eCD4-Ig promotes ADCC activity of sera from HIV-1-infected patients

Antibody-dependent cell-mediated cytotoxicity (ADCC) is a crucial mechanism by which the immune system targets and destroys HIV-1 infected cells. In this process, antibodies bind to the HIV-1 envelope glycoprotein (Env) on infected cells, recruiting natural killer (NK) cells to perform the killing. A significant challenge in treating HIV-1 is the persistence of a latent viral reservoir that remains invisible to most traditional immune responses. This study explores the potential of eCD4-Ig—a potent HIV-1 entry inhibitor—to act as an adjuvant for enhancing ADCC activity against these hidden reservoirs.

eCD4-Ig is an engineered protein that mimics the HIV-1 receptor, CD4, and coreceptor binding sites, allowing it to neutralize a wide array of HIV-1 isolates. The researchers investigated whether eCD4-Ig could do more than just block viral entry. They discovered that by binding to Env, eCD4-Ig induces conformational changes that expose previously hidden (occluded) epitopes on the viral surface. These epitopes are targets for various non-neutralizing antibodies commonly found in the blood of HIV-1 infected patients. By exposing these sites, eCD4-Ig allows endogenous antibodies to effectively bind and tag infected cells for NK-mediated destruction.

A critical finding of this study is the synergy between eCD4-Ig and patient-derived serum antibodies. The researchers tested an ADCC-inactive variant, eCD4-IgG2, which cannot kill cells on its own, but found it increased the potency of serum-mediated ADCC by approximately 100-fold. This effect was notably absent when using other broadly neutralizing antibodies (bNAbs). Furthermore, when testing latently infected T-cell lines reactivated by latency-reversing agents (like vorinostat or TNFα), the combination of eCD4-Ig and patient serum significantly enhanced the clearance of these reactivated cells. This suggests that eCD4-Ig may be a vital component in a 'shock and kill' strategy to deplete the HIV-1 reservoir.