A pilot study found that the BCG tuberculosis vaccine — already known to retrain the immune system — changed key Alzheimer's-related biomarkers in participants without existing Alzheimer's pathology. Researchers observed shifts in amyloid-beta levels in both cerebrospinal fluid and blood, alongside enhanced immune activity in the fluid surrounding the brain. These changes were not seen in people who already had Alzheimer's pathology, suggesting timing matters. The findings build on earlier epidemiological data linking BCG bladder cancer treatment to lower dementia risk. While this small, open-label study was designed to assess safety and biological mechanisms — not prove prevention — it provides a credible biological rationale for a larger randomized trial to test whether BCG could help prevent cognitive decline.
