Identification of a novel cell culture adaptation site on the capsid of foot-and-mouth disease virus
Vaccination remains the most effective tool for control of foot-and-mouth disease (FMD) both in endemic countries and as an emergency preparedness for new outbreaks. FMD vaccines are chemically inactivated virus preparations and the production of new vaccines is critically dependent upon cell culture adaptation of field viruses which can prove problematical. A major driver of cell culture adaptation is receptor availability. Field isolates of FMD virus (FMDV) use RGD-dependent integrins as receptors whereas cell culture adaptation often selects for variants with altered receptor preferences. Previously, two independent sites on the capsid have been identified where mutations are associated with improved cell culture growth. One is a shallow depression formed by the three major structural proteins (VP1-3) where mutations create a heparan sulphate (HS) binding site (the canonical HS-binding site). The other involves residues of VP1 and located at the 5-fold symmetry axis. For some viruses changes at this site results in HS binding while for others the receptors are unknown. Here we report the identification of a novel site on VP3 where mutations result in an expanded cell tropism of a vaccine variant of A/IRN/87 (called A-). Furthermore, we show that introducing the same mutations into a different type A field virus (A/TUR/2/2006) results in the same expanded cell culture tropism as the A/IRN/87 A- vaccine variant. These observations add to the evidence for multiple cell-attachment mechanisms for FMDV and may be useful for vaccine manufacture when cell culture adaptation proves difficult.