Intracutaneous vaccination of rabbits with the cottontail rabbit papillomavirus (CRPV) L1 gene protects against virus challenge

Ovine papillomavirus type 3 virus-like particle-based tools for diagnosis and detection of infection

The design of prophylactic and diagnostic tools specific to animal papillomaviruses is hampered by the difficulties of viral in vitro manipulation and by the scarce availability of dedicated biotechnological tools. This paper reports the production of Ovine Papillomavirus 3 (OaPV3)-based virus-like particles (OaPV3-VLPs) in the baculovirus system and their use to investigate host humoral immune response through the establishment of an indirect ELISA test., Polyclonal sera and monoclonal antibodies were generated against OaPV3-VLPs, and their isotype and reactivity were determined. Additionally, antibodies allowed OaPV3 detection in ovine squamous cell carcinoma (SCC) samples by immunohistochemistry. Results encourage the standardization of OaPV3-specific prophylactic and serological diagnostic tools, and open new perspectives for the study of host-viral interaction and SCC development.

Molecular typing of equine papillomavirus and autovaccination to treat horses with cutaneous papillomatosis

OBJECTIVE

The aim of this study was to evaluate formalin-inactivated autovaccination to treat cutaneous papillomatosis and to perform molecular typing of the papillomavirus in four horses (two foals, one 3-year-old filly and a 5-year-old stallion).

METHODS

Histopathological slides of lesions were prepared and stained with haematoxylin and eosin (H&E) to establish a diagnosis that was based on observation koilocytosis, which is a pathognomonic cytopathic change that is associated with papillomatosis, using light microscopy. Polymerase chain reaction (PCR) and DNA sequencing were performed using the EPV-R and EPV-F primer set.

RESULTS

In histopathological examination, koilocyte formation and occasional intranuclear viral inclusions were detected in the papillomas. A 334-base pair (bp) fragment of the E2 and L2 genes from the EPV genome was amplified using the EPV-R and EPV-F primer set. This fragment contained 215 bp from the E2 gene and 56 bp from the L2 gene; these were found to be 98.78% to 98.97% identical to the known EcPV type-1 sequence (AF498323).

CONCLUSION

Three horses with cutaneous papillomatosis were administered two doses of a formalin-inactivated preparation of papillomatous lesions at 7-day intervals. The papillomatous lesions were observed to decrease gradually 1 week after the last vaccination, and all warts had resolved within 2-3 weeks. One horse with cutaneous papillomatosis was left as an unvaccinated control, and no changes to the lesions were noted. To the best of our knowledge, this is the first report of EcPV type-1 infection, autovaccine preparation and molecular typing in Turkey.

The rabbit papillomavirus model: a valuable tool to study viral-host interactions

Cottontail rabbit papillomavirus (CRPV) was the first DNA virus shown to be tumorigenic. The virus has since been renamed and is officially known as Sylvilagus floridanus papillomavirus 1 (SfPV1). Since its inception as a surrogate preclinical model for high-risk human papillomavirus (HPV) infections, the SfPV1/rabbit model has been widely used to study viral-host interactions and has played a pivotal role in the successful development of three prophylactic virus-like particle vaccines. In this review, we will focus on the use of the model to gain a better understanding of viral pathogenesis, gene function and host immune responses to viral infections. We will discuss the application of the model in HPV-associated vaccine testing, in therapeutic vaccine development (using our novel HLA-A2.1 transgenic rabbits) and in the development and validation of novel anti-viral and anti-tumour compounds. Our goal is to demonstrate the role the SfPV1/rabbit model has played, and continues to play, in helping to unravel the intricacies of papillomavirus infections and to develop tools to thwart the disease. This article is part of the theme issue 'Silent cancer agents: multi-disciplinary modelling of human DNA oncoviruses'.

Immunogenicity of bivalent human papillomavirus DNA vaccine using human endogenous retrovirus envelope-coated baculoviral vectors in mice and pigs

Human papillomavirus is known to be the major pathogen of cervical cancer. Here, we report the efficacy of a bivalent human papillomavirus type 16 and 18 DNA vaccine system following repeated dosing in mice and pigs using a recombinant baculovirus bearing human endogenous retrovirus envelope protein (AcHERV) as a vector. The intramuscular administration of AcHERV-based HPV16L1 and HPV18L1 DNA vaccines induced antigen-specific serum IgG, vaginal IgA, and neutralizing antibodies to levels comparable to those achieved using the commercially marketed vaccine Cervarix. Similar to Cervarix, AcHERV-based bivalent vaccinations completely blocked subsequent vaginal challenge with HPV type-specific pseudovirions. However, AcHERV-based bivalent vaccinations induced significantly higher cell-mediated immune responses than Cervarix, promoting 4.5- (HPV16L1) and 3.9-(HPV18L1) fold higher interferon-γ production in splenocytes upon stimulation with antigen type-specific pseudovirions. Repeated dosing did not affect the immunogenicity of AcHERV DNA vaccines. Three sequential immunizations with AcHERV-HP18L1 DNA vaccine followed by three repeated dosing with AcHERV-HP16L1 over 11 weeks induced an initial production of anti-HPV18L1 antibody followed by subsequent induction of anti-HPV16L1 antibody. Finally, AcHERV-based bivalent DNA vaccination induced antigen-specific serum IgG immune responses in pigs. These results support the further development of AcHERV as a bivalent human papillomavirus DNA vaccine system for use in preventing the viral infection as well as treating the infected women by inducing both humoral and cell-mediated immune responses. Moreover, the possibility of repeated dosing indicates the utility of AcHERV system for reusable vectors of other viral pathogen vaccines.

Increased immunity to cottontail rabbit papillomavirus infection in EIII/JC inbred rabbits after vaccination with a mutant E6 that correlates with spontaneous regression

Our previous studies showed that a progressive cottontail rabbit papillomavirus (CRPV) strain containing a single amino acid change in E6 (E6G252E) induced papilloma regression in EIII/JC inbred rabbits. This finding implied that the point mutation might cause an increase in the antigenicity of the mutant versus the wild-type E6. To test this hypothesis, groups of four EIII/JC inbred rabbits were immunized with wild-type CRPVE6, CRPVE6G252E, CRPV E5, or with vector alone. A gene gun delivery system was used to deliver the DNA vaccines. Two of four rabbits from both E6G252E- and wild-type E6-vaccinated groups were free of papillomas at week 12 after viral challenge. Significantly smaller papillomas were found on E6G252E-vaccinated rabbits than on E6-, E5-, and control vector-vaccinated rabbits (p = 0.01, unpaired Student t test) and these small papillomas regressed at week 20 after viral challenge. E5 vaccination failed to provide protection against viral challenge, and the mean papilloma size was also comparable to that of the control vector-vaccinated rabbits (p > 0.05, unpaired Student t test). We conclude that a single amino acid change in the CRPV E6 protein (G252E) increased protection against wild-type infectious CRPV.

