How risky are stem cell trials for Parkinson’s beginning in China?

New human clinical trials using derivatives of pluripotent stem cells in China for Parkinson’s Disease (PD) have raised expectations and some eyebrows. PD is a neurodegenerative condition, sometimes diagnosed or followed by PET scans such as the one at left, characterized by loss of dopaminergic neurons leading to severe and sometimes life-threatening symptoms.

Pluripotent stem cells are powerful as their name implies and they have great clinical potential, but if they are not utilized properly they have robust tumor forming potential. This risk can be substantially reduced to near zero if the cells used in any given clinical trial are fully differentiated from the embryonic stem cells (ESC) or induced pluripotent stem cells (IPSC) and subject to thorough pre-transplant vetting such as biological, genomic, and epigenetic screening.

Brain PET scan

Wikimedia image available for reuse

The Chinese Parkinson’s Disease trial using ESC as a starting point is unusual because the derivatives that will be transplanted are not fully differentiated cells, but rather neural precursor cells. From a Nature piece by David Cyranoski on these ESC trials:

“Both studies will take place at the First Affiliated Hospital of Zhengzhou University in Henan province. In the first, surgeons will inject ES-cell-derived neuronal-precursor cells into the brains of individuals with Parkinson’s disease. The only previous trial using ES cells to treat Parkinson’s began last year in Australia; participants there received stem cells from parthenogenetic embryos — unfertilized eggs that are triggered in the lab to start embryonic development.

In the other Zhengzhou trial, surgeons will take retinal cells derived from ES cells and transplant them into the eyes of people with age-related macular degeneration. The team will follow a similar procedure to that of previous ES-cell trials carried out by researchers in the United States and South Korea.”

Both trials will be led by Qi Zhou and for Parkinson’s the teams have selected ten candidate patients for trial participation who they believe are good matches to the allogeneic ESCs in the bank.

Neural precursors are multipotent, often highly proliferative cells that can have their own kind of tumorigenic potential. This makes the new China Parkinson’s study inherently risky and raises a number of questions. Will the ESC-derived precursors mostly differentiate into the desired dopaminergic neurons following transplant? Even if most do, could some of the other precursors make distinct, undesired cell types? Could some of the transplanted precursors continue to proliferate within the recipient brain and cause problems via benign growth? What about potential malignant growth? There is also potential that the patients will reject the allografts.

Unfortunately the pre-clinical data from this team remains unpublished so the stem cell community does not have concrete, peer-reviewed data to go on to address such questions or concerns. Some stem cell/Parkinson’s experts have concerns. For instance, Jeanne Loring was quoted by Cyranoski about her concerns related to the fate of the transplanted precursors, “Not knowing what the cells will become is troubling” and Loring had this comment when I asked her for additional thoughts:

“From the Nature piece readers may not have clearly understood that the different clinical trial teams are using somewhat distinct cell types produced from ESCs and those differences have important potential functional implications. For instance, we are using immature DA neurons, that haven’t arborized much in the dish.  Malin Parmar is using slightly less differentiated cells.  The point is that we get >90% live cells after dissociation. The cells that the Chinese group and International Stem Cell Corp. are using are actually better termed neural stem cells- their fate is neuronal but not specific.  Our cells are committed to the DA lineage.  They’re hoping for trophic effects, not cell replacement. Also, the identification of dopamine neurons has to include their function- synthesis and release of dopamine when stimulated.”

Lorenz Studer was also concerned according to Nature:

“Lorenz Studer, a stem-cell biologist at the Memorial Sloan Kettering Cancer Center in New York City who has spent years characterizing such neurons ahead of his own planned clinical trials, says that “support is not very strong” for the use of precursor cells. “I am somewhat surprised and concerned, as I have not seen any peer-reviewed preclinical data on this approach,” he says.”

Clinical trials being based on unpublished data is not that unusual and regulators get to see the data even if we do not, but it raises risks. Both the Chinese and Australian teams are nonetheless enthusiastic:

“But Zhou and the Australian team defend their choices. Russell Kern, chief scientific officer of the International Stem Cell Corporation in Carlsbad, California, which is providing the cells for and managing the Australian trial, says that in preclinical work, 97% of them became dopamine-releasing cells.”

The reported 97% specificity is astonishingly good if correct. Such specificity is not easily obtained even in vitro under very defined conditions, whereas in vivo inside a transplant recipient’s brain there is a high degree of complexity with a mix of growth factors, extracellular matrix, cellular interactions, and potential niche conditions.

It’s not clear to me why transplanted ESC-derived neural precursors could be expected to almost entirely adopt one very specific fate in vivo. Are they pushed firmly in a certain direction prior to transplantation? The possible advantages of using precursors may be that they can potentially yield higher net engraftment since there remains proliferative activity and the cells may respond to in vivo signals, potentially yielding better functional engraftment. Precursors may also survive transplant better since neurons are complex cells that can be damaged during injection into the brain.

