Gene therapies are powerful research tools which deliver nucleic acids into diseased cells to directly treat illness – these are also being tested in human clinical trials for a range of applications. A thorough understanding of the currently available gene therapy methods is critical for successfully developing new gene therapy strategies and projects. Herein, we will discuss 4 gene therapy strategies: gene augmentation, gene silencing/inhibition, genome editing and gene suicide. (Since gene suicide is mainly used to destroy tumor cells with an oncolytic virus, this page will not explore this topic in detail.)
Gene augmentation therapy is used to treat diseases caused by loss-of-function mutations, which prevent the gene from producing a functional product. This gene therapy technique introduces DNA containing a functional version of the lost gene into the cell and aims to produce a functioning product at sufficient levels to replace the protein that was originally missing.
Gene augmentation therapy is the most common treatment option for spinal muscular atrophy (SMA). SMA is caused by a deficiency of a motor neuron protein called SMN1, so the basic concept of gene therapy treatment is to insert the normal SMN1 gene into the diseased cell. Importantly, vector AAV9 can deliver cDNA of SMN1 gene to the cells. The first gene therapy treatment for SMA was approved by the Food and Drug Administration (FDA) in 2019. Despite being an effective option to minimize the progression of SMA and improve survival, this treatment is costly. At present, the commonly used strategies of gene augmentation therapies include delivering of a new protein-coding gene, increasing the expression of growth factors and cytokines, as well as cellular cytokines and autophagy activation of the diseased protein.
If the mutation fragment length of the diseased gene is too large for the vector, one solution is to adopt alternative splicing. The alternative splicing method has achieved great success in Duchenne Muscular Dystrophy (DMD) treatment. Scientists have used antisense oligonucleotides (ASOs) to interfere with the translation of protein mRNA, preventing the mutant exons from being translated, and thereby avoiding the loss of protein function caused by disease-causing nonsense and frameshift mutations.
In cases where the addition of a functional gene does not resolve the disease phenotype, gene silencing therapy may be used to shut down (silence) the expression of an abnormal gene. For diseases caused by dominantly inherited disorders, just one abnormal allele can manifest the disease phenotype and related dysfunctionality of cells or organs. A common example is the constitutive expression of oncogene mutations in tumor cells, which requires gene therapy to inhibit the function and expression of pathogenic genes. RNA interference (RNAi) therapy has been applied in research across many polyglutamine (PolyQ)-related diseases, including Huntington’s disease (HD) and spinocerebellar ataxias (SCAs), with the aim to reduce the expression of toxic proteins. Although single-stranded ASOs can mediate gene silencing – small/short interfering RNA (siRNA), short hairpin RNA (shRNA), and microRNA (miRNA) therapies typically provide stronger inhibitory function and durability.
In gene therapy applications, the use of gene editing technology has been closely tied to the development of CRISPR-Cas9 technology, which has made gene editing in organisms much easier and inexpensive. Importantly, CRISPR-Cas9 gene editing technology has become widely used in gene therapy and served as a breakthrough approach to many previous restrictions, such as the limitations by disease type (recessive or dominant disease), gene length, and in vitro or in vivo experimental model development. Those experimental limitations and others could be solved by gene editing (CRISPR-Cas9) technology. Below are four key gene editing strategies for gene therapy:
Gene Editing Applications in Rare Disease Research
More than 80% of rare diseases are caused by genetic disorders. With the development of a gene therapy for a rare disease, it can provide hope of a one-time treatment for numerous rare diseases that currently have no specific therapeutic options.
At present, there are gene editing-based gene therapy R&D pipelines in progress for several rare diseases, including Duchenne muscular dystrophy (DMD), congenital immune deficiency, hepatitis B, hemophilia, and cystic fibrosis.
With Cyagen’s professional gene editing platform, we provide accurate genetic engineering disease models to help researchers explore key information on rare disease mechanisms and potential treatment approaches. Our model services may be customized to support drug development programs more efficiently transition from gene discovery and validation to pre-clinical safety and efficacy evaluations.>> Check here to learn more about Cyagen Rare Disease Model Program.