In this exclusive interview, Jun Takahashi discusses his current trial evaluating iPSC-derived dopaminergic progenitor cells for Parkinson’s disease.
Professor Jun Takahashi received his MD from Kyoto University and his PhD in neurosurgery and neurobiology from Kyoto University Graduate School of Medicine (both Kyoto, Japan). He has been at the Center for iPS Cell Research and Application at Kyoto University since 2010 and is currently a Professor in the Department of Clinical Application. His research interest is the development of cell replacement therapy using iPSCs for intractable neurological diseases and is currently leading the first clinical trial to investigate induced pluripotent stem cell (iPSC)-derived cells for Parkinson’s disease, which started recruiting on 1 August