Live vaccination with an H5-hemagglutinin-expressing infectious laryngotracheitis virus recombinant protects chickens against different highly pathogenic avian influenza viruses of the H5 subtype

Current Status of Poultry Recombinant Virus Vector Vaccine Development

Inactivated and live attenuated vaccines are the mainstays of preventing viral poultry diseases. However, the development of recombinant DNA technology in recent years has enabled the generation of recombinant virus vector vaccines, which have the advantages of preventing multiple diseases simultaneously and simplifying the vaccination schedule. More importantly, some can induce a protective immune response in the presence of maternal antibodies and offer long-term immune protection. These advantages compensate for the shortcomings of traditional vaccines. This review describes the construction and characterization of primarily poultry vaccine vectors, including fowl poxvirus (FPV), fowl adenovirus (FAdV), Newcastle disease virus (NDV), Marek's disease virus (MDV), and herpesvirus of turkey (HVT). In addition, the pathogens targeted and the immunoprotective effect of different poultry recombinant virus vector vaccines are also presented. Finally, this review discusses the challenges in developing vector vaccines and proposes strategies for improving immune efficacy.

Poultry Vaccine Technology Platforms

The different technology platforms used to make poultry vaccines are reviewed. Vaccines based on classical technologies are either live attenuated or inactivated vaccines. Genetic engineering is applied to design by deletion, mutation, insertion, or chimerization, genetically modified target microorganisms that are used either as live or inactivated vaccines. Other vaccine platforms are based on one or a few genes of the target pathogen agent coding for proteins that can induce a protective immune response ("protective genes"). These genes can be expressed in vitro to produce subunit vaccines. Alternatively, vectors carrying these genes in their genome or nucleic acid-based vaccines will induce protection by in vivo expression of these genes in the vaccinated host. Properties of these different types of vaccines, including advantages and limitations, are reviewed, focusing mainly on vaccines targeting viral diseases and on technologies that succeeded in market authorization.

Identification and Characterization of a Novel Epitope of ASFV-Encoded dUTPase by Monoclonal Antibodies

Deoxyuridine 5'-triphosphate nucleotidohydrolase (dUTPase) of African swine fever virus (ASFV) is an essential enzyme required for efficient virus replication. Previous crystallography data have indicated that dUTPase (E165R) may serve as a therapeutic target for inhibiting ASFV replication; however, the specificity of the targeting site(s) in ASFV dUTPase remains unclear. In this study, 19 mouse monoclonal antibodies (mAbs) were produced, in which four mAbs showed inhibitory reactivity against E165R recombinant protein. Epitope mapping studies indicated that E165R has three major antigenic regions: 100-120 aa, 120-140 aa, and 140-165 aa. Three mAbs inhibited the dUTPase activity of E165R by binding to the highly conserved 149-RGEGRFGSTG-158 amino acid sequence. Interestingly, 8F6 mAb specifically recognized ASFV dUTPase but not Sus scrofa dUTPase, which may be due to structural differences in the amino acids of F151, R153, and F154 in the motif V region. In summary, we developed anti-E165R-specific mAbs, and identified an important antibody-binding antigenic epitope in the motif V of ASFV dUTPase. Our study provides a comprehensive analysis of mAbs that target the antigenic epitope of ASFV dUTPase, which may contribute to the development of novel antibody-based ASFV therapeutics.

Examination of the protective efficacy of two avian influenza H5 vaccines against clade 2.3.4.4b H5N8 highly pathogenic avian influenza virus in commercial broilers

The highly pathogenic avian influenza (HPAI) H5N8 virus of clade 2.3.4.4 was detected in 2017 in Egypt, which is one of the few countries using vaccination as a control strategy in poultry farms. This study was conducted to evaluate the efficacy of the commercial recombinant turkey herpes virus-H5 (rHVT-H5) vaccine (clade 2.2), alone or in combination with commercial inactivated reverse genetically engineered H5N1 vaccine (rgH5N1) (clade 2.2), in preventing the genetically distinct HPAI H5N8 virus of clade 2.3.4.4b in commercial broiler chickens. Four experimental groups of chickens were used as follows: G1, non-vaccinated and non-challenged; G2, non-vaccinated and challenged; G3, vaccinated with rHVT-H5; and G4, prime-boost vaccinated with rHVT-H5/rgH5N1. For challenge with the Egyptian HPAI H5N8 (2.3.4.4b) virus, the groups were divided into two subgroups (A and B); chickens in subgroups A were challenged at the age of 28 days, whereas those in subgroups B were challenged at the age of 35 days. Results showed that a protective efficacy (survival rate) of 40%-50% was obtained in the vaccinated subgroups A. By delaying challenge for 1 week (subgroups B), a single rHVT-H5 vaccination provided 80% protection, whereas prime-boost vaccination induced full protection and reduced viral shedding very efficiently (1/10 birds and only detected on the 3rd day post challenge) against HPAI H5N8 virus (2.3.4.4b). Moreover, body weight loss improved from 31.39% and 43.65% in G3A and G4A, respectively, to 16.34% and 7.7% in G3B and G4B, respectively. The HI titers obtained in G3A and G4A on the challenge day (28^th d) using H5N8 antigen were 3 and 3.75 log₂ (p > 0.05), respectively, whereas those in G3B and G4B on the challenge day (35^th d) were 6.25 and 6 log₂ (p > 0.05), respectively, which increased post-challenge in all vaccinated subgroups. Therefore, the dual use of vectored rHVT-H5 and inactivated rgH5N1 vaccines in the vaccination schedule in poultry farms is the most efficient tool for preventing the disease (mortality and viral shedding) caused by the genetically distinct virus (clade 2.3.3.4b HPAI H5N8) in combination with strict biosecurity and sanitary measures.

