PHA-Exchange> TB vaccines 'won't work in poor nations'

[Claudio]

From: "Vern Weitzel" <vern.weitzel at undp.org>

http://www.scidev.net/News/index.cfm?fuseaction=readNews&itemid=2271&languag
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TB vaccines 'won't work in poor nations'

Priya Shetty
4 August 2005
Source: SciDev.Net

Tuberculosis vaccines under development might be powerless in developing
countries, researchers have
warned.

They say this is because research is not taking into account the different
immune systems of people
in the South.

The standard BCG vaccine is used worldwide against tuberculosis. It works by
stimulating the
production of 'TH1' immune cells. New vaccines in development mimic this
mechanism.

Yet, while boosting TH1 cells has been effective in industrialised
countries, it is failing in
developing countries — where the disease kills the most people.

Writing in Nature Review Immunology, the researchers say the BCG vaccine
does not work in people in
developing countries because their immune system has a separate response
that counteracts with the
protective 'TH1' response.

In poor countries, people often come into contact with bacteria related to
Mycobacterium
tuberculosis — the microbe that causes tuberculosis. This means that their
immune system is already
primed to produce TH1 cells against the bacterium.

However, they are also exposed to parasitic worms that provoke a response
from a second type of
immune cell, known as TH2.

As a result, their bodies continually produce a baseline level of TH2 cells.
These cells are able to
oppose the TH1 response.

The BCG vaccine boosts the TH1 response, but does not dampen the TH2 one. As
a result, the vaccine
does not prevent people in developing countries from getting the disease.

Designing a vaccine that targets this harmful mechanism would be more likely
to work, say the
researchers.
So far, however, their theory has only been tested in animals, and is
awaiting tests in people.

Reference: Nature Reviews Immunology 5, 661 (2005)