Rabbit oral papillomavirus complete genome sequence and immunity following genital infection

Identification and characterization of the genome of a papillomavirus from skin lesions of four-toed hedgehogs (Atelerix albiventris)

The present study describes the clinical and pathological characteristics of skin lesions in two four-toed hedgehogs (Atelerix albiventris). We performed inverse PCR to identify the genome of papillomavirus (PV) in the skin lesions and subsequently sequenced the full genome of the virus, which was tentatively named Atelerix albiventris papillomavirus 1 (AalbPV1). The overall sequences of the viral genomes of both four-toed hedgehogs were identical. This study first identified the presence of a novel PV in Japanese four-toed hedgehogs and provided genetic information about this virus.

Modeling HPV-Associated Disease and Cancer Using the Cottontail Rabbit Papillomavirus

Approximately 5% of all human cancers are attributable to human papillomavirus (HPV) infections. HPV-associated diseases and cancers remain a substantial public health and economic burden worldwide despite the availability of prophylactic HPV vaccines. Current diagnosis and treatments for HPV-associated diseases and cancers are predominantly based on cell/tissue morphological examination and/or testing for the presence of high-risk HPV types. There is a lack of robust targets/markers to improve the accuracy of diagnosis and treatments. Several naturally occurring animal papillomavirus models have been established as surrogates to study HPV pathogenesis. Among them, the Cottontail rabbit papillomavirus (CRPV) model has become known as the gold standard. This model has played a pivotal role in the successful development of vaccines now available to prevent HPV infections. Over the past eighty years, the CRPV model has been widely applied to study HPV carcinogenesis. Taking advantage of a large panel of functional mutant CRPV genomes with distinct, reproducible, and predictable phenotypes, we have gained a deeper understanding of viral–host interaction during tumor progression. In recent years, the application of genome-wide RNA-seq analysis to the CRPV model has allowed us to learn and validate changes that parallel those reported in HPV-associated cancers. In addition, we have established a selection of gene-modified rabbit lines to facilitate mechanistic studies and the development of novel therapeutic strategies. In the current review, we summarize some significant findings that have advanced our understanding of HPV pathogenesis and highlight the implication of the development of novel gene-modified rabbits to future mechanistic studies.

Gene Editing in Rabbits: Unique Opportunities for Translational Biomedical Research

The rabbit is a classic animal model for biomedical research, but the production of gene targeted transgenic rabbits had been extremely challenging until the recent advent of gene editing tools. More than fifty gene knockout or knock-in rabbit models have been reported in the past decade. Gene edited (GE) rabbit models, compared to their counterpart mouse models, may offer unique opportunities in translational biomedical research attributed primarily to their relatively large size and long lifespan. More importantly, GE rabbit models have been found to mimic several disease pathologies better than their mouse counterparts particularly in fields focused on genetically inherited diseases, cardiovascular diseases, ocular diseases, and others. In this review we present selected examples of research areas where GE rabbit models are expected to make immediate contributions to the understanding of the pathophysiology of human disease, and support the development of novel therapeutics.

Cryotherapy plus low-dose oral isotretinoin vs cryotherapy only for the treatment of anogenital warts: a randomized clinical trial

BACKGROUND

Anogenital warts are a common human papillomavirus infection. They cause emotional distress, especially when they are in the anogenital region. Cryotherapy is a first-line treatment. Previous clinical trials and case series have reported variable results with retinoids (isotretinoin) as adjuvant therapy.

OBJECTIVE

To determine the safety and efficacy of low-dose oral isotretinoin as adjuvant treatment of anogenital warts.

METHODS

Forty-six patients with anogenital warts were randomly assigned to isotretinoin + cryotherapy (n = 23) or only cryotherapy (n = 23). Patients were allocated via an interactive web-based randomization system. Evaluators were blinded to treatments. Isotretinoin 20 mg/daily + cryotherapy or cryotherapy were prescribed for 6 weeks. Patients were followed for 4 months. Genotyping of lesions was performed before treatment started. Dermatology Life Quality Index (DLQI) and Columbia-Suicide Severity Rating Scale (C-SSRS) were measured at the beginning and end of therapy. All patients completed the study.

RESULTS

Both Groups had 50% clearance at the end of treatment. Recurrence in the combined group was not significantly lower than in the cryotherapy group (P = 0.59). Improvement was observed in the DLQI of all patients in both groups (P = 0.001). No suicidal intention was detected with the C-SSRS. Two patients (one in each group) had liver function test abnormalities after treatment.

CONCLUSION

Combined therapy showed a slight not significant efficacy for anogenital warts in Hispanic patients. Low-dose isotretinoin seems to be safe even when it is used with cryotherapy on anogenital warts.

TRIAL REGISTRATION

On April 25, 2019 with registration number DE19-00004, CONBIOÉTICA-19-CEI-001-20160404. Prospectively registered.