Contributions of HA1 and HA2 Subunits of Highly Pathogenic Avian Influenza Virus in Induction of Neutralizing Antibodies and Protection in Chickens

Highly pathogenic avian influenza virus (HPAIV) subtype H5N1 causes a devastating disease in poultry. Vaccination is an effective method of controlling avian influenza virus (AIV) infection in poultry. The hemagglutinin (HA) protein is the major determinant recognized by the immune system of the host. Cleavage of the HA precursor HA0 into HA1 and HA2 subunits is required for infectivity of the AIV. We evaluated the individual contributions of HA1 and HA2 subunits to the induction of HPAIV serum neutralizing antibodies and protective immunity in chickens. Using reverse genetics, recombinant Newcastle disease viruses (rNDVs) were generated, each expressing HA1, HA2, or HA protein of H5N1 HPAIV. Chickens were immunized with rNDVs expressing HA1, HA2, or HA. Immunization with HA induced high titers of serum neutralizing antibodies and prevented death following challenge. Immunization with HA1 or HA2 alone neither induced serum neutralizing antibodies nor prevented death following challenge. Our results suggest that interaction of HA1 and HA2 subunits is necessary for the display of epitopes on HA protein involved in the induction of neutralizing antibodies and protection. These epitopes are lost when the two subunits are separated. Therefore, vaccination with either a HA1 or HA2 subunit may not provide protection against HPAIV.

Coexpression of soluble and membrane-bound avian influenza virus H5 by recombinant Newcastle disease virus leads to an increase in antigen levels

Newcastle disease virus (NDV) vectors expressing avian influenza virus (AIV) haemagglutinin (HA) of subtype H5 simultaneously protect chickens from Newcastle disease (ND) as well as avian influenza (AI). The expressed, membrane-bound surface protein HA is incorporated into virions while soluble HA has been described as a potent antigen. We tested whether co-expression of both HA variants from the same NDV vector increased the overall level of HA, which could be important for optimal immunogenicity. Recombinant NDVsolH5_H5 co-expressed membrane-bound H5 of highly pathogenic (HP) AIV H5N1, detectable in infected cells, and soluble H5, which was secreted into the supernatant. This virus was compared to recombinant NDV that express either membrane-bound (rNDVH5) or soluble H5 (rNDVsolH5). Replication in embryonated chicken eggs (ECEs) and in cell culture, as well as pathogenicity in ECEs, was not influenced by the second heterologous transcriptional unit. However, the co-expression of soluble H5 with membrane-bound H5 increased total protein level about 5.25-fold as detected by MS quantification. Hence, this virus is very interesting as a vaccine virus in chickens against HPAIV infections in situations in which previous H5-expressing NDVs have reached their limit, such as in the face of pre-existing AIV maternal immunity.

A recombinant avian paramyxovirus serotype 3 expressing the hemagglutinin protein protects chickens against H5N1 highly pathogenic avian influenza virus challenge

Highly pathogenic avian influenza (HPAI) is a devastating disease of poultry and a serious threat to public health. Vaccination with inactivated virus vaccines has been applied for several years as one of the major policies to control highly pathogenic avian influenza virus (HPAIV) infections in chickens. Viral-vectored HA protein vaccines are a desirable alternative for inactivated vaccines. However, each viral vector possesses its own advantages and disadvantages for the development of a HA-based vaccine against HPAIV. Recombinant Newcastle disease virus (rNDV) strain LaSota expressing HA protein vaccine has shown promising results against HPAIV; however, its replication is restricted only to the respiratory tract. Therefore, we thought to evaluate avian paramyxovirus serotype 3 (APMV-3) strain Netherlands as a safe vaccine vector against HPAIV, which has high efficiency replication in a greater range of host organs. In this study, we generated rAPMV-3 expressing the HA protein of H5N1 HPAIV using reverse genetics and evaluated the induction of neutralizing antibodies and protection by rAPMV3 and rNDV expressing the HA protein against HPAIV challenge in chickens. Our results showed that immunization of chickens with rAPMV-3 or rNDV expressing HA protein provided complete protection against HPAIV challenge. However, immunization of chickens with rAPMV-3 expressing HA protein induced higher level of neutralizing antibodies compared to that of rNDV expressing HA protein. These results suggest that a rAPMV-3 expressing HA protein might be a better vaccine for mass-vaccination of commercial chickens in field conditions.