Prophylactic DNA immunization against multiple papillomavirus types

At least 15 different papillomavirus types are causatively associated with the development of tumors in humans. Since the middle of 2006 a protective, virus-like particle based vaccine against the tumor-related HPV types 16 and 18 is commercially available. We investigated the possibility of applying DNA vaccination to obtain protective antibody responses against multiple papillomavirus types. Our data indicate that low amounts of DNA were sufficient to induce neutralizing antibodies in mice although a DNA dose-dependency in respect to the L1-specific antibody titers was observed. Furthermore, we found that immune responses against different PV types could be induced by simultaneous DNA vaccination with a mixture of expression vectors encoding L1 proteins of different papillomavirus types. However, we observed that there was a strong interference when plasmids encoding different L1 genes were used together. HPV 16 responses were repressed by co-administration of HPV 11 and/or BPV 1 L1 expression constructs. Likewise, BPV 1 responses were repressed by co-administration of HPV 16 or HPV 11 L1 plasmids. This interference could be overcome by administration of the different constructs into different sites of the animals or by sequential immunization. Thus, our results suggest that the mode of repression was due to interference with L1 particle assembly and was not a consequence of immunodominance of certain L1 proteins.

Vesicular stomatitis virus-based therapeutic vaccination targeted to the E1, E2, E6, and E7 proteins of cottontail rabbit papillomavirus

Persistent human papillomavirus (HPV)-associated benign and malignant lesions are a major cause of morbidity and mortality worldwide. Vaccination against HPV early proteins could provide an effective means of treating individuals with established infections. Recombinant vesicular stomatitis virus (VSV) vectors have been used previously to elicit strong humoral and cellular immune responses and develop prophylactic vaccines. We have shown that VSV vectors also can be used to elicit therapeutic immunity in the cottontail rabbit papillomavirus (CRPV)-rabbit model of high-risk HPV infection. In the present study, three new VSV vectors expressing the CRPV E1, E2, or E7 protein were produced and compared to the previously generated VSV-E6 vector for therapeutic efficacy. To determine whether vaccine efficacy could be augmented by simultaneous vaccination against two CRPV proteins, the four vaccines were delivered individually and in all possible pairings to rabbits 1 week after CRPV infection. Control rabbits received the recombinant wild-type VSV vector or medium only. Cumulative papilloma volumes were computed for analysis of the data. The analyses showed that VSV-based vaccination against the E1, E2, E6, or E7 protein significantly reduced papilloma volumes relative to those of the controls. Furthermore, VSV-based CRPV vaccination cured all of the papillomas in 5 of 30 rabbits. Of the individual vaccines, VSV-E7 was the most effective. The VSV-E7 vaccine alone was the most effective, as it reduced cumulative papilloma volumes by 96.9% overall, relative to those of the controls, and ultimately eliminated all of the disease in all of the vaccinees. Vaccine pairing was not, however, found to be beneficial, suggesting antigenic competition between the coexpressed CRPV proteins. These preclinical results, obtained in a physiologically relevant animal model of HPV infection, demonstrate that VSV vectors deserve serious consideration for further development as therapeutic antitumor vaccines.

Particle-Mediated Gene Delivery and Human Skin: Ultrastructural Observations on Stratum Corneum Barrier Structures

The particle-mediated delivery systems are becoming a clinically relevant tool in dermatology and immunology. We investigated the qualitative ultrastructural morphology of skin following pressure-driven delivery of gold particles to ex vivo human breast skin, at different pressures ranging from 350 to 1,000 psi. Pressures of 800 and 1,000 psi appear to be more effective, as indicated by distribution of particles in the viable epidermis and dermis. Particle bombardment of the skin with gold beads caused microwounds that spanned the stratum corneum (SC). The SC lipids did not reseal these wounds in the SC after 24 h in organ culture. The implications of particle-mediated delivery to permeability barrier functions of the SC are discussed.

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.

Therapeutic efficacy of vesicular stomatitis virus-based E6 vaccination in rabbits

Millions of people worldwide are currently infected with human papillomaviruses (HPVs). A therapeutic HPV vaccine would have widespread applicability because HPV-associated lesions are difficult to treat and may progress to carcinoma. We developed three attenuated VSV recombinants expressing the cottontail rabbit papillomavirus (CRPV) early protein E6 for use as vaccines. In cultured cells, two vectors expressed different levels of the E6 protein, and one expressed a ubiquitin-E6 fusion protein. All three were tested for therapeutic efficacy in the cottontail rabbit papillomavirus (CRPV)-rabbit model. Mock vaccination had no effect on papilloma growth. In contrast, inoculation with any of the VSV-E6 vaccines reduced the rate of papilloma growth to as little as 24% the rate in the controls. In five experiments, these effects were achieved after a single immunization. Furthermore, complete papilloma regression occurred in some rabbits observed for 4 months. A VSV-based papillomavirus E6 vaccine could have significant advantages over other therapeutic HPV vaccine candidates described to date.

DNA vaccine against hamster oral papillomavirus-associated oral cancer

Previously we developed a carcinogenesis model involving the combination of 9,10-dimethyl-1,2-benzanthracene (DMBA) application with physical wounding of hamster lingual mucosa. The presence of a novel hamster oral papillomavirus (HOPV) was demonstrated and its genome sequenced. In the present study, this HOPV hamster model was used to test whether vaccination with the L1 gene could prevent the development of oral carcinoma. DNA plasmids encoding the L1 gene or the vector alone were injected intramuscularly into 20 vaccinated and 20 control hamsters, respectively. The lingual tips of the hamsters were painted with DMBA for 8 weeks. A portion of the lingual tips was excised, and the tips were then painted daily with DMBA until the animals were killed 13 days later. All control hamsters developed lingual carcinoma, whereas 12 of the L1-vaccinated hamsters showed no lesions. These results suggest that immunization with L1 DNA vaccines may prevent the development of papillomavirus-associated oral cancer.

