Infectious bursal disease virus structural protein VP2 expressed by a fowlpox virus recombinant confers protection against disease in chickens

Efficacy of Fowlpox Virus Vector Vaccine Expressing VP2 and Chicken Interleukin-18 in the Protection against Infectious Bursal Disease Virus

In mammals, the role of interleukin-18 (IL-18) in the immune response is to drive inflammatory and, normally therefore, anti-viral responses. IL-18 also shows promise as a vaccine adjuvant in mammals. Chicken IL-18 (chIL-18) has been cloned. The aim of this study was to investigate the potential of chIL-18 to act as a vaccine adjuvant in the context of a live recombinant Fowlpox virus vaccine (fpIBD1) against Infectious bursal disease virus (IBDV). fpIBD1 protects against mortality, but not against damage to the bursa of Fabricius caused by IBDV infection. The Fowlpox virus genome itself contains several candidate immunomodulatory genes, including potential IL-18 binding proteins (IL-18bp). We knocked out (Δ) the potential IL-18bp genes in fpIBD1 and inserted (::) the cDNA encoding chIL-18 into fpIBD1 in the non-essential ORF030, generating five new viral constructs -fpIBD1::chIL-18, fpIBD1ΔORF073, fpIBD1ΔORF073::chIL-18, fpIBD1ΔORF214, and fpIBD1ΔORF214::chIL-18. The subsequent protection from challenge with virulent IBDV, as measured by viral load and bursal damage, given by these altered fpIBD1 strains, was compared to that given by the original fpIBD1. Complete protection was provided following challenge with IBDV in chicken groups vaccinated with either fpIBDIΔ073::IL-18 or fpIBD1Δ214::IL-18, as no bursal damage nor IBDV was detected in the bursae of the birds. The results show that chIL-18 can act as an effective vaccine adjuvant by improving the fpIBD1 vaccine and providing complete protection against IBDV challenge.

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.

The expression in plants of an engineered VP2 protein of Infectious Bursal Disease Virus induces formation of structurally heterogeneous particles that protect from a very virulent viral strain

Infectious Bursal Disease Virus (IBDV), the etiological agent of Gumboro disease, causes mortality and immunosuppression in chickens and major losses to poultry industry worldwide. The IBDV major capsid protein VP2 is considered the best candidate for the production of novel subunit vaccines. This structural protein contains the major conformational epitopes responsible for the induction of IBDV neutralizing antibodies in chickens and has been demonstrated able to form supramolecular structures in yeast and insect cells. The aim of this study was to express an engineered version of the VP2 protein (His-pVP2) to verify its ability to self-assemble into virus-like particles in plants. The recombinant VP2 was transiently expressed by agroinfiltration in Nicotiana benthamiana and transmission electron microscopy of sucrose density gradient fractions revealed the presence of a mixed population of differently shaped particles ranging from spherical capsids, with a diameter between ~25 and ~70 nm, to tubular structures, with variable length (from 100 to 400 nm). The recombinant VP2-based particles when used for the intramuscular immunization of specific-pathogen-free chicks resulted able to induce the production of anti-IBDV specific antibodies at titers comparable to those induced by a commercial vaccine. Moreover, all the immunized birds survived to the challenge with a Moroccan very virulent IBDV strain with no major histomorphological alterations of the Bursa of Fabricius, similarly to what obtained with the commercial inactivated vaccine.

Current status of virus-vectored vaccines against pathogens that affect poultry

The most effective strategies for the control of disease in poultry are vaccination and biosecurity. Vaccines useful against pathogens affecting poultry must be safe, effective with a single dose, inexpensive, applicable by mass vaccination methods, and able to induce a protective immune response in the presence of maternal antibodies. Viral vector meet some of these characteristics and if the attenuated virus used as vector infects birds, the vaccine will have the advantage of being bivalent. Thus, viral vectors are currently a tool of choice for the development of new poultry vaccines. This review describes the main viruses used as vectors for the delivery and in vivo expression of antigens of poultry pathogens. It also presents the methodologies most frequently used to obtain recombinant viral vectors and summarizes the state-of-the-art related to vectored vaccines in poultry (some of them currently licensed), the pathogens targeted and their antigens, and the ability of these vaccines to induce an effective immune response. Finally, the review discusses the results of a few studies comparing recombinant viral vector vaccines and live-attenuated vaccines in vaccine matching challenges, and mentions strategies and future researches that can help to improve the efficacy of vectored vaccines in poultry birds.

Expressing the immunodominant projection domain of infectious bursal disease virus fused to the fragment crystallizable of chicken IgY in yellow maize for a prospective edible vaccine

Control of Infectious bursal disease virus (IBDV) in endemic countries has been based on early immunization of chicks using conventional live or inactivated vaccines that became not fully effectual and have biosafety concerns. This endeavor seeks generating a recombinant chimeric protein merging the projection domain (PD) of IBDV VP2 capsid with the fragment crystallizable (Fc) of avian IgY (FcIgY), in maize as a prospective poultry edible vaccine. The PD sequence was built on the basis of very virulent IBDV isolates circulating in Egypt. After optimization of codon-usage in maize, sequences of PD and FcIgY were effectively expressed in two elites of yellow maize via bombardment transformation in immature embryos. Chimeric protein amount in stable transgenic samples ranged from1.36% to 3.03% of the total soluble protein based on tissue age and maize cultivar. IBDV VP2 coding sequence was amplified from viral RNA, cloned, and expressed in E. coli. A group of Balb/C mice were hyper-immunized with purified recombinant VP2 protein for raising anti- recombinant VP2 antibodies (anti-rVP2 Ab). Proper expression in maize and immunoreactivity of the chimeric protein (PD-FcIgY) to chicken anti- IBDV and anti-rVP2 Ab were confirmed by both direct and indirect double antibody sandwich (DAS)-ELISAs as well as western blotting. Seeds of regenerated transgenic maize will be validated for chickens as edible vaccination in further studies.

Infectious bursal disease virus in chickens: prevalence, impact, and management strategies

Infectious bursal disease (IBD), also known as Gumboro disease, is a highly contagious, immunosuppressive disease of young chickens. Although first observed about 60 years ago, to date, the disease is responsible for major economic losses in the poultry industry worldwide. IBD virus (IBDV), a double-stranded RNA virus, exists as two serotypes with only serotype 1 causing the disease in young chickens. The virus infects the bursa of Fabricius of particularly the actively dividing and differentiating lymphocytes of the B-cells lineage of immature chickens, resulting in morbidity, mortality, and immunosuppression. Immunosuppression enhances the susceptibility of chickens to other infections and interferes with vaccination against other diseases. Immunization is the most important measure to control IBD; however, rampant usage of live vaccines has resulted in the evolution of new strains. Although the immunosuppression caused by IBDV is more directed toward the B lymphocytes, the protective immunity in birds depends on inducement of both humoral and cell-mediated immune responses. The interference with the inactivated vaccine induced maternally derived antibodies in young chicks has become a hurdle in controlling the disease, thus necessitating the development of newer vaccines with improved efficacy. The present review illustrates the overall dynamics of the virus and the disease, and the recent developments in the field of virus diagnosis and vaccine research.

