Intro by Dr. Stephen Collett: Vectored vaccines have from their conception been promoted as the ultimate answer to the problems encountered when using immunization to reduce the impact of disease challenge on flock health and productivity. This interesting and thorough but succinct mini-review shows that the quest has unfortunately proven more complex than initially anticipated. Only recently have scientists been able to provide the field veterinarian and producer with a glimpse of what will likely become a standard and invaluable part of our disease management programs.
The poultry industry has witnessed a boom in the development and use of viral-vectored recombinant vaccines in recent years. These vaccines have been used with some success for the control of a number of poultry diseases. Recombinant vaccine development is a rapidly evolving field, as scientists learn more about pathogen virulence factors, host-pathogen interactions, host immune response mechanisms, and how best to harness the immune response to stimulate a protective immunity. In this article we spotlight the current commercially available and experimental viral-vectored vaccines, and discuss the advantages and disadvantages of these vaccines in the light of their published safety and efficacy. This article is not intended to be an exhaustive review of vectored vaccines; the objective is instead to provide a broad overview of our current knowledge of these vaccines.
Viral-vectored recombinant vaccines comprise viruses serving as vectors, into which foreign viral or bacterial genes coding for immunogenic antigens are integrated for expression by the vector. The immune response generated after infection of the host with these vectors targets both the vector and the expressed foreign antigen(s), and is thus bi- or multivalent. With a view to augmenting the immune response, some vectored vaccines also incorporate genes for the expression of immunostimulatory molecules (e.g. interferon-γ (IFN-γ) and interleukin-18 (IL-18)). Herpesvirus of turkey (HVT), Mareks Disease virus (MDV), Fowlpox virus (FPV), Newcastle Disease virus (NDV) and Adenovirus (AdV) have all been used as vectors into which selected genes of infectious laryngotracheitis virus (ILTV), NDV, infectious bronchitis virus (IBV), avian influenza virus (AIV), infectious bursal disease virus (IBDV) and Mycoplasma gallisepticum (MG) have been inserted to generate recombinant viral-vectored vaccines.
The efficacy of vectored vaccines is dependent on a number of variables; including the viral vector used (latency, replication, immunogenicity), the gene(s) inserted and promoter(s) selected (immunogenicity, expression), the route of administration (in ovo, subcutaneous, eye-drop, etc.), the characteristics of the pathogen targeted (intracellular vs. extracellular, systemic vs. local infection) and the nature of the immune response stimulated (humoral vs. cell-mediated immunity). The relative efficacy of these vaccines is often difficult to deduce, because few studies have evaluated vectored vaccines alongside other vectored and live vaccines, and different bird types, challenge routes, dosages, strains and criteria for protection are common. Many studies have, for instance, evaluated the efficacy of vectored vaccines only in SPF chickens, which does not facilitate evaluation of the effect of maternally-derived antibody (MDA). In addition, several vaccines targeting respiratory pathogens (e.g. NDV) have been evaluated using only intramuscular challenge models, which may not accurately represent their efficacy at the level of the respiratory tract. There is currently no standardized protocol facilitating comparison of the efficacy of viral vectored vaccines for specific poultry pathogens. In the table shown below we present a list of current commercially available and experimental viral-vectored poultry vaccines.
A technological challenge for vectored vaccine development is the construction of a recombinant virus whose replication competency is not compromised by insertion of the foreign genetic material, since this would compromise the generation of protective immunity. The use of viral vectors with large DNA genomes (e.g. FPV and HVT) allows the insertion, by homologous recombination, of larger gene inserts or multiple genes; however, the careful selection of insertion sites is vital. Negative-sense RNA virus vectors like NDV have a more limited capacity for the insertion of genetic material, and require the use of reverse genetics technology for their development. The selection of a suitable promoter for optimal expression of the foreign gene(s) inserts is also an important determinant of vectored vaccine efficacy.
