Narrator: Our team at Children's Hospital of Philadelphia wants to help you understand in vivo gene therapy. But before we can get into what in vivo means, we should start by explaining what is gene therapy? Gene therapy is a way to treat or prevent disease by using genetic material like DNA. First, the basics.

Our bodies are made up of cells. And inside each cell is its DNA. DNA is divided into short sections called genes. Genes act as instruction manuals, telling our cells how to make proteins. Proteins are necessary for our bodies to function. Proteins do important work like helping us digest food and helping our blood clot when we get a cut.

But sometimes, a gene's instructions for making a protein are not correct. This can cause changes in how a protein works. These incorrect instructions can result in a genetic disease. Gene therapy can deliver new instructions to the body to make proteins that function correctly.

Hannah: I was going blind. After I received a healthy gene to replace the bad gene in my eyes, I was able to see so much better.

Narrator: How does gene therapy work? There are two types of gene therapy. Ex vivo and in vivo. Ex vivo means outside the body. When a child receives ex vivo gene therapy, it means their cells are removed from their body, treated with gene therapy, and then put back into their body. In vivo means inside the body.

Let's talk more about how in vivo gene therapy works. When a child receives in vivo gene therapy, we use something called a vector, which acts like a delivery truck. Vectors with the new or corrected gene can get into the body through an iv, or doctors can put them in a specific spot, like the eye. The vector then travels to the cells where the corrected gene is needed.

With the help of the new gene, the cells start making the proper kind of protein. One condition that can be treated with an in vivo gene therapy, is spinal muscular atrophy, which is a nerve disease that used to be fatal for children with a severe type. Children with a disease now can receive an in vivo gene therapy that stops the progression of the condition.

William: Because of spinal muscular atrophy, I couldn't even roll over after gene therapy. I can now stand and take steps.

Narrator: Gene therapy is changing and saving children's lives and CHOP has been at the forefront of gene therapy breakthroughs from the start. CHOP was the first in the world to use in vivo gene therapy delivered into the bloodstream, which is the most commonly used method today.

And we've pioneered many other groundbreaking discoveries. Our determined researchers are exploring the use of in vivo gene therapy for all kinds of diseases so that more children worldwide will have bright futures.