Long-term effects of BCG vaccination on telomere length and telomerase activity

This study explores the effects of Bacillus Calmette-Guérin (BCG) vaccination on telomere maintenance, an aging-related process, in immune cells. While BCG reduces systemic inflammation and enhances innate immune responsiveness by inducing trained immunity, its effects on other immune aging hallmarks, such as telomere shortening, are not fully understood. We assessed telomere length in two independent human cohorts before and three months after BCG vaccination. Telomere shortening was consistently observed after BCG, but not after placebo vaccination. Trained immunity non-responders were likelier to lose telomere length, but only among males. Higher pre-vaccination testosterone levels were associated with greater telomere loss in males. In vitro, BCG training activated telomerase, particularly in females, and this was partially prevented by exogenous testosterone. These findings suggest BCG vaccination influences telomere dynamics in a sex-specific manner, contributing to understanding BCG's broader effects on aging-related processes.