Early life humoral response of ducks to DNA immunization against hepadnavirus large envelope protein

Passive Immunotherapy of Cynomolgus Monkeys with Anti-Rotavirus IgY

Immunoglobulins Y (IgY) purified from egg yolks of hens represents an attractive, cost-effective alternative for the development of new diagnostic and therapeutic platforms. In this study, we evaluated the therapeutic efficacy of rotavirus-specific IgY in a cynomolgus monkey (Macaca fascicularis) model. Animals were experimentally infected with human rotavirus Group A (RVA), the most common cause of severe acute diarrhoea among young children worldwide. Animals were administered human RVA (3.1 × 107 FFU/mL) by oral gavage, challenged with 2.5 mg of anti-RVA IgY orally, and monitored for five days according to clinical, haematological and biochemical parameters; serum electrolyte levels; viral shedding; and histopathological changes. Immunotherapy with anti-RVA IgY had a protective effect against severe rotavirus-induced enteritis in four of the ten treated monkeys, as evidenced by histopathological findings. Although only one animal had diarrhoea, all but one exhibited virus shedding regardless of the treatment.

Immunoglobulin Y for Potential Diagnostic and Therapeutic Applications in Infectious Diseases

Antiviral, antibacterial, and antiparasitic drugs and vaccines are essential to maintaining the health of humans and animals. Yet, their production can be slow and expensive, and efficacy lost once pathogens mount resistance. Chicken immunoglobulin Y (IgY) is a highly conserved homolog of human immunoglobulin G (IgG) that has shown benefits and a favorable safety profile, primarily in animal models of human infectious diseases. IgY is fast-acting, easy to produce, and low cost. IgY antibodies can readily be generated in large quantities with minimal environmental harm or infrastructure investment by using egg-laying hens. We summarize a variety of IgY uses, focusing on their potential for the detection, prevention, and treatment of human and animal infections.

DNA vaccination of poultry: The current status in 2015

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Poultry DNA vaccination studies are regularly being published since 1993.

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These studies are mainly, but not only, concerned with vaccination against viruses.

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The different strategies of improving DNA vaccine efficacies are presented.

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The fate of the vaccine plasmid, immune properties and other applications are described.

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Despite the compiling preclinical reports, a poultry DNA vaccine is yet unavailable in the market.

DNA vaccination is a promising alternative strategy for developing new human and animal vaccines. The massive efforts made these past 25 years to increase the immunizing potential of this kind of vaccine are still ongoing. A relatively small number of studies concerning poultry have been published. Even though there is a need for new poultry vaccines, five parameters must nevertheless be taken into account for their development: the vaccine has to be very effective, safe, inexpensive, suitable for mass vaccination and able to induce immune responses in the presence of maternal antibodies (when appropriate). DNA vaccination should meet these requirements. This review describes studies in this field performed exclusively on birds (chickens, ducks and turkeys). No evaluations of avian DNA vaccine efficacy performed on mice as preliminary tests have been taken into consideration. The review first describes the state of the art for DNA vaccination in poultry: pathogens targeted, plasmids used and different routes of vaccine administration. Second, it presents strategies designed to improve DNA vaccine efficacy: influence of the route of administration, plasmid dose and age of birds on their first inoculation; increasing plasmid uptake by host cells; addition of immunomodulators; optimization of plasmid backbones and codon usage; association of vaccine antigens and finally, heterologous prime-boost regimens. The final part will indicate additional properties of DNA vaccines in poultry: fate of the plasmids upon inoculation, immunological considerations and the use of DNA vaccines for purposes other than preventing infectious diseases.