Newcastle Disease Virus Vectored Bivalent Vaccine against Virulent Infectious Bursal Disease and Newcastle Disease of Chickens

Newcastle disease virus (NDV) strain F is a lentogenic vaccine strain used for primary vaccination in day-old chickens against Newcastle disease (ND) in India and Southeast Asian countries. Recombinant NDV-F virus and another recombinant NDV harboring the major capsid protein VP2 gene of a very virulent infectious bursal disease virus (IBDV); namely rNDV-F and rNDV-F/VP2, respectively, were generated using the NDV F strain. The rNDV-F/VP2 virus was slightly attenuated, as compared to the rNDV-F virus, as evidenced from the mean death time and intracerebral pathogenicity index analysis. This result indicates that rNDV-F/VP2 behaves as a lentogenic virus and it is stable even after 10 serial passages in embryonated chicken eggs. When chickens were vaccinated with the rNDV F/VP2, it induced both humoral and cell mediated immunity, and was able to confer complete protection against very virulent IBDV challenge and 80% protection against virulent NDV challenge. These results suggest that rNDV-F could be an effective and inherently safe vaccine vector. Here, we demonstrate that a bivalent NDV-IBDV vaccine candidate generated by reverse genetics method is safe, efficacious and cost-effective, which will greatly aid the poultry industry in developing countries.

Recombinant fowlpox virus vector-based vaccines: expression kinetics, dissemination and safety profile following intranasal delivery

We have previously established that mucosal uptake of recombinant fowlpox virus (rFPV) vaccines is far superior to other vector-based vaccines. Specifically, intranasal priming with rFPV vaccines can recruit unique antigen-presenting cells, which induce excellent mucosal and systemic HIV-specific CD8+ T-cell immunity. In this study, we have for the first time investigated the in vivo dissemination, safety and expression kinetics of rFPV post intranasal delivery using recombinant viruses expressing green fluorescent protein or mCherry. Both confocal microscopy of tissue sections using green fluorescent protein and in vivo Imaging System (IVIS) spectrum live animal and whole organ imaging studies using mCherry revealed that (i) the peak antigen expression occurs 12 to 24 h post vaccination and no active viral gene expression is detected 96 h post vaccination. (ii) The virus only infects the initial vaccination site (lung and nasal cavity) and does not disseminate to distal sites such as the spleen or gut. (iii) More importantly, rFPV does not cross the olfactory receptor neuron pathway. Collectively, our findings indicate that rFPV vector-based vaccines have all the hallmarks of a safe and effective mucosal delivery vector, suitable for clinical evaluation.

Advances in vaccine research against economically important viral diseases of food animals: Infectious bursal disease virus

Numerous reviews have been published on infectious bursal disease (IBD) and infectious bursal disease virus (IBDV). Many high quality vaccines are commercially available for the control of IBD that, when used correctly, provide solid protection against infection and disease caused by IBDV. Viruses are not static however; they continue to evolve and vaccines need to keep pace with them. The evolution of IBDV has resulted in very virulent strains and new antigenic types of the virus. This review will discuss some of the limitations associated with existing vaccines, potential solutions to these problems and advances in new vaccines for the control of IBD.

The evolution of poxvirus vaccines

After Edward Jenner established human vaccination over 200 years ago, attenuated poxviruses became key players to contain the deadliest virus of its own family: Variola virus (VARV), the causative agent of smallpox. Cowpox virus (CPXV) and horsepox virus (HSPV) were extensively used to this end, passaged in cattle and humans until the appearance of vaccinia virus (VACV), which was used in the final campaigns aimed to eradicate the disease, an endeavor that was accomplished by the World Health Organization (WHO) in 1980. Ever since, naturally evolved strains used for vaccination were introduced into research laboratories where VACV and other poxviruses with improved safety profiles were generated. Recombinant DNA technology along with the DNA genome features of this virus family allowed the generation of vaccines against heterologous diseases, and the specific insertion and deletion of poxvirus genes generated an even broader spectrum of modified viruses with new properties that increase their immunogenicity and safety profile as vaccine vectors. In this review, we highlight the evolution of poxvirus vaccines, from first generation to the current status, pointing out how different vaccines have emerged and approaches that are being followed up in the development of more rational vaccines against a wide range of diseases.

Novel HIV IL-4R antagonist vaccine strategy can induce both high avidity CD8 T and B cell immunity with greater protective efficacy

We have established that the efficacy of a heterologous poxvirus vectored HIV vaccine, fowlpox virus (FPV)-HIV gag/pol prime followed by attenuated vaccinia virus (VV)-HIV gag/pol booster immunisation, is strongly influenced by the cytokine milieu at the priming vaccination site, with endogenous IL-13 detrimental to the quality of the HIV specific CD8+ T cell response induced. We have now developed a novel HIV vaccine that co-expresses a C-terminal deletion mutant of the mouse IL-4, deleted for the essential tyrosine (Y119) required for signalling. In our vaccine system, the mutant IL-4C118 can bind to IL-4 type I and II receptors with high affinity, and transiently prevent the signalling of both IL-4 and IL-13 at the vaccination site. When this IL-4C118 adjuvanted vaccine was used in an intranasal rFPV/intramuscular rVV prime-boost immunisation strategy, greatly enhanced mucosal/systemic HIV specific CD8+ T cells with higher functional avidity, expressing IFN-γ, TNF-α and IL-2 and greater protective efficacy were detected. Surprisingly, the IL-4C118 adjuvanted vaccines also induced robust long-lived HIV gag-specific serum antibody responses, specifically IgG1 and IgG2a. The p55-gag IgG2a responses induced were of a higher magnitude relative to the IL-13Rα2 adjuvant vaccine. More interestingly, our recently tested IL-13Rα2 adjuvanted vaccine which only inhibited IL-13 activity, even though induced excellent high avidity HIV-specific CD8+ T cells, had a detrimental impact on the induction of gag-specific IgG2a antibody immunity. Our observations suggest that (i) IL-4 cell-signalling in the absence of IL-13 retarded gag-specific antibody isotype class switching, or (ii) IL-13Rα2 signalling was involved in inducing good gag-specific B cell immunity. Thus, we believe our novel IL-4R antagonist adjuvant strategy offers great promise not only for HIV-1 vaccines, but also against a range of chronic infections where sustained high quality mucosal and systemic T and B cell immunity are required for protection.

Progresses in DNA-based heterologous prime-boost immunization strategies

Although recombinant DNA and recombinant viral vectors expressing HIV antigens have yielded positive outcomes in animal models, these vaccines have not been effectively translated to humans. Despite this, there is still a high level of optimism that poxviral-based vaccine strategies could offer the best hope for developing an effective vaccine against not only HIV-1 but also other chronic diseases where good-quality T and B cell immunity is needed for protection. In this chapter we discuss step by step (1) how recombinant poxviral vectors co-expressing HIV antigens and promising mucosal/systemic adjuvants (e.g., IL-13Rα2) are constructed, (2) how these vectors can be used in alternative heterologous prime-boost immunization strategies, (3) how systemic and mucosal samples are prepared for analysis, followed by (4) two immunological assays: multicolor intracellular cytokine staining and tetramer/homing maker analysis that are used to evaluate effective systemic and mucosal T cell immunity.

