Genotypic and phenotypic characterization of a neutralization-resistant breakthrough population of HIV-1

Certain antibody neutralization escape mutants of HIV-1 map outside of the antibody recognition epitope, thereby suggesting the presence of nonlinear conformational domains. In an effort to begin to define the interacting regions of the HIV envelope proteins, a neutralization-sensitive clone of HIV-1, HXB2/BH10Sal-Bam, was passaged in the presence of the V3-specific monoclonal antibody 0.5beta. DNA sequence analysis of the V3 domain of the breakthrough viral populations revealed one population that retained the parental V3 genotype. Quantitative DNA sequence analysis of this breakthrough population revealed the presence of mutational "hotspots" in several envelope domains that are noncontiguous with V3. Mutations were seen throughout gp41 and the C1, V1/V2, C2, and C5 domains of gp120. In contrast, other regions of gp120, C3, V4, C4, and V5 remained totally unchanged. Within V1, three residues within a 14-amino acid stretch experienced five substitutions and in C5 three residues within a 7-amino acid stretch experienced four substitutions. This finding, that certain residues clustered within particular domains (V1/V2, C5, and gp41) experienced multiple substitutions under a defined environmental stressor, suggests that the degree of adaptive plasticity exhibited by the HIV envelope is limited. Based on this observation it may be possible, using a set of antibodies to various envelope epitopes, to discern a set of rules which explain the interactions of the various envelope domains with each other and with their environment. The insight gained into the physiologic constraints that the envelope proteins are subject to may be useful in developing therapeutic and vaccination strategies.