DNA gives hope for TB vaccine

by Mike Miller
DNA gives hope for TB vaccine

Scientists will soon launch the first clinical trial of a new, but controversial, vaccine for tuberculosis (TB). Analysis from laboratory testing, moreover, shows that the vaccine may go beyond traditional preventative vaccines. It also works as a therapeutic treatment for patients who already have the disease.

The product is one of a new class of vaccines in trials around the world. Called DNA vaccines, these yet-to-be-approved inoculations involve the direct injection of isolated genes from disease organisms (bacteria or viruses) into the muscles of patients. The foreign DNA is taken into cells and used just like the patient’s own DNA to make bacterial or viral protein.

When the foreign, unrecognised protein is spotted by the patient’s immune system, the body acts in the same way as for conventional vaccines. It triggers an immune response against the protein, and ‘memorises’ the invader. Next time the protein is encountered – probably during a real infection – the immune response is bigger and better, helping the patient to fight off the disease.

The new TB vaccine uses a gene from Mycobacterium leprae, a bacterium closely related to the disease-causing Mycobacterium tuberculosis. However, some scientists argue that the gene is too similar to one found in humans. They suggest that the immune system could suddenly react against its own proteins. Perhaps the vaccine could do more harm than good, the critics argue.

Dr Doug Lowrie, the immunologist who developed the TB vaccine at the MRC National Institute for Medical Research in London, defends the safety of his product. “Our clinical trial is very exciting. Two to three million people die each year from TB and the bacteria are becoming resistant to current drugs. A new treatment is desperately needed. This vaccine is an effective therapeutic; in some mice we found that inoculation produced a complete eradication of the disease and lasting protection. If our vaccine proves effective in this and successive trials, perhaps we could get it on the market by 2005.”