FLT3L governs the development of partially overlapping hematopoietic lineages in humans and mice.

FMS-related tyrosine kinase 3 ligand (FLT3L), encoded by FLT3LG, is a hematopoietic factor essential for the development of natural killer (NK) cells, B cells, and dendritic cells (DCs) in mice. We describe three humans homozygous for a loss-of-function FLT3LG variant with a history of various recurrent infections, including severe cutaneous warts. The patients' bone marrow (BM) was hypoplastic, with low levels of hematopoietic progenitors, particularly myeloid and B cell precursors. Counts of B cells, monocytes, and DCs were low in the patients' blood, whereas the other blood subsets, including NK cells, were affected only moderately, if at all. The patients had normal counts of Langerhans cells (LCs) and dermal macrophages in the skin but lacked dermal DCs. Thus, FLT3L is required for B cell and DC development in mice and humans. However, unlike its murine counterpart, human FLT3L is required for the development of monocytes but not NK cells.

Humans with inherited T cell CD28 deficiency are susceptible to skin papillomaviruses but are otherwise healthy.

We study a patient with the human papilloma virus (HPV)-2-driven "tree-man" phenotype and two relatives with unusually severe HPV4-driven warts. The giant horns form an HPV-2-driven multifocal benign epithelial tumor overexpressing viral oncogenes in the epidermis basal layer. The patients are unexpectedly homozygous for a private CD28 variant. They have no detectable CD28 on their T cells, with the exception of a small contingent of revertant memory CD4+ T cells. T cell development is barely affected, and T cells respond to CD3 and CD2, but not CD28, costimulation. Although the patients do not display HPV-2- and HPV-4-reactive CD4+ T cells in vitro, they make antibodies specific for both viruses in vivo. CD28-deficient mice are susceptible to cutaneous infections with the mouse papillomavirus MmuPV1. The control of HPV-2 and HPV-4 in keratinocytes is dependent on the T cell CD28 co-activation pathway. Surprisingly, human CD28-dependent T cell responses are largely redundant for protective immunity.

Passive Immunization with a Single Monoclonal Neutralizing Antibody Protects against Cutaneous and Mucosal Mouse Papillomavirus Infections.

We have established a mouse papillomavirus (MmuPV1) model that induces both cutaneous and mucosal infections and cancers. In the current study, we use this model to test our hypothesis that passive immunization using a single neutralizing monoclonal antibody can protect both cutaneous and mucosal sites at different time points after viral inoculation. We conducted a series of experiments involving the administration of either a neutralizing monoclonal antibody, MPV.A4, or control monoclonal antibodies to both outbred and inbred athymic mice. Three clinically relevant mucosal sites (lower genital tract for females and anus and tongue for both males and females) and two cutaneous sites (muzzle and tail) were tested. At the termination of the experiments, all tested tissues were harvested for virological analyses. Significantly lower levels of viral signals were detected in the MPV.A4-treated female mice up to 6 h post-viral inoculation compared to those in the isotype control. Interestingly, males displayed partial protection when they received MPV.A4 at the time of viral inoculation, even though they were completely protected when receiving MPV.A4 at 24 h before viral inoculation. We detected MPV.A4 in the blood starting at 1 h and up to 8 weeks postadministration in some mice. Parallel to these in vivo studies, we conducted in vitro neutralization using a mouse keratinocyte cell line and observed complete neutralization up to 8 h post-viral inoculation. Thus, passive immunization with a monoclonal neutralizing antibody can protect against papillomavirus infection at both cutaneous and mucosal sites and is time dependent. IMPORTANCE This is the first study testing a single monoclonal neutralizing antibody (MPV.A4) by passive immunization against papillomavirus infections at both cutaneous and mucosal sites in the same host in the mouse papillomavirus model. We demonstrated that MPV.A4 administered before viral inoculation can protect both male and female athymic mice against MmuPV1 infections at cutaneous and mucosal sites. MPV.A4 also offers partial protection at 6 h post-viral inoculation in female mice. MPV.A4 can be detected in the blood from 1 h to 8 weeks after intraperitoneal (i.p.) injection. Interestingly, males were only partially protected when they received MPV.A4 at the time of viral inoculation. The failed protection in males was due to the absence of neutralizing MPV.A4 at the infected sites. Our findings suggest passive immunization with a single monoclonal neutralizing antibody can protect against diverse papillomavirus infections in a time-dependent manner in mice.

