Intracutaneous DNA Vaccination with the E8 Gene of Cottontail Rabbit Papillomavirus Induces Protective Immunity against Virus Challenge in Rabbits

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Abstract
The cottontail rabbit papillomavirus (CRPV)-rabbit model has been used in several studies for testing prophylactic and therapeutic papillomavirus vaccines. Earlier observations had shown that the CRPV nonstructural genes E1, E2, and E6 induced strong to partial protective immunity against CRPV infection. In this study, we found that CRPV E8 immunization eliminated virus-induced papillomas in EIII/JC inbred rabbits (100%) and provided partial protection (55%) against virus challenge in outbred New Zealand White rabbits. CRPV-E8 is a small open reading frame, coding for a 50-amino-acid protein, that is colinear with the CRPV E6 gene and has features similar to those of the bovine papillomavirus and human papillomavirus E5 genes. Papillomas that grew on E8-vaccinated outbred rabbits were significantly smaller than those on vector-vaccinated rabbits ( P < 0.01; t test). Delayed-type hypersensitivity skin tests showed that some of the E8-vaccinated rabbits had positive responses to E8-specific peptides.