Intercellular trafficking of the major tegument protein VP22 of bovine herpesvirus-1 and its application to improve a DNA vaccine

Cell-penetrating Peptides: Efficient Vectors for Vaccine Delivery

Subunit vaccines are composed of pathogen fragments that, on their own, are generally poorly immunogenic. Therefore, the incorporation of an immunostimulating agent, e.g. adjuvant, into vaccine formulation is required. However, there are only a limited number of licenced adjuvants and their immunostimulating ability is often limited, while their toxicity can be substantial. To overcome these problems, a variety of vaccine delivery systems have been proposed. Most of them are designed to improve the stability of antigen in vivo and its delivery into immune cells. Cell-penetrating peptides (CPPs) are especially attractive component of antigen delivery systems as they have been widely used to enhance drug transport into the cells. Fusing or co-delivery of antigen with CPPs can enhance antigen uptake, processing and presentation by antigen presenting cells (APCs), which are the fundamental steps in initiating an immune response. This review describes the different mechanisms of CPP intercellular uptake and various CPP-based vaccine delivery strategies.

DNA-epitope vaccine provided efficient protection to mice against lethal dose of influenza A virus H1N1

Swine influenza virus (SIV) is a fast-evolving viral pathogen in pig populations. However, commercial vaccines, based on inactivated viruses, cannot provide complete protection with induced humoral immunity only and require frequent updates to fight against current isolates. A DNA vaccine delivering conservative epitopes was designed in this study in the hope of meeting the need. In this study, a B-cell epitope (HA2.30-130), a quadruplicated Th-cell epitope (NP55-69), and a quadruplicated CTL epitope (NP147-158) were fused separately to the C-terminal of VP22c gene in the modified pcDNA3.1 plasmid. The expression of epitopes was confirmed by in vitro transfection of 293FT cells. The DNA vaccine administered intramuscularly stimulated epitope-specific immunity against the two T-cell epitopes in all ten mice before the virus challenge. Only two out of ten mice were ELISA positive against the B-cell epitope. All vaccinated mice survived a lethal dose of virus challenge, while all mice in the challenge control group died. The DNA vaccine delivering epitopes in this study showed promising protection against influenza virus in an animal model; however, more work needs to be done to evaluate the best conserved protective epitopes which can be applied in developing a universal DNA vaccine.

DNA-vaccine platform development against H1N1 subtype of swine influenza A viruses

Swine influenza virus (SIV) is an important viral pathogen in pig populations. However, commercial vaccines cannot provide complete protection with induced humoral immunity only, and require frequent updates to fight against current isolates. DNA vaccination is an effective means of eliciting both arms of the immune system, the humoral and cellular immune responses. In this study, DNA vector pcDNA3.1 was inserted with a chimeric intron downstream of the CMV promoter region followed by a Kozak sequence to enhance the expression of gene inserts. The C-terminal of the VP22 gene (VP22c), encoding the tegument protein of bovine herpesvirus-1, was fused separately to the N-terminal of four quadruplicated epitopes: two B-cell epitopes (HA91-108 and M2e), and two T-cell epitopes (NP366-374 and NP380-393), which were conserved, at least among the three SIV subtypes prevailing in pig populations in North America. Linker -KK- was used to space between each copy of the two B-cell epitopes, and -RVKR- was used for the two T-cell epitopes, in order to enhance the presentation of epitopes to the immune system. The expression of epitopes was confirmed in in vitro transfection of 293FT cells, and higher percentages of epitope-positive cells were achieved from the plasmids containing VP22c than those without. After the DNA plasmids were administered to mice intramuscularly in combination or separately, or boosted with recombinant proteins of quadruplicated epitopes fused to VP22c, the vaccine stimulated the desired epitope-specific humoral immunity to the two B-cell epitopes, and cellular immunity to the epitope NP380-393. Our results indicate that plasmids with quadruplicated epitopes fused to the VP22c may be a potential vehicle in developing epitopes as vaccines against SIV.

Peptides in cancer nanomedicine: drug carriers, targeting ligands and protease substrates

Peptides are attracting increasing attention as therapeutic agents, as the technologies for peptide development and manufacture continue to mature. Concurrently, with booming research in nanotechnology for biomedical applications, peptides have been studied as an important class of components in nanomedicine, and they have been used either alone or in combination with nanomaterials of every reported composition. Peptides possess many advantages, such as smallness, ease of synthesis and modification, and good biocompatibility. Their functions in cancer nanomedicine, discussed in this review, include serving as drug carriers, as targeting ligands, and as protease-responsive substrates for drug delivery.

