Identification of this complicated bacterial survival strategy will lead to new anti-TB drugs in the future. Researchers said they already had positive leads.
TB remains one of the major killers causing two million deaths worldwide each year. In India, it kills 1,000 people daily with multi-drug resistance TB (MDR) and extreme drug resistance TB (XDR) emerging as major public health threats.
“These stem cells will provide us with a new drug target,” Gobardhan Das, lead scientist at the International Centre for Genetic Engineering and Biotechnology (ICGEB), told Deccan Herald. Das headed a team of researchers from the AIIMS, Delhi, and Vanderbilt University in Tennessee that made the discovery.
Both MDR and XDR TB happen because a handful of bacteria manage to survive inside a protective barrier, provided by a type of stem cell called mesenchymal stem cells. According to a 2004 estimate, more than 4 per cent of TB cases in India is MDR. There is no XDR count.
Public health researchers warn that the extent of drug-resistant TB may be much more because most of the diagnostic laboratories are not capable of detecting them.
TB bacteria evade the immune system by hiding inside compartments called granulomas—a group of immune cells—in infected lung, spleen and extra-pulmonary spots.
The protective cover is provided by the mesenchymal stem cell, which the bacteria recruit for creating the barrier, leading to latent infections. The common TB test (sputum) does not help as it cannot detect the bacteria if their level falls.
The world has not seen a new drug against TB in the last four decades. Rifampicin was the last medicine discovered in 1963. Though it continues to be the mainstay of TB treatment, the emergence of MDR and XDR TB has necessitated the need to have new drugs.
“These stem cells are Janus-faced. They do not give the immune system access to the bacteria while keeping the bacteria’s replication under check so that a limited number of bugs can stay safely for a long time,” Das said.
Among other things, these stem cells produce nitric oxide, which not only stave off the surrounding immune cells but also helps check multiplication of the bacteria, the team said reporting their results in the Proceedings of National Academy of Sciences.