Understanding the pathogenesis of the target pathogen, including its tissue tropism, and the nature of protective immunity against that pathogen is crucial to determining the type of vector that would be most suitable for use in a vectored vaccine. The method and age of application of vectored vaccines is determined by the type of viral vector selected (e.g. HVT – in ovo / subcutaneous at 1 day of age). All commercially available vectored vaccines for poultry utilize the HVT (i.e. recombinant HVT-ILT (rHVTILT), rHVT-ND and rHVT-IBD) or FPV vectors (i.e. rFPV-ILT, rFPV-ND, rFPV-AI and rFPV-MG), and are registered for in ovo and/or parenteral (subcutaneous and/or wing-web) application.
Currently available vectored vaccines (which are applied by the in ovo or parenteral routes) tend to be more effective against systemically-invasive pathogens (e.g. IBDV, HPAIV), compared with pathogens which replicate primarily in the respiratory tract and do not typically invade systemically (e.g. MG, IBV, ILTV). A mucosally-applied respiratory virus such as lentogenic NDV, which replicates in the upper respiratory tract and stimulates local immune responses might be a suitable alternate vector for the expression of antigens of such non-invasive respiratory pathogens. In addition, vectored vaccines targeting viral pathogens with only one (or few) immunodominant antigens (e.g. IBDV) are likely to stimulate a more effective immune response than those targeting bacterial pathogens with complex and variable surface antigen profiles (e.g. MG), or viruses with complex host-pathogen interactions (e.g. ILTV). In general, currently available viral-vectored vaccines appear to provide good protection against AIV and IBDV challenge, moderate protection against NDV, ILTV and IBV challenge and limited protection against MG challenge. The ability of vectored vaccines to protect against viral shedding is often limited. This has been observed for vectored ILTV vaccines; vaccinated broilers show significant reductions in clinical signs, but not in virus shedding after ILTV challenge (Johnson et al., 2010; Vagnozzi et al., 2012).
HVT is the most commonly used vaccine vector, and is characterized by its ability to establish persistent infection in the host; this has facilitated the development of long-lasting immunity with HVT recombinant vaccines, e.g. rHVT-ND (Esaki et al., 2013) and rHVT-IBD (Tsukamoto et al., 2002). FPV vectored vaccines are also capable of stimulating long-lived immune responses, e.g. rFPV-AI (Swayne et al., 1997; Bublot et al., 2006). Several studies with rFPV and rHVT vectored vaccines have, however, indicated that the development of protective immunity may be delayed compared with that induced by live vaccines (Palya et al., 2012; Vagnozzi, et al., 2012; Esaki, et al., 2013).
The effect of circulating antibodies on the efficacy of viral-vectored vaccines is an important consideration; particularly for vaccines that are applied in the presence of MDA (passive immunity), or in flocks previously vaccinated with or exposed to the pathogen(s) (active immunity). Circulating vector- or insert -specific antibodies may interfere with the generation of immunity to either the vector, or the insert, or both (Morgan et al., 1993; Taylor et al., 1996; Sakaguchi et al., 1998; Sonoda et al., 2000; Sarfati- Mizrahi et al., 2010; Mesonero et al., 2011; Schroer et al., 2011). This highlights the importance of assessing vectored vaccine efficacy in chickens with antibodies against both the vector and the insert.
The efficacy of rFPV vaccines is significantly compromised by previous exposure to FPV (activeimmunity); this has been observed for rFPV-ND (Iritani et al., 1991) and rFPV-AI (Swayne et al., 2000a; Bublot, et al., 2006) vaccines. In general, FPV- and HVT-vectored vaccines are not significantly affected by thepresence of vector-targeted MDA (passive immunity), as immunity against the vector is primarily cellmediated. HVT-vectored vaccine efficacy is probably compromised to a lesser extent by the presence of MDA, due to the longer infection periods characteristic of HVT.
An inhibitory effect of MDA against the inserted antigen has been reported for both rFPV-ND (Taylor, et al., 1996) and rHVT-ND (Morgan, et al., 1993) vaccines; with somewhat reduced protection against NDV seen in chickens with ND MDA (Taylor, et al., 1996). The field performance of rHVT-IBD vaccines in the presence of high levels of insert -specific MDA suggests that MDA does not compromise the efficacy of this vaccine. This is not the case for live IBD vaccines, which are neutralized by MDA when applied at an early age (Goutebroze et al., 2003).