Antibody-Mediated Immune Subset Depletion Modulates the Immune Response in a Rabbit (Oryctolagus cuniculus) Model of Epstein-Barr Virus Infection

Epstein-Barr Virus (EBV) is a γ-herpesvirus which infects over 90% of the adult human population. Most notably, this virus causes infectious mononucleosis but it is also associated with cancers such as Hodgkin and Burkitt lymphoma. EBV is a species-specific virus and has been studied in many animal models, including nonhuman primates, guinea pigs, humanized mice, and tree shrews. However, none of these animal models are considered the "gold standard" for EBV research. Recently, rabbits have emerged as a viable alternative model, as they are susceptible to EBV infection. In addition, the EBV infection progresses after immune suppression with cyclosporine A (CsA), modeling the reactivation of EBV after latency. We sought to refine this model for acute or active EBV infections by performing antibody-mediated depletion of certain immune subsets in rabbits. Fourteen 16 to 20-wk old, NZW rabbits were intravenously inoculated with EBV and concurrently treated with either anti-CD4 T-cell antibody, anti-pan-T-cell antibody (anti CD45), CSA, or, as a control, anti-HPV antibody. Rabbits that received the depleting antibodies were treated with CsA 3 times at a dose of 15 mg/kg SC once per day for 4 d starting at the time of EBV inoculation then the dose was increased to 20 mg/kg SC twice weekly for 2 wk. Weights, temperatures, and clinical signs were monitored, and rabbits were anesthetized once weekly for blood collection. When compared with the control group, anti-CD4-treated rabbits had fewer clinical signs and displayed higher levels of viral DNA via qPCR in splenocytes; however, flow cytometry results showed only a partial depletion of CD4 T-cells. Treatment with anti-pan-T-cell antibody did not result in noticeable T-cell depletion. These data suggest the EBV-infected rabbit is a promising model for testing antiviral medications and prophylactic vaccines for EBV.

Detection and genome characterization of two novel papillomaviruses and a novel polyomavirus in tree shrew (Tupaia belangeri chinensis) in China

Background

Papillomaviruses (PVs) and polyomaviruses (PyVs) infect diverse vertebrates including human and cause a broad spectrum of outcomes from asymptomatic infection to severe disease. There has been no PV and only one PyV detected in tree shrews, though the genomic properties of tree shrews are highly similar to those of the primates.

Methods

Swab and organ samples of tree shrews collected in the Yunnan Province of China, were tested by viral metagenomic analysis and random PCR to detect the presence of PVs and PyVs. By PCR amplification using specific primers, cloning, sequencing and assembling, genomes of two PVs and one PyV were identified in the samples.

Results

Two novel PVs and a novel PyV, named tree shrew papillomavirus 1 and 2 (TbelPV1 and TbelPV2) and polyomavirus 1 (TbelPyV1) were characterized in the Chinese tree shrew (Tupaia belangeri chinensis). The genomes of TbelPV1, TbelPV2, and TbelPyV1 are 7410 bp, 7526 bp, and 4982 bp in size, respectively. The TbelPV1 genome contains 7 putative open-reading frames (ORFs) coding for viral proteins E1, E2, E4, E6, E7, L1, and L2; the TbelPV2 genome contains 6 ORFs coding for viral proteins E1, E2, E6, E7, L1, and L2; and the TbelPyV1 genome codes for the typical small and large T antigens of PyV, as well as the VP1, VP2, and VP3 capsid proteins. Genomic comparison and phylogenetic analysis indicated that TbelPV1 and TbelPV2 represented 2 novel PV genera of Papillomaviridae, and TbelPyV1 represented a new species of genus Alphapolyomavirus. Our epidemiologic study indicated that TbelPV1 and TbelPV2 were both detected in oral swabs, while TbelPyV1 was detected in oral swabs and spleens.

Conclusion

Two novel PVs (TbelPV1 and TbelPV2) and a novel PyV (TbelPyV) were discovered in tree shrews and their genomes were characterized. TbelPV1, TbelPV2, and TbelPyV1 have the highest similarity to Human papillomavirus type 63, Ursus maritimus papillomavirus 1, and Human polyomavirus 9, respectively. TbelPV1 and TbelPV2 only showed oral tropism, while TbelPyV1 showed oral and spleen tropism.

Electronic supplementary material

The online version of this article (10.1186/s12985-019-1141-9) contains supplementary material, which is available to authorized users.

Genomic characterization of the first oral avian papillomavirus in a colony of breeding canaries (Serinus canaria)

Papillomaviruses are non-enveloped, DNA viruses that infect skin and mucosa of a wide variety of vertebrates, causing neoplasias or simply persisting asymptomatically. Avian papillomaviruses, with six fully sequenced genomes, are the second most studied group after mammalian papillomaviruses. In this study, we describe the first oral avian papillomavirus, detected in the tongue of a dead Yorkshire canary (Serinus canaria) and in oral swabs of the same bird and other two live canaries from an aviary in Madrid, Spain. Its genome is 8,071 bp and presents the canonical papillomavirus architecture with six early (E6, E7, E1, E9, E2, E4) and two late open reading frames (L1 and L2) and a long control region between L1 and E6. This new avian papillomavirus L1 gene shares a 64% pairwise identity with FcPV1 L1, so it has been classified as a new species (ScPV1) within the Ethapapillomavirus genus. Although the canary died after showing breathing problems, there is no evidence that the papillomavirus caused those symptoms so it could be part of the oral microbiota of the birds. Hence, future investigations are needed to evaluate the clinical relevance of the virus.

