New TB vaccine design called for in poor nations
LONDON, Tuesday (Reuters) 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 realised 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 Organisation 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. |