Cooperativity Enables Non-neutralizing Antibodies to Neutralize Ebolavirus

Abstract

Summary: Drug combinations are synergistic when their combined efficacy exceeds the sum of the individual actions, but they rarely include ineffective drugs that become effective only in combination. We identified several “enabling pairs” of neutralizing and non-neutralizing anti-ebolavirus monoclonal antibodies, whose combination exhibited new functional profiles, including transforming a non-neutralizing antibody to a neutralizer. Sub-neutralizing concentrations of antibodies 2G4 or m8C4 enabled non-neutralizing antibody FVM09 (IC50 >1 μM) to exhibit potent neutralization (IC50 1–10 nM). While FVM09 or m8C4 alone failed to protect Ebola-virus-infected mice, a combination of the two antibodies provided 100% protection. Furthermore, non-neutralizers FVM09 and FVM02 exponentially enhanced the potency of two neutralizing antibodies against both Ebola and Sudan viruses. We identified a hotspot for the binding of these enabling antibody pairs near the interface of the glycan cap and GP2. Enabling cooperativity may be an underappreciated phenomenon for viruses, with implications for the design and development of immunotherapeutics and vaccines. : Howell et al. describe the phenomenon of “enabling, cooperative neutralization” where weakly neutralizing and/or non-neutralizing ebolavirus monoclonal antibodies exhibit potent neutralization when combined. The previously identified antibodies m8C4 and FVM09, which are non-protective alone, offer 100% protection against Ebola and Sudan virus challenge in mice when combined. Keywords: Ebola virus, vaccine, filovirus, monoclonal antibody, antibody therapeutics, antibody synergy, cooperative neutralization, synergistic neutralization