Assessment of immune response to repeat stimulation with BCG vaccine using in vitro PBMC model

BACKGROUND Tuberculosis (TB) is one of the most prevalent cause of death due to a single pathogen. Bacillus Calmette Guérin (BCG) is the only vaccine available for clinical use that protects against miliary TB; however, this vaccine has shown variable levels of efficacy against pulmonary TB. In India, a single dose of BCG vaccine is given and there are few countries where repeated doses of BCG are given. The incidence of TB in India is very high inspite of primary vaccination in neonatal period and therefore requires consideration for repeated immunization. METHODS To improve BCG immunogenicity, we have evaluated specific antimycobacterial immune responses (anti-BCG IgG and IFN-gamma), T cell activity-ADA, CD4 and CD8 T cell count, and CD4/CD8 ratio in a peripheral blood mononuclear cells (PBMC) model using boost immunization protocols with the BCG vaccine. PBMC were induced with a repeat dose of BCG at 24 and 72 hrs of cell culture. RESULTS At the end of the experimental time, supernatant was collected to estimate anti-BCG IgG titer, interferon gamma, ADA activity, CD 4 and CD8 T cell count, and CD4/CD8 ratio. We demonstrated that PBMC induced with a repeat dose of BCG showed an increased specific anti-mycobacterial immune responses, T cell activity, and ADA activity as compared to PBMC induced with BCG alone or without BCG induction. CONCLUSION The repeat BCG stimulation of PBMC obtained from BCG vaccinated individuals shows enhanced immune activation with respect to increased anti-BCG titre, IFN-gamma and ADA activity without concomitant increase in CD4 and CD8 cells. This study provides some basic data in future experiments in animal models with respect to repeat BCG vaccination.