Association of papillomavirus E6 proteins with either MAML1 or E6AP clusters E6 proteins by structure, function, and evolutionary relatedness

Papillomavirus E6 proteins bind to LXXLL peptide motifs displayed on targeted cellular proteins. Alpha genus HPV E6 proteins associate with the cellular ubiquitin ligase E6AP (UBE3A), by binding to an LXXLL peptide (ELTLQELLGEE) displayed by E6AP, thereby stimulating E6AP ubiquitin ligase activity. Beta, Gamma, and Delta genera E6 proteins bind a similar LXXLL peptide (WMSDLDDLLGS) on the cellular transcriptional co-activator MAML1 and thereby repress Notch signaling. We expressed 45 different animal and human E6 proteins from diverse papillomavirus genera to ascertain the overall preference of E6 proteins for E6AP or MAML1. E6 proteins from all HPV genera except Alpha preferentially interacted with MAML1 over E6AP. Among animal papillomaviruses, E6 proteins from certain ungulate (SsPV1 from pigs) and cetacean (porpoises and dolphins) hosts functionally resembled Alpha genus HPV by binding and targeting the degradation of E6AP. Beta genus HPV E6 proteins functionally clustered with Delta, Pi, Tau, Gamma, Chi, Mu, Lambda, Iota, Dyokappa, Rho, and Dyolambda E6 proteins to bind and repress MAML1. None of the tested E6 proteins physically and functionally interacted with both MAML1 and E6AP, indicating an evolutionary split. Further, interaction of an E6 protein was insufficient to activate degradation of E6AP, indicating that E6 proteins that target E6AP co-evolved to separately acquire both binding and triggering of ubiquitin ligase activation. E6 proteins with similar biological function clustered together in phylogenetic trees and shared structural features. This suggests that the divergence of E6 proteins from either MAML1 or E6AP binding preference is a major event in papillomavirus evolution.

Mouse papillomavirus MmuPV1 infects oral mucosa and preferentially targets the base of the tongue

In 2010, a new mouse papillomavirus, MmuPV1, was discovered in a colony of NMRI- Foxn1(nu)/Foxn1(nu) athymic mice in India. This finding was significant because it was the first papillomavirus to be found in a laboratory mouse. In this paper we report successful infections of both dorsal and ventral surfaces of the rostral tongues of outbred athymic nude mice. We also report the observation that the base of the tongue, the area of the tongue often targeted by cancer-associated high-risk papillomavirus infections in humans, is especially susceptible to infection. A suitable animal model for the study of oral papillomavirus infections, co-infections, and cancers has long been sought. The work presented here suggests that such a model is now at hand.

A Century of Shope Papillomavirus in Museum Rabbit Specimens

Sylvilagus floridanus Papillomavirus (SfPV) causes growth of large horn-like tumors on rabbits. SfPV was described in cottontail rabbits (probably Sylvilagus floridanus) from Kansas and Iowa by Richard Shope in 1933, and detected in S. audubonii in 2011. It is known almost exclusively from the US Midwest. We explored the University of Kansas Natural History Museum for historical museum specimens infected with SfPV, using molecular techniques, to assess if additional wild species host SfPV, and whether SfPV occurs throughout the host range, or just in the Midwest. Secondary aims were to detect distinct strains, and evidence for strain spatio-temporal specificity. We found 20 of 1395 rabbits in the KU collection SfPV symptomatic. Three of 17 lagomorph species (S. nuttallii, and the two known hosts) were symptomatic, while Brachylagus, Lepus and eight additional Sylvilagus species were not. 13 symptomatic individuals were positive by molecular testing, including the first S. nuttallii detection. Prevalence of symptomatic individuals was significantly higher in Sylvilagus (1.8%) than Lepus. Half of these specimens came from Kansas, though new molecular detections were obtained from Jalisco—Mexico’s first—and Nebraska, Nevada, New Mexico, and Texas, USA. We document the oldest lab-confirmed case (Kansas, 1915), pre-dating Shope’s first case. SfPV amplification was possible from 63.2% of symptomatic museum specimens. Using multiple methodologies, rolling circle amplification and, multiple isothermal displacement amplification in addition to PCR, greatly improved detection rates. Short sequences were obtained from six individuals for two genes. L1 gene sequences were identical to all previously detected sequences; E7 gene sequences, were more variable, yielding five distinct SfPV1 strains that differing by less than 2% from strains circulating in the Midwest and Mexico, between 1915 and 2005. Our results do not clarify whether strains are host species specific, though they are consistent with SfPV specificity to genus Sylvilagus.

