Identification of CD4-Binding Site Dependent Plasma Neutralizing Antibodies in an HIV-1 Infected Indian Individual.

Dissecting antibody specificities in the plasma of HIV-1 infected individuals that develop broadly neutralizing antibodies (bNAbs) is likely to provide useful information for refining target epitopes for vaccine design. Several studies have reported CD4-binding site (CD4bs) antibodies as neutralization determinants in the plasma of subtype B-infected individuals; however there is little information on the prevalence of CD4bs specificities in HIV-infected individuals in India. Here, we report on the presence of CD4bs antibodies and their contribution to virus neutralization in the plasma from a cohort of HIV-1 infected Indian individuals. Plasma from 11 of the 140 HIV-1 infected individuals (7.9%) studied here exhibited cross-neutralization activity against a panel of subtype B and C viruses. Analyses of these 11 plasma samples for the presence of CD4bs antibodies using two CD4bs-selective probes (antigenically resurfaced HXB2gp120 core protein RSC3 and hyperglycosylated JRFLgp120 mutant ΔN2mCHO) revealed that five (AIIMS 617, 619, 627, 642, 660) contained RSC3-reactive plasma antibodies and only one (AIIMS 660) contained ΔN2mCHO-reactive antibodies. Plasma antibody depletion and competition experiments confirmed that the neutralizing activity in the AIIMS 660 plasma was dependent on CD4bs antibodies. To the best of our knowledge, this is the first study to report specifically on the presence of CD4bs antibodies in the plasma of a cohort of HIV-1 infected Indian donors. The identification of CD4bs dependent neutralizing antibodies in an HIV-1 infected Indian donor is a salient finding of this study and is supportive of ongoing efforts to induce similar antibodies by immunization.

The presence of glutamine at position 315 but not epitope masking predominantly hinders HIV subtype C neutralization by the anti-V3 antibody B4e8.

Antibody B4e8 exhibits modest cross-neutralizing activity, with preference for HIV subtype B. This preference might be explained by B4e8׳s extensive interaction with Arg315, which occurs at the center of most subtype B V3 sequences but is replaced by Gln in subtype C. The extent to which B4e8׳s ability to neutralize subtype C strains is hindered by Gln315 and/or other factors, e.g. epitope masking, is unclear. We confirmed here that an Arg315-to-Gln substitution in a subtype B virus abrogates B4e8 neutralizing activity. Conversely, B4e8-resistant subtype C viruses were rendered sensitive upon Gln 315-to-Arg substitution. V2 region swapping between B4e8-sensitive and- resistant subtype C strains revealed a role for V2 in limiting B4e8 access, but this was less significant than the absence of Arg315. Our findings, while illustrating the importance of Arg315 for B4e8, suggest that some subtype C strains may be vulnerable to B4e8 derivatives capable of binding stronger to Gln315-containing sequences.

A bacterial lipooligosaccharide that naturally mimics the epitope of the HIV-neutralizing antibody 2G12 as a template for vaccine design.

The broadly neutralizing antibody 2G12 binds a fairly conserved cluster of oligomannose sugars on the HIV surface glycoprotein gp120, which has led to the hypothesis that these sugars pose potential vaccine targets. Here, we present the chemical analysis, antigenicity, and immunogenicity of a bacterial lipooligosaccharide (LOS) comprised of a manno-oligosaccharide sequence analogous to the 2G12 epitope. Antigenic similarity of the LOS to oligomannose was evidenced by 2G12 binding to the LOS and the inability of sera elicited against synthetic oligomannosides, but incapable of binding natural oligomannose, to bind the LOS. Immunization with heat-killed bacteria yielded epitope-specific serum antibodies with the capacity to bind soluble gp120. Although these sera did not exhibit specific anti-HIV activity, our data suggest that this LOS may find utility as a template for the design of glycoconjugates to target HIV.