Mouse papillomavirus infections spread to cutaneous sites with progression to malignancy.

We report secondary cutaneous infections in the mouse papillomavirus (MmuPV1)/mouse model. Our previous study demonstrated that cutaneous MmuPV1 infection could spread to mucosal sites. Recently, we observed that mucosal infections could also spread to various cutaneous sites including the back, tail, muzzle and mammary tissues. The secondary site lesions were positive for viral DNA, viral capsid protein and viral particles as determined by in situ hybridization, immunohistochemistry and transmission electron microscopy analyses, respectively. We also demonstrated differential viral production and tumour growth at different secondarily infected skin sites. For example, fewer viral particles were detected in the least susceptible back tissues when compared with those in the infected muzzle and tail, although similar amounts of viral DNA were detected. Follow-up studies demonstrated that significantly lower amounts of viral DNA were packaged in the back lesions. Lavages harvested from the oral cavity and lower genital tracts were equally infectious at both cutaneous and mucosal sites, supporting the broad tissue tropism of this papillomavirus. Importantly, two secondary skin lesions on the forearms of two mice displayed a malignant phenotype at about 9.5 months post-primary infection. Therefore, MmuPV1 induces not only dysplasia at mucosal sites such as the vagina, anus and oral cavity but also skin carcinoma at cutaneous sites. These findings demonstrate that MmuPV1 mucosal infection can be spread to cutaneous sites and suggest that the model could serve a useful role in the study of the viral life cycle and pathogenesis of papillomavirus.

Broad Cross-Protection Is Induced in Preclinical Models by a Human Papillomavirus Vaccine Composed of L1/L2 Chimeric Virus-Like Particles.

UNLABELLED: At least 15 high-risk human papillomaviruses (HPVs) are linked to anogenital preneoplastic lesions and cancer. Currently, there are three licensed prophylactic HPV vaccines based on virus-like particles (VLPs) of the L1 major capsid protein from HPV-2, -4, or -9, including the AS04-adjuvanted HPV-16/18 L1 vaccine. The L2 minor capsid protein contains HPV-neutralizing epitopes that are well conserved across numerous high-risk HPVs. Therefore, the objective of our study was to assess the capacity to broaden vaccine-mediated protection using AS04-adjuvanted vaccines based on VLP chimeras of L1 with one or two L2 epitopes. Several chimeric VLPs were constructed by inserting L2 epitopes within the DE loop and/or C terminus of L1. Based on the shape, yield, size, and immunogenicity, one of seven chimeras was selected for further evaluation in mouse and rabbit challenge models. The chimeric VLP consisted of HPV-18 L1 with insertions of HPV-33 L2 (amino acid residues 17 to 36; L1 DE loop) and HPV-58 L2 (amino acid residues 56 to 75; L1 C terminus). This chimeric L1/L2 VLP vaccine induced persistent immune responses and protected against all of the different HPVs evaluated (HPV-6, -11, -16, -31, -35, -39, -45, -58, and -59 as pseudovirions or quasivirions) in both mouse and rabbit challenge models. The degree and breadth of protection in the rabbit were further enhanced when the chimeric L1/L2 VLP was formulated with the L1 VLPs from the HPV-16/18 L1 vaccine. Therefore, the novel HPV-18 L1/L2 chimeric VLP (alone or in combination with HPV-16 and HPV-18 L1 VLPs) formulated with AS04 has the potential to provide broad protective efficacy in human subjects. IMPORTANCE: From evaluations in human papillomavirus (HPV) protection models in rabbits and mice, our study has identified a prophylactic vaccine with the potential to target a wide range of HPVs linked to anogenital cancer. The three currently licensed vaccines contain virus-like particles (VLPs) of the L1 major capsid protein from two, four, or nine different HPVs. Rather than increasing the diversity of L1 VLPs, this vaccine contains VLPs based on a recombinant chimera of two highly conserved neutralizing epitopes from the L2 capsid protein inserted into L1. Our study demonstrated that the chimeric L1/L2 VLP is an effective vehicle for displaying two different L2 epitopes and can be used in a quantity equivalent to what is used in the licensed vaccines. Hence, using the chimeric L1/L2 VLP may be a more cost-effective approach for vaccine formulation than adding different VLPs for each HPV.

