Protection of rabbits from viral challenge by gene gun-based intracutaneous vaccination with a combination of cottontail rabbit papillomavirus E1, E2, E6, and E7 genes.
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In this study, cottontail rabbit papillomavirus infection of domestic rabbits was used as an animal model to develop papillomavirus early gene-based vaccines. Groups of rabbits were intracutaneously vaccinated with single papillomavirus early genes E1, E2, E6, and E7 or with a combination of these four genes. Only a fraction of rabbits were protected from subsequent viral challenge when vaccinated with the E1 or E6 gene. Viral tumor growth in those rabbits vaccinated with the E1 or E2 gene was suppressed compared to that in controls. In contrast, seven of nine rabbits vaccinated with the combination of the E1, E2, E6, and E7 genes were completely protected against viral challenge. These data indicated that intracutaneous genetic vaccination with the combination of the E1, E2, E6, and E7 genes can be an effective strategy for immunoprophylaxis of papillomavirus infection. (+info)
Induction of E6/E7 expression in cottontail rabbit papillomavirus latency following UV activation.
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Latent human papillomavirus (HPV) infections are widespread in the genital and respiratory tracts and are a source of recurrent disease. This study used a cottontail rabbit papillomavirus (CRPV) model to determine the presence of E1, E6, and E7 transcripts in latent infection and to determine the temporal change in transcripts following UV activation. We found E1 transcripts in all latently infected sites but no detectable E6 and E7 transcripts, consistent with our earlier studies of HPV6/11 latency. These results suggest that this transcription pattern is broadly characteristic of latent papillomavirus infections. E6/E7 transcripts were detectable within 1 week of irradiation, with maximal induction (approximately 40% of sites) at 2 weeks postirradiation. Papillomas were induced in approximately 26% of irradiated sites after a 3- to 5-week lag. Sites that did not form papillomas by 3 months after irradiation were CRPV DNA positive but E6/E7 RNA negative. Thus, only a subset of latent infections can be induced to express E6/E7 transcripts and form papillomas. We propose that CRPV can be used to study the molecular processes regulating papillomavirus activation. (+info)
Rabbit oral papillomavirus complete genome sequence and immunity following genital infection.
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Rabbit oral papillomavirus (ROPV) infects mucosal tissues of domestic rabbits. The viral genomic sequence has been determined and the most related papillomavirus type was the cutaneous cottontail rabbit papillomavirus (CRPV). Homologies between the open reading frames (ORFs) of ROPV and CRPV, however, ranged from 68% amino acid identity for L1 to only 23% identity for E4. Shared features unique to the two rabbit viruses included a large E6 ORF and a small E8 ORF that overlapped the E6 ORF. Serological responses to ROPV L1 viruslike particles (VLPs) were detected in rabbits infected at either the genital or oral mucosa with ROPV. The antibody response was specific to intact ROPV L1 VLP antigen, was first detected at the time of late regression, and persisted at high levels for several months after complete regression. Both oral and genital lesions regressed spontaneously, accompanied by a heavy infiltrate of lymphocytes. ROPV infection of rabbit genital mucosa is a useful model to study host immunological responses to genital papillomavirus infections. (+info)
Granulocyte-macrophage colony-stimulating factor priming plus papillomavirus E6 DNA vaccination: effects on papilloma formation and regression in the cottontail rabbit papillomavirus--rabbit model.
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A cottontail rabbit papillomavirus (CRPV) E6 DNA vaccine that induces significant protection against CRPV challenge was used in a superior vaccination regimen in which the cutaneous sites of vaccination were primed with an expression vector encoding granulocyte-macrophage colony-stimulating factor (GM-CSF), a cytokine that induces differentiation and local recruitment of professional antigen-presenting cells. This treatment induced a massive influx of major histocompatibility complex class II-positive cells. In a vaccination-challenge experiment, rabbit groups were treated by E6 DNA vaccination, GM-CSF DNA inoculation, or a combination of both treatments. After two immunizations, rabbits were challenged with CRPV at low, moderate, and high stringencies and monitored for papilloma formation. As expected, all clinical outcomes were monotonically related to the stringency of the viral challenge. The results demonstrate that GM-CSF priming greatly augmented the effects of CRPV E6 vaccination. First, challenge sites in control rabbits (at the moderate challenge stringency) had a 0% probability of remaining disease free, versus a 50% probability in E6-vaccinated rabbits, and whereas GM-CSF alone had no effect, the interaction between GM-CSF priming and E6 vaccination increased disease-free survival to 67%. Second, the incubation period before papilloma onset was lengthened by E6 DNA vaccination alone or to some extent by GM-CSF DNA inoculation alone, and the combination of treatments induced additive effects. Third, the rate of papilloma growth was reduced by E6 vaccination and, to a lesser extent, by GM-CSF treatment. In addition, the interaction between the E6 and GM-CSF treatments was synergistic and yielded more than a 99% reduction in papilloma volume. Finally, regression occurred among the papillomas that formed in rabbits treated with the E6 vaccine and/or with GM-CSF, with the highest regression frequency occurring in rabbits that received the combination treatment. (+info)
DNA vaccination prevents and/or delays carcinoma development of papillomavirus-induced skin papillomas on rabbits.