Unique IL-13Rα2-based HIV-1 vaccine strategy to enhance mucosal immunity, CD8(+) T-cell avidity and protective immunity

We have established that mucosal immunization can generate high-avidity human immunodeficiency virus (HIV)-specific CD8(+) T cells compared with systemic immunization, and interleukin (IL)-13 is detrimental to the functional avidity of these T cells. We have now constructed two unique recombinant HIV-1 vaccines that co-express soluble or membrane-bound forms of the IL-13 receptor α2 (IL-13Rα2), which can "transiently" block IL-13 activity at the vaccination site causing wild-type animals to behave similar to an IL-13 KO animal. Following intranasal/intramuscular prime-boost immunization, these IL-13Rα2-adjuvanted vaccines have shown to induce (i) enhanced HIV-specific CD8(+) T cells with higher functional avidity, with broader cytokine/chemokine profiles and greater protective immunity using a surrogate mucosal HIV-1 challenge, and also (ii) excellent multifunctional mucosal CD8(+) T-cell responses, in the lung, genito-rectal nodes (GN), and Peyer's patch (PP). Data revealed that intranasal delivery of these IL-13Rα2-adjuvanted HIV vaccines recruited large numbers of unique antigen-presenting cell subsets to the lung mucosae, ultimately promoting the induction of high-avidity CD8(+) T cells. We believe our novel IL-13R cytokine trap vaccine strategy offers great promise for not only HIV-1, but also as a platform technology against range of chronic infections that require strong sustained high-avidity mucosal/systemic immunity for protection.

Codon optimization and woodchuck hepatitis virus posttranscriptional regulatory element enhance the immune responses of DNA vaccines against infectious bursal disease virus in chickens

The present study was undertaken to evaluate the protective efficacy of DNA vaccines against infectious bursal disease virus (IBDV) in chickens and to determine whether codon optimization and the woodchuck hepatitis virus posttranscriptional regulatory element (WPRE) could improve the immunogenicity of the DNA vaccines. The VP2, VP243 and codon-optimized VP243 genes of IBDV were cloned into pCAGGS vector, and designated as pCAGVP2, pCAGVP243 and pCAGoptiVP243, respectively. Plasmids pCAGWVP243 and pCAGWoptiVP243 carrying the WPRE elements were also constructed as DNA vaccines. To evaluate vaccine efficacy, 2-week-old chickens were injected intramuscularly with the constructed plasmids twice at 2-week intervals and challenged with very virulent IBDV 2 weeks post-boost. Plasmid pCAGVP243 induced better immune responses than pCAGVP2. Chickens immunized with pCAGoptiVP243 and pCAGWVP243 had higher levels of antibody titers, lymphoproliferation responses and cytokine production compared with pCAGVP243. Furthermore, plasmid pCAGWoptiVP243 induced the highest levels of immune responses among the groups. After challenged, DNA vaccines pCAGVP2, pCAGVP243, pCAGoptiVP243, pCAGWVP243 and pCAGWoptiVP243 conferred protection for 33%, 60%, 80%, 87% and 100% of chickens, respectively, as evidenced by the absence of clinical signs, mortality, and bursal atrophy. These results indicate that codon optimization and WPRE could enhance the protective efficacy of DNA vaccines against IBDV and these two approaches could work together synergistically in a single DNA vaccine.

Role of novel type I interferon epsilon in viral infection and mucosal immunity

Intranasal infection with vaccinia virus co-expressing interferon epsilon (VV-HIV-IFN-ε) was used to evaluate the role of IFN-ε in mucosal immunity. VV-HIV- IFN-ε infection induced a rapid VV clearance in lung that correlated with (i) an elevated lung VV-specific CD8(+)CD107a(+)IFN-γ(+) population expressing activation markers CD69/CD103, (ii) enhanced lymphocyte recruitment to lung alveoli with reduced inflammation, and (iii) an heightened functional/cytotoxic CD8(+)CD4(+) T-cell subset (CD3(hi)CCR7(hi)CD62L(lo)) in lung lymph nodes. These responses were different to that observed with intranasal VV-HA-IFN-α(4) or VV-HA-IFN-β infections. When IFN-ε was used in an intranasal/intramuscular heterologous HIV prime-boost immunization, elevated HIV-specific effector, but not memory CD8(+)T cells responses, were observed in spleen, genito-rectal nodes, and Peyer's patch. Homing marker α4β7 and CCR9 analysis indicated that unlike other type I IFNs, IFN-ε could promote migration of antigen-specific CD8(+)T cells to the gut. Our results indicate that IFN-ε has a unique role in the mucosae and most likely can be used to control local lung and/or gut infections (i.e., microbicide) such as tuberculosis, HIV-1, or sexually transmitted diseases.

Protective vaccination against infectious bursal disease virus with whole recombinant Kluyveromyces lactis yeast expressing the viral VP2 subunit

Here we report on vaccination approaches against infectious bursal disease (IBD) of poultry that were performed with complete yeast of the species Kluyveromyces lactis (K. lactis). Employing a genetic system that enables the rapid production of stably transfected recombinant K. lactis, we generated yeast strains that expressed defined quantities of the virus capsid forming protein VP2 of infectious bursal disease virus (IBDV). Both, subcutaneous as well as oral vaccination regiments with the heat-inactivated but otherwise untreated yeast induced IBDV-neutralizing antibodies in mice and chickens. A full protection against a subsequent IBDV infection was achieved by subcutaneous inoculation of only milligram amounts of yeast per chicken. Oral vaccination also generated protection: while mortality was observed in control animals after virus challenge, none of the vaccinees died and ca. one-tenth were protected as indicated by the absence of lesions in the bursa of Fabricius. Recombinant K. lactis was thus indicated as a potent tool for the induction of a protective immune response by different applications. Subcutaneously applied K. lactis that expresses the IBDV VP2 was shown to function as an efficacious anti-IBD subunit vaccine.

Current status of vaccines against infectious bursal disease

Infectious bursal disease virus (IBDV) is the aetiological agent of the acute and highly contagious infectious bursal disease (IBD) or "Gumboro disease". IBD is one of the economically most important diseases that affects commercially produced chickens worldwide. Along with strict hygiene management of poultry farms, vaccination programmes with inactivated and live attenuated viruses have been used to prevent IBD. Live vaccines show a different degree of attenuation; many of them may cause bursal atrophy and thus immunosuppression with poor immune response to vaccination against other pathogens and an increase in vulnerability to various types of infections as possible consequences. Depending on their intrinsic characteristics or on the vaccination procedures, some of the vaccines may not induce full protection against the very virulent IBDV strains and antigenic variants observed in the last three decades. As chickens are most susceptible to IBDV in their first weeks of life, active immunity to the virus has to be induced early after hatching. However, maternally derived IBDV-specific antibodies may interfere with early vaccination with live vaccines. Thus new technologies and second-generation vaccines including rationally designed and subunit vaccines have been developed. Recently, live viral vector vaccines have been licensed in several countries and are reaching the market. Here, the current status of IBD vaccines is discussed.