Tracking vaginal, anal and oral infection in a mouse papillomavirus infection model.

Noninvasive and practical techniques to longitudinally track viral infection are sought after in clinical practice. We report a proof-of-principle study to monitor the viral DNA copy number using a newly established mouse papillomavirus (MmuPV1) mucosal infection model. We hypothesized that viral presence could be identified and quantified by collecting lavage samples from cervicovaginal, anal and oral sites. Nude mice infected at these sites with infectious MmuPV1 were tracked for up to 23 weeks starting at 6 weeks post-infection. Viral DNA copy number was determined by SYBR Green Q-PCR analysis. In addition, we tracked viral DNA load through three complete oestrous cycles to pinpoint whether there was a correlation between the DNA load and the four stages of the oestrous cycle. Our results showed that high viral DNA copy number was reproducibly detected from both anal and cervicovaginal lavage samples. The infection and disease progression were further confirmed by histology, cytology, in situ hybridization, immunohistochemistry and transmission electron microscopy. Interestingly, the viral copy number fluctuated over the oestrous cycle, with the highest level at the oestrus stage, implying that multiple sampling might be necessary to provide a reliable diagnosis. Virus DNA was detected in oral lavage samples at a later time after infection. Lower viral DNA load was found in oral samples when compared with those in anal and vaginal tracts. To our knowledge, our study is the first in vivo study to sequentially monitor papillomavirus infection from mucosal anal, oral and vaginal tracts in a preclinical model.

Antibody detection in tear samples as a surrogate to monitor host immunity against papillomavirus infections in vaccinated and naturally infected hosts.

Monitoring serum antibodies against natural infections or after immunizations has been a standard clinical diagnostic procedure. However, collecting blood samples requires trained personnel, and may cause discomfort and increase the risk of complications. In this study, we investigated whether tear samples could serve as a surrogate for serum samples to measure specific antibodies. A widely used preclinical cottontail rabbit papillomavirus (CRPV)/rabbit model has been a surrogate model for high-risk human papillomavirus (HPV) infections. New Zealand white rabbits, either naturally infected with CRPV or immunized with two clinically available HPV vaccines (Gardasil and Cervarix), were examined for antibody generation in both tear and serum samples. We demonstrated that antibodies were detectable in tears from both naturally infected as well as vaccinated animals. Overall, the antibody levels in tears were ~10-fold lower than those from the corresponding serum samples, but background noise was lower in tear samples. The isotypes of antibodies in tears were predominantly IgA and IgG. These findings showed clearly that tears could be a surrogate for serum samples for monitoring antibody responses. As collecting tears causes no discomfort and poses no risk to patients, it represents a novel and promising method for monitoring future HPV epidemiological studies as well as for use in clinical practice.

Secondary infections, expanded tissue tropism, and evidence for malignant potential in immunocompromised mice infected with Mus musculus papillomavirus 1 DNA and virus.

