Tuberculosis vaccines being tested in developed countries will not protect people living in parts of the developing world where they are most needed because they trigger a different body response, researchers said on Monday.

Scientists at University College London (UCL), who looked at variations in immune system responses around the globe, found that in countries near the equator the tuberculosis bacteria turn the body’s normal protective response into a harmful one.

So like the BCG, or bacille Calmette-Guerin vaccine, used against TB in some countries, the latest vaccines which use the same approach will not work in developing countries, according to the researchers.

“What we have done is identify the mechanisms that we think lead to the fact that BCG vaccine does not work close to the equator, where the problem really is,” Professor Graham Rook, an immunologist at UCL, said in an interview.

“We realized that the vaccine candidates going into clinical trials at the cost of hundreds of millions of dollars haven’t in any way answered that particular problem,” he added.

In countries in the northern hemisphere, the immune system protects the body against TB with TH1 cells. BCG and new candidate TB vaccines are designed to boost the TH1 cells.

But in people living near the equator, the TH1 cells are already on alert, so the protective mechanism is switched on but does not work because another inappropriate response is also turned on which undermines it.

“What is needed, in our opinion, is not a vaccine that turns on the protective mechanism because that is already there but rather a vaccine that turns off the subversive mechanism that shouldn’t be there,” said Rook, who reported the findings in the journal Nature Reviews Immunology.

TB is a contagious airborne disease that affects about 9 million people each year and kills 2 million. The World Health Organization has warned that TB has reached alarming proportions in Africa where co-infection with HIV makes a lethal combination.

“We are not saying that funding for TB vaccination in developing countries should be stopped — quite the contrary, given that TB kills between 2 and 3 million people every year. But we are concerned that the BCG vaccine is failing these countries and that TB vaccines currently on trial are likely to go the same way,” Rook added.

The researchers believe a new vaccine approach — turning off the damaging immune response — could be used to develop vaccines to combat other infections including HIV.

By Patricia Reaney

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