A novel pre-clinical murine model to study the life cycle and progression of cervical and anal papillomavirus infections

Background

Papillomavirus disease and associated cancers remain a significant health burden in much of the world. The current protective vaccines, Gardasil and Cervarix, are expensive and not readily available to the underprivileged. In addition, the vaccines have not gained wide acceptance in the United States nor do they provide therapeutic value. Papillomaviruses are strictly species specific and thus human viruses cannot be studied in an animal host. An appropriate model for mucosal disease has long been sought. We chose to investigate whether the newly discovered mouse papillomavirus, MmuPV1, could infect mucosal tissues in Foxn1^nu/Foxn1^nu mice.

Methods

The vaginal and anal canals of Foxn1^nu/Foxn1^nu mice were gently abraded using Nonoxynol-9 and “Doctor’s BrushPicks” and MmuPV1 was delivered into the vaginal tract or the anal canal.

Results

Productive vaginal, cervical and anal infections developed in all mice. Vaginal/cervical infections could be monitored by vaginal lavage. Dysplasias were evident in all animals.

Conclusions

Anogenital tissues of a common laboratory mouse can be infected with a papillomavirus unique to that animal. This observation will pave the way for fundamental virological and immunological studies that have been challenging to carry out heretofore due to lack of a suitable model system.

Protective vaccination against papillomavirus-induced skin tumors under immunocompetent and immunosuppressive conditions: a preclinical study using a natural outbred animal model

Certain cutaneous human papillomaviruses (HPVs), which are ubiquitous and acquired early during childhood, can cause a variety of skin tumors and are likely involved in the development of non-melanoma skin cancer, especially in immunosuppressed patients. Hence, the burden of these clinical manifestations demands for a prophylactic approach. To evaluate whether protective efficacy of a vaccine is potentially translatable to patients, we used the rodent Mastomys coucha that is naturally infected with Mastomys natalensis papillomavirus (MnPV). This skin type papillomavirus induces not only benign skin tumours, such as papillomas and keratoacanthomas, but also squamous cell carcinomas, thereby allowing a straightforward read-out for successful vaccination in a small immunocompetent laboratory animal. Here, we examined the efficacy of a virus-like particle (VLP)-based vaccine on either previously or newly established infections. VLPs raise a strong and long-lasting neutralizing antibody response that confers protection even under systemic long-term cyclosporine A treatment. Remarkably, the vaccine completely prevents the appearance of benign as well as malignant skin tumors. Protection involves the maintenance of a low viral load in the skin by an antibody-dependent prevention of virus spread. Our results provide first evidence that VLPs elicit an effective immune response in the skin under immunocompetent and immunosuppressed conditions in an outbred animal model, irrespective of the infection status at the time of vaccination. These findings provide the basis for the clinical development of potent vaccination strategies against cutaneous HPV infections and HPV-induced tumors, especially in patients awaiting organ transplantation.

Organ transplant recipients (OTR) frequently suffer from fulminant warts that are induced by cutaneous human papillomaviruses (HPV). Moreover, some skin HPV types may also be involved in the development of non-melanoma skin cancer. Mimicking the situation of immunosuppressed OTR who acquire cutaneous HPV infections already in childhood, we explored the efficacy of a vaccine in infected animals that additionally underwent immunosuppression. We demonstrate for the first time the success of a vaccine against a skin papillomavirus in a natural outbred animal system, which completely prevents both benign and malignant skin tumor formation even under immunosuppressed conditions. Hence, our study provides the basis for clinical development of a vaccine against cutaneous HPV infections, which may be particularly useful in transplant recipients.

Immunosuppression facilitates the reactivation of latent papillomavirus infections

At mucosal sites, papillomavirus genomes can persist in the epithelial basal layer following immune-mediated regression. Subsequent T-cell depletion stimulates a 3- to 5-log increase in the viral copy number, to levels associated with productive infection. Reappearance of microlesions was rare within the short time frame of our experiments but was observed in one instance. Our studies provide direct evidence that immunosuppression can trigger the reactivation of latent papillomavirus genomes, as previously proposed in humans.

Latent papillomavirus infections and their regulation

Model systems show that papillomavirus DNA can persist after lesion-regression, and be maintained in a subset of epithelial basal cells. These are very likely long-lived 'stem-cells' or 'stem-like cells', with latency arising via at least two distinct mechanisms. The first involves low-titre virus infection and the retention of viral DNA at levels that are too low to allow life-cycle completion. The second involves lesion-formation, and clearance by the adaptive immune system, followed by persistence with low-level viral gene expression, and possible reactivation upon immune depletion. Mechanical irritation, inflammation and other extracellular influences affect viral copy number in the latently infected cell, and may predispose to lesion-reappearance. Reactivation may account for the recurrence of 'apparently cleared' cervical lesions caused by high-risk types, the appearance of Beta HPV-lesions following immunosuppression, and the development of recurrent respiratory papillomatosis in afflicted children.

