Gene Therapy

What is gene therapy?

Gene therapy is a technique used in an effort to treat or prevent disease. When a gene mutation (a permanent alteration in the DNA sequence) causes a protein to be missing or faulty, gene therapy may be able to restore the normal function of that protein. There are several different approaches to gene therapy:

• introducing a new or modified copy of a gene
• turning on or off genes to avoid disease
• replacing the disease-causing sequence of a gene with a healthy copy of that sequence

The goal of gene therapy is to change the course of disease by targeting its genetic cause.

Understanding genes

Genes come from our parents. They dictate everything from the color of our eyes to our immune system to our likelihood to develop diseases. Genes contain the information needed to build and maintain cells by encoding proteins.

A gene is a small section of a cell’s DNA, consisting of four chemicals called bases. These bases form the backbone of DNA and — much like a manual — provide instructions for assembling proteins, the building blocks of the human body, such as the muscles, organs and immune system.

The trouble is genes aren’t always built correctly. When this happens, it changes the gene's DNA. This is called a mutation. Mutations can be passed down from someone's parents or can occur for the first time in that person. A mutation in the gene can alter how proteins work. Sometimes, mutations can cause disease. That’s where gene therapy may help.

How does gene therapy work?

		Gene Addition
		Gene addition is used to treat conditions caused by a variation in a single gene. This one-time therapy involves the insertion of a functional copy of a missing or faulty gene into a person’s cells by way of a viral or non-viral genetically-engineered vector (delivery vehicle). The goal of this therapy is for the new gene to produce a protein the body couldn’t (previously) produce adequately.
		Post-Transcriptional Gene Silencing
		Post-transcriptional gene silencing inactivates specific messenger RNAs (mRNAs) to prevent the expression of a gene. The mRNA of a particular gene, which ordinarily would be expressed (turned on), is suppressed (knocked down). When the mRNA is knocked down, it no longer creates an active protein at the same level as before the silencing. Gene silencing methods are used to combat cancer and other conditions, such assickle cell disease.
		Gene Editing
		Gene editing is a precise technology used to add, remove or alter specific DNA sections. It involves making cuts to DNA at the specific spot where it is malfunctioning. After cutting the DNA, the cell naturally repairs itself. By disrupting unwanted sequence elements or by copying and pasting in new sequences to fix faulty sequences, gene editing can lead to permanent genetic changes. Cells can function normally and reverse disease processes.
		基本编辑
		Base editing targets single point mutations and creates precise changes in the genetic code. These small changes can silence a disease-causing gene or help activate a specific gene. Base editors do not cut the double-stranded DNA but instead deliver an additional enzyme to a desired sequence to change the base on one strand. Finally, cellular repair proteins recognize the base change and convert it to a permanent mutation. With the corrected gene, the cells can now take on new functions normally, and conditions caused by specific mutations can potentially be cured.

How is genetic material delivered?

For any of these four gene therapy platforms to work, the genetic material needs to be delivered to a person’s cells. Often, a viral or non-viral genetically-engineered vector, a "delivery vehicle," carrying the genetic material is used. Modified viruses with the infectious capability turned off are used as vectors, because of their natural ability to invade the target cell, delivering the new gene. The vector can be introduced in one of two ways — outside the body (ex vivo) or inside the body (in vivo). In this way, the gene therapy occurs in the organ or tissue relevant to the disease.

Although still relatively new and often considered experimental, gene therapy is a promising treatment option for a number of diseases that don’t respond well to other therapies, including inherited conditions — such as immunodeficiencies, metabolic disorders and hematologic disorders — and certain types of cancers.

What are the potential risks of gene therapy?

The potential risks associated with gene therapy depend upon the type of therapy, type of delivery mechanism (vector) and the way in which it is delivered to the cells. They may include:

• a negative immune system reaction
• complications from inadvertently targeting the wrong cells
• adverse effects associated with inserted genetic material
• unexpected gene expression

The Food and Drug Administration and the National Institutes of Health closely monitor gene therapy trials, and techniques are continually researched and refined. Patients are closely monitored by their treatment team for years after gene therapy.