A gene is the key to a more effective tuberculosis vaccine

 That human and bovine tuberculosis are caused by two different bacteria is anything but a surprise: Robert Koch, the discoverer of the disease-causing bacterium, often known as Koch's bacillus, has already pointed out. Microbiologists from the University of Zaragoza, the Carlos III Institute in Madrid and their colleagues in Paris have discovered the reason why Mycobacterium bovis, the cow microbe, is truly useless when it comes to infecting humans: it is about few mutations in a single gene, already known for its drastic effect on virulence. The work suggests a simple mechanism for creating a better human vaccine than the current one. It will take 10 years at best.

The bacterial species that infects humans is called Mycobacterium tuberculosis, which creeps into the lungs, forms nodules, and slowly destroys the airways and blood capillaries. Hygiene and antibiotics have reduced the cases and their severity, shortening the endless - and almost literary - stays in mountain hospitals to a few months' treatments in Western countries. The situation, of course, is very different in the developing world.

"The current vaccine against tuberculosis is based on bacteria from cows," explains the first author of the research, Jesús Gonzalo-Asensio, from the Faculty of Medicine of the University of Zaragoza. As this vaccine bacteria is very clumsy infecting humans, it is easy to attenuate it so that, without causing the disease, it induces human antibodies capable of neutralizing it. In return, these antibodies show only limited efficacy, since they are not directed against human bacteria, but against their distant bovine cousin.

"The problem we ask ourselves is: Why don't bovine bacteria spread easily to humans?", Gonzalo says, "What are the keys that prevent it?" The problem may seem intractable when you consider that cow and human bacteria are 99% identical in their genome. "But that's more or less the difference between a human and a chimpanzee," Gonzalo says. And that is a difference that should not be overlooked if one is dedicated to medicine.

Research by Spanish and French scientists has shown that the great difference between human and bovine bacteria is located in a single gene called PhoP, a known regulator of the virulence of this bacterium. Gonzalo and his colleagues believe that this will make it possible to generate a more effective and safe tuberculosis vaccine, based on human bacteria, but with the virulence gene (PhoP) inactivated for its action in humans. They feel optimistic if they estimate its clinical application in 10 years. But that's nothing when it comes to this 10,000-year-old disease.