Evaluation of Protective Efficacy When Combining Turkey Herpesvirus-Vector Vaccines

Immunogenicity and protective efficacy of a multivalent herpesvirus vectored vaccine against H9N2 low pathogenic avian influenza in chicken

The application of recombinant herpesvirus of turkey, expressing the H9 hemagglutinin gene from low pathogenic avian influenza virus (LPAIV) H9N2 and the avian orthoavulavirus-1 (AOAV-1) (commonly known as Newcastle Disease virus (NDV)) fusion protein (F) as an rHVT-H9-F vaccine, is an alternative to currently used classical vaccines. This study investigated H9- and ND-specific humoral and mucosal responses, H9-specific cell-mediated immunity, and protection conferred by the rHVT-H9-F vaccine in specific pathogen-free (SPF) chickens. Vaccination elicited systemic NDV F- and AIV H9-specific antibody response but also local antibodies in eye wash fluid and oropharyngeal swabs. The ex vivo H9-specific stimulation of splenic and pulmonary T cells in the vaccinated group demonstrated the ability of vaccination to induce systemic and local cellular responses. The clinical protection against a challenge using a LPAIV H9N2 strain of the G1 lineage isolated in Morocco in 2016 was associated with a shorter duration of shedding along with reduced viral genome load in the upper respiratory tract and reduced cloacal shedding compared to unvaccinated controls.

Simultaneous construction strategy using two types of fluorescent markers for HVT vector vaccine against infectious bursal disease and H9N2 avian influenza virus by NHEJ-CRISPR/Cas9

Recently, herpesvirus of turkeys (HVT), which was initially employed as a vaccine against Marek's disease (MD), has been shown to be a highly effective viral vector for producing recombinant vaccines that can simultaneously express the protective antigens of multiple poultry diseases. Prior to the development of commercial HVT-vectored dual-insert vaccines, the majority of HVT-vectored vaccines in use only contained a single foreign gene and were often generated using time-consuming and inefficient traditional recombination methods. The development of multivalent HVT-vectored vaccines that induce simultaneous protection against several avian diseases is of great value. In particular, efficacy interference between individual recombinant HVT vaccines can be avoided. Herein, we demonstrated the use of CRISPR/Cas9 gene editing technology for the insertion of an IBDV (G2d) VP2 expression cassette into the UL45/46 region of the recombinant rHVT-HA viral genome to generate the dual insert rHVT-VP2-HA recombinant vaccine. The efficacy of this recombinant virus was also evaluated in specific pathogen-free (SPF) chickens. PCR and sequencing results showed that the recombinant virus rHVT-VP2-HA was successfully constructed. Vaccination with rHVT-VP2-HA produced high levels of specific antibodies against IBDV (G2d) and H9N2/Y280. rHVT-VP2-HA can provide 100% protection against challenges with IBDV (G2d) and H9N2/Y280. These results demonstrate that rHVT-VP2-HA is a safe and highly efficacious vaccine for the simultaneous control of IBDV (G2d) and H9N2/Y280.

Efficacy of multivalent recombinant herpesvirus of turkey vaccines against high pathogenicity avian influenza, infectious bursal disease, and Newcastle disease viruses

Vaccines are an essential tool for the control of viral infections in domestic animals. We generated recombinant vector herpesvirus of turkeys (vHVT) vaccines expressing computationally optimized broadly reactive antigen (COBRA) H5 of avian influenza virus (AIV) alone (vHVT-AI) or in combination with virus protein 2 (VP2) of infectious bursal disease virus (IBDV) (vHVT-IBD-AI) or fusion (F) protein of Newcastle disease virus (NDV) (vHVT-ND-AI). In vaccinated chickens, all three vHVT vaccines provided 90-100% clinical protection against three divergent clades of high pathogenicity avian influenza viruses (HPAIVs), and significantly decreased number of birds and oral viral shedding titers at 2 days post-challenge compared to shams. Four weeks after vaccination, most vaccinated birds had H5 hemagglutination inhibition antibody titers, which significantly increased post-challenge. The vHVT-IBD-AI and vHVT-ND-AI vaccines provided 100% clinical protection against IBDVs and NDV, respectively. Our findings demonstrate that multivalent HVT vector vaccines were efficacious for simultaneous control of HPAIV and other viral infections.