Antiviral Biologic Produced in DNA Vaccine/Goose Platform Protects Hamsters Against Hantavirus Pulmonary Syndrome When Administered Post-exposure

Andes virus (ANDV) and ANDV-like viruses are responsible for most hantavirus pulmonary syndrome (HPS) cases in South America. Recent studies in Chile indicate that passive transfer of convalescent human plasma shows promise as a possible treatment for HPS. Unfortunately, availability of convalescent plasma from survivors of this lethal disease is very limited. We are interested in exploring the concept of using DNA vaccine technology to produce antiviral biologics, including polyclonal neutralizing antibodies for use in humans. Geese produce IgY and an alternatively spliced form, IgYΔFc, that can be purified at high concentrations from egg yolks. IgY lacks the properties of mammalian Fc that make antibodies produced in horses, sheep, and rabbits reactogenic in humans. Geese were vaccinated with an ANDV DNA vaccine encoding the virus envelope glycoproteins. All geese developed high-titer neutralizing antibodies after the second vaccination, and maintained high-levels of neutralizing antibodies as measured by a pseudovirion neutralization assay (PsVNA) for over 1 year. A booster vaccination resulted in extraordinarily high levels of neutralizing antibodies (i.e., PsVNA80 titers >100,000). Analysis of IgY and IgYΔFc by epitope mapping show these antibodies to be highly reactive to specific amino acid sequences of ANDV envelope glycoproteins. We examined the protective efficacy of the goose-derived antibody in the hamster model of lethal HPS. α-ANDV immune sera, or IgY/IgYΔFc purified from eggs, were passively transferred to hamsters subcutaneously starting 5 days after an IM challenge with ANDV (25 LD50). Both immune sera, and egg-derived purified IgY/IgYΔFc, protected 8 of 8 and 7 of 8 hamsters, respectively. In contrast, all hamsters receiving IgY/IgYΔFc purified from normal geese (n=8), or no-treatment (n=8), developed lethal HPS. These findings demonstrate that the DNA vaccine/goose platform can be used to produce a candidate antiviral biological product capable of preventing a lethal disease when administered post-exposure.

In vivo electroporation improves therapeutic potency of a DNA vaccine targeting hepadnaviral proteins

This preclinical study investigated the therapeutic efficacy of electroporation (EP)-based delivery of plasmid DNA (pDNA) encoding viral proteins (envelope, core) and IFN-γ in the duck model of chronic hepatitis B virus (DHBV) infection. Importantly, only DNA EP-therapy resulted in a significant decrease in mean viremia titers and in intrahepatic covalently closed circular DNA (cccDNA) levels in chronic DHBV-carrier animals, compared with standard needle pDNA injection (SI). In addition, DNA EP-therapy stimulated in all virus-carriers a humoral response to DHBV preS protein, recognizing a broader range of major antigenic regions, including neutralizing epitopes, compared with SI. DNA EP-therapy led also to significant higher intrahepatic IFN-γ RNA levels in DHBV-carriers compared to other groups, in the absence of adverse effects. We provide the first evidence on DNA EP-therapy benefit in terms of hepadnaviral infection clearance and break of immune tolerance in virus-carriers, supporting its clinical application for chronic hepatitis B.

DNA vaccine-generated duck polyclonal antibodies as a postexposure prophylactic to prevent hantavirus pulmonary syndrome (HPS)

Andes virus (ANDV) is the predominant cause of hantavirus pulmonary syndrome (HPS) in South America and the only hantavirus known to be transmitted person-to-person. There are no vaccines, prophylactics, or therapeutics to prevent or treat this highly pathogenic disease (case-fatality 35–40%). Infection of Syrian hamsters with ANDV results in a disease that closely mimics human HPS in incubation time, symptoms of respiratory distress, and disease pathology. Here, we evaluated the feasibility of two postexposure prophylaxis strategies in the ANDV/hamster lethal disease model. First, we evaluated a natural product, human polyclonal antibody, obtained as fresh frozen plasma (FFP) from a HPS survivor. Second, we used DNA vaccine technology to manufacture a polyclonal immunoglobulin-based product that could be purified from the eggs of vaccinated ducks (Anas platyrhynchos). The natural “despeciation" of the duck IgY (i.e., Fc removed) results in an immunoglobulin predicted to be minimally reactogenic in humans. Administration of ≥5,000 neutralizing antibody units (NAU)/kg of FFP-protected hamsters from lethal disease when given up to 8 days after intranasal ANDV challenge. IgY/IgYΔFc antibodies purified from the eggs of DNA-vaccinated ducks effectively neutralized ANDV in vitro as measured by plaque reduction neutralization tests (PRNT). Administration of 12,000 NAU/kg of duck egg-derived IgY/IgYΔFc protected hamsters when administered up to 8 days after intranasal challenge and 5 days after intramuscular challenge. These experiments demonstrate that convalescent FFP shows promise as a postexposure HPS prophylactic. Moreover, these data demonstrate the feasibility of using DNA vaccine technology coupled with the duck/egg system to manufacture a product that could supplement or replace FFP. The DNA vaccine-duck/egg system can be scaled as needed and obviates the necessity of using limited blood products obtained from a small number of HPS survivors. This is the first report demonstrating the in vivo efficacy of any antiviral product produced using DNA vaccine-duck/egg system.

