Chapter Adenovirus as Tools in Animal Health

Adenoviruses have long been identified as good candidates for use as viral vectors in gene therapy and as vaccines. These viruses can infect multiple cell types, while in division or in quiescence, and are relatively easy to manipulate so that parts of their genome can be replaced with exogenous genes. Progressive safety improvements in replication-deficient adenoviral vectors have been achieved with the second and third generation, and ending with the gutless adenoviral vectors. Adenoviral vectors are immunogenic and can act as adjuvants. Nonetheless, the potency of human recombinant adenoviral vaccines was below expectations in clinical trials mainly because of the pre-existing adenoviral immunity found in the general population. This drawback can however become advantageous in animal health, as no previous immunity to human adenoviral vectors exists in animals. Other viral vectors viruses are used as vaccine, but adenoviruses remain the most employed and promising recombinant vector in veterinary medicine. In this chapter, we review the generation of adenoviral vectors, the immune response they trigger, and their advantages and disadvantages for veterinary use in terms of safety and efficacy. This chapter also describes how recombinant adenoviral vectors can be integrated as tools for vaccination and immunomodulation in veterinary medicine

Adenovirus as Tools in Animal Health

Adenoviruses have long been identified as good candidates for use as viral vectors in gene therapy and as vaccines. These viruses can infect multiple cell types, while in division or in quiescence, and are relatively easy to manipulate so that parts of their genome can be replaced with exogenous genes. Progressive safety improvements in replication-deficient adenoviral vectors have been achieved with the second and third generation, and ending with the gutless adenoviral vectors. Adenoviral vectors are immunogenic and can act as adjuvants. Nonetheless, the potency of human recombinant adenoviral vaccines was below expectations in clinical trials mainly because of the pre-existing adenoviral immunity found in the general population. This drawback can however become advantageous in animal health, as no previous immunity to human adenoviral vectors exists in animals. Other viral vectors viruses are used as vaccine, but adenoviruses remain the most employed and promising recombinant vector in veterinary medicine. In this chapter, we review the generation of adenoviral vectors, the immune response they trigger, and their advantages and disadvantages for veterinary use in terms of safety and efficacy. This chapter also describes how recombinant adenoviral vectors can be integrated as tools for vaccination and immunomodulation in veterinary medicine

Mutagenesis-Mediated Decrease of Pathogenicity as a Feature of the Mutant Spectrum of a Viral Population

Background: RNA virus populations are heterogeneous ensembles of closely related genomes termed quasispecies. This highly complex distribution of variants confers important properties to RNA viruses and influences their pathogenic behavior. It has been hypothesized that increased mutagenesis of viral populations, by treatment with mutagenic agents, can induce alterations in the pathogenic potential of a virus population. In this work we investigate whether mutagenized foot-and-mouth disease virus (FMDV) populations display changes in their virulence in mice. Methodology and Principal Findings: FMDV C-S8c1 was passaged in BHK cells in the presence of the mutagenic agent ribavirin. Decline in viral titer and viral RNA progeny was observed in the first passage, fluctuating around a constant value thereafter. Hence, the specific infectivity remained stable during the passages. The viral population harvested from passage 9 (P9 R) showed decreased virulence in mice, with a lethal dose 50 (LD 50) >10 4 PFU, as compared with LD 50 of 50 PFU of the parental population FMDV C-S8c1. This decrease in virulence was associated to a 20-fold increase in the mutation frequency of the P9 R population with respect to C-S8c1. Interestingly, individual biological clones isolated from the attenuated population P9 R were as virulent as the parental virus C-S8c1. Furthermore, a mixed population of C-S8c1 and P9 R was inoculated into mice and showed decreased virulence as compared to C-S8c1, suggesting that population P9 R is able to suppress the virulent phenotype of C-S8c1. Conclusion: Ribavirin-mediated mutagenesis of an FMDV population resulted in attenuation in vivo, albeit a large proportion of its biological clones displayed a highly virulent phenotype. These results, together with the suppression of C-S8c1 by mutagenized P9 R population, document a suppressive effect of mutagenized viral quasispecies in vivo, and suggest novel approaches to the treatment and prevention of viral diseases. © 2012 Sanz-Ramos et al.CISA-INIA Centro de Investigación en Sanidad Animal; Ministerio de Ciencia e Innovación (MCINN); 228394-NADIR-Integrating Activities 7th EU; Fundación Ramón ArecesPeer Reviewe