Immunisation with recombinant BCG expressing the cottontail rabbit papillomavirus (CRPV) L1 gene provides protection from CRPV challenge

Recombinant Bacille Calmette-Guerin (rBCG) could potentially be the vaccine vehicle of choice to deliver foreign antigens from multiple pathogens. In this study we have used the cottontail rabbit papillomavirus (CRPV) rabbit model to provide a "proof of concept" that immunisation with rBCG expressing the CRPV major capsid protein, L1 (rBCG/CRPVL1), will protect outbred New Zealand White rabbits against CRPV challenge. Rabbits immunised with rBCG/CRPVL1 (10(7) cfu/ml) were protected 5 weeks post-CRPV challenge. Rabbits immunised with rBCG/CRPVL1 (10(5) cfu/ml) had papillomas, which were smaller and took longer to appear than the control rabbits. None of the negative control rabbits vaccinated with rBCG expressing an irrelevant gene or PBS were protected from CRPV challenge. Sera from rabbits immunised with rBCG/CRPVL1 (10(7) cfu/ml) were able to neutralise 54.5% of CRPV at serum dilutions of 1:200. These results provide evidence that BCG could potentially be used as a vaccine delivery vehicle for human papillomavirus proteins as a possible prophylactic vaccine.

The role of particle-mediated DNA vaccines in biodefense preparedness

Particle-mediated epidermal delivery (PMED) of DNA vaccines is based on the acceleration of DNA-coated gold directly into the cytoplasm and nuclei of living cells of the epidermis, facilitating DNA delivery and gene expression. Professional antigen-presenting cells and keratinocytes in the skin are both targeted, resulting in antigen presentation via direct transfection and cross-priming mechanisms. Only a small number of cells need to be transfected to elicit humoral, cellular and memory responses, requiring only a low DNA dose. In recent years, data have accumulated on the utility of PMED for delivery of DNA vaccines against a number of viral pathogens, including filoviruses, flaviviruses, poxviruses, togaviruses and bunyaviruses. PMED DNA immunization of rodents and nonhuman primates results in the generation of neutralizing antibody, cellular immunity, and protective efficacy against a broad range of viruses of public health concern.

Epidermal delivery of protein and DNA vaccines

Targeting vaccines to the skin epidermis results in the activation of an immune inductive site that is rich in antigen-presenting cells. The superficial location of the skin makes it accessible to vaccine delivery. However, it is difficult to access the epidermis using needle and syringe delivery, and vaccine antigens are too large to be effectively delivered using standard topical formulations. Needle-free vaccine delivery systems have been developed for efficient delivery of particulate vaccines into the epidermal tissue. Particle-mediated epidermal delivery of DNA vaccines is based on the delivery of DNA-coated gold particles directly into the cytoplasm and nuclei of living cells of the epidermis, facilitating DNA delivery and gene expression. Alternatively, protein vaccines can be formulated into a dense powder, which can be propelled into the skin epidermis by epidermal powder immunisation using similar delivery devices and principles, but in this instance the protein is delivered to the extracellular space. Preclinical and clinical data will be reviewed, demonstrating applications of epidermal vaccine delivery to a wide range of experimental infectious disease vaccines.

Emerging human papillomavirus vaccines

Human papillomavirus (HPV) infections are a leading cause of virus-associated cancers of the anogenital, oropharyneal and cutaneous epithelium. The most prevalent of these is cervical cancer, which is responsible for approximately 500,000 deaths annually worldwide. A group of about 15 serologically unrelated 'high-risk' HPV types are responsible for almost all HPV-associated cancers. Prevention of papillomavirus infection can be achieved by induction of capsid-specific neutralising antibodies in preclinical animal papillomavirus models and in recent human clinical trials. High titres of conformationally-dependent, type-specific HPV-neutralising antibodies are triggered by HPV virus-like particle (VLP) vaccines. Overcoming the problems of type-specificity of the responses to these VLP vaccines is a potentially important area of current HPV vaccine research, with an emphasis on induction of more broadly cross-protective neutralising responses. Viral oncogenes E6 and E7 are continuously present in HPV-associated cancers and are prime targets for HPV therapeutic vaccines. A variety of approaches are being tested in therapeutic vaccine clinical trials and in various preclinical animal papillomavirus models for efficacy. Approaches include genetic vaccines, recombinant virus vaccines, dendritic cell-based strategies, immunomodulatory strategies and various combination strategies to maximise cell-mediated immunity to papillomavirus proteins present in HPV infections and cancers. The success of preventive HPV VLP vaccines in clinical trials is clear. However, current therapeutic vaccine trials are less effective with respect to disease clearance. Nevertheless, a series of combination approaches have shown significant therapeutic enhancement in preclinical papillomavirus models and await testing in patient populations to determine the most effective strategy. There is much encouragement that HPV vaccines will be the most effective approach to prevention and cure of infections caused by this group of viruses, which re-present a significant human pathogen.

Particle-mediated DNA vaccine delivery to the skin

Particle-mediated DNA vaccines employ a physical, intracellular delivery device to achieve the deposition of plasmid DNA-based expression vectors directly into the interior of cells of the skin. The resultant bolus of transient antigen expression in keratinocytes and trafficking dendritic cells results in the induction of humoral and cellular immune responses in various animal models and humans, mimicking characteristics of live or live-vectored vaccines. Ultimately, DNA vaccine success in the clinic will depend on both the successful intracellular delivery of a plasmid vector and an immunostimulator or adjuvant to maximise humoral and cellular immune responses to the encoded antigen(s). To this end, recent DNA vaccine clinical trials are confirming the importance of an intracellular delivery system, while preclinical studies in animal models are demonstrating the feasibility of augmenting responses through the use of DNA-encoded immunostimulators. Particle-mediated DNA vaccines represent a promising tool for developing candidate vaccines against some of the more difficult infectious, parasitic and oncologic disease targets.

Vaccination to prevent and treat cervical cancer

Human papillomaviruses (HPVs) are the primary etiologic agents of cervical cancer. Thus, cervical cancer and other HPV-associated malignancies might be prevented or treated by HPV vaccines. Transmission of papillomavirus may be prevented by the generation of antibodies to capsid proteins L1 and L2 that neutralize viral infection. However, because the capsid proteins are not expressed at detectable levels by infected basal keratinocytes or in HPV-transformed cells, therapeutic vaccines generally target nonstructural early viral antigens. Two HPV oncogenic proteins, E6 and E7, are critical to the induction and maintenance of cellular transformation and are coexpressed in the majority of HPV-containing carcinomas. Thus, therapeutic vaccines targeting E6 and E7 may provide the best option for controlling HPV-associated malignancies. Various candidate therapeutic HPV vaccines are currently being tested whereby E6 and/or E7 are administered in live vectors, as peptides or protein, in nucleic acid form, as components of chimeric virus-like particles, or in cell-based vaccines. Encouraging results from experimental vaccination systems in animal models have led to several prophylactic and therapeutic vaccine clinical trials. If these preventive and therapeutic HPV vaccines prove successful in patients, as they have in animal models, then oncogenic HPV infection and its associated malignancies may be controllable by vaccination.

