CpG motif in ATCGAT hexamer improves DNA-vaccine efficiency against lethal Pseudorabies virus infection in pigs

Path to Success and Future Impact of Nucleic Acid Vaccines: DNA and mRNA

The rapid development of mRNA vaccines for COVID-19 has both astonished the world and raised concerns about their safety, perhaps because many people do not realize the decades’ long efforts for nucleic acid vaccines, both mRNA and DNA vaccines, including the licensure of several veterinary DNA vaccines. This manuscript traces the milestones for nucleic acid vaccine research and development (R&D), with a focus on the immune and safety issues they both raised and answered. The characteristics of the two entities are compared, demonstrating the similarities and differences between them, the advantages and disadvantages, which might lead toward using one or the other technology for different indications. In addition, as the SARS-CoV-2 pandemic has once again highlighted the importance of One Health, that is, the interactions between animal and human pathogens, focus will also be given to how DNA vaccine utilization and studies both in large domestic animals and in wildlife pave the way for more integrated approaches for vaccines to respond quickly to, and prevent, the global impacts of emerging diseases.

The Key Role of Nucleic Acid Vaccines for One Health

The ongoing SARS-CoV-2 pandemic has highlighted both the importance of One Health, i.e., the interactions and transmission of pathogens between animals and humans, and the potential power of gene-based vaccines, specifically nucleic acid vaccines. This review will highlight key aspects of the development of plasmid DNA Nucleic Acid (NA) vaccines, which have been licensed for several veterinary uses, and tested for a number of human diseases, and will explain how an understanding of their immunological and real-world attributes are important for their efficacy, and how they helped pave the way for mRNA vaccines. The review highlights how combining efforts for vaccine development for both animals and humans is crucial for advancing new technologies and for combatting emerging diseases.

The expression level of gC1qR is down regulated at the early time of infection with porcine circovirus of type 2 (PCV-2) and gC1qR interacts differently with the Cap proteins of porcine circoviruses

Porcine circoviruses (PCV) are small, non-enveloped single-stranded DNA-viruses. Porcine circovirus type 2 (PCV-2) is the causal agent of post-weaning multisystemic wasting syndrome (PMWS) whereas porcine circovirus of type 1 (PCV-1) is non- pathogenic. gC1qR is a membrane-located receptor of the complement protein subunit C1q and interacts with PCV capsid proteins. The mechanisms associated with the triggering of PMWS are not well known and gC1qR may have a role in the life cycle and eventually in the pathogenicity of PCV. The objectives of this study were to determine the level of expression of gC1qR during early PCV-2 infection, to determine the region of PCV-2 capsid protein (Cap) required for the interaction with gC1qR and to evaluate the interaction of gC1qR with Cap proteins of different PCV strains. The results indicate that gC1qR transcripts are downregulated in the tonsils and the tracheo-bronchial lymph nodes of piglets infected by PCV-2 at the early time of the infection. The N-terminal amino acids (a.a. 1-59) of PCV-2b Cap, an arginine rich region, are involved in the interaction with gC1qR. Porcine gC1qR interacts with Cap proteins of two pathogenic viral strains, PCV-2a and PCV-2b, while interaction has been observed with only one Cap protein of two investigated strains of PCV-1. The amino acids 30 and 49 of PCV-1Cap, solely, were not responsible of the difference of interaction observed. We have also shown that gC1qR interacts strongly with PCV-2Caps and PCV-1 GER Cap. This result suggests that the different interaction of gC1qR with PCV Cap proteins may have an impact on the pathogenicity of the PCV.

Comparative analysis of routes of immunization of a live porcine reproductive and respiratory syndrome virus (PRRSV) vaccine in a heterologous virus challenge study