Simultaneous Deletion of Virulence Factors and Insertion of Antigens into the Infectious Laryngotracheitis Virus Using NHEJ-CRISPR/Cas9 and Cre-Lox System for Construction of a Stable Vaccine Vector

Infectious laryngotracheitis virus (ILTV) is a promising vaccine vector due to its heterologous gene accommodation capabilities, low pathogenicity, and potential to induce cellular and humoral arms of immunity. Owing to these characteristics, different gene-deletion versions of ILTVs have been successfully deployed as a vector platform for the development of recombinant vaccines against multiple avian viruses using conventional recombination methods, which are tedious, time-demanding, and error-prone. Here, we applied a versatile, and customisable clustered regularly interspaced short palindromic repeats (CRISPR)/Cas9 accompanied with Cre–Lox system to simultaneously delete virulence factors and to insert foreign genes in the ILTV genome. Using this pipeline, we successfully deleted thymidine kinase (TK) and unique short 4 (US4) genes and inserted fusion (F) gene of the Newcastle disease virus without adversely affecting ILTV replication and expression of the F protein. Taken together, the proposed approach offers novel tools to attenuate (by deletion of virulence factor) and to generate multivalent (by insertion of heterologous genes) vaccine vectors to protect chickens against pathogens of poultry and public health importance.

Improvement of a recombinant avian avulavirus serotype 10 vectored vaccine by the addition of untranslated regions

BACKGROUND

We have previously developed a recombinant avian avulavirus serotype 10 (rAAvV-10/HA) expressing the hemagglutinin (HA) gene of a highly pathogenic avian influenza virus (HPAIV) as an emergency vaccine for poultry. rAAvV-10/HA can overcome the activity of the anti-AAvV-1 (Newcastle disease virus) antibody acquired by commercial chickens upon routine vaccination. Most chickens do not have the anti-AAvV-10 antibody, which could interfere with the vaccine efficacy. However, the vaccine efficacy of rAAvV-10/HA is not satisfactory in chickens even though it affords protection against an HPAIV challenge. In the present study, we improved the rAAvV-10/HA vaccine by enhancing the expression of the exogenous HA protein.

METHODS

The 5' and 3' untranslated regions (UTR) of each AAvV-10 gene were flanked with the exogenous HA gene cassette to modify rAAvV-10/HA, yielding different rAAv10-UTRs. As a control, rAAv10-nonUTR that did not contain any UTRs was generated. The effects of UTRs on mRNA transcription, HA protein expression, and vaccine efficacy were then examined using embryonated chicken eggs and white leghorn chickens.

RESULTS

The proportion of the HA gene mRNA among the vector-derived mRNAs (1.55-1.84-fold increase vs. the control) and HA protein levels (148-1151-fold increase vs. the control) in cells infected with rAAv10-UTRs were higher than in those infected with rAAv10-nonUTR. In vivo, vaccination of chickens with rAAv10-UTRs resulted in 100% protection against an HPAIV challenge. No chickens vaccinated with rAAv10-NP-UTR, rAAv10-F-UTR, or rAAv10-HN-UTR shed the virus in the throat and cloaca swabs. By contrast, rAAv10-nonUTR vaccination offered 70% protection, with 50% of chickens shedding the virus in the cloaca or throat swabs after the challenge. We conclude that the AAvV-10 UTRs can enhance the expression of the exogenous HA gene, resulting in improved efficacy of the rAAvV-10/HA vector vaccine. This improvement aids in the protection of flocks worldwide from the highly pathogenic avian influenza.

Innovation in Newcastle Disease Virus Vectored Avian Influenza Vaccines

Highly pathogenic avian influenza (HPAI) and Newcastle disease are economically important avian diseases worldwide. Effective vaccination is critical to control these diseases in poultry. Live attenuated Newcastle disease virus (NDV) vectored vaccines have been developed for bivalent vaccination against HPAI viruses and NDV. These vaccines have been generated by inserting the hemagglutinin (HA) gene of avian influenza virus into NDV genomes. In laboratory settings, several experimental NDV-vectored vaccines have protected specific pathogen-free chickens from mortality, clinical signs, and virus shedding against H5 and H7 HPAI viruses and NDV challenges. NDV-vectored H5 vaccines have been licensed for poultry vaccination in China and Mexico. Recently, an antigenically chimeric NDV vector has been generated to overcome pre-existing immunity to NDV in poultry and to provide early protection of poultry in the field. Prime immunization of one-day-old poults with a chimeric NDV vector followed by boosting with a conventional NDV vector has shown to protect broiler chickens against H5 HPAI viruses and a highly virulent NDV. This novel vaccination approach can provide efficient control of HPAI viruses in the field and facilitate poultry vaccination.

