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The Pharmaceutical Journal Vol 267 No 7168 p470-481
6 October 2001

BPC 2001 summary

Advances in tuberculosis vaccine research

The only way to control TB was with a combination of improved diagnosis, drugs and vaccines, said Professor Douglas Young, department of infectious disease and microbiology, Imperial College School of Technology and Medicine, London.

Results of trials of the efficacy of BCG vaccine had been confusing. In some, 80 per cent of people vaccinated had become immune to TB whereas, in others, none had. Many explanations had been put forward for this — substrains of the bacteria in BCG vaccine might have developed over time, some of which might work better than others, or it could be that the strains used in the vaccine were less effective now than they had been originally. Another theory was that BCG vaccine was ineffective but that exposure to environmental mycobacteria reproduced its effects. Conversely, such bacteria could produce an immune response that prevented the vaccine from working. The lowest efficacy of BCG vaccine had occurred in trials that took place in countries near the equator, where exposure to environmental mycobacteria was most common.

Professor Young said that BCG vaccine was effective at preventing childhood forms of TB even in parts of the world where it was ineffective in adults. This was why children were still given the vaccine. Researchers had noted that people were less likely to develop TB before puberty than after. This suggested that there was an association between susceptibility to TB and sex hormones but it was not known what this was.

Live attenuated vaccines could be made by deleting the genes that made Mycobacterium tuberculosis virulent and subunit vaccines could be produced by cloning protective antigens that would induce an immune response before infection took place. Researchers were also investigating vaccines that reduced the severity of existing disease. Of those that were currently under investigation, animal studies had suggested that subunit vaccines seemed to be as good as BCG vaccine, whereas live attenuated and modified-BCG vaccines appeared to be slightly better. Results with these new vaccines had been interesting but it remained to be seen whether they offered protection to man.

“The problem with studies into vaccines is that the BCG vaccine would have to be withheld in some study groups. It would then take 25 to 30 years before anyone knew if the new vaccines worked, by which time the patent has been lost. So companies are much more interested in post-exposure vaccines,” Professor Young said.

Immunotherapy (which limits active infection) was also being investigated. If successful, it could allow the length of courses of drug treatment to be reduced, although it would have no effect on the incidence of TB. However, reducing the length of antibiotic courses would only be feasible if the rate of relapse remained unaffected.

“Our incomplete understanding of how immunity to TB occurs presents a serious challenge to rational vaccine design,” he concluded.

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