Genetically distinct pestiviruses pave the way to improved classical swine fever marker vaccine candidates based on the chimeric pestivirus concept

Abstract

Classical swine fever (CSF) is one of the most important viral diseases of pigs. In many countries, the use of vaccines is restricted due to limitations of subunit vaccines with regard to efficacy and onset of protection as well as failure of live vaccines to d ifferentiate i nfected from v accinated a nimals (DIVA principle). Chimeric pestiviruses based on CSF virus (CSFV) and the related bovine viral diarrhea virus (BVDV) have been licensed as live marker vaccines in Europe and Asia, but cross-reactive antibodies can cause problems in DIVA application due to close antigenic relationship. To develop marker vaccine candidates with improved DIVA properties, three chimeric viruses were generated by replacing E rns of CSFV Alfort-Tübingen with homologue proteins of only distantly related pestiviruses. The chimeric viruses “Ra”, “Pro”, and “RaPro” contained E rns sequences of Norway rat and Pronghorn pestiviruses or a combination of both, respectively. In porcine cells, the “Pro” chimera replicated to high titers, while replication of the “Ra” chimera was limited. The “RaPro” chimera showed an intermediate phenotype. All vaccine candidates were attenuated in a vaccination/ challenge trial in pigs, but to different extents. Inoculation induced moderate to high levels of neutralizing antibodies that protected against infection with a genetically heterologous, highly virulent CSFV. Importantly, serum samples of vaccinated animals did not show any cross-reactivity in a CSFV E rns antibody ELISA. In conclusion, the E rns antigen from distantly related pestiviruses can provide a robust serological negative marker for a new generation of improved CSFV marker vaccines based on the chimeric pestivirus concept.

Abrogation of the RNase activity of Erns in a low virulence classical swine fever virus enhances the humoral immune response and reduces virulence, transmissibility, and persistence in pigs

“…In this regard, the abrogation of the E rns RNase activity enhanced E rns -specific antibody response significantly, suggesting a better E rns protein immunogenicity following the loss of the RNase activity. Therefore, the difficulties in the development of diagnostics and DIVA assays based on seroconversion against E rns [ 40 , 41 ] may be attributable to a dampening effect on E rns -specific immunity related to the RNase activity of E rns . Further studies are required to clarify the role of the RNase activity of E rns in the host immune modulation [ 11 ] by CSFV strains of different virulence.…”

A Critical Review about Different Vaccines against Classical Swine Fever Virus and Their Repercussions in Endemic Regions

“…However, the use of pestiviruses genetically and antigenically distant to CSFV has emerged as an attractive option, taking into consideration mainly the DIVA concept. Thus, three recent chimeric viruses have been developed by replacing the Erns of CSFV strain Alfort-Tübingen with the homologue gene of largely distant pestiviruses members [ 139 ]. The engineered chimeric viruses “Ra,” “Pro,” and “RaPro” contained Erns sequences from Norway rat and Pronghorn pestiviruses or a combination of both, respectively [ 139 ].…”

“…Thus, three recent chimeric viruses have been developed by replacing the Erns of CSFV strain Alfort-Tübingen with the homologue gene of largely distant pestiviruses members [ 139 ]. The engineered chimeric viruses “Ra,” “Pro,” and “RaPro” contained Erns sequences from Norway rat and Pronghorn pestiviruses or a combination of both, respectively [ 139 ]. In this first study, all vaccine candidates conferred complete protection against clinical signs of CSF at 28 dpv.…”

Research Progress and Challenges in Vaccine Development against Classical Swine Fever Virus

“…Chimerization of closely related viruses could facilitate viral replication, but at the same time may be problematic in terms of induction of the production of cross-reactive antibodies. A recent study posed the hypothesis that genetically distinct pestiviruses might create replicating chimeric viruses with improved DIVA capacity due to a significantly reduced risk of inducing the cross-reactive antibodies [ 67 ]. In this study, the chimeric pestivirus vaccine candidates were generated using the cDNA clone of CSFV strain Alfort-p447, in which the E rns encoding sequence was replaced by the homologous sequences from pestiviruses distantly related to CSFV.…”