In descriptions of gene therapy, you often see the term “viral vector.” What is a viral vector?

Think of a viral vector as a delivery truck that carries a new, working copy of a gene and delivers it to the proper, targeted cells in the patient’s body.

Naturally occurring viruses are often used as vectors because they are very good at getting inside of cells in people — like a delivery truck knows how to find the address to drop a package. But unlike a typical virus that can give you a cold or the flu, scientists remove the illness-causing portion of the virus so that it won’t make the patient sick when it’s used as a vector. They replace the virus genetic material with a therapeutic gene.

For gene therapy to work, the vector needs to evade multiple defenses of the human immune system, just as a delivery truck will avoid traffic jams or dead-end streets, to find its way to the cells that need correcting. When the vector reaches the cell, it is internalized (enters the cells) and then traffics to the cells data center, the nucleus, where it releases the corrected gene — like the truck delivers a package. The delivered package (gene) has the instructions needed for the cells to start making the proper protein the body needs to stop the genetic disease.

The exact type of vector chosen depends on the types of cells in the body the gene therapy is designed to repair. A very common type of vector is the adeno-associated virus, or AAV. Natural AAVs are not known to make patients sick and can deliver cargo to many different kinds of cells in people through delivery to blood, through brain fluid, and other routes.

For some gene therapies, an enhancer is added to the vector, which acts as a booster to help the new gene work better.

Researchers, like those at Children’s Hospital of Philadelphia Research Institute, are continually exploring how to make vectors more effective by testing different types of viruses and creating innovative ways to re-engineer the vectors so they can carry a larger payload of reparative genes, reach more of the target cells, or stay active for a longer period. The Research Vector Core can help prepare the tools so researchers don’t have to learn the complicated processes of production themselves.  And, when studies are promising, the Clinical Vector Core helps advance those studies to children with a variety of genetic disorders.