Effect of CpG-Oligonucleotide in Enhancing Recombinant Herpes Virus of Turkey-Laryngotracheitis Vaccine-Induced Immune Responses in One-Day-Old Broiler Chickens

Infectious laryngotracheitis (ILT) is an economically important disease of chickens. While the recombinant vaccines can reduce clinical disease severity, the associated drawbacks are poor immunogenicity and delayed onset of immunity. Here, we used CpG-oligonucleotides (ODN) as an in ovo adjuvant in boosting recombinant herpesvirus of turkey-laryngotracheitis (rHVT-LT) vaccine-induced responses in one-day-old broiler chickens. Two CpG-ODN doses (5 and 10 μg/egg) with no adverse effect on the vaccine-virus replication or chick hatchability were selected for immune-response evaluation. Results showed that while CpG-ODN adjuvantation induced an increased transcription of splenic IFNγ and IL-1β, and lung IFNγ genes, the IL-1β gene expression in the lung was significantly downregulated compared to the control. Additionally, the transcription of toll-like receptor (TLR)21 in the spleen and lung and inducible nitric oxide synthase (iNOS) in the spleen of all vaccinated groups was significantly reduced. Furthermore, splenic cellular immunophenotyping showed that the CpG-ODN-10μg adjuvanted vaccination induced a significantly higher number of macrophages, TCRγδ+, and CD4+ T cells as well as a higher frequency of activated T cells (CD4+CD44+) when compared to the control. Collectively, the findings suggested that CpG-ODN can boost rHVT-LT-induced immune responses in day-old chicks, which may help in anti-ILT defense during their later stages of life.

CRISPR/Cas System Toward the Development of Next-Generation Recombinant Vaccines: Current Scenario and Future Prospects

The initially developed vaccines were relying mostly on attenuation and inactivation of pathogens. The use of recombinant DNA technology allows the targeting of immune responses focused against a few protective antigens. The conventional recombination methods for generating vaccines are time-consuming, laborious, and less efficient. To overcome these limitations, a new precise CRISPR/Cas9 with high efficacy, specificity, and low-cost properties has solved a lot of current problems of recombinant vaccines that intrigued the inspiration for novel recombinant vaccine development. CRISPR/Cas9 system was discovered as a bacterial adaptive immune system. In the domain of virology, CRISPR/Cas9 is used to engineer the virus genome to understand the fundamentals of viral pathogenesis, gene therapy, and virus-host interactions. One step ahead CRISPR/Cass9 bypassed the vaccine to precisely engineer the B-cells to secrete the specific antibodies against deadly viral pathogens. There is a critical literature review gap especially in the use of CRISPR/Cas9 to generate recombinant vaccines against viral diseases and its prospective application to engineering the B-cells in immunocompromised people. This review heights the application of CRISPR/Cas9 compared to conventional approaches for the development of recombinant vaccine vectors, editing the genes of B-cells, and challenges that need to be overcome. The factors affecting CRISPR/Cas9-edited recombinant vaccines and prospects in the context of viral genome editing for the development of vaccines will be discussed.

Assessing the Efficacy of Recombinant Newcastle Disease Virus Vaccines (Double-Insert vHVT-IBD-ND and Single-Insert vHVT-ND) Followed by a Vaccination with a Live Newcastle Disease Vaccine Against a Moroccan Velogenic Newcastle Disease Challenge in Commercial Broilers

The advent of turkey herpesvirus (HVT) vector vaccine technology (vHVT) has made a huge improvement in the prevention and control of several poultry diseases. The objective of this study was to compare, under experimental conditions, the protection conferred by different vaccination programs based on an HVT double-insert (infectious bursal disease {IBD] and Newcastle disease [ND]) vector vaccine (vHVT-IBD-ND) and an HVT single-insert (vHVT-ND) vector vaccine followed by a vaccination with a live ND vaccine at Day 1 only or at Days 1 and 14. Commercial broilers were vaccinated by the recombinant ND virus vaccines subcutaneously at 1 day old, in the hatchery, and challenged at 30 days of age using the Moroccan ND virus velogenic viscerotropic JEL strain. The results showed that the tested vaccine induced 95% to 100% clinical protection against mortality and clinical signs. The humoral immune response to vaccination was detected from 3 wk of age using enzyme-linked immunosorbent assay and hemagglutination inhibition tests. ND challenge virus shedding was significantly reduced in the vaccinated birds as compared to controls. Significant reduction of the cloacal shedding suggests that the vHVT-IBD-ND vaccine stimulates actively the immunity against the tested ND challenge virus. No significant differences were found between the vaccination programs based on vHVT-IBD-ND or on vHVT-ND.

