Gene therapy of brain injury
Gene therapy reduces brain damage in mice with traumatic brain injury
Georgy Chistov, PCR.news
Injuries to the central nervous system are very diverse, but they all lead to damage or loss of neurons. An important role in this process is played by the infiltration of immune cells into the parenchyma of the brain. At the first stages, immune cells try to protect the surrounding tissues, but their prolonged activation causes inflammation and death of neurons.
A team of scientists from Belgium, the Netherlands and the UK has developed a system based on an adeno-associated vector that allows you to modulate the immune system. Interleukin-2 (IL-2) was chosen for expression. This molecule promotes the proliferation of regulatory T cells (Treg), which regulate the immune response. So far, Treg levels in the blood have been analyzed in studies on the effect of IL-2 and Treg on neuroinflammation. The role of resident Tregs in the CNS was unclear. Scientists have tested whether it is possible to control neuroinflammation with IL-2, affecting only the immune cells of the central nervous system and not involving the peripheral immune system.
At the first stage, transgenic mice were created in which the IL-2 gene was placed under a promoter specific to brain nerve cells. With the help of flow cytofluorimetry, microscopy and RNA sequencing of single cells, the researchers showed effective activation of Treg cells. The level of lymphocytes increased only in brain tissues. The cells had normal transcription profiles and did not affect the electrophysiology of neurons. Moreover, the blood-brain barrier cells contributed to the activation of Treg cells.
Additional expression of IL-2 in transgenic mice led to a decrease in inflammation after traumatic brain injury. This allowed scientists to move further and move on to gene therapy. They used an adeno-associated virus to deliver the IL-2 gene to the astroglia cells of mice. The design was injected intravenously. To avoid gene expression outside the brain, scientists used AAV with the PHP.B capsid. It is known for selectively infecting only brain cells. Moreover, scientists have placed the IL-2 gene under the GFAP promoter, which works exclusively in astrocytes.
Treatment with the virus resulted in a threefold increase in the level of IL-2 in the brain in 14 days. This change was local in nature — no such thing was observed in peripheral organs and tissues. As scientists have shown, treatment with such a design does not give excessive mortality and does not violate the electrophysiology of the brain and the activity of astrocytes. The therapeutic effect of the vector was observed both at the morphological level and at the behavioral level. Mice that received the virus before the induction of traumatic brain injury showed less cortical tissue loss and better results in behavioral tests.
Further studies have shown that the expression of IL-2 ultimately leads to the transformation of astroglia associated with the disease — it acquires an atypical phenotype with an increased level of MHCII. This population of cells serves as a buffer at the damage boundary and prevents the neurotoxic effect. The therapeutic effect of the vector was preserved in other types of damage. Thus, he reduced tissue damage in ischemia caused by two different ways.
The researchers also adapted their design for clinical trials. They added the rtTA regulatory protein gene and placed it under the GFAP promoter, and the IL-2 gene was embedded under the rtTA promoter. The rtTA protein activates IL-2 expression only in the presence of minocycline, a semisynthetic antibiotic capable of passing through the blood—brain barrier. In experiments on mice, the cancellation of minocycline led to a decrease in the level of Treg in the brain to the initial one. Scientists called the adapted design locked with three locks (triple lock). In their opinion, such a gene delivery system has all the characteristics necessary for further clinical development: it is effective and controlled by minocycline.
Article by Yshii et al. Astrocyte-targeted gene delivery of interleukin 2 specifically increases brain-resident regulatory T cell numbers and protects against pathological neuroinflammation published in the journal Nature Immunology.
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