Background

Developing gene therapies for brain diseases has long been hindered by significant obstacles. The blood-brain barrier (BBB), which surrounds the brain's blood vessels, is a protective system that prevents the entry of external substances, but it also completely blocks the delivery of therapeutic genetic material. Adeno-associated viruses (AAVs), commonly used as delivery vectors for gene therapies, carry the risk of inducing immune responses and have the limitation of not allowing for repeated administration. Furthermore, they have a very limited capacity for carrying genetic material. As an alternative, the use of non-viral vectors, specifically lipid nanoparticles (LNPs), has emerged. LNPs are drug delivery agents that offer the advantages of high safety, the ability to package large amounts of genetic material, and the possibility of repeated administration. However, due to their physical size, they cannot cross the BBB on their own, limiting their use in brain therapies. The development of a technology that can precisely deliver gene editing tools to specific areas of the brain to prevent side effects and enhance therapeutic efficacy has been a long-standing challenge in the field of brain gene therapy.

Key Findings

Recent research has overcome this challenge by combining focused ultrasound (FUS) and LNP technology. The research team administered gene-editing material to patients intravenously and then applied FUS to specific areas of the brain, temporarily opening the BBB. At this time, microbubbles delivered into the bloodstream vibrate in response to ultrasound stimulation, widening the gaps between brain blood vessel cells and allowing the drug to enter the brain tissue. The plasmid DNA (pDNA)-LNP genetic material developed by the research team targeted astrocytes in the brain. The pDNA contained a GfaABC1D promoter that induces astrocyte-specific activity and two guide RNAs (gRNAs) that target apolipoprotein E4 (APOE4), a key risk gene for Alzheimer's disease, and were packaged into LNPs. In the experiments, the BBB was temporarily opened only in the brain regions that underwent FUS treatment, allowing the pDNA-LNPs to enter the brain cells. In particular, the astrocyte-specific promoter ensured that the gene editing tools were expressed only inside astrocytes, without affecting the genome of neurons or other glial cells. This resulted in the selective removal of the APOE4 gene within astrocytes, demonstrating a high degree of selective gene editing. This study demonstrates the ability to control target genes with high precision without using viral vectors.

Significance and Prospects

This research demonstrates that the combination of chemical drug delivery and physical ultrasound stimulation is the key to successful brain gene editing. In particular, the use of LNPs, which can be repeatedly administered and have a low risk of immune side effects, significantly increases the potential for clinical application. By using ultrasound to target only specific areas of the brain, the treatment area can be finely adjusted, preventing the toxicity problems that can be caused by the indiscriminate delivery of gene editing tools throughout the brain. However, there are still challenges to be addressed before this can be applied to actual patients. The safety of temporarily opening the BBB with FUS stimulation needs to be verified in the long term, and a customized ultrasound output control technology is required to adapt to the different brain structures and vascular conditions of each patient. The key milestones for the commercialization of the next generation of brain therapies will be to confirm whether the gene editing efficiency observed in animal models is maintained in humans and to obtain long-term safety data using large animal experiments.