Immunogenicity and antigenicity of chimeric picornaviruses which express hepatitis A virus (HAV) peptide sequences: evidence for a neutralization domain near the amino terminus of VP1 of HAV.

We evaluated the antigenic characteristics of chimeric picornaviruses created by inserting peptide sequences from hepatitis A virus (HAV) capsid proteins into the B-C loop of VP1 of Sabin strain type 1 poliovirus (PV-1). Fifteen viable chimeras were generated. Each retained the ability to be neutralized by polyclonal PV-1 antisera. Two chimeras (H15 and H2) stimulated production of low levels of HAV neutralizing antibodies in immunized rabbits or mice, although in both cases only a small fraction of immunized animals produced this response. The H15 chimera, which contains residues 13-24 of HAV VP1, elicited HAV neutralizing antibodies in three of nine rabbits and at least one of seven immunized mice. These results indicate that a neutralization domain exists in this region of VP1. However, human sera with high titers of antibodies to HAV failed to neutralize or immunoprecipitate this chimera, suggesting the absence of a significant antibody response to this neutralization domain following natural infection. Sera from rabbits immunized with H15 that did not develop HAV neutralizing antibodies contained antibodies reactive with the HAV peptide segment expressed by the H15 virus, indicating substantial differences in the specificities of antibodies elicited by this peptide segment among individual immunized rabbits. The H15 peptide insert was an effective antigen, as indicated by a high level of sensitivity of the H15 chimera to neutralization by a related anti-peptide antibody which was itself devoid of HAV neutralizing activity. One of 16 rabbits immunized with the H2 chimera (residues 101-108 of HAV VP1) developed HAV neutralizing antibodies, confirming both the presence and the highly conformational nature of a neutralization antigenic site involving these residues of HAV.