Papillomavirus disease poses a special challenge to people with compromised immune systems. Appropriate models to study infections in these individuals are lacking. We report here the development of a model that will help to address these deficiencies. The MmuPV1 genome was synthesized and used successfully to produce virus from DNA infections in immunocompromised mice. In these early studies, we have demonstrated both primary and secondary infections, expanded tissue tropism, and extensive dysplasia.

Gender Difference in DNA Damage Induced by the Environmental Carcinogen Dibenzo[def,p]chrysene Individually and in Combination with Mouse Papillomavirus Infection in the Mouse Oral Cavity.

Tobacco smoking and human papillomavirus infection are established etiological agents in the development of head and neck squamous cell carcinoma (HNSCC). The incidence and mortality of HNSCC are higher in men than women. To provide biochemical basis for sex differences, we tested the hypothesis that carcinogen treatment using dibenzo[def,p]chrysene, which is an environmental pollutant and tobacco smoke constituent, in the absence or presence of the mouse papillomavirus infection results in significantly higher levels of DNA damage in the oral cavity in male than in female mice. However, the results of the present investigation do not support our hypothesis since we found that females were more susceptible to carcinogen-induced covalent DNA damage than males independent of the viral infection. Since DNA damage represents only a single-step in the carcinogenesis process, additional factors may contribute to sex differences in humans.

Immune Responses in Oral Papillomavirus Clearance in the MmuPV1 Mouse Model.

Human papillomavirus (HPV)-induced oropharyngeal cancer now exceeds HPV-induced cervical cancer, with a noticeable sex bias. Although it is well established that women have a more proficient immune system, it remains unclear whether immune control of oral papillomavirus infections differs between sexes. In the current study, we use genetically modified mice to target CCR2 and Stat1 pathways, with the aim of investigating the role of both innate and adaptive immune responses in clearing oral papillomavirus, using our established papillomavirus (MmuPV1) infection model. Persistent oral MmuPV1 infection was detected in Rag1ko mice with T and B cell deficiencies. Meanwhile, other tested mice were susceptible to MmuPV1 infections but were able to clear the virus. We found sex differences in key myeloid cells, including macrophages, neutrophils, and dendritic cells in the infected tongues of wild type and Stat1ko mice but these differences were not observed in CCR2ko mice. Intriguingly, we also observed a sex difference in anti-MmuPV1 E4 antibody levels, especially for two IgG isotypes: IgG2b and IgG3. However, we found comparable numbers of interferon-gamma-producing CD8 T cells stimulated by E6 and E7 in both sexes. These findings suggest that males and females may use different components of innate and adaptive immune responses to control papillomavirus infections in the MmuPV1 mouse model. The observed sex difference in immune responses, especially in myeloid cells including dendritic cell (DC) subsets, may have potential diagnostic and prognostic values for HPV-associated oropharyngeal cancer.

Depo Medroxyprogesterone (DMPA) Promotes Papillomavirus Infections but Does Not Accelerate Disease Progression in the Anogenital Tract of a Mouse Model.

Contraceptives such as Depo-medroxyprogesterone (DMPA) are used by an estimated 34 million women worldwide. DMPA has been associated with increased risk of several viral infections including Herpes simplex virus-2 (HSV-2) and Human immunodeficiency virus (HIV). In the current study, we used the mouse papillomavirus (MmuPV1) anogenital infection model to test two hypotheses: (1) contraceptives such as DMPA increase the susceptibility of the anogenital tract to viral infection and (2) long-term contraceptive administration induces more advanced disease at the anogenital tract. DMPA treatments of both athymic nude mice and heterozygous NU/J (Foxn1nu/+) but ovariectomized mice led to a significantly increased viral load at the anogenital tract, suggesting that endogenous sex hormones were involved in increased viral susceptibility by DMPA treatment. Consistent with previous reports, DMPA treatment suppressed host anti-viral activities at the lower genital tract. To test the impact of long-term contraceptive treatment on the MmuPV1-infected lower genital tract, we included two other treatments in addition to DMPA: 17ß-estradiol and a non-hormone based contraceptive Cilostazol (CLZ, Pletal). Viral infections were monitored monthly up to nine months post infection by qPCR. The infected vaginal and anal tissues were harvested and further examined by histological, virological, and immunological analyses. Surprisingly, we did not detect a significantly higher grade of histology in animals in the long-term DMPA and 17ß-estradiol treated groups when compared to the control groups in the athymic mice we tested. Therefore, although DMPA promotes initial papillomavirus infections in the lower genital tract, the chronic administration of DMPA does not promote cancer development in the infected tissues in our mouse model.

