Each year, more than a million people die of tuberculosis, a disease caused by the pathogen Mycobacterium tuberculosis. The only available defence against it today is a vaccine named Bacillus Calmette-Guérin, commonly known as BCG, which is an attenuated (weakened) form of the pathogen. But BCG is not evenly effective and poses safety issues for patients with weakened immune systems. Scientists, therefore, have been trying to develop a better vaccine against TB.

In this quest, a group of scientists at the Indian Institute of Science (IISc), Bengaluru, has achieved significant success. Instead of attenuated mycobacterium, they decided to try the pathogen’s secretion, known as outer membrane vesicles (OMV). Vesicles are membrane bubbles that hold several proteins and lipids.

OMVs are good antigens — substances that prod our immune system to produce antibodies to kill invading pathogens. Attenuated pathogens are still pathogens — therefore, instead of teaching our bodies to produce antibodies to fight the invaders they might, like a good vaccine, end up producing a severe disease that could even kill. But OMVs, which also trigger an immuno-response, cannot cause disease — hence they are safe. Further, OMVs contain a variety of antigens and can, therefore, elicit a better immuno-response.

However, the disadvantage is that OMVs come in many sizes and shapes, and are not stable.

The scientists, led by Edna George, of the IISc’s Centre for BioSystems Science and Engineering, have overcome this problem by bringing into the picture gold nanoparticles. OMVs that swallowed gold nanoparticle became uniform in size and lived longer (more stable).

An article on the IISc website quotes George as saying that to synthesise OMV coated on gold nanoparticles, “the OMVs and gold nanoparticles are forced through a 100 nm filter”. The OMVs break up in the process and encapsulate the gold nanoparticles.

For the research, the scientists used OMVs derived from another bacterium, Mycobacterium smegmatis, which is related to the deadly Mycobacterium tuberculosis but is not disease-causing.

In the next phase, the team intends to use OMVs derived from Mycobacterium tuberculosis and test the vaccine on animals. When this work is taken to its logical end, after clinical trials, the world would have a brand new weapon to fight TB.