Vaccine may work against tuberculosis

WASHINGTON (Reuters) -- A new and improved vaccine against tuberculosis might be ready for testing in people as early as next year, researchers said Wednesday.

They said their vaccine, based on a formulation nearly a century old, was dramatically better and protected all tested guinea pigs against disease.

"It's a pretty potent vaccine," Dr. Marcus Horwitz, a professor at the University of California Los Angeles who led the study, said in a telephone interview.

"The difference between the unvaccinated guinea pigs and those that were vaccinated is just day and night."

Mycobacterium tuberculosis bacteria infect 2 billion people worldwide. The bacteria are infectious and can be passed on by sneezing or even by breathing dust into which infected people have spit.

"Tuberculosis is the greatest cause of death from a single infectious agent, killing 2 million people each year worldwide," Horwitz, who reported his team's findings in this week's issue of the Proceedings of the National Academy of Sciences, said.

AIDS has recently outpaced TB, having killed 3 million people in 1999, but many AIDS victims actually die of tuberculosis because of their weakened immune systems.

There is a vaccine -- the BCG vaccine made between 1906 and 1919 from weakened Mycobacterium bovis bacilli, which infect cattle. More then 3 billion doses of the vaccine have been given to people worldwide, but it is only about 50 percent effective.

No one has been able to make a better vaccine.

Horwitz's team tested guinea pigs, which develop tuberculosis very similar to the human disease. They started out with two versions of the BCG vaccine, and added a protein they thought might work, based on previous studies.

"The protein is the major secretory protein of the organism that causes tuberculosis," Horwitz said. "Most proteins of a bacteria are inside, but there are some proteins which are actually excreted."

This particular protein helps build the cell wall of the bacterium, and is out in the open where the body's immune system can see it, Horwitz said.

"Tuberculosis is inside white blood cells," he said. "You have to have a way for the immune system to know that the cell is infected so it can do something about it."

The researchers genetically engineered the BCG vaccine so that it also produced this protein. The immune systems of the animals recognized it and were able to attack TB bacteria when the guinea pigs were infected.

"The unvaccinated animals, their lungs just become completely covered with tubercles and destroyed and the animals protected with the vaccine have one or two lesions which are contained," Horwitz said.

He said the vaccine would be cheap and easy to administer, costing just pennies a dose. He said UCLA is negotiating with pharmaceutical companies, which he declined to name, to set up a program to produce and test the vaccine in people.

One bit of bad news -- it will probably not be useful for people with HIV.

"One of the drawbacks of BCG is it can cause disease in immunocompromised patients," Horwitz said. Any AIDS patients who got the vaccine would have to be carefully monitored to make sure they did not develop disease from the vaccine itself.

Copyright 2000 Reuters. All rights reserved. This material may not be published, broadcast, rewritten, or redistributed.

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