An experimental vaccine has been found to protect mice from a lethal dose of the bacterium that causes the plague.
Famous for killing millions in Europe in the Middle Ages, the bacterium Yersinia pestis still causes frequent deadly outbreaks, including recent ones in Madagascar, India, China and the US. It is usually treated with antibiotics, but if antibiotic-resistant strains of Y. pestis emerge, other measures will be needed, such as vaccines.
Vaccines containing live or dead Y. pestis bacteria have been used in the past, but they have major drawbacks, such as short-lived immunity, serious side effects and the risk of live viruses mutating so that they cause disease.
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at Tel Aviv University in Israel and his colleagues have developed a plague vaccine containing genetic code in the form of mRNA 鈥� an approach that was pioneered by the Pfizer/BioNTech and Moderna covid-19 vaccines.
The mRNA in the vaccine encodes a molecule found on the surface of Y. pestis called the F1 capsular protein. When a person receives the vaccine, their cells would take up the mRNA and start producing the bacterial protein, which lets their immune system learn to recognise it.
To test the mRNA plague vaccine, the team injected 12 mice with three doses and another 12 mice with a dummy vaccine coding for a non-plague protein. They then exposed all the mice to a dose of Y. pestis that is normally lethal.
All of the mice given the plague vaccine were still alive after 20 days, when the experiment ended, whereas all mice given the dummy vaccine died within a week of exposure to Y. pestis.
By analysing blood samples from the mice, the team found the vaccine generated two types of immune responses: antibodies 鈥� small molecules that can stop viruses entering cells 鈥� and T-cells, which can kill infected cells.
鈥淭his is the first demonstration of a fully protective mRNA vaccine against a lethal bacterial pathogen [that lives outside host cells],鈥� said Peer in a presentation at the
鈥淚t is really exciting to see that this novel mRNA-based plague vaccine gave full protection against bubonic plague in a mouse model,鈥� says at the National Taiwan University in Taipei.
However, some Y. pestis strains lack the F1 capsular protein targeted by the vaccine, meaning it is unlikely to work against them, says Lin, and further work is needed to test the vaccine against antibiotic-resistant strains.
It is also unclear how long the vaccine鈥檚 protection lasts, and whether the findings in mice will translate to people, says Lin.
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