A replication analysis of foot-and-mouth disease virus in swine lymphoid tissue might indicate a putative carrier stage in pigs

Foot-and-mouth disease virus (FMVD), one of the most contagious viruses of cloven-hoofed animals, may cause a prolonged, asymptomatic but persistent infection in ruminants, named the "carrier state". However, it remains an open question whether this carrier state occurs in pigs. Here we present quantitative analyses of the duration of FMDV RNA and infectivity in lymphoid and epithelial tissues in experimentally infected pigs with FMDV C-S8c1. The data indicated that although FMDV RNA remained in blood until day 14 post-infection (pi), viremia was cleared by day 7 pi. However, all tissues tested were positive for FMDV until day 14-17 pi. Interestingly, the specific infectivity of FMDV in these tissues was in some cases even higher than the FMDV C-S8c1. We therefore propose that a "pseudopersistent state" may occur in pigs in which virus replicates in lymphoid tissues for a prolonged period of time, thereby representing a potential source of virus

IL-10: A Multifunctional Cytokine in Viral Infections

The anti-inflammatory master regulator IL-10 is critical to protect the host from tissue damage during acute phases of immune responses. This regulatory mechanism, central to T cell homeostasis, can be hijacked by viruses to evade immunity. IL-10 can be produced by virtually all immune cells, and it can also modulate the function of these cells. Understanding the effects of this multifunctional cytokine is therefore a complex task. In the present review we discuss the factors driving IL-10 production and the cellular sources of the cytokine during antiviral immune responses. We particularly focus on the IL-10 regulatory mechanisms that impact antiviral immune responses and how viruses can use this central regulatory pathway to evade immunity and establish chronic/latent infections

New vaccine design based on defective genomes that combines features of attenuated and inactivated vaccines

Background: New vaccine designs are needed to control diseases associated with antigenically variable RNA viruses. Foot-and-mouth disease (FMD) is a highly contagious disease of livestock that inflicts severe economic losses. Although the current whole-virus chemically inactivated vaccine has proven effective, it has led to new outbreaks of FMD because of incomplete inactivation of the virus or the escape of infectious virus from vaccine production premises. We have previously shown that serial passages of FMD virus (FMDV) C-S8c1 at high multiplicity of infection in cell culture resulted in virus populations consisting of defective genomes that are infectious by complementation (termed C-S8p260). Principal Finding: Here we evaluate the immunogenicity of C-S8p260, first in a mouse model system to establish a proof of principle, and second, in swine, the natural host of FMDV C-S8c1. Mice were completely protected against a lethal challenge with FMDV C-S8c1, after vaccination with a single dose of C-S8p260. Pigs immunized with different C-S8p260 doses and challenged with FMDV C-S8c1 either did not develop any clinical signs or showed delayed and mild disease symptoms. C-S8p260 induced high titers of both FMDV-specific, neutralizing antibodies and activated FMDV-specific T cells in swine, that correlated with solid protection against FMDV. Conclusions: The defective virus-based vaccine did not produce detectable levels of transmissible FMDV. Therefore, a segmented, replication-competent form of a virus, such as FMDV C-S8p260, can provide the basis of a new generation of attenuated antiviral vaccines with two safety barriers. The design can be extended to any viral pathogen that encodes trans-acting gene products, allowing complementation between replication-competent, defective forms. © 2010 Rodríguez-Calvo et al.Ministerio de Ciencia e Innovación, Spain, and European Union, Network of Excellence, EPIZONE (Contract # FOOD-CT-2006-016236). CIBERehd (Centro de Investigación Biomédica en Red de Enfermedades Hepáticas y Digestivas) is funded by Instituto de Salud Carlos III. Work at Centro de Biología Molecular ‘‘Severo Ochoa’’ (CISC-UAM) was supported by an institutional grant from Fundación Ramón Arece

