Intramuscular injection of plasmid DNA encoding cottontail rabbit papillomavirus E1, E2, E6 and E7 induces T cell-mediated but not humoral immune responses in rabbits

To test the efficacy of genetic vaccination against papillomavirus infection, plasmid DNA encoding cottontail rabbit papillomavirus (CRPV) E1, E2, E6, E7 or without insert were intramuscularly injected into five groups of rabbits. Peripheral blood mononuclear cells (PBMCs) showed specific proliferation upon in vitro stimulation with E1, E2, E6 or E7 proteins in a majority of vaccinated rabbits but Western blot analysis did not detect antibodies specific for these viral proteins in rabbit serum. All rabbits grew papillomas after virus challenge and none of the rabbits showed systemic papilloma regression. These observations showed that intramuscular injection of plasmid DNA encoding CRPV E1, E2, E6 or E7 induced CD4+ T cell-mediated but not humoral immune responses, and did not result in the protection of rabbits from virus infection.