Is that precursor potential worth the risks? We’ll soon find out, but I see it as a high-risk approach. Still precursor-based trials such as these will be fascinating to watch.

16 thoughts on “How risky are stem cell trials for Parkinson’s beginning in China?

  1. Paul – I believe there is a misquote in Cyranoski article with regard to the “97% of them became dopamine-releasing cells” in the Australian trial’s pre-clincial work. I’ll pull out my interview with Dr. Kern’s when I get a moment later and post the related passage. Cheers

    • Thanks. I agree that it’s not a realistic number. The best methods for directed differentiation of DA neurons from hESCs and iPSCs, as developed by Lorenz Studer and colleagues, provide yields of 40-50%. These are clearly authentic DA neurons, as defined by functional release of DA neurotransmitter and electrophysiological profile.

  2. Here’s the published Q&A from about a year ago with Dr. Kern:

    Q: What is being transplanted, and what is the proposed mechanism of action?

    A: The clinical trial will be transplanting human parthenogenetic stem cells (ISC-hpNSCs). Human parthenogenetic stem cells are pluripotent stem cells that express all the pluripotent stem cell markers and, more importantly, have the ability to differentiate into all three germ layers, including dopaminergic neurons. The therapeutic potential of parthenogenetic stem cells derived cells have been tested by ISCO and other laboratories in various animal disease models, including Parkinson’s disease (PD).

    ISCO’s preclinical work indicates that the proposed mechanism of action of ISC-hpNSCs is neurotrophic support and cell replacement to the dying dopaminergic neurons of the recipient PD brain. The ISC-hpNSCs secrete neurotrophic cytokines in vitro and have been shown to significantly increase the levels of these cytokines in vivo.3

    ISCO has shown that ISC-hpNSCs differentiate into dopaminergic (DA) neurons (TH+, FOXA2+, GIRK2+, and DAT+) that secrete dopamine and fire spontaneous action potentials.3

    Additionally, in a recent publication from Roger Barker’s lab titled “PAX6 expression may be protective against dopaminergic cell loss in Parkinson’s disease” they found that the transcription factor, PAX6 is expressed in midbrain dopaminergic neurons and concluded that it may be protective against dopaminergic cell loss in Parkinson’s disease.4

    We have shown that ISC-hpNSCs also differentiate in situ into DA neurons in two different PD animal models, 6-OHDA lesioned rats and MPTP-lesioned African green monkeys.5 The percentage of ISC-hpNSCs differentiating into DA neurons in vivo is around 1-2% of the engrafted cells, which is enough to have a significant increase in the total number of DA neurons in the substantia nigra and fiber innervation in the striatum.

    3. Gonzalez, R., et al. Deriving dopaminergic neurons for clinical use. A practical approach. Scientific Reports 3, 1-5 (2013).
    4. Thomas, M.G., et al. PAX6 expression may be protective against dopaminergic cell loss in Parkinson’s disease. CNS & neurological disorders drug targets 15, 73-79 (2016).
    5. Gonzalez, R., et al. Proof of concept studies exploring the safety and functional activity of human parthenogenetic-derived neural stem cells for the treatment of Parkinson’s disease. Cell transplantation 24, 681-690 (2015).

  3. I also have an unpublished follow-up Q&A with Dr. Kern from early this year of which the following is taken –

    “Results from the fetal PD trials indicate that grafts containing only 50,000–100,000 TH+ DA neurons are sufficient to provide long-term symptomatic relief in patients10-14. We have shown that approximately 10% of the transplanted ISC-hpNSC cells survive and 2% of the engrafted cells differentiate into DA neurons15. We are transplanting 30-70 million ISC-hpNSC cells in patients, which means that approximately 3-7 million cells will survive transplantation and out of which, 60,000-140,000 will become DA neurons. Therefore, we believe our therapeutic approach will provide the necessary number of DA neurons for clinical efficacy. Additionally, ISC-hpNSC provide neurotrophic support and immunomodulation that can be critical in rescuing the dying host DA neurons and treating non-motor related symptoms16,17, which cannot be achieved with a dopaminergic replacement approach18.”

