Harnessing the Immune System to Treat Traumatic Brain Injury

Traumatic brain injury is a significant cause of death worldwide and can cause long-lasting cognitive impairment and dementia in people who survive. While inflammation in other parts of the body can be addressed therapeutically, in the brain it is problematic due to the presence of the blood-brain barrier, which prevents common anti-inflammatory molecules from getting to the site of trauma.

Prof. Liston explained their approach: “Our bodies have their own anti-inflammatory response, regulatory T cells, which have the ability to sense inflammation and produce a cocktail of natural anti-inflammatories. Unfortunately there are very few of these regulatory T cells in the brain, so they are overwhelmed by the inflammation following an injury. We sought to design a new therapeutic to boost the population of regulatory T cells in the brain, so that they could manage inflammation and reduce the damage caused by traumatic injury.”

The research team found that regulatory T cell numbers were low in the brain because of a limited supply of the crucial survival molecule interleukin 2, also known as IL2. Levels of IL2 are low in the brain compared to the rest of the body as it can’t pass the blood-brain barrier.

Together the team devised a new therapeutic approach that allows more IL2 to be made by brain cells, thereby creating the conditions needed by regulatory T cells to survive. A ‘gene delivery’ system based on an engineered adeno-associated viral vector (AAV) was used: this system can actually cross an intact blood brain barrier and deliver the DNA needed for the brain to produce more IL2 production.

The new therapeutic designed by the research teams was able to boost the levels of the survival molecule IL2 in the brain, up to the same levels found in the blood. This allowed the number of regulatory T cells to build up in the brain, up to 10-fold higher than normal. To test the efficacy of the treatment in a mouse model that closely resembles traumatic brain injury accidents, mice were given carefully controlled brain impacts and then treated with the IL-2 gene delivery system. The scientists found that the treatment was effective at reducing the amount of brain damage following the injury, assessed by comparing both the loss of brain tissue and the ability of the mice to perform in cognitive tests.

“By understanding and manipulating the immune response in the brain, we were able to develop a gene delivery system for IL2 as a potential treatment for neuroinflammation. With tens of millions of people affected every year, and few treatment options, this has real potential to help people in need. We hope that this system will soon enter clinical trials, essential to test whether the treatment also works in patients.” said Prof. Liston.

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Sources:

Yshii, L., Pasciuto, E., Bielefeld, P. et al. Astrocyte-targeted gene delivery of interleukin 2 specifically increases brain-resident regulatory T cell numbers and protects against pathological neuroinflammation. Nat Immunol, 2022 DOI: 10.1038/s41590-022-01208-z

Babraham Institute. “Harnessing the immune system to treat traumatic brain injury in mice: Pioneering new treatment leads to improved recovery from brain trauma in mice.” ScienceDaily. ScienceDaily, 26 May 2022. <www.sciencedaily.com/releases/2022/05/220526112749.htm>.

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