DNA vaccination in combination or not with lamivudine treatment breaks humoral immune tolerance and enhances cccDNA clearance in the duck model of chronic hepatitis B virus infection

This study used a duck hepatitis B virus (DHBV) model to evaluate whether a novel DNA vaccination protocol alone or associated with antiviral (lamivudine) treatment was able to clear the intrahepatic covalently closed, circular viral DNA (cccDNA) pool responsible for persistence of infection. DHBV carriers received DNA vaccine (on weeks 6, 10, 13, 14, 28 and 35) targeting the large envelope and/or core proteins alone or combined with lamivudine treatment (on weeks 1-8) or lamivudine monotherapy. After 10 months of follow-up, a dramatic decrease in viraemia and liver DHBV cccDNA (below 0.08 cccDNA copies per cell) was observed in 9/30 ducks (30 %) receiving DNA mono- or combination therapy, compared with 0/12 (0 %) from lamivudine monotherapy or the control groups, suggesting a significant antiviral effect of DNA immunization. However, association with the drug did not significantly improve DHBV DNA vaccine efficacy (33 % cccDNA clearance for the combination vs 27 % for DNA monotherapy), probably due to the low antiviral potency of lamivudine in the duck model. Seroconversion to anti-preS was observed in 6/9 (67 %) ducks showing cccDNA clearance, compared with 1/28 (3.6 %) without clearance, suggesting a significant correlation (P<0.001) between humoral response restoration and cccDNA elimination. Importantly, an early (weeks 10-12) drop in viraemia was observed in seroconverted animals, and virus replication did not rebound following the cessation of immunotherapy, indicating a sustained effect. This study provides the first evidence that therapeutic DNA vaccination is able to enhance hepadnaviral cccDNA clearance, which is tightly associated with a break in humoral immune tolerance. These results also highlight the importance of antiviral drug potency and an effective DNA immunization protocol for the design of therapeutic vaccines against chronic hepatitis B.

Gene therapy for viral hepatitis

Hepatitis B and C infections are two of the most prevalent viral diseases in the world. Existing therapies against chronic viral hepatitis are far from satisfactory due to low response rates, undesirable side effects and selection of resistant viral strains. Therefore, new therapeutic approaches are urgently needed. This review, after briefly summarising the in vitro and in vivo systems for the study of both diseases and the genetic vehicles commonly used for liver gene transfer, examines the existing status of gene therapy-based antiviral strategies that have been employed to prevent, eliminate or reduce viral infection. In particular, the authors focus on the results obtained in clinical trials and experimental clinically relevant animal models.

