Minor displacements in the insertion site provoke major differences in theinduction of antibody responses by chimeric parvovirus-like particles

An antigen-delivery system based on hybrid virus-like particles (VLPs) form ed by the self-assembly of the capsid VP2 protein of canine parvovirus (CPV ) and expressing foreign peptides was investigated. In this report, we have studied the effects of inserting the poliovirus C3:B epitope in the four l oops and the C terminus of the CPV VP2 on the particle structure and immuno genicity. Epitope insertions in the four loops allowed the recovery of caps ids in all of the mutants. However, only insertions of the C3:B epitope in VP2 residue 225 of the loop 2 were able to elicit a significant anti-peptid e antibody response, but not poliovirus-neutralizing antibodies, probably b ecause residue 225 is located in an small depression of the surface. To fin e modulate the insertion site in loop 2, a cassette-mutagenesis was carried out to insert the epitope in adjacent positions 226, 227, and 228. The epi tope C3:B inserted into these positions was well recognized by the specific monoclonal antibody C3 by immunoelectron microscopy. BALB/c mice immunized with these chimeric C3:B CPV:VLPs were able to elicit an strong neutralizi ng antibody response (>3 log(10) units) against poliovirus type 1 (Mahoney strain). Therefore, minor displacements in the insertion place cause dramat ic changes in the accessibility of the epitope and the induction of antibod y responses. (C) 1999 Academic Press.