Recognition Patterns of the C1/C2 Epitopes Involved in Fc-Mediated Response in HIV-1 Natural Infection and the RV114 Vaccine Trial

Abstract

Antibodies (Abs) specific for CD4-induced envelope (Env) epitopes within constant region 1 and 2 (C1/C2) were induced in the RV144 vaccine trial, where antibody-dependent cellular cytotoxicity (ADCC) correlated with reduced risk of HIV-1 infection. We combined X-ray crystallography and fluorescence resonance energy transfer-fluorescence correlation spectroscopy to describe the molecular basis for epitopes of seven RV144 Abs and compared them to A32 and C11, C1/C2 Abs induced in HIV infection. Our data indicate that most vaccine Abs recognize the 7-stranded β-sandwich of gp120, a unique hybrid epitope bridging A32 and C11 binding sites. Although primarily directed at the 7-stranded β-sandwich, some accommodate the gp120 N terminus in C11-bound 8-stranded conformation and therefore recognize a broader range of CD4-triggered Env conformations. Our data also suggest that Abs of RV144 and RV305, the RV144 follow-up study, although likely initially induced by the ALVAC-HIV prime encoding full-length gp120, matured through boosting with truncated AIDSVAX gp120 variants. IMPORTANCE Antibody-dependent cellular cytotoxicity (ADCC) correlated with a reduced risk of infection from HIV-1 in the RV144 vaccine trial, the only HIV-1 vaccine trial to date to show any efficacy. Antibodies specific for CD4-induced envelope (Env) epitopes within constant region 1 and 2 (cluster A region) were induced in the RV144 trial and their ADCC activities were implicated in the vaccine efficacy. We present structural analyses of the antigen epitope targets of several RV144 antibodies specific for this region and C11, an antibody induced in natural infection, to show what the differences are in epitope specificities, mechanism of antigen recognition, and ADCC activities of antibodies induced by vaccination and during the course of HIV infection. Our data suggest that the truncated AIDSVAX gp120 variants used in the boost of the RV144 regimen may have shaped the vaccine response to this region, which could also have contributed to vaccine efficacy.

Detection of the HIV-1 accessory proteins Nef and Vpu by flow cytometry represents a new tool to study their functional interplay within a single infected CD4+ T cell

“…A series of recent studies using LucR.T2A IMCs have hypothesized that Vpu can compensate for the absence of Nef expression by fully downregulating cell-surface CD4 (93)(94)(95)(96)(97). Our results show that this is not the case.…”

“…Infectious molecular clones encoding for the Renilla luciferase (LucR) reporter gene upstream of the nef sequence, and a T2A ribosome-skipping peptide to drive Nef expression are widely employed to quantify anti-HIV-1 ADCC responses (81)(82)(83)(84)(85)(86)(87)(88)(89)(90)(91)(92). Despite evidence that Nef-mediated CD4 downregulation is impaired when using these IMCs (54,79), a series of recent studies have hypothesized that Vpu can compensate for the absence of Nef expression and completely downregulate CD4 on its own (93)(94)(95)(96)(97). To evaluate this hypothesis, we used our intracellular staining to measure Nef and Vpu expression levels and study their impact on ADCC responses mediated by nnAbs against cells infected with IMC-LucR.T2A constructs.…”

Effects of gp120 Inner Domain (ID2) Immunogen Doses on Elicitation of Anti-HIV-1 Functional Fc-Effector Response to C1/C2 (Cluster A) Epitopes in Mice

“…Sera from RV305 subjects were capable of effective ADCC with increased potency and breadth compared to C1/C2 mAbs isolated from RV144 subjects [ 48 , 49 ]. Our structural analyses RV144 and RV305 mAbs confirmed their Cluster A specificity [ 50 ].…”

“…Relative fluorescence antibody dependent cellular cytotoxicity assays were carried out as previously described, with minor adjustments [ 50 , 52 , 53 ]. Briefly, EGFP-CEM-NKR-CCR5SNAP cells were coated with one of three antigen targets: gp120 93TH057 core, full-length gp120 93TH057 or gp120 BaL , all at 50 µg/mL.…”

Incorporating the Cluster A and V1V2 Targets into a Minimal Structural Unit of the HIV-1 Envelope to Elicit a Cross-Clade Response with Potent Fc-Effector Functions

“…We recently developed an immunogen referred to as inner domain 2 (ID2), which stably expresses the conformational Cluster A epitope target within a minimal structural unit of gp120 [ 26 ]. Immunization studies in BALB/c mice with ID2 demonstrated that ID2 was highly immunogenic and that the Cluster A-specific responses were induced at levels that provided potent Fc-effector activities, including ADCC [ 27 , 28 , 29 , 30 ]. Here, we describe the engineering, functional analyses and immunogenicity of ID2-V1V2, an immunogen variant that incorporates both the Cluster A and V1V2 regions of HIV-1 Env to induce Fc-effector function responses to both epitope targets implicated in the protective effect of the RV144 vaccine trial.…”