Researchers from the University of Luxembourg have successfully transplanted stem cells into the brains of adult mice and demonstrated their long-term stability. After six months, the stem cells were found to have functionally integrated into brain circuits and formed connections with other cells. The researchers hope that with further research, this technique could one day be used to replace dead or damaged brain cells in individuals with diseases such as Parkinson’s. The study has been published in Stem Cell Reports.

For some time now, researchers have been able to transform adult cells into induced pluripotent stem cells. These cells, which have the ability to differentiate into virtually any cell type in the body, raised hopes in the field of regenerative and personalized medicine, but so far major hurdles have limited their usefulness in the clinical setting. In particular, the cells have gone on to form tumors in many animal studies.

Researchers are able to bypass the pluripotent stage and convert specialized cells into neural stem cells, which may be useful in treatments for neurodegenerative diseases where patients experience brain cell death or damage. However, researchers did not know whether these induced neural stem cells (iNSCs) were less tumorigenic than induced pluripotent stem cells or whether they would successfully differentiate in the brains of mice.

To address this issue, researchers generated iNSCs from mouse fibroblasts, which are the most common cell type in connective tissue. Next, they labeled these cells with a fluorescent protein so that they could track their progress and then transplanted them into the brains of adult mice.

The researchers analyzed the fate of these cells in the mouse brains for the next 6 months. They found that the stem cells not only survived, but they differentiated into both neurons and astrocytes, which are star shaped cells that perform a variety of critical functions in the brain. Incredibly, the cells integrated into existing neural circuits, formed connections with other brain cells and demonstrated activity. Furthermore, the cells did not lead to tumor formation, suggesting that the procedure is safe.

While the researchers acknowledge they have a long way to go before this therapy can be used in humans, they believe that this is certainly a step in the right direction. According to lead researcher Dr. Jens Schwamborn, the team is now taking this work forward by looking at the type of neurons that die in the brains of Parkinson’s patients. The scientists hope that one day they could replace the damaged dopamine-producing neurons, leading to an increase in dopamine levels in the brain.