DNA vaccines for poultry: the jump from theory to practice

DNA vaccines could offer a solution to a number of problems faced by the poultry industry; they are relatively easy to manufacture, stable, potentially easy to administer, can overcome neonatal tolerance and the deleterious effects of maternal antibody, and do not cause disease pathology. Combined with this, in ovo vaccination offers the advantage of reduced labor costs, mass administration and the induction of an earlier immune response. Together, this list of advantages is impressive. However, this combined technology is still in its infancy and requires many improvements. The potential of CpG motifs, DNA vaccines and in ovo vaccination, however, can be observed by the increasing number of recent reports investigating their application in challenge experiments. CpG motifs have been demonstrated to be stimulatory both in vitro and in vivo. In addition, DNA vaccines have been successfully delivered via the in ovo route, albeit not yet through the amniotic fluid. Lastly, a recent report has demonstrated that a DNA vaccine against infectious bronchitis virus administered via in ovo vaccination, followed by live virus boost, can slightly improve on the protective effect induced by the live virus alone. Therefore, DNA vaccination via the in ovo route is promising and offers potential as a poultry vaccine, however, efficacy needs to be improved and the costs of production reduced before it is likely to be beneficial to the poultry industry in the long term.

Rise in gamma interferon expression during resolution of duck hepatitis B virus infection

Gamma interferon (IFN-γ) expression plays a crucial role in the control of mammalian hepatitis B virus (HBV) infection. However, the role of duck INF-γ (DuIFN-γ) in the outcome of duck HBV (DHBV) infection, a reference model for hepadnavirus replication studies, has not yet been investigated. This work explored the dynamics of DuIFN-γ expression in liver and peripheral blood mononuclear cells (PBMCs) during resolution of DHBV infection in adolescent ducks in relation to serum and liver markers of virus replication, histological changes and humoral response induction. DHBV infection of 3-week-old ducks resulted in transient expression of intrahepatic preS protein (days 3–14) and mild histological changes. Low-level viraemia was detected only during the first 10 days of infection and was accompanied by early anti-preS antibody response induction. Importantly, a strong increase in intrahepatic DuIFN-γ RNA was detected by real-time RT-PCR at days 6–14, which coincided with a sharp decrease in both viral DNA and preS protein in the liver. Interestingly, liver DuIFN-γ expression remained augmented to the end of the follow-up period (day 66) and correlated with portal lymphocyte infiltration and persistence of trace quantities of intrahepatic DHBV DNA in animals that had apparently completely resolved the infection. Moreover, in infected ducks, a moderate increase was detected in the levels of DuIFN-γ in PBMCs (days 12–14), which coincided with the peak in liver DuIFN-γ RNA levels. These data reveal that increased DuIFN-γ expression in liver and PBMCs is concomitant with viral clearance, characterizing the resolution of infection, and provide new insights into the host–virus interactions that control DHBV infection.

DNA-designed avian IgY antibodies: novel tools for research, diagnostics and therapy

We have recently demonstrated, using the duck Hepatitis B virus (DHBV) model, closely related to human HBV, that following DNA immunization of breeding ducks with a plasmid encoding the targeted protein, specific and biologically active IgY (egg yolk immunoglobulines) are vertically transmitted from their serum into the egg yolk from which they can be extracted and purified. Thus an egg can be considered as a small "factory" for antibody production, since about 60-100 mg of purified IgY can be obtained from each egg yolk of a DNA-immunized duck. One of the major advantages of this new method of "DNA-designed" IgY antibodies is their production via immunization with a gene vector that expresses a corresponding antibody in situ in the cells of an avian host. Therefore this approach allows direct generation of antibodies from plasmid DNA and avoids the costly and tedious preparation of purified antigens required for conventional antibody production. In addition, duck IgY are of remarkable high affinity, avidity and are highly neutralizing. Moreover, the epitope pattern of IgY generated by DNA immunization of ducks is closely related to that observed in viral infection. Such duck IgY are also of particular value as immunodiagnostic tools, since they do not cross-react serologically with mammalian immunoglobulins and complement. Because IgY are resistant to the gastric barrier, the recently described DNA-designed IgY specific to H. pylori Urease B can be of particular interest for passive immunotherapy of gastrointestinal tract infections. Another interesting application is the recent generation in our laboratory of DNA-designed IgY antibodies specific to HBsAg mutants. These antibodies are currently being used to design new diagnostic assay for detection of HBV mutants that are undetectable by actual tests. Moreover, this approach allowing a quick and inexpensive production of a new generation of antibodies will provide pertinent tools to link the fields of genomics and protcomics.

