The Bacillus Calmette-Guérin (BCG) vaccine, typically used to prevent tuberculosis, may remodel the brain’s immune environment to potentially lower Alzheimer’s disease risk, according to research published in Communications Medicine. A year-long study led by Mass General Brigham investigators found the vaccine increased immune cell responsiveness and altered Alzheimer’s-related biomarkers in older adults without pre-existing pathology.
How does the BCG vaccine affect brain health?
Researchers observed that the BCG vaccine appears to trigger “trained immunity,” a biological process that boosts the body’s defenses against unrelated infections. According to the study, led by co-first authors Marc Weinberg, MD, PhD, Mahesh Chandra Kodali, PhD, and Zhaozhi Li, PhD, the vaccine promoted enhanced immune responses without causing the inflammatory markers often linked to neurodegeneration.
The study involved 23 participants aged 55 and older. The team monitored cerebrospinal fluid (CSF) and blood samples over 12 months. In participants who did not show signs of Alzheimer’s pathology, the vaccine led to a significant decline in amyloid-beta levels in the brain and spinal fluid, while levels of the protein increased in the blood. This suggests the vaccine may assist in the clearance of proteins from the central nervous system.
The BCG vaccine has been studied for over two decades for “off-target” benefits, including ongoing Phase III clinical trials in type 1 diabetes and past Phase II and Phase III trials in COVID-19.
Why was the effect limited to healthy participants?
The research found no measurable effect on amyloid-beta levels in participants who already exhibited evidence of Alzheimer’s pathology. Steven Arnold, MD, senior and co-corresponding author, managing director of the Interdisciplinary Brain Center, Mass General Brigham Neuroscience Institute, noted that these findings suggest the timing of the intervention is critical. The potential for the vaccine to preserve brain health appears highest before significant disease development occurs.
These findings contrast with previous preclinical models and retrospective studies, which suggested a broader reduction in Alzheimer’s risk. While prior research focused largely on blood, this study provides new insight into how immune cells in the fluid surrounding the brain and spinal cord respond to the vaccine.
What are the next steps for this research?
The authors emphasize that these results come from open-label clinical trials and require verification through larger, placebo-controlled studies. Because the study focused on a specific vaccination strategy for older adults, it does not provide data on the long-term effects of childhood BCG vaccinations, which remain common in many parts of sub-Saharan Africa, Southeast Asia, and Eastern Europe.
“Although more research is needed, these findings suggest they may also influence biological processes involved in brain aging and neurodegenerative disease,” said Marc Weinberg, a former research scientist at Mass General Brigham who now works at AbbVie.
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Frequently Asked Questions
Does the BCG vaccine cure Alzheimer’s disease?
No. Current research suggests it may help remodel the brain’s immune environment and alter Alzheimer’s-related biomarkers in individuals who do not yet have the disease. It is not a cure for established Alzheimer’s pathology.
Is this study definitive?
The study, published in Communications Medicine, provides initial evidence from open-label trials. The researchers state that larger, placebo-controlled studies are necessary to confirm these effects.
What is “trained immunity”?
Trained immunity is a process where the innate immune system is “reprogrammed” to respond more effectively to future, unrelated immune challenges, such as infections or disease markers.
Have questions about the intersection of immunology and brain health? Leave a comment below or explore our archives on neurodegenerative research to learn more about ongoing clinical trials.