Author:

Keywords:

High-grade glioma, dendritic cell immunotherapy, cancer cell death, brain immune contexture, antitumor immunity, oxidation-associated molecular patterns

Abstract:

High-grade glioma (HGG) represents a highly aggressive central nervous system (CNS) malignancy with mortality rates matching incidence rates. Dendritic cell vaccines aiming to stimulate the endogenous antiglioma immune response constitute a safe and promising treatment modality. Thus far, the efficacy of DC vaccines is considered suboptimal, in part owing to a lack of attention towards the immunogenicity of the tumor lysate used as an antigen source for loading the DC vaccines. Given the recent evidence that oxidation and the resultant oxidation-associated molecular patterns (OAMPs) can impact tumor cell immunogenicity, we applied two physico-chemical oxidizing therapies to obtain a more immunogenic tumor cell cargo: x-ray irradiation and hypericin-based photodynamic therapy (Hyp-PDT). DC vaccine immunogenicity was investigated in the orthotopic, syngeneic GL261 HGG model. Mice prophylactically immunized with DC vaccines loaded with x-ray irradiated freeze-thawed lysates survived significantly longer as compared to mice vaccinated with DCs loaded with freeze-thaw lysate only. This was associated, both in prophylactic and curative vaccination setups, with increased intrabrain infiltration of T helper-1 cells (Th1)/Cytotoxic T lymphocytes (CTLs) and reduced infiltration of regulatory T cells (Tregs), myeloid-derived suppressor cells (MDSCs) and tumor-associated macrophages (TAMs). Through further application of anti-oxidants and hydrogenperoxide, we found a striking correlation between the amount of lysate-associated protein carbonylation/OAMPs and the capacity of the DC vaccines to mediate glioma rejection. This result fostered the preclinical investigation of other strong oxidizers like Hyp-PDT, a potent type II inducer of ICD, in our HGG model. Hyp-PDT induced prototypical ICD in the GL261 cell line. In prophylactic as well as curative vaccination settings, both biologically and clinically-relevant versions of Hyp-PDT-based ICD-based DC vaccines provided strong anti-HGG survival benefit. The ability of DC vaccines to elicit HGG rejection was significantly blunted if cancer cell-associated reactive oxygen species (ROS) and emanating danger signals were blocked (either singly or concomitantly; showing hierarchical effect on immunogenicity i.e. extracellular-HMGB1>extracellular-ATP>ecto-calreticulin) or if DCs, the DCs-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 Tregs to Th1/CTLs/Th17 cells. Analysis of the TCGA glioblastoma-cohort confirmed that increased intra-tumor prevalence of Th1/CTLs/Th17 cells-linked genetic signatures associated with good patient prognosis. Our research demonstrates that combining DC vaccination with oxidizing treatment modalities can induce Th1-driven antitumor immune responses, enabling CTL-mediated glioma rejection. ICD-based DC vaccines exploiting ER-directed oxidative stress might be considered next generation DC vaccines.