Mucosal AIDS virus transmission is enhanced by antiviral IgG isolated early in infection

Abstract

Objective:Antibody-dependent enhancement (ADE) affects host-virus dynamics in fundamentally different ways: i) enhancement of initial virus acquisition, and/or ii) increased disease progression/severity. Here we address the question whether anti-HIV-1 antibodies can enhance initial infection. While cell-culture experiments hinted at this possibility, in-vivo proof remained elusive.Design:We used passive immunization in nonhuman primates challenged with simian-human immunodeficiency virus (SHIV), a chimera expressing HIV-1 envelope. We purified IgG from rhesus monkeys with early-stage SHIV infection-before cross-neutralizing anti-HIV-1 antibodies had developed-and screened for maximal complement-mediated antibody-dependent enhancement (C'-ADE) of viral replication with a SHIV strain phylogenetically distinct from that harbored by IgG donor macaques. IgG fractions with maximal C'-ADE but lacking neutralization were combined to yield enhancing anti-SHIV IgG (enSHIVIG).Results:We serially enrolled naive macaques (Group 1) to determine the minimal and 50% animal infectious doses required to establish persistent infection after intrarectal SHIV challenge. The first animal was inoculated with a 1:10 virus-stock dilution; after this animal's viral RNA load was >104copies/ml, the next macaque was challenged with 10x less virus, a process repeated until viremia no longer ensued. Group 2 was pretreated intravenously with enSHIVIG 24h before SHIV challenge. Overall, Group 2 macaques required 3.4-fold less virus compared to controls (P=0.002). This finding is consistent with enhanced susceptibility of the passively immunized animals to mucosal SHIV challenge.Conclusion:These passive immunization data give proof of IgG-mediated enhanced virus acquisition after mucosal exposure-a potential concern for antibody-based AIDS vaccine development.