Gene Therapy: Genes As Medicine

A gene is the basic physical and functional unit of heredity, and is made up of DNA.¹ The Human Genome Project estimated that humans have between 20,000 and 25,000 genes.¹ Though small, our genes are a blueprint for how each cell in the body functions, made up of 30 million codes of DNA.²

A genetic disease is caused by an alteration in an individual’s DNA, oftentimes inherited or, in rare cases, occurring spontaneously.3 Genes play an essential role in determining the function of each cell in the body, made up of 30 million codes of DNA.^1,2 If even one of these codes is damaged, a gene alteration may occur causing a genetic disease,³ some of which can be debilitating and life-threatening.⁴

Gene therapy is a new generation of medicine where a functioning gene is delivered to a targeted tissue in the body to produce a missing or nonfunctioning protein. By using genes as medicine, the underlying cause of a disease can be targeted at the cellular level, potentially with just one treatment.^5,6,7

For in vivo, the functioning gene is transferred to the cell inside the body via an infusion and is used as a blueprint to produce the missing or nonfunctioning protein.⁸ For ex vivo, patient’s cells are removed and exposed to the desired gene outside of the body, then re-infused to add the functioning gene back in the body.⁹

Gene editing is a precise change of a patient’s DNA using site-specific, targeted nucleases (eg, CRISPR, Zinc Finger).^10,11 This approach either permanently removes or modifies a gene, or adds a functioning gene within the patient’s body.¹⁰

Another approach uses RNAi technology to change the expression of a gene by targeting product of DNA transcription (RNA). This approach more or less “silences” the dysfunctional gene attributed to the genetic disease.¹²

Unlike traditional medications, which often require frequent administration and focus on managing symptoms and disease progression, gene therapy aims to address the non-functioning gene and provide a long-term treatment benefit with potentially just one dose.^5,6,7

However, while gene therapy holds promise for people with genetic diseases, it will not be an appropriate solution for every patient. The potential risks and benefits of gene therapy will emerge with continued research and evaluation.¹³

Some patients may have been exposed to AAV and may have developed antibodies to this virus and therefore would not be a candidate for treatment. These patients may develop an immune response immediately post treatment, where the body neutralizes the therapeutic gene’s function.¹³ If caught early, clinical experience shows these responses may be able to be treated with steroids, potentially leading to a stabilization of the gene’s functioning.¹⁴

Eligibility for gene therapy treatments will be determined by a number of criteria, including a blood test to check for antibodies to the custom vector. Patients can discuss the test criteria and results with their physicians and determine how to proceed on an individual basis.^15,16 Factors that may make someone ineligible to receive gene therapy treatment include patients with preexisting antibodies that would neutralize the specific gene therapy treatment, patients who have previously received gene therapy and developed these antibodies, and for certain diseases, the age of the patient at the time of treatment.

Clinical trials are currently underway to explore the many unknowns, including how long a particular gene therapy may last.¹⁵ That said, evidence to date indicates gene therapy has the potential to increase or restore function in affected tissues or cells over a long period of time and may enable a patient to manage his or her disease without the need for ongoing treatments.