Abstract
Identification of broadly cross-reactive HIV-1-neutralizing antibodies (bnAbs) may assist vaccine immunogen design. Here we report a novel human monoclonal antibody (mAb), designated m43, which co-targets the gp120 and gp41 subunits of the HIV-1 envelope glycoprotein (Env). M43 bound to recombinant gp140 s from various primary isolates, to membrane-associated Envs on transfected cells and HIV-1 infected cells, as well as to recombinant gp120 s and gp41 fusion intermediate structures containing N-trimer structure, but did not bind to denatured recombinant gp140 s and the CD4 binding site (CD4bs) mutant, gp120 D368R, suggesting that the m43 epitope is conformational and overlaps the CD4bs on gp120 and the N-trimer structure on gp41. M43 neutralized 34% of the HIV-1 primary isolates from different clades and all the SHIVs tested in assays based on infection of peripheral blood mononuclear cells (PBMCs) by replication-competent virus, but was less potent in cell line-based pseudovirus assays. In contrast to CD4, m43 did not induce Env conformational changes upon binding leading to exposure of the coreceptor binding site, enhanced binding of mAbs 2F5 and 4E10 specific for the membrane proximal external region (MPER) of gp41 Envs, or increased gp120 shedding. The overall modest neutralization activity of m43 is likely due to the limited binding of m43 to functional Envs which could be increased by antibody engineering if needed. M43 may represent a new class of bnAbs targeting conformational epitopes overlapping structures on both gp120 and gp41. Its novel epitope and possibly new mechanism(s) of neutralization could helpdesign improved vaccine immunogens and candidate therapeutics.
Highlights
Development of an effective HIV-1 vaccine will likely require elicitation of broad and potent neutralizing antibody responses against the envelope glycoprotein (Env)
PG9/16, VRC01-03 and PG9/16-like Abs were isolated by single memory B-cell-sorting in combination with high-throughput screening for broadly cross-reactive HIV-neutralizing antibodies (bnAbs)-secreting B cells [12,22]. 2F5, 4E10 and 2G12 were isolated by conventional Epstein-Barr Virus (EBV)-mediated immortalization of antibodysecreting B cells, while HJ16 was isolated by using an improved EBV-mediated memory B cell immortalization method in combination with high-throughput parallel screening with a panel of recombinant Env-based antigens
CD4 induced (CD4i) scFv m9 showed increased potency in peripheral blood mononuclear cells (PBMCs)-p24 assays than in TZM-bl assays, which is consistent with the observation we reported previously [44]
Summary
Development of an effective HIV-1 vaccine will likely require elicitation of broad and potent neutralizing antibody (nAb) responses against the envelope glycoprotein (Env). Numerous new bnmAbs that are more potent than these four bnmAbs have been identified in the past two to three years, including PG9/PG16 [10], HJ16 [11], VRC01-03 [12], and very recently reported PGTs [13], VRC01-like Abs (VRC-CHs, VRC-PG04) [14], and 8ANCs, Among the above mentioned bnmAbs, b12 was the only mAb isolated by antibody phage display [5]. PG9/16, VRC01-03 and PG9/16-like Abs were isolated by single memory B-cell-sorting in combination with high-throughput screening for bnAb-secreting B cells [12,22]. We developed the competitive antigen panning (CAP) methodology for isolation of gp41specific mAbs that bind to Env. After panning a phage-displayed immune antibody Fab library by CAP and screening the panned libraries for gp41-specific mAbs, we found one mAb, designated m43, which bound to both gp120 and gp, as well as to recombinant gp140s. M43 exhibited unique features in binding to Env trimers and may represent a new class of bnAbs
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