embryonic stem cells, glial cells and GDNF
 

replacement embryonic stem cells are being studied as a drug delivery system in als. Instead of neurons being made from the stem cells, these cells are turned into specialized glial cells that are transplanted around the functioning motor neurons in patients with als. trophic factors such as GDNF are excreted by these newly manufactured cells, improving support to the surviving neurons. These cells do not need to make neuronal connection--they just release their factors into the surrounding environment, thus this process is thought to be more easily achieveable than the use of manufactured neurons themselves.
seems same process could be utilized to transplant glial cells around dopamine producing structures for PD