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Malignant progression is a life-threatening consequence of human papillomavirus-associated lesions. In this study, we tested the efficacy of papillomavirus early-gene-based vaccines for prevention of carcinoma development of papillomavirus-induced skin papillomas on rabbits. Rabbit skin papillomas were initiated by infection with cottontail rabbit papillomavirus (CRPV). The papillomas were allowed to grow for 3 months without any treatment intervention. Rabbits were then immunized by gene gun-mediated intracutaneous administration of four DNA plasmids encoding CRPV E1, E2, E6, and E7 genes, respectively. All eight control rabbits receiving vector alone developed invasive carcinoma within 8 to 13 months. In contrast, only two of eight vaccinated rabbits developed carcinoma at 12 and 15 months, respectively. Papilloma growth was suppressed in the majority of vaccinated rabbits but not completely eradicated. These results indicate that gene gun-mediated immunization with papillomavirus early genes may be a promising strategy for prevention of malignant progression of human papillomavirus-associated lesions in humans. (+info)
High and low levels of cottontail rabbit papillomavirus E2 protein generate opposite effects on gene expression.
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The papillomavirus E2 protein plays an important role in viral transcriptional regulation and replication. We chose to study the cottontail rabbit papillomavirus (CRPV) E2 protein as a transcriptional regulator because of the availability of an animal model for papilloma formation, which may be relevant for human papillomavirus (HPV) infection and replication. We studied the effect of expression levels of E2 on the long control region, which contains transcriptional promoter and enhancer elements, and synthetic E2-dependent artificial promoters in which the E2 was the dominant factor in the transcriptional activation. These experiments indicated that high levels of E2 were inhibitory and low levels were stimulatory for transactivation. In addition, we showed that the complex formed between CRPV E2 and the cognate binding site was less stable than the complex formed between HPV E2 and the same cognate binding site. Furthermore, we showed that CRPV E2 binding to its transcriptional regulatory sequence was stabilized by other proteins such as E1, which produced increments in transcriptional activation of E2-dependent genes. The data may be used to define conditions in which the rabbit model can be used for the screening of drugs which are inhibitory to the HPV and CRPV replication and gene expression. (+info)
Variation in the nucleotide sequence of cottontail rabbit papillomavirus a and b subtypes affects wart regression and malignant transformation and level of viral replication in domestic rabbits.
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We previously reported the partial characterization of two cottontail rabbit papillomavirus (CRPV) subtypes with strikingly divergent E6 and E7 oncoproteins. We report now the complete nucleotide sequences of these subtypes, referred to as CRPVa4 (7,868 nucleotides) and CRPVb (7,867 nucleotides). The CRPVa4 and CRPVb genomes differed at 238 (3%) nucleotide positions, whereas CRPVa4 and the prototype CRPV differed by only 5 nucleotides. The most variable region (7% nucleotide divergence) included the long regulatory region (LRR) and the E6 and E7 genes. A mutation in the stop codon resulted in an 8-amino-acid-longer CRPVb E4 protein, and a nucleotide deletion reduced the coding capacity of the E5 gene from 101 to 25 amino acids. In domestic rabbits homozygous for a specific haplotype of the DRA and DQA genes of the major histocompatibility complex, warts induced by CRPVb DNA or a chimeric genome containing the CRPVb LRR/E6/E7 region showed an early regression, whereas warts induced by CRPVa4 or a chimeric genome containing the CRPVa4 LRR/E6/E7 region persisted and evolved into carcinomas. In contrast, most CRPVa, CRPVb, and chimeric CRPV DNA-induced warts showed no early regression in rabbits homozygous for another DRA-DQA haplotype. Little, if any, viral replication is usually observed in domestic rabbit warts. When warts induced by CRPVa and CRPVb virions and DNA were compared, the number of cells positive for viral DNA or capsid antigens was found to be greater by 1 order of magnitude for specimens induced by CRPVb. Thus, both sequence variation in the LRR/E6/E7 region and the genetic constitution of the host influence the expression of the oncogenic potential of CRPV. Furthermore, intratype variation may overcome to some extent the host restriction of CRPV replication in domestic rabbits. (+info)
Combination treatment with intralesional cidofovir and viral-DNA vaccination cures large cottontail rabbit papillomavirus-induced papillomas and reduces recurrences.
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We used the cottontail rabbit papillomavirus (CRPV) New Zealand White rabbit model to test a combination treatment of large established papillomas with intralesional cidofovir and DNA vaccination to cure sites and reduce recurrences. Intralesional 1% (wt/vol) (0.036 M) cidofovir treatment of rabbit papillomas led to elimination, or "cure," of the papillomas over a 6- to 8-week treatment period (N. D. Christenson, M. D. Pickel, L. R. Budgeon, and J. W. Kreider, Antivir. Res. 48:131-142, 2000). However, recurrences at periods from 1 to 8 weeks after treatment cessation were observed at approximately 50% of cured sites. DNA vaccinations with CRPV E1, E2, E6, and E7 were initiated either after or at the time of intralesional treatments, and the recurrence rates were observed. When DNA vaccinations were started after intralesional cures, recurrence rates were similar to those of vector-vaccinated rabbits. A small proportion of recurrent sites subsequently regressed (4 out of 10, or 40%) in the vaccinated group versus no regression of recurrences in the vector-immunized group (0 out of 19, or 0%), indicating partial effectiveness. In contrast, when DNA vaccinations were conducted during intralesional treatments, a significant reduction of recurrences (from 10 out of 19, or 53%, of sites in vector-immunized rabbits to 3 out of 20, or 15%, of sites in viral-DNA-immunized rabbits) was observed. DNA vaccination without intralesional treatments had a minimal effect on preexisting papillomas. These data indicated that treatment with a combination of antiviral compounds and specific immune stimulation may lead to long-term cures of lesions without the ensuing problem of papilloma recurrence. (+info)