Objective Although passive immunization with anti-HIV-1 Env IgG1 neutralizing monoclonal Abs (nmAbs) prevented simian-human immunodeficiency virus (SHIV) infection in rhesus monkeys (RMs), 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 RMs. Design DIgA1, dIgA2, and IgG1 versions of nmAb HGN194 were applied intrarectally (i.r.) in three RM groups 30 min before i.r. SHIV challenge. Methods After a control pharmacokinetic study showed that nmAb concentrations in rectal fluids over time were similar for all HGN194 isotypes, control and nmAb-treated animals were challenged i.r. 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 RMs 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 RMs 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 first-line of defense against HIV-1, a virus predominantly transmitted mucosally.
Although IgA is the most abundantly produced immunoglobulin in humans, its role in preventing HIV-1 acquisition, which occurs mostly via mucosal routes, remains unclear. In our passive mucosal immunizations of rhesus macaques (RMs), the anti-HIV-1 neutralizing monoclonal antibody (nmAb) HGN194, given either as dimeric IgA1 (dIgA1) or dIgA2 intrarectally (i.r.), protected 83% or 17% of the RMs against i.r. simian-human immunodeficiency virus (SHIV) challenge, respectively. Data from the RV144 trial implied that vaccine-induced plasma IgA counteracted the protective effector mechanisms of IgG1 with the same epitope specificity. We thus hypothesized that mucosal dIgA2 might diminish the protection provided by IgG1 mAbs targeting the same epitope. To test our hypothesis, we administered HGN194 IgG1 intravenously (i.v.) either alone or combined with i.r. HGN194 dIgA2. We enrolled SHIV-exposed, persistently aviremic RMs protected by previously administered nmAbs; RM anti-human IgG responses were undetectable. However, low-level SIV Gag-specific proliferative T-cell responses were found. These animals resemble HIV-exposed, uninfected humans, in which local and systemic cellular immune responses have been observed. HGN194 IgG1 and dIgA2 used alone and the combination of the two neutralized the challenge virus equally well in vitro. All RMs given only i.v. HGN194 IgG1 became infected. In contrast, all RMs given HGN194 IgG1 + dIgA2 were completely protected against high-dose i.r. SHIV-1157ipEL-p challenge. These data imply that combining suboptimal defenses at the mucosal and systemic levels can completely prevent virus acquisition. Consequently, active vaccination should focus on defense-in-depth, a strategy that seeks to build up defensive fall-back positions well behind the fortified frontline.
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