Can a TB Vaccine Protect the Brain? New Hopkins Study

A century-old tuberculosis vaccine reduced the buildup of tau protein and protected memory in mice bred to develop dementia, according to a Johns Hopkins study published in Science Advances on Oct. 21, 2026. The BCG vaccine dementia research is early, preclinical work in animals, but it adds lab evidence to a puzzle researchers have been chasing for years: why people who received BCG for bladder cancer appear to develop dementia less often.

Image: A laboratory mouse, used for illustration. Photo: Rama, via Wikimedia Commons (CC BY-SA 2.0 FR).

What the BCG vaccine dementia study found

The Bacillus Calmette-Guérin (BCG) vaccine was first given to a human infant in 1921 and remains the only licensed vaccine against tuberculosis, Drug Discovery News noted. It is also used to treat bladder cancer and leprosy. BCG is a live, weakened vaccine made from a strain of Mycobacterium bovis.

The Hopkins team used PS19 mice, a strain engineered to develop tau pathology, the clumps and tangles of tau protein linked to late stages of Alzheimer’s disease. According to Genetic Engineering & Biotechnology News (GEN), the researchers gave one group the BCG vaccine at three months of age and gave comparison groups saline injections. They then measured brain imaging, memory, inflammation and gene activity eight to nine months later.

The reported results:

Vaccinated mice were about five times more likely to show signs of reduced tau deposits.
They were about four times less likely to show markers of sustained inflammation in the brain.
Untreated mice showed activation of 716 genes connected to Alzheimer’s disease, cell death and neuroinflammation. BCG normalized all but nine of them.
Vaccinated mice showed less brain atrophy, performed better on an object recognition memory test, kept their body weight better and lived longer.

The paper is titled “BCG vaccination mitigates tau pathology and restores cognitive functions in PS19 mice.” Its authors concluded, as quoted by GEN, that “dementia protection by BCG is a credible observation that merits future basic research and large-scale prospective clinical trials to provide definitive answers.”

Why researchers point to trained immunity

The leading explanation is a process called trained immunity. Normally, the innate immune system responds to threats in a general way, while T cells and other adaptive immune cells learn to recognize specific invaders. Trained immunity describes innate cells such as monocytes and macrophages undergoing lasting changes after a first exposure, so they respond more strongly to a later, unrelated challenge.

“BCG is an intracellular pathogen,” senior author William Bishai, co-director of the Johns Hopkins Center for Tuberculosis Research, told Drug Discovery News. “It goes inside our myeloid cells and lives inside phagosomal vesicles. And while it’s doing that, it’s releasing various antigens that the myeloid cell experiences.”

The team found that brain immune cells called microglia were overactive in mice with tau pathology, and that this activation fell toward healthy levels in vaccinated animals. “I think the money is on the microglial cells being stimulated to clear the tau tangles as they’re forming, and they do it rapidly without the need for inflammation of the brain,” Bishai said. He also told GEN, “We’re hard at work trying to understand the detailed mechanism for how it works, but this research points to early clues that aspects of trained immunity are likely driving this response.”

Bishai noted the vaccine was injected into the skin months before the brain tissue was examined. “So, it’s an effect that is long-lived and can act remotely in the body of these mice at quite a distance,” he said.

What the human evidence shows, and what it doesn’t

The study builds on observational research in people. GEN reported that earlier studies cited by the team linked BCG immunotherapy for non-muscle invasive bladder cancer to a 12% to 78% lower risk of dementia over periods of three to 15 years, and that the shingles vaccine has been linked to a 20% reduced incidence of dementia. Studies like these can show an association, but they are not designed to prove that the vaccine caused the difference.

Co-author Barbara Slusher, director of the Johns Hopkins Drug Discovery program, called the project “a great example of translational science working in reverse—starting with an intriguing observation in people and then going back to the laboratory to understand why it might be happening.” GEN reported that she cautioned researchers still need to understand more of the underlying biology before they can say who might benefit, when treatment would need to be given, and whether the effect can be safely reproduced in people at risk for dementia.

That caution matters. Mouse results often fail to carry over to humans, and this study does not show that BCG prevents or treats Alzheimer’s disease in people. Nobody should seek the vaccine for that purpose based on this research.

What comes next

The Hopkins group has built a modified vaccine called BCG STING, engineered to boost a molecule that stimulates innate immune signaling, and wants to test it in its tau model, Drug Discovery News reported. Bishai also pointed to a practical hurdle: the United States is already facing a BCG shortage that has left some bladder cancer patients unable to finish treatment. He said new recombinant versions could help, since modified vaccines could carry new patents and give companies more reason to invest in making them.

For more on recent Alzheimer’s research, see our report on a newly identified genetic repeat linked to Alzheimer’s risk. We also covered the Bundibugyo Ebola outbreak in Congo, another fast-moving health story this month.

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BCG Vaccine Dementia Study: TB Shot Cut Tau Tangles in Mice