Candidate peptide-vaccine induced potent protection against CSFV and identified a principal sequential neutralizing determinant on E2

Previously, two candidate multi-peptide-vaccines (MPVs) consisted of five overlapping synthetic peptides covering the antigenic domain B/C (aa693–777) on envelope protein E2 were prepared in our lab. And they successfully induced peptide-specific neutralizing antibodies and provided pigs with complete protection from the lethal challenge of virulent classical swine fever virus (CSFV) strain Shimen. In this study, these five peptides were conjugated to bovine serum albumin (BSA), with which five groups of pigs (n = 10) were inoculated, respectively. Among these candidate peptide-vaccines (PVs), PV-BC1 (BC1: aa693–716) exhibited the most potent protective activity, PV-BC3, PV-BC4 and PV-BC5 (BC3: aa723–745; BC4: aa741–760; BC5: aa757–777) had weaker effects, while no effect of PV-BC2 (BC2: aa712–727) had been detected. Moreover, the polyclonal antibodies induced by PV-BC1 and PV-BC4 were capable of neutralizing C-strain virus in vitro. Thus, a principal sequential neutralizing determinant (aa693–716) and a minor sequential neutralizing determinant (aa741–760) were proved to lie in the antigenic domain B/C, which can be recruited into developing more effective “marker vaccine” by epitope-vaccine strategy. Our study also indicates that scanning with a panel of sequential peptide-immunogens is an effective method to locate sequential neutralizing epitopes.