What's Happening?
A preclinical study led by researchers at Johns Hopkins University School of Medicine indicates that the Bacillus Calmette-Guerin (BCG) vaccine, commonly used for tuberculosis prevention and bladder cancer treatment, may also reduce the risk of dementia.
The study, published in Science Advances, found that mice genetically engineered to develop dementia symptoms (PS19 mice) that received the BCG vaccine showed fewer hallmark signs of the disease. These signs included reduced neurofibrillary (tau) tangles in the brain, decreased sustained immune cell activation, and improved memory compared to unvaccinated mice. BCG-treated mice performed better in novel object recognition tests and exhibited better body-weight maintenance and survival. Dr. William Bishai, co-director of the Johns Hopkins Center for Tuberculosis Research and senior author, suggests that myeloid cells in the central nervous system and brain utilize information from BCG to recognize and respond to the plaques and tangles characteristic of Alzheimer's disease and related dementias. This protective effect is believed to be driven by 'trained immunity,' where innate immune cells learn to respond more effectively to future threats after an initial stimulus.
Why It's Important?
This research is significant because it proposes a novel approach to dementia prevention using an existing, widely available vaccine. Dementia, particularly Alzheimer's disease, is a growing public health crisis with limited treatment options. The concept of 'trained immunity' offers a new paradigm for understanding how the immune system can be modulated to protect against neurodegenerative diseases. If these preclinical findings translate to humans, the BCG vaccine could offer a cost-effective and accessible strategy for reducing dementia risk, especially in populations where the vaccine is already routinely administered. Observational studies in humans have previously linked off-target effects of vaccines, such as the shingles vaccine, to a reduced incidence of dementia. The potential for BCG to induce a protective immune response against tau pathology, a key feature of Alzheimer's, could lead to large-scale prospective clinical trials to confirm these benefits. This could shift the focus of dementia prevention towards leveraging the body's own immune mechanisms.
What's Next?
The researchers emphasize that further basic research is needed to fully understand the detailed mechanism by which BCG confers protection against dementia. Dr. Bishai's team is actively studying other characteristics of trained immunity in the lab. Following these mechanistic studies, the next crucial step will be to conduct large-scale prospective clinical trials in humans to provide definitive answers regarding the BCG vaccine's efficacy in preventing or delaying dementia. Co-author Dr. Barbara Slusher cautions that more needs to be understood about the underlying biology, including who might benefit, when treatment would need to be given, and whether the effect can be safely reproduced in people at risk for dementia. If specific protective immune changes can be identified, it could lead to the development of even more targeted approaches for Alzheimer's disease prevention. These trials would be essential to determine appropriate dosing, timing, and patient populations for any potential clinical application.