Induction of protective immunity in chickens immunized with plant-made chimeric Bamboo mosaic virus particles expressing very virulent Infectious bursal disease virus antigen

Very virulent Infectious bursal disease virus (vvIBDV) causes a highly contagious disease in young chickens and leads to significant economic loss in the poultry industry. Effective new vaccines are urgently needed. Autonomously replicating plant virus-based vector provides attractive means for producing chimeric virus particles (CVPs) in plants that can be developed into vaccines. In this study, we demonstrate the potential for vaccine development of Bamboo mosaic virus (BaMV) epitope-presentation system, where the antigen from vvIBDV VP2 was fused to the N-terminus of BaMV coat protein. Accordingly, an infections plasmid, pBIBD2, was constructed. Inoculation of the recombinant BaMV clone pBIBD2 enabled the generation of chimeric virus, BIBD2, and stable expression of IBDV VP2 antigen on its coat protein. After intramuscular immunization with BIBD2 CVPs, chickens produced antibodies against IBDV and were protected from vvIBDV (V263/TW strain) challenges. These results corroborate the feasibility of BaMV-based CVP platform in plants for the development and production of vaccines against IBDV.

Protection from infectious bursal disease virus (IBDV)-induced immunosuppression by immunization with a fowlpox recombinant containing IBDV-VP2

Immunosuppression resulting from infectious bursal disease virus (IBDV) infection has critical health and welfare implications for birds, yet it is incompletely understood and largely overlooked as a measure of vaccine efficacy. The ability of a fowlpoxvirus recombinant (fpIBD1) containing the VP2 protein of IBDV to protect against IBDV-induced immunosuppression was investigated by measuring the convalescent chicken's ability to mount antibody responses to IBDV infection, and to inactivated IBDV and salmonella vaccines. An immunoglobulin (Ig)M response, but no IgG response, occurred after IBDV infection. Uninfected chickens produced a sustained IgM response and some IgG response to inactivated IBDV vaccine, while in previously infected birds only a transient IgM response was detected. A moderate suppression of the response to a commercial salmonella vaccine was evident after IBDV infection, which was largely prevented by immunization with fpIBD1. These results indicate that measurement of immunosuppression could be a useful strategy for assessing the efficacy of vaccines to protect against the consequences of IBDV infection.

A safety assessment of a fowlpox-vectored Mycoplasma gallisepticum vaccine in chickens

A recombinant fowlpox virus vaccine expressing key protective Mycoplasma gallisepticum antigens could facilitate in the prevention both of fowlpox virus and M. gallisepticum infections. Vectormune FP-MG vaccine, a recombinant fowlpox virus expressing both M. gallisepticum 40k and mgc genes, was assessed for its safety in 8-wk-old specific-pathogen-free White Leghorn chickens. The vaccine virus was serially passaged 5 times by wing-web inoculation. Based on the postinoculation clinical observation, gross pathological examination of air sacs and peritoneum, genetic stability evaluation, virus shedding and tissue distribution detection, horizontal transmission ability determination, and protection against fowlpox virus challenge, the Vectormune FP-MG vaccine possesses a high level of safety.

Interleukin-15 mediates potent antiviral responses via an interferon-dependent mechanism

Interleukin-15 (IL-15) is a potent growth factor for activated T and natural killer (NK) cells, stimulator of memory T cells and plays an important role in viral immunity. To investigate mechanisms underlying the antiviral activity of IL-15, a recombinant vaccinia virus (rVV) encoding murine IL-15 (VV-IL-15) was constructed. Following infection of mice with VV-IL-15, virus titres in the ovaries were significantly reduced compared to mice infected with control VV. Growth of VV-IL-15 was also reduced in nude athymic mice, indicating the antiviral activity of IL-15 does not require T cells. Additionally, VV-IL-15 augmented the cytolytic activity of natural NK cells in the spleen and enhanced interferon (IFN) mRNA expression and transcription factors associated with IFN induction. Using knockout mice and antibody depletion studies, we showed for the first time that the control of VV-IL-15 replication in mice is dependent on NK cells and IFNs and, in their absence, the protective role of IL-15 is abolished.

Antigen delivery systems for veterinary vaccine development. Viral-vector based delivery systems

The recent advances in molecular genetics, pathogenesis and immunology have provided an optimal framework for developing novel approaches in the rational design of vaccines effective against viral epizootic diseases. This paper reviews most of the viral-vector based antigen delivery systems (ADSs) recently developed for vaccine testing in veterinary species, including attenuated virus and DNA and RNA viral vectors. Besides their usefulness in vaccinology, these ADSs constitute invaluable tools to researchers for understanding the nature of protective responses in different species, opening the possibility of modulating or potentiating relevant immune mechanisms involved in protection.

Construction and characterization of a recombinantFowlpox virusexpressing chicken type II interferon

Interferon, an important cytokine, is an immunomodulator and possesses antiviral and anti-tumour activity.In vitro, it can be administrated in the treatment of diseases alone or with genetically engineered vaccine to enhance the immune effect of the latter. The recombinant transferring vector pSY681–ChIFN-γ was obtained in this study by inserting the chicken type II interferon (ChIFN-γ) gene into theFowlpox virus(FPV) transferring vector pSY681. The resulting plasmid was then transfected into chicken embryo fibroblast (CEF) cell cultures pre-infected with the parental FPV S-FPV-017. Finally, the recombinantFowlpox virus(rFPV) expressingChIFN-γ (rFPV–ChIFN-γ) was produced by homologous recombination with the FPV gene in CEF. rFPV-positive plaques were verified by polymerase chain reaction (PCR), restriction analysis and indirect immunofluorescence assays. The rFPV–ChIFN-γ supernatants, cultured in CEF for 72 h and inoculated into rat fibroblasts (L929), had an inhibitory effect on the replication ofRous sarcoma virus(RSV) with an antiviral titre of 2048 U/ml.

Antiviral therapy with entecavir combined with post-exposure "prime-boost" vaccination eliminates duck hepatitis B virus-infected hepatocytes and prevents the development of persistent infection

Short-term antiviral therapy with the nucleoside analogue entecavir (ETV), given at an early stage of duck hepatitis B virus (DHBV) infection, restricts virus spread and leads to clearance of DHBV-infected hepatocytes in approximately 50% of ETV-treated ducks, whereas widespread and persistent DHBV infection develops in 100% of untreated ducks. To increase the treatment response rate, ETV treatment was combined in the current study with a post-exposure "prime-boost" vaccination protocol. Four groups of 14-day-old ducks were inoculated intravenously with a dose of DHBV previously shown to induce persistent DHBV infection. One hour post-infection (p.i.), ducks were primed with DNA vaccines that expressed DHBV core (DHBc) and surface (pre-S/S and S) antigens (Groups A, B) or the DNA vector alone (Groups C, D). ETV (Groups A, C) or water (Groups B, D) was simultaneously administered by gavage and continued for 14 days. Ducks were boosted 7 days p.i. with recombinant fowlpoxvirus (rFPV) strains also expressing DHBc and pre-S/S antigens (Groups A, B) or the FPV-M3 vector (Groups C, D). DHBV-infected hepatocytes were observed in the liver of all ducks at day 4 p.i. with reduced numbers in the ETV-treated ducks. Ducks treated with ETV plus the control vectors showed restricted spread of DHBV infection during ETV treatment, but in 60% of cases, infection became widespread after ETV was stopped. In contrast, at 14 and 67 days p.i., 100% of ducks treated with ETV and "prime-boost" vaccination had no detectable DHBV-infected hepatocytes and had cleared the DHBV infection. These findings suggest that ETV treatment combined with post-exposure "prime-boost" vaccination induced immune responses that eliminated DHBV-infected hepatocytes and prevented the development of persistent DHBV infection.