A Comparative Study on Delivery of Externally Attached DNA by Papillomavirus VLPs and Pseudoviruses.

Human papillomavirus (HPV) 16 capsids have been chosen as a DNA delivery vehicle in many studies. Our preliminary studies suggest that HPV58 capsids could be better vehicles than HPV16 capsids to deliver encapsidated DNA in vitro and in vivo. In the current study, we compared HPV16, HPV58, and the cottontail rabbit papillomavirus (CRPV) capsids either as L1/L2 VLPs or pseudoviruses (PSVs) to deliver externally attached GFP-expressing DNA. Both rabbit and human cells were used to test whether there was a species-specific effect. DNA delivery efficiency was determined by quantifying either GFP-expressing cell populations or mean fluorescent intensities (MFI) by flow cytometry. Interestingly, CRPV and 58-VLPs and PSVs were significantly more efficient at delivering attached DNA when compared to 16-VLPs and PSVs. A capsid/DNA ratio of 2:1 showed the highest efficiency for delivering external DNA. The PSVs with papillomavirus DNA genomes also showed higher efficiency than those with irrelevant plasmid DNA. HPV16L1/58L2 hybrid VLPs displayed increased efficiency compared to HPV58L1/16L2 VLPs, suggesting that L2 may play a critical role in the delivery of attached DNA. Additionally, we demonstrated that VLPs increased in vivo infectivity of CRPV DNA in rabbits. We conclude that choosing CRPV or 58 capsids to deliver external DNA could improve DNA uptake in in vitro and in vivo models.

Mouse Papillomavirus L1 and L2 Are Dispensable for Viral Infection and Persistence at Both Cutaneous and Mucosal Tissues.

Papillomavirus L1 and L2, the major and minor capsid proteins, play significant roles in viral assembly, entry, and propagation. In the current study, we investigate the impact of L1 and L2 on viral life cycle and tumor growth with a newly established mouse papillomavirus (MmuPV1) infection model. MmuPV1 L1 knockout, L2 knockout, and L1 plus L2 knockout mutant genomes (designated as L1ATGko-4m, L2ATGko, and L1-L2ATGko respectively) were generated. The mutants were examined for their ability to generate lesions in athymic nude mice. Viral activities were examined by qPCR, immunohistochemistry (IHC), in situ hybridization (ISH), and transmission electron microscopy (TEM) analyses. We demonstrated that viral DNA replication and tumor growth occurred at both cutaneous and mucosal sites infected with each of the mutants. Infections involving L1ATGko-4m, L2ATGko, and L1-L2ATGko mutant genomes generally resulted in smaller tumor sizes compared to infection with the wild type. The L1 protein was absent in L1ATGko-4m and L1-L2ATGko mutant-treated tissues, even though viral transcripts and E4 protein expression were robust. Therefore, L1 is not essential for MmuPV1-induced tumor growth, and this finding parallels our previous observations in the rabbit papillomavirus model. Very few viral particles were detected in L2ATGko mutant-infected tissues. Interestingly, the localization of L1 in lesions induced by L2ATGko was primarily cytoplasmic rather than nuclear. The findings support the hypothesis that the L2 gene influences the expression, location, transport, and assembly of the L1 protein in vivo.