Rapid, Sensitive, and Species-Specific Detection of Conventional and Recombinant Herpesvirus of Turkeys Vaccines Using Loop-Mediated Isothermal Amplification Coupled With a Lateral Flow Device Readout

Marek's disease, an economically important disease of chickens caused by virulent serotype 1 strains of the Mardivirus Marek's disease virus (MDV-1), is effectively controlled in the field by live attenuated vaccine viruses including herpesvirus of turkeys (HVT)—both conventional HVT (strain FC126) and, in recent years, recombinant HVT viruses carrying foreign genes from other avian viruses to protect against both Marek's disease and other avian viral diseases. Testing to monitor and confirm successful vaccination is important, but any such test must differentiate HVT from MDV-1 and MDV-2, as vaccination does not prevent infection with these serotypes. End-point and real-time PCR tests are widely used to detect and differentiate HVT, MDV-1 and MDV-2 but require expensive specialist laboratory equipment and trained operators. Here, we developed and validated two tube-based loop-mediated isothermal amplification tests coupled with detection by lateral flow device readout (LAMP-LFD): an HVT-specific test to detect both conventional and recombinant HVT strains, and a second test using novel LAMP primers to specifically detect the Vaxxitek® recombinant HVT. Specificity was confirmed using DNA extracted from virus-infected cultured cells, and limit of detection was determined using plasmid DNA carrying either the HVT or Vaxxitek® genome. The LAMP-LFD tests accurately detected all HVT vaccines, or Vaxxitek® only, in crude DNA as well as purified DNA extracted from field samples of organs, feathers, or poultry house dust that were confirmed positive for HVT by real-time PCR. These LAMP-LFD tests have potential for specific, rapid, simple, and inexpensive detection of HVT vaccines in the field.

Vaccines against Major Poultry Viral Diseases: Strategies to Improve the Breadth and Protective Efficacy

The poultry industry is the largest source of meat and eggs for human consumption worldwide. However, viral outbreaks in farmed stock are a common occurrence and a major source of concern for the industry. Mortality and morbidity resulting from an outbreak can cause significant economic losses with subsequent detrimental impacts on the global food supply chain. Mass vaccination is one of the main strategies for controlling and preventing viral infection in poultry. The development of broadly protective vaccines against avian viral diseases will alleviate selection pressure on field virus strains and simplify vaccination regimens for commercial farms with overall savings in husbandry costs. With the increasing number of emerging and re-emerging viral infectious diseases in the poultry industry, there is an urgent need to understand the strategies for broadening the protective efficacy of the vaccines against distinct viral strains. The current review provides an overview of viral vaccines and vaccination regimens available for common avian viral infections, and strategies for developing safer and more efficacious viral vaccines for poultry.

Review of Poultry Recombinant Vector Vaccines

The control of poultry diseases has relied heavily on the use of many live and inactivated vaccines. However, over the last 30 yr, recombinant DNA technology has been used to generate many novel poultry vaccines. Fowlpox virus and turkey herpesvirus are the two main vectors currently used to construct recombinant vaccines for poultry. With the use of these two vectors, more than 15 recombinant viral vector vaccines against Newcastle disease, infectious laryngotracheitis, infectious bursal disease, avian influenza, and Mycoplasma gallisepticum have been developed and are commercially available. This review focuses on current knowledge about the safety and efficacy of recombinant viral vectored vaccines and the mechanisms by which they facilitate the control of multiple diseases. Additionally, the development of new recombinant vaccines with novel vectors will be briefly discussed.

Advances in Development and Application of Influenza Vaccines

Influenza A virus is one of the most important zoonotic pathogens that can cause severe symptoms and has the potential to cause high number of deaths and great economic loss. Vaccination is still the best option to prevent influenza virus infection. Different types of influenza vaccines, including live attenuated virus vaccines, inactivated whole virus vaccines, virosome vaccines, split-virion vaccines and subunit vaccines have been developed. However, they have several limitations, such as the relatively high manufacturing cost and long production time, moderate efficacy of some of the vaccines in certain populations, and lack of cross-reactivity. These are some of the problems that need to be solved. Here, we summarized recent advances in the development and application of different types of influenza vaccines, including the recent development of viral vectored influenza vaccines. We also described the construction of other vaccines that are based on recombinant influenza viruses as viral vectors. Information provided in this review article might lead to the development of safe and highly effective novel influenza vaccines.

