Identification of Neutralizing Epitopes in Measles Fusion Protein for Antibody-Based Therapies

Measles virus (MeV) is a highly contagious respiratory pathogen and remains a significant global health threat. Resurgent infections, driven by insufficient vaccine coverage, declining herd immunity, and the vulnerability of immunocompromised individuals who cannot be vaccinated, highlight the urgent need for effective therapeutics. Monoclonal antibodies (mAbs) offer promise both as antiviral agents and powerful tools for probing the structure and entry mechanisms of the virus. While most vaccine-elicited neutralizing antibodies target the MeV hemagglutinin (H) protein, antibodies targeting the fusion (F) protein can also neutralize infection. Targeting the F protein in its pre-fusion, post-fusion, or intermediate conformational states may reveal distinct mechanisms of neutralization and offer valuable structural insights. We selected hybridomas producing mAbs against different states of the MeV F protein (pre-fusion, post-fusion and pre-and post-fusion independently) and characterized their binding specificities and antiviral activities. Using structural analyses, we mapped antibody binding to both the pre-fusion and post-triggering conformations of MeV F. Functional assays were employed to assess the neutralization of live virus, the mechanisms of viral inhibition in vitro, and the protective efficacy in vivo. Our studies revealed that the most potent neutralizing antibodies bind to the pre-fusion form of MeV F and inhibits fusion by stabilizing the protein in either pre-fusion state, an extended intermediate conformation following activation, or by actively triggering the fusion protein. This work provides the first detailed mapping of neutralizing epitopes on the MeV F protein, establishing a framework for the development of F-targeted therapeutics.