Reversal of papilloma growth in rabbits therapeutically vaccinated against E6 with naked DNA and/or vesicular stomatitis virus vectors

Fusion Expression and Immune Effect of PCV2 Cap Protein Tandem Multiantigen Epitopes with CD154/GM-CSF

Porcine circovirus associated diseases (PCVAD) is a contagious disease of swine caused by porcine circovirus type 2 (PCV2). The capsid protein (Cap) is the sole structural protein and the main antigen of PCV2. Cap is the principal immunogenic protein and induces humoral and cellular immunity. CD154 and GM-CSF are immune adjuvants that enhance responses to vaccines. However, whether these two cellular molecules could produce an enhanced effect in PCV2 vaccines still needs to be further studied. The results of PCR and restriction enzyme showed that the recombinant lentiviral plasmids pCDH-TB-Cap, pCDH-TB-Cap-CD154 and pCDH-TB-Cap were successfully constructed. Western blot and IFA showed that the three fusion proteins TB-Cap, TB-Cap-CD154 and TB-Cap-GM-CSF were stably expressed in CHO-K1 cells. Indirect ELISA assay showed that mice immunized with TB-Cap-CD154 and TB-Cap-GM-CSF fusion proteins produced higher PCV2-specific antibodies than mice immunized with the TB-Cap and a commercial vaccine (p < 0.0001). Moreover, lymphocyte proliferation and flow cytometry showed that the cellular immune response of each immune group was significantly enhanced (p < 0.0001). After PCV2 challenge, the results revealed that the viral loads in serum, lung and kidney of all vaccinated groups were significantly lower than the PBS group (p < 0.0001). The transcription levels of IL-2, IFN-gamma, IL-4 and IL-10 cytokines in the TB-Cap, TB-Cap-CD154 and TB-Cap-GM-CSF groups were significantly higher than those in the PBS and recombinant vaccine groups (p < 0.0001). These results indicated that CD154 and GM-CSF could enhance the ability of TB-Cap protein to induce the body to produce PCV2 specific antibodies and increase the transcription level of cytokines. Thus, CD154 and GM-CSF molecules were a powerful immunoadjuvant for PCV2 subunit vaccines. The novel TB-Cap-CD154 and TB-Cap-GM-CSF subunit vaccine has the potential to be used for the prevention and control of PCVAD.

Rhabdoviruses as vectors for vaccines and therapeutics

Appropriate choice of vaccine vector is crucial for effective vaccine development. Rhabdoviral vectors, such as rabies virus and vesicular stomatitis virus, have been used in a variety of vaccine strategies. These viruses have small, easily manipulated genomes that can stably express foreign glycoproteins due to a well-established reverse genetics system for virus recovery. Both viruses have well-described safety profiles and have been demonstrated to be effective vaccine vectors. This review will describe how these Rhabdoviruses can be manipulated for use as vectors, their various applications as vaccines or therapeutics, and the advantages and disadvantages of their use.

Orf Virus-Based Therapeutic Vaccine for Treatment of Papillomavirus-Induced Tumors