Animal papillomaviruses

We provide an overview of the host range, taxonomic classification and genomic diversity of animal papillomaviruses. The complete genomes of 112 non-human papillomavirus types, recovered from 54 different host species, are currently available in GenBank. The recent characterizations of reptilian papillomaviruses extend the host range of the Papillomaviridae to include all amniotes. Although the genetically diverse papillomaviruses have a highly conserved genomic lay-out, deviations from this prototypic genome organization are observed in several animal papillomaviruses, and only the core ORFs E1, E2, L2 and L1 are present in all characterized papillomavirus genomes. The discovery of papilloma-polyoma hybrids BPCV1 and BPCV2, containing a papillomaviral late region but an early region encoding typical polyomaviral nonstructural proteins, and the detection of recombination breakpoints between the early and late coding regions of cetacean papillomaviruses, could indicate that early and late gene cassettes of papillomaviruses are relatively independent entities that can be interchanged by recombination.

Viral infections of rabbits

Viral diseases of rabbits have been used historically to study oncogenesis (e.g. rabbit fibroma virus, cottontail rabbit papillomavirus) and biologically to control feral rabbit populations (e.g. myxoma virus). However, clinicians seeing pet rabbits in North America infrequently encounter viral diseases although myxomatosis may be seen occasionally. The situation is different in Europe and Australia, where myxomatosis and rabbit hemorrhagic disease are endemic. Advances in epidemiology and virology have led to detection of other lapine viruses that are now recognized as agents of emerging infectious diseases. Rabbit caliciviruses, related to rabbit hemorrhagic disease, are generally avirulent, but lethal variants are being identified in Europe and North America. Enteric viruses including lapine rotavirus, rabbit enteric coronavirus and rabbit astrovirus are being acknowledged as contributors to the multifactorial enteritis complex of juvenile rabbits. Three avirulent leporid herpesviruses are found in domestic rabbits. A fourth highly pathogenic virus designated leporid herpesvirus 4 has been described in Canada and Alaska. This review considers viruses affecting rabbits by their clinical significance. Viruses of major and minor clinical significance are described, and viruses of laboratory significance are mentioned.

The biology of papillomavirus latency

The presence of viral DNA in the absence of disease has suggested that papillomaviruses, like many other viruses, can exist as latent infections in the skin or other epithelial sites. In animal models, where detailed investigation has been carried out, papillomavirus DNA can be found at sites of previous infection following immune regression, with the site of latent infection being the epithelial basal layer. Such studies suggest that immune surveillance can restrict viral gene expression in the basal and parabasal layers without efficiently suppressing viral genome replication, most probably through the action of memory T-cells in the skin or dermis. Although gradual papillomavirus genome loss appears to occur over time at latent sites, immunosuppression can arrest this, and can lead to an elevation in viral genome copy number in experimental systems. In addition to immune-mediated latency, it appears that a similar situation can be achieved following infection at low virus titres and/or infection at epithelial sites where the virus life cycle is not properly supported. Such silent of asymptomatic infections do not necessarily involve the host immune system and may be controlled by different mechanisms. It appears that virus reactivation can be triggered by mechanical irritation, wounding or by UV irradiation which changes the local environment. Although the duration of papillomavirus latency in humans is not yet known, it is likely that some of the basic principles will resemble those elucidated in these model systems, and that persistence in the absence of disease may be the default outcome for at least some period of time following regression.

Evolution of linear motifs within the papillomavirus E7 oncoprotein

Many protein functions can be traced to linear sequence motifs of less than five residues, which are often found within intrinsically disordered domains. In spite of their prevalence, their role in protein evolution is only beginning to be understood. The study of papillomaviruses has provided many insights on the evolution of protein structure and function. We have chosen the papillomavirus E7 oncoprotein as a model system for the evolution of functional linear motifs. The multiple functions of E7 proteins from paradigmatic papillomavirus types can be explained to a large extent in terms of five linear motifs within the intrinsically disordered N-terminal domain and two linear motifs within the globular homodimeric C-terminal domain. We examined the motif inventory of E7 proteins from over 200 known papillomavirus types and found that the motifs reported for paradigmatic papillomavirus types are absent from many uncharacterized E7 proteins. Several motif pairs occur more often than expected, suggesting that linear motifs may evolve and function in a cooperative manner. The E7 linear motifs have appeared or disappeared multiple times during papillomavirus evolution, confirming the evolutionary plasticity of short functional sequences. Four of the motifs appeared several times during papillomavirus evolution, providing direct evidence for convergent evolution. Interestingly, the evolution pattern of a motif is independent of its location in a globular or disordered domain. The correlation between the presence of some motifs and virus host specificity and tissue tropism suggests that linear motifs play a role in the adaptive evolution of papillomaviruses.

