What is gene therapy?

What is gene therapy?

­Gene therapy is an experimental method that uses genes to treat or prevent disease. There are different types of gene therapy.38 Some basic strategies are listed below.

What is gene knockdown?


Gene knockdown is a technique used in gene therapy strategies to reduce or block the expression of a mutant gene.39 


What is gene augmentation?


Gene augmentation is a strategy that introduces a working copy of a gene into cells to correct for missing function. Introducing a functional copy of the gene into the cell could restore the presence and natural function of the protein.39 

adeno-associated virus delivering the functional gene to potentially treat genetic disease
The protein shell of a non-pathogenic virus, such as adeno-associated virus (AAV), can be repurposed as a vector to protect and deliver the functional gene to potentially treat genetic disease.39

Examples of gene therapy in clinical research include those for

Huntington's disease (HD)

In some genetic diseases, the gene mutation results in excess generation of a dysfunctional or non-functional protein. For example, in dominant genetic diseases with a gain of toxic function like HD, it is necessary to inhibit mutant gene expression to knock down or block a disease-causing effect in cells.#sup_39# To achieve this, scientists can introduce microRNAs (miRNAs) that interfere with production of toxic proteins, such as mutant huntingtin protein (mHTT) in HD or mutant ataxin-3 in SCA3.#sup_40#

Hemophilia

Recessive genetic diseases, including X-linked diseases, such as hemophilia, are typically caused by a gene mutation that leads to reduced expression and functionality of a protein. Gene therapy for hemophilia involves gene augmentation, whereby a working version of the mutated gene is introduced into the cell to augment production of a functional blood-clotting factor.#sup_39# This functional gene uses cellular machinery to produce the missing or dysfunctional protein, a process that has the potential to reverse the disease phenotype and, in the case of hemophilia, prevent bleeding.

Are there different ways to administer in vivo gene therapy?


Broadly, there are two routes of administration to consider when designing a gene therapy application: intravenous and direct injection into the target tissue.

Different ways to administer in vivo gene therapy

How is gene therapy administered into the brain?


During a single surgery, a small catheter is used to administer investigational gene therapies directly into target tissue.39 The size of the catheter may be more easily understood when it is compared to something more familiar. The catheter used to administer experimental gene therapies is a very thin catheter (~1/32”), or about the same thickness of the graphite in a mechanical pencil.

Genetic engineering

Are there other types of genetic engineering?


With advances in science and technology, other types of genetic engineering, such as gene editing techniques, are now being studied.


Gene editing is a method that lets scientists delete, insert, or modify specific DNA sequences in the genome of many organisms, including animals, plants, and bacteria.41 Scientists are working to find ways to develop therapies that use gene editing to potentially treat children or adults with genetic diseases, such as fragile X syndrome, spinocerebellar ataxia, and Huntington’s disease.

What are some different types of gene editing?

CRISPR

Clustered Regularly Interspaced Short Palindromic Repeats is a technology that can be used to edit genes. The concept of CRISPR is simple: it’s a way of locating a specific piece of DNA inside of a cell for alteration. This technology enables scientists to manipulate a specific gene of interest. For example, scientists may knockout a gene by targeting and inactivating a gene or knock-in a sequence of a gene by integrating a foreign genetic sequence into a cell’s genome.41 

ZFNs 

Zinc-Finger Nucleases are engineered, DNA-binding proteins that facilitate gene editing by creating a double-stranded break in DNA at specific locations. ZFNs have a high degree of specificity to target particular base pair sequences.41

TALENs 

Transcription Activator-Like Effector Nucleases are a set of engineered nucleases that can be used for gene editing. Similar to ZFNs, TALENs are a two-component system with a DNA-binding domain and a DNA-cleavage domain, enabling editing of DNA at specific locations.41

Is cell therapy the same as gene therapy?


Cell therapy and gene therapy are not the same but are overlapping fields of biomedical research. Cell therapy is the transfer of modified cells into a patient, whereas gene therapy is the transfer of genes or genetic material into a patient. CAR T-cell therapy, or chimeric antigen receptor T-cell therapy, is an example of cell therapy. Learn more about CAR T-cell therapy below.


CAR T-cell therapy

CAR T-cell therapy is a cancer immunotherapy that involves the use of programmed targeted tumor-associated antigens. A patient’s T cells are removed from the body and changed in a lab. Scientists then deliver genetically modified cells back into the body. These modified cells are able to recognize and target cancer cells.42 CAR T-cell therapy has been approved for use for certain types of lymphomas.

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