Tuberculosis relative could be new vaccine

Injecting modified bacteria related to those which cause tuberculosis could protect against the lung disease, US scientists say.

Experiments on mice showed the injections could completely eliminate tuberculosis bacteria in some cases, Nature Medicine reports.

The only TB vaccine – the BCG jab – is not very effective.

The research is in its early stages and the potential for a human vaccine is unknown, campaign group TB Alert says.

Tuberculosis is caused by Mycobacterium tuberculosis. It is one of the top 10 leading causes of death, according to the World Health Organization, killing 1.7 million people each year.

The BCG vaccine has variable results. It has been shown to be between 0% and 80% effective in different parts of the world.
There are also potential problems giving the live vaccine to some of the most at risk patients – those with HIV.
In the family

Researchers at the Albert Einstein College of Medicine in New York were investigating a cluster of genes called esx-3, variants of which are in all types of Mycobacterium and help the organisms evade the immune system.

Mycobacterium tuberculosis cannot survive without its esx-3 genes but its relative, Mycobacterium smegmatis, can.

Scientists deleted the genes from M. smegmatis and injected an otherwise deadly dose into mice. Within three days the mice had cleared the bacteria from the lungs and kidneys.

The research team then tried putting the esx-3 genes from M. tuberculosis into M. smegmatis, which they then called Ikeplus.
Mice were still able to rapidly clear an Ikeplus infection but it seemed to leave a lasting immunity against M. tuberculosis.

Survival

In mice infected with the TB bacteria, those which received no vaccine died after 54 days on average.

Those vaccinated with BCG lasted 65 days, while mice immunised with Ikeplus survived for 135 days.

In the mice which survived the longest, more than 200 days, researchers were no longer able to detect the deadly bacteria.

Lead researcher Prof William Jacobs said: “We consistently protected mice better with Ikeplus than with BCG.

“This is something we’ve dreamed about for years, to be able to get longer protection and bactericidal immunity.”

He warned that only 20% of the mice were long-term survivors so the vaccine would need further development.

He added: “Ikeplus is different from any other TB vaccine and it’s a new tool for the TB arsenal.”

A TB Alert spokesperson said: “These are interesting experiments but it is too early to tell what impact they will have on the development of a safe and effective vaccine.” (James Gallagher/BBC News)