Gene Therapy
Gene therapies aim to treat a disorder by delivering nucleic acid into a patient's cells to alter the genome and fix a genetic problem at its source. Gene therapy research is focused on treating genetic disorders caused by a single gene mutation, for example cystic fibrosis or sickle cell anemia.
There are several approaches under investigation within gene therapy research: replace a mutated gene that causes disease with a healthy copy of the gene, delete a mutated gene, or introduce a new gene into the body that will help to fight disease. Commonly, DNA that encodes a protein to replace a mutated protein is transferred to the cell packaged in a viral vector, a process known as viral transduction. The transferred genetic material enters the target cell nucleus, where it is translated into a functional protein, either to replace a faulty protein or to affect the functioning of other proteins.
More recently, direct DNA-editing techniques, such as zinc finger nucleases (ZFNs) and CRISPR-Cas9 have been investigated as gene therapies. ZFNs are synthetic proteins that bind DNA and create double stranded DNA breaks to prevent translation of a gene into a protein. Similarly, CRISPR-Cas9 technology enables modification of specific DNA sequences and has the potential to fix disease-causing mutations.
Approved Gene Therapies
There are a small number of gene therapies approved for the treatment of specific genetic disorders. One example is Voretigene neparvovec (trade name; Luxturna), which is approved for the treatment of Lebel's congenital amaurosis, also known as biallelic RPE65-mediated inherited retinal disease; an inherited eye disorder causing progressive blindness. Luxturna is an adeno-associated virus containing RPE65 cDNA, which improves vision when given as a subretinal injection. Another example, which combines stem cell therapy and gene therapy, is Strimvelis for the treatment of severe combined immunodeficiency due to adenosine deaminase deficiency (ADA-SCID). Hematopoetic stem cells (HSCs) are extracted from the patient, then CD34+ cells are isloated and the human adenosine deaminase gene is introduced to them by viral transduction. The stem cells are then given back to the patient, where they replciate within bone marrow and create a functional adenosine deaminase protein.
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