The environmental pollutant and tobacco smoke constituent dibenzo[def,p]chrysene is a co-factor for malignant progression of mouse oral papillomavirus infections.

HPV infections in the oral cavity that progress to cancer are on the increase in the USA. Model systems to study co-factors for progression of these infections are lacking as HPVs are species-restricted and cannot grow in preclinical animal models. We have recently developed a mouse papillomavirus (MmuPV1) oral mucosal infection model that provides opportunities to test, for the first time, the hypothesis that tobacco carcinogens are co-factors that can impact the progression of oral papillomas to squamous cell carcinoma (SCC). Four cohorts of mice per sex were included: (1) infected with MmuPV1 and treated orally with DMSO-saline; (2) infected with MmuPV1 and treated orally with the tobacco carcinogen, dibenzo[def,p]chrysene (DBP); (3) uninfected and treated orally with DMSO-saline, and (4) uninfected and treated orally with DBP. Oral swabs were collected monthly for subsequent assessment of viral load. Oral tissues were collected for in situ viral DNA/RNA detection, viral protein staining, and pathological assessment for hyperplasia, papillomas and SCC at study termination. We observed increased rates of SCC in oral tissue infected with MmuPV1 and treated with DBP when compared to mice treated with DBP or virus individually, each of which showed minimal disease. Virally-infected epithelium showed strong levels of viral DNA/RNA and viral protein E4/L1 staining. In contrast, areas of SCC showed reduced viral DNA staining indicative of lower viral copy per nucleus but strong RNA signals. Several host markers (p120 ctn, p53, S100A9) were also examined in the mouse oral tissues; of particular significance, p120 ctn discriminated normal un-infected epithelium from SCC or papilloma epithelium. In summary, we have confirmed that our infection model is an excellent platform to assess the impact of co-factors including tobacco carcinogens for oral PV cancerous progression. Our findings can assist in the design of novel prevention/treatment strategies for HPV positive vs. HPV negative disease.

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.

Papillomavirus can be transmitted through the blood and produce infections in blood recipients: Evidence from two animal models.

Human papillomaviruses (HPV) contribute to most cervical cancers and are considered to be sexually transmitted. However, papillomaviruses are often found in cancers of internal organs, including the stomach, raising the question as to how the viruses gain access to these sites. A possible connection between blood transfusion and HPV-associated disease has not received much attention. Here we show, in rabbit and mouse models, that blood infected with papillomavirus yields infections at permissive sites with detectable viral DNA, RNA transcripts, and protein products. The rabbit skin tumours induced via blood infection displayed decreased expression of SLN, TAC1, MYH8, PGAM2, and APOBEC2 and increased expression of SDRC7, KRT16, S100A9, IL36G, and FABP9, as seen in tumours induced by local infections. Furthermore, we demonstrate that blood from infected mice can transmit the infection to uninfected animals. Finally, we demonstrate the presence of papillomavirus infections and virus-induced hyperplasia in the stomach tissues of animals infected via the blood. These results indicate that blood transmission could be another route for papillomavirus infection, implying that the human blood supply, which is not screened for papillomaviruses, could be a potential source of HPV infection as well as subsequent cancers in tissues not normally associated with the viruses.

Wounding prior to challenge substantially improves infectivity of cottontail rabbit papillomavirus and allows for standardization of infection.

The cottontail rabbit papillomavirus (CRPV)/rabbit model has proved useful for the investigation of prophylactic and therapeutic vaccines and for the study of the pathogenesis of papillomavirus infection. It is currently the only animal model in which the entire viral program can be recapitulated, including progression to cancer. CRPV DNA is infectious in domestic rabbits and therefore mutants can be studied without the need to generate corresponding viruses. Although the CRPV animal model is used widely in various laboratories, no optimized or standardized method is used for creating CRPV viral and especially DNA infections. These different methods have made it difficult for investigators to compare results from laboratory to laboratory. A simple and highly efficient method is reported here; it has been refined based on previous methodology for the production of CRPV infections from both virus and plasmid DNA. This method can be adapted easily by other investigators in the field. The resulting standardization will aid in the evaluation of data from different laboratories.

