Because transplanted stem cells are viewed by the human body as an unknown and potentially dangerous foreign organism, the immune system often kicks into high gear when the cells are detected. That can lead to transplant rejection. While there are some drugs that help to suppress the immune system's response, it also leaves the patient exposed to other diseases that can complicate matters. The modified stem cells created at UCSF present a potential solution to this problem by simply not setting off the immune system's alarms in the first place.

The discovery at UCSF marks the first time engineered cells have managed to survive inside their recipients without any sort of immune response. The process is done by using the powerful and occasionally controversial CRISPR technology to delete two genes, major histocompatibility complex (MHC) class I and II, that would typically signal to the immune system that a cell is foreign. The scientists then added CD47, a cell protein that essentially tells the immune system not to destroy a cell.

The technique was tested on mice and proved to be a success, suggesting the process could also work on humans. While there have been risks associated with using CRISPR modified cells in humans the past, the new process could significantly lower the risks associated with stem cells and other transplants. That would open up new possibilities for procedures that save, extend and improve people's lives.