Till date, the location in the body where the TB bacteria hide was not known making it difficult to completely eliminate it even after rigorous treatment. The bacteria remain in dormant but viable state but may reactivate to cause active TB in people who have been successively treated earlier. Now, in a significant breakthrough, Bikul Das, an Indian researcher at Stanford University has finally discovered the hiding place of dormant tuberculosis bacteria
The study published in the journal Science Translational Medicine reveals that the dormant TB bacteria hide in CD271CD45, a particular kind of bone marrow mesenchymal stem cell which is beyond the reach of antibiotics and the body’s own immune system. The scientists explained that qualities like a natural resistance to drugs, irregular division and a advantaged immune status allow these cells to survive various types of treatment.
‘We never knew where TB bacteria used to hide; but now that we know that the bacteria invade and hide in stem cells in the bone marrow, it would be possible to hunt them down and kill them in future. The present medicines don’t help much in this respect,’ said co-author Deepjyoti Kalita, a professor of microbiology with Gauhati Medical College.
In a previous study, Das and his team tested their theory on mice. They then carried out a small clinical trial in the Idu-Mishimi community of Arunachal Pradesh that has a very high occurrence of TB. Bone marrow biopsies were taken from nine tuberculosis treated patients who had no traces of the bacteria in their lungs. In eight of the nine patients, the team found genetic material from bacteria inside the stem cells. They also isolated active bacteria from the cells in two of these cases.
‘Not only is this strong evidence that the tuberculosis can remain dormant in stem cells, but it shows that the living bacteria could be recovered from these cells after a long period of time,’ said Dr Bikul Das, lead author of the study. ‘We now need to learn how the bacteria find and infect this tiny population of stem cells, and what triggers it to reactivate years or decades after successful treatment of the disease,’ he said. ‘It’s also very suggestive of how the reactivation could be triggered: These stem cells are known to migrate to sites of injury or inflammation and begin dividing. So, migrating stem cells harbouring dormant bacteria might reactivate the disease in the lung,’ he added.
Other infectious diseases may also employ similar ‘wolf-in-stem-cell-clothing’ tactics, the scientists suggest. According to Dr Dean Felsher, co-senior author, ‘Other infectious agents might use stem cells in a similar manner. We’d like to further characterise whether and how these stem cells provide a protective niche for other infectious agents.’
TB still kills around 1.9 million people across the world. According to Press Information Bureau, tuberculosis in India continues to take a toll of 1,000 per day or one every minute. It is estimated that there are 14 million TB cases in our country. The WHO recommended strategy for tuberculosis control is DOTS – Directly Observed Treatment, Short-Course. It provides cure for tuberculosis with a course lasting six to eight months.