Recombinant turkey herpesvirus expressing H9 hemagglutinin providing protection against H9N2 avian influenza

H9N2 avian influenza viruses (AIVs) were prevailing in chickens, causing great economic losses and public health threats. In this study, turkey herpesviruses (HVT) was cloned as an infectious bacterial artificial chromosomes (BAC). Recombinant HVT (rHVT-H9) containing hemagglutinin (HA) gene from H9N2 virus were constructed via galactokinase (galK) selection and clustered regularly interspaced short palindromic repeats/associated 9 (CRISPR/Cas9) gene editing system. The recombinant rHVT-H9 showed no difference with parent HVT in plague morphology and virus replication kinetics. H9 protein expression of rHVT-H9 could be detected by western blot and indirect immunofluorescence assay (IFA) in vitro and in vivo. Immunization with rHVT-H9 could induce robust humoral and cellular immunity in chickens. In the challenge study, no chicken shed H9N2 virus from oropharynx and cloaca, and no H9N2 virus was found in viscera in vaccination groups. The result suggests that rHVT-H9 provides effective protection against H9N2 AIV in chickens.

Efficient transgene insertion in a pseudorabies virus vector by CRISPR/Cas9 and marker rescue-enforced recombination

For development of vectored vaccines against porcine pathogens the genome of the pseudorabies virus vaccine strain Bartha (PrV-Ba) was previously cloned as an infectious bacterial artificial chromosome (BAC), containing the bacterial replicon and a reporter gene cassette encoding enhanced green fluorescent protein (EGFP) at the nonessential glycoprotein G locus. To facilitate substitution of this insertion, this BAC was now modified by deletion of the adjacent promoter and initiation codon of the essential glycoprotein D (gD) gene of PrV-Ba. Furthermore, rabbit kidney (RK13) cells stably expressing Cas9 nuclease and an EGFP gene-specific guide RNA were prepared to induce site specific cleavage of the BAC DNA. After co-transfection of these cells with the modified BAC and recombination plasmids containing expression cassettes for new transgenes flanked by PrV DNA sequences including the intact 5'-end of the gD gene, >95% of the recombinants exhibited the desired gene substitutions, while no EGFP-expressing progeny virus was detectable. This approach was used for insertion and expression of the open reading frames E199L, CP204L (p30) and KP177R (p22) of African swine fever virus. The studies revealed that codon adaptation significantly enhanced expression of E199L, and that the chimeric CAG promoter increased transgene expression compared to cytomegalovirus immediate-early promoters.

Efficient inhibition of African swine fever virus replication by CRISPR/Cas9 targeting of the viral p30 gene (CP204L)

African swine fever is a devastating viral disease of domestic and wild pigs against which no vaccine or therapy is available. Therefore, we applied the CRISPR (clustered regularly interspaced short palindromic repeats) – Cas9 nuclease system to target the double-stranded DNA genome of African swine fever virus (ASFV). To this end, a permissive wild boar lung (WSL) cell line was modified by stable transfection with a plasmid encoding Cas9 and a guide RNA targeting codons 71 to 78 of the phosphoprotein p30 gene (CP204L) of ASFV. Due to targeted Cas9 cleavage of the virus genome, plaque formation of ASFV was completely abrogated and virus yields were reduced by four orders of magnitude. The specificity of these effects could be demonstrated by using a natural ASFV isolate and escape mutants possessing nucleotide exchanges within the target sequence, which were not inhibited in the Cas9-expressing cell line. Growth of the cell line was not affected by transgene expression which, as well as virus inhibition, proved to be stable over at least 50 passages. Thus, CRISPR-Cas9 mediated targeting of the ASFV p30 gene is a valid strategy to convey resistance against ASF infection, which may also be applied in its natural animal host.

Viral vector-based influenza vaccines

Antigenic drift of seasonal influenza viruses and the occasional introduction of influenza viruses of novel subtypes into the human population complicate the timely production of effective vaccines that antigenically match the virus strains that cause epidemic or pandemic outbreaks. The development of game-changing vaccines that induce broadly protective immunity against a wide variety of influenza viruses is an unmet need, in which recombinant viral vectors may provide. Use of viral vectors allows the delivery of any influenza virus antigen, or derivative thereof, to the immune system, resulting in the optimal induction of virus-specific B- and T-cell responses against this antigen of choice. This systematic review discusses results obtained with vectored influenza virus vaccines and advantages and disadvantages of the currently available viral vectors.