New Vaccine Design Based on Defective Genomes That Combines Features of Attenuated and Inactivated Vaccines

[Background] New vaccine designs are needed to control diseases associated with antigenically variable RNA viruses. Foot-and-mouth disease (FMD) is a highly contagious disease of livestock that inflicts severe economic losses. Although the current whole-virus chemically inactivated vaccine has proven effective, it has led to new outbreaks of FMD because of incomplete inactivation of the virus or the escape of infectious virus from vaccine production premises. We have previously shown that serial passages of FMD virus (FMDV) C-S8c1 at high multiplicity of infection in cell culture resulted in virus populations consisting of defective genomes that are infectious by complementation (termed C-S8p260).[Principal Finding] Here we evaluate the immunogenicity of C-S8p260, first in a mouse model system to establish a proof of principle, and second, in swine, the natural host of FMDV C-S8c1. Mice were completely protected against a lethal challenge with FMDV C-S8c1, after vaccination with a single dose of C-S8p260. Pigs immunized with different C-S8p260 doses and challenged with FMDV C-S8c1 either did not develop any clinical signs or showed delayed and mild disease symptoms. C-S8p260 induced high titers of both FMDV-specific, neutralizing antibodies and activated FMDV-specific T cells in swine, that correlated with solid protection against FMDV.[Conclusions] The defective virus-based vaccine did not produce detectable levels of transmissible FMDV. Therefore, a segmented, replication-competent form of a virus, such as FMDV C-S8p260, can provide the basis of a new generation of attenuated antiviral vaccines with two safety barriers. The design can be extended to any viral pathogen that encodes trans-acting gene products, allowing complementation between replication-competent, defective forms.This research was supported by grants AGL2004-0049, AGL2007-61374, CSD2006-07 and BFU2008-02816/BMC from Ministerio de Ciencia e Innovación, Spain, and European Union, Network of Excellence, EPIZONE (Contract # FOOD-CT-2006-016236). CIBERehd (Centro de Investigacio´n Biome´dica en Red de Enfermedades Hepa´ticas y Digestivas) is funded by Instituto de Salud Carlos III. Work at Centro de Biologı´a Molecular ‘‘Severo Ochoa’’ (CISC-UAM) was supported by an institutional grant from Fundacio´n Ramo´n Areces. T.R-C. was supported by a contract from Comunidad Auto´noma de Madrid; S.O. and M.S-R were supported by a predoctoral fellowship from the Ministerio de Educacio´n y Ciencia. The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript.Peer reviewe

Follicular dendritic cell disruption as a novel mechanism of virus-induced immunosuppression

Arboviruses cause acute diseases that increasingly affect global health. We used bluetongue virus (BTV) and its natural sheep host to reveal a previously uncharacterized mechanism used by an arbovirus to manipulate host immunity. Our study shows that BTV, similarly to other antigens delivered through the skin, is transported rapidly via the lymph to the peripheral lymph nodes. Here, BTV infects and disrupts follicular dendritic cells, hindering B-cell division in germinal centers, which results in a delayed production of high affinity and virus neutralizing antibodies. Moreover, the humoral immune response to a second antigen is also hampered in BTV-infected animals. Thus, an arbovirus can evade the host antiviral response by inducing an acute immunosuppression. Although transient, this immunosuppression occurs at the critical early stages of infection when a delayed host humoral immune response likely affects virus systemic dissemination and the clinical outcome of disease