BET bromodomain inhibitors show anti-papillomavirus activity in vitro and block CRPV wart growth in vivo.

The DNA papillomaviruses infect squamous epithelium and can cause persistent, benign and sometimes malignant hyperproliferative lesions. Effective antiviral drugs to treat human papillomavirus (HPV) infection are lacking and here we investigate the anti-papillomavirus activity of novel epigenetic targeting drugs, BET bromodomain inhibitors. Bromodomain and Extra-Terminal domain (BET) proteins are host proteins which regulate gene transcription, they bind acetylated lysine residues in histones and non-histone proteins via bromodomains, functioning as scaffold proteins in the formation of transcriptional complexes at gene regulatory regions. The BET protein BRD4 has been shown to be involved in the papillomavirus life cycle, as a co-factor for viral E2 and also mediating viral partitioning in some virus types. We set out to study the activity of small molecule BET bromodomain inhibitors in models of papillomavirus infection. Several BET inhibitors reduced HPV11 E1ˆE4 mRNA expression in vitro and topical therapeutic administration of an exemplar compound I-BET762, abrogated CRPV cutaneous wart growth in rabbits, demonstrating translation of anti-viral effects to efficacy in vivo. Additionally I-BET762 markedly reduced viability of HPV16 infected W12 cells compared to non-infected C33A cells. The molecular mechanism for the cytotoxicity to W12 cells is unknown but may be through blocking viral-dependent cell-survival factors. We conclude that these effects, across multiple papillomavirus types and in vivo, highlight the potential to target BET bromodomains to treat HPV infection.

The Mouse Papillomavirus Infection Model.

The mouse papillomavirus (MmuPV1) was first reported in 2011 and has since become a powerful research tool. Through collective efforts from different groups, significant progress has been made in the understanding of molecular, virological, and immunological mechanisms of MmuPV1 infections in both immunocompromised and immunocompetent hosts. This mouse papillomavirus provides, for the first time, the opportunity to study papillomavirus infections in the context of a small common laboratory animal for which abundant reagents are available and for which many strains exist. The model is a major step forward in the study of papillomavirus disease and pathology. In this review, we summarize studies using MmuPV1 over the past six years and share our perspectives on the value of this unique model system. Specifically, we discuss viral pathogenesis in cutaneous and mucosal tissues as well as in different mouse strains, immune responses to the virus, and local host-restricted factors that may be involved in MmuPV1 infections and associated disease progression.

Mouse papillomavirus infection persists in mucosal tissues of an immunocompetent mouse strain and progresses to cancer.

Mouse papillomavirus has shown broad tissue tropism in nude mice. Previous studies have tested cutaneous infections in different immunocompromised and immunocompetent mouse strains. In the current study, we examined mucosal infection in several immunocompetent and immunocompromised mouse strains. Viral DNA was monitored periodically by Q-PCR of lavage samples. Immunohistochemistry and in situ hybridization were used to determine viral capsid protein and viral DNA respectively. All athymic nude mouse strains showed active infections at both cutaneous and mucosal sites. Interestingly, NOD/SCID mice, which have a deficiency in T, B, and NK cells, showed minimal disease at cutaneous sites but developed persistent infection at the mucosal sites including those of the anogenital region and the oral cavity. Three strains of immunocompetent mice supported mucosal infections. Infections of the lower genital tract in heterozygous (immunocompetent) mice of the NU/J strain progressed to high grade dysplasia and to carcinoma in situ. Anti-MmuPV1 neutralizing antibodies were detected in the sera of all immunocompetent animals. Our findings demonstrate that the mucosae may be the preferred sites for this virus in mice. The mouse model is expected to be a valuable model for the study of mucosal papillomavirus disease, progression, and host immune control.