Human neutralizing antibodies targeting the measles virus hemagglutinin and fusion surface proteins

Measles virus (MeV), a highly transmissible paramyxovirus, can cause severe complications and death, particularly in infants and young children. How and where human antibodies target and neutralize MeV remain unclear. Here, we report a panel of human monoclonal antibodies (mAbs) specific for MeV hemagglutinin (H) and fusion (F) surface proteins, derived from the memory B cells of a Measles-Mumps-Rubella (MMR) vaccinee. We mapped four and five major epitope clusters on H and F, respectively, and structurally characterized representative mAbs from each epitope cluster. MAbs against both H and F offer broad, potent, picomolar-level neutralization and substantially reduce viral loads in vivo when delivered before or after viral exposure. High-resolution cryo-electron microscopy of mAb complexes with H and F reveal highly conserved contact sites of the most protective antibodies. Characterization of these fully human mAbs provides avenues for prophylactic or therapeutic intervention against re-emerging MeV.