HIV-1 Receptor Binding Site-Directed Antibodies Using a VH1-2 Gene Segment Orthologue Are Activated by Env Trimer Immunization

Abstract

Broadly neutralizing antibodies (bNAbs) isolated from chronically HIV-1 infected individuals reveal important information regarding how antibodies target conserved determinants of the envelope glycoprotein (Env) spike such as the primary receptor CD4 binding site (CD4bs). Many CD4bs-directed bNAbs use the same heavy (H) chain variable (V) gene segment, VH1-2*02, suggesting that activation of B cells expressing this allele is linked to the generation of this type of Ab. Here, we identify the rhesus macaque VH1.23 gene segment to be the closest macaque orthologue to the human VH1-2 gene segment, with 92% homology to VH1-2*02. Of the three amino acids in the VH1-2*02 gene segment that define a motif for VRC01-like antibodies (W50, N58, flanking the HCDR2 region, and R71), the two identified macaque VH1.23 alleles described here encode two. We demonstrate that immunization with soluble Env trimers induced CD4bs-specific VH1.23-using Abs with restricted neutralization breadth. Through alanine scanning and structural studies of one such monoclonal Ab (MAb), GE356, we demonstrate that all three HCDRs are involved in neutralization. This contrasts to the highly potent CD4bs-directed VRC01 class of bNAb, which bind Env predominantly through the HCDR2. Also unlike VRC01, GE356 was minimally modified by somatic hypermutation, its light (L) chain CDRs were of average lengths and it displayed a binding footprint proximal to the trimer axis. These results illustrate that the Env trimer immunogen used here activates B cells encoding a VH1-2 gene segment orthologue, but that the resulting Abs interact distinctly differently with the HIV-1 Env spike compared to VRC01.

Hyperglycosylated Stable Core Immunogens Designed To Present the CD4 Binding Site Are Preferentially Recognized by Broadly Neutralizing Antibodies

“…As shown in Table 1, most of the animals tested elicited CD4bs-directed HXBc2-neutralizing antibodies, as determined by the fold difference in ID 50 values with the CD4bs-binding-competent and -defective core inhibitors, except for the first two animals from the 3G prime-trimer boost group. These results indicate that most of the CD4bs-directed neutralizing activity detected was elicited by the YU2 gp140-F trimer boost alone, consistent with the ability of these trimers to elicit CD4bs-directed antibodies, as we have reported previously (15,43).…”

Diverse Antibody Genetic and Recognition Properties Revealed following HIV-1 Envelope Glycoprotein Immunization

“…Otherwise, we found a broad VH gene usage for all Env sub-specificities suggesting no overall bias toward a given gene segment by any of the epitopes. This is consistent with the notion that Ab HCDR3 region, not predominantly encoded by VH, dictates much of the specificity of typical vaccine-induced antibodies, as shown for previously isolated vaccine-elicited CD4bs-directed MAbs (50, 51). …”

“…The CD4bs-specific MAbs isolated in this study display similar neutralizing properties to previously described vaccine-elicited CD4bs-specific MAbs, GE136, GE148 and GE356 (30, 50). Based on mutagenesis and binding studies to define the antibody-antigen interface combined with modelling studies these MAbs attempt to bind the Env spike by a vertical angle of approach that is not permitted on tier 2 viruses, thus limiting their neutralization capacities to tier 1 viruses only (50, 51).…”

“…In contrast, for vaccines that do not induce desired Ab responses, such as the HIV-1 Env immunogens studied to date, MAb isolation provides concrete information about the fine specificities of the response. This analysis both increases our understanding of biological events taking place following vaccination and reveals the fine specificities that are induced by a given immunogen (30, 50, 56). This information can guide the design of improved immunogens aimed to favorably alter the elicited B cell response to accelerate the development of HIV-1 vaccine candidates.…”

“…Based on mutagenesis and binding studies to define the antibody-antigen interface combined with modelling studies these MAbs attempt to bind the Env spike by a vertical angle of approach that is not permitted on tier 2 viruses, thus limiting their neutralization capacities to tier 1 viruses only (50, 51). A similar mode of binding is likely for the CD4bs-directed MAbs isolated here.…”