According the desired gene directly into theAccording the desired gene directly into the

According to the U.S. National Library of Medicine, a simple definition of gene therapy is that it is a recombinant DNA technique “uses genes to prevent disease” (1). Gene therapy typically works by the addition of new genes into a cell, which ultimately replaces missing or damaged genes (2). To date, there are two main ways that are used to deliver the new functioning gene – in vivo and ex vivo (2). The most widely used method, ex vivo involves isolating cells from the affected area, growing the cells in culture, and genetically modifying the virus (i.e. retrovirus) with the desired or therapeutic gene and inactivating it so it does not pose any harm to the individual (3, 4). From there, the cultured cells become infected by the modified virus (3). This occurs by the virus using the enzyme reverse transcriptase to create cDNA (3). The cDNA containing the correct gene integrates itself into the host cells, ultimately creating transfected cells (3). The corrected cells are screened/selected for and infused back into the host (3). In-vivo gene therapy works by inserting the desired gene directly into the viral vector (i.e. retrovirus, adenovirus, etc.) and subsequently implanting it into the patient (3). In-vivo is less commonly used as it carries a significantly higher risk, for instance the individual could have a severe reaction, which could ultimately lead to death (3). This was observed in the case of Jesse Gelsinger in 1999, who participated in a gene therapy trial in effort to cure his ornithine transcarbamylase (OTC) deficiency (5). An adenovirus was used in the trial, which can create an immune response despite being inactivated (5). Retroviruses are capable of inserting the gene wherever, which can lead to mutations and even cancer (2, 6).  Despite the area of gene therapy existing for several decades and the risks associated with it, significant advancements have been made. Currently, gene therapy with viral vectors are being explored to treat a number of diseases including but not limited to: severe-combined immune deficiency (SCID), chronic granulomatous disorder, hemophilia, and congenital blindness (7). For instance, in late 2017 the Food and Drug Administration (FDA) approved the first gene therapy drug, called Luxturna (8). Luxturna utilizes an adeno-associated virus to treat a specific form of vision loss called RPE65-mediated inherited retinal disease (9). The drug works by injecting each eye with the drug, which ultimately slowing the progression of the disease (9). One of the major downsides of Luxturna is the cost. For treatment on both eyes, it costs nearly $1 million (8). Moreover, also in late 2017, researchers also made an advancement in viral gene therapy treating hemophilia, which is a genetic disorder that prevents individuals from making blood clots (10, 11). A lack of clotting factors leads to excessive and uncontrollable bleeding (11). In the study, 10 research participants were injected with a virus that was carrying a clotting protein that is not present in individuals with hemophilia B (10). The study highlighted the fact that 90% of the participants did not experience any bleeding episodes and 80% did not need the injections as frequently (10).  Gene therapy has come a long way and many advancements have been made. As previously mentioned, in 2017 the first drug for gene therapy was approved by the FDA and progress has been made in the attempt to combat hemophilia. Both of these advancements will only lead to more success and new avenues to explore, especially with respect to Luxturna and treating other eye diseases