Background
Considering the high number of new cases of cervical cancer each year caused by human papilloma viruses (HPVs), the development of an effective vaccine for the prevention and therapy of HPV-associated cancers, and in particular against the high-risk HPV-16 genotype, remains a priority. Vaccines expressing the E6 and E7 proteins, which are detectable in all HPV-positive pre-cancerous and cancer cells, might support the treatment of HPV-related lesions and clear already established tumors.
Methods
In this study, DNA and fowlpox virus recombinants expressing the E6F47R and E7GGG mutated forms of the HPV-16 E6 and E7 oncoproteins were generated, and their correct expression verified by RT-PCR, Western blotting and immunofluorescence. The immune responses were determined by ELISA and ELISPOT assays and the therapeutic efficacy was evaluated In mice, as a pre-clinical model of HPV-16 tumorigenicity, using heterologous (DNA/FP) or homologous (DNA/DNA and FP/FP) prime/ boost regimens after challenge with syngeneic TC-1* cells.
Results
The analyses of the different recombinants showed the correct expression of the inserted heterologous genes. After mice immunization, while specific anti-E6 and anti-E7 humoral responses were just detectable, specific T-cell responses were elicited. In the therapeutic protocols, after the challenge and the subsequent immunizations, a delay in cancer appearance was shown, thus confirming the pivotal role of the T-cell response in the control of tumor growth also in the absence of E6- and E7-specific antibodies. These in-vivo experiments resulted in higher numbers of tumor-free mice after either the homologous or heterologous immunizations compared to the controls.
Conclusions
These data establish a preliminary indication for the prevention and treatment of HPV-related tumors by the use of DNA and avipox constructs as safe and effective immunogens administered by the prime/boost strategy. The combined use of the recombinants expressing both the E6F47R and E7GGG proteins should improve the antitumor efficacy and represent an important approach to control/clear HPV-associated cancers
