Anti-HIV IgA isotypes: differential virion capture and inhibition of transcytosis are linked to prevention of mucosal R5 SHIV transmission.

OBJECTIVE: Although passive immunization with anti-HIV-1 Env IgG1 neutralizing monoclonal antibodies (nmAbs) prevented simian-human immunodeficiency virus (SHIV) infection in rhesus monkeys, IgA nmAbs have not been tested. Here, we sought to determine whether human anti-HIV-1 dimeric (d)IgA1, dIgA2, and IgG1 differ in their ability to prevent mucosal R5 SHIV acquisition in rhesus monkeys.
DESIGN: DIgA1, dIgA2, and IgG1 versions of nmAb HGN194 were applied intrarectally in three rhesus monkey groups 30 min before intrarectal SHIV challenge.
METHODS: After a control pharmacokinetic study confirmed that nmAb concentrations in rectal fluids over time were similar for all HGN194 isotypes, control and nmAb-treated animals were challenged intrarectally with an R5 SHIV, and viral loads were monitored.
RESULTS: Unexpectedly, dIgA1 provided the best protection in vivo--although all nmAbs showed similar neutralizing activity in vitro. Five out of the six dIgA1-treated rhesus monkeys remained virus-free compared to only one out of six animals given dIgA2 (P=0.045 by log-rank test) and two out of six rhesus monkeys treated with IgG1 forms of the nmAb (P=0.12). Protection correlated significantly with virion capture activity by a given nmAb form, as well as inhibition of transcytosis of cell-free virus across an epithelial cell layer in vitro.
CONCLUSIONS: Our data imply that dIgA1-mediated capturing of virions in mucosal secretions and inhibition of transcytosis can provide significant prevention of lentiviral acquisition--over and above direct virus neutralization. Vaccine strategies that induce mucosal IgA, especially IgA1, should be developed as a first line of defense against HIV-1, a virus predominantly transmitted mucosally.