Researchers have genetically modified stem cells inside the bodies of mice for the first time, in a study that could lead eventually to new potential for stem cell therapies. The study also shows potential for studying genetically-edited stem cells within the body, rather than in the lab.

Currently, stem cells must commonly be removed from the body and modified outside it before being reintroduced to the patient. This can cause the cells to go into a kind of shock, which could change them and even damage the regulatory interactions of the cells.

The study was done with an adeno-associated virus (AAV) that can find and alter the cells without causing disease. In their mouse study, scientists found the AAV changed 60% of skeletal muscle stem cells, 38% of bone marrow stem cells and 27% of skin progenitor cells. Scientists also found evidence of these changes spreading through the animals’ bodies.

The Broad Institute’s Sharif Tabebordbar, who worked on the study, said that so far the concept of using AAVs to deliver healthy genes wasn’t practical because the cells divide so quickly in animals, diluting the cells as this happens: “Our study demonstrates that we can permanently modify the genome of stem cells, and therefore their progenies, in their normal anatomical niche. There is a lot of potential to take this approach forward and develop more durable therapies for different forms of genetic diseases.”

From here, the scientists will attempt to use the same approach in humans.