TB shot found promising in animal tests

September 5th, 2011 - 12:22 pm ICT by IANS  

Washington, Sep 5 (IANS) A tuberculosis (TB) shot developed by researchers has proved both potent and safe in animal studies.

TB kills an estimated 1.7 million people every year globally, according to the World Health Organisation (WHO). It estimates that nearly 20 lakh people in India develop tuberculosis each year, of which 8.7 lakh are infectious cases.

“Producing effective TB vaccines requires a better understanding of mechanisms used by M tuberculosis (the bug that causes TB) to evade our body’s immune responses,” said William Jacobs.

Jacobs, professor of microbiology & immunology at Einstein College of Medicine, said the currently used Bacille Calmette-Guerin (BCG) vaccine has been notoriously inconsistent in protecting against TB.

To figure out how M. tuberculosis hoodwinks our immune system, Jacobs and colleagues worked with a sister species, M. smegmatis — lethal to mice at high doses but does not harm people, the journal Nature Medicine reports.

Researchers modified M. smegmatis through ESX-3 genes, which helps TB bugs outwit the immune system, according to an Einstein statement.

When high doses of the modified M smegmatis bug were infused into mice, they cleared the infection - eliciting the same response as a successful TB vaccine. But M. tuberculosis could not be manipulated in this way to make a vaccine.

Jacobs and colleagues found a way around this stumbling block. They took the modified M. smegmatis bug and inserted the similar set of ESX-3 genes from M tuberculosis.

These M. smegmatis bacteria were then infused into mice, which once again fought off the infection.

And eight weeks later, when the mice were challenged with high doses of M. tuberculosis-which kills mice as well as people-these “vaccinated” mice lived much longer than control mice: an average survival time of 135 days vs. 54 days.

“Most notably,” said Jacobs, “those vaccinated animals that survived for more than 200 days had livers that were completely clear of TB bacteria, and nobody has ever seen that before.”

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