Analysis of the neutralization breadth of the anti-V3 antibody F425-B4e8 and re-assessment of its epitope fine specificity by scanning mutagenesis

Abstract

The identification of cross-neutralizing antibodies to HIV-1 is important for designing antigens aimed at eliciting similar antibodies upon immunization. The monoclonal antibody (mAb) F425-B4e8 had been suggested previously to bind an epitope at the base of V3 and shown to neutralize two primary HIV isolates. Here, we have assessed the neutralization breadth of mAb F425-B4e8 using a 40-member panel of primary HIV-1 and determined the epitope specificity of the mAb. The antibody was able to neutralize 8 clade B viruses (n=16), 1 clade C virus (n=11), and 2 clade D viruses (n=6), thus placing it among the more broadly neutralizing anti-V3 antibodies described so far. Contrary to an initial report, results from our scanning mutagenesis of the V3 region suggest that mAb F425-B4e8 interacts primarily with the crown/tip of V3, notably Ile(309), Arg(315), and Phe(317). Despite the somewhat limited neutralization breadth of mAb F425-B4e8, the results presented here, along with analyses from other cross-neutralizing anti-V3 mAbs, may facilitate the template-based design of antigens that target V3 and permit neutralization of HIV-1 strains in which the V3 region is accessible to antibodies.

Human Immunodeficiency Virus Type 2 (HIV-2)/HIV-1 Envelope Chimeras Detect High Titers of Broadly Reactive HIV-1 V3-Specific Antibodies in Human Plasma

“…Previously, we along with others have demonstrated that HIV-2 Env could be used as a scaffold to present HIV-1 MPER and CD4i epitopes in the context of a functional glycoprotein and that such viruses could serve as sensitive and specific probes for HIV-1-elicited epitope-specific NAbs (18,19,34,61,102 In the present study, we focused on HIV-1 V3, which continues to attract substantial attention as a target of NAbs (2,54,72,74,76,99,107). Mamounas and colleagues first demonstrated that a chimeric virus containing an HIV-2 backbone and an HIV-1 MN V3 loop was capable of infecting human T cells and showed susceptibility to HIV-1 V3-specific antiserum (64).…”

“…We tested the ability of the HIV-2 KR.X7 /HIV-1 V3 chimeras to detect V3-specific antibodies using two HIV-1 MAbs, 447-52D and F425 B4e8, whose V3 epitope specificities are well established (2,72,93,108). HIV-2 KR.X7 YU2 V3 was potently neutralized by both 447-52D and F425 B4e8 (IC 50 s of 0.001 g/ml and 0.004 g/ml, respectively), and HIV-2 KR.X7 Ccon V3 was also effectively neutralized by the same antibodies but at higher concentrations (IC 50 s of 0.03 g/ml and 0.48 g/ml, respectively) ( Table 1 and Fig.…”

“…The V3 region of such viruses was found to be highly immunogenic and to be a sensitive target of V3-specific NAbs (33,45,69,71,81,88). Certain viruses of the CCR5 phenotype, including the brain-derived HIV-1 YU2 molecular clone (60), were also found to be moderately sensitive to V3 NAbs as were some other HIV-1 strains that were variably laboratory adapted (5,58,72). Conversely, most primary (non-laboratory adapted) CCR5-tropic viruses, including molecularly derived transmitted/ early founder viral Envs from more than 50 subjects acutely infected with clade B virus (49), were found to be resistant to neutralization by V3-specific NAbs, including the human MAbs 447-52D and F425 B4e8.…”

“…This approach, however, is limited to NAbs with linear epitopes that have sufficient affinity for peptide binding outside the context of the native glycoprotein trimer. A third strategy has been to make site-directed mutations in NAb epitopes in Env glycoproteins and to use these proteins as probes in binding, absorption, or infectivity experiments (54,61,62,72). A fourth approach has been to make reciprocal exchanges between homologous regions of different HIV-1 Env glycoproteins to look for gain or loss of NAb sensitivity (54,68,76,86,87,89).…”

Applications of immunochemistry in human health: advances in vaccinology and antibody design (IUPAC Technical Report)

“…The tip of the V3 loop is then able to dock with the cellular chemokine co-receptor (CXCR4 or CCR5), which ultimately leads to virus entry into the cell. Several crystal structures are now available for neutralizing antibody fragments bound to peptides derived from the HIV-1-gp120 V3 loop [166][167][168][169][170].…”