Precise and Efficient Gene Delivery Systems: Advances and Challenges

Abstract：Gene delivery systems are transforming medicine, offering innovative solutions for treating genetic disorders, cancers, and infectious diseases. Overcoming current challenges in toxicity and targeting specificity will further enhance their safety and efficacy, paving the way for a new era in precision medicine.

A gene delivery system refers to a mechanism capable of transporting specific gene fragments to targeted organs, tissues, or cells.

Such systems play a critical role in the prevention and treatment of many diseases. For example, if a disease is caused by a defective gene, introducing a normal gene sequence into the affected cells via a delivery system could potentially cure it. Conversely, some diseases result from overactive genes. In these cases, tools like CRISPR/cas9, delivered through gene delivery systems, can suppress gene expression and address the root cause effectively.

Lipid Nanoparticles (LNPs) and Viral Vectors

Modern gene delivery systems fall broadly into two categories: lipid nanoparticle (LNP)-based systems and viral vector-based systems.

LNP-Based Systems

The use of LNP systems became widely recognised during the COVID-19 pandemic, as mRNA vaccines relied heavily on this technology. The mechanism involves encapsulating RNA encoding the spike protein of the SARS-CoV-2 virus within hollow lipid nanoparticles. Once injected, these nanoparticles fuse with human cells to deliver the RNA, prompting the cells to produce the spike protein and trigger an immune response.

Beyond COVID-19, LNP systems have been leveraged to develop vaccines for other pathogens such as influenza, RSV, VZV, and CMV. Several of these products are already in clinical trials.

LNP systems have broader applications beyond vaccines. For example, Moderna has explored using LNPs to deliver RNA encoding interleukin-12 into tumour tissues, inducing immune responses in the tumour microenvironment to kill cancer cells. Similarly, Intellia has used LNPs to deliver CRISPR/cas9 tools targeting the TTR gene in the liver, successfully treating hereditary transthyretin amyloidosis with sustained clinical effects.

Viral Vector-Based Systems

Viral vector-based systems utilise the natural ability of viruses to infect host cells and transfer genetic material. For instance, SARS-CoV-2 introduces its RNA into host cells, enabling the production of proteins essential for viral replication. By modifying viruses to carry therapeutic genes, researchers can achieve targeted delivery.

The first successful gene therapy involved retroviruses to deliver the ADA gene into immune cells of patients with SCID in the 1990s. Decades later, viral vectors continue to dominate the gene therapy landscape, with products like Zynteglo (lentivirus-based therapy for beta-thalassemia) and Zolgensma (AAV-based therapy for SMA) receiving regulatory approval.

Other viral vectors, including HSV-1 and modified AAVs, are under development for diseases like RDEB, showing promising clinical results.

Challenges in Gene Delivery Systems

Despite significant advancements, gene delivery systems face several challenges, particularly in toxicity and targeting specificity.

• Toxicity: LNPs and viral vectors can trigger strong immune responses, causing side effects like fever, fatigue, or even severe immune reactions, as seen in a 1999 adenovirus vector-related death. Additionally, some viral vectors, such as retroviruses, integrate their genetic material into the host genome, posing risks of genomic instability.

• Targeting Specificity: Ensuring precise delivery to the intended cells or tissues is another critical challenge. For example, LNPs naturally accumulate in the liver due to their interaction with apolipoproteins in the bloodstream. Researchers have attempted to overcome this by altering lipid compositions or attaching molecular markers to enhance targeting precision. Similarly, viral vectors are being engineered to improve their tropism for specific cell types, such as CNS cells or immune cells.

Innovations in Protein Delivery Systems

Beyond DNA/RNA delivery, direct protein delivery is an emerging area. Tools like engineered extracellular contractile injection systems (eCIS), inspired by bacterial structures, have shown promise for delivering proteins into specific cells with high precision. These systems, developed by Zhang Feng's lab, utilise modified bacterial components to target and inject therapeutic proteins into cells.