Genetic mapping reveals TB vaccine may have evolved beyond usefulness

A genetic investigation by an international research team including McGill University researcher Marcel Behr suggests a bacterium commonly used as a vaccine against tuberculosis may have outlived – or out-evolved – its usefulness.

Dr. Behr, along with researchers from France’s Institut Pasteur and genetics labs in the United Kingdom, mapped and analyzed the genetic code of bacillus Calmette-Guérin (BCG), a derivative of Mycobacterium bovis that is part of the World Health Organization’s Expanded Program on Immunization.

“We’ve determined that this bacteria, which is given as a vaccine two million times a week around the world, is highly evolved from when it was first used in 1921,” said Dr. Behr. “Consequently, we’re not really sure if it’s as effective as it’s been in the past or as it could be.”

Their findings, published by the Proceedings of the National Academy of Sciences (PNAS) Online, indicate that the vaccine’s decreased virulence against tuberculosis appears to be attributable to genetic factors such as the loss of the protein secretion system ESX-1.

Though previous trials dating back to the 1960s have called into question the efficacy of BCG, the new study “puts a punctuation mark” on the need to develop a more effective vaccine, said Dr. Behr. He said the research has been presented to the World Health Organization, which has declared worldwide tuberculosis control among its top priorities for 2007, to draw attention to the issue.

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Proceedings of the National Academy of Sciences
McGill Reporter