Impacts of poultry vaccination on viruses of wild bird

Spillover of viruses from farmed poultry into wild birds is a relatively new area of study at the livestock-wildlife interface. These transmission events can threaten the health of wild birds. There is growing evidence of transmission of vaccine viruses from poultry to wild birds, including attenuated vaccine strains of Newcastle disease virus and infectious bronchitis virus, and also spread of virulent viruses that may have evolved under the pressure of vaccine use, such as Marek's disease virus. Viral contaminants of poultry vaccines, including reticuloendotheliosis virus, may also be transmitted to wild birds and result in disease. New, vectored vaccines are less likely to directly spread to wild birds but this risk may rise as a result of recombination.

Protective efficacy of a single dose of baculovirus hemagglutinin-based vaccine in chickens and ducks against homologous and heterologous H5N1 virus infections

Outbreaks of the highly pathogenic H5N1 virus in poultry and humans are ongoing. Vaccination is an efficient method for prevention of H5N1 infection. Using chickens and ducks, we assessed the efficacy of a vaccine comprising H5N1 hemagglutinin (HA) protein produced in a baculovirus expression system. The immunized chickens and ducks were protected against lethal infection by H5N1 in an antigen dose-dependent manner. Complete protection against homologous challenge and partial protection against heterologous challenge were achieved in chickens immunized with 5 μg HA protein and in ducks immunized with 10 μg HA protein. The IgG antibody subtype was mainly detected in the sera and tissues, including the lungs. The neuraminidase (NA) inhibition assay was negative in immunized chickens and ducks. Our results indicated that the expressed HA protein by baculovirus was immunogenic to both chickens and ducks, and the immunized chickens and ducks were protected from the lethal infections of highly pathogenic H5N1 influenza virus, though ducks required more HA protein than chickens to be protected. Also, baculovirus HA-vaccinated poultry can be differentiated from infected poultry by NA inhibition assay.

Avian influenza vaccines against H5N1 'bird flu'

H5N1 avian influenza viruses (AIVs) have spread widely to more than 60 countries spanning three continents. To control the disease, vaccination of poultry is implemented in many of the affected countries, especially in those where H5N1 viruses have become enzootic in poultry and wild birds. Recently, considerable progress has been made toward the development of novel avian influenza (AI) vaccines, especially recombinant virus vector vaccines and DNA vaccines. Here, we will discuss the recent advances in vaccine development and use against H5N1 AIV in poultry. Understanding the properties of the available, novel vaccines will allow for the establishment of rational vaccination protocols, which in turn will help the effective control and prevention of H5N1 AI.

Comparison of single 1-day-old chick vaccination using a Newcastle disease virus vector with a prime/boost vaccination scheme against a highly pathogenic avian influenza H5N1 challenge

Avian influenza (AI) vaccines should be used as part of a whole comprehensive AI control programme. Vectored vaccines based on Newcastle disease virus (NDV) are very promising, but are so far licensed in only a few countries. In the present study, the immunogenicity and protection against a highly pathogenic H5N1 influenza challenge were evaluated after vaccination with an enterotropic NDV vector expressing an H5 haemagglutinin (rNDV-H5) in 1-day-old specific pathogen free chickens inoculated once, twice or once followed by a heterologous boost with an inactivated H5N9 vaccine (iH5N9). The heterologous prime/boost rNDV-H5/iH5N9 combination afforded the best level of protection against the H5N1 challenge performed at 6 weeks of age. Two rNDV-H5 administrations conferred a good level of protection after challenge, although only a cellular H5-specific response could be detected. Interestingly, a single administration of rNDV-H5 gave the same level of protection as the double administration but without any detectable H5-specific immune response. In contrast to AI immunity, a high humoral, mucosal and cellular NDV-specific immunity could be detected up to 6 weeks post vaccination after using the three different vaccination schedules. NDV-specific mucosal and cellular immune responses were slightly higher after double rNDV-H5 vaccination when compared with single inoculation. Finally, the heterologous prime/boost rNDV-H5/iH5N9 combination induced a broader detectable immunity including systemic, mucosal and cellular AI and NDV-specific responses.

