Young Indian adults vaccinated at birth, but given the BCG vaccine once again, see an improvement in their immune response against tuberculosis (TB) by boosting the numbers and response of a specific subset of white blood cells called Th17 cells involved in fighting TB, a new study has found. Re-vaccination may make them less likely to develop the disease, it said.
The study, led by scientists at the Centre for Infectious Diseases Research (CIDR), Indian Institute of Science (IISc.), and published in the journal JCI Insight , was carried out in collaboration with clinicians and researchers in India, USA, Europe and the UK.
An IISc. release said about a quarter of the world’s population is thought to have latent TB, but have no disease symptoms, and have a 5 to 15% chance of falling ill with TB in their lifetime. The only clinically-approved TB vaccine is BCG, a weakened form of a bacterium called Mycobacterium bovis , which is administered at birth in India. It is effective in preventing tuberculosis meningitis and military disease in infants, but its effects rarely persist beyond 15 to 20 years, and young adults are particularly at risk of falling ill from TB.
“BCG is a tried and tested vaccine. There is now a lot of interest in trying to see if re-vaccination of young adults in the age group of 18 to 22 years is capable of boosting anti-TB immunity...We are able to demonstrate for the first time that re-vaccination is immunogenic in the Indian context. It induces the right type of immune cells,” Annapurna Vyakarnam, Fellow and Visiting Scientist at CIDR, and a senior author of the paper, was quoted as saying in the release.
According to the release, she and her colleagues recruited 200 young adults from Madanapalle in Andhra Pradesh, home to one of the oldest tuberculosis sanatoriums in the country. All the volunteers had been given BCG at birth. They were split into two groups: those who had latent TB – determined using a standard assay called QuantiFERON-TB Gold test, and those who did not carry the bacteria. Within each group, half of the individuals were re-vaccinated with BCG. Blood samples were extracted and analysed over nine months, and detailed flow cytometry investigations were carried out to check for the presence of up to 256 immune cell subsets.
“Compared to un-vaccinated individuals, re-vaccinated 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 response against TB. Re-vaccination also boosted the numbers of innate immune cells that form the first line of defence against TB,” the release said.