Human monoclonal antibodies identified with potential to prevent and treat measles

A scientific team funded by the National Institutes of Health has isolated and mapped in detail the first comprehensive group of human antibodies targeting the measles virus. The findings identify specific antibodies capable of reducing the virus to undetectable levels in an animal model and may form the basis for future medical therapies against measles infection.

Measles cases have recently increased in the United States and worldwide. More than 470,000 measles cases were reported globally in 2024, and at least 72 outbreaks have been recorded in the United States since January 2025. While effective prevention in the form of vaccination is available, no safe and effective therapies have received regulatory approval in the United States.

The research team, led by scientists at La Jolla Institute for Immunology, isolated memory B cells from a donor who had been vaccinated for measles three times. From those cells, the team engineered and purified more than 100 individual human monoclonal antibodies, each targeting a specific site on the measles virus.

Using cryo-electron microscopy, the scientists produced the first-ever atomic-resolution structural maps of human antibodies bound to measles virus proteins, identifying nine distinct sites on the virus’s two surface proteins, Hemagglutinin (H) and Fusion (F), that the antibodies target. The antibodies bind to key H and F surface virus proteins, preventing viral entry into host cells.

The findings challenge a long-held assumption in the field. Scientists had believed protection against measles was driven almost exclusively by antibodies targeting the H protein, with antibodies against the F protein playing a minor role. This study found that antibodies against both proteins can confer powerful, independent protection.

Most strikingly, one antibody targeting the F protein, designated 4F09, was the single most protective antibody in the study, reducing measles virus levels in the lungs of infected rats to completely undetectable levels. In the study, an infusion of the antibodies resulted in 500-fold lower viral load in a rodent model of measles infection.

The protective antibodies identified also target regions of the virus that look nearly identical across all known measles strains circulating globally, suggesting the virus may not be able to mutate enough to escape the antibodies and still survive. The study concluded that characterization of these fully human monoclonal antibodies provides avenues for prophylactic or therapeutic intervention against re-emerging measles virus.

There are currently no measles-specific therapies to help patients. The scientists are now seeking partners to do the extensive research and testing needed to translate their discovery into a medicine that could serve as both a rapid post-exposure preventive and a therapeutic for people who are infected.