HUMAN-IMMUNODEFICIENCY-VIRUS TYPE-1 MUTANTS THAT ESCAPE NEUTRALIZATION BY HUMAN MONOCLONAL-ANTIBODY IGG1B12

IgG1b12, a human monoclonal antibody (MAb) to an epitope overlapping t he CD4-binding site on gp120, has broad and potent neutralizing activi ty against most primary human immunodeficiency virus type 1 (HIV-1) is olates. To assess whether and how escape mutants resistant to IgG1b12 can be generated, we cultured primary HIV-1 strain JRCSF in its presen ce. An escape mutant emerged which aas approximately 100-fold more res istant to neutralization by IgG1b12. Both virion-associated and solubi lized gp120 from this variant had a reduced affinity for IgG1b12, and sequencing of its env gene showed that amino acid substitutions had oc curred at three positions within gp120, Two (D164N and D182N) were loc ated in V2, and one (P365L) was in C3. By site-directed mutagenesis, w e demonstrated that the D182N and P365L mutations, but not D164N, cont ribute to the IgG1b12-resistant phenotype. However, the former two sub stitutions, individually or in combination, hinder the replication of the neutralization-resistant virus. Introduction of the D164N substitu tion into the P365L variant results in a nonviable virus (D164N/P365L) . In contrast, addition of D164N to the D182N or D182N/P365L mutant pa rtially restored replicative function to near wild-type levels. Furthe rmore, we found that all of the IgG1b12-resistant mutant viruses remai ned sensitive to other human MAbs, such as 2G12 and 2F5, and to the CD 4-IgG molecule, except that the P365L-containing mutant was slightly r esistant to CD4-IgG. These results suggest that escape from IgG1b12 ne utralization is due to a local rather than a global modification of th e gp120 structure. Our findings have implications for the therapeutic and prophylactic applications of antibodies for HIV-1 infection.