Infectious laryngotracheitis: Etiology, epidemiology, pathobiology, and advances in diagnosis and control - a comprehensive review

Infectious laryngotracheitis (ILT) is a highly contagious upper respiratory tract disease of chicken caused by a Gallid herpesvirus 1 (GaHV-1) belonging to the genus Iltovirus, and subfamily Alphaherpesvirinae within Herpesviridae family. The disease is characterized by conjunctivitis, sinusitis, oculo-nasal discharge, respiratory distress, bloody mucus, swollen orbital sinuses, high morbidity, considerable mortality and decreased egg production. It is well established in highly dense poultry producing areas of the world due to characteristic latency and carrier status of the virus. Co-infections with other respiratory pathogens and environmental factors adversely affect the respiratory system and prolong the course of the disease. Latently infected chickens are the primary source of ILT virus (ILTV) outbreaks irrespective of vaccination. Apart from conventional diagnostic methods including isolation and identification of ILTV, serological detection, advanced biotechnological tools such as PCR, quantitative real-time PCR, next generation sequencing, and others are being used in accurate diagnosis and epidemiological studies of ILTV. Vaccination is followed with the use of conventional vaccines including modified live attenuated ILTV vaccines, and advanced recombinant vector vaccines expressing different ILTV glycoproteins, but still these candidates frequently fail to reduce challenge virus shedding. Some herbal components have proved to be beneficial in reducing the severity of the clinical disease. The present review discusses ILT with respect to its current status, virus characteristics, epidemiology, transmission, pathobiology, and advances in diagnosis, vaccination and control strategies to counter this important disease of poultry.

Replication of Marek's disease vaccines in turkey embryos and their effect on TLR-3 and IFN-γ transcripts

Understanding the pathogenesis of herpesvirus of turkeys (HVT) in its natural host is necessary before recombinant HVT (rHVT) can be used efficiently in turkey flocks. The objectives of this study were to evaluate when commercial turkey flocks get infected with wild type HVT, to study replication of HVT (conventional and recombinant rHVT-Newcastle disease, rHVT-ND) and other Marek's disease (MD) vaccines (SB-1 and CVI988) in turkey embryonic tissues, and to evaluate the expression of TLR-3 and IFN-γ in the lung and spleen of one-day-old turkeys after in ovo vaccination with MD vaccines. Our results demonstrated that commercial turkeys got exposed to wild type HVT within the first days of life; therefore, there is a potential of interaction between wild type HVT and rHVT when administered at day of age. On the other hand, all evaluated vaccines (especially HVT and rHVT-ND) replicated very well in turkey embryonic tissues. In ovo vaccination with HVT and CVI988 increased transcription of TLR-3 in the spleen of one-day-old turkeys. However, no effect on the transcription of TLR-3 or IFN-γ in the lungs and IFN-γ in the spleen in newly hatched turkeys was detected in the present study. Because of the limitations of evaluated genes, timepoints, and studied tissues, future studies are warranted to better understand the effect of MD vaccines on the turkey embryo immune responses.RESEARCH HIGHLIGHTS Commercial turkey flocks get infected with wild type HVT within the first days of life.HVT and rHVT replicates readily in turkey embryonic tissues.SB-1 and CVI988 also replicate in turkey embryonic tissues, but at lower rates than HVT and rHVT.HVT and CVI988 increase transcription of TLR-3 in the spleen.

Application of CRISPR/Cas9 in Understanding Avian Viruses and Developing Poultry Vaccines

Clustered regularly interspaced short palindromic repeats associated protein nuclease 9 (CRISPR-Cas9) technology offers novel approaches to precisely, cost-effectively, and user-friendly edit genomes for a wide array of applications and across multiple disciplines. This methodology can be leveraged to underpin host-virus interactions, elucidate viral gene functions, and to develop recombinant vaccines. The successful utilization of CRISPR/Cas9 in editing viral genomes has paved the way of developing novel and multiplex viral vectored poultry vaccines. Furthermore, CRISPR/Cas9 can be exploited to rectify major limitations of conventional approaches including reversion to virulent form, recombination with field viruses and transgene, and genome instability. This review provides comprehensive analysis of the potential of CRISPR/Cas9 genome editing technique in understanding avian virus-host interactions and developing novel poultry vaccines. Finally, we discuss the simplest and practical aspects of genome editing approaches in generating multivalent recombinant poultry vaccines that conform simultaneous protection against major avian diseases.