Other vectors that are being investigated for use, but are not yet commercially available, are NDV, MDV and AdV. These vectors have been used to deliver ILTV, NDV, IBV, IBDV and AIV antigens (see table below). Experimentally, NDV has shown great promise as a vector for respiratory vaccines targeting ILTV (Kanabagatte Basavarajappa et al., 2014; Zhao et al., 2014), IBV (Toro et al., 2014b) and AIV (Veits et al., 2006; Romer-Oberdorfer et al., 2008; Nayak et al., 2009; Sarfati-Mizrahi, et al., 2010; Schroer, et al., 2011; Lardinois et al., 2012). One important consideration for the use of NDV as a vector is its efficacy in the presence of both vector- and insert-specific MDAs. The efficacy of rNDV-AI vaccines was reduced when administered in the presence of ND and AI-specific MDAs; however, MDA interference was overcome by increasing the vaccine dose (Sarfati-Mizrahi, et al., 2010; Schroer, et al., 2011).
Serotype I MDV has been used as an experimental vector for NDV, IBV, AIV and IBDV. MDV is an attractive alternative vector for IBDV (VP2), as an rMDV-IBD vaccine provided good protection against both IBDV and very virulent (vv) MDV (Tsukamoto et al., 1999). The Serotype 5 replication defective AdV may be a safe alternative for the delivery of AIV antigens (Toro et al., 2007; Toro et al., 2008; Mesonero, et al., 2011), although high MDA levels against the insert (H5) interfered with an AdV-vectored antibody response (Mesonero, et al., 2011). The co-expression of immunostimulatory cytokines (IFN-γ, IL-6, IL-18 or granulocyte-macrophage colony-stimulating factor (GM-CSF) with foreign antigens by virus vectors has been reported to improve the efficacy of several experimental vaccines, including rFPVILT (Chen et al., 2011), rFPV-AI (Mingxiao et al., 2006; Qian et al., 2012), rFPV-IB (Y. F. Wang et al., 2009; Chen et al., 2010; Shi et al., 2011) and rAdV-IB (Zeshan et al., 2011).
The safety of viral-vectored vaccines is one of their most appealing characteristics. The viral vectors are characterized by a lack of transmission to non-vaccinated birds, are species-specific, replicate poorly (or not at all) in other hosts and do not revert to virulence (Bublot, et al., 2006). This is a major advantage over many live viral or bacterial vaccines, e.g. live ILTV vaccines (especially ILTV CEO vaccine), for which vaccine reversion to virulence and transmission have been reported (Neff et al., 2008; Oldoni et al., 2008; Chacon et al., 2009).
Another argument for the use of vectored vaccines is to facilitate the differentiation between infected and vaccinated animals (DIVA). This is particularly important for notifiable diseases like AI, to ensure that vaccinal immunity does not complicate disease detection and control. Since no AIV-specific nucleoprotein or matrix antibodies are induced by vectored AI vaccines expressing HA, vaccinated uninfected birds will be serologically negative on ELISA and AGP tests, facilitating DIVA strategies (Iqbal, 2012).
In ovo vaccination technology has facilitated the delivery of recombinant vaccines, which represents a significant saving in cost and time compared with manual parenteral application of inactivated vaccines. Currently registered viral-vectored vaccines do, however, require in ovo or parenteral administration, as opposed to most live viral and some bacterial vaccines, which can be mass applied by spray or in the drinking water. Vectored vaccines are also more costly to manufacture than conventional live virus vaccines, and are consequently more expensive. The use of respiratory viruses as vectors is likely to facilitate mass application of viral-vectored vaccines in the future, in a similar way to conventional attenuated live virus vaccines.
In conclusion, knowledge of the composition and construction of vectored vaccines, host-pathogen interactions and the generation of protective immunity is fundamental to understanding the efficacy and harnessing the success of these vaccines. This field of vaccinology is an exciting and rapidly evolving one, with important implications for the current and future control of poultry diseases.
