Construction and Evaluation of a Recombinant Foot‐and‐Mouth Disease Virus

Abstract

The South African Territories (SAT) types of foot-and-mouth disease virus (FMDV) show marked genomic and antigenic variation throughout sub-Saharan Africa. This variation is geographically linked and requires the use of custom-made vaccines. Adaptation of field isolates as vaccine strains is cumbersome, time consuming, and expensive. As an alternative to the adaptation process, the construction of recombinant FMD viruses followed by the production of conventional, inactivated vaccines utilizing these viruses is proposed. The advantage of such a strategy would be the ability to manipulate the antigenicity of these viruses by substituting the antigenic coding regions (i.e., structural proteins) of a full-length cDNA clone of a suitable strain. A chimeric cDNA clone between types A and SAT 2 was constructed by inserting the external capsid-coding region of the vaccine strain ZIM/7/83/2 into the genetic backbone of the A12 cDNA clone. Preliminary evaluation of the recombinant FMD virus revealed a slower growth rate for the recombinant than the parental ZIM/7/83/2, although similar antigen yields could be obtained. The chimera was found to be thermally less stable than the parental strain, suggesting it to be an inferior strain for inactivated vaccine production.

Studies of genetically defined chimeras of a European type A virus and a South African Territories type 2 virus reveal growth determinants for foot-and-mouth disease virus

“…This finding, and studies showing that 3C pro (which cleaves the capsid proteins of SAT2) differs significantly from type A 3C pro , lead us to propose that the poor growth properties of vSAT2/A12 were due to suboptimal processing of the SAT2 external capsid proteins by the A 12 3C pro (Van Rensburg & Mason, 2002 1 . 0e+04…”

“…ml 21 (20-fold lower than the titre produced by vSAT2) 10 h post-infection. The poorer performance of vSAT2/A12 in comparison to the parental virus has been observed previously (Van Rensburg & Mason, 2002), but the experiments were performed in the absence of vRMC 35 (the genetic backbone used for this construct). However, in Fig.…”

“…We previously reported that vSAT2/A12, a chimeric virus with the SAT2 capsid in an A 12 genome, performed poorly in BHK cells when compared to the parental ZIM/7/83 (Van Rensburg & Mason, 2002). This finding, and studies showing that 3C pro (which cleaves the capsid proteins of SAT2) differs significantly from type A 3C pro , lead us to propose that the poor growth properties of vSAT2/A12 were due to suboptimal processing of the SAT2 external capsid proteins by the A 12 3C pro (Van Rensburg & Mason, 2002 1 .…”

“…This paper describes how we have overcome this problem by constructing a genome-length cDNA copy of a SAT2 strain. Characterization of this strain (and several derivatives) together with our previously described chimera, demonstrated that the virus recovered from the genome-length SAT2 cDNA displayed the excellent growth properties of the parental ZIM/7/83 strain, performing considerably better than our previously reported chimera (Van Rensburg & Mason, 2002).…”

“…In a recent study, the usefulness of a type A genome-length clone in the construction of chimeras containing the structural proteins of SAT type 2 was reported (Van Rensburg & Mason, 2002). These studies showed that this chimera, created using a previously constructed type A 12 genome-length backbone (Rieder et al, 1993), exhibited a slower growth rate than the parental SAT2 virus, suggesting that the A 12 genome-length clone is not optimal for the expression of SAT2 capsid proteins.…”