Orf virus (ORFV) represents a suitable vector for the generation of efficient, prophylactic antiviral vaccines against different pathogens. The present study investigated for the first time the therapeutic application of ORFV vector-based vaccines against tumors induced by cottontail rabbit papillomavirus (CRPV). ORFV-CRPV recombinants were constructed expressing the early CRPV gene E1, E2, E7, or LE6. In two independent experiments we used in total 23 rabbits which were immunized with a mixture of the four ORFV-CRPV recombinants or empty ORFV vector as a control 5 weeks after the appearance of skin tumors. For the determination of the therapeutic efficacy, the subsequent growth of the tumors was recorded. In the first experiment, we could demonstrate that three immunizations of rabbits with high tumor burden with the combined four ORFV-CRPV recombinants resulted in significant growth retardation of the tumors compared to the control. A second experiment was performed to test the therapeutic effect of 5 doses of the combined vaccine in rabbits with a lower tumor burden than in nonimmunized rabbits. Tumor growth was significantly reduced after immunization, and one vaccinated rabbit even displayed complete tumor regression until the end of the observation period at 26 weeks. Results of delayed-type hypersensitivity (DTH) skin tests suggest the induction of a cellular immune response mediated by the ORFV-CRPV vaccine. The data presented show for the first time a therapeutic potential of the ORFV vector platform and encourage further studies for the development of a therapeutic vaccine against virus-induced tumors.IMPORTANCE Viral vectors are widely used for the development of therapeutic vaccines for the treatment of tumors. In our study we have used Orf virus (ORFV) strain D1701-V for the generation of recombinant vaccines expressing cottontail rabbit papillomavirus (CRPV) early proteins E1, E2, LE6, and E7. The therapeutic efficacy of the ORFV-CRPV vaccines was evaluated in two independent experiments using the outbred CRPV rabbit model. In both experiments the immunization achieved significant suppression of tumor growth. In total, 84.6% of all outbred animals benefited from the ORFV-CRPV vaccination, showing reduction in tumor size and significant tumor growth inhibition, including one animal with complete tumor regression without recurrence.

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'.

A prime/boost strategy using DNA/fowlpox recombinants expressing the genetically attenuated E6 protein as a putative vaccine against HPV-16-associated cancers

BACKGROUND

Considering the high number of new cases of cervical cancer each year that are caused by human papilloma viruses (HPVs), the development of an effective vaccine for prevention and therapy of HPV-associated cancers, and in particular against the high-risk HPV-16 genotype, remains a priority. Vaccines expressing the E6 and E7 proteins that are detectable in all HPV-positive pre-cancerous and cancer cells might support the treatment of HPV-related lesions and clear already established tumors.

METHODS

In this study, DNA and fowlpox virus recombinants expressing the E6F47R mutant of the HPV-16 E6 oncoprotein were generated, and their correct expression verified by RT-PCR, Western blotting and immunofluorescence. Immunization protocols were tested in a preventive or therapeutic pre-clinical mouse model of HPV-16 tumorigenicity using heterologous (DNA/FP) or homologous (DNA/DNA and FP/FP) prime/boost regimens. The immune responses and therapeutic efficacy were evaluated by ELISA, ELISPOT assays, and challenge with TC-1* cells.

RESULTS

In the preventive protocol, while an anti-E6-specific humoral response was just detectable, a specific CD8(+) cytotoxic T-cell response was elicited in immunized mice. After the challenge, there was a delay in cancer appearance and a significant reduction of tumor volume in the two groups of E6-immunized mice, thus confirming the pivotal role of the CD8(+) T-cell response in the control of tumor growth in the absence of E6-specific antibodies. In the therapeutic protocol, in-vivo experiments resulted in a higher number of tumor-free mice after the homologous DNA/DNA or heterologous DNA/FP immunization.

CONCLUSIONS

These data establish a preliminary indication for the prevention and treatment of HPV-related tumors by the use of DNA and avipox constructs as safe and effective immunogens following a prime/boost strategy. The combined use of recombinants expressing both E6 and E7 proteins might improve the antitumor efficacy, and should represent an important approach to control HPV-associated cancers.

A viable recombinant rhabdovirus lacking its glycoprotein gene and expressing influenza virus hemagglutinin and neuraminidase is a potent influenza vaccine