Genetic immunisation against hepatitis B using whole bacteriophage lambda particles

Mice and rabbits have been vaccinated with whole bacteriophage lambda particles containing a DNA vaccine expression cassette under the control of the CMV promoter (enhanced green fluorescent protein [lambda-EGFP] or hepatitis B surface antigen [lambda-HBsAg]). Mice were vaccinated twice intramuscularly (i.m.) with 5x10(9) of lambda-EGFP phage (containing 250 ng DNA) and exhibited specific anti-EGFP responses 28 days post-vaccination. Rabbits were vaccinated i.m. with 4x10(10) of lambda-HBsAg phage (2 microg DNA) or recombinant HBsAg protein. Following two vaccinations with lambda-HBsAg, one out of four rabbits exhibited high level anti-HBsAg responses (comparable to those seen using the recombinant HBsAg protein). Following a third vaccination with lambda-HBsAg, all four rabbits showed similar high level responses which have not decreased after more than 6 months. High anti-phage responses were observed in all animals following the first immunization with lambda-HBsAg, indicating that a high antibody titre against the phage carrier did not prevent a subsequent immune response against the DNA vaccine component. Compared to results in mice using equivalent lambda-HBsAg doses, anti-HBsAg responses were much higher in rabbits, which could indicate a swamping effect in mice. Since phage lambda DNA is approximately 50 kb in size (tenfold larger than most plasmid vectors used for naked DNA immunisation), a comparable dose of phage lambda DNA given as intact phage particles actually delivers tenfold less vaccine DNA on a per gene copy (molar) basis. Thus the efficiency of the technique may be even higher than the data at first suggests.

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.

Vaccination of rabbits with an adenovirus vector expressing the papillomavirus E2 protein leads to clearance of papillomas and infection

Cervical cancer arises from lesions caused by infection with high-risk types of human papillomavirus (HPV). Therefore, vaccination against HPV could prevent carcinogenesis by preventing HPV infection or inducing lesion regression. HPV E2 protein is an attractive candidate for vaccine development because it is required for papilloma formation, is involved in all stages of the virus life cycle, and is expressed in all premalignant lesions as well as some cancers. This study reports vaccination against E2 protein using a rabbit model of papillomavirus infection. A recombinant adenovirus (Ad) vector expressing the E2 protein of cottontail rabbit papillomavirus (CRPV) was tested for therapeutic efficacy in CRPV-infected rabbits. Primary immunization with the Ad-E2 vaccine, compared to immunization with a control Ad vector, reduced the number of papilloma-forming sites from 17 of 45 to 4 of 45. After booster immunization, vaccinated rabbits formed no new papillomas versus an additional 23 papillomas in rabbits that received the control vector. Papillomas in the Ad-E2 vaccinees were significantly smaller than those in the control rabbits, and all four papillomas in the Ad-E2 vaccinated rabbits regressed. No CRPV DNA was detected either in the regression sites or in sites that did not form papillomas, indicating that the vaccination led to clearance of CRPV from all infected sites.

Intradermal immunization with novel plasmid DNA-coated nanoparticles via a needle-free injection device

A high population of dendritic cells in the skin makes intradermal (ID) immunization an attractive route. We sought to further enhance immune responses from a previously reported novel nanoparticle-based DNA vaccine delivery system by administering the system intradermally into mouse skin using Biojector 2000, a needle-free jet injection device. Two mouse studies were carried out. Balb/C mice (n=5-6) were immunized on day 0, 7, and 14 by subcutaneous injection or via the Biojector 2000 with pDNA alone (CMV-beta-galactosidase, 5 micro g), pDNA-coated nanoparticles, or beta-galactosidase protein (10 micro g) adjuvanted with 'Alum' (15 micro g). On day 28, mice were sacrificed and specific serum IgG and IgA titer, in vitro cytokine release, and cell proliferation of isolated splenocytes were determined. Similar to previous reports, in both mouse studies, SC immunization with pDNA-coated nanoparticles led to over a log increase in specific serum IgG titer as compared to immunization with pDNA alone. For pDNA alone, jet and SC injection did not result in significant differences in IgG titer. In contrast, for pDNA-coated nanoparticles, jet injection led to as high as a 20-fold enhancement in IgG titer over SC injection. In addition, jet injection of pDNA-coated nanoparticles enhanced the IgG titer by more than 200-fold over jet injection of pDNA alone. Also, jet injection of pDNA-coated nanoparticles resulted in significantly enhanced specific serum IgA titer. For in vitro cytokine release, immunization with pDNA-coated nanoparticles by jet injection enhanced IFN-gamma and IL-4 release over pDNA alone by 6- and 5-fold, respectively. SC injection of pDNA-coated nanoparticles also resulted in enhanced IFN-gamma and IL-4 release over pDNA alone although with less magnitude. Finally, immunization with pDNA-coated nanoparticles, by both jet injection and SC injection, led to improved splenocyte proliferation over pDNA alone. In conclusion, a combination of a novel cationic nanoparticle-based DNA delivery system with ID jet injection led to enhanced antibody production, Th-1/Th-2 balanced cytokine release, and enhanced splenocyte proliferation.

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.

Intranasal vaccination with a recombinant vesicular stomatitis virus expressing cottontail rabbit papillomavirus L1 protein provides complete protection against papillomavirus-induced disease

Immunizations with live recombinant vesicular stomatitis viruses (rVSV) expressing foreign viral proteins have successfully protected animals from challenges with several heterologous viruses. We developed an rVSV expressing the major capsid protein (L1) of cottontail rabbit papillomavirus (CRPV) and tested the efficacy of protection following CRPV challenge. An rVSV expressing L1 of CRPV (VSV-L1) was characterized for the protective ability afforded by intranasal, intradermal, or intramuscular vaccination in rabbits subsequently challenged with CRPV. Protein expression of L1 in VSV-L1 was confirmed by radioimmunoprecipitation assays. Nuclear localization of L1 was demonstrated by indirect immunofluorescence assays. Immunized rabbits elicited significant VSV neutralization and VLP-L1 enzyme-linked immunosorbent assay titers. VSV-L1 vaccination was not associated with weight loss or any other adverse clinical signs in the rabbit model. VSV shedding in nasal secretions occurred in some rabbits, peaking at 4 to 6 days after intranasal vaccination, with no further shedding after day 6. Specific humoral immunity to the L1 protein was consistently seen after a single VSV-L1 vaccination when administered through an intradermal or intramuscular route or after a boost via the intranasal route. Rabbits were completely protected from CRPV-induced papillomas after VSV-L1 vaccination and boost given intranasally or intramuscularly. Vaccination with VSV-L1 is a novel approach to prevent papillomavirus-induced disease and demonstrates a potential strategy for developing a human papillomavirus vaccine that can be given without injection.