Alphaherpesviruses and the cytoskeleton in neuronal infections

Following infection of exposed peripheral tissues, neurotropic alphaherpesviruses invade nerve endings and deposit their DNA genomes into the nuclei of neurons resident in ganglia of the peripheral nervous system. The end result of these events is the establishment of a life-long latent infection. Neuroinvasion typically requires efficient viral transmission through a polarized epithelium followed by long-distance transport through the viscous axoplasm. These events are mediated by the recruitment of the cellular microtubule motor proteins to the intracellular viral particle and by alterations to the cytoskeletal architecture. The focus of this review is the interplay between neurotropic herpesviruses and the cytoskeleton.

Current strategies for subunit and genetic viral veterinary vaccine development

Developing vaccines for livestock provides researchers with the opportunity to perform efficacy testing in the natural hosts. This enables the evaluation of different strategies, including definition of effective antigens or antigen combinations, and improvement in delivery systems for target antigens so that protective immune responses can be modulated or potentiated. An impressive amount of knowledge has been generated in recent years on vaccine strategies and consequently a wide variety of antigen delivery systems is now available for vaccine research. This paper reviews several antigen production and delivery strategies other than those based on the use of live viral vectors. Genetic and protein subunit vaccines as well as alternative production systems are considered in this review.

Therapeutic HPV DNA vaccines

It is now well established that most cervical cancers are causally associated with HPV infection. This realization has led to efforts to control HPV-associated malignancy through prevention or treatment of HPV infection. Currently, commercially available HPV vaccines are not designed to control established HPV infection and associated premalignant and malignant lesions. To treat and eradicate pre-existing HPV infections and associated lesions which remain prevalent in the U.S. and worldwide, effective therapeutic HPV vaccines are needed. DNA vaccination has emerged as a particularly promising form of therapeutic HPV vaccines due to its safety, stability and ability to induce antigen-specific immunity. This review focuses on improving the potency of therapeutic HPV vaccines through modification of dendritic cells (DCs) by [1] increasing the number of antigen-expressing/antigen-loaded DCs, [2] improving HPV antigen expression, processing and presentation in DCs, and [3] enhancing DC and T cell interaction. Continued improvement in therapeutic HPV DNA vaccines may ultimately lead to an effective DNA vaccine for the treatment of HPV-associated malignancies.

Bovine herpesvirus-1 US3 protein kinase: critical residues and involvement in the phosphorylation of VP22

The US3 gene product of bovine herpesvirus-1 (BoHV-1) is a protein kinase that is expressed early during infection and capable of autophosphorylation. By examining differentially labelled US3 moieties by co-immunoprecipitation, we demonstrated that the protein kinase interacts with itself in vitro, which supports autophosphorylation by US3. Based on its homology to other serine/threonine protein kinases, we defined two highly conserved lysines in US3, at position 195 within the ATP-binding pocket and at position 282 within the catalytic loop; altering either residue resulted in kinase-dead mutants, demonstrating that these two residues are critical for the catalytic activity of BoHV-1 US3. During immunoprecipitation experiments, US3 interacted weakly with VP22, another tegument protein of BoHV-1. Furthermore, VP22 co-localized with US3 inside the nucleus in BoHV-1-infected cells. In vitro kinase assays demonstrated that VP22 is phosphorylated not only by US3, but also by the cellular casein kinase 2 (CK2) protein. The selective CK2 protein kinase inhibitor, 2-dimethylamino-4,5,6,7-tetrabromo-1H-benzimidazole (DMAT) and the less specific CK2 inhibitor Kenpaullone reduced VP22 phosphorylation, while CK1, protein kinase C or protein kinase A inhibitors did not affect phosphorylation. When US3 was included with VP22 in the kinase assay in the presence of DMAT, a low level of VP22 phosphorylation was observed. These data demonstrate that BoHV-1 VP22 interacts with both CK2 and US3, and that CK2 is the major kinase phosphorylating VP22, with US3 playing a minor role.

