The complete nucleotide sequence of VP5 of a strain of bluetongue virus of serotype 2 isolated in the USA reveals its close relationship with a virus of serotype 1 isolated in Australia

Oncolytic bluetongue viruses: promise, progress, and perspectives

Humans are sero-negative toward bluetongue viruses (BTVs) since BTVs do not infect normal human cells. Infection and selective degradation of several human cancer cell lines but not normal ones by five US BTV serotypes have been investigated. We determined the susceptibilities of many normal and human cancer cells to BTV infections and made comparative kinetic analyses of their cytopathic effects, survival rates, ultra-structural changes, cellular apoptosis and necrosis, cell cycle arrest, cytokine profiles, viral genome, mRNAs, and progeny titers. The wild-type US BTVs, without any genetic modifications, could preferentially infect and degrade several types of human cancer cells but not normal cells. Their selective and preferential BTV-degradation of human cancer cells is viral dose–dependent, leading to effective viral replication, and induced apoptosis. Xenograft tumors in mice were substantially reduced by a single intratumoral BTV injection in initial in vivo experiments. Thus, wild-type BTVs, without genetic modifications, have oncolytic potentials. They represent an attractive, next generation of oncolytic viral approach for potential human cancer therapy combined with current anti-cancer agents and irradiation.

Persistence of bluetongue virus serotype 2 (BTV-2) in the southeast United States

The prototype United States (US) strains of bluetongue virus serotype 2 [BTV-2 (OnaA) and BTV-2 (OnaB)] made in Florida in 1982 were compared to a recent BTV-2 (FL99) isolate made in Florida in 1999 to determine if the original strain(s) had persisted or if a new strain of BTV-2 had been re-introduced into the southeast US. Viral RNA and protein electropherotypes, and sequence analysis of five RNA genome segments for these early and later BTV-2 isolates were compared. These comparisons indicated that BTV-2 (OnaB) has persisted in the southeast US since its first isolation in 1982. Sequence analysis of concurrent isolates of BTV-13 (FL99) and BTV-17 (FL99) from the same location in Florida in 1999 provides evidence of genetic reassortment between BTV-2 and other co-circulating serotypes of BTV.

New generation of African horse sickness virus vaccines based on structural and molecular studies of the virus particles

African horse sickness virus (AHSV) is a member of the genus Orbivirus, which also includes bluetongue virus (BTV) and epizootic haemorrhagic disease (EHDV) virus. These orbiviruses have similar morphological and biochemical properties, with distinctive pathobiological properties and host ranges. Sequencing studies of the capsid proteins have revealed evolutionary relationships between these viruses. Biochemical studies of the viruses together with the expression of individual proteins and protein complexes have resulted in the development of new generation vaccines. Baculovirus expressed AHSV VP2 provides protection against death caused by AHSV challenge. Similarly, BTV VP2 alone elicits protective neutralising antibodies against BTV in sheep, which is enhanced in the presence of VP5. Recent developments in biotechnology (multiple gene expression baculovirus systems) have made it possible to synthesise orbivirus particles that biochemically and immunologically mimic authentic virions but lack the genetic material. Particle doses as low as 10 micrograms elicit responses that are sufficient to protect sheep 15 months post vaccination, against virulent virus challenge. Moreover, knowledge of the three dimensional structure of these particles enables us to engineer them to deliver multiple foreign peptide components representing other viral epitopes (e.g. foot and mouth disease virus and influenza virus) in order to elicit protective immunity.

Comparative sequence analysis and expression of the M6 gene, encoding the outer capsid protein VP5, of African horsesickness virus serotype nine

The entire nucleotide and deduced amino acid sequence of the M6 gene of African horsesickness virus (AHSV) serotype nine has been determined from four overlapping cDNA clones. The gene was found to be 1566 bp long, encoding a protein of 505 amino acids with a molecular weight of 56 737 Da and a nett charge of - 1 at neutral pH Comparative sequence analysis of the deduced amino acid sequence with the VP5 protein of AHSV-4, showed that only 81% of amino acids were conserved in type and position, although alternating regions of lower and higher conservation was identified by alignment of the primary sequences of different orbiviral VP5 proteins. Antigenically authentic AHSV-9 VP5 was also expressed in a baculovirus expression system and the expressed protein was shown to react specifically with anti-AHSV-9 as well as AHSV-3 serum in Western blot analysis.

Epitopic mapping of linear and conformation-dependent antigenic determinants on GP5 of five U.S. bluetongue viruses

Two distinct antigenic determinants of the major outer capsid protein, GP5, of five U.S. bluetongue viruses have been identified and mapped using monoclonal and oligoclonal antibodies. One antigenic site, identified by oligoclonal antibody AK-15, was found to be common and conserved in all five U.S. BTV serotypes. This linear epitope was located between amino acid residues 175 and 189 (ALQREAAERSEDEIK). The second determinant identified by monoclonal antibody 34.7 was present in BTV-2, -10, -11, and -17 but absent in BTV-13. The binding of this monoclonal antibody to GP5 could be blocked specifically by one of three short synthetic peptides located among amino acid residues 33-42 (KAAERFAESE), 159-168 (EKILKEEDSK), and 206-215 (EIERDGMQEE), indicating that this antigenic determinant is conformation-dependent. Oligoclonal antibody (AK-15) reacted with denatured GP5 immobilized on nitrocellulose membrane after Western transfer as well as with native GP5 present on the surface of purified BTV virions. Monoclonal antibody (34.7) reacted only with denatured GP5 but not native GP5 using an ELISA assay. However, these two antigenic epitopes alone did not elicit detectable neutralizing antibodies as determined by plaque reduction assay.