Ubiquitin-fused and/or multiple early genes from cottontail rabbit papillomavirus as DNA vaccines

Human papillomavirus (HPV) vaccines have the potential to prevent cervical cancer by preventing HPV infection or treating premalignant disease. We previously showed that DNA vaccination with the cottontail rabbit papillomavirus (CRPV) E6 gene induced partial protection against CRPV challenge and that the vaccine's effects were greatly enhanced by priming with granulocyte-macrophage colony-stimulating factor (GM-CSF). In the present study, two additional strategies for augmenting the clinical efficacy of CRPV E6 vaccination were evaluated. The first was to fuse a ubiquitin monomer to the CRPV E6 protein to enhance antigen processing and presentation through the major histocompatibility complex class I pathway. Rabbits vaccinated with the wild-type E6 gene plus GM-CSF or with the ubiquitin-fused E6 gene formed significantly fewer papillomas than the controls. The papillomas also required a longer time to appear and grew more slowly. Finally, a significant proportion of the papillomas subsequently regressed. The ubiquitin-fused E6 vaccine was significantly more effective than the wild-type E6 vaccine plus GM-CSF priming. The second strategy was to vaccinate with multiple CRPV early genes to increase the breadth of the CRPV-specific response. DNA vaccines encoding the wild-type CRPV E1-E2, E6, or E7 protein were tested alone and in all possible combinations. All vaccines and combinations suppressed papilloma formation, slowed papilloma growth, and stimulated subsequent papilloma regression. Finally, the two strategies were merged and a combination DNA vaccine containing ubiquitin-fused versions of the CRPV E1, E2, and E7 genes was tested. This last vaccine prevented papilloma formation at all challenge sites in all rabbits, demonstrating complete protection.

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.

Parenteral and oral immunization with a plasmid DNA expressing the human papillomavirus 16-L1 gene induces systemic and mucosal antibodies and cytotoxic T lymphocyte responses

The association of human papillomavirus (HPV) infection and cervical cancer has been demonstrated. The development of a prophylactic vaccine to protect against primary HPV infection may therefore be an efficient means to reduce the incidence of this cancer worldwide. To assess the capacity of a plasmid DNA that expresses the L1 gene of HPV type 16 to induce a protective immune response, mice were immunized by parenteral and oral routes. Animals that received the DNA vaccine intramuscularly, subcutaneously and orally, developed systemic anti-L1 IgG antibodies. Antibodies developed in mice vaccinated subcutaneously were detectable twelve months post-immunization. Specific IgA antibodies were also found in vaginal washes from immunized mice. Both systemic and local antibodies proved effective in a surrogate neutralization assay. Splenic T cells extracted from experimental mice showed cytotoxic T lymphocytes (CTL) activity mediated by CD8 + cells. Mice were challenged with a syngeneic melanoma cell line, engineered to express the HPV16-L1 protein, tumours in vaccinated animals showed slower growth rate, correlated directly with a longer survival of mice. The results suggest that the L1-based DNA vaccine may be useful for the prevention of primary infections by HPV16.

Optimization of cottontail rabbit papilloma virus challenge technique

Disease induced by Cottontail Rabbit Papilloma Virus (CRPV) scarification in domestic rabbits shares many attributes with disease induced by human papilloma virus (HPV). CRPV induces squamous papillomas in domestic rabbits, of which approximately 70% transform into invasive carcinomas. In advanced tumors, virus is often undetectable, and occasionally, some rabbits undergo spontaneous regression of papillomas. Techniques utilized to scarify rabbit skin are diverse, often labor intensive and time consuming with the possibility for significant variability. Using four unique infection techniques, resultant papilloma incidence, time to onset, and total papilloma volumes were compared to determine an optimal challenge method. Five rabbits were each infected with CRPV via a tattoo gun with and without ink, an intradermal injection, manual use of a tattoo needle, or a sterile blade followed by manual use of a tattoo needle. Papilloma formation was monitored weekly after inoculation for 6 weeks. CRPV papillomas began as pinpoint foci at 3 weeks post challenge and grew exponentially throughout the course of measurement. Individual foci coalesced rapidly to form larger papilloma aggregates. Although intradermal injection was well tolerated and easily performed, it was the worst method of papilloma production (2.2 mm(3) at 6 weeks). The best method, a sterile blade followed by manual use of a tattoo needle, produced significantly larger papillomas over all time periods (>1100 mm(3) at 6 weeks, P<0.01). Inoculation of CRPV using this method produces highly repeatable papillomas beginning 3 weeks post-infection.

Papillomavirus pseudovirus: a novel vaccine to induce mucosal and systemic cytotoxic T-lymphocyte responses

Intestinal mucosa is a portal for many infectious pathogens. Systemic immunization, in general, does not induce a cytotoxic T-lymphocyte (CTL) response at the mucosal surface. Because papillomavirus (PV) naturally infects mucosa and skin, we determined whether PV pseudovirus, i.e., PV-like particles in which unrelated DNA plasmids are packaged, could generate specific mucosal immunity. We found that the pseudovirus that encoded the lymphocytic choriomeningitis virus gp33 epitope induced a stronger CTL response than a DNA vaccine (plasmid) encoding the same epitope given systemically. The virus-like particles that were used to make the pseudoviruses provided an adjuvant effect for induction of CTLs by the DNA vaccine. The PV pseudovirus pseudoinfected mucosal and systemic lymphoid tissues when administered orally. Oral immunization with the pseudovirus encoding human PV type 16 mutant E7 induced mucosal and systemic CTL responses. In comparison, a DNA vaccine encoding E7, when given orally, did not induce a CTL response in intestinal mucosal lymphoid tissue. Further, oral immunization with the human PV pseudovirus encoding E7 protected mice against mucosal challenge with an E7-expressing bovine PV pseudovirus. Thus, PV pseudovirus can be used as a novel vaccine to induce mucosal and systemic CTL responses.

Intra-epithelial vaccination with COPV L1 DNA by particle-mediated DNA delivery protects against mucosal challenge with infectious COPV in beagle dogs

Protection against viral challenge with canine oral papillomavirus (COPV) was achieved by immunisation via particle-mediated DNA delivery (PMDD) of a plasmid encoding the COPV L1 gene to cutaneous and oral mucosal sites in beagle dogs. The initial dose of approximately 9 microg of DNA was followed by two booster doses at 6 week intervals. A similar approach was used to vaccinate a control group of animals with plasmid DNA encoding the Hepatitis B virus S gene. Following challenge at the oral mucosa with COPV all animals vaccinated with the COPV L1 gene were protected against disease. However five of six animals in the control group developed COPV induced papillomas at the oral mucosa. Both cell-mediated lymphoproliferative and humoral antibody responses to the DNA vaccine were observed. Our data indicate that PMDD of plasmid DNA can protect against mucosal challenge with papillomavirus.

