title: Direct antibody access to the HIV-1 membrane-proximal external region positively correlates with neutralization sensitivity.
abstract: On the prereceptor-engaged HIV-1 envelope glycoprotein (Env) spike, epitope access by the membrane-proximal external region (MPER)-directed broadly neutralizing antibodies 2F5 and 4E10 remains unresolved. Data on binding to cell surface Env and entry data using primary isolates suggest inaccessibility of the 2F5 and 4E10 epitopes on the viral spike prior to receptor engagement, but trimer gel shift analysis and slow kinetics of shedding induced by 2F5 and 4E10 indicate otherwise. Therefore, it remains unclear if the epitopes themselves are formed in their antibody-bound state (or at least sampled) prior to receptor/coreceptor engagement or if receptor interactions both expose and form the MPER epitopes, presumably in the putative prefusion transitional intermediate. Here, we performed antibody-virus "washout experiments" using both lab-adapted and a panel of clade B primary isolates to analyze MPER accessibility. The neutralization activity of 2F5 and 4E10 against lab-adapted viruses and sensitive and moderately resistant viruses was largely unaffected by relatively rapid antibody-virus washing, suggesting direct interaction with the "static" spike. However, for more neutralization-resistant viruses, the 2F5 and 4E10 antibodies could neutralize only under the "no antibody-virus wash" conditions, implying that the MPER epitopes were not accessible prior to receptor engagement. Accessibility in the washout conditions could be precisely predicted by the relative resistance to neutralization in a standard neutralization format. These data are consistent with a model in which the local MPER antibody epitope conformations may be sampled on the native spike but are occluded to antibody by local steric or distal quaternary constraints adopted by highly resistant HIV-1 isolates.
authors.affiliation: IAVI Neutralizing Antibody Center at TSRI, The Scripps Research Institute, La Jolla, CA 92037, USA. bchakrabarti@iavi.org
authors.forename: B K
authors.initials: BK
authors.lastname: Chakrabarti
authors.forename: L M
authors.initials: LM
authors.lastname: Walker
authors.forename: J F
authors.initials: JF
authors.lastname: Guenaga
authors.forename: A
authors.initials: A
authors.lastname: Ghobbeh
authors.forename: P
authors.initials: P
authors.lastname: Poignard
authors.forename: D R
authors.initials: DR
authors.lastname: Burton
authors.forename: R T
authors.initials: RT
authors.lastname: Wyatt
mesh_terms: D000911:Antibodies, Monoclonal / Q000276:immunology* / Q000378:metabolism; D057134:Antibodies, Neutralizing / Q000276:immunology* / Q000378:metabolism; D000915:Antibody Affinity; D001666:Binding Sites, Antibody; D005434:Flow Cytometry; D057809:HEK293 Cells; D015483:HIV Antibodies / Q000276:immunology* / Q000378:metabolism; D015699:HIV Envelope Protein gp120 / Q000276:immunology* / Q000378:metabolism; D019302:HIV Envelope Protein gp160 / Q000276:immunology* / Q000378:metabolism; D015700:HIV Envelope Protein gp41 / Q000276:immunology* / Q000378:metabolism; D015497:HIV-1 / Q000276:immunology*; D006367:HeLa Cells; D006801:Humans; D009500:Neutralization Tests; D020836:Protein Structure, Quaternary
chemical_list: D000911:Antibodies, Monoclonal; D057134:Antibodies, Neutralizing; D015483:HIV Antibodies; D015699:HIV Envelope Protein gp120; D019302:HIV Envelope Protein gp160; D015700:HIV Envelope Protein gp41