Enhanced immune response and protection efficacy of a DNA vaccine constructed by linkage of the Mycobacterium tuberculosis Ag85B-encoding gene with the BVP22-encoding gene

Plasmid DNA vaccines have been widely explored for use in tuberculosis immunization but their immunogenicity needs improvement. In the present study, we incorporated the bovine herpesvirus 1 VP22 (BVP22)-encoding gene, which encodes a protein that demonstrates a capability for disseminating the expressed antigen to neighbouring cells, into a DNA vector in which it was fused to the Ag85B-encoding gene of Mycobacterium tuberculosis (Mtb), and investigated whether this linkage could enhance immune response and protective efficacy in C57BL/6 mice compared to plasmid DNA encoding Ag85B alone. After immunization in mice, Ag85B-specific ELISA antibodies and spleen lymphocyte proliferative responses induced by DNA co-expressing BVP22 and Ag85B were significantly higher than those obtained in mice immunized with Ag85B-encoding DNA alone, except for the number of gamma interferon secreting cells. In addition, based on histopathological examination and bacterial-load determination in lung and spleen, protection against intravenous Mtb H37Rv challenge evoked by the BVP22–Ag85B DNA immunization exceeded the response elicited by Ag85B DNA alone, which was not significantly different from that provided by Bacillus Calmette–Guérin (BCG). These results suggested that DNA vaccine consisting of BVP22 and Ag85B-encoding DNA enhanced immune response and protection against intravenous Mtb H37Rv challenge in mice, indicating that BVP22-encoding DNA might be a promising tool to enhance TB DNA vaccine efficacy.

Assessment of the cell-mediated immunity induced by alphavirus replicon-vectored DNA vaccines against classical swine fever in a mouse model

We have previously shown that an alphavirus replicon-vectored DNA vaccine (pSFV1CS-E2) encoding the E2 glycoprotein of classical swine fever virus (CSFV) completely protected the immunized pigs from lethal challenge. These animals developed only low or moderate level viral-specific antibody titers before challenge, implying that cell-mediated immunity (CMI) probably played an important role in the protective immunity against CSFV conferred by the DNA vaccine. In this study, the CMI induced by pSFV1CS-E2 and its derivative pSFV1CS-E2-UL49 encoding a fusion protein of CSFV E2 and pseudorabies virus (PRV) VP22 was evaluated in a mouse model by lymphoproliferation assays based on CFSE or WST-8, intracellular cytokine staining, and cytokine ELISA. The results showed that both vaccines induced CSFV-specific lymphoproliferative responses and cytokine production, and pSFV1CS-E2-UL49 induced stronger lymphoproliferative responses and higher cytokine levels than pSFV1CS-E2. These findings suggest that the alphavirus replicon-delivered DNA vaccines are capable of inducing CMI, and PRV VP22 is able to enhance the immunogenicity of the co-delivered antigen.

Optimization of a DNA vaccine against SARS

Severe acute respiratory syndrome coronavirus (SARS-CoV) first appeared in Southern China in November 2002, and then quickly spread to 33 countries on five continents along international air travel routes. Although the SARS epidemic has been contained, there is a clear need for a safe and effective vaccine should an outbreak of a SARS-CoV infection reappear in human population. In this study, we tested four DNA-vaccine constructs: (1) pLL70, containing cDNA for the SARS-CoV spike (S) gene; (2) pcDNA-SS, containing codon-optimized S gene for SARS-CoV S protein (residues 12-1255) fused with a leader sequence derived from the human CD5 gene; (3) pcDNA-St, containing the gene encoding the N-portion of the codon-optimized S gene (residues 12-532) with the CD5 leader sequence; (4) pcDNA-St-VP22C, containing the gene encoding the N-portion of the codon-optimized S protein with the CD5 leader sequence fused with the C-terminal 138 amino acids of the bovine herpesvirus-1 (BHV-1) major tegument protein VP22. Each of these plasmids was intradermally administered to C57BL/6 mice in three separate immunizations. Analysis of humoral and cellular immune responses in immunized mice demonstrated that pcDNA-SS and pcDNA-St-VP22C are the most immunogenic SARS vaccine candidates.

Enhancing DNA vaccine potency by modifying the properties of antigen-presenting cells

DNA vaccines represent a potentially promising approach for antigen-specific immunotherapy. Advances in our knowledge of the adaptive immune system have indicated that professional antigen-presenting cells, especially dendritic cells (DCs), play a key role in the generation of antigen-specific immune responses. Thus, the modification of the properties of DCs represents an important strategy for enhancing the potency of DNA vaccines. This review discusses strategies to increase the number of antigen-expressing DCs, enhance antigen expression, processing and presentation in DCs, promote the activation and function of DCs, and improve DC and T-cell interaction, in order to optimize DNA vaccine-elicited immune responses. Continuing progress in our understanding of DC and T-cell biology serves as a foundation for further improvement of DNA vaccine potency, which may lead to future clinical applications of DNA vaccines for the control of infectious diseases and malignancies.