Genus Avipoxvirus

Poxviruses identified in skin lesions of domestic, pet or wild birds are assigned largely by default to the Avipoxvirus genus within the subfamily Chordopoxvirinae of the family Poxviridae. Avipoxviruses have been identified as the causative agent of disease in at least 232 species in 23 orders of birds. Vaccines based upon attenuated avipoxvirus strains provide good disease control in production poultry, although with the large and intensive production systems there are suggestions and real risks of emergence of strains against which current vaccines might be ineffective. Sequence analysis of the whole genome has revealed overall genome structure and function resemblance to the Chordopoxvirinae; however, avipoxvirus genomes exhibit large-scale genomic rearrangements with more extensive gene families and novel host range gene in comparison with the other Chordopoxvirinae. Phylogenetic analysis places the avipoxviruses externally to the Chorodopoxvirinae to such an extent that in the future it might be appropriate to consider the Avipoxviruses as a separate subfamily within the Poxviridae. A unique relationship exists between Fowlpox virus (FWPV) and reticuloendothelosis viruses. All FWPV strains carry a remnant long terminal repeat, while field strains carry a near full-length provirus integrated at the same location in the FWPV genome. With the development of techniques to construct poxviruses expressing foreign vaccine antigens, the avipoxviruses have gone from neglected obscurity to important vaccine vectors in the past 20 years. The seminal observation of their utility for delivery of vaccine antigens to non-avian species has driven much of the interest in this group of viruses. In the veterinary area, several recombinant avipoxviruses are commercially licensed vaccines. The most successful have been those expressing glycoprotein antigens of enveloped viruses, e.g. avian influenza, Newcastle diseases and West Nile viruses. Several recombinants have undergone extensive human clinical trials as experimental vaccines against HIV/AIDS and malaria or as treatment regimens in cancer patients. The safety profile of avipoxvirus recombinants for use as veterinary and human vaccines or therapeutics is now well established.

Mucosal delivery of vaccines in domestic animals

Mucosal vaccination is proving to be one of the greatest challenges in modern vaccine development. Although highly beneficial for achieving protective immunity, the induction of mucosal immunity, especially in the gastro-intestinal tract, still remains a difficult task. As a result, only very few mucosal vaccines are commercially available for domestic animals. Here, we critically review various strategies for mucosal delivery of vaccines in domestic animals. This includes live bacterial and viral vectors, particulate delivery-systems such as polymers, alginate, polyphosphazenes, immune stimulating complex and liposomes, and receptor mediated-targeting strategies to the mucosal tissues. The most commonly used routes of immunization, strategies for delivering the antigen to the mucosal surfaces, and future prospects in the development of mucosal vaccines are discussed.

Development of a synthetic consensus sequence scrambled antigen HIV-1 vaccine designed for global use

Induction of high levels of broadly reactive cytotoxic T lymphocytes (CTL) remains a promising approach for an effective HIV-1 vaccine. We have developed a novel genetic-based vaccine strategy that encodes consensus overlapping peptide sets from all HIV-1 proteins scrambled together. This synthetic scrambled antigen vaccine (SAVINE) strategy has significant advantages, e.g. capacity to encode more antigens safely and is very flexible compared to traditional isolate-based strategies. The SAVINE vaccine strategy is clearly immunogenic, being able to restimulate a range of human HIV-1 specific responses in vitro and induce HIV-1 specific immunity in vivo in mice. Interestingly, different in vivo delivery strategies affected the resulting immunity and immunodominance pattern in mice. This platform strategy could be used for other infections and cancers where T cell responses are important for protection.

Recombinant fowlpox virus forin vitrogene delivery to pancreatic islet tissue

The feasibility of using avipox virus as a vector for gene delivery to islet tissue (adult islets and fetal proislets) was examined using a recombinant fowlpox virus (FPV) engineered to express the reporter gene LacZ (FPV-LacZ). The efficiency of in vitro transduction was dose-dependent and influenced by the donor species and maturation status of the islet tissue. Reporter gene expression in FPV-LacZ-transduced islet grafts was transient (3-7 days) in immunoincompetent nude mice and was not prolonged by in vivo treatment with anti-IFN-gamma mAb. In contrast, FPV-LacZ-transduced NIT-1 cells (a mouse islet beta cell line) expressed the LacZ gene beyond 18 days in vitro. Silencing of transgene expression therefore appeared to occur in vivo and was T cell- and IFN-gamma-independent. Isografts of FPV-LacZ-transduced islets in immunocompetent mice underwent immunological destruction by 7 days, suggesting that either FPV proteins or the reporter protein beta-galactosidase induced an adaptive immune response. Co-delivery of the rat bioactive immunoregulatory cytokine gene TGF-beta to islets using FPV-TGF-beta led to enhanced expression of TGF-beta mRNA in isografts but no long-term protection. Nevertheless, compared to control islet isografts at 5 days, FPV-transduced islets remained embedded in the clotted blood used to facilitate implantation. This phenomenon was TGF-beta transgene-independent, correlated with lack of cellular infiltration, and suggested that the FPV vector transformed the blood clot into a temporary immunological barrier.

Comparison of whole gene and whole virus scrambled antigen approaches for DNA prime and fowlpox virus boost HIV type 1 vaccine regimens in macaques

T cell immunity plays a critical role in controlling HIV-1 viremia, and encoding a limited set of HIV-1 genes within DNA and poxvirus vectors can, when used sequentially, induce high levels of T cell immunity in primates. However, a limited breadth of T cell immunity exposes the host to potential infection with either genetically diverse HIV-1 strains or T cell escape variants of HIV-1. In an attempt to induce maximally broad immunity, we examined DNA and recombinant fowlpox virus (rFPV) vaccines encoding all HIV-1 genes derived from a global HIV-1 consensus sequence, but expressed as multiple overlapping scrambled 30-amino acid segments (scrambled antigen vaccines, or SAVINEs). Three groups of seven pigtail macaques were immunized with sets of DNA and rFPV expressing Gag/Pol antigens only, the whole genome SAVINE antigens, or no HIV-1 antigens and T cell immunity was monitored by ELISpot and intracellular cytokine staining. High levels of cross-subtype HIV-specific T cell immunity to Gag were consistently induced in the seven macaques primed with DNA and rFPV vaccines expressing Gag/Pol as intact proteins. It was, however, difficult to repeatedly boost immunity with further rFPV immunizations, presumably reflecting high levels of anti- FPV immunity. Unfortunately, this vaccine study did not consistently achieve a broadened level of T cell immunity to multiple HIV genes utilizing the novel whole-virus SAVINE approach, with only one of seven immunized animals generating broad T cell immunity to multiple HIV-1 proteins. Further refinements are planned with alternative vector strategies to evaluate the potential of the SAVINE technology.

