title: Deficient synthesis of class-switched, HIV-neutralizing antibodies to the CD4 binding site and correction by electrophilic gp120 immunogen.
abstract: OBJECTIVE
  HIV is vulnerable to antibodies that recognize a linear CD4 binding site epitope of gp120 (C), but inducing C-directed antibody synthesis by traditional vaccine principles is difficult. We wished to understand the basis for deficient C-directed antibody synthesis and validate correction of the deficiency by an electrophilic gp120 analog (E-gp120) immunogen that binds B-cell receptors covalently.
  
  
  METHODS
  Serum antibody responses to a C peptide and full-length gp120 epitopes induced by HIV infection in humans and immunization of mice with gp120 or E-gp120 were monitored. HIV neutralization by monoclonal and variable domain-swapped antibodies was determined from tissue culture and humanized mouse infection assays.
  
  
  RESULTS
  We describe deficient C-directed IgG but not IgM antibodies in HIV-infected patients and mice immunized with gp120 accompanied by robust synthesis of IgGs to the immunodominant gp120 epitopes. Immunization with the E-gp120 corrected the deficient C-directed IgG synthesis without overall increased immunogenicity of the C or other gp120 epitopes. E-gp120-induced monoclonal IgGs neutralized diverse HIV strains heterologous to the immunogen. A C-directed IgG neutralized HIV more potently compared to its larger IgM counterpart containing the same variable domains, suggesting obstructed access to HIV surface-expressed C. An E-gp120-induced IgG suppressed HIV infection in humanized mice, validating the tissue culture neutralizing activity.
  
  
  CONCLUSIONS
  A C-selective physiological defect of IgM→IgG class-switch recombination (CSR) or restricted post-CSR B-cell development limits the functional utility of the humoral immune response to gp120. The E-gp120 immunogen is useful to bypass the restriction and induce broadly neutralizing C-directed IgGs (see Supplemental Video Abstract, http://links.lww.com/QAD/A551).
authors.affiliation: aChemical Immunology Research Center, Department of Pathology and Laboratory Medicine, University of Texas - Houston Medical School, Houston, Texas bCenter for Neurodegenerative Disorders and Department of Pharmacology and Experimental Neuroscience, University of Nebraska Medical Center, Omaha, Nebraska cDepartment of Medicine, University of Alabama at Birmingham, Birmingham, Alabama dCalifornia Department of Public Health, Center for Infectious Diseases, Viral and Rickettsial Disease Laboratory, Richmond, California eCovalent Bioscience Inc., New York, USA. *Stephanie A. Planque and Yukie Mitsuda contributed equally to this article. †Current address: The Vanderbilt University Vaccine Center, Nashville, Tennessee, USA. ‡Current address: The University of Texas MD Anderson Cancer Center Departments of Dermatology and Immunology, Houston, Texas, USA.
authors.forename: Stephanie A
authors.initials: SA
authors.lastname: Planque
authors.forename: Yukie
authors.initials: Y
authors.lastname: Mitsuda
authors.forename: Vida
authors.initials: V
authors.lastname: Chitsazzadeh
authors.forename: Santhi
authors.initials: S
authors.lastname: Gorantla
authors.forename: Larisa
authors.initials: L
authors.lastname: Poluektova
authors.forename: Yasuhiro
authors.initials: Y
authors.lastname: Nishiyama
authors.forename: Christina
authors.initials: C
authors.lastname: Ochsenbauer
authors.forename: Mary-Kate
authors.initials: MK
authors.lastname: Morris
authors.forename: Gopal
authors.initials: G
authors.lastname: Sapparapu
authors.forename: Carl V
authors.initials: CV
authors.lastname: Hanson
authors.forename: Richard J
authors.initials: RJ
authors.lastname: Massey
authors.forename: Sudhir
authors.initials: S
authors.lastname: Paul
mesh_terms: D000328:Adult; D000818:Animals; D057134:Antibodies, Neutralizing / Q000097:blood*; D001665:Binding Sites; D015496:CD4-Positive T-Lymphocytes / Q000821:virology*; D015483:HIV Antibodies / Q000097:blood*; D015699:HIV Envelope Protein gp120 / Q000737:chemistry / Q000276:immunology*; D015658:HIV Infections / Q000276:immunology*; D006801:Humans; D017578:Immunoglobulin Class Switching; D007074:Immunoglobulin G / Q000097:blood; D007075:Immunoglobulin M / Q000097:blood; D008297:Male; D008807:Mice, Inbred BALB C; D008875:Middle Aged
chemical_list: D057134:Antibodies, Neutralizing; D015483:HIV Antibodies; D015699:HIV Envelope Protein gp120; D007074:Immunoglobulin G; D007075:Immunoglobulin M; C514793:gp120 protein, Human immunodeficiency virus 1