Commercially-available and experimental viral-vectored vaccines for chickens
a gB, gD and gI = glycoproteins B, D and I; F = fusion protein; HN = haemagglutinin/neuraminidase protein; HA = haemagglutinin protein; NA = neuraminidase protein; S1 and
S2 = spike proteins 1 and 2; HPAIV and LPAIV = high pathogenic and low pathogenic AIV; AdV(5) = serotype 5 replication defective human adenovirus
b Merck = Merck Animal Health; Ceva = Ceva Animal Health; Merial = Merial Ltd.
c In-ovo = 18-day-old embryos; SC = subcutaneous; WW = wing-web; IM = intramuscular; IO = intraocular; IN = intranasal.
This article was originally published in the Jul / Aug 2014 edition of the Poultry Informed Professional and is reprinted per the authors' permission.
1. Boursnell, M. E., Green, P. F., Campbell, J. I., Deuter, A., Peters, R. W., Tomley, F. M., et al. (1990a). Insertion of the fusion gene from Newcastle disease virus into a non-essential region in the terminal repeats of fowlpox virus and demonstration of protective immunity induced by the recombinant. J Gen Virol, 71 ( Pt 3), 621-628.
2. Boursnell, M. E., Green, P. F., Campbell, J. I., Deuter, A., Peters, R. W., Tomley, F. M., et al. (1990b). A fowlpox virus vaccine vector with insertion sites in the terminal repeats: demonstration of its efficacy using the fusion gene of Newcastle disease virus. Vet Microbiol, 23, 305-316.
3. Boursnell, M. E., Green, P. F., Samson, A. C., Campbell, J. I., Deuter, A., Peters, R. W., et al. (1990c). A recombinant fowlpox virus expressing the hemagglutinin-neuraminidase gene of Newcastle disease virus (NDV) protects chickens against challenge by NDV. Virology, 178, 297-300.
4. Bublot, M., Pritchard, N., Swayne, D. E., Selleck, P., Karaca, K., Suarez, D. L., et al. (2006). Development and use of fowlpox vectored vaccines for avian influenza. Ann N Y Acad Sci, 1081, 193-201. doi: 10.1196/annals.1373.023
5. Chacon, J. L., & Ferreira, A. J. (2009). Differentiation of field isolates and vaccine strains of infectious laryngotracheitis virus by DNA sequencing. Vaccine, 27, 6731-6738. doi: 10.1016/ j.vaccine.2009.08.083
6. Chen, H. Y., Cui, P., Cui, B. A., Li, H. P., Jiao, X. Q., Zheng, L. L., et al. (2011). Immune responses of chickens inoculated with a recombinant fowlpox vaccine coexpressing glycoprotein B of infectious laryngotracheitis virus and chicken IL-18. FEMS Immunol Med Microbiol, 63, 289-295. doi: 10.1111/j.1574-695X.2011.00850.x
7. Chen, H. Y., Yang, M. F., Cui, B. A., Cui, P., Sheng, M., Chen, G., et al. (2010). Construction and immunogenicity of a recombinant fowlpox vaccine coexpressing S1 glycoprotein of infectious bronchitis virus and chicken IL-18. Vaccine, 28, 8112-8119. doi: 10.1016/j.vaccine.2010.09.106
8. Cui, H., Gao, H., Cui, X., Zhao, Y., Shi, X., Li, Q., et al. (2013). Avirulent Marek's disease virus type 1 strain 814 vectored vaccine expressing avian influenza (AI) virus H5 haemagglutinin induced better protection than turkey herpesvirus vectored AI vaccine. PLoS One, 8, e53340. doi: 10.1371/journal.pone.0053340
9. Darteil, R., Bublot, M., Laplace, E., Bouquet, J. F., Audonnet, J. C., & Riviere, M. (1995). Herpesvirus of turkey recombinant viruses expressing infectious bursal disease virus (IBDV) VP2 immunogen induce protection against an IBDV virulent challenge in chickens. Virology, 211, 481-490. doi: 10.1006/viro.1995.1430
10. Davison, S., Gingerich, E. N., Casavant, S., & Eckroade, R. J. (2006). Evaluation of the efficacy of a live fowlpox-vectored infectious laryngotracheitis/avian encephalomyelitis vaccine against ILT viral challenge. Avian Dis, 50, 50-54.