The emergence of novel influenza viruses that cause devastating human disease is an ongoing threat and serves as an impetus for the continued development of novel approaches to influenza vaccines. Influenza vaccine development has traditionally focused on producing humoral and/or cell-mediated immunity, often against the viral surface glycoproteins hemagglutinin (HA) and neuraminidase (NA). Here, we describe a new vaccine candidate that utilizes a replication-defective vesicular stomatitis virus (VSV) vector backbone that lacks the native G surface glycoprotein gene (VSVΔG). The expression of the H5 HA of an H5N1 highly pathogenic avian influenza virus (HPAIV), A/Vietnam/1203/04 (VN1203), and the NA of the mouse-adapted H1N1 influenza virus A/Puerto Rico/8/34 (PR8) in the VSVΔG vector restored the ability of the recombinant virus to replicate in cell culture, without the requirement for the addition of trypsin. We show here that this recombinant virus vaccine candidate was nonpathogenic in mice when given by either the intramuscular or intranasal route of immunization and that the in vivo replication of VSVΔG-H5N1 is profoundly attenuated. This recombinant virus also provided protection against lethal H5N1 infection after a single dose. This novel approach to vaccination against HPAIVs may be widely applicable to other emerging strains of influenza virus.

IMPORTANCE

Preparation for a potentially catastrophic influenza pandemic requires novel influenza vaccines that are safe, can be produced and administered quickly, and are effective, both soon after administration and for a long duration. We have created a new influenza vaccine that utilizes an attenuated vesicular stomatitis virus (VSV) vector, to deliver and express influenza virus proteins against which vaccinated animals develop potent antibody responses. The influenza virus hemagglutinin and neuraminidase proteins, expressed on the surface of VSV particles, allowed this vaccine to grow in cell culture and induced a potent antibody response in mice that was effective against infection with a lethal influenza virus. The mice showed no adverse reactions to the vaccine, and they were protected against an otherwise lethal influenza infection after only 14 days postvaccination and after as many as 140 days postvaccination. The ability to rapidly produce this safe and effective vaccine in cell culture is additionally advantageous.

Long-peptide therapeutic vaccination against CRPV-induced papillomas in HLA-A2.1 transgenic rabbits

Long peptide immunization is a promising strategy to clear established tumors. In the current study, we investigated the therapeutic effect of a naturally existing long peptide that contained two HLA-A2.1 restricted epitopes (CRPVE1/149-157 and CRPVE1/161-169) from cottontail rabbit papillomavirus (CRPV) E1 using our CRPV/HLA-A2.1 transgenic rabbit model. A universal Tetanus Toxin helper motif (TT helper) was tagged at either the N-terminus or the carboxyl-terminus of this long peptide and designated as TT-E1 peptide and E1 peptide-TT respectively. Four groups of HLA-A2.1 transgenic rabbits were infected with wild type CRPV DNA. Three weeks post-infection, the rabbits were immunized four times with TT-E1 peptide, E1peptide only, E1 peptide -TT or TT-control peptide with two-week intervals between immunizations. Tumor outgrowth was monitored and recorded weekly. After the third booster immunization, tumors on two of the four E1 peptide-TT immunized rabbits began to shrink. One animal from this group was free of tumors at the termination of the study. The mean papilloma size of E1 peptide-TT immunized rabbits was significantly smaller when compared with that of the three other groups (P<0.05, one way ANOVA analysis). It is interesting that E1 peptide-TT vaccination not only stimulated stronger T cell mediate immune responses but also stronger antibody generations. We conclude that the location of a TT helper motif tagged at the long peptide vaccine is critical for the outcome of therapeutic responses to persistent tumors in our HLA-A2.1 transgenic rabbit model.

Highly attenuated recombinant vesicular stomatitis virus VSV-12'GFP displays immunogenic and oncolytic activity