Construction of recombinant fowlpox viruses carrying multiple vaccine antigens and immunomodulatory molecules

Here we describe plasmid vectors and selection protocols developed to allow the construction of recombinant fowlpox viruses (rFPVs) with up to three insertions of foreign DNA in the viral genome. Transient dominant selection allows the construction of recombinant viruses that do not retain the selection markers and can therefore be used for the insertion of additional genes at other sites in the viral genome. A SYBR Green real-time PCR sequence detection assay was applied to the identification of recombinant viruses from individual plaques, eliminating the need for amplification and hybridization from the transient dominant protocol and resulting in significant savings in time at each round of plaque purification. Dominant selection techniques allow more rapid recombinant virus construction; however, as the markers are retained along with the gene of interest, they can only be used to generate the final recombinant. rFPV vaccines constructed using these techniques have reached preclinical nonhuman primate and phase I human clinical trials in prime/boost vaccination studies as human immunodeficiency virus (HIV) therapeutic andprophylactic vaccines.

A recombinant Newcastle disease virus (NDV) expressing VP2 protein of infectious bursal disease virus (IBDV) protects against NDV and IBDV

Infectious bursal disease virus (IBDV) causes a highly immunosuppressive disease in chickens. Currently available, live IBDV vaccines can lead to generation of variant viruses. We have developed an alternative vaccine that will not create variant IBDV. By using the reverse genetics approach, we devised a recombinant Newcastle disease virus (NDV) vector from a commonly used vaccine strain LaSota to express the host-protective immunogen VP2 of a variant IBDV strain GLS-5. The gene encoding the VP2 protein of the IBDV was inserted into the most 3'-proximal locus of a full-length NDV cDNA for high-level expression. We successfully recovered the recombinant virus, rLaSota/VP2. The rLaSota/VP2 was genetically stable, at least up to 12 serial passages in chicken embryos, and was shown to express the VP2 protein. The VP2 protein was not incorporated into the virions of recombinant virus. Recombinant rLaSota/VP2 replicated to a titer similar to that of parental NDV strain LaSota in chicken embryos and cell cultures. To assess protective efficacy of the rLaSota/VP2, 2-day-old specific-pathogen-free chickens were vaccinated with the recombinant virus and challenged with a highly virulent NDV strain Texas GB or IBDV variant strain GLS-5 at 3 weeks postvaccination. Vaccination with rLaSota/VP2 generated antibody responses against both NDV and IBDV and provided 90% protection against NDV and IBDV. Booster immunization induced higher levels of antibody responses against both NDV and IBDV and conferred complete protection against both viruses. These results indicate that the recombinant NDV can be used as a vaccine vector for other avian pathogens.

A recombinant vaccinia virus encoding the interferon-inducible T-cell alpha chemoattractant is attenuated in vivo

Murine interferon-inducible T-cell alpha chemoattractant (I-TAC) is a potent non-ELR CXC chemokine that predominantly attracts activated T lymphocytes, binds to the receptor CXCR3 and is induced by interferon-gamma (IFN-gamma). We analysed I-TAC expression by reverse transcriptase-polymerase chain reaction during three different virus-infection models in mice, respiratory syncytial virus (RSV), influenza A and vaccinia virus western reserve (VV-WR). In the lungs from mice infected with RSV or influenza A viruses, peak expression of I-TAC coincided with peak viraemia. Surprisingly, there was no expression in the lungs of mice infected with vaccinia, unlike the elevated expression shown previously for other interferon-regulated chemokines, such as Crg2 and Mig. To further investigate the importance of this difference during vaccinia infection in mice, a recombinant virus encoding I-TAC (rVV I-TAC) was generated. Studies in C57BL/6 and Swiss nude mice showed that I-TAC expression caused increased mononuclear cell infiltration and significantly attenuated the VV. Infection of the footpads of naïve or already immune (with VV-WR) mice with either rVV I-TAC or VV-WR demonstrated that I-TAC expression reduced overall inflammation during infection and that this reduction was more pronounced in already immune mice. The data presented here show that I-TAC can have an important role during virus infections and that vaccinia has evolved ways to avoid inducing I-TAC expression.

Efficacy of DNA vaccines against infectious bursal disease virus in chickens enhanced by coadministration with CpG oligodeoxynucleotide

The objective of the present study was to investigate the feasibility of a DNA vaccine and CpG oligodeoxynucleotide (ODN) to protect chickens against infectious bursal disease virus (IBDV) infection. Two plasmids DNA carrying VP2 genes of the very virulent (vv) strain of IBDV were constructed with reverse transcription-polymerase chain reaction and designated as pcDNA3.1-VP2 and pCI-VP2. The VP2 protein expressed in COS-7 cells transfected with the plasmid was confirmed by indirect immunofluorescence assay. Seven-day-old chickens were intramuscularly injected with the plasmids alone or plus commercial attenuated infectious bursal disease (IBD) vaccine or synthetic CpG ODN twice at weekly intervals. Chickens at 5 wk old were orally inoculated with vvIBDV strain 99J1 and observed for 7 days after challenge. Immunization with plasmid plus commercial attenuated IBD vaccine or CpG ODN conferred protection for 70%-80% of chickens, as evidenced by the absence of dinical signs, mortality, and atrophy in the cloacal bursa. About 25%-45% of chickens vaccinated with commercial attenuated IBD vaccine or pcDNA3.1-VP2 or pCI-VP2 plasmid alone had dinical signs and died after challenge. Furthermore, there were significantly different histopathologic lesion scores in the clocal bursae between the pcDNA3.1-VP2 or pCI-VP2 plus CpG or live vaccine and pcDNA3.1-VP2, pCI-VP2, or live vaccine vaccinated group. Enzyme-linked immunosorbent assay antibody titers in chickens vaccinated the constructs DNA plus live vaccine or CpG ODN were significantly higher than in those inoculated with the constructs or the live vaccine alone. These results suggest that coadministration of the constructed plasmid pcDNA3.1-VP2 or pCI-VP2 with CpG ODN or commercial attenuated IBD vaccine could protect chickens efficiently from direct vvIBDV challenge.

Vaccination with E. coli recombinant empty viral particles of infectious bursal disease virus (IBDV) confer protection

The A genome segment of the highly virulent Infectious bursal disease virus (IBDV) was amplified using long and accurate-RT-PCR (LA-RT-PCR). The entire sequence region encoding VP2, VP4, and VP3 in that order was cloned and sequenced. Following subcloning into the Escherichia coli expression vector pET21a under the T7 promoter, viral proteins were expressed and processed as demonstrated by Western blot analysis. Virus-like particles could be visualized by immuno-electron microscopy in IPTG-induced cells suggesting that viral assembly can take place in E. coli. Induction of anti-IBDV antibodies was detected in chickens immunized with purified recombinant IBDV by intra muscular (i.m.) injection. Furthermore, the vaccinated chickens were protected when challenged with the Gep 5 isolate of IBDV.

