A Heterologous Prime/Boost Vaccination Strategy Enhances the Immunogenicity of Therapeutic Vaccines for Hepatitis C Virus

Background. We explored the concept of heterologous prime/boost vaccination using 2 therapeutic vaccines currently in clinical development aimed at treating chronically infected hepatitis C virus (HCV) patients: prime with a DNA-based vaccine expressing HCV genotype 1a NS3/4A proteins (ChronVac-C) and boost with a modified vaccinia virus Ankara vaccine expressing genotype 1b NS3/4/5B proteins (MVATG16643). Methods. Two ChronVac-C immunizations 4 weeks apart were delivered intramuscularly in combination with in vivo electroporation and subsequently 5 or 12 weeks later boosted by 3 weekly subcutaneous injections of MVATG16643. Two mouse strains were used, and we evaluated quality, magnitude, and functionality of the T cells induced. Results. DNA prime/MVA boost regimen induced significantly higher levels of interferon gamma (IFN-gamma) or interleukin 2 (IL-2) ELISpot responses compared with each vaccine alone, independent of the time of analysis and the time interval between vaccinations. Both CD8(+) and CD4(+) T-cell responses as well as the spectrum of epitopes recognized was improved. A significant increase in polyfunctional IFN-gamma/tumor necrosis factor alpha (TNF-alpha)/CD107a(+) CD8(+) T cells was detected following ChronVac-C/MVATG16643 vaccination (from 3% to 25%), and prime/boost was the only regimen that activated quadrifunctional T cells (IFN-gamma/TNF-alpha/CD107a/IL-2). In vivo functional protective capacity of DNA prime/MVA boost was demonstrated in a Listeria-NS3-1a challenge model. Conclusions. We provide a proof-of-concept that immunogenicity of 2 HCV therapeutic vaccines can be improved using their combination, which merits further clinical development.