Efficacy of a turkey herpesvirus double construct vaccine (HVT-ND-IBD) against challenge with different strains of Newcastle disease, infectious bursal disease and Marek's disease viruses

A double construct vaccine of turkey herpesvirus (HVT) was prepared that contains the fusion (F) gene from Newcastle disease virus (NDV) and the viral protein 2 (VP2) gene from infectious bursal disease virus (IBDV). Safety of the vaccine (HVT-ND-IBD) was confirmed and efficacy was evaluated after subcutaneous (SC) vaccination at 1 day of age or the in ovo route of vaccination. Challenges were performed with velogenic NDV strains (Texas GB and Herts Weybridge 33/56), with different strains of IBDV (classical strain STC; very virulent strain CS89 and variant E strain) and with Marek's disease virus (MDV) strain RB1B. Vaccination with HVT-ND-IBD induced a high level of protection against these challenges. Vaccination with HVT is often combined with Rispens CVI988 vaccine and live ND vaccines for higher and earlier, MD and ND protection, respectively. HVT-ND-IBD vaccination in combination with these vaccines showed MD protection as early as 4 days post vaccination and ND protection as early as 2 weeks post vaccination. The long protection as seen with HVT vaccination was confirmed by demonstrating protection against NDV up to 60 weeks. Finally, to evaluate the performance of the vaccine in commercial birds with maternally-derived antibodies, two field trials were performed, using in ovo vaccination in broilers and SC vaccination in combination with Rispens CVI988 vaccine in layer-type birds. The efficacy was confirmed for all components by challenges. These results demonstrate that HVT-ND-IBD is a safe and highly efficacious vaccine for simultaneous control of ND, IBD and MD. RESEARCH HIGHLIGHTS A double construct HVT vaccine with the NDV F and the IBDV VP2 genes was prepared. The vaccine protects against three important diseases: MDV, NDV and IBDV. In ovo and sub-cutaneous vaccination was evaluated in the field in commercial chickens.

Effectiveness of a Simultaneous rHVT-F(ND) and rHVT-H5(AI) Vaccination of Day-Old Chickens and the Influence of NDV- and AIV-Specific MDA on Immune Response and Conferred Protection

The recombinant herpesvirus of turkey (rHVT) vaccines targeting Newcastle disease (ND) and H5Nx avian influenza (AI) have been demonstrated efficient in chickens when used individually at day-old. Given the practical field constraints associated with administering two vaccines separately and in the absence of a currently available bivalent rHVT vector vaccine expressing both F(ND) and H5(AI) antigens, the aim of this study was to investigate whether interference occurs between the two vaccines when simultaneously administered in a single shot. The studies have been designed to determine (i) the ND and AI-specific protection and antibody response conferred by these vaccines inoculated alone or in combination at day-old, (ii) the influence of maternally-derived antibodies (MDA), and (iii) the potential interference between the two vaccine. Our results demonstrate that their combined administration is efficient to protect chickens against clinical signs of velogenic Newcastle disease virus (vNDV) and H5-highly pathogenic avian influenza virus (HPAIV) infections. Viral shedding following co-vaccination is also markedly reduced, while slightly lower NDV- and AIV-specific antibody responses are observed. NDV- and AIV-specific MDA show negative effects on the onset of the specific antibody responses. However, if AIV-specific MDA reduce the protection against H5-HPAIV induced by rHVT-H5(AI) vaccine, it was not observed for ND.

Commercial Vaccines and Vaccination Strategies Against Infectious Laryngotracheitis: What We Have Learned and Knowledge Gaps That Remain

Infectious laryngotracheitis (ILT) is an upper respiratory disease of chickens, pheasants, and peafowl caused by the alphaherpesvirus Gallid alpha herpesvirus 1 (GaHV-1), commonly known as infectious laryngotracheitis virus. ILT is an acute respiratory disease characterized by clinical signs of conjunctivitis, nasal discharge, dyspnea, and lethargy. In severe forms of the disease, hemorrhagic tracheitis together with gasping, coughing, and expectoration of bloody mucus are common. The morbidity and mortality rates of the disease vary depending on the virulence of the strain circulating, the level of virus circulating in the field, and the presence of other respiratory infections. Since the identification of the disease in the 1920s, ILT continues to affect the poultry industry negatively across the globe. The disease is primarily controlled by a combination of biosecurity and vaccination. The first commercial vaccines, introduced in the late 1950s and early 1960s, were the chicken embryo origin live attenuated vaccines. The tissue culture origin vaccine was introduced in late 1970s. Recombinant viral vector ILT vaccines were first introduced in the United States in the 2000s, and now they are being used worldwide, alone or in combination with live attenuated vaccines. This review article provides a synopsis of what we have learned about vaccines and vaccination strategies used around the world and addresses knowledge gaps about the virus and host interactions that remain unknown.

