title: Detailed characterization of antibody responses against HIV-1 group M consensus gp120 in rabbits.
abstract: BACKGROUND
  We recently reported induction of broadly neutralizing antibodies (bnAbs) against multiple HIV-1 (human immunodeficiency virus type 1) isolates in rabbits, albeit weak against tier 2 viruses, using a monomeric gp120 derived from an M group consensus sequence (MCON6). To better understand the nature of the neutralizing activity, detailed characterization of immunological properties of the protein was performed. Immunogenic linear epitopes were identified during the course of immunization, and spatial distribution of these epitopes was determined. Subdomain antibody target analyses were done using the gp120 outer domain (gp120-OD) and eOD-GT6, a protein based on a heterologous sequence. In addition, refined epitope mapping analyses were done by competition assays using several nAbs with known epitopes.
  
  
  RESULTS
  Based on linear epitope mapping analyses, the V3 loop was most immunogenic, followed by C1 and C5 regions. The V1/V2 loop was surprisingly non-immunogenic. Many immunogenic epitopes were clustered together even when they were distantly separated in primary sequence, suggesting the presence of immunogenic hotspots on the protein surface. Although substantial antibody responses were directed against the outer domain, only about 0.1% of the antibodies bound eOD-GT6. Albeit weak, antibodies against peptides that corresponded to a part of the bnAb VRC01 binding site were detected. Although gp120-induced antibodies could not block VRC01 binding to eOD-GT6, they were able to inhibit VRC01 binding to both gp120 and trimeric BG505 SOSIP gp140. The immune sera also efficiently competed with CD4-IgG2, as well as nAbs 447-52D, PGT121 and PGT126, in binding to gp120.
  
  
  CONCLUSIONS
  The results suggest that some antibodies that bind at or near known bnAb epitopes could be partly responsible for the breadth of neutralizing activity induced by gp120 in our study. Immunization strategies that enhance induction of these antibodies relative to others (e.g. V3 loop), and increase their affinity, could improve protective efficacy of an HIV-1 vaccine.
authors.affiliation: Department of Biomedical Sciences, College of Veterinary Medicine, Iowa State University, 1600 S 16th Street, Ames, IA, 50011-1250, USA. yaliq@hotmail.com.|Center for Advanced Host Defenses, Immunobiotics and Translational Comparative Medicine, Iowa State University, Ames, IA, 50011, USA. yaliq@hotmail.com.
authors.forename: Yali
authors.initials: Y
authors.lastname: Qin
authors.affiliation: Department of Biomedical Sciences, College of Veterinary Medicine, Iowa State University, 1600 S 16th Street, Ames, IA, 50011-1250, USA. shiyxtox@iastate.edu.|Center for Advanced Host Defenses, Immunobiotics and Translational Comparative Medicine, Iowa State University, Ames, IA, 50011, USA. shiyxtox@iastate.edu.
authors.forename: Heliang
authors.initials: H
authors.lastname: Shi
authors.affiliation: Department of Biomedical Sciences, College of Veterinary Medicine, Iowa State University, 1600 S 16th Street, Ames, IA, 50011-1250, USA. skt3187@iastate.edu.|Center for Advanced Host Defenses, Immunobiotics and Translational Comparative Medicine, Iowa State University, Ames, IA, 50011, USA. skt3187@iastate.edu.
authors.forename: Saikat
authors.initials: S
authors.lastname: Banerjee
authors.affiliation: Department of Biomedical Sciences, College of Veterinary Medicine, Iowa State University, 1600 S 16th Street, Ames, IA, 50011-1250, USA. aditiag@iastate.edu.|Center for Advanced Host Defenses, Immunobiotics and Translational Comparative Medicine, Iowa State University, Ames, IA, 50011, USA. aditiag@iastate.edu.
authors.forename: Aditi
authors.initials: A
authors.lastname: Agrawal
authors.affiliation: Department of Biomedical Sciences, College of Veterinary Medicine, Iowa State University, 1600 S 16th Street, Ames, IA, 50011-1250, USA. mbanasik@iastate.edu.|Center for Advanced Host Defenses, Immunobiotics and Translational Comparative Medicine, Iowa State University, Ames, IA, 50011, USA. mbanasik@iastate.edu.
authors.forename: Marisa
authors.initials: M
authors.lastname: Banasik
authors.affiliation: Department of Biomedical Sciences, College of Veterinary Medicine, Iowa State University, 1600 S 16th Street, Ames, IA, 50011-1250, USA. mcho@iastate.edu.|Center for Advanced Host Defenses, Immunobiotics and Translational Comparative Medicine, Iowa State University, Ames, IA, 50011, USA. mcho@iastate.edu.
authors.forename: Michael W
authors.initials: MW
authors.lastname: Cho
mesh_terms: D000818:Animals; D057134:Antibodies, Neutralizing / Q000097:blood; D000917:Antibody Formation; D018604:Epitope Mapping; D000939:Epitopes / Q000276:immunology; D015483:HIV Antibodies / Q000097:blood; D015699:HIV Envelope Protein gp120 / Q000276:immunology*; D015497:HIV-1 / Q000276:immunology*; D011817:Rabbits
chemical_list: D057134:Antibodies, Neutralizing; D000939:Epitopes; D015483:HIV Antibodies; D015699:HIV Envelope Protein gp120; C514793:gp120 protein, Human immunodeficiency virus 1