Structural prerequisites for intersubtype B and D antigenicity of the third variable envelope region (V3) of human immunodeficiency virus type 1.

To elucidate the structural requirements for intersubtype antigenicity of human immunodeficiency virus type 1 (HIV-1) third variable envelope region (V3), synthetic peptides were used in enzyme immunoassays (EIAs) with serum samples from persons with proven or probable subtype B and D infections. Mathematical analyses of results from EIAs with singly substituted V3 peptides revealed important residues determining overall N-terminal V3 peptide antigenicity. This information was used to design V3 immunogens, rabbit antiserum to which were tested in EIA and for in vitro neutralization of molecular clones of HIV-1(MN) and HIV-1(MAL). Intersubtype-reactive epitopes were distributed toward the N-terminal half of the V3 loop. Lysine at position 310, arginine at position 311, and isoleucine at position 314, all derived from the MN primary sequence, were major determinants of intersubtype V3 antigenicity. Combinations of residues that enhanced antigenicity often contained lysine at position 310. Threonine at position 308 was common in the least advantageous combinations. V3 immunogens modified to achieve optimal antigenicity induced antiserum with augmented cross-neutralization of virus from MAL and MN molecular clones, suggesting one approach to subunit vaccine development.