11. Esaki, M., Godoy, A., Rosenberger, J. K., Rosenberger, S. C., Gardin, Y., Yasuda, A., et al. (2013). Protection and antibody response caused by turkey herpesvirus vector Newcastle disease vaccine. Avian Dis, 57, 750-755.
12. Ferguson-Noel, N., Cookson, K., Laibinis, V. A., & Kleven, S. H. (2012). The efficacy of three commercial Mycoplasma gallisepticum vaccines in laying hens. Avian Dis, 56, 272-275.
13. Goutebroze, S., Curet, M., Jay, M. L., Roux, C., & Le Gros, F. X. (2003). Efficacy of a recombinant vaccine HVT-VP2 against Gumboro disease in the presence of maternal antibodies. Br Poult Sci, 44, 824-825.
14. Iqbal, M. (2012). Progress toward the development of polyvalent vaccination strategies against multiple viral infections in chickens using herpesvirus of turkeys as vector. Bioengineered, 3, 222-226. doi: 10.4161/bioe.20476
15. Iritani, Y., Aoyama, S., Takigami, S., Hayashi, Y., Ogawa, R., Yanagida, N., et al. (1991). Antibody response to Newcastle disease virus (NDV) of recombinant fowlpox virus (FPV) expressing a hemagglutinin-neuraminidase of NDV into chickens in the presence of antibody to NDV or FPV. Avian Dis, 35, 659-661.
16. Johnson, D. I., Vagnozzi, A., Dorea, F., Riblet, S. M., Mundt, A., Zavala, G., et al. (2010). Protection against infectious laryngotracheitis by in ovo vaccination with commercially available viral vector recombinant vaccines. Avian Dis, 54, 1251-1259.
17. Kanabagatte Basavarajappa, M., Kumar, S., Khattar, S. K., Gebreluul, G. T., Paldurai, A., & Samal, S. K. (2014). A recombinant Newcastle disease virus (NDV) expressing infectious laryngotracheitis virus (ILTV) surface glycoprotein D protects against highly virulent ILTV and NDV challenges in chickens. Vaccine, 32, 3555-3563. doi: 10.1016/j.vaccine.2014.04.068
18. Lardinois, A., Steensels, M., Lambrecht, B., Desloges, N., Rahaus, M., Rebeski, D., et al. (2012). Potency of a recombinant NDV-H5 vaccine against various HPAI H5N1 virus challenges in SPF chickens. Avian Dis, 56, 928-936.
19. Mesonero, A., Suarez, D. L., van Santen, E., Tang, D. C., & Toro, H. (2011). Avian influenza in ovo vaccination with replication defective recombinant adenovirus in chickens: vaccine potency, antibody persistence, and maternal antibody transfer. Avian Dis, 55, 285-292.
20. Mingxiao, M., Ningyi, J., Zhenguo, W., Ruilin, W., Dongliang, F., Min, Z., et al. (2006). Construction and immunogenicity of recombinant fowlpox vaccines coexpressing HA of AIV H5N1 and chicken IL18. Vaccine, 24, 4304-4311. doi: 10.1016/j.vaccine.2006.03.006
21. Morgan, R. W., Gelb, J., Jr., Pope, C. R., & Sondermeijer, P. J. (1993). Efficacy in chickens of a herpesvirus of turkeys recombinant vaccine containing the fusion gene of Newcastle disease virus: onset of protection and effect of maternal antibodies. Avian Dis, 37, 1032-1040.
