title: In vivo efficacy of human immunodeficiency virus neutralizing antibodies: estimates for protective titers.
abstract: The definition of plasma neutralizing antibody titers capable of controlling human immunodeficiency virus (HIV) infection in vivo is considered a critical step in vaccine development. Here we provide estimates for effective neutralization titers by assessing samples from a recent passive immunization trial with the neutralizing monoclonal antibodies (MAbs) 2G12, 2F5, and 4E10 using an analytic strategy that dissects the contributions of these MAbs to the total neutralization activity in patient plasma. Assessment of neutralization activities for six responding patients with partial or complete control of viremia during the MAb treatment and for the eight nonresponding patients revealed a significant difference between these groups: Among responders, MAb-mediated activity exceeded the autologous neutralization response by 1 to 2 log units (median difference, 43.3-fold), while in the nonresponder group, the autologous activity prevailed (median difference, 0.63-fold). In order to reach a 50% proportion of the responders in our study cohort, MAb neutralizing titers higher than 1:200 were required based on this analysis. The disease stage appears to have a significant impact on the quantities needed, since titers above 1:1,000 were needed to reach the same effect in chronic infection. Although our analysis is based on very small sample numbers and thus cannot be conclusive, our data provide a first estimate on how in vitro-measured neutralizing antibody activity can relate to in vivo efficacy in controlling HIV infection and may therefore provide valuable information for vaccine development. Interestingly, lower neutralizing antibody levels showed an effect in acute compared to chronic infection, suggesting that in early disease stages, therapeutic vaccination may show promise. Equally, this raises hopes that a preventive vaccine could become effective at comparatively lower neutralizing antibody titers.
authors.affiliation: Division of Infectious Diseases and Hospital Epidemiology, University Hospital Zurich, Rämistrasse 100, 8091 Zürich, Switzerland. alexandra.trkola@usz.ch.
authors.forename: Alexandra
authors.initials: A
authors.lastname: Trkola
authors.forename: Herbert
authors.initials: H
authors.lastname: Kuster
authors.forename: Peter
authors.initials: P
authors.lastname: Rusert
authors.forename: Viktor
authors.initials: V
authors.lastname: von Wyl
authors.forename: Christine
authors.initials: C
authors.lastname: Leemann
authors.forename: Rainer
authors.initials: R
authors.lastname: Weber
authors.forename: Gabriela
authors.initials: G
authors.lastname: Stiegler
authors.forename: Hermann
authors.initials: H
authors.lastname: Katinger
authors.forename: Beda
authors.initials: B
authors.lastname: Joos
authors.forename: Huldrych F
authors.initials: HF
authors.lastname: Günthard
mesh_terms: D000911:Antibodies, Monoclonal / Q000276:immunology* / Q000627:therapeutic use; D015483:HIV Antibodies / Q000276:immunology*; D015658:HIV Infections / Q000188:drug therapy / Q000276:immunology*; D006801:Humans; D007116:Immunization, Passive / Q000379:methods*; D009500:Neutralization Tests; D013223:Statistics as Topic; D014766:Viremia
chemical_list: D000911:Antibodies, Monoclonal; D015483:HIV Antibodies