Success factors for avian influenza vaccine use in poultry and potential impact at the wild bird-agricultural interface

Thirty-two epizootics of high pathogenicity avian influenza (HPAI) have been reported in poultry and other birds since 1959. The ongoing H5N1 HPAI epizootic that began in 1996 has also spilled over to infect wild birds. Traditional stamping-out programs in poultry have resulted in eradication of most HPAI epizootics. However, vaccination of poultry was added as a control tool in 1995 and has been used during five epizootics. Over 113 billion doses of AI vaccine have been used in poultry from 2002 to 2010 as oil-emulsified, inactivated whole AIV vaccines (95.5%) and live vectored vaccines (4.5%). Over 99% of the vaccine has been used in the four H5N1 HPAI enzootic countries: China including Hong Kong (91%), Egypt (4.7%), Indonesia (2.3%), and Vietnam (1.4%) where vaccination programs have been nationwide and routine to all poultry. Ten other countries used vaccine in poultry in a focused, risk-based manner but this accounted for less than 1% of the vaccine used. Most vaccine "failures" have resulted from problems in the vaccination process; i.e., failure to adequately administer the vaccine to at-risk poultry resulting in lack of population immunity, while fewer failures have resulted from antigenic drift of field viruses away from the vaccine viruses. It is currently not feasible to vaccinate wild birds against H5N1 HPAI, but naturally occurring infections with H5 low pathogenicity avian influenza viruses may generate cross-protective immunity against H5N1 HPAI. The most feasible method to prevent and control H5N1 HPAI in wild birds is through control of the disease in poultry with use of vaccine to reduce environmental burden of H5N1 HPAIV, and eventual eradication of the virus in domestic poultry, especially in domestic ducks which are raised in enzootic countries on range or in other outdoor systems having contact with wild aquatic and periurban terrestrial birds.

Chimeric newcastle disease virus protects chickens against avian influenza in the presence of maternally derived NDV immunity

Newcastle disease virus (NDV), an avian paramyxovirus type 1, is a promising vector for expression of heterologous proteins from a variety of unrelated viruses including highly pathogenic avian influenza virus (HPAIV). However, pre-existing NDV antibodies may impair vector virus replication, resulting in an inefficient immune response against the foreign antigen. A chimeric NDV-based vector with functional surface glycoproteins unrelated to NDV could overcome this problem. Therefore, an NDV vector was constructed which carries the fusion (F) and hemagglutinin-neuraminidase (HN) proteins of avian paramyxovirus type 8 (APMV-8) instead of the corresponding NDV proteins in an NDV backbone derived from the lentogenic NDV Clone 30 and a gene expressing HPAIV H5 inserted between the F and HN genes. After successful virus rescue by reverse genetics, the resulting chNDVFHN PMV8H5 was characterized in vitro and in vivo. Expression and virion incorporation of the heterologous proteins was verified by Western blot and electron microscopy. Replication of the newly generated recombinant virus was comparable to parental NDV in embryonated chicken eggs. Immunization with chNDVFHN PMV8H5 stimulated full protection against lethal HPAIV infection in chickens without as well as with maternally derived NDV antibodies. Thus, tailored NDV vector vaccines can be provided for use in the presence or absence of routine NDV vaccination.

Vaccination of gallinaceous poultry for H5N1 highly pathogenic avian influenza: current questions and new technology

Vaccination of poultry for avian influenza virus (AIV) is a complex topic as there are numerous technical, logistic and regulatory aspects which must be considered. Historically, control of high pathogenicity (HP) AIV infection in poultry has been accomplished by eradication and stamping out when outbreaks occur locally. Since the H5N1 HPAIV from Asia has spread and become enzootic, vaccination has been used on a long-term basis by some countries to control the virus, other countries have used it temporarily to aid eradication efforts, while others have not used it at all. Currently, H5N1 HPAIV is considered enzootic in China, Egypt, Viet Nam, India, Bangladesh and Indonesia. All but Bangladesh and India have instituted vaccination programs for poultry. Importantly, the specifics of these programs differ to accommodate different situations, resources, and industry structure in each country. The current vaccines most commonly used are inactivated whole virus vaccines, but vectored vaccine use is increasing. Numerous technical improvements to these platforms and novel vaccine platforms for H5N1 vaccines have been reported, but most are not ready to be implemented in the field.

Avirulent Marek's disease virus type 1 strain 814 vectored vaccine expressing avian influenza (AI) virus H5 haemagglutinin induced better protection than turkey herpesvirus vectored AI vaccine

Background

Herpesvirus of turkey (HVT) as a vector to express the haemagglutinin (HA) of avian influenza virus (AIV) H5 was developed and its protection against lethal Marek’s disease virus (MDV) and highly pathogenic AIV (HPAIV) challenges was evaluated previously. It is well-known that avirulemt MDV type 1 vaccines are more effective than HVT in prevention of lethal MDV infection. To further increase protective efficacy against HPAIV and lethal MDV, a recombinant MDV type 1 strain 814 was developed to express HA gene of HPAIV H5N1.