Vaccinal efficacy of molecularly cloned Gallid alphaherpesvirus 3 strain 301B/1 against very virulent Marek's disease virus challenge

Marek's disease virus (MDV), a causative agent of Marek's disease, has evolved its virulence partly because the current control strategies fail to provide sterilizing immunity. Gallid alphaherpesvirus 3 (GaHV-3) and turkey herpesvirus have been developed as bivalent vaccines to improve upon the level of protection elicited by single formulations. Since the in vitro passage of vaccines can result in attenuation, a GaHV-3 strain 301B/1 was cloned as a bacterial artificial chromosome (BAC) by inserting the mini-F replicon into the virus genome. A fully infectious virus, v301B-BAC, was reconstituted from the 301B/1 BAC clone and had similar growth kinetics comparable to that of the parental 301B/1 virus with strong reactivity against anti-301B/1 chicken sera. Protective efficacies of v301B-BAC, parental 301B/1, and SB-1 vaccine were evaluated against a very virulent MDV Md5 challenge. Clinical signs were significantly lower in the v301B-BAC vaccinated groups (24-25 %), parental 301B/1 (29 %) compare to that of non-vaccinated control (100%) and the removal of BAC sequences from v301B-BAC genome further reduced this to 17 %. The protective indices of v301B-BACs (75-76 %) were comparable with those of both the 301B/1 and the SB-1 vaccine (71%). Removal of the mini-F replicon resulted in a reconstituted virus with a protective index of 83 %. The shedding of challenge virus was notably lower in the v301B-BAC, and v301B-delBAC vaccinated groups. Overall, the protective efficacy of the 301B-BAC-derived vaccine virus against a very virulent MDV challenge was comparable to that of the parental 301B/1 virus as well as the SB-1 vaccine virus.

Pathogen transmission from vaccinated hosts can cause dose-dependent reduction in virulence

Many livestock and human vaccines are leaky because they block symptoms but do not prevent infection or onward transmission. This leakiness is concerning because it increases vaccination coverage required to prevent disease spread and can promote evolution of increased pathogen virulence. Despite leakiness, vaccination may reduce pathogen load, affecting disease transmission dynamics. However, the impacts on post-transmission disease development and infectiousness in contact individuals are unknown. Here, we use transmission experiments involving Marek disease virus (MDV) in chickens to show that vaccination with a leaky vaccine substantially reduces viral load in both vaccinated individuals and unvaccinated contact individuals they infect. Consequently, contact birds are less likely to develop disease symptoms or die, show less severe symptoms, and shed less infectious virus themselves, when infected by vaccinated birds. These results highlight that even partial vaccination with a leaky vaccine can have unforeseen positive consequences in controlling the spread and symptoms of disease.

Generation of A Triple Insert Live Avian Herpesvirus Vectored Vaccine Using CRISPR/Cas9-Based Gene Editing

Herpesvirus of turkeys (HVT), used originally as a vaccine against Marek’s disease (MD), has recently been shown to be a highly effective viral vector for generation of recombinant vaccines that deliver protective antigens of other avian pathogens. Until the recent launch of commercial HVT-vectored dual insert vaccines, most of the HVT-vectored vaccines in the market carry a single foreign gene and are usually developed with slow and less efficient conventional recombination methods. There is immense value in developing multivalent HVT-vectored vaccines capable of inducing simultaneous protection against multiple avian pathogens, particularly to overcome the interference between individual recombinant HVT vaccines. Here we demonstrate the use of a previously developed CRISPR/Cas9 gene editing protocol for the insertion of ILTV gD-gI and the H9N2 AIV hemagglutinin expression cassettes into the distinct locations of the recombinant HVT-IBDV VP2 viral genome, to generate the triple insert HVT-VP2-gDgI-HA recombinant vaccine. The insertion, protein expression, and stability of each insert were then evaluated by PCR, immunostaining and Western blot analyses. The successful generation of the first triple insert recombinant HVT vaccine with the potential for the simultaneous protection against three major avian viral diseases in addition to MD is a major innovation in vaccination-based control of major poultry diseases.