    10 Hauser, R. A. et al. Long-term evaluation of bilateral fetal nigral transplantation in Parkinson disease. Archives of neurology 56, 179-187 (1999).
    11 Lindvall, O. Developing dopaminergic cell therapy for Parkinson’s disease–give up or move forward? Movement disorders : official journal of the Movement Disorder Society 28, 268-273, doi:10.1002/mds.25378 (2013).
    12 Mendez, I. et al. Cell type analysis of functional fetal dopamine cell suspension transplants in the striatum and substantia nigra of patients with Parkinson’s disease. Brain : a journal of neurology 128, 1498-1510, doi:10.1093/brain/awh510 (2005).
    13 Li, W. et al. Extensive graft-derived dopaminergic innervation is maintained 24 years after transplantation in the degenerating parkinsonian brain. Proceedings of the National Academy of Sciences of the United States of America 113, 6544-6549, doi:10.1073/pnas.1605245113 (2016).
    14 Freed, C. R., Zhou, W. & Breeze, R. E. Dopamine cell transplantation for Parkinson’s disease: the importance of controlled clinical trials. Neurotherapeutics : the journal of the American Society for Experimental NeuroTherapeutics 8, 549-561, doi:10.1007/s13311-011-0082-9 (2011).
    15 Gonzalez, R. et al. Neural Stem Cells Derived from Human Parthenogenetic Stem Cells Engraft and Promote Recovery in a Nonhuman Primate Model of Parkinson’s Disease. Cell transplantation, doi:10.3727/096368916X691682 (2016).
    16 Pantcheva, P., Reyes, S., Hoover, J., Kaelber, S. & Borlongan, C. V. Treating non-motor symptoms of Parkinson’s disease with transplantation of stem cells. Expert review of neurotherapeutics 15, 1231-1240, doi:10.1586/14737175.2015.1091727 (2015).
    17 Evans, J. R. & Barker, R. A. Neurotrophic factors as a therapeutic target for Parkinson’s disease. Expert opinion on therapeutic targets 12, 437-447, doi:10.1517/14728222.12.4.437 (2008).
    18 Barker, R. A., Barrett, J., Mason, S. L. & Bjorklund, A. Fetal dopaminergic transplantation trials and the future of neural grafting in Parkinson’s disease. Lancet neurology 12, 84-91, doi:10.1016/S1474-4422(12)70295-8 (2013).

  4. So what happens to the NSCs that survive but do not become DA neurons? These are usually highly proliferative and as much trophic support they might be providing to the degenerating host DA neurons, what stops them from proliferating and/or differentiating into other cell types that are undesirable?..

  5. SG, that is my main concern. Dividing cells acquire mutations, and although most are harmless, there is an opportunity for an unwanted subpopulation to take over. I think that’s what happened with StemCells, Inc’s clinical grade fetal neural stem cells – the research grade cells worked well in an Alzheimer’s disease mouse model, but the same cells that were expanded and selected for the clinical stocks were very different- ineffective and prone to forming tumor-like blobs:

  6. Yes that’s correct, I noticed the change of name when doing background reading on the work. Dr. Kern is actually the son of the 85% owner of the company, Dr. Andrey Semechkin, who is primarily responsible for funding of the company’s ongoing investigative research.

    More pertinent I would imagine on the pre-clinical basis is the 2016 primate data referred to doi:10.3727/096368916X691682.

    As Ibon Garitaonandia, who used to be a colleague in the Loring Lab, is a primary scientist at ISCO perhaps his view on that paper would be helpful.

    I recall Jeanne your concern when we discussed the Stem Cell Inc. issue, it’s protocol(s) and donor specific derivation issues.

    Certainly the use of proliferative cells of any sort, especially pluripotent derived, are inheriently more risky. Robust pre-clinical work is essential. Also imo a methodology that, if safe and effective, can be scaled and commercially viable.

    Risk reward in trialing potential treatments for such serious unmet medical conditions as Parkinson’s Disease, as in most other areas of translational science, has historically been worth the effort on the road to advancing patient care.


    • Thanks ms for your input. My insight would be to use embryonic MSC to treat the auto immune diseases. Reboot TH Response and alter the the microbiome . Antigen presentation leads to Act T cells and MHC/ TCR to biomakers such as CTLA-4.

    • Michael, Ibon was my postdoc. He did excellent work in my lab, showing that long term culture of human pluripotent stem cells resulted in selection for mutations, including p53.

  7. I agree Andy, indeed we were keen to see that line of products develop at Ocata/ACT given the unique nature/potential of pluripotent derived MSC cell therapies. Perhaps there will be news on that front from Lanza/Astellas, other than the eye program. Maybe add that to the Q list Paul. In the meantime, Cynata are in the clinic with a promising early stage product for GvHD and with ties to Japan too. The future might be rosier than we think on this front. I’m a fan of hpMSCs.

    Yes Jeanne I remember your reference to Ibon’s work during the presentation in Stockholm you gave at the ISSCR conference. 2 years of individual repetitive work to produce data! The bravo was justified imo. I’ve been down to San Diego twice to interview Ibon and his team.


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