Porcine reproductive and respiratory syndrome (PRRS) is caused by PRRS virus (PRRSV), which infects primarily the respiratory tract of pigs. Thus intranasal (IN) delivery of a potent vaccine-adjuvant formulation is promising. In this study, PRRS-MLV (VR2332) was coadministered ± an adjuvant Mycobacterium vaccae whole cell lysate or CpG ODN through intramuscular (IM) or IN route as a mist, and challenged with a heterologous PRRSV 1-4-4 IN at 42 days post-vaccination (dpv). At 14 and 26 dpv, vaccine viral RNA copies were one log greater in the plasma of PRRS-MLV IM compared to IN vaccinated pigs, and the infectious replicating vaccine virus was detected only in the IM group. In PRRS-MLV ± adjuvant IM vaccinated pigs, reduced viral RNA load and absence of the replicating challenged virus was observed at 7, 10 and 14 days post-challenge (dpc). At 14 dpc, in BAL fluid ≥ 5 log viral RNA copies were detected in all the pig groups, but the replicating challenged virus was undetectable only in IM groups. Immunologically, virus neutralizing antibody titers in the plasma of IM (but not IN) vaccine groups was ≥ 8 against the vaccine and challenged viruses. At 26 dpv, PRRS-MLV IM (without adjuvant) received pigs had significantly increased population of CD4 and CD8 T cells in PBMC. At 14 dpc, relatively increased population of IFN-γ(+) total lymphocytes, NK, CD4, CD8 and γδ T cells were observed in the MLV-IM group. In conclusion, PRRS-MLV IM vaccination induced the virus specific T cell response in pigs, but still it is required to improve its cross-protective efficacy.

Adjuvants and delivery systems in veterinary vaccinology: current state and future developments

Modern adjuvants should induce strong and balanced immune responses, and it is often desirable to induce specific types of immunity. As an example, efficient Th1-immunity-inducing adjuvants are highly in demand. Such adjuvants promote good cell-mediated immunity against subunit vaccines that have low immunogenicity themselves. The development of such adjuvants may take advantage of the increased knowledge of the molecular mechanisms and factors controlling these responses. However, knowledge of such molecular details of immune mechanisms is relatively scarce for species other than humans and laboratory rodents, and in addition, there are special considerations pertaining to the use of adjuvants in veterinary animals, such as production and companion animals. With a focus on veterinary animals, this review highlights a number of approaches being pursued, including cytokines, CpG oligonucleotides, microparticles and liposomes.

Evaluation of protective effect of multi-epitope DNA vaccine encoding six antigen segments of Toxoplasma gondii in mice

To investigate the vaccine potential of multi-epitope vaccines against toxoplasmosis, a multi-epitope DNA vaccine, eukaryotic plasmid pcDNA3.1/T-ME expressing six antigen segments (SAG1(238-256), SAG1(281-320), GRA1(170-193), GRA4(331-345), GRA4(229-245), and GRA2(171-185)) of Toxoplasma gondii was constructed. We investigated the efficacy of pcDNA3.1/T-ME with or without co-administration of a CpG-oligodeoxynucleotide (CpG-ODN) as an adjuvant to protect mice (BALB/c and C57BL/6) against toxoplasmosis. High survival rates were observed in mice immunized with pcDNA3.1/T-ME when challenged with T. gondii RH strain. Lymphocyte proliferation assays, cytokine, and antibody determinations show that mice immunized with pcDNA3.1/T-ME produced stronger humoral and Th1-type cellular immune responses compared to untreated mice or those immunized with empty plasmids. However, co-immunization with CpG-ODN resulted in impaired immune responses. Our data demonstrates that multi-epitope DNA vaccination is a potential strategy for the control of toxoplasmosis and paves the way for further investigations into producing a multi-epitope anti-T. gondii DNA vaccine.

Adjuvants for porcine reproductive and respiratory syndrome virus vaccines

This review deals with present and past efforts in utilization of vaccine adjuvants for porcine reproductive and respiratory syndrome virus (PRRSV) vaccines. PRRSV vaccines elicit delayed and weak cell-mediated immune (CMI) and antibody responses after vaccination. Several kinds of vaccine adjuvants have been utilized to accelerate and magnify immune responses to PRRSV vaccines. These adjuvants include cytokines, chemical reagents, and bacterial products. Of 11 vaccine adjuvants tested, five (i.e. interleukin-2 (IL-2), IL-12, interferon alpha (IFNalpha), polyinosinic and polycytidylic acid, and cytidine-phosphate-guanosine oligodeoxynucleotides (CpG ODN)) significantly enhance CMI response to PRRSV vaccines. The response is characterized by proliferation, cytotoxicity, and IFNgamma secretion of peripheral blood mononuclear cells or T cells in response to recall PRRSV antigens in vitro. Two (i.e. CpG ODN and cholera toxin) significantly enhance PRRSV-specific antibody response after vaccination. Two (i.e. IL-2 and CpG ODN) significantly enhance protective efficacy of PRRSV vaccines in challenge models. Improvement of immune responses to PRRSV vaccines should focus in future studies on assessing more vaccine adjuvants for their efficiency in enhancing both CMI and antibody responses and on identifying PRRSV components and strategies that down-modulate pig immune responses in order to devise vaccine adjuvants that can regulate such strategies of the virus.

