This is a great question!

You have identified a really big challenge when it comes to using cell based therapies in the central nervous system, especially the brain. You've probably heard about the "blood - brain barrier" and how it prevents substances like toxins from entering the brain. Now we are talking about trying to provide new neurons to the brain as a repair therapy. Right now, the only way we have to do that is through an invasive mechanism - by delivering the cells directly into the brain, to the location where we need the repair/replacement to occur.

Even if we can do that, we still have a worry that using a stem cell based therapy could result in cells that "misbehave" - for example, will they know when to stop dividing? If not, the patient may develop a brain tumor. Cell based therapies - whether or not they involve any kind of gene editing - are still in the early days of development. But already there are some successes, such as delivering retinal cells derived from stem cells into the eyes of people with macular degeneration (a type of age-related blindness).

Some of those therapies are actually developed right here at UCSB!