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A repurposed TB vaccine shows early promise against diseases like diabetes and MS

The effects of the BCG shot on infections and autoimmune diseases is beginning to make sense

Around the world, volunteers are getting a vaccine developed to prevent tuberculosis in studies that have nothing to do with TB. Called Bacillus Calmette-Guérin, or BCG, the shot is being tested as a treatment for type 1 diabetes, Alzheimer’s disease, multiple sclerosis and even COVID-19.

BCG is a live but weakened version of Mycobacterium bovis, a relative of M. tuberculosis, the bacterium that causes the infectious lung disease known as TB. The vaccine has been around for 100 years and is routinely given to children in nearly all non-Western nations.

Almost as soon as BCG was introduced in the 1920s, researchers noticed a drop in infant deaths in some places where the vaccine was used. Later studies revealed that the vaccine protects against a range of infections. Much more recently, a single dose of the vaccine reduced the risk of respiratory infections in elderly study participants compared with those who got a placebo, according to an October 15 report in Cell.

The vaccine appears to boost immunity in some situations, but paradoxically, BCG may also calm an overactive immune system. It’s this soothing effect that made researchers take a look at BCG for autoimmune and inflammatory diseases, including eczema, asthma, allergies and multiple sclerosis. In MS, a disease in which the immune system attacks nerve cells in the brain and spinal cord, BCG appears to slow damage to the brain.

“Everybody kept getting signals, often from human data, saying this microorganism is doing beneficial things … whether it was allergy or autoimmunity or multiple sclerosis or diabetes,” says immunologist Denise Faustman of Harvard Medical School. “Over the last 10 years, that dataset has just grown and grown.” Faustman is testing BCG as a therapy for people with type 1 diabetes. In this autoimmune disease, the immune system attacks insulin-producing cells in the pancreas, leaving the body unable to make the insulin needed to control blood sugar levels.

Faustman is in the midst of a 150-person safety and efficacy trial of BCG in adults with type 1 diabetes. Her team previously showed, in a small study published in 2018, that the vaccine can safely improve blood glucose control in patients with long-term disease who continued taking insulin. The vaccine appears to reprogram immune cells to take up extra glucose, her team reported in iScience in May 2020.

Now, she and other researchers are digging into the basic science behind their observations, while also launching clinical trials of BCG in patients with type 1 diabetes, MS and Alzheimer’s. The scientists hope the answers will help drum up support for this line of research, which has drawn skepticism in the scientific community.