Stem Cell Therapies for Parkinson’s: Five Questions to Ask Before Participating in a Clinical Trial

How can people with Parkinson’s disease (PD) assess the safety of clinical trials for stem cell therapies? After years of study, stem cell treatments, which involve transplanting cells to replace the brain cells lost in PD are being tested in clinicaltrials around the world. But the history of these therapies has been fraught with confusion and disappointment. For people with Parkinson’s disease, it can be difficult to make informed decisions about whether to participate in trials.

Recently, the community has taken steps to streamline stem cell research and help people with Parkinson’s to better understand the therapies. For example, the Parkinson’s Disease Foundation (PDF), in order to set standards for research and prevent therapies from being rushed to the clinic without proof that they are safe and effective, is supporting a global consortium called G-Force PD. In addition, experts led by Roger Barker, M.D., Ph.D., at the University of Cambridge, UK, (also part of G-Force PD) have written guidelines, which were published in the March 30 online edition of the Journal of Parkinson’s Disease.

In this article, they set out to answer five questions that everyone should ask when they hear news of a new PD stem cell study:

Questions to Ask

  • What type of cells are being transplanted? How do they work?Researchers have experimented with several sources of stem cells (e.g., taking skin cells from people who live with Parkinson’s) and have had varied success in transforming them into the very specific cells needed in PD. If you’re considering a clinical trial, find out whether the cells being transplanted have been proven to replace the dopamine neurons that are lost/harmed in Parkinson’s disease.
  • What is the proof that a stem cell treatment is safe and effective? Have the cells being transplanted in this trial been thoroughly tested in a series of laboratory studies and trials in animal models of Parkinson’s disease?
  • Have the cells being used for this clinical trial been chosen for a reason besides their safety and effectiveness? Stem cell science is difficult. Researchers may choose to experiment with certain types of cells for strategic reasons, e.g., because a supply of cells is readily available or because the cells work without having to suppress a recipient’s immune system. But a cell supply should not be chosen simply for profit reasons – this is not a place for shortcuts. Therefore, researchers need to prove that transplanted cells can survive and become integrated and functional in the brains of animal models regardless of their source.
  • Is the stem cell-based therapy claiming to help better control PD symptoms or provide a cure? Beware of claims that cell transplants can cure PD. These therapies aim to replace lost cells, restore dopamine in the brain, and ultimately improve quality of life without the side effects of levodopa therapy. But they cannot prevent the build-up of alpha-synuclein protein in brain cells, which is the hallmark of PD progression. Even the best current experimental approaches for cell replacement therapy take several years to see maximal benefit and only provide symptomatic relief.
  • What is the regulatory oversight of the trial and is it guided by input from experts in the field? In particular, find out whether a clinical trial has the independent ethical and regulatory approval of the country in which it is being done, and whether it has a follow-up period long enough for rigorous evaluation of risks and benefits, ideally several years. The data should be made publicly available. Finally, study participants should never be asked to pay for the therapy or to participate in the trial.


The prospect of clinical trials of stem cell therapies in people with PD is exciting. Those clinical trials are critical for determining whether any stem cell therapies have potential future as real therapies for people with PD.

For more insights on the use of stem cells in treating and researching Parkinson’s disease, listen to our podcast episodes "Stem Cells and Parkinson’s," “Cell-Based Therapies for Parkinson’s Disease” and “Gene-Based Therapies for Parkinson’s Disease.


Barker RA, Parmar M, Kirkeby A, Björklund A, Thompson L, Brundin P (2016). Are Stem Cell-Based Therapies for Parkinson’s Disease Ready for the Clinic in 2016? Journal of Parkinson’s Disease 6:57-63 DOI 10.3233/JPD-160798

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