DNA vaccines and their applications in veterinary practice: current perspectives

Inoculation of plasmid DNA, encoding an immunogenic protein gene of an infectious agent, stands out as a novel approach for developing new generation vaccines for prevention of infectious diseases of animals. The potential of DNA vaccines to act in presence of maternal antibodies, its stability and cost effectiveness and the non-requirement of cold chain have heightened the prospects. Even though great strides have been made in nucleic acid vaccination, still there are many areas that need further research for its wholesome practical implementation. Major areas of concern are vaccine delivery, designing of suitable vectors and cytotoxic T cell responses. Also, the induction of immune responses by DNA vaccines is inconclusive due to the lack of knowledge regarding the concentration of the protein expressed in vivo. Alternative delivery systems having higher transfection efficiency and the use of cytokines, as immunomodulators, needs to be further explored. Recently, efforts are being made to modulate and prolong the active life of dendritic cells, in order to make antigen presentation a more efficacious one. For combating diseases like acquired immunodeficiency syndrome (AIDS), influenza, malaria and tuberculosis in humans; and foot and mouth disease, Aujesky’s disease, swine fever, rabies, canine distemper and brucellosis in animals, DNA vaccine clinical trials are underway. This review highlights the salient features of DNA vaccines, and measures to enhance their efficacy so as to devise an effective and novel vaccination strategy against animal diseases.

Limited protection conferred by a DNA vaccine against a lethal pseudorabies virus infection at day 5 postvaccination

No pseudorabies virus (PRV)-specific neutralizing or immunoglobulin G1-type antibodies were detected in sera 5 days after injection of a DNA vaccine against PRV infection in pigs. PRV-stimulated peripheral blood mononuclear cells produced gamma interferon mRNA in vitro. Two out of five pigs recovered from lethal PRV infection without attenuation of nasal viral excretion.

The effect of CpG-ODN on antigen presenting cells of the foal

Background

Cytosine-phosphate-guanosine oligodeoxynucleotide (CpG-ODN) has been used successfully to induce immune responses against viral and intracellular organisms in mammals. The main objective of this study was to test the effect of CpG-ODN on antigen presenting cells of young foals.

Methods

Peripheral blood monocytes of foals (n = 7) were isolated in the first day of life and monthly thereafter up to 3 months of life. Adult horse (n = 7) monocytes were isolated and tested once for comparison. Isolated monocytes were stimulated with IL-4 and GM-CSF (to obtain dendritic cells, DC) or not stimulated (to obtain macrophages). Macrophages and DCs were stimulated for 14–16 hours with either CpG-ODN, LPS or not stimulated. The stimulated and non-stimulated cells were tested for cell surface markers (CD86 and MHC class II) using flow cytometry, mRNA expression of cytokines (IL-12, IFNα, IL-10) and TLR-9 using real time quantitative RT-PCR, and for the activation of the transcription factor NF-κB p65 using a chemiluminescence assay.

Results

The median fluorescence of the MHC class II molecule in non-stimulated foal macrophages and DCs at birth were 12.5 times and 11.2 times inferior, respectively, than adult horse cells (p = 0.009). That difference subsided at 3 months of life (p = 0.3). The expression of the CD86 co-stimulatory molecule was comparable in adult horse and foal macrophages and DCs, independent of treatment. CpG-ODN stimulation induced IL-12p40 (53 times) and IFNα (23 times) mRNA expression in CpG-ODN-treated adult horse DCs (p = 0.078), but not macrophages, in comparison to non-stimulated cells. In contrast, foal APCs did not respond to CpG-ODN stimulation with increased cytokine mRNA expression up to 3 months of age. TLR-9 mRNA expression and NF-kB activation (NF-kB p65) in foal DCs and macrophages were comparable (p > 0.05) to adult horse cells.

