BENGALURU: A new study led by scientists at the Centre for Infectious Diseases Research (CIDR) at the Indian Institute of Science (IISc) found that when young Indian adults who have been vaccinated at birth are once again given the Bacillus Calmette–Guérin (BCG) anti-tuberculosis (TB) vaccine, their immune response against TB improves and they are less likely to develop the disease.
It showed that the revaccination boosted the numbers and response of a specific subset of white blood cells (WBC)—called Th17 cells—which fight TB bacteria. The study, published in the journal JCI Insight, was carried out in collaboration with clinicians and researchers in India, USA, Europe and the UK.
The only clinically-approved TB vaccine is BCG, a weakened form of a bacterium called Mycobacterium bovis, which is administered at birth in India, IISc said in a realease. It is effective in preventing TB, meningitis and military disease (vector-borne diseases) in infants, but its effect rarely persists beyond 15-20 years, and young adults are particularly at risk of falling ill from TB.
“We demonstrated for the first time that revaccination is immunogenic (able to produce an immune response) in the Indian context,” said Annapurna Vyakarnam, Ramalingaswami Fellow and visiting scientist at CIDR, and a senior author of the paper. “It induces the right type of immune cells.”
She and her colleagues recruited 200 young adults from Madanapalle, Andhra Pradesh, home to one of the oldest TB sanatoriums in India. All the volunteers had been given BCG at birth. They were split into two groups: those who had latent TB and those who did not carry the bacteria. Within each group, half of the individuals were revaccinated with BCG. Blood samples were extracted and analyzed over nine months to discover how it boosted the WBCs which fight TB bacteria.
Compared to unvaccinated individuals, revaccinated individuals were found to have more than twice as many immune cells belonging to specific subsets called CD4 and CD8 T-cells. These cells produce signalling proteins called cytokines that rally the body’s immune responses against TB. Revaccination also boosted the number of innate immune cells that form the first line of defense against TB. About a quarter of the world’s population is thought to have latent TB — they carry the bacterium mycobacterium tuberculosis, but have no disease symptoms. They have a 5-15% chance of falling ill with TB.