cytotoxic T lymphocyte/TH17 cells linked genetic signatures was associated with good patient prognosis. Therefore, pending final preclinical checks, ICD-based vaccines can be clinically translated for glioma treatment.
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