10.5: Ex vivo modification

Remember the story of the first gene therapy, earlier? Researchers cured a child’s immunodeficiency by adding a working adenosine deaminase gene to her cells. They didn’t do this in her body – instead, they extracted some of her bone marrow, isolated hematopoetic stem cells, modified them, then expanded the culture so that there were millions of modified cells before transfusing them back into her.

We call this kind of modification an ex vivo gene therapy – literally outside of the body – as opposed to in vivo, or in the body. And ex vivo therapy allows for two important improvements. First, because you can use methods other than viruses, you can add more transgenes – maybe one day even entire gene networks. And second, you can do more quality control. You can check to see that the cells you expand are modified in the way that you want and only the way that you want. And these methods have made it into the clinic as well – several approved therapies for cancer involve engineering a patient’s T cells to target cells with tumor-specific antigens, then transfusing them back into the patient.