Plasmid DNA encoding antigens of infectious bursal disease viruses induce protective immune responses in chickens: factors influencing efficacy

The complete polyprotein (VP2/4/3) and VP2 genes of two infectious bursal disease viruses (IBDVs) (one attenuated strain JD1 and one virulent strain ZJ2000) were amplified by long and accurate polymerase chain reaction (LA-PCR), cloned, sequenced and inserted into plasmids pCI and pcDNA3 under the control of human cytomegalovirus (hCMV) immediate early enhancer and promoter. A series of DNA vaccine preparations were made using liposome as the adjuvant to examine their immunogenicity. Although VP2 is the main protective immunogen of IBDV, DNA encoding VP2 initiated a very low level of neutralizing antibody and only protected chickens from clinical outbreak and morality, but not bursal damage. In contrast, DNA encoding VP2/4/3 induced neutralizing antibody and satisfactory protection against virulent IBDV. Recombinant plasmids encoding the polyprotein gene of strain ZJ2000 were more efficient at inducing an immune response than that of strain JD1. Polyprotein expressed by the pCI vector induced better immune response than that expressed by the pcDNA3. Delivery of DNA through intramuscular and/or intradermal routes elicited much higher protective responses than that of oral and eyedrop routes. Most of the chickens vaccinated with high doses of DNA were protected from challenge. Additionally, the immune response to the DNA vaccine was significantly enhanced by a liposome adjuvant. These results indicate that the source of the target genes (from different IBDV strains), the eukaryotic expression vector, the adjuvant, the delivery route and the dosage might play a role of varying degree in influencing the efficacy of the DNA vaccine against IBDV.

Expression of VP2 gene protein of infectious bursal disease virus detected in Korea

The VP2 gene DNA (1.4 kb in approximate) of a very virulent infectious bursal disease virus (vvIBDV) Chinju strain detected in Chinju, Korea was cloned into the bacmid, a baculovirus shuttle vector, through transposition of the gene from initially cloned pFastBacHTa plasmid, a baculovirus expression vector, and was subsequently expressed in Spodoptera frugiperda (Sf) cells. Biological properties of the expressed VP2 subunit protein were characterized to aid in the development of genetically engineered diagnostic reagents and vaccines against the vvIVDV. When the VP2 DNA-recombinant bacmid was transfected and propagated in the Sf cells, the cells showed no occlusion formation, which is a positive evidence for the insertion of the VP2 DNA into the polyhedrin gene of the bacmid, whereas the occlusions were observed in the cells infected by the Autographa californica nuclear polyhedrosis virus, a wild baculovirus. The expression of VP2 DNA was identified by strong positive reaction in fluorescent antibody test using chicken anti-IBDV serum. The VP2 protein was determined as a polypeptide band with Mr of 48 kDa by the sodium dodecyl-polyacrylamide gel electrophoresis for the lysate of the Sf cells infected with the recombinant bacmid. The VP2 protein was successfully purified from the cell lysate by Ni-NTA affinity chromatography. The expressed VP2 subunit protein reacted specifically with chicken anti-IBDV serum in Western blotting.

Structure-dependent efficacy of infectious bursal disease virus (IBDV) recombinant vaccines

The immunogenicity and protective capability of several baculovirus-expressed infectious bursal disease virus (IBDV)-derived assemblies as VP2 capsids, VPX tubules and polyprotein (PP)-derived mixed structures, were tested. Four-week-old chickens were immunised subcutaneously with one dose of each particulate antigen. VP2 icosahedral capsids induced the highest neutralising response, followed by PP-derived structures and then VPX tubules. All vaccinated animals were protected when challenged with a very virulent IBDV (vvIBDV) isolate, however the degree of protection is directly correlated with the levels of neutralising antibodies. VP2 capsids elicited stronger protective immunity than tubular structures and 3 micrograms of them were sufficient to confer a total protection comparable to that induced by an inactivated vaccine. Therefore, VP2 capsids represent a suitable candidate recombinant vaccine instead of virus-like particles (VLPs) for IBDV infections. Our results also provide clear evidence that the recombinant IBDV-derived antigens are structure-dependent in order to be efficient as vaccine components.

DNA vaccination with plasmids containing various fragments of large segment genome of infectious bursal disease virus

The present study was undertaken to determine the effectiveness in including VP2 gene of the large segment genome of infectious bursal disease virus (IBDV) in the DNA vaccine for protection of chickens against infectious bursal disease (IBD). Different fragments of the large segment gene of IBDV standard challenge (STC) strain were successfully amplified by reverse transcription-polymerase chain reaction (RT-PCR) followed by cloning into a eukaryotic expression plasmid vector (pCR3.1) as DNA vaccines. Transient expression of the encoded genes from various constructed plasmids was characterized in COS-7 cells by positive immunofluorescent staining with polyclonal or monoclonal antibody to IBDV. Chickens (1-day old) were intramuscularly injected with the individual plasmid three times at weekly intervals, challenged with IBDV strain STC at 21-day old, and observed for 10 days. Chickens receiving the plasmids containing VP2 genes, including VP243, VP24, or VP2 fragment, did not have clinical signs, mortality, and bursal atrophy and were effectively protected against IBDV infection. On the contrary, chickens receiving plasmids without containing VP2 genes, including VP4, VP3, or VP43 fragment, had marked bursal atrophy and were not protected against IBD. Antigen detection was correlated with protection; chickens protected from IBDV infection had undetectable IBDV antigen in bursae. Enzyme-linked immunosorbent assay (ELISA) antibody titer to IBDV was low or undetectable prior to or after challenge with IBDV in protected chickens receiving the plasmids containing the VP2 gene. The results indicate that inclusion of VP2 gene in the plasmid DNA is essential in achieving effective protection mediated by DNA vaccination against IBDV infection in chickens.

Complete, long-lasting protection against lethal infectious bursal disease virus challenge by a single vaccination with an avian herpesvirus vector expressing VP2 antigens

Marek's disease herpesvirus is a vaccine vector of great promise for chickens; however, complete protection against foreign infectious diseases has not been achieved. In this study, two herpesvirus of turkey recombinants (rHVTs) expressing large amounts of infectious bursal disease virus (IBDV) VP2 antigen under the control of a human cytomegalovirus (CMV) promoter or CMV/beta-actin chimera promoter (Pec promoter) (rHVT-cmvVP2 and rHVT-pecVP2) were constructed. rHVT-pecVP2, which expressed the VP2 antigen approximately four times more than did rHVT-cmvVP2 in vitro, induced complete protection against a lethal IBDV challenge in chickens, whereas rHVT-cmvVP2 induced 58% protection. All of the chickens vaccinated with rHVT-pecVP2 had a protective level of antibodies to the VP2 antigen at the time of challenge, whereas only 42 and 67% of chickens vaccinated with rHVT-cmvVP2 or the conventional live IBDV vaccine, respectively, had the antibodies. The antibody level of chickens vaccinated with rHVT-pecVP2 increased for 16 weeks, and the peak antibody level persisted throughout the experiment. The serum antibody titer at 30 weeks of age was about 20 or 65 times higher than that of chickens vaccinated with rHVT-cmvVP2 or the conventional live vaccine, respectively. rHVT-pecVP2, isolated consistently for 30 weeks from the vaccinated chickens, expressed the VP2 antigen after cultivation, and neither nucleotide mutations nor deletion in the VP2 gene was found. These results demonstrate that the amount of VP2 antigen expressed in the HVT vector was correlated with the vaccine efficacy against lethal IBDV challenge, and complete protective immunity that is likely to persist for the life of the chickens was induced.

