title: Development and immunological assessment of VLP-based immunogens exposing the membrane-proximal region of the HIV-1 gp41 protein.
abstract: BACKGROUND
  The membrane-proximal external region (MPER) of HIV-1 gp41 is particularly conserved and target for the potent broadly neutralizing monoclonal antibodies (bnMAbs) 2F5, 4E10 and 10E8. Epitope focusing and stabilization present promising strategies to enhance the quality of immune responses to specific epitopes.
  
  
  RESULTS
  The aim of this work was to design and evaluate novel immunogens based on the gp41 MPER with the potential to elicit cross-clade neutralizing antibodies. For that purpose, gp41 was truncated N-terminally in order to dispose immunodominant, non-neutralizing sites and enhance the exposure of conserved regions. To stabilize a trimeric conformation, heterologous GCN4 and HA2 zipper domains were fused based on an in silico "best-fit" model to the protein's amino terminus. Cell surface exposure of resulting proteins and their selective binding to bnMAbs 2F5 and 4E10 could be shown by cytometric analyses. Incorporation into VLPs and preservation of antigenic structures were verified by electron microscopy, and the oligomeric state was successfully stabilized by zipper domains. These gp41 immunogens were evaluated for antigenicity in an immunization study in rabbits primed with homologous DNA expression plasmids and boosted with virus-like particle (VLP) proteins. Low titers of anti-MPER antibodies were measured by IgG ELISA, and low neutralizing activity could be detected against a clade C and B viral isolate in sera.
  
  
  CONCLUSIONS
  Thus, although neutralizing titers were very moderate, induction of cross-clade neutralizing antibodies seems possible following immunization with MPER-focusing immunogens. However, further refinement of MPER presentation and immunogenicity is clearly needed to induce substantial neutralization responses to these epitopes.
authors.forename: Thomas D
authors.initials: TD
authors.lastname: Benen
authors.forename: Paul
authors.initials: P
authors.lastname: Tonks
authors.forename: Alexander
authors.initials: A
authors.lastname: Kliche
authors.forename: Ruth
authors.initials: R
authors.lastname: Kapzan
authors.forename: Jonathan L
authors.initials: JL
authors.lastname: Heeney
authors.affiliation: Molecular Microbiology and Gene Therapy Unit, Institute of Medical Microbiology and Hygiene, University of Regensburg, Franz-Josef-Strauss-Allee 11, Regensburg, 93053, Germany. ralf.wagner@klinik.uni-regensburg.de.
authors.forename: Ralf
authors.initials: R
authors.lastname: Wagner
mesh_terms: D016915:AIDS Vaccines / Q000235:genetics / Q000276:immunology / Q000494:pharmacology; D000818:Animals; D057134:Antibodies, Neutralizing / Q000276:immunology*; D057809:HEK293 Cells; D015483:HIV Antibodies / Q000276:immunology*; D015700:HIV Envelope Protein gp41 / Q000235:genetics / Q000276:immunology / Q000494:pharmacology; D015497:HIV-1 / Q000235:genetics / Q000276:immunology*; D006801:Humans; D011817:Rabbits; D011993:Recombinant Fusion Proteins / Q000235:genetics / Q000276:immunology / Q000494:pharmacology; D014614:Vaccines, Synthetic / Q000276:immunology / Q000494:pharmacology; D058425:Vaccines, Virus-Like Particle / Q000235:genetics / Q000276:immunology / Q000494:pharmacology
chemical_list: D016915:AIDS Vaccines; D057134:Antibodies, Neutralizing; D015483:HIV Antibodies; D015700:HIV Envelope Protein gp41; D011993:Recombinant Fusion Proteins; D014614:Vaccines, Synthetic; D058425:Vaccines, Virus-Like Particle; C514787:gp41 protein, Human immunodeficiency virus 1