22. Morgan, R. W., Gelb, J., Jr., Schreurs, C. S., Lutticken, D., Rosenberger, J. K., & Sondermeijer, P. J. (1992). Protection of chickens from Newcastle and Marek's diseases with a recombinant herpesvirus of turkeys vaccine expressing the Newcastle disease virus fusion protein. Avian Dis, 36, 858-870.
23. Nayak, B., Rout, S. N., Kumar, S., Khalil, M. S., Fouda, M. M., Ahmed, L. E., et al. (2009). Immunization of chickens with Newcastle disease virus expressing H5 hemagglutinin protects against highly pathogenic H5N1 avian influenza viruses. PLoS One, 4, e6509. doi: 10.1371/ journal.pone.0006509
24. Neff, C., Sudler, C., & Hoop, R. K. (2008). Characterization of western European field isolates and vaccine strains of avian infectious laryngotracheitis virus by restriction fragment length polymorphism and sequence analysis. Avian Dis, 52, 278-283.
25. Okamura, H., Sakaguchi, M., Yokogawa, K., Tokunaga, E., Abe, S., Tokiyoshi, S., et al. (2001). Lack of contact transmission of recombinant Marek's disease virus type 1 expressing the fusion protein of Newcastle disease virus. Vaccine, 20, 483-489.
26. Oldoni, I., Rodriguez-Avila, A., Riblet, S., & Garcia, M. (2008). Characterization of infectious laryngotracheitis virus (ILTV) isolates from commercial poultry by polymerase chain reaction and restriction fragment length polymorphism (PCR-RFLP). Avian Dis, 52, 59-63.
27. Palya, V., Kiss, I., Tatar-Kis, T., Mato, T., Felfoldi, B., & Gardin, Y. (2012). Advancement in vaccinationagainst Newcastle disease: recombinant HVT NDV provides high clinical protection and reduces challenge virus shedding with the absence of vaccine reactions. Avian Dis, 56, 282-287.
28. Perozo, F., Villegas, A. P., Fernandez, R., Cruz, J., & Pritchard, N. (2009). Efficacy of single dose recombinant herpesvirus of turkey infectious bursal disease virus (IBDV) vaccination against a variant IBDV strain. Avian Dis, 53, 624-628.
29. Qian, C., Chen, S., Ding, P., Chai, M., Xu, C., Gan, J., et al. (2012). The immune response of a recombinant fowlpox virus coexpressing the HA gene of the H5N1 highly pathogenic avian influenza virus and chicken interleukin 6 gene in ducks. Vaccine, 30, 6279-6286. doi: 10.1016/ j.vaccine.2012.08.008
30. Qiao, C., Jiang, Y., Tian, G., Wang, X., Li, C., Xin, X., et al. (2009). Recombinant fowlpox virus vectorbased vaccine completely protects chickens from H5N1 avian influenza virus. Antiviral Res, 81, 234-238. doi: 10.1016/j.antiviral.2008.12.002
31. Romer-Oberdorfer, A., Veits, J., Helferich, D., & Mettenleiter, T. C. (2008). Level of protection of chickens against highly pathogenic H5 avian influenza virus with Newcastle disease virus based live attenuated vector vaccine depends on homology of H5 sequence between vaccine and challenge virus. Vaccine, 26, 2307-2313. doi: 10.1016/j.vaccine.2008.02.061
32. Sakaguchi, M., Nakamura, H., Sonoda, K., Okamura, H., Yokogawa, K., Matsuo, K., et al. (1998). Protection of chickens with or without maternal antibodies against both Marek's and Newcastle diseases by one-time vaccination with recombinant vaccine of Marek's disease virus type 1. Vaccine, 16, 472-479.
33. Sarfati-Mizrahi, D., Lozano-Dubernard, B., Soto-Priante, E., Castro-Peralta, F., Flores-Castro, R., Loza- Rubio, E., et al. (2010). Protective dose of a recombinant Newcastle disease LaSota-avian influenza virus H5 vaccine against H5N2 highly pathogenic avian influenza virus and velogenic viscerotropic Newcastle disease virus in broilers with high maternal antibody levels. Avian Dis, 54, 239-241.