Recombinant Semliki Forest virus vector exhibits potential for avian virus vaccine development

The Semliki Forest virus (SFV) expression system was evaluated as a basis for avian vaccine development. Initial studies indicated that 1-day-old specific pathogen-free (SPF) chicks were susceptible to infection with an infectious strain of SFV, producing SFV-specific antibodies but no clinical disease. One-day-old SPF chicks immunised intramuscularly with recombinant replication-defective SFV (rSFV) particles expressing the Escherichia coli (E. coli) lacZ reporter gene developed high titres of beta-gal- specific antibodies at 4 weeks p.i. after two inoculations. In contrast, significantly lower antibody levels were elicited in chicks immunised with a recombinant SFV-based DNA construct or a conventional CMV promoter-based DNA plasmid. rSFV particles encoding the protective VP2 protein or the VP2/VP4/VP3 polyprotein of infectious bursal disease virus (IBDV) were produced and the expressed antigens were characterised in cell culture. Proteins of the correct size were generated and found to react against a range of IBDV-specific monoclonal antibodies. Immunisation of 1-day-old SPF chicks with rSFV particles encoding the IBDV proteins resulted in specific antibodies being elicited in all birds, neutralising antibodies being induced in some but not all birds.

A recombinant avipoxvirus HIV-1 vaccine expressing interferon-gamma is safe and immunogenic in macaques

Complex recombinant fowlpoxvirus (rFPV) vaccines expressing both HIV-1 antigens and type 1 cytokines could facilitate the induction of cellular immunity against HIV-1. A single rFPV expressing both HIV-1gag/pol and human interferon-gamma (FPVgag/pol-IFNgamma) was constructed and assessed as a therapeutic vaccine for safety and immunogenicity in macaques (Macaca nemestrina) previously infected with HIV-1. FPV gag/pol-IFNgamma vaccinations were safe and enhanced T cell proliferative responses to Gag antigens (but not control tetanus antigens). Enhanced CTL responses to gag/pol antigens were also observed following IFNgamma expressing vaccinations. Since cellular immunity may be critical to controlling or preventing HIV-1 infection, these observations suggest that avipox vectors co-expressing IFNgamma should be further evaluated as therapeutic or preventive HIV-1 vaccines.

Dual-viral vector approach induced strong and long-lasting protective immunity against very virulent infectious bursal disease virus

To induce strong protective immunity against very virulent infectious bursal disease virus (vvIBDV) in chickens, two viral vector systems, Marek's disease and Fowlpox viruses expressing the vvIBDV host-protective antigen VP2 (rMDV, rFPV), were used. Most of chickens vaccinated with the rFPV or rMDV alone, or vaccinated simultaneously with both at their hatch (rMDV-rFPV(1d)), were protected against developing clinical signs and mortality; however, only zero to 14% of the chickens were protected against gross lesions. In contrast, gross lesions were protected in 67% of chickens vaccinated primarily with the rMDV followed by boosting with the rFPV 2 weeks later (rMDV-rFPV(14d)). Protection against the severe histopathological lesions of rFPV, rMDV, rMDV-rFPV(1d), and rMDV-rFPV(14d) vaccine groups were 33, 42, 53, and 73%, respectively. Geometric mean antibody titers to VP2 of chickens vaccinated with the rFPV, rMDV, rMDV-rFPV(1d), and rMDV-rFPV(14d) before the challenge were 110, 202, 254, and 611, respectively. Persistent infection of the rMDV in chickens after the booster vaccination with rFPV was suggested by detection of the rMDV genes from peripheral blood lymphocyte DNA at 28 weeks of age. These results indicate that the dual-viral vector approach is useful for quickly and safely inducing strong and long-lasting protective immunity against vvIBDV in chickens.

Development of an effective polyvalent vaccine against both Marek's and Newcastle diseases based on recombinant Marek's disease virus type 1 in commercial chickens with maternal antibodies

An earlier report (M. Sakaguchi et al., Vaccine 16:472-479, 1998) showed that recombinant Marek's disease virus type 1 (rMDV1) expressing the fusion (F) protein of Newcastle disease virus (NDV-F) under the control of the simian virus 40 late promoter [rMDV1-US10L(F)] protected specific pathogen-free chickens from NDV challenge, but not commercial chickens with maternal antibodies against NDV and MDV1. In the present study, we constructed an improved polyvalent vaccine based on MDV1 against MDV and NDV in commercial chickens with maternal antibodies. The study can be summarized as follows. (i) We constructed rMDV1 expressing NDV-F under the control of the MDV1 glycoprotein B (gB) promoter [rMDV1-US10P(F)]. (ii) Much less NDV-F protein was expressed in cells infected with rMDV1-US10P(F) than in those infected with rMDV1-US10L(F). (iii) The antibody response against NDV-F and MDV1 antigens of commercial chickens vaccinated with rMDV1-US10P(F) was much stronger and faster than with rMDV1-US10L(F), and a high level of antibody against NDV-F persisted for over 80 weeks postvaccination. (iv) rMDV1-US10P(F) was readily reisolated from the vaccinated chickens, and the recovered viruses were found to express NDV-F. (v) Vaccination of commercial chickens having maternal antibodies to rMDV1-US10P(F) completely protected them from NDV challenge. (vi) rMDV1-US10P(F) offered the same degree of protection against very virulent MDV1 as the parental MDV1 and commercial vaccines. These results indicate that rMDV1-US10P(F) is an effective and stable polyvalent vaccine against both Marek's and Newcastle diseases even in the presence of maternal antibodies.

Infectious bursal disease virus of chickens: pathogenesis and immunosuppression

Infectious bursal disease virus (IBDV) is an important immunosuppressive virus of chickens. The virus is ubiquitous and, under natural conditions, chickens acquire infection by the oral route. IgM+ cells serve as targets for the virus. The most extensive virus replication takes place in the bursa of Fabricius. The acute phase of the disease lasts for about 7-10 days. Within this phase, bursal follicles are depleted of B cells and the bursa becomes atrophic. Abundant viral antigen can be detected in the bursal follicles and other peripheral lymphoid organs such as the cecal tonsils and spleen. CD4(+) and CD8(+) T cells accumulate at and near the site of virus replication. The virus-induced bursal T cells are activated, exhibit upregulation of cytokine genes, proliferate in response to in vitro stimulation with IBDV and have suppressive properties. Chickens may die during the acute phase of the disease although IBDV induced mortality is highly variable and depends, among other factors, upon the virulence of the virus strain. Chickens that survive the acute disease clear the virus and recover from its pathologic effects. Bursal follicles are repopulated with IgM(+) B cells. Clinical and subclinical infection with IBDV may cause immunosuppression. Both humoral and cellular immune responses are compromised. Inhibition of the humoral immunity is attributed to the destruction of immunoglobulin-producing cells by the virus. Other mechanisms such as altered antigen-presenting and helper T cell functions may also be involved. Infection with IBDV causes a transient inhibition of the in vitro proliferative response of T cells to mitogens. This inhibition is mediated by macrophages which are activated in virus-exposed chickens and exhibit a marked enhancement of expression of a number of cytokine genes. We speculate that T cell cytokines such as interferon (IFN)-gamma may stimulate macrophages to produce nitric oxide (NO) and other cytokines with anti-proliferative activity. Additional studies are needed to identify the possible direct immunosuppressive effect of IBDV on T cells and their functions. Studies are also needed to examine effects of the virus on innate immunity. Earlier data indicate that the virus did not affect normal natural killer (NK) cell levels in chickens.