Methodology/Principal Findings

A recombinant MDV-1 strain 814 expressing HA gene of HPAIV H5N1 virus A/goose/Guangdong/3/96 at the US2 site (rMDV-HA) was developed under the control of a human CMV immediate-early promoter. The HA expression in the rMDV-HA was tested by immunofluorescence and Western blot analyses, and in vitro and in vivo growth properties of rMDV-HA were also analyzed. Furthermore, we evaluated and compared the protective immunity of rMDV-HA and previously constructed rHVT-HA against HPAIV and lethal MDV. Vaccination of chickens with rMDV-HA induced 80% protection against HPAIV, which was better than the protection rate by rHVT-HA (66.7%). In the animal study with MDV challenge, chickens immunized with rMDV-HA were completely protected against virulent MDV strain J-1 whereas rHVT-HA only induced 80% protection with the same challenge dose.

Conclusions/Significance

The rMDV-HA vaccine was more effective than rHVT-HA vaccine for protection against lethal MDV and HPAIV challenges. Therefore, avirulent MDV type 1 vaccine is a better vector than HVT for development of a recombinant live virus vaccine against virulent MDV and HPAIV in poultry.

Infectious laryngotracheitis virus in chickens

Infectious laryngotracheitis (ILT) is an important respiratory disease of chickens and annually causes significant economic losses in the poultry industry world-wide. ILT virus (ILTV) belongs to alphaherpesvirinae and the Gallid herpesvirus 1 species. The transmission of ILTV is via respiratory and ocular routes. Clinical and post-mortem signs of ILT can be separated into two forms according to its virulence. The characteristic of the severe form is bloody mucus in the trachea with high mortality. The mild form causes nasal discharge, conjunctivitis, and reduced weight gain and egg production. Conventional polymerase chain reaction (PCR), nested PCR, real-time PCR, and loop-mediated isothermal amplification were developed to detect ILTV samples from natural or experimentally infected birds. The PCR combined with restriction fragment length polymorphism (RFLP) can separate ILTVs into several genetic groups. These groups can separate vaccine from wild type field viruses. Vaccination is a common method to prevent ILT. However, field isolates and vaccine viruses can establish latent infected carriers. According to PCR-RFLP results, virulent field ILTVs can be derived from modified-live vaccines. Therefore, modified-live vaccine reversion provides a source for ILT outbreaks on chicken farms. Two recently licensed commercial recombinant ILT vaccines are also in use. Other recombinant and gene-deficient vaccine candidates are in the developmental stages. They offer additional hope for the control of this disease. However, in ILT endemic regions, improved biosecurity and management practices are critical for improved ILT control.

Progress toward the development of polyvalent vaccination strategies against multiple viral infections in chickens using herpesvirus of turkeys as vector

Vaccination is the most cost effective strategy for the control and prevention of the plethora of viral diseases affecting poultry production. The major challenge for poultry vaccination is the design of vaccines that will protect against multiple pathogens via a single protective dose, delivered by mass vaccination. The Marek disease virus and the highly pathogenic avian influenza virus cause severe disease outbreaks in chickens. Vaccination with live herpesvirus of turkeys protects chickens from Marek disease and inactivated influenza viruses are used as antigens to protect chickens against influenza virus infections. We developed herpesvirus of turkeys (HVT) as a vaccine vector that can act as a dual vaccine against avian influenza and Marek disease. The HVT vector was developed using reverse genetics based on an infectious bacterial artificial chromosome (BAC) clone of HVT. The BAC carrying the HVT genome was genetically modified to express the haemagglutinin (HA) gene of a highly pathogenic H7N1 virus. The resultant recombinant BAC construct containing the modified HVT sequence was transfected into chicken embryo fibroblast (CEF) cells and HVT recombinants (rHVT-H7HA) harbouring the H7N1 HA were recovered. Analysis of cultured CEF cells infected with the rHVT-H7HA showed that HA was expressed and that the rescued rHVT-H7HA stocks were stable during several in vitro passages with no difference in growth kinetics compared with the parent HVT. Immunization of one-day-old chicks with rHVT-H7HA induced H7-specific antibodies and protected chickens challenged with homologous H7N1 virus against virus shedding, clinical disease and death. The rHVT-H7HA vaccine also induced strong and long-lasting antibody titers against H7HA in chickens that were vaccinated in ovo 3 d before hatching. This vaccine supports differentiation between infected and vaccinated animals (DIVA), because no influenza virus nucleoprotein-specific antibodies were detected in the rHVT-H7HA vaccinated birds. The rHVT-H7HA not only provided protection against a lethal challenge with highly pathogenic H7N1 virus but also against highly virulent Marek disease virus and can be used as a DIVA vaccine.