DNA vaccines expressing the duck hepatitis B virus surface proteins lead to reduced numbers of infected hepatocytes and protect ducks against the development of chronic infection in a virus dose-dependent manner

We tested the efficacy of DNA vaccines expressing the duck hepatitis B virus (DHBV) pre-surface (pre-S/S) and surface (S) proteins in modifying the outcome of infection in 14-day-old ducks. In two experiments, Pekin Aylesbury ducks were vaccinated on days 4 and 14 of age with plasmid DNA vaccines expressing either the DHBV pre-S/S or S proteins, or the control plasmid vector, pcDNA1.1Amp. All ducks were then challenged intravenously on day 14 of age with 5 x 10(7) or 5 x 10(8) DHBV genomes. Levels of initial DHBV infection were assessed using liver biopsy tissue collected at day 4 post-challenge (p.c.) followed and immunostained for DHBV surface antigen to determine the percentage of infected hepatocytes. All vector vaccinated ducks challenged with 5 x 10(7) and 5 x 10(8) DHBV genomes had an average of 3.21% and 20.1% of DHBV-positive hepatocytes respectively at day 4 p.c. and 16 out of 16 ducks developed chronic DHBV infection. In contrast, pre-S/S and S vaccinated ducks challenged with 5 x 10(7) DHBV genomes had reduced levels of initial infection with an average of 1.38% and 1.93% of DHBV-positive hepatocytes at day 4 p.c. respectively and 10 of 18 ducks were protected against chronic infection. The pre-S/S and the S DNA vaccinated ducks challenged with 5 x 10(8) DHBV genomes had an average of 31.5% and 9.2% of DHBV-positive hepatocytes on day 4 p.c. respectively and only 4 of the 18 vaccinated ducks were protected against chronic infection. There was no statistically significant difference in the efficacy of the DHBV pre-S/S or S DNA vaccines. In conclusion, vaccination of young ducks with DNA vaccines expressing the DHBV pre-S/S and S proteins induced rapid immune responses that reduced the extent of initial DHBV infection in the liver and prevented the development of chronic infection in a virus dose-dependent manner.

Genetic vaccination for production of DNA-designed antibodies specific to Hepadnavirus envelope proteins

We propose a method of avian antibodies production based on DNA immunization of laying ducks with a plasmid encoding specified antigen, followed by egg collection and purification of egg yolk immunoglobulins (IgY). We have validated this approach in the Duck hepatitis B virus (DHBV) model. We report here that following immunization of female ducks with plasmids encoding DHBV envelope proteins, large amounts (at least 50 mg/egg) of specific antibodies can be obtained from eggs of these ducks. Interestingly, the comparison of different plasmid constructs showed the important differences in their efficacy of specific IgY antibodies induction in the sera and eggs of immunized ducks.

IFN-γ increases efficiency of DNA vaccine in protecting ducks against infection

AIM: To detect the effects of DNA vaccines in combination with duck IFN-γ gene on the protection of ducks against duck hepatitis B virus (DHBV) infection.

METHODS: DuIFN-γ cDNA was cloned and expressed in COS-7 cells, and the antiviral activity of DuIFN-γ was detected and neutralized by specific antibodies. Ducks were vaccinated with DHBpreS/S DNA alone or co-immunized with plasmid expressing DuIFN-γ. DuIFN-γ mRNA in peripheral blood mononuclear cells (PBMCs) from immunized ducks was detected by semi-quantitative competitive RT-PCR. Anti-DHBpreS was titrated by enzyme-linked immunosorbent assay (ELISA). DHBV DNA in sera and liver was detected by Southern blot hybridization, after ducks were challenged with high doses of DHBV.