Complete genomic sequences of the GP5 protein gene of bluetongue virus serotype 11 and 17

The complete nucleotide sequences of full-length copies of genomic segment 6 or M3 of US bluetongue virus serotype 11 and 17 consisted of 1638 nucleotides. The plus-strand contained an open reading frame for a protein of 526 amino acids which was equivalent to about 59,000 Da, similar to the molecular weight of GP5 as determined by SDS-PAGE analysis. This long open reading frame was flanked by a 5' non-coding region of 29 nucleotides and a 3' non-coding region of 28 bases. When the predicted amino acid sequences of GP5 of BTV-11 and -17 were aligned and compared with those of BTV-2, -10, -13, -1AU and -1SA, four major highly conserved domains interrupted by several variable regions were detected. The potential significance of these discrete domains is discussed. Evolutionary and phylogenetic characteristics of these US BTV serotypes were consistent with our finding concerning BTV-1AU and -1SA.

Genetic variation and evolutionary relationships amongst bluetongue viruses endemic in the United States

The genetic variation and evolutionary relationships amongst the five serotypes of bluetongue virus (BTV) endemic to the United States were investigated by oligonucleotide fingerprint analysis. The viruses analyzed include prototype viruses of the five U.S. serotypes, and 32 viruses isolated from domestic and wild ruminants from the U.S. in the years 1979-1981. With the exception of serotype 2, most genes encoding the viral core and non-structural proteins were demonstrated to be highly conserved both within and between serotypes and some also appear to have reassorted in nature. Gene segments 2 and 6, which encode the outer capsid proteins VP2 and VP5 respectively, were more variable and were not consistently linked as serotype determination was dependent solely on gene segment 2. Gene segment 2 was the most variable gene between serotypes, but it was highly conserved within serotypes and stable over time. This suggests that the emergence of new BTV serotypes, which would require the stable incorporation of numerous mutations, must be a very slow process. Fingerprint comparisons further suggested that BTV serotypes 10, 11, 13 and 17 have evolved together in the U.S. over a considerable period of time, whereas serotype 2, which is genetically distinct, has evolved elsewhere and is most likely a recent introduction to North America.

Complete nucleotide and deduced amino acid sequence of genome segment 5 encoding the outer capsid protein, VP5, of a U.S. isolate of bluetongue virus serotype 11

The complete nucleotide sequence of the RNA genome segment coding for the outer capsid protein, VP5, of the United States prototypic strain of bluetongue virus (BTV) serotype 11 was determined from two overlapping cDNA clones. The genome segment was found to be 1638 nucleotides in length with a single open reading frame coding for a 526 amino acid protein of MW 59,278 and having a net charge of -4.0 at neutral pH. Comparisons of the predicted amino acid sequence of VP5 of BTV 11 with those of the United States serotypes 2, 10, and 13 and two isolates of BTV 1 from Australia and South Africa confirmed earlier reports that VP5 is a conserved protein with no clear regions of variability. A computer generated consensus sequence suggested VP5 of BTV 2 to be representative of the average VP5 sequences reported thus far.

Expression of the outer capsid protein VP5 of two bluetongue viruses, and synthesis of chimeric double-shelled virus-like particles using combinations of recombinant baculoviruses

We have previously reported the assembly of virus-like particles (VLPs), consisting of the four major structural proteins of bluetongue virus (BTV), in Spodoptera frugiperda cells coinfected with recombinant baculoviruses (French et al. (1990). J. Virol. 64, 5695-5700). In this paper we report further studies using this system to assemble heterologous VLPs containing the outer capsid proteins (VP2 and VP5) of a range of different BTV serotypes. S. frugiperda cells were coinfected with three recombinant baculoviruses; a dual recombinant expressing VP3 and VP7 (of BTV-17 and -10, respectively) in combination with a single recombinant expressing VP2 of BTV-1, -2, -10, -11, 13, or -17 and an additional single recombinant expressing VP5 of BTV-2, BTV-10, or BTV-13. The resultant VLPs were purified and analyzed by electronmicroscopy, Western immunoblotting, and hemagglutination assays to determine whether double-shelled VLPs had been assembled. In the course of these experiments the VP2 proteins of all six available serotypes were successfully incorporated into VLPs. Particles from two different combinations of chimeric VLPs (having VP2 derived from BTV-1 or that of BTV-17) were used to raise antisera in guinea pigs. Both of these sera showed high neutralizing antibody titers against live BTV, indicating that heterologous VLPs may have potential for use in anti-BTV vaccines.