34. Schroer, D., Veits, J., Keil, G., Romer-Oberdorfer, A., Weber, S., & Mettenleiter, T. C. (2011). Efficacy of Newcastle disease virus recombinant expressing avian influenza virus H6 hemagglutinin against Newcastle disease and low pathogenic avian influenza in chickens and turkeys. Avian Dis, 55, 201-211.
35. Shi, X. M., Zhao, Y., Gao, H. B., Jing, Z., Wang, M., Cui, H. Y., et al. (2011). Evaluation of recombinant fowlpox virus expressing infectious bronchitis virus S1 gene and chicken interferon-gamma gene for immune protection against heterologous strains. Vaccine, 29, 1576-1582. doi: 10.1016/ j.vaccine.2010.12.102
36. Sonoda, K., Sakaguchi, M., Okamura, H., Yokogawa, K., Tokunaga, E., Tokiyoshi, S., et al. (2000). 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. J Virol, 74, 3217-3226.
37. Swayne, D. E., Beck, J. R., & Kinney, N. (2000a). Failure of a recombinant fowl poxvirus vaccine containing an avian influenza hemagglutinin gene to provide consistent protection against influenza in chickens preimmunized with a fowl pox vaccine. Avian Dis, 44, 132-137.
38. Swayne, D. E., Beck, J. R., & Mickle, T. R. (1997). Efficacy of recombinant fowl poxvirus vaccine in protecting chickens against a highly pathogenic Mexican-origin H5N2 avian influenza virus. Avian Dis, 41, 910-922.
39. Swayne, D. E., Garcia, M., Beck, J. R., Kinney, N., & Suarez, D. L. (2000b). Protection against diverse highly pathogenic H5 avian influenza viruses in chickens immunized with a recombinant fowlpox vaccine containing an H5 avian influenza hemagglutinin gene insert. Vaccine, 18, 1088- 1095.
40. Taylor, J., Christensen, L., Gettig, R., Goebel, J., Bouquet, J. F., Mickle, T. R., et al. (1996). Efficacy of a recombinant fowl pox-based Newcastle disease virus vaccine candidate against velogenic and respiratory challenge. Avian Dis, 40, 173-180.
41. Taylor, J., Weinberg, R., Kawaoka, Y., Webster, R. G., & Paoletti, E. (1988). Protective immunity against avian influenza induced by a fowlpox virus recombinant. Vaccine, 6, 504-508.
42. Tong, G. Z., Zhang, S. J., Wang, L., Qiu, H. J., Wang, Y. F., & Wang, M. (2001). Protection of chickens from infectious laryngotracheitis with a recombinant fowlpox virus expressing glycoprotein B of infectious laryngotracheitis virus. Avian Pathol, 30, 143-148. doi: 10.1080/03079450120044542
43. Toro, H., Tang, D. C., Suarez, D. L., Sylte, M. J., Pfeiffer, J., & Van Kampen, K. R. (2007). Protective avian influenza in ovo vaccination with non-replicating human adenovirus vector. Vaccine, 25, 2886-2891. doi: 10.1016/j.vaccine.2006.09.047
44. Toro, H., Tang, D. C., Suarez, D. L., Zhang, J., & Shi, Z. (2008). Protection of chickens against avian influenza with non-replicating adenovirus-vectored vaccine. Vaccine, 26, 2640-2646. doi: 10.1016/j.vaccine.2008.02.056
45. Toro, H., Zhang, J. F., Gallardo, R. A., van Santen, V. L., van Ginkel, F. W., Joiner, K. S., et al. (2014a). S1 of distinct IBV population expressed from recombinant adenovirus confers protection against challenge. Avian Dis, 58, 211-215.
46. Toro, H., Zhao, W., Breedlove, C., Zhang, Z., & Yub, Q. (2014b). Infectious bronchitis virus S2 expressed from recombinant virus confers broad protection against challenge. Avian Dis, 58, 83-89.
