title: Structural definition of an antibody-dependent cellular cytotoxicity response implicated in reduced risk for HIV-1 infection.
abstract: The RV144 vaccine trial implicated epitopes in the C1 region of gp120 (A32-like epitopes) as targets of potentially protective antibody-dependent cellular cytotoxicity (ADCC) responses. A32-like epitopes are highly immunogenic, as infected or vaccinated individuals frequently produce antibodies specific for these determinants. Antibody titers, as measured by enzyme-linked immunosorbent assay (ELISA) against these epitopes, however, do not consistently correlate with protection. Here, we report crystal structures of CD4-stabilized gp120 cores complexed with the Fab fragments of two nonneutralizing, A32-like monoclonal antibodies (MAbs), N5-i5 and 2.2c, that compete for antigen binding and have similar antigen-binding affinities yet exhibit a 75-fold difference in ADCC potency. We find that these MAbs recognize overlapping epitopes formed by mobile layers 1 and 2 of the gp120 inner domain, including the C1 and C2 regions, but bind gp120 at different angles via juxtaposed VH and VL contact surfaces. A comparison of structural and immunological data further showed that antibody orientation on bound antigen and the capacity to form multivalent antigen-antibody complexes on target cells were key determinants of ADCC potency, with the latter process having the greater impact. These studies provide atomic-level definition of A32-like epitopes implicated as targets of protective antibodies in RV144. Moreover, these studies establish that epitope structure and mode of antibody binding can dramatically affect the potency of Fc-mediated effector function against HIV-1. These results provide key insights for understanding, refining, and improving the outcome of HIV vaccine trials, in which relevant immune responses are facilitated by A32-like elicited responses.
  
  
  OBJECTIVE
  HIV-1 Env is a primary target for antibodies elicited during infection. Although a small number of infected individuals elicit broadly neutralizing antibodies, the bulk of the humoral response consists of antibodies that do not neutralize or do so with limited breadth but may effect protection through Fc receptor-dependent processes, such as antibody-dependent cellular cytotoxicity (ADCC). Understanding these nonneutralizing responses is an important aspect of elucidating the complete spectrum of immune response against HIV-1 infection. With this report, we provide the first atomic-level definition of nonneutralizing CD4-induced epitopes in the N-terminal region of the HIV-1 gp120 (A32-like epitopes). Further, our studies point to the dominant role of precise epitope targeting and mode of antibody attachment in ADCC responses even when largely overlapping epitopes are involved. Such information provides key insights into the mechanisms of Fc-mediated function of antibodies to HIV-1 and will help us understand the outcome of vaccine trials based on humoral immunity.
authors.affiliation: Vaccine Research Center, National Institute of Allergy and Infectious Diseases, National Institutes of Health, Bethesda, Maryland, USA.
authors.forename: Priyamvada
authors.initials: P
authors.lastname: Acharya
authors.affiliation: Institute of Human Virology, University of Maryland School of Medicine, Baltimore, Maryland, USA Department of Biochemistry and Molecular Biology, University of Maryland School of Medicine, Baltimore, Maryland, USA.
authors.forename: William D
authors.initials: WD
authors.lastname: Tolbert
authors.affiliation: Institute of Human Virology, University of Maryland School of Medicine, Baltimore, Maryland, USA Department of Biochemistry and Molecular Biology, University of Maryland School of Medicine, Baltimore, Maryland, USA.
authors.forename: Neelakshi
authors.initials: N
authors.lastname: Gohain
authors.affiliation: Institute of Human Virology, University of Maryland School of Medicine, Baltimore, Maryland, USA Department of Biochemistry and Molecular Biology, University of Maryland School of Medicine, Baltimore, Maryland, USA.
authors.forename: Xueji
authors.initials: X
authors.lastname: Wu
authors.affiliation: Institute of Human Virology, University of Maryland School of Medicine, Baltimore, Maryland, USA Department of Microbiology and Immunology, University of Maryland School of Medicine, Baltimore, Maryland, USA.
authors.forename: Lei
authors.initials: L
authors.lastname: Yu
authors.affiliation: Institute of Human Virology, University of Maryland School of Medicine, Baltimore, Maryland, USA Department of Microbiology and Immunology, University of Maryland School of Medicine, Baltimore, Maryland, USA.
authors.forename: Tongyun
authors.initials: T
authors.lastname: Liu
authors.affiliation: Institute of Human Virology, University of Maryland School of Medicine, Baltimore, Maryland, USA Department of Microbiology and Immunology, University of Maryland School of Medicine, Baltimore, Maryland, USA.
authors.forename: Wensheng
authors.initials: W
authors.lastname: Huang
authors.affiliation: Vaccine Research Center, National Institute of Allergy and Infectious Diseases, National Institutes of Health, Bethesda, Maryland, USA.
authors.forename: Chih-Chin
authors.initials: CC
authors.lastname: Huang
authors.affiliation: Vaccine Research Center, National Institute of Allergy and Infectious Diseases, National Institutes of Health, Bethesda, Maryland, USA.
authors.forename: Young Do
authors.initials: YD
authors.lastname: Kwon
authors.affiliation: Vaccine Research Center, National Institute of Allergy and Infectious Diseases, National Institutes of Health, Bethesda, Maryland, USA.