Modified HPV16 E7 Genes as DNA Vaccine against E7-Containing Oncogenic Cells

Therapeutic vaccines against tumors associated with human papillomaviruses (HPV) should elicit cellular immune responses against early HPV antigens, primarily the oncoproteins E7 and E6. Because of safety concerns, the direct use of an unmodified oncogene is impossible in human DNA vaccination. Therefore, we introduced three point mutations into the pRb-binding site of HPV16 E7 oncogene to eliminate its transformation potential. The resultant gene was denoted E7GGG. The rates of expression and the cellular localization of E7 and E7GGG proteins were comparable. In immunization-challenge experiments, the efficacy of plasmids containing the E7, E7GGG, or fusion genes of HPV16 E7, viz. L1DeltaCE7(1-60) (M. Muller et al., 1997, Virology 234, 93-111), and Sig/E7/LAMP-1 (T. C. Wu et al., 1995, Proc. Natl. Acad. Sci. USA 92, 11671-11675), was compared. While tumors developed in all animals immunized with the wild-type E7 gene, a significant proportion of mice remained tumor-free after vaccination with the E7GGG gene. The fusion gene L1DeltaCE7(1-60) induced negligible protection, but Sig/E7/LAMP-1 conferred the highest protection. Intradermal immunization by gene gun proved superior to i.m. inoculation. In "therapeutic" experiments, a 1-day delay between inoculation of oncogenic cells and the start of DNA immunization resulted in partial therapeutic effect, but a 3-day delay produced a substantially lower immunization effect. A combination of Sig/E7/LAMP-1 and E7GGG genes did not enhance the immune response. These results demonstrate a significant enhancement of HPV16 E7 immunogenicity after mutagenesis of the pRb-binding site, but the mutated E7 gene did not excel the Sig/E7/LAMP-1 fusion gene.

Establishment of gene-vaccinated skin grafting against Toxoplasma gondii infection in mice

Vaccine effects of in vivo gene-vaccinated skin graft were evaluated against Toxoplasma gondii (T. gondii) infection. By using a gene gun, cDNA coding T. gondii SAG1 molecule was intracutaneously vaccinated into C57BL/6 (B6; a susceptible strain), BALB/c (a resistant strain) and (C57BL/6 x BALB/c) F1 (CBF1) mice, and the gene-vaccinated skin of these strains was transplanted to CBF1 mice. Regarding the antibody production against SAG1, CBF1-recipient mice transplanted with the SAG1 gene-vaccinated B6 skin were high responders, whereas CBF1 mice skin grafted with vaccinated skin of both BALB/c and CBF1 mice were low responders. The donor-derived LC/DC migrated to the draining lymph nodes of the recipients from the skin graft within 3 days. The vaccine effect against T. gondii challenge infection was obtained in CBF1 mice which received the skin graft of the SAG1 gene-vaccinated BALB/c mice.

Nasal immunization of mice with peptide having a cross-neutralization epitope on minor capsid protein L2 of human papillomavirus type 16 elicit systemic and mucosal antibodies

A common cross-neutralization epitope for human papillomavirus types 6 and 16 (HPV 6 and 16) is present in the region of amino acids (aa) 108-120 of HPV-16 minor capsid protein, L2. We nasally immunized Balb/c mice with a synthetic peptide with the 13 aa HPV 16 L2 sequence, and examined the antibodies elicited. ELISA showed that the immunization induced predominantly IgG and IgA antibodies cross-binding to L1/L2-capsids of HPVs 6, 16, and 18 in sera and in vaginal secretions, respectively. The serum containing the IgG antibody and the vaginal wash containing the IgA antibody neutralized HPV 16 pseudovirions and HPV 11 authentic virions, as shown by surrogate infectivity assays. From their cross-binding activity for HPV 16 and 18, the peptide-induced antibodies can probably cross-neutralize most of the genital HPVs. The peptide-induced neutralizing activity in vaginal wash was comparable to that induced by nasally immunization with HPV 16 L1-capsids. Unlike Balb/c, C57BL/10, which has different MHC class II, did not respond to the peptide immunization, but aa substitutions in the peptide to fulfill the requirement for the C57BL/10 agretope rendered the modified peptides immunogenic. The results provide a basis for development of a peptide vaccine against broad-spectrum of genital HPVs for humans.

A truncated variant of the hepatitis C virus core induces a slow but potent immune response in mice following DNA immunization

Vaccination of BALB/c mice with pIDKCo, a plasmid containing the coding sequence for the first 176 amino acids of the hepatitis C virus (HCV) core protein, induced both humoral and cellular specific immune responses. Particularly, the level of anti-core antibodies increased slowly with time up to a mean value above 1:8000 that was generally superior than that found in anti-HCV positive individuals. Six out of nine anti-HCV positive human sera were able to inhibit at different extent the binding of mouse anti-core sera to a recombinant capsid protein. Our results show that it is possible to elicit a potent humoral and cellular immune response against the HCV core antigen in mice following DNA immunization.

Induction of an HPV 6bL1-specific mucosal IgA response by DNA immunization

Human papillomavirus (HPV) plays a crucial role in the development of human anogenital dysplasia. To prevent infection, it is important to induce an HPV-specific mucosal immune response. We investigated whether DNA vaccination would induce an intravaginal mucosal antibody response against HPV 6bL1. New Zealand White rabbits were immunized with an HPV 6bL1 DNA vaccine by one of the three routes: muscular, vaginal, or rectal. We found that vaginal immunization of rabbits with HPV 6bL1 DNA induced 6bL1 virus-like particle-specific lgA antibodies in vaginal secretions. They were detectable until at least 14 weeks after the first immunization. The antibodies also showed neutralizing activity in a hemagglutination inhibition assay. No mucosal immune response was detected in vaginal secretions of rabbits immunized intramuscularly or intrarectally. Our data suggest that vaginal immunization with HPV 6bL1 DNA induces long-lasting IgA responses with neutralizing activity in vaginal secretions of rabbits.

Granulocyte-macrophage colony-stimulating factor priming plus papillomavirus E6 DNA vaccination: effects on papilloma formation and regression in the cottontail rabbit papillomavirus--rabbit model

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.

