Scientists at La Jolla Institute for Immunology (LJI), in San Diego, California, are the first in the world to characterise human antibodies capable of neutralising measles virus. These antibodies bind to key sites on measles virus and prevent the virus from entering host cells.
The new panel of human antibodies may form the basis for future medical therapies against measles infection. In the study, an infusion of these antibodies resulted in a 500-fold lower viral load in a rodent model of measles infection.
"These antibodies work as prophylaxis - to protect from initial infection - and they work after viral exposure as a treatment to fight measles infection," said LJI Professor, President and CEO Erica Ollmann Saphire PhD, who led the new Cell Host & Microbe study.
In recent years, decreased vaccination rates have led to deadly measles outbreaks across the United States and around the world. This sharp rise in measles cases is especially dangerous for the millions of people who cannot receive a measles vaccine.
Monoclonal antibody therapies work because they contain many copies of a neutralising antibody. These therapies are widely used for a variety of infectious diseases. Even infants receive monoclonal antibody therapies each year to prevent respiratory syncytial virus (RSV). To design a monoclonal antibody treatment for measles, researchers need a clear picture of how human antibodies fight the virus.
Professor Saphire and her colleagues began by harnessing an imaging technique called cryo-electron microscopy (cryo-EM) to capture the first-ever glimpses of how antibodies bind to the measles virus. They started by examining mouse antibodies, and they published that work in a recent Nature Communications paper. That initial study showed where measles virus is vulnerable to antibody attack. The mouse antibodies latched onto one key part of the measles virus, called the fusion protein, to block the virus from entering a host cell.
To find out if human antibodies could do the same thing the researchers analysed blood from a clinical research volunteer. This volunteer had been vaccinated against measles many years before, so they already had antibodies ready to fight measles virus. From this one blood sample, the LJI scientists isolated antibodies that bind to the measles fusion protein, and other antibodies that bind to the second key piece of the virus, an attachment protein called ‘H’. They then captured 3D images of these antibodies bound together with the measles virus. The image above is a rendering showing a key measles protein (white) targeted by neutralising human antibodies (pink). These antibodies were found to be exceptionally potent, two orders of magnitude better than comparable molecules reported at conferences.
Measles virus is a shape-shifting virus. When it meets a human cell, it unfolds to reveal viral machinery that fuses with the host cell membrane. The new study shows that antibodies targeting the fusion protein work by locking the protein in place, leaving the virus unable to shape shift and infect a host cell.
The next step was to test these antibodies in a preclinical animal model. Study collaborators at The Ohio State University carried out key experiments using cotton rats as a model. They found that all four lead antibodies reduced the viral load when given either before measles exposure or within 24 to 48 hours after infection. One, an antibody called 3A12, which binds to a site on the F protein, rendered the circulating virus undetectable.
While more work needs to be done, the researchers see these antibodies as promising tools in the fight against measles. Their new images of the antibody structures provide the materials needed to make the world’s first before- or after exposure treatment for measles virus.
- Acciani M, Zyla D, Niemeyer G, et al. Human neutralizing antibodies targeting the measles virus hemagglutinin and fusion surface proteins. Cell Host Microbe. Published online May 7, 2026. doi:10.1016/j.chom.2026.04.010