Enhanced therapeutic effects conferred by an experimental DNA vaccine targeting human papillomavirus-induced tumors.

Human papillomavirus (HPV) infection is responsible for all cervical cancer cases, other anogenital cancers and head and neck tumors. The epidemiological relevance of HPV-induced tumors reinforces the need for the development of therapeutic anti-tumor vaccines. Clinical trials with different vaccine formulations, particularly DNA vaccines, have provided promising results but have still been unable to achieve the immunogenicity required for use in infected patients. In experimental conditions, anti-cancer HPV-specific vaccines induced E7-specific CD8+ T cells responses but did not confer full therapeutic anti-tumor protection in mice with transplanted HPV-expressing TC-1 cells, which are the most frequently used non-clinical protection correlate for anti-tumor effects. Our group has developed a DNA vaccine strategy based on the fusion of HPV oncoproteins to the herpes virus gD protein. This vaccine promoted the induction of antigen-specific cytotoxic CD8+ T cell responses and partial anti-tumor therapeutic effects based on the blockade of co-inhibitory signals and the enhancement of co-activation mechanisms. In the present study, we report conditions leading to full therapeutic anti-tumor effects using the TC-1 cell murine model after a single vaccine dose. The combination of a co-administered plasmid encoding IL-2, optimization of the coding sequence for mammalian cells and the use of different delivery routes resulted in enhancements of the E7-specific cytotoxic CD8+ T cell responses and full therapeutic protection under experimental conditions. The combination of these strategies augmented the potency of the DNA vaccine formulation to levels not previously achieved by other therapeutic anti-tumor vaccines under similar experimental conditions, including some that have been taken to clinical trials.