Two Families of Env Antibodies Efficiently Engage Fc-Gamma Receptors and Eliminate HIV-1-Infected Cells

Abstract

HIV-1 conceals epitopes of its envelope glycoproteins (Env) recognized by antibody (Ab)-dependent cellular cytotoxicity (ADCC)-mediating antibodies. These Abs, including anti-coreceptor binding site (CoRBS) and anti-cluster A antibodies, preferentially recognize Env in its “open” conformation. The binding of anti-CoRBS Abs has been shown to induce conformational changes that further open Env, allowing interaction of anti-cluster A antibodies. We explored the possibility that CoRBS Abs synergize with anti-cluster A Abs to engage Fc-gamma receptors to mediate ADCC. We found that binding of anti-CoRBS and anti-cluster A Abs to the same gp120 is required for interaction with soluble dimeric FcγRIIIa in enzyme-linked immunosorbent assays (ELISAs). We also found that Fc regions of both Abs are required to optimally engage FcγRIIIa and mediate robust ADCC. Taken together, our results indicate that these two families of Abs act together in a sequential and synergistic fashion to promote FcγRIIIa engagement and ADCC. IMPORTANCE The “open” CD4-bound conformation of HIV-1 envelope glycoproteins is the primary target of antibody-dependent cellular cytotoxicity (ADCC)-mediating antibodies present in HIV-positive (HIV+) sera, such as anti-coreceptor binding site and anti-cluster A antibodies. Here we report that the binding of these two families of antibodies is required to engage FcγRIIIa and mediate ADCC.

Antibody-Induced Internalization of HIV-1 Env Proteins Limits Surface Expression of the Closed Conformation of Env

“…To determine whether Env-Abs complexes can remain stable over time at the surface of infected cells, we selected nine anti-Env Abs that recognize different conformations and epitopes of Env. These Abs target different sites on Env, such as the gp120-gp41 interface (PGT151) (29), glycans on the gp120 outer domain (2G12) (30), the V1/V2 apex (PG9) (31), and V3 glycans (PGT121, PGT126) (32), as well as CD4-induced (CD4i) targeting epitopes, including the coreceptor binding site (CoRBS; 17b and N12-i2) and the cluster A region in the gp120 inner domain (A32, N5-i5) (33). This panel of antibodies was selected because it can distinguish "closed" versus "open" trimers.…”

“…It is now well established that the conformation of Env at the cell surface influences antibody binding and ADCC responses (38)(39)(40). Nonneutralizing antibodies and bNAbs target different Env conformations, with most bNAbs preferentially recognizing Env in its "closed" conformation (state 1) (36), whereas the nNAbs used here target epitopes that are only exposed upon Env interaction with CD4 (9,33,37,42). To verify whether the differences in cell surface reduction of Env between bNAbs and nNAbs was due to their differential recognition of infected cells, we infected primary CD4 ϩ T cells with NL4.3 ADA defective for Nef and Vpu accessory proteins (Nef-Vpu-) that fails to downregulate CD4.…”

An Asymmetric Opening of HIV-1 Envelope Mediates Antibody-Dependent Cellular Cytotoxicity

“…Indeed, it was shown that CD4mcs initially open the Env trimer allowing for CoRBS Abs engagement, which further opens the trimer, exposing cluster A epitopes . Binding of both CoRBS and cluster A Abs to Env efficiently engages FcgRIIIa and mediates robust ADCC (Anand et al, 2018).…”

Exposing HIV-1 Env: Implications for therapeutic strategies

“…Finzi HIV-1 Env: Joe Doupe Lecture vivo settings. The CD4mc have been shown to sensitize HIV-1-infected cells to ADCC mediated by antibodies present in sera, cervicovaginal fluids and breast milk from HIV-1-infected individuals [22][23][24][25][26][27][28], as well as sera from gp120-vaccinated non-human primates [29,30]. This strategy was also shown to work against primary CD4 T cells isolated from HIV+ individuals using their own (autologous) sera [27,28].…”

“…From the different CD4i antibodies present in HIV+ sera that recognize the CD4-bound conformation, those Finzi HIV-1 Env: Joe Doupe Lecture recognizing the gp120 inner domain cluster A region present the most potent ADCC-mediating activity [5,31]. Interestingly, CD4mc are unable to enhance recognition of HIV-1-infected cells by anti-cluster A Abs in the absence of co-receptor binding site (CoRBS) antibodies (such as 17b) [22,24]. These results indicate that CD4mc initially open the trimeric Env enough to allow the binding of CoRBS antibodies but not anti-cluster A antibodies.…”