authors.forename: Robert K
authors.initials: RK
authors.lastname: Louder
authors.affiliation: Vaccine Research Center, National Institute of Allergy and Infectious Diseases, National Institutes of Health, Bethesda, Maryland, USA.
authors.forename: Timothy S
authors.initials: TS
authors.lastname: Luongo
authors.affiliation: Vaccine Research Center, National Institute of Allergy and Infectious Diseases, National Institutes of Health, Bethesda, Maryland, USA.
authors.forename: Jason S
authors.initials: JS
authors.lastname: McLellan
authors.affiliation: Vaccine Research Center, National Institute of Allergy and Infectious Diseases, National Institutes of Health, Bethesda, Maryland, USA.
authors.forename: Marie
authors.initials: M
authors.lastname: Pancera
authors.affiliation: Vaccine Research Center, National Institute of Allergy and Infectious Diseases, National Institutes of Health, Bethesda, Maryland, USA.
authors.forename: Yongping
authors.initials: Y
authors.lastname: Yang
authors.affiliation: Vaccine Research Center, National Institute of Allergy and Infectious Diseases, National Institutes of Health, Bethesda, Maryland, USA.
authors.forename: Baoshan
authors.initials: B
authors.lastname: Zhang
authors.affiliation: Institute of Human Virology, University of Maryland School of Medicine, Baltimore, Maryland, USA Department of Microbiology and Immunology, University of Maryland School of Medicine, Baltimore, Maryland, USA.
authors.forename: Robin
authors.initials: R
authors.lastname: Flinko
authors.affiliation: Institute of Human Virology, University of Maryland School of Medicine, Baltimore, Maryland, USA Department of Medicine, University of Maryland School of Medicine, Baltimore, Maryland, USA.
authors.forename: James S
authors.initials: JS
authors.lastname: Foulke
authors.affiliation: Institute of Human Virology, University of Maryland School of Medicine, Baltimore, Maryland, USA Department of Medicine, University of Maryland School of Medicine, Baltimore, Maryland, USA Medical Care Clinical Center, VA Maryland Health Care Center, Baltimore, Maryland, USA.
authors.forename: Mohammad M
authors.initials: MM
authors.lastname: Sajadi
authors.affiliation: Institute of Human Virology, University of Maryland School of Medicine, Baltimore, Maryland, USA Department of Microbiology and Immunology, University of Maryland School of Medicine, Baltimore, Maryland, USA.
authors.forename: Roberta
authors.initials: R
authors.lastname: Kamin-Lewis
authors.affiliation: Department of Pediatrics, Tulane University Medical Center, New Orleans, Louisiana, USA.
authors.forename: James E
authors.initials: JE
authors.lastname: Robinson
authors.affiliation: CEA, iBiTecS, Service d'Ingénierie Moléculaire des Protéines, Gif-sur-Yvette, France.
authors.forename: Loïc
authors.initials: L
authors.lastname: Martin
authors.affiliation: Vaccine Research Center, National Institute of Allergy and Infectious Diseases, National Institutes of Health, Bethesda, Maryland, USA.
authors.forename: Peter D
authors.initials: PD
authors.lastname: Kwong
authors.affiliation: Institute of Human Virology, University of Maryland School of Medicine, Baltimore, Maryland, USA Department of Microbiology and Immunology, University of Maryland School of Medicine, Baltimore, Maryland, USA.
authors.forename: Yongjun
authors.initials: Y
authors.lastname: Guan
authors.affiliation: Institute of Human Virology, University of Maryland School of Medicine, Baltimore, Maryland, USA Department of Medicine, University of Maryland School of Medicine, Baltimore, Maryland, USA.
authors.forename: Anthony L
authors.initials: AL
authors.lastname: DeVico
authors.affiliation: Institute of Human Virology, University of Maryland School of Medicine, Baltimore, Maryland, USA Department of Microbiology and Immunology, University of Maryland School of Medicine, Baltimore, Maryland, USA.
authors.forename: George K
authors.initials: GK
authors.lastname: Lewis
authors.affiliation: Institute of Human Virology, University of Maryland School of Medicine, Baltimore, Maryland, USA Department of Biochemistry and Molecular Biology, University of Maryland School of Medicine, Baltimore, Maryland, USA mpazgier@ihv.umaryland.edu.
authors.forename: Marzena
authors.initials: M
authors.lastname: Pazgier
mesh_terms: D000911:Antibodies, Monoclonal / Q000737:chemistry / Q000276:immunology; D000920:Antibody-Dependent Cell Cytotoxicity; D018360:Crystallography, X-Ray; D000939:Epitopes / Q000737:chemistry / Q000276:immunology; D015483:HIV Antibodies / Q000737:chemistry / Q000276:immunology*; D015699:HIV Envelope Protein gp120 / Q000737:chemistry / Q000276:immunology*; D015658:HIV Infections / Q000276:immunology*; D015497:HIV-1 / Q000276:immunology*; D006801:Humans; D007140:Immunoglobulin Fab Fragments / Q000737:chemistry / Q000276:immunology; D008958:Models, Molecular; D011485:Protein Binding; D011487:Protein Conformation
chemical_list: D000911:Antibodies, Monoclonal; D000939:Epitopes; D015483:HIV Antibodies; D015699:HIV Envelope Protein gp120; D007140:Immunoglobulin Fab Fragments