Coexpression of avian influenza virus H5 and N1 by recombinant Newcastle disease virus and the impact on immune response in chickens

To analyze the contribution of neuraminidase (NA) toward protection against avian influenza virus (AIV) infection, three different recombinant Newcastle disease viruses (NDVs) expressing hemagglutinin (HA) or NA, or both, of highly pathogenic avian influenza virus (HPAIV) were generated. The lentogenic NDV Clone 30 was used as backbone for the insertion of HA of HPAIV strain A/chicken/Vietnam/P41/05 (H5N1) and NA of HPAIV strain A/duck/Vietnam/TG24-01/05 (H5N1). The HA was inserted between the genes encoding NDV phosphoprotein (P) and matrixprotein (M), and the NA was inserted between the fusion (F) and hemagglutinin-neuraminidase protein (HN) genes, resulting in NDVH5VmPMN1FHN. Two additional recombinants were constructed carrying the HA gene between the NDV P and M genes (NDVH5VmPM) or the NA between F and HN (NDVN1FHN). All recombinants replicated well and stably expressed the HA gene, the NA gene, or both. Chickens immunized with NDVH5VmPMN1FHN or NDVH5VmPM were protected against two different HPAIV H5N1 and also against HPAIV H5N2. In contrast, immunization of chickens with NDVN1FHN induced NDV- and AIV N1-specific antibodies but did not protect the animals against a lethal dose of HPAIV H5N1. Furthermore, expression of AIV N1, in addition to AIV H5 by NDV, did not increase protection against HPAIV H5N1.

Recombinant herpesvirus of turkeys as a vector-based vaccine against highly pathogenic H7N1 avian influenza and Marek's disease

A major challenge for poultry vaccination is the design of vaccines that protect against multiple pathogens via a single protective dose delivered through mass vaccination methods. In this investigation, we examined herpesvirus of turkeys (HVT) as a vaccine vector for delivery of haemagglutinin (HA) antigen of highly pathogenic H7N1 avian influenza virus that can act as a dual vaccine against avian influenza and Marek's disease. The HVT vector was developed using reverse genetics based on an infectious bacterial artificial chromosome (BAC) clone of HVT. The BAC carrying the HVT genome was genetically modified to express the HA gene of a highly pathogenic H7N1 virus. The resultant recombinant BAC construct containing the modified HVT sequence was transfected into chicken embryo fibroblast (CEF) cells, and HVT recombinants (rHVT-H7HA) harbouring the H7N1 HA were recovered. Analysis of cultured CEF cells infected with the rHVT-H7HA showed that HA was expressed and that the rescued rHVT-H7HA stocks were stable during several in vitro passages with no difference in growth kinetics compared with the parent HVT. Immunisation of one-day-old chicks with rHVT-H7HA induced H7-specific antibodies and protected chickens challenged with homologous H7N1 virus against virus shedding, clinical disease and death. This vaccine supports differentiation between infected and vaccinated animals (DIVA) vaccination strategies because no nucleoprotein-(NP) specific antibodies were detected in the rHVT-H7HA vaccinated birds. The rHVT-H7HA not only provided protection against a lethal challenge with highly pathogenic H7N1 virus but also against highly virulent Marek's disease virus and can be used as a DIVA vaccine.

Newcastle disease virus-vectored vaccines expressing the hemagglutinin or neuraminidase protein of H5N1 highly pathogenic avian influenza virus protect against virus challenge in monkeys

H5N1 highly pathogenic avian influenza virus (HPAIV) causes periodic outbreaks in humans, resulting in severe infections with a high (60%) incidence of mortality. The circulating strains have low human-to-human transmissibility; however, widespread concerns exist that enhanced transmission due to mutations could lead to a global pandemic. We previously engineered Newcastle disease virus (NDV), an avian paramyxovirus, as a vector to express the HPAIV hemagglutinin (HA) protein, and we showed that this vaccine (NDV/HA) induced a high level of HPAIV-specific mucosal and serum antibodies in primates when administered through the respiratory tract. Here we developed additional NDV-vectored vaccines expressing either HPAIV HA in which the polybasic cleavage site was replaced with that from a low-pathogenicity strain of influenza virus [HA(RV)], in order to address concerns of enhanced vector replication or genetic exchange, or HPAIV neuraminidase (NA). The three vaccine viruses [NDV/HA, NDV/HA(RV), and NDV/NA] were administered separately to groups of African green monkeys by the intranasal/intratracheal route. An additional group of animals received NDV/HA by aerosol administration. Each of the vaccine constructs was highly restricted for replication, with only low levels of virus shedding detected in respiratory secretions. All groups developed high levels of neutralizing antibodies against homologous and heterologous strains of HPAIV and were protected against challenge with 2 x 10(7) PFU of homologous HPAIV. Thus, needle-free, highly attenuated NDV-vectored vaccines expressing either HPAIV HA, HA(RV), or NA have been developed and demonstrated to be individually immunogenic and protective in a primate model of HPAIV infection. The finding that HA(RV) was protective indicates that it would be preferred for inclusion in a vaccine. The study also identified NA as an independent protective HPAIV antigen in primates. Furthermore, we demonstrated the feasibility of aerosol delivery of NDV-vectored vaccines.