Abstract: Classical Swine Fever Virus (CSFV) E2 glycoprotein is a major inducer of neutralizing antibodies and protective immunity in swine. E2 mediates virus adsorption to the target cell, and harbors genetic determinants associated with virus virulence. CSFV E2 also contains between residues 829 and 837 a discrete epitope (TAVSPTTLR) recognized by monoclonal antibody (mAb) WH303, used to differentiate CSFV from related Pestiviruses Bovine Viral Diarrhea Virus (BVDV) and Border Disease Virus (BDV). In this report, a CSFV infectious clone of the virulent Brescia isolate (BICv) was used to progressively mutate the mAb WH303 epitope of CSFV E2 to the homologous amino acid sequence of BVDV strain NADL E2 (TSFNMDTLA).

Abstract: E1, along with Erns and E2 is one of the three envelope glycoproteins of Classical Swine Fever Virus (CSFV). Our previous studies indicated that glycosylation status of either E2 or Erns strongly influence viral virulence in swine. Here, we have investigated the role of E1 glycosylation of highly virulent CSFV strain Brescia during infection in the natural host. The three putative glycosylation sites in E1 were modified by site directed mutagenesis of a CSFV Brescia infectious clone (BICv). A panel of virus mutants was obtained and used to investigate whether the removal of putative glycosylation sites in the E1 glycoprotein would affect viral virulence/pathogenesis in swine. We observed that rescue of viable virus was completely impaired by removal of all three putative glycosylation sites in E1. Single mutations of each of the E1 glycosylation sites showed that CSFV amino acid N594 (E1.N3 virus), as well the combined mutation of N500 and N513 (E1.N1N2 virus) resulted in BICv attenuation.

Abstract: Classical swine fever virus is a world-wide distributed highly-contagious disease affecting swine. The two main strategies for diseases control are prophylactic vaccination and non-vaccination stamping out policies. Marker vaccines are a promising strategy. Here we report the rational development of a doubly antigenic marker CSFV experimental live attenuated candidate strain vaccine (Flag/T4 virus). Flag/T virus (Flag/T4v) is based in the combination of two Brescia derived recombinant attenuated viruses: RB-C22 and T4. RB-C22v contains a 19mer insertion in the structural glycoprotein E1, while T4v posses mutated CSFV amino acid residues 830 to 834 in the structural glycoprotein E2, deleting the highly conserved epitope recognized by monoclonal antibody (mAb) WH303. Flag/T4 virus contains a positive foreign antigenic marker, due to the insertion of the highly antigenic epitope Flag in the 19mer insertion of E1, as well as a negative antigenic marker, the lack of reactivity with mAb WH303.

Abstract: NS4B is one of the non-structural proteins of classical swine fever virus. By using functional genetics, we have discovered, in the predicted amino acid sequence of NS4B of CSFV strain Brescia, a motif that resembles those found in the toll-like receptor (TLR) proteins, a group of host cell proteins involved in the development of anti-viral mechanisms. We have located the TLR motif in two groups of amino acid triplets at amino acid positions 2531-3 (residues IYK) and 2566-8 (residues VGI) of the CSFV NS4B glycoprotein. We have constructed a recombinant CSFV (derived from an infectious clone containing the genetic information of the highly virulent strain Brescia) containing amino acid substitutions in the three amino acid residues at positions 2566, 2567 and 2568, where the VGI triplet has been replaced by an AAA triplet inside the NS4B glycoprotein. The obtained virus, named NS4B-VGIv, was completely attenuated in swine, showing a limited ability in spreading during the infection in vivo.

Abstract: NS4B is one of the non-structural proteins of classical swine fever virus. By using functional genetics, we have discovered, in the predicted amino acid sequence of NS4B of CSFV strain Brescia, a motif that resembles those found in the toll-like receptor (TLR) proteins, a group of host cell proteins involved in the development of anti-viral mechanisms. We have located the TLR motif in two groups of amino acid triplets at amino acid positions 2531-3 (residues IYK) and 2566-8 (residues VGI) of the CSFV NS4B glycoprotein. We have constructed a recombinant CSFV (derived from an infectious clone containing the genetic information of the highly virulent strain Brescia) containing amino acid substitutions in the three amino acid residues at positions 2566, 2567 and 2568, where the VGI triplet has been replaced by an AAA triplet inside the NS4B glycoprotein. The obtained virus, named NS4B-VGIv, was completely attenuated in swine, showing a limited ability in spreading during the infection in vivo.

Abstract: Classical swine fever virus is a world-wide distributed highly-contagious disease affecting swine. The two main strategies for diseases control are prophylactic vaccination and non-vaccination stamping out policies. Marker vaccines are a promising strategy. Here we report the rational development of a doubly antigenic marker CSFV experimental live attenuated candidate strain vaccine (Flag/T4 virus). Flag/T virus (Flag/T4v) is based in the combination of two Brescia derived recombinant attenuated viruses: RB-C22 and T4. RB-C22v contains a 19mer insertion in the structural glycoprotein E1, while T4v posses mutated CSFV amino acid residues 830 to 834 in the structural glycoprotein E2, deleting the highly conserved epitope recognized by monoclonal antibody (mAb) WH303. Flag/T4 virus contains a positive foreign antigenic marker, due to the insertion of the highly antigenic epitope Flag in the 19mer insertion of E1, as well as a negative antigenic marker, the lack of reactivity with mAb WH303.

Abstract: Transposon linker insertion mutagenesis of a full-length infectious clone of the highly pathogenic classical swine fever virus (CSFV) isolate Brescia (pBIC) was used to identify genetic determinants of CSFV virulence and host range. A virus mutant, RB-C22 (RB-C22v), possessing a 19-residue tag insertion at the carboxyl end of E1 was constructed. RB-C22v and the parental virus pBIC (pBICv) exhibited similar growth characteristics on primary porcine macrophage cell cultures although RB-C22v produced significantly smaller plaques on SK6 cell cultures. In vivo, RB-C22v was markedly attenuated in swine. In contrast with pBIC infection, where mortality was 100%, all RB-C22v-infected pigs survived infection remaining clinically normal. Additionally, chimeras of the Brescia strain and the attenuated vaccine strain CS were constructed and evaluated for viral virulence in swine. Chimeras 138.8v and 337.14v, chimeras containing the E2 glycoprotein of CS and chimeric virus 319.

Abstract: Classical Swine Fever Virus (CSFV) E2 glycoprotein is a major inducer of neutralizing antibodies and protective immunity in swine. E2 mediates virus adsorption to the target cell, and harbors genetic determinants associated with virus virulence. CSFV E2 also contains between residues 829 and 837 a discrete epitope (TAVSPTTLR) recognized by monoclonal antibody (mAb) WH303, used to differentiate CSFV from related Pestiviruses Bovine Viral Diarrhea Virus (BVDV) and Border Disease Virus (BDV). In this report, a CSFV infectious clone of the virulent Brescia isolate (BICv) was used to progressively mutate the mAb WH303 epitope of CSFV E2 to the homologous amino acid sequence of BVDV strain NADL E2 (TSFNMDTLA).