Nucleic acid vaccines: research tool or commercial reality

Polynucleotide immunization has captured the imagination of numerous researchers and commercial companies around the world as a novel approach for inducing immunity in animals. Clearly, the 'proof-of-principle' has been demonstrated both in rodents and various animal species. However, to date, no commercial veterinary vaccine has been developed, or to our knowledge, is in the licensing phase. The present review summarizes the types of pathogens and host species for which polynucleotide immunization has been tried. We have tried to identify possible barriers to commercialization of this technology and areas that need attention if this promising technology is ever to become a reality in the commercial arena.

Recent advances in diagnosis and therapy of human papillomaviruses

Infection with human papillomavirus is extremely common throughout the world. Almost 50% of sexually active young women are infected with human papillomavirus and although most infections are transient, a subset has the potential to progress to invasive cancer. During the last 20 years, our understanding of the human papillomavirus life cycle and the role of human papillomavirus in human cancer has dramatically increased. Recent technological advances in human papillomavirus detection have provided the means to detect the presence of human papillomavirus with great sensitivity. In the context of patient care, there is still substantial debate regarding the optimal diagnostic and prognostic use of information derived from hybrid capture or polymerase chain reaction-based detection. The inventory of available treatment options is growing somewhat slowly. The most promising advances are being made in the clinical evaluation of candidates for prophylactic vaccination. This review is focused on the current status and future directions of prevention, diagnosis and therapy.

Immunization of rabbits with cottontail rabbit papillomavirus E1 and E2 genes: protective immunity induced by gene gun-mediated intracutaneous delivery but not by intramuscular injection

We previously demonstrated that gene gun-based intracutaneous vaccination of rabbits with a combination of, but not with individual papillomavirus E1, E2, E6 and E7 genes provided complete protection against cottontail rabbit papillomavirus (CRPV) infection. In the present study, we tested whether vaccination of inbred and outbred rabbits with a combination of CRPV E1 and E2 genes could provide complete protection against virus infection. In the first experiment, gene gun-based intracutaneous vaccination with E1 and E2 genes prevented papilloma formation in the majority of inbred rabbits and promoted systemic papilloma regression in one non-protected rabbit. In contrast, needle-mediated intramuscular injection of E1 and E2 genes did not prevent papilloma formation nor promoted systemic papilloma regression, indicating an absence of strong protective immunity. In the second experiment, six outbred rabbits were immunized by gene gun-based intracutaneous administration of the E1 and E2 genes. Prevention of papilloma formation or systemic papilloma regression was observed in three vaccinated rabbits. Papillomas persisted on the remaining three rabbits, but were significantly smaller than that on control rabbits. These results suggested that gene gun-based intracutaneous vaccination with the combination of papillomavirus E1 and E2 genes induced strong protective antivirus immunity but may be insufficient for complete protection in an outbred population.

The immunology of animal papillomaviruses

Papillomaviruses are species- and tissue-specific double-stranded DNA viruses. These viruses cause epithelial tumours in many animals, including man. Typically, the benign warts undergo spontaneous, immune-mediated regression, most likely effected by T-cells (especially CD4, but also CD8 subsets), whereas humoral immunity can prevent new infections. Some papillomavirus infections fail to regress spontaneously and others progress to malignant epithelial tumours. Additionally, the impact of these lesions is greater in immunosuppressed individuals. Many therapies are ineffective, and there is much interest in the potential for immunological intervention in papillomavirus infections of man and animals. Vaccination can be achieved with 'live' virus, formalin-inactivated virus, synthetic virus-like particles, and DNA vaccination. There has been much recent progress in the development of such vaccines for papillomavirus infections in the rabbit, ox and dog. Success in these animal models suggests that similar approaches may prove useful for prophylactic or therapeutic vaccination against the important human papillomaviruses involved in the development of cutaneous and anogenital warts, laryngeal papillomatosis, and cervical cancer.

DNA vaccination of mice with plasmid expressing human papillomavirus 6 major capsid protein L1 elicits type-specific antibodies neutralizing pseudovirions constructed in vitro

Human papillomavirus 6 (HPV 6) causes benign condylomata. As a model for HPV vaccine development, we tested a HPV 6 DNA vaccine candidate, constructed by subcloning the major capsid protein (L1) gene into an expression plasmid having the cytomegalovirus promoter, for its immunogenicity in BALB/c mice. Three intracutaneous inoculations of the plasmid with a gene gun at 2-week intervals elicited anti-L1 serum antibodies. The antibodies were found to recognize highly type-specific, conformation-dependent epitopes, including those to neutralize pseudovirions capable of inducing beta-galactosidase in infected monkey COS-1 cells. The data support the idea that immunization with DNA capable of expressing HPV L1 can be used as an HPV vaccine strategy for humans.

Immunization of animals: from DNA to the dinner plate

Recently, there has been a great deal of interest in polynucleotide vaccination also referred to as DNA vaccines or genetic immunization for inducing long-term immunity in various animals and humans. The main attraction of this technology is the possibility to induce a broad range of immune responses without the use of conventional adjuvants. To date, most of the studies (>500 reports) have focused on DNA vaccination in mice. The present report summarizes the limited number of trials that have used target animal species to not only test the immune responses but also correlate them to protection.

Human papillomavirus vaccines

Genital human papillomavirus (HPV) infections are the viral sexually transmitted diseases most frequently diagnosed that include anogenital condylomas and squamous intra-$bepithelial lesions, among which the precursors of invasive carcinomas of the uterine cervix. In animal PV models, vaccination against L1 and/or L2 viral capsid proteins provides an efficient protection against infection, involving virus type-specific neutralizing antibodies. Vaccination against non-structural E1, E2, E6 or E7 viral proteins does not prevent infection, unless administered altogether, but tends to stimulate regression, warranting the design of therapeutic vaccines. Prophylactic vaccines based on the use of virus-like particles (VLPs) obtained by auto-assembly of L1 or L1 and L2 proteins produced by recombinant DNA technology are under phase I/II clinical trials for HPV6/11 associated with condylomas and for HPV16, the most frequent oncogenic genotype. Second generation vaccines are chimeric proteins or VLPs incorporating one of the structural proteins (L1 or L2) fused to a non-structural protein (E6, E7 or E2), which should induce both humoral and cellular immunity. Vaccine valency (number of genotypes), route of administration (humoral versus local immunity), vaccinees (children, young adults, gender) and forms of vaccines (recombinant $LSalmonella typhimurium*I$L, edible plants expressing L1 and L2 proteins, DNA vaccines, synthetic antigenic peptides) are under study. End points to evaluate vaccine efficacy in phase III trials should include viral DNA detection and typing, and screening for low or high grade intraepithelial lesions. Therapeutic vaccines based on recombinant HPV E6 and/or E7 vaccinia virus, L2-E7 fusion proteins or E7 peptides corresponding to cytotoxic T cell epitopes are currently tested (phase I/II trials) in patients with cervical carcinomas of advanced clinical stages or high grade intraepithelial lesions. Animal studies, phase I/II clinical trials and implementation of the community support that HPV vaccines will constitute an efficient means to prevent carcinoma of the uterine cervix.

