adeno-associated virus (AAV)

Adeno-associated virus, or AAV, is a small, mild virus that has become the favourite delivery vehicle for gene therapy. On its own it causes no known disease in people, which makes it a gentle, low-drama courier. Think of it as a reliable compact delivery van: it does not carry much, but it shows up quietly, gets into a lot of useful places, and rarely makes a scene.

Engineers empty the AAV shell and pack a therapeutic gene inside. Once injected, the AAV finds its way into cells and releases the gene, which usually settles beside the cell's own DNA and keeps producing its protein for a long time, especially in cells that divide slowly like those in muscle, liver, eye, or nerve. Its small cargo hold is the catch: big genes simply will not fit.

AAV sits behind several approved gene therapies, which is why it is called the workhorse vector. Its main limits are that tiny cargo space and the fact that many people already carry immune memory against it from natural exposure, which can blunt a dose or rule out giving the same vector twice.