Vesicular stomatitis virus (VSV) has shown considerable promise both as an immunization vector and as an oncolytic virus. In both applications, an important concern is the safety profile of the virus. To generate a highly attenuated virus, we added two reporter genes to the 3' end of the VSV genome, thereby shifting the NPMGL genes from positions 1 to 5 to positions 3 to 7. The resulting virus (VSV-12'GFP) was highly attenuated, generating smaller plaques than four other attenuated VSVs. In one-step growth curves, VSV-12'GFP displayed the slowest growth kinetics. The mechanism of attenuation appears to be due to reduced expression of VSV genes downstream of the reporter genes, as suggested by a 10.4-fold reduction in L-protein RNA transcript. Although attenuated, VSV-12'GFP was highly effective at generating an immune response, indicated by a high-titer antibody response against the green fluorescent protein (GFP) expressed by the virus. Although VSV-12'GFP was more attenuated than other VSVs on both normal and cancer cells, it nonetheless showed a greater level of infection of human cancer cells (glioma and melanoma) than of normal cells, and this effect was magnified in glioma by interferon application, indicating selective oncolysis. Intravenous VSV-12'GFP selectively infected human gliomas implanted into SCID mice subcutaneously or intracranially. All postnatal day 16 mice given intranasal VSV-12'GFP survived, whereas only 10% of those given VSV-G/GFP survived, indicating reduced neurotoxicity. Intratumoral injection of tumors with VSV-12'GFP dramatically suppressed tumor growth and enhanced survival. Together these data suggest this recombinant virus merits further study for its oncolytic and vaccine potential.

A vesicular stomatitis virus-based hepatitis B virus vaccine vector provides protection against challenge in a single dose

As one of the world's most common infectious diseases, hepatitis B virus (HBV) is a serious worldwide public health problem, with HBV-associated liver disease accounting for more than half a million deaths each year. Although there is an effective prophylactic vaccine currently available to prevent infection, it has a number of characteristics that are suboptimal: multiple doses are needed to induce long-lasting immunity, immunity declines over time, it does not elicit protection in some individuals, and it is not effective therapeutically. We produced a recombinant vesicular stomatitis virus (VSV)-based vaccine vector expressing the HBV middle envelope surface protein (MS) and found that this vector was able to efficiently generate a strong HBs-specific antibody response following a single immunization in mice. A single immunization with the VSV-MS vector also induced robust CD8 T-cell activation. The CD8 T-cell response was greater in magnitude and broader in specificity than the response generated by a vaccinia virus-based vaccine vector or by recombinant protein immunization. Furthermore, a single VSV-MS immunization provided protection against virus challenge in mice. Given the similar antibody titers and superior T-cell responses elicited from a single immunization, a VSV-based HBV vaccine may have advantages over the current recombinant protein vaccine.

Combined administration with DNA encoding vesicular stomatitis virus G protein enhances DNA vaccine potency

DNA vaccines have recently emerged at the forefront of approaches to harness the immune system in the prevention and treatment of viral infections, as well as the prevention and treatment of cancers. However, these vaccines suffer from limited efficacy since they often fail to produce significant antigen-specific CD8(+) T-cell responses. We report here a novel concept for DNA vaccine design that exploits the unique and powerful ability of viral fusogenic membrane glycoproteins (FMGs) to couple concentrated antigen transfer to dendritic cells (DCs) with local induction of the acute inflammatory response. Intramuscular administration into mice by electroporation technology of a plasmid containing the FMG gene from vesicular stomatitis virus (VSV-G)-together with DNA encoding the E7 protein of human papillomavirus type 16, a model cervical cancer antigen-elicited robust E7-specific CD8(+) T-cell responses, as well as therapeutic control of E7-expressing tumors. This effect could potentially be mediated through the immunogenic form of cellular fusion and necrosis induced by VSV-G, which in a concerted fashion provokes leukocyte infiltration into the inoculation site, enhances cross-presentation of antigen to DCs, and stimulates them to mature efficiently. Thus, the incorporation of FMGs into DNA vaccines holds promise for the successful control of viral infections and cancers in the clinic.

Papillomavirus prophylactic vaccines: established successes, new approaches

Vaccines against the human papillomaviruses (HPVs) most frequently associated with cancer of the cervix are now available. These prophylactic vaccines, based on virus-like particles (VLPs), are extremely effective, providing protection from infection in almost 100% of cases. However, the vaccines present some limitations: they are effective primarily against the HPV type present in the vaccine, are expensive to produce, and need a cold chain. Vaccines based on the minor capsid protein L2 have been very successful in animal models and have been shown to provide a good level of protection against different papillomavirus types. The potential of L2-based vaccines to protect against many types of HPVs is discussed.