47. Tsukamoto, K., Kojima, C., Komori, Y., Tanimura, N., Mase, M., & Yamaguchi, S. (1999). Protection of chickens against very virulent infectious bursal disease virus (IBDV) and Marek's disease virus (MDV) with a recombinant MDV expressing IBDV VP2. Virology, 257, 352-362. doi: 10.1006/ viro.1999.9641
48. Tsukamoto, K., Saito, S., Saeki, S., Sato, T., Tanimura, N., Isobe, T., et al. (2002). Complete, long-lasting protection against lethal infectious bursal disease virus challenge by a single vaccination with an avian herpesvirus vector expressing VP2 antigens. J Virol, 76, 5637-5645.
49. Vagnozzi, A., Zavala, G., Riblet, S. M., Mundt, A., & Garcia, M. (2012). Protection induced by commercially available live-attenuated and recombinant viral vector vaccines against infectious laryngotracheitis virus in broiler chickens. Avian Pathol, 41, 21-31. doi: 10.1080/03079457.2011.631983
50. Veits, J., Wiesner, D., Fuchs, W., Hoffmann, B., Granzow, H., Starick, E., et al. (2006). Newcastle disease virus expressing H5 hemagglutinin gene protects chickens against Newcastle disease and avian influenza. Proc Natl Acad Sci U S A, 103, 8197-8202. doi: 10.1073/pnas.0602461103
51. Wang, X., Schnitzlein, W. M., Tripathy, D. N., Girshick, T., & Khan, M. I. (2002). Construction and immunogenicity studies of recombinant fowl poxvirus containing the S1 gene of Massachusetts 41 strain of infectious bronchitis virus. Avian Dis, 46, 831-838.
52. Wang, Y. F., Sun, Y. K., Tian, Z. C., Shi, X. M., Tong, G. Z., Liu, S. W., et al. (2009). Protection of chickens against infectious bronchitis by a recombinant fowlpox virus co-expressing IBV-S1 and chicken IFNgamma. Vaccine, 27, 7046-7052. doi: 10.1016/j.vaccine.2009.09.065
53. Yu, L., Liu, W., Schnitzlein, W. M., Tripathy, D. N., & Kwang, J. (2001). Study of protection by recombinant fowl poxvirus expressing C-terminal nucleocapsid protein of infectious bronchitis virus against challenge. Avian Dis, 45, 340-348.
54. Zeshan, B., Mushtaq, M. H., Wang, X., Li, W., & Jiang, P. (2011). Protective immune responses induced by in ovo immunization with recombinant adenoviruses expressing spike (S1) glycoprotein of infectious bronchitis virus fused/co-administered with granulocyte-macrophage colony stimulating factor. Vet Microbiol, 148, 8-17. doi: 10.1016/j.vetmic.2010.08.003
55. Zeshan, B., Zhang, L., Bai, J., Wang, X., Xu, J., & Jiang, P. (2010). Immunogenicity and protective efficacy of a replication-defective infectious bronchitis virus vaccine using an adenovirus vector and administered in ovo. J Virol Methods, 166, 54-59. doi: 10.1016/j.jviromet.2010.02.019
56. Zhang, G. Z., Zhang, R., Zhao, H. L., Wang, X. T., Zhang, S. P., Li, X. J., et al. (2010). A safety assessment of a fowlpox-vectored Mycoplasma gallisepticum vaccine in chickens. Poult Sci, 89, 1301-1306. doi: 10.3382/ps.2009-00447
57. Zhang, X., Wu, Y., Huang, Y., & Liu, X. (2012). Protection conferred by a recombinant Marek's disease virus that expresses the spike protein from infectious bronchitis virus in specific pathogen-free chicken. Virol J, 9, 85. doi: 10.1186/1743-422X-9-85
58. Zhao, W., Spatz, S., Zhang, Z., Wen, G., Garcia, M., Zsak, L., et al. (2014). Newcastle Disease Virus (NDV) Recombinants Expressing Infectious Laryngotracheitis Virus (ILTV) Glycoproteins gB and gD Protect Chickens against ILTV and NDV Challenges. J Virol, 88, 8397-8406. doi: 10.1128/JVI.01321-14