Factors determining the breadth and potency of neutralization by V3-specific human monoclonal antibodies derived from subjects infected with clade A or clade B strains of human immunodeficiency virus type 1

Abstract

The neutralizing activities of anti-V3 antibodies for HIV-1 isolates is affected both by sequence variation within V3 and by epitope masking by the V1/V2 domain. To analyze the relative contribution of V3 sequence variation, chimeric Env genes that contained consensus V3 sequences from seven HIV-1 subtypes in the neutralization-sensitive SF162 Env backbone were constructed. Resulting viral pseudotypes were tested for neutralization by 15 anti-V3 MAbs isolated from humans infected with viruses of either subtype B (anti-V3(B) MAbs) or subtype A (anti-V3(A) MAbs). Pseudovirions with the subtype B consensus V3 sequence were potently neutralized (IC(50) < 0.006 microg/ml) by all but one of these MAbs, while pseudovirions with V3 subtypes A, C, F, H, AG, and AE were generally neutralized more effectively by anti-V3(A) MAbs than by anti-V3(B) MAbs. A V1/V2-masked Env version of SF162 Env with the consensus B V3 sequence was also neutralized by these MAbs, although with considerably lower potency, while similarly masked chimeras with V3 sequences of subtype A, C, or AG were weakly neutralized by anti-V3(A) MAbs but not by anti-V3(B) MAbs. Mutations in the V1/V2 domain of YU-2 Env increased the sensitivity of this highly resistant Env to a pool of anti-V3(B) MAbs several thousand-fold. These results demonstrated (i) the exceptional sensitivity of representative V3 domains of multiple subtypes to neutralization in the absence of epitope masking, (ii) the broader neutralizing activity of anti-V3(A) MAbs for viruses containing diverse V3 sequences, and (iii) the generality and dominant effect of V1/V2 masking on restriction of V3-mediated neutralization.

FIG. 1.

(A) Structures of chimeric envelopes used for examining the roles of the V1/V2 domains on neutralization sensitivity of V3 epitopes. Chimeric envelopes were constructed in the SF162 backbone (gray bars) by exchanging the V1/V2 and/or V3 domains with the corresponding domains of JR-FL Env (white bars). (B) Comparison of V3 loop sequences of JR-FL and SF162 Env proteins.

FIG. 2.

Structures of chimeric envelopes used for preparing HIV-1 pseudotypes. (A) Model of chimeric Envs used in these studies. The Envs utilized the SF162 backbone (gray bars) with modified V3 sequences (white bars). The V1/V2 domains of several of the V3 chimeric Envs were replaced by that of JR-FL, resulting in epitope-masked Envs which were relatively resistant to V3-mediated neutralization. (B) Sequences of substituted V3 domains. Residues that vary from the subtype B consensus sequence residues are indicated.

FIG. 3.

Neutralization curves obtained for pooled anti-V3_B MAbs against SF162 Env with the consensus B V3 sequence (circles), SF162 Env with the YU-2 V2 sequence (triangles), parental YU-2 Env (squares), and YU-2 Env in which the indicated four positions in the V1/V2 domain were mutated (diamonds).