Abstract

Yellow fever virus (YFV) causes sporadic outbreaks of infection in South America and sub-Saharan Africa. While live-attenuated yellow fever virus vaccines based on three substrains of 17D are considered some of the most effective vaccines in use, problems with production and distribution have created large populations of unvaccinated, vulnerable individuals in endemic areas. To date, specific antiviral therapeutics have not been licensed for human use against YFV or any other related flavivirus. Recent advances in monoclonal antibody (mAb) technology have allowed for identification of numerous candidate therapeutics targeting highly pathogenic viruses, including many flaviviruses. Here, we sought to identify a highly neutralizing antibody targeting YFV envelope (E) protein as a therapeutic candidate. We used human B cell hybridoma technology to isolate mAbs from the circulating memory B cells from human YFV vaccine recipients. These antibodies bound to recombinant YFV E protein and recognized at least five major antigenic sites on E. Two mAbs (designated YFV-136 and YFV-121) recognized a shared antigenic site and neutralized the YFV 17D vaccine strain in vitro. YFV-136 also potently inhibited infection by multiple wild-type YFV strains, in part, at a post-attachment step in the virus replication cycle. YFV-136 showed therapeutic protection in two animal models of YFV challenge including hamsters and immunocompromised mice engrafted with human hepatocytes. These studies define features of the antigenic landscape on YFV E protein recognized by the human B cell response and identify a therapeutic antibody candidate that inhibits infection and disease caused by highly virulent strains of YFV.