http://www.technologyreview.com/news/520031/a-trojan-treatment-for-parkinsons-disease/

Scientists use immune cells to smuggle molecules across the blood-brain barrier in the hopes of treating neurodegenerative diseases. [...]

Batrakova hopes macrophages will ultimately cure Parkinson’s, and she is exploring other ways of using them. Her next step is to promote the growth of new neurons in the brain by smuggling in growth factors past the blood-brain barrier the same way. “We don’t only want to stop the progression of Parkinson’s disease, we want to reverse it,” she says.