A Highly Conserved Residue of the HIV-1 gp120 Inner Domain Is Important for Antibody-Dependent Cellular Cytotoxicity Responses Mediated by Anti-cluster A Antibodies

Abstract

i Previous studies have shown that sera from HIV-1-infected individuals contain antibodies able to mediate antibody-dependent cellular cytotoxicity (ADCC). These antibodies preferentially recognize envelope glycoprotein (Env) epitopes induced upon CD4 binding. Here, we show that a highly conserved tryptophan at position 69 of the gp120 inner domain is important for ADCC mediated by anti-cluster A antibodies and sera from HIV-1-infected individuals. Human immunodeficiency virus type 1 (HIV-1) infection elicits a potent B cell response resulting in the production of antibodies (Abs) against the envelope glycoproteins (Env), which are exposed at the surface of viral particles and infected cells (1). We recently reported that these antibodies have the potential to eliminate HIV-1-infected cells by mediating antibody-dependent cellular cytotoxicity (ADCC) (2, 3). We found that these nonneutralizing CD4-induced (CD4i) ADCC-mediating antibodies are present in sera (2, 4), breast milk (4), and cervicovaginal lavage fluid (3, 4) of HIV-1-infected individuals and preferentially target Env in its CD4-bound "open" conformation. However, in order to evade ADCC responses, HIV-1 has developed a highly sophisticated strategy to keep Env at the surface of infected cells in the unbound "closed" conformation. HIV-1 accomplishes this through its accessory proteins Nef and Vpu, which decrease the overall amount of Env (via Vpu-mediated BST-2 downregulation) and CD4 at the cell surface (2, 5-7). In addition, decreased amounts of Env at the cell surface due to efficient internalization also help the virus to avoid ADCC responses (8). In agreement with the necessity for HIV-1 to avoid exposing Env in the CD4-bound conformation, we recently showed that forcing Env to adopt this conformation with small CD4 mimetics (CD4mc) sensitizes HIV-1-infected cells to ADCC mediated by sera, breast milk, and cervicovaginal fluids from HIV-1-infected subjects (4).Previous studies showed that the human monoclonal antibody (MAb) A32 targets an ADCC epitope commonly detected by antibodies present in sera from HIV-1-infected individuals (2, 5, 9, 10). Accordingly, an A32 Fab fragment blocked the majority of ADCC-mediating antibody (Ab) activity in plasma from chronically HIV-1-infected individuals (9). A subsequent study showed that the majority of ADCC responses were targeted against the gp120 core but not its variable regions V1, V2, V3, and V5 (2). Here, we evaluated the ADCC-mediating capacity of a panel of human antibodies targeting several well-defined epitopes in gp120 and gp41 and sera from randomly selected chronically HIV-1 clade B-infected individuals (HIV ϩ sera).We infected CEM.NKr cells with a panel of HIV-1 NL4.3-green fluorescent protein (GFP) constructs containing the ADA-Env and either wild-type or defective nef and vpu genes, as described previously (2, 5). Furthermore, we examined a wellcharacterized infectious molecular HIV-1 clone constructed from a transmitted/founder (T/F) virus (CH77) (11-14) containing intact or defective nef an...

Influence of the Envelope gp120 Phe 43 Cavity on HIV-1 Sensitivity to Antibody-Dependent Cell-Mediated Cytotoxicity Responses

“…infected individuals and to mediate potent ADCC responses (13,14,18,(20)(21)(22)(23)(24)(25)(26). Therefore, our results raise the intriguing possibility that histidine 375 present in the predominant strain replicating in Thailand might have contributed to the efficacy of the trial by spontaneously exposing epitopes recognized by ADCC-mediating antibodies elicited by the RV144 vaccine regimen.…”

“…In contrast to the limited recognition of clade B, C, and D HIV-1-infected cells by A32, 17b, and antibodies within HIV ϩ sera (Fig. 2) (13,18,20,22,37), cells infected with wild-type CRF01_AE Env (H375) were better recognized by both CD4i monoclonal antibodies (MAbs) as well as polyclonal sera (Fig. 4C to F).…”

“…In parallel, primary CD4 ϩ T cells were infected with SHIVs expressing clade C and D HIV-1 Env with the same substitutions in residue 375 (WT and S375H and S375W mutants). Since it is now well established that CD4 present on the cell surface affects Env conformation by forcing it to assume the CD4-bound conformation (13,14,21,22,35), we first evaluated the ability of all the IMCs to downregulate CD4. Figure 2 shows that all IMCs tested, independently of the residue present at position 375, efficiently downregulated CD4 from the cell surface ( Fig.…”

“…Accordingly, we recently reported that the transition of Env to the CD4-bound conformation is required for efficient interactions with ADCC-mediating antibodies (14). We reported that the replacement of serine 375 by a tryptophan residue (S375W) enhanced the exposure of epitopes recognized by anti-cluster A antibodies, known to mediate potent ADCC responses (13,14,18,(20)(21)(22)(23)(24)(25)(26). Thus, the transition of Env from the unbound to the CD4-bound conformation appears to be a prerequisite for the exposure of inner-domain ADCC epitopes.…”

A Highly Conserved gp120 Inner Domain Residue Modulates Env Conformation and Trimer Stability

“…Moreover, among these residues, W69 was recently shown to be important for efficient Env recognition by antibody-dependent cellular cytotoxicity (ADCC)-mediating anti-cluster A antibodies and also by sera from HIV-1-infected individuals (17)(18)(19)(20). Since W69 is located at the interface between layer 1 and layer 2 of the inner domain, we evaluated the contribution of hydrophobicity at this position to Env conformational changes.…”