On page 117, Giefing et al. report the discovery of two new vaccine candidates that might protect humans against all 90 versions of a deadly bacterium.

This bacterium, Pneumococcus, invades the lungs, blood, and eventually brain to cause pneumonia, sepsis, and meningitis, respectively. Surface proteins from this bug are currently being used as vaccines to induce the body to produce protective antibodies. But these vaccines, which comprise proteins from only a few types of Pneumococcus, are not effective against other variants, due to extreme sequence diversity in the surface proteins.

Giefing et al. now identify two bacterial antigens that are nearly identical among all pneumococcal strains and that induce potent antibodies in vivo. The authors hunted for conserved bacterial antigens that would be exposed on the pathogen during disease. Antibodies isolated from exposed but healthy humans and from those recovering from infection were used to identify pneumococcal proteins that were targeted by the protective antibody response.

Both of the newly identified antigens induced antibodies that protected immunized mice against several other pneumococcal variants. The antigens might be potent targets because they come from a protein that is essential for bacterial growth and survival and thus unlikely to mutate. The team is currently testing their vaccines in clinical trials.