Persistence of viral DNA in the epithelial basal layer suggests a model for papillomavirus latency following immune regression

Rabbit oral papillomavirus (ROPV) causes benign and spontaneously regressing oral lesions in rabbits, and is a useful model of disease associated with low-risk human papillomavirus types. Here we have adapted the ROPV system to study papillomavirus latency. Following lesion regression, ROPV DNA persists at the majority of regressed sites at levels substantially lower than those found in productive papillomas. Spliced viral transcripts were also detected. ROPV persistence in the absence of disease could be demonstrated for a year following infection and lesion-regression. This was not associated with completion of the virus life-cycle or new virion production, indicating that ROPV persists in a latent state. Using novel laser capture microdissection techniques, we could show that the site of latency is a subset of basal epithelial cells at sites of previous experimental infection. We hypothesize that these cells are epithelial stem cells and that reactivation of latency may be a source of recurrent disease.

Classification of papillomaviruses (PVs) based on 189 PV types and proposal of taxonomic amendments

We present an expansion of the classification of the family Papillomaviridae, which now contains 29 genera formed by 189 papillomavirus (PV) types isolated from humans (120 types), non-human mammals, birds and reptiles (64, 3 and 2 types, respectively). To accommodate the number of PV genera exceeding the Greek alphabet, the prefix "dyo" is used, continuing after the Omega-PVs with Dyodelta-PVs. The current set of human PVs is contained within five genera, whereas mammalian, avian and reptile PVs are contained within 20, 3 and 1 genera, respectively. We propose standardizations to the names of a number of animal PVs. As prerequisite for a coherent nomenclature of animal PVs, we propose founding a reference center for animal PVs. We discuss that based on emerging species concepts derived from genome sequences, PV types could be promoted to the taxonomic level of species, but we do not recommend implementing this change at the current time.

Prophylaktische und therapeutische HPV-Impfstoffe

Papilloma viruses (PV) have been known to cause benign and malignant tumors in animals for more than 100 years. It took over 20 years to win general acceptance for their causative role in anogenital carcinomas in humans in particular in cervial carcinoma. Extensive research has led to the development of a prophylactic vaccine which is now commercially available. It remains to be investigated if HPV-specific therapeutic vaccines can be developed.

Protective cell-mediated immunity by DNA vaccination against Papillomavirus L1 capsid protein in the Cottontail Rabbit Papillomavirus model

Papillomavirus major capsid protein L1 has successfully stimulated protective immunity against virus infection by induction of neutralizing antibodies in animal models and in clinical trials. However, the potential impact of L1-induced protective cell-mediated immune (CMI) responses is difficult to measure in vivo because of the coincidence of anti-L1 antibody. In this study, we tested the hypothesis that L1 could activate CMI, using the Cottontail Rabbit Papillomavirus (CRPV)-rabbit model. A unique property of this model is that infections can be initiated with viral DNA, thus bypassing all contributions to protection via neutralizing anti-L1 antibody. DNA vaccines containing either CRPV L1, or subfragments of L1 (amino-terminal two-thirds of L1 [L1N] and the carboxylterminal two-thirds of L1 [L1C]), were delivered intracutaneously into rabbits, using a gene gun. After three booster immunizations, the rabbits were challenged with several viral DNA constructs: wild-type CRPV, CRPV L1ATGko (an L1 ATG knockout mutation), and CRPV-ROPV hybrid (CRPV with a replacement L1 from Rabbit Oral Papillomavirus). Challenge of L1 DNA-vaccinated rabbits with wild-type CRPV resulted in significantly fewer papillomas when compared with challenge with CRPV L1ATGko DNA. Significantly smaller papillomas were found in CRPV L1-, L1N-, and L1C-vaccinated rabbits. In addition, rabbits vaccinated with either L1 or L1N grew significantly fewer and smaller papillomas when challenged with CRPV-ROPV hybrid DNA. Therefore, CRPV L1 DNA vaccination induced CMI responses to CRPV DNA infections that can contribute to protective immunity. Cross-protective immunity against CRPV L1 and ROPV L1 was elicited in these CRPV L1- and subfragment-vaccinated rabbits.

Molecular biology of human papillomavirus infection and cervical cancer

HPVs (human papillomaviruses) infect epithelial cells and cause a variety of lesions ranging from common warts/verrucas to cervical neoplasia and cancer. Over 100 different HPV types have been identified so far, with a subset of these being classified as high risk. High-risk HPV DNA is found in almost all cervical cancers (>99.7%), with HPV16 being the most prevalent type in both low-grade disease and cervical neoplasia. Productive infection by high-risk HPV types is manifest as cervical flat warts or condyloma that shed infectious virions from their surface. Viral genomes are maintained as episomes in the basal layer, with viral gene expression being tightly controlled as the infected cells move towards the epithelial surface. The pattern of viral gene expression in low-grade cervical lesions resembles that seen in productive warts caused by other HPV types. High-grade neoplasia represents an abortive infection in which viral gene expression becomes deregulated, and the normal life cycle of the virus cannot be completed. Most cervical cancers arise within the cervical transformation zone at the squamous/columnar junction, and it has been suggested that this is a site where productive infection may be inefficiently supported. The high-risk E6 and E7 proteins drive cell proliferation through their association with PDZ domain proteins and Rb (retinoblastoma), and contribute to neoplastic progression, whereas E6-mediated p53 degradation prevents the normal repair of chance mutations in the cellular genome. Cancers usually arise in individuals who fail to resolve their infection and who retain oncogene expression for years or decades. In most individuals, immune regression eventually leads to clearance of the virus, or to its maintenance in a latent or asymptomatic state in the basal cells.

