Antitumor activity, immunogenicity and safety of a novel PD-1 vaccine in combination with two chimeric HER-2 peptide vaccine in syngeneic Balb/c, C57Bl/6 models and in beagle dogs

Abstract

Background: Anti-PD-1 blocking monoclonal antibodies (mAbs) such as nivolumab or pembrolizumab have shown potent anti-tumor effects in different metastatic cancers. Similarly, anti-HER-2 mAbs such as Herceptin and Perjeta are approved for breast cancer. These mAbs are only effective in 10-25%of cancer patients, and are limited by high costs, side effects and development of resistance. Contrary to treatment with monoclonal antibodies, chimeric B-cell cancer vaccines incorporating a 'promiscuous' T cell epitope have the advantage of safer and cheaper alternatives, producing a specific immune response that induces memory B & T cell responses, while reducing immune evasion, suppression and resistance. Methods: We have translated two HER-2 combination peptide vaccines (B-Vaxx) to the clinic in a Phase 1/2b trial to safely deliver curative and transformative cancer immunotherapies to advanced cancer patients. We have created and established the development of a novel B-cell peptide vaccine (Key-Vaxx) with high immunogenicity that binds to human PD-1 and produces tumor inhibition in vivo in two animal models of colon cancer. We will describe the CT-26, CT26-HER2 and MC38 tumor models in Balb/c and C57/Bl6 used to test for synergistic effects of anti-PD1 immunization therapy in combination with anti-HER2 immunization therapy. The immunogenicity/ optimal immunologic dose and toxicity profile was investigated in beagle dogs. Results: We show robust HER-2 and PD-1 antibody responses in mice, beagle dogs and non-human primates. The individual (PD-1) or combined vaccination (B-Vaxx)) was effective in reducing tumor growth in a Balb/c and C57Bl/6 syngeneic model of colon carcinoma and exhibited superior activity compared to the positive gold control antimouse PD-1 (CD279) monoclonal antibody. Conclusions: Development of PD-1 B-cell vaccine was successful, showing no evidence of toxicity or autoimmunity in mice, rabbits and beagle dogs. The combination vaccines could provide improved outcomes in early stage disease sparing patients the toxicity of chemotherapy. A phase 1 clinical trial with the PD-1 vaccine is under planning.