Full protection against African horsesickness (AHS) in horses induced by baculovirus-derived AHS virus serotype 4 VP2, VP5 and VP7

Abstract

African horsesickness virus serotype 4 (AHSV-4) outer capsid protein VP2, or VP2 and VP5 plus inner capsid protein VP7, derived from single or dual recombinant baculovirus expression vectors were used in different combinations to immunize horses. When the proteins were purified by affinity chromatography, the combination of all three proteins induced low levels of neutralizing antibodies and conferred protection against virulent virus challenge. However, purified VP2 or VP2 and VP5 in the absence of VP7 failed to induce neutralizing antibodies and protection. Immunization with non-purified proteins enhanced the titres of neutralizing antibodies. Again, the combination of the three proteins was able to confer total protection to immunized horses, which showed absence of viraemia. The antigenicity of recombinant VP2 was analysed with a collection of 30 MAbs. Both purified and unpurified recombinant VP2 proteins showed different antigenic patterns in comparison to that of VP2 on virions. An immunization experiment with four more horses confirmed these results. The vaccine described here would not only prevent the disease, but would drastically reduce the propagation of the virus by vectors.

A first full outer capsid protein sequence data-set in the Orbivirus genus (family Reoviridae): cloning, sequencing, expression and analysis of a complete set of full-length outer capsid VP2 genes of the nine African horsesickness virus serotypes

“…The importance of the availability of a complete set of full-length AHSV VP2 cDNA clones for each of the nine serotypes for recombinant vaccine development is underscored by the fact that thus far full protection against disease has only been achieved with full-length, soluble baculovirusexpressed AHSV VP2, notably for serotypes 4 and 5 Martinez-Torrecuadrada et al, 1996;Du Plessis et al, 1998;Scanlen et al, 2002). We are now developing recombinant VP2-based vaccines for all nine serotypes of AHSV using our set of full-length cDNA copies of the VP2 genes described in this paper.…”

“…Outer capsid protein VP2 is encoded by genome segment 2. Data showing that recombinant baculovirus-expressed VP2 of AHSV serotypes 4 and 5 induced protective, serotype-specific immunity in horses (Martinez-Torrecuadrada et al, 1996;Roy et al, 1996;Du Plessis et al, 1998;Scanlen et al, 2002) has formed the basis for the development of recombinant vaccines for AHS. Currently, live attenuated vaccines are available for seven AHSV serotypes, namely 1, 2, 3, 4, 6, 7 and 8.…”

Scientific review on African Horse Sickness

“…In other study carried out in 1996 (Martinez-Torrecuadrada et al, 1996), AHS virus-like particles were successfully assayed in a small group of horses. These particles provide a stable vaccine, unable to revert or recombine.…”

African horsesickness virus VP7 sub-unit vaccine protects mice against a lethal, heterologous serotype challenge.

“…indicate that VP7 may be involved in protecting horses against AHSV (Roy, 1995 ;Martı! nez-Torrecuadrada et al, 1996).…”