BCG vaccine shows dementia prevention promise in mice
A Johns Hopkins-led study found the century-old BCG vaccine, given to mice before symptoms, sharply reduced tau tangles and brain inflammation linked to Alzheimer's disease. Human observational data supports a potential link, but researchers stress critical gaps remain before considering human use.
The BCG vaccine, a century-old tuberculosis shot, reduced key markers of dementia in a mouse study. When given to genetically engineered PS19 mice at three months of age-before symptoms typically emerge at six to seven months-the vaccine cut tau protein tangles and brain inflammation.
Led by physician-scientist Dr. William R. Bishai, the study found vaccinated mice were about five times more likely to show reduced tau deposition and four times less likely to exhibit markers of persistent immune activation. Brain imaging showed less atrophy, and memory tests showed better performance. Gene analysis revealed the vaccine normalized the expression of hundreds of genes linked to Alzheimer's disease and neuroinflammation.
Mechanisms suggest trained immunity may explain effects
The protective effect appears linked to a concept called trained immunity. Microglial cells, the brain's immune cleaners, from vaccinated mice showed higher activity in clearing debris. The mice also had raised levels of certain peripheral immune cells, suggesting a reprogrammed, more responsive immune system that may better combat the processes leading to dementia.
Human observational data support potential link
This animal work aligns with existing human data. Retrospective studies in bladder cancer patients, who receive BCG as a standard therapy, have shown a correlation with a lower incidence of dementia. These analyses indicated risk reductions ranging from 12% to 78% over follow-up periods of three to 15 years. Small prospective trials have also reported improvements in dementia-related biomarkers following BCG treatment.
BCG has a long safety record. At least 340 million infants receive it annually globally, and several hundred thousand adults are treated with it for bladder cancer each year. Its uses have expanded beyond tuberculosis to include protection against leprosy and as an immunotherapy for other conditions.
Critical gaps remain before human use
Despite promising signals, the mouse results and human associations do not prove BCG reduces dementia risk or is safe and effective for prevention in people. Researchers emphasize substantial questions about who might benefit, the optimal timing for vaccination, and safety in aging populations. They note that trained immunity in humans may wane after about a year.
A US-based consortium has proposed a large prospective clinical trial to test BCG for dementia prevention. The next step involves moving to early clinical trials in aged patients at risk for dementia to assess long-term cognitive impact.
