Novel oncolytic adenovirus-based PEPvIII vaccine displays a super antitumor effect in glioma models

Currently, an epidermal growth factor receptor variant III (EGFRvIII)-specific peptide (PEPvIII) vaccine has not achieved satisfactory outcomes in several clinical trials for glioblastoma. This is probably due to the poor immunogenicity of the PEPvIII peptide vaccine and the harshly immunosuppressive tumor microenvironment. Hence, identifying strategies to enhance tumor-specific T cell immune responses and reverse immune suppression is crucial for achieving the maximum beneficial therapeutic effect.

To enhance the immunogenicity of the PEPvIII vaccine, we have developed a novel oncolytic adenovirus-based vaccine by genetically incorporating the PEPvIII peptide into the adenovirus hexon protein, naming this construct Ad5-D24-PEPvIII. However, the upregulation of programmed cell death-ligand 1 (PD-L1) expression in the tumor microenvironment following oncolytic virus therapy may limit its therapeutic effectiveness. To address this, we first attempted to co-express soluble programmed cell death 1 (sPD-1) and granulocyte-macrophage colony-stimulating factor (GM-CSF) in the E4 region of Ad5-D24-PEPvIII. Subsequently, we combined the oncolytic adenovirus-based PEPvIII vaccine carrying GM-CSF with a PD-L1 inhibitor. Two immunocompetent mouse glioma models were used to evaluate their antitumor effects in vivo. The immune cell status within the tumor microenvironment was assessed using flow cytometry and immunohistochemistry. CD8⁺ T cell immune responses were evaluated by ELISA.

Local administration of Ad5-D24-PEPvIII, which presents high copies of tumor-specific antigen PEPvIII in the hexon protein, successfully activated PEPvIII-specific T cell responses. Co-expression of sPD-1 and GM-CSF in the E4 region of Ad5-D24-PEPvIII could increase the release of proinflammatory cytokines, activate myeloid cells and promote the maturation of dendritic cells, thereby further enhancing the activation and proliferation of CD8⁺ T cells targeting tumor antigens. More importantly, when the oncolytic adenovirus-based PEPvIII vaccine carrying GM-CSF was combined with a PD-L1 inhibitor, it could also broaden the tumor antigenic epitopes and significantly inhibit tumor growth in immunocompetent glioma mouse models.

Our work suggests that the efficient presentation of PEPvIII, achieved by modifying the hexon protein of the oncolytic adenovirus, combined with the adjuvant function of GM-CSF and blockade of the PD-1/PD-L1 axis, significantly enhances the therapeutic efficacy of the PEPvIII vaccine against glioblastoma. In addition, this combination strategy also provides a promising and personalized treatment for patients with cancer.