How do you insert genes in the right place?

We put this question to Adrian Thrasher from Great Ormond Street Hospital:

Right, so there are several strategies. One is the "safe-harbours" within the genome. So the virus that Tim works on, adeno-associated virus, has developed a strategy of inserting itself into chromosome 19 in a very specific locus. We can use the mechanisms of that virus to put other genes into that same locus, and what we believe now is that's a very safe locus in which to put genes, so it's unlikely that any genes inserted there will affect surrounding genes. That's one way of doing it. The second way of doing it is a process of "homologous recombination", so using homologous DNA sequences to actually target a therapeutic gene into the right place.