Efficiency of neutralizing antibodies targeting the CD4-binding site: influence of conformational masking by the V2 loop in R5-tropic clade C simian-human immunodeficiency virus

Abstract

In R5-tropic clade C simian-human immunodeficiency viruses (SHIV-Cs), we identified a 3-asparagine (3N) deletion mutation in the V2 loop stem of gp120 as the major determinant of neutralization escape of the anti-CD4-binding site (anti-CD4-bs) neutralizing monoclonal antibody (nMAb) b12. However, the more potent anti-CD4-bs nMAbs VRC01 and VRC03 were not sensitive to this mutation. Using isogenic tier 1 or tier 2 proviruses differing only in the 3N mutation, we showed that this mutation might result in selective conformational b12 epitope masking. Therefore, human immunodeficiency virus (HIV) Env immunogens targeting the CD4-bs and designed to neutralize tier 2 viruses should take conformational masking by the V2 loop into account.

Fig. 1.

Sequence alignment of the V1V2 loop of SHIV-1157ipEL-p (early stage), carrying the recently transmitted env of the Zambian clade C isolate 1157i, and its mutant SHIV-1157ipEL-pΔ3N, as well as SHIV-1157ipd3N4 (late stage) and its mutant SHIV-1157ipd3N4+3N. The black box highlights the insertion/deletion of 3 asparagines in the V2 stem.

Fig. 2.

Neutralization sensitivities of SHIV-1157ipEL-p (early stage) and its mutant SHIV-1157ipEL-pΔ3N to b12 and sCD4 (A) and SHIV-1157ipd3N4 (late stage) and its mutant SHIV-1157ipd3N4+3N to b12 and sCD4 (B) and of SHIV-1157ipEL-p (early stage) and its mutant SHIV-1157ipEL-pΔ3N to VRC01 and VRC03 (C) and SHIV-1157ipd3N4 (late stage) and its mutant SHIV-1157ipd3N4+3N to VRC01 and VRC03 (D). The data shown are representative results obtained from three independent experiments.

Fig. 3.

Virion capture assay of SHIV-1157ipEL-p (early stage) and its mutant SHIV-1157ipEL-pΔ3N and SHIV-1157ipd3N4 (late stage) and its mutant SHIV-1157ipd3N4+3N, using nMAbs b12 and VRC01. Herceptin is used as a negative control. The error bars represent the standard deviations measured in one experiment carried out in triplicate. The data shown are representative results obtained from three independent experiments.

Fig. 4.

Molecular modeling of SHIV-1157ipEL-p in b12-bound conformation, with contact residues between b12 and gp120 shown in yellow (A), and of SHIV-1157ipEL-p in VRC01-bound conformation, with contact residues between VRC01 and gp120 shown in yellow (B). In both conformations, the potential location of the V2 loop is indicated in pink for SHIV-1157ipEL-p (early) and in green for SHIV-1157ipd3N4 (late).