DNA vaccines: a review

Therapeutic and prophylactic DNA vaccine clinical trials for a variety of pathogens and cancers are underway (Chattergoon et al., 1997; Taubes, 1997). The speed with which initiation of these trials occurred is no less than astounding; clinical trials for a human immunodeficiency virus (HIV) gp160 DNA-based vaccine were underway within 36 months of the first description of "genetic immunization" (Tang et al., 1992) and within 24 months of publication of the first article describing intramuscular delivery of a DNA vaccine (Ulmer et al., 1993). Despite the relative fervor with which clinical trials have progressed, it can be safely stated that DNA-based vaccines will not be an immunological "silver bullet." In this regard, it was satisfying to see a publication entitled "DNA Vaccines--A Modern Gimmick or a Boon to Vaccinology?" (Manickan et al., 1997b). There is no doubt that this technology is well beyond the phenomenology phase of study. Research niches and models have been established and will allow the truly difficult questions of mechanism and application to target species to be studied. These two aspects of future studies are intricately interwoven and will ultimately determine the necessity for mechanistic understanding and the evolution of target species studies. The basic science of DNA vaccines has yet to be clearly defined and will ultimately determine the success or failure of this technology to find a place in the immunological arsenal against disease. In a commentary on a published study describing DNA vaccine-mediated protection against heterologous challenge with HIV-1 in chimpanzees, Ronald Kennedy (1997) states, "As someone who has been in the trenches of AIDS vaccine research for over a decade and who, together with collaborators, has attempted a number of different vaccine approaches that have not panned out, I have a relatively pessimistic view of new AIDS vaccine approaches." Kennedy then goes on to summarize a DNA-based multigene vaccine approach and the subsequent development of neutralizing titers and potent CTL activity in immunized chimpanzees (Boyer et al., 1997). Dr. Kennedy closes his commentary by stating. "The most exciting aspect of this report is the experimental challenge studies.... Viraemia was extremely transient and present at low levels during a single time point. These animals remained seronegative ... for one year after challenge" and "Overall, these observations engender some excitement". (Kennedy, 1997). Although this may seem a less than rousing cheer for DNA vaccine technology, it is a refreshingly hopeful outlook for a pathogen to which experience has taught humility. It has also been suggested that DNA vaccine technology may find its true worth as a novel alternative option for the development of vaccines against diseases that conventional vaccines have been unsuccessful in controlling (Manickan et al., 1997b). This is a difficult task for any vaccine, let alone a novel technology. DNA-based vaccine technology represents a powerful and novel entry into the field of immunological control of disease. The spinoff research has also been dramatic, and includes the rediscovery of potent bacterially derived immunomodulatory DNA sequences (Gilkeson et al., 1989), as well as availability of a methodology that allows extremely rapid assessment and dissection of both antigens and immunity. The benefits of potent Th1-type immune responses to DNA vaccines must not be overlooked, particularly in the light of suggestions that Western culture immunization practices may be responsible for the rapid increases in adult allergic and possibly autoimmune disorders (Rook and Stanford, 1998). The full utility of this technology has not yet been realized, and yet its broad potential is clearly evident. Future investigations of this technology must not be hindered by impatience, misunderstanding, and lack of funding or failure of an informed collective and collaborative effort.

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

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.

Genetic vaccines

In a few short years, genetic vaccine technology has moved rapidly from a novel concept to an important strategy for the development of human and veterinary vaccines, for numerous indications. This article discusses current areas in which further refinements in technology will influence a variety of infectious disease treatments, including intramuscular and intradermal inoculation, gene gun inoculation, the mechanism of antigen presentation, and the use of genetic adjuvants.

DNA vaccines for viral diseases

DNA vaccines, with which the antigen is synthesized in vivo after direct introduction of its encoding sequences, offer a unique method of immunization that may overcome many of the deficits of traditional antigen-based vaccines. By virtue of the sustained in vivo antigen synthesis and the comprised stimulatory CpG motifs, plasmid DNA vaccines appear to induce strong and long-lasting humoral (antibodies) and cell-mediated (T-help, other cytokine functions and cytotoxic T cells) immune responses without the risk of infection and without boost. Other advantages over traditional antigen-containing vaccines are their low cost, the relative ease with which they are manufactured, their heat stability, the possibility of obtaining multivalent vaccines and the rapid development of new vaccines in response to new strains of pathogens. The antigen-encoding DNA may be in different forms and formulations, and may be introduced into cells of the body by numerous methods. To date, animal models have shown the possibility of producing effective prophylactic DNA vaccines against numerous viruses as well as other infectious pathogens. The strong cellular responses also open up the possibility of effective therapeutic DNA vaccines to treat chronic viral infections.

Intracutaneous vaccination of rabbits with the E6 gene of cottontail rabbit papillomavirus provides partial protection against virus challenge

DNA vaccination of rabbit skin with the L1 gene of cottontail rabbit papillomavirus (CRPV) has previously been shown to induce prophylactic immunity against CRPV. We now describe the effects of vaccination with the CRPV E6 gene, using the same approach. The experimental vaccine pdCMV-E6 encoded both the truncated and full length forms of CRPV E6 protein. The control vaccine pCMV-beta encoded beta galactosidase. Rabbits were vaccinated with DNA-coated gold particles, using a gene gun. Each rabbit received an initial vaccination with 30 micrograms DNA and 3 weeks later a booster vaccination, also with 30 micrograms DNA. pdCMV-E6-vaccinated rabbits developed E6-specific cellular immunity as determined by proliferation assays using peripheral blood mononuclear cells from animals prior to challenge, but did not develop detectable humoral immunity to E6 proteins, as evaluated by ELISA using two different E6 antigen preparations. Control rabbits developed humoral immunity to beta galactosidase. All rabbits were challenged by infection of nine skin sites with live CRPV virus and monitored for papilloma formation. None of four control rabbits was protected at any of the challenge sites. Of six rabbits vaccinated with pdCMV-E6, two were completely protected and one was virtually completely protected (tiny papillomas at just two of nine challenge sites). These three rabbits also exhibited significant E6-specific in vitro proliferative responses. The four E6 DNA-vaccinated rabbits that were not completely protected exhibited evidence of partial protection: some challenge sites did not form papillomas; papilloma onset was delayed; papilloma burden was less. These results demonstrate that partial prophylaxis against papillomavirus-induced disease can be achieved by intracutaneous vaccination with a recombinant plasmid encoding the papillomavirus.