Here is my two cents worth on (umbilical cord) mesenchymal stem cells (MSCs) and induced pluripotent stem cells (IPSCs).

There is a theory that chronic neuroinflammation in PD is a result of chronic inflammation in the gut. Assuming that this is correct, it is conceivable that MSCs (perhaps given intravenously) might be able to halt the inflammation in the gut, thereby possibly bringing to a halt the inflammation in the brain. This would be a form of neuroprotection, possibly halting/slowing the progression of the disease.

For those PwPs in more advanced stages of the disease, neuroprotection is not sufficient. What is required is neuroregeneration, possibly via new dopamine neurons made from IPSCs.

NB: I haven't read any of the papers on MSCs yet, so my view is likely to change!