A Global Neutralization Resistance Phenotype of Human Immunodeficiency Virus Type 1 Is Determined by Distinct Mechanisms Mediating Enhanced Infectivity and Conformational Change of the Envelope Complex

Abstract

We have described previously genetic characterization of neutralization-resistant, high-infectivity, and neutralization-sensitive, low-infectivity mutants of human immunodeficiency virus type 1 (HIV-1) MN envelope. The distinct phenotypes of these clones are attributable to six mutations affecting functional interactions between the gp120 C4-V5 regions and the gp41 leucine zipper. In the present study we examined mechanisms responsible for the phenotypic differences between these envelopes using neutralization and immunofluorescence assays (IFA). Most monoclonal antibodies (MAbs) tested against gp120 epitopes (V3, CD4 binding site, and CD4-induced) were 20 to 100 times more efficient at neutralizing pseudovirus expressing sensitive rather than resistant envelope. By IFA cells expressing neutralization sensitive envelope bound MAbs to gp120 epitopes more, but gp41 epitopes less, than neutralization-resistant envelope. This binding difference appeared to reflect conformational change, since it did not correlate with the level of protein expression or gp120-gp41 dissociation. This conformational change was mostly attributable to one mutation, L544P, which contributes to neutralization resistance but not to infectivity enhancement. The V420I mutation, which contributes a major effect to both high infectivity and neutralization resistance, had no apparent effect on conformation. Notably, a conformation-dependent V3 neutralization epitope remained sensitive to neutralization and accessible to binding by MAbs on neutralization-resistant HIV-1 envelope. Sensitivity to sCD4 did not distinguish the clones, suggesting that the phenotypes may be related to post-CD4-binding effects. The results demonstrate that neutralization resistance can be determined by distinguishable effects of mutations, which cause changes in envelope conformation and/or function(s) related to infectivity. A conformation-dependent V3 epitope may be an important target for neutralization of resistant strains of HIV-1.The principal mechanism by which effective viral vaccines confer protective immunity is by induction of antibodies capable of neutralizing prevalent strains of virus (21). Efforts to develop a vaccine to protect against human immunodeficiency virus type 1 (HIV-1) infection are complicated by the fact that virus strains in infected patients tend to be highly resistant to neutralization. Studies that clarify the mechanisms responsible for this neutralization resistance may provide important leads regarding possible methods for the induction of potent neutralizing antibody responses capable of neutralizing these primary isolates. Previously, we described the selection and characterization of a neutralization-resistant mutant of the MN strain of HIV-1, which generally resists neutralization by human sera. The resistance phenotype was found to be determined by polymorphisms located in the C-terminal region of gp120 and N-terminal region of gp41 (16,17). There were two residues in gp120 and four in gp41 involved. Genetic analysis demonstrated t...

Concordant Modulation of Neutralization Resistance and High Infectivity of the Primary Human Immunodeficiency Virus Type 1 MN Strain and Definition of a Potential gp41 Binding Site in gp120

“…The neutralization-resistant phenotype was found to be associated with a high-infectivity phenotype, which was attributable to five of the six mutations. The high infectivity is, in turn, probably the result of a number of steps leading to a very high efficiency of virus-cell membrane fusion (33). Here we report additional studies on the mechanisms of these phenotypes.…”

“…Previous studies involved the neutralization-sensitive, T-cellline-adapted (TCLA), MN strain (MN-TCLA) strain and a clone derived from it, designated E6, by in vitro selection with a highly neutralizing human serum (33)(34)(35). The neutralization-resistant mutant phenotype of MN-E6 was attributable to two mutations in gp120 and four mutations in the leucine zipper (LZ) structure of gp41.…”

Multiple Interactions across the Surface of the gp120 Core Structure Determine the Global Neutralization Resistance Phenotype of Human Immunodeficiency Virus Type 1

“…Induction of potent neutralizing antibodies is a common property of successful viral vaccines (26). Insights into the mechanisms of neutralization resistance of primary isolates of HIV-1 may indicate possible approaches to neutralization of such viruses and facilitate vaccine development.Our laboratory has previously reported studies of the MN strain of HIV-1 that have begun to address this issue (14,(21)(22)(23). The original isolate of the MN virus was propagated in a continuous T-cell line and is considered T-cell line adapted (TCLA) (12, 30).…”

“…Our laboratory has previously reported studies of the MN strain of HIV-1 that have begun to address this issue (14,(21)(22)(23). The original isolate of the MN virus was propagated in a continuous T-cell line and is considered T-cell line adapted (TCLA) (12,30).…”

“…In an early study a neutralization-resistant variant of this strain was studied that was produced by growth of the MN strain virus in the presence of a highly neutralizing human serum (22). Through evaluation of env genes cloned from the parent strain (MN-TCLA) and neutralization-resistant virus (MN-E6), it was determined that the neutralization resistance was due to mutations that altered functional interactions between gp120 and gp41 (21)(22)(23). Moreover, the responsible mutations included amino acid substitutions in the CD4 and putative coreceptor binding domains of gp120 and in the first heptad repeat (HR1) of gp41.…”