Gene therapy is transforming modern medicine, with viral vectors playing a central role in this advancement. These engineered viruses deliver therapeutic genetic sequences to specific cells, offering potential treatments for genetic disorders, cancers, and neurodegenerative diseases. This article will explore how viral vectors work, their applications, and the successes and challenges shaping the future of gene therapy in healthcare.
Several methods exist for delivering gene therapies into cells. Each is better suited for particular applications, which must be considered early in development.
Gene therapy delivery can be broadly categorized based on how it is administered: directly into patients (in-vivo) or into cells that have been removed from a patient (autologous) or a donor (allogeneic) and then reintroduced after modification (ex-vivo) (Mendell et al., 2021). In-vivo methods can be more appropriate for transfecting postmitotic cells, which are more likely to express the therapeutic gene for extended periods, and for treating widespread disorders that don’t require tissue specificity. Ex-vivo approaches are often more suitable for targeting specific, easy-to-access cellular populations, such as immune cells, as in CAR T-cell therapies (Bui et al., 2024).
Adenoviruses (Ads) have a high transfection efficiency and have been shown to yield prolonged production of their therapeutic instructions, with one study reporting the expression of CRISPR machinery for 200 days after adenovirus administration (Stephens et al., 2018).
Lentiviruses have a single-stranded RNA genome and integrate into the host genome, making them more suitable for long-term expression that isn’t lost during cell division. This makes them more applicable for treating genetic disorders that require longstanding corrective treatment. These therapies carry the risk of insertional mutagenesis, but non-integrating lentiviral vectors are being investigated to combat this (Milone & O’Doherty, 2018).
Adeno-associated viruses (AAVs) are single-stranded DNA viruses that rarely integrate into the host genome and have broad tissue tropism. Luxturna, the first FDA-approved in-vivo gene therapy, was introduced in 2017 to treat inherited vision loss and uses AAV as its delivery method (Darrow, 2019). Despite their advantages, AAVs face challenges like genotoxicity from insertional mutagenesis and hepatotoxicity from the high doses needed for IV administration (Wang et al., 2024).
Gene therapies have a wide range of applications across various disease types, showing particular promise for neurodegenerative diseases, cancer, genetic disorders, and infectious diseases.
CAR T-cell therapy is the most prominent example of gene therapy to treat cancer. This technology involves modifying a patient’s T cells to recognize and attack cancer cells (Feins et al., 2019).
Many therapies in this area focus on introducing gene products that restore tissue function. For example, viral vectors are being investigated to introduce glutamic acid decarboxylase and glial cell line-derived neurotrophic factor, which help restore dopaminergic nerve function in Parkinson’s patients (Sudhakar & Richardson, 2019).
Viral vectors are increasingly used as the basis for vaccines, where the genetic information carried by the vector encodes an antigen that trains the immune system to attack a specific pathogen. Vaccines of this type are already on the market for COVID-19 and Ebola, and exciting progress is being made toward a vaccine for the Zika virus (Fig. 2) (Liu et al., 2024; McCann et al., 2022; Woodson & Morabito, 2024).
Viral vectors can be used to carry corrective versions of genes to restore tissue function (Wang et al., 2024), and progress is being made to use viral vectors to deliver gene editing machinery to correct harmful mutations within the genome (Asmamaw Mengstie, 2022).
These success stories showcase the power of gene therapies to transform the lives of patients suffering from longstanding and acute conditions.
Despite the promise of viral vectors for gene therapies, several bottlenecks prevent the widespread application of this methodology to more prevalent diseases.
Different applications require customized development and production pipelines for viral vector production. Scaling up production comes with increased costs, and low yields remain a constant issue. Many processes struggle to obtain high ratios of full to empty capsids, which has direct implications for therapeutic dosage and patient safety (Wang et al., 2024).
Potential side effects, limited long-term data, and the absence of standardized processes are prompting regulators to take a cautious approach to gene therapy approvals (Moffit et al., 2022; Research, 2024). One critical factor is demonstrating the monoclonality of cell lines that produce viral vectors; without proof of monoclonality, development timelines and regulatory approvals can face significant delays.
Gene therapy has shown tremendous potential, particularly through its successes in treating cancers and genetic disorders. Future efforts will focus on refining vector production and delivery methods to enhance safety, reduce off-target effects, and address immunogenicity challenges. Continued progress in vector development and regulatory frameworks will support wider accessibility, enabling gene therapy to transform healthcare across more diseases and patient populations.
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