Protection of rabbits against cutaneous papillomavirus infection using recombinant tobacco mosaic virus containing L2 capsid epitopes

Cottontail rabbit papillomavirus (CRPV) and rabbit oral papillomavirus (ROPV) represent distantly related, cutaneous and mucosal tissue tropic papillomaviruses respectively that can infect the same host. These two viruses were used to test the effectiveness of an L2 peptide-based vaccine (aa 94-122) that was delivered on the surface of recombinant tobacco mosaic virus (rTMV) particles. Groups of NZW rabbits received combinations of CRPVL2, ROPVL2 and CRPV+ROPVL2 rTMV vaccines, and were then challenged with infectious CRPV and ROPV. The rabbits developed antibodies that reacted to whole L2 protein and these sera were able to neutralize CRPV pseudovirions at half-maximal titers that were between 50 and 500. Rabbits receiving the CRPV L2 vaccine alone or in combination with ROPV L2 vaccines were completely protected against CRPV infections. Those rabbits vaccinated with the ROPV L2 vaccines showed a weak response in some rabbits against CRPV infection. These studies demonstrate that L2-based vaccines provide strong protection against experimental papillomavirus infection that is most likely based upon the induction of virus-neutralizing antibody. Notably, we observed some limited cross-protection induced by the L2 sequences tested in these vaccines. Finally, the study demonstrated that rTMV were excellent agents for the induction of strong protection in a pre-clinical disease model of papillomavirus infection.

The papillomavirus life cycle

Papillomaviruses infect epithelial cells, and depend on epithelial differentiation for completion of their life cycle. The expression of viral gene products is closely regulated as the infected basal cell migrates towards the epithelial surface. Expression of E6 and E7 in the lower epithelial layers drives cells into S-phase, which creates an environment that is conducive for viral genome replication and cell proliferation. Genome amplification, which is necessary for the production of infectious virions, is prevented until the levels of viral replication proteins rise, and depends on the co-expression of several viral proteins. Virus capsid proteins are expressed in cells that also express E4 as the infected cell enters the upper epithelial layers. The timing of these events varies depending on the infecting papillomavirus, and in the case of the high-risk human papillomaviruses (HPVs), on the severity of neoplasia. Viruses that are evolutionarily related, such as HPV1 and canine oral papillomavirus (COPV), generally organize their productive cycle in a similar way, despite infecting different hosts and epithelial sites. In some instances, such as following HPV16 infection of the cervix or cottontail rabbit papillomavirus (CRPV) infection of domestic rabbits, papillomaviruses can undergo abortive infections in which the productive cycle of the virus is not completed. As with other DNA tumour viruses, such abortive infections can predispose to cancer.

Characterization of three rabbit oral papillomavirus oncogenes

Rabbit oral papillomavirus (ROPV) induces warts in mucosal tissues, and represents a useful model for understanding host-virus interactions that are reflected in mucosal/HPV infections. ROPV induces benign papillomas that regress in 100% of infected rabbits. We previously reported the complete genome sequence of ROPV. However, the oncogenic potential of this virus is unknown because of immunologically mediated regression. The purpose of this study was to characterize the transforming proteins of E6, E7, and E8 genes of ROPV. E6, E7, and E8 genes of ROPV were cloned into the expression vector PCR3. Two hybrid CRPV-ROPV E6 genes were also constructed and tested together with the three wild-type ROPV genes. Each construct was transfected into NIH3T3 cells and stable transfected cell lines were established. Transforming properties of ROPV E6, E7, and E8 were tested via anchorage-independent growth of cells in agar plates and tumor growth in athymic mice. Cells with ROPV E6, E7, or E8 formed colonies in agar and tumors in athymic mice. These observations suggest that ROPV E6, E7, and E8 are oncogenic.

GM-CSF enhances protective immunity to cottontail rabbit papillomavirus E8 genetic vaccination in rabbits

We have reported previously that cottontail rabbit papillomavirus (CRPV) E8 gene immunization induced strong protection against virus challenge. In this study, we primed E8 gene vaccination with mouse granulocyte-macrophage colony-stimulating factor (mGM-CSF), a cytokine that induces differentiation and local recruitment of professional antigen-presenting cells. EIII/JC inbred rabbits were divided into four groups receiving vaccinations with the following constructs: mGM-CSF plus E8, mGM-CSF only, E8 only and vector only. After three immunizations at intervals of 3 weeks, rabbits were challenged with viral DNA at six scarified sites. Papillomas grew on all vaccinated rabbits 4 weeks after inoculation. At week 5, papillomas on four rabbits of mGM-CSF plus E8 and one of E8 only rabbits began to regress. At week 11, all the papillomas on rabbits in the GM-CSF plus E8 vaccination group regressed (regression rate = 100%); regression rates of the mGM-CSF only and E8 only vaccination groups were 50 and 25%, respectively. All papillomas on the vector immunized rabbits remained persistent until the end of the experiment (0%). Antibodies to mGM-CSF were detected in rabbit serum by Western blot. Rabbits vaccinated with E8 plus mGM-CSF or E8 only group had positive Delayed-type hypersensitivity (DTH) skin test to different E8 peptides. These results demonstrated that mGM-CSF could enhance the effects of E8 immunization in rabbits to CRPV infection through cell-mediated immune responses.

