Broadly neutralizing antibodies suppress post-transcytosis HIV-1 infectivity

Abstract

Broadly neutralizing antibodies (bNAbs) offer promising opportunities for preventing HIV-1 infection in humans. Immunoprophylaxis with potent bNAbs efficiently protects non-human primates from mucosal transmission even after repeated challenges. However, the precise mechanisms of bNAb-mediated viral inhibition in mucosal tissues are currently unknown. Here, we show that immunoglobulin (Ig)G and IgA bNAbs do not interfere with the endocytic transport of HIV-1 across epithelial cells, a process referred to as transcytosis. Instead, both viruses and antibodies are translocated to the basal pole of epithelial cells, possibly in the form of an immune complex. Importantly, as opposed to free virions, viral particles bound by bNAbs are no longer infectious after transepithelial transit. Post-transcytosis neutralization activity of bNAbs displays comparable inhibitory concentrations as those measured in classical neutralization assays. Thus, bNAbs do not block the transport of incoming HIV-1 viruses across the mucosal epithelium but rather neutralize the transcytosed virions, highlighting their efficient prophylactic and protective activity in vivo.

HIV-1 Envelope Recognition by Polyreactive and Cross-Reactive Intestinal B Cells

“…The isolated high-affinity gp140 antibodies targeted mainly gp41 and lacked neutralizing activity, potent ADCC breadth, and blocking capacity against HIV-1 transcytosis. In contrast to HIV-1 bNAbs ( Lorin et al., 2017 ), mucosal HIV-1 nnAbs did not suppress post-transcytosis infectivity in vitro . Although HIV-1 nnAbs may modestly diminish the number of transmitted viruses ( Santra et al., 2015 ), recent reports demonstrated that viral neutralization is required to confer protection against mucosal HIV-1 transmission in vitro and in vivo ( Astronomo et al., 2016 , Cheeseman et al., 2016 ).…”

“…Transcytosis assays were performed using epithelial monolayer-forming human endometrial carcinoma type A HEC-1A cells (ATCC ® HTB-112) cultivated on 0.4 μm polyethylene terephthalate transwell membranes (Millicell ® , Millipore) as recently described ( Lorin et al., 2017 ). Briefly, the confluence, tightness and integrity of HEC-1A monolayers were controlled by measuring the transepithelial electrical resistance, the paracellular permeability to 40 kDa FITC-labeled DEAE-dextran (Molecular Probes) and by assaying the expression of tight junction proteins by confocal microscopy as previously described ( Lorin et al., 2017 ). HIV-1 viruses (10 ng of p24 HIV-1 NLAD8) were incubated v/v for 1 h at 37°C with purified antibodies (66.67 nM final concentration), and mixtures were added onto HEC-1A monolayers at day 6 of culture.…”

“…The percentage of transcytosis was determined using the following formula: (concentration p24 sample / mean concentration p24 CTL) ∗ 100. The infectivity of virions transcytosed in the presence or not of antibodies (0.05 ng p24) was measured using a previously described TZM-bl cells assay ( Lorin et al., 2017 ). Two independent experiments were performed in quadruplicate, and included negative (mGO53) and positive (10-1074) controls.…”

Conformational Plasticity in Broadly Neutralizing HIV-1 Antibodies Triggers Polyreactivity

“…Antibody binding to viruses on infected cells was assayed by flow cytometry as recently described ( Bruel et al., 2016 ). Neutralization of cell-free HIV-1 was measured using TZM-bl cells as previously described ( Li et al., 2005 , Lorin et al., 2017 ). To assay for CHIKV neutralization, luciferase-based and plaque neutralization assays were used, as described in the Supplemental Experimental Procedures .…”

Increasing the Clinical Potential and Applications of Anti-HIV Antibodies

“…The reason for this discrepancy is unknown but may be related to the utilization of older-generation or less potent bNAbs in the prior studies (2F5, 2G12, 4E10), whereas the most recent studies investigate newer-generation, more potent bNAbs. In that study of bNAbs targeting a wide range of epitopes, bNAbs did not block the transcytosis of either cell-free or cell-associated HIV-1 in vitro and instead relied upon neutralization to decrease the infectivity of transcytosed viruses ( 105 ). Thus, increasing the local concentration and neutralization breadth and potency of bNAbs at mucosal sites may enhance protection against mucosal infection.…”