title: Induction of Heterologous Tier 2 HIV-1-Neutralizing and Cross-Reactive V1/V2-Specific Antibodies in Rabbits by Prime-Boost Immunization.
abstract: Poxvirus prime-protein boost used in the RV144 trial remains the only immunization strategy shown to elicit a modest level of protection against HIV-1 acquisition in humans. Although neutralizing antibodies (NAb) were generated, they were against sensitive viruses, not the more resistant "tier 2" isolates that dominate circulating strains. Instead, risk reduction correlated with antibodies recognizing epitopes in the V1/V2 region of HIV-1 envelope glycoprotein (Env). Here, we examined whether tier 2 virus NAb and V1/V2-specific non-NAb could be elicited by a poxvirus prime-gp120 boost strategy in a rabbit model. We studied two clade B Envs that differ in multiple parameters, including tissue origin, neutralization sensitivity, and presence of the N197 (N7) glycan that was previously shown to modulate the exposure of conserved epitopes on Env. We demonstrate that immunized rabbits generated cross-reactive neutralizing activities against >50% of the tier 2 global HIV-1 isolates tested. Some of these activities were directed against the CD4 binding site (CD4bs). These rabbits also generated antibodies that recognized protein scaffolds bearing V1/V2 sequences from diverse HIV-1 isolates and mediated antibody-dependent cellular cytotoxicity. However, there are subtle differences in the specificities and the response rates of V1/V2-specific antibodies between animals immunized with different Envs, with or without the N7 glycan. These findings demonstrate that antibody responses that have been correlated with protection against HIV-1 acquisition in humans can be elicited in a preclinical model by a poxvirus prime-gp120 boost strategy and that improvements may be achievable by optimizing the nature of the priming and boosting immunogens.
  
  
  
  The only vaccine approach shown to elicit any protective efficacy against HIV-1 acquisition is based on a poxvirus prime-protein boost regimen (RV144 Thai trial). Reduction of risk was associated with nonneutralizing antibodies targeting the V1/V2 loops of the envelope protein gp120. However, the modest efficacy (31.2%) achieved in this trial highlights the need to examine approaches and factors that may improve vaccine-induced responses, including cross-reactive neutralizing activities. We show here that rabbits immunized with a novel recombinant vaccinia virus prime-gp120 protein boost regimen generated antibodies that recognize protein scaffolds bearing V1/V2 sequences from diverse HIV-1 isolates and mediated antibody-dependent cellular cytotoxicity. Importantly, immunized rabbits also showed neutralizing activities against heterologous tier 2 HIV-1 isolates. These findings may inform the design of prime-boost immunization approaches and help improve the protective efficacy of candidate HIV-1 vaccines.
authors.affiliation: Department of Microbiology, University of Washington, Seattle, Washington, USA.
authors.forename: Samantha
authors.initials: S
authors.lastname: Townsley
authors.affiliation: Washington National Primate Research Center, Seattle, Washington, USA.
authors.forename: Zeinab
authors.initials: Z
authors.lastname: Mohamed
authors.affiliation: Department of Pharmaceutics, University of Washington, Seattle, Washington, USA.
authors.forename: Wenjin
authors.initials: W
authors.lastname: Guo
authors.affiliation: Washington National Primate Research Center, Seattle, Washington, USA.
authors.forename: Jennifer
authors.initials: J
authors.lastname: McKenna
authors.affiliation: Department of Pharmaceutics, University of Washington, Seattle, Washington, USA.
authors.forename: Brad
authors.initials: B
authors.lastname: Cleveland
authors.affiliation: Duke University Medical Center, Durham, North Carolina, USA.
authors.forename: Celia
authors.initials: C
authors.lastname: LaBranche
authors.affiliation: Duke University Medical Center, Durham, North Carolina, USA.
authors.forename: David
authors.initials: D
authors.lastname: Beaumont
authors.affiliation: Duke University Medical Center, Durham, North Carolina, USA.
authors.forename: Xiaoying
authors.initials: X
authors.lastname: Shen
authors.affiliation: Duke University Medical Center, Durham, North Carolina, USA.
authors.forename: Nicole L
authors.initials: NL
authors.lastname: Yates
authors.affiliation: Rutgers University, Newark, New Jersey, USA.
authors.forename: Abraham
authors.initials: A
authors.lastname: Pinter
authors.affiliation: Duke University Medical Center, Durham, North Carolina, USA.
authors.forename: Georgia D
authors.initials: GD
authors.lastname: Tomaras
authors.affiliation: Duke University Medical Center, Durham, North Carolina, USA.
authors.forename: Guido
authors.initials: G
authors.lastname: Ferrari
authors.affiliation: Duke University Medical Center, Durham, North Carolina, USA.
authors.forename: David C
authors.initials: DC
authors.lastname: Montefiori
authors.affiliation: Department of Microbiology, University of Washington, Seattle, Washington, USA Washington National Primate Research Center, Seattle, Washington, USA Department of Pharmaceutics, University of Washington, Seattle, Washington, USA hus@uw.edu.
authors.forename: Shiu-Lok
authors.identifier: 0000-0003-4336-7964
authors.initials: SL
authors.lastname: Hu
mesh_terms: D016915:AIDS Vaccines / Q000008:administration & dosage* / Q000276:immunology*; D000818:Animals; D057134:Antibodies, Neutralizing / Q000097:blood*; D004337:Drug Carriers; D015483:HIV Antibodies / Q000097:blood*; D015699:HIV Envelope Protein gp120 / Q000235:genetics / Q000276:immunology*; D015497:HIV-1 / Q000235:genetics / Q000276:immunology*; D007114:Immunization / Q000379:methods*; D011817:Rabbits; D022223:Vaccines, Subunit / Q000008:administration & dosage / Q000276:immunology; D014614:Vaccines, Synthetic / Q000008:administration & dosage / Q000276:immunology; D014616:Vaccinia virus / Q000235:genetics
chemical_list: D016915:AIDS Vaccines; D057134:Antibodies, Neutralizing; D004337:Drug Carriers; D015483:HIV Antibodies; D015699:HIV Envelope Protein gp120; D022223:Vaccines, Subunit; D014614:Vaccines, Synthetic; C514793:gp120 protein, Human immunodeficiency virus 1