ASSEMBLY AND IMMUNOGENICITY OF CHIMERIC GAG-ENV PROTEINS DERIVED FROMTHE HUMAN-IMMUNODEFICIENCY-VIRUS TYPE-1

We evaluated the potential of the precursor Gag protein (Pr55) of the human immunodeficiency virus type 1 (HIV-1) as a carrier for the prese ntation of envelope epitopes, Recombinant chimeric core-envelope prote in-expressing constructs were derived by deletion of regions within th e gag gene, especially of regions encoding p24 capsid epitopes, Sequen ces encoding either the principal neutralization determinant (PND) and /or the CD4-binding domains (CD4BS) were then inserted. Deletion of re sidues 196-226 within the p24 capsid protein did not prevent self-asse mbly into virus-like particles (VLPs) whereas deletion of residues 299 -328 completely abolished VLP formation. Thus the major homology regio n (MHR) and proximal sequences are required for capsid assembly. An im munization study in mice showed that assembled chimeric proteins elici ted strong anti-Gag, weak anti-envelope, and no neutralizing humoral r esponses, Nonassembled chimeric proteins were poor immunogens. Mapping of Pr55 antigenic sites using sera from immunized mice and peptides o verlapping the entire Gag precursor showed that p24 capsid and p17 mat rix epitopes presented to the immune system differed from the mature f orm (p24 or p17) and the multimeric immature form (Pr55).