Conclusion

CpG-ODN treatment did not induce specific maturation and cytokine expression in foal macrophages and DCs. Nevertheless, adult horse DCs, but not macrophages, increased their expression of IL-12 and IFNα cytokines upon CpG-ODN stimulation. Importantly, foals presented an age-dependent limitation in the expression of MHC class II in macrophages and DCs, independent of treatment.

CpG oligodeoxynucleotides augment the immune responses of piglets to swine Pasteurella multocida living vaccine in vivo

Oligodeoxynucleotides containing unmethylated CpG motifs (CpG ODN) prevent development of T-helper type 2 (Th2) immune response and reverse established allergic responses in mouse models. However, little work on immune responses in piglets has been conducted in vivo. In this report, the ability of a porcine-specific CpG ODN to act as an immunostimulant and enhance immune responses of piglets to swine Pasteurella multocida living vaccine (SPML vaccine) was determined. The titre of IgG and IgG1/IgG2 isotype to SPML vaccine in serum, the proliferation of lymphocytes, SPML-specific interferon-gamma (IFN-gamma) and IL-6, TNF-alpha, IL-4 production of PBMCs in vitro and IFN-gamma, IL-6, TNF-alpha, IL-4, IL-10 in piglets serum were examined to identify the immune responses of the piglets. Immune responses of the piglets vaccinated with SPML and CpG ODN were significantly stronger than responses of piglets vaccinated with SPML alone. All these data summarized that immunostimulatory CpG ODN could modulate the immune response towards a Th1-like response when co-administered to piglets during SPML vaccination, which suggested that the therapeutic uses envisioned for these ODNs (as vaccine adjuvants and immunoprotective agents) may be applicable to husbandry animals.

Formulation with CpG ODN enhances antibody responses to an equine influenza virus vaccine

Previous studies have shown that protection against equine influenza virus (EIV) is partially mediated by virus-specific IgGa and IgGb. In this study we tested whether addition of a CpG ODN formulation to a commercial killed virus vaccine would enhance EIV-specific IgGa and IgGb antibody responses, and improve protection against an experimental EIV challenge. Thirty naïve horses were assigned to one of three groups and vaccinated as follows: 10 were given vaccine (Encevac TC4, Intervet Inc.) alone, 10 were given vaccine plus 0.25 mg CpG ODN 2007 formulated with 30% Emulsigen (CpG/Em), and 10 controls were given saline. All horses were challenged with live virus 12 weeks after the final vaccination. Antibody responses were tested by single radial hemolysis (SRH) and ELISA, and protection was evaluated by determination of temperature, coughing, and clinical scores. Killed virus vaccine combined with CpG/Em induced significantly greater serologic responses than did the vaccine alone. All antibody isotypes tested increased after the addition of CpG/Em, although no shift in relative antibody isotypes concentrations was detected. Vaccination significantly improved protection against challenge but the differences between the two vaccine groups were not statistically significant. This study is the first demonstration that CpG/Em enhances antigen-specific antibody responses in horses and supports its potential to be used as an adjuvant for vaccines against equine infections.

C3d enhanced DNA vaccination induced humoral immune response to glycoprotein C of pseudorabies virus

Murine C3d were utilized to enhance immunogenicity of pseudorabies virus (PrV) gC DNA vaccination. Three copies of C3d and four copies of CR2-binding domain M28(4) were fused, respectively, to truncated gC gene encoding soluble glycoprotein C (sgC) in pcDNA3.1. BALB/c mice were, respectively, immunized with recombinant plasmids, blank vector, and inactivated vaccine. The antibody ELISA titer for sgC-C3d3 DNA was 49-fold more than that for sgC DNA, and the neutralizing antibody obtained 8-fold rise. Protection of mice from death after lethal PrV (316 LD50) challenge was augmented from 25% to 100%. Furthermore, C3d fusion increased Th2-biased immune response by inducing IL-4 production. The IL-4 level for sgC-C3d3 DNA immunization approached that for the inactivated vaccine. Compared to C3d, M28 enhanced sgC DNA immunogenicity to a lesser extent. In conclusion, we demonstrated that murine C3d fusion significantly enhanced gC DNA immunity by directing Th1-biased to a balanced and more effective Th1/Th2 response.