Protective immunity to rabbit oral and cutaneous papillomaviruses by immunization with short peptides of L2, the minor capsid protein

The papillomavirus minor capsid protein, L2, has been shown to exhibit immunogenicity, whereby a variety of B-cell epitopes, predominantly in the amino terminus of L2, have been deduced. However, immunity to L2 in vivo has not been examined extensively. Notably, a common neutralization epitope for human papillomavirus (HPV) types 6 and 16 was mapped to amino acids (aa) 108 to 120. The objectives of this study were to derive antisera from rabbits using the corresponding sequences from rabbit viruses and to assess the ability of these peptides to protect against infection. Synthetic peptides consisting of two overlapping sequences each in the region of aa 94 to 122 of the rabbit oral (ROPV) and cottontail rabbit (CRPV) papillomaviruses were used to immunize rabbits. Rabbits were then infected with both ROPV and CRPV and monitored for the development of oral and cutaneous papillomas, respectively. Serum derived from rabbits immunized with either of the two peptides was shown to (i) react to purified L2 from the cognate virus, (ii) specifically recognize L2 within virus-infected cells, and (iii) neutralize virus in vitro. Following viral challenge, cutaneous papilloma growth was completely absent in rabbits immunized with either CRPV peptide. Likewise, ROPV peptide-immunized rabbits were protected from oral papillomatosis. Challenge of CRPV peptide-immune rabbits with the viral genome resulted in efficient papilloma growth, suggesting a neutralizing antibody-mediated mechanism of protection. These results afford in vivo evidence for the immunogenicity provided by a distinct region of L2 and further support previous evidence for the ability of this region to elicit antiviral immunity.

Life cycle heterogeneity in animal models of human papillomavirus-associated disease

Animal papillomaviruses are widely used as models to study papillomavirus infection in humans despite differences in genome organization and tissue tropism. Here, we have investigated the extent to which animal models of papillomavirus infection resemble human disease by comparing the life cycles of 10 different papillomavirus types. Three phases in the life cycles of all viruses were apparent using antibodies that distinguish between early events, the onset of viral genome amplification, and the expression of capsid proteins. The initiation of these phases follows a highly ordered pattern that appears important for the production of virus particles. The viruses examined included canine oral papillomavirus, rabbit oral papillomavirus (ROPV), cottontail rabbit papillomavirus (CRPV), bovine papillomavirus type 1, and human papillomavirus types 1, 2, 11, and 16. Each papillomavirus type showed a distinctive gene expression pattern that could be explained in part by differences in tissue tropism, transmission route, and persistence. As the timing of life cycle events affects the accessibility of viral antigens to the immune system, the ideal model system should resemble human mucosal infection if vaccine design is to be effective. Of the model systems examined here, only ROPV had a tissue tropism and a life cycle organization that resembled those of the human mucosal types. ROPV appears most appropriate for studies of the life cycles of mucosal papillomavirus types and for the development of prophylactic vaccines. The persistence of abortive infections caused by CRPV offers advantages for the development of therapeutic vaccines.

Intracutaneous DNA vaccination with the E8 gene of cottontail rabbit papillomavirus induces protective immunity against virus challenge in rabbits

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.

Polynucleotide viral vaccines: codon optimisation and ubiquitin conjugation enhances prophylactic and therapeutic efficacy

Papillomavirus infection is a major antecedent of anogenital malignancy. We have previously established that the L1 and L2 capsid genes of papillomavirus have suboptimal codon usage for expression in mammalian cells. We now show that the lack of immunogenicity of polynucleotide vaccines based on the L1 gene can be overcome with codon modified L1, which induces strong immune responses, including conformational virus neutralising antibody and delayed type hypersensitivity. Conjugation of a ubiquitin gene to a hybrid gene incorporating L1 and the E7 non-structural papillomavirus protein improved E7 specific CTL responses, and induced protection against an E7 expressing tumour, but induced little neutralising antibody. However, a mixture of ubiquitin conjugated and non-ubiquitin conjugated polynucleotides induced virus neutralising antibody and E7 specific CD8 T cells. An optimal combined prophylactic/therapeutic viral vaccine might therefore comprise ubiquitin conjugated and non-ubiquitinated genes, to induce prophylactic neutralising antibody and therapeutic cell mediated immune responses.