Journal of virology 2017 01 25() pii 10.1128/JVI.02325-16
In light of weak or absent neutralizing activity mediated by anti-V2 monoclonal Abs (mAbs), we tested whether they can mediate Ab-dependent cellular phagocytosis (ADCP) which is an important element of anti-HIV-1 immunity. We tested six anti-V2 mAbs and compared them with 21 mAbs specific for V3, the CD4-binding site (CD4bs), and gp41 derived from HIV-1 chronically infected individuals and produced by hybridoma cells. ADCP activity was measured by flow cytometry using uptake by THP-1 monocytic cells of fluorescent beads coated with gp120, gp41, BG505 SOSIP.664 or BG505 DS-SOSIP.664 complexed with mAbs. The ADCP activity measured by the area under the curve showed significantly higher activity of anti-gp41 mAbs compared to three other groups of mAbs tested using beads coated with monomeric gp41 or gp120; anti-V2 mAbs were dominant over anti-V3 and anti-CD4bs against clade C gp120ZM109. ADCP mediated by V2 and V3 mAbs was positive against stabilized DS-SOSIP.664 trimer but negligible against SOSIP.664 targets, suggesting a closed envelope conformation better exposes the variable loops. Two IgG3 mAbs against V2 and V3 regions displayed dominant ADCP activity over a panel of IgG1 mAbs. This superior ADCP activity was confirmed when two of three recombinant IgG3 anti-V2 mAbs were compared to IgG1 counterparts. The study demonstrated dominant ADCP activity of anti-gp41 against monomers but not trimers with some higher activity of anti-V2 mAbs over anti-V3 and anti-CD4bs mAbs. The ability to mediate ADCP suggests a mechanism by which anti-HIV-1 envelope Abs can contribute to protective efficacy.
Anti-V2 antibodies (Abs) correlated with reduced risk of HIV-1 infection in recipients of the RV144 vaccine suggesting that they play a protective role, but a mechanism providing such protection remains to be determined. The rare and weak neutralizing activities of anti-V2 mAbs prompted us to study Fc-mediated activities. We compared anti-V2 mAbs with other mAbs specific for V3, CD4bs and gp41 for Ab-dependent cellular phagocytosis (ADCP) activity, implicated in protective immunity. The anti-V2 mAbs displayed stronger activity compared to other anti-gp120 mAbs when screened against one of two gp120s and against DS-SOSIP which mimics the native trimer. Anti-gp41 mAbs were superior when targeting monomeric gp41, but were comparable against trimers which may not adequately expose gp41 epitopes. While anti-envelope mAbs in general mediated ADCP, anti-V2 mAbs displayed some dominance compared to other mAbs. Our demonstration that anti-V2 mAbs mediate ADCP suggests a functional mechanism for their contribution to protective efficacy.