Fusion Protein Vaccines Targeting Two Tumor Antigens Generate Synergistic Anti-Tumor Effects

Introduction: Human papillomavirus (HPV) has been consistently implicated in causing several kinds of malignancies, and two HPV oncogenes, E6 and E7, represent two potential target antigens for cancer vaccines. We developed two fusion protein vaccines, PE(Delta III)/E6 and PE(Delta III)/E7 by targeting these two tumor antigens to test whether a combination of two fusion proteins can generate more potent anti-tumor effects than a single fusion protein. Materials and Methods: In vivo antitumor effects including preventive, therapeutic, and antibody depletion experiments were performed. In vitro assays including intracellular cytokine staining and ELISA for Ab responses were also performed. Results: PE(Delta III)/E6+PE(Delta III)/E7 generated both stronger E6 and E7-specific immunity. Only 60% of the tumor protective effect was observed in the PE(Delta III)/E6 group compared to 100% in the PE(Delta III)/E7 and PE(Delta III)/E6+PE(Delta III)/E7 groups. Mice vaccinated with the PE(Delta III)/E6+PE(Delta III)/E7 fusion proteins had a smaller subcutaneous tumor size than those vaccinated with PE(Delta III)/E6 or PE(Delta III)/E7 fusion proteins alone. Conclusion: Fusion protein vaccines targeting both E6 and E7 tumor antigens generated more potent immunotherapeutic effects than E6 or E7 tumor antigens alone. This novel strategy of targeting two tumor antigens together can promote the development of cancer vaccines and immunotherapy in HPV-related malignancies.