RESULTS: DuIFN-γ expressed by COS-7 was able to protect duck fibroblasts against vesicular stomatitis virus (VSV) infection in a dose-dependent fashion, and anti-DuIFN-γ antibodies neutralized the antiviral effects. DuIFN-γ in the supernatant also inhibited the release of DHBV DNA from LMH-D2 cells. When ducks were co-immunized with DNA vaccine expressing DHBpreS/S and DuIFN-γ gene as an adjuvant, the level of DuIFN-γ mRNA in PBMCs was higher than that in ducks vaccinated with DHBpreS/S DNA alone. However, the titer of anti-DHBpreS elicited by DHBpreS/S DNA alone was higher than that co-immunized with DuIFN-γ gene and DHBpreS/S DNA. After being challenged with DHBV at high doses, the load of DHBV in sera dropped faster, and the amount of total DNA and cccDNA in the liver decreased more significantly in the group of ducks co-immunized with DuIFN-γ gene and DHBpreS/S DNA than in other groups.

CONCLUSION: DHBV preS/S DNA vaccine can protect ducks against DHBV infection, DuIFN-γ gene as an immune adjuvant enhances its efficacy.

DNA vaccination in the avian

Inoculation of naked DNA represents a novel approach to vaccine and immune therapeutic development. DNA vaccines or genetic immunization offers several advantages over the conventional vaccines for specific immune activation. Although a large number of vaccines have been made and are being used in the poultry industry, there have been no major advances in vaccine technology for this animal industry sector for decades. The potential advantages of DNA vaccines, such as over coming maternal immunity, in ovo delivery and absence of requirement for a cold-chain, combined with immunological efficacy make this new vaccine technology very attractive for the poultry industry. This review lists all of the published reports of experimental DNA vaccines developed for use in poultry and focuses on the trends, potentials and remaining barriers in the development of this new revolution in poultry vaccinology.

Genetic immunization of neonates

The vaccination of neonates is generally difficult due to immaturity of the immune system, higher susceptibility to tolerance and potential negative interference of maternal antibodies. Studies carried out in rodents and non-human primates showed that plasmid vaccines expressing microbial antigens, rather than inducing tolerance, triggered significant humoral and cellular immunity with a Th1 component. The ability of bacterial CpG motifs to activate immature antigen-presenting cells is critical for the neonatal immunogenicity of DNA vaccines. In addition, the endogenous production of antigen subsequent to transfection of antigen-presenting cells may explain the lack of inhibition by maternal antibodies of cellular responses. Together, these features make the plasmid vaccines an appealing strategy to prime immune responses against foreign pathogens, during early life. In combination with subsequent boosting using conventional vaccines, DNA vaccine-based regimens may provide a qualitatively superior immunity against microbes. Thorough understanding of immunomodulatory properties of plasmid-vectors may extend their use for early prophylaxis of inflammatory disorders.

Immune defence in bumble-bee offspring

Immune-challenged vertebrate females transfer specific antibodies to their offspring, but this gratuitous immunity cannot operate in invertebrates. Here we show that constitutive immune defence is enhanced in sexual offspring of the bumble-bee Bombus terrestris L. when the parental colony is immune-challenged. Our findings indicate that invertebrates may use a different component of the immune system to generate a facultative trans-generational increase in the immune response.

DNA vaccination against v-src oncogene-induced tumours in congenic chickens

DNA vaccination is particularly efficient for induction of cytotoxic T-lymphocyte (CTL) response. In our experiments, we used MHC(B) congenic chicken lines CB and CC (regressors and progressors of v-src-induced tumours, respectively) and a mutated, non-oncogenic v-src gene construct as the DNA vaccine. A high degree of vaccine protection against oncogenic v-src challenge was achieved in the CB line chickens. CTL response was demonstrated in vitro and by adoptive transfer of immune cells to the syngeneic host and to the CC line chickens rendered tolerant to CB cells. In the CC line chickens we observed tumour growth retardation after a low-dose DNA vaccination administered to immature recipients while higher amounts of DNA vaccine in immunocompetent chickens exerted an enhancing effect.