Bio-tick-nology yields Lyme disease vaccine.

Bio-tick-nology yields Lyme disease vaccine

An experimental vaccine made from bacterial proteins has completely protected mice against Lyme disease, raising hopes that people may someday benefit from a similar vaccine. But researchers say the road to human trials remains as twisted as the corkscrew-shaped bacterium that causes the syndrome.

The incidence of Lyme disease, which can bring serious nerve, joint and heart problems, has skyrocketed in the United States and Europe in recent years. But the causative bacterium, Borrelia burgdorferi, has a knack for deceiving the body's defenses. That trait -- coupled with the lack of a good animal model in which to test candidate vaccines -- has impeded the search for a shot that could help the immune system repel the tick-borne troublemaker.

Recently, Erol Fikrig and his co-workers at the Yale University School of Medicine developed a strain of mice that, when infected with B. burgdorferi, show many of the arthritic and cardiac symptoms seen in humans with Lyme disease. Now they've used those mice to test a new vaccine.

With recombinant DNA methods, Fikrig's team mass-produced a protein called OspA, which normally sprouts from the surface of B. burgdorferi. They vaccinated their mice with doses of the protein, then challenged each mouse with one of three different strains of B. burgdorferi. Vaccinated mice fought off the infection and showed no evidence of joint inflammation or heart disease at autopsy, the researchers report in the Oct. 26 SCIENCE. In contrast, they say, unvaccinated mice remained infected and showed clear signs of disease.

The results are "very encouraging," Fikrig says, noting that the vaccine -- made from a Westchester County, N.Y., variety of B. burgdorferi OspA -- protected against all three Lyme-causing strains tested.

Unfortunately, the jump to human application "is not so simple," says Alan G. Barbour, a medical microbiologist at the University of Texas Health Sciences Center in San Antonio. He says further work must establish that the vaccine works when the bacteria are transmitted by live ticks rather than by injection. Barbour cites unpublished evidence suggesting that tick saliva may somehow enhance infectivity or that lab strains living couch-potato existences in culture plates may lack the vigor of wild-type bacteria.

He and Fikrig also caution that some strains of B. burgdorferi may bear OspA variants different enough to sneak past the immune systems of hosts vaccinated with the Westchester OspA. The Yale team is now testing its vaccine against additional U.S. and foreign strains and determining how long immunity lasts against the strains already used.

The lack of a primate model to confirm rodent findings still slows the path to a human vaccine. "There's not enough money to do that research now," Barbour says, noting the high cost of primate studies. "But we'll need to do it" if a Lyme vaccine is ever to reach the market.