Plant-derived Plague Vaccine Protects Guinea Pigs

NEW YORK (Reuters Health) – A vaccine against Yersinia pestis, which scientists grew in tobacco plants, effectively protected guinea pigs against a lethal aerosol exposure to this bacterium that causes the plague, also known as the "bubonic plague," or the "black death," which killed millions of people in Europe during the Middle Ages.

This report demonstrates the ability of a "rapid and highly scalable" plant expression system to produce a vaccine that generates an immune response against Y. pestis and perhaps other potential agents of biological warfare, the scientists note in the current issue of the Proceedings of the National Academy of Sciences, Early Edition.

The plague is usually spread by bites of a rodent flea that carries Y. pestis or by handling an infected animal. Antibiotics are effective against the plague, but if not treated promptly, the infection is still often lethal.

Small outbreaks of Y. pestis infection still occur in Africa, Asia, and the Americas and there is a "great need" for improved plague vaccines that can be manufactured quickly and inexpensively, Dr. Luca Santi from Arizona State University in Tempe and colleagues point out in the paper.

Santi’s group developed a genetically engineered Y. pestis vaccine based on two key Y. pestis antigens — F1 and V – proteins that trigger the body to produce an immune response. These two proteins were successfully and rapidly grown separately or as a combined fusion protein in the leaves of tobacco plants.

"All of the plant-derived purified antigens, administered subcutaneously to guinea pigs, generated systemic immune responses and provided protection against an aerosol challenge with virulent Y. pestis," Santi and colleagues report.

A majority of vaccinated guinea pigs survived exposure to the plague bacterium and those that did develop plague survived markedly longer than animals vaccinated with a placebo.

The scientists believe their plant-based expression system offers the potential to make high quantities of this vaccine at relatively low cost.

In the United States, the last urban plague epidemic occurred in Los Angeles in 1924-25. Since then, there have been mostly scattered cases in rural areas (an average of 10 to 15 persons each year), according to the Centers for Disease Control and Prevention.

Globally, the World Health Organization reports 1,000 to 3,000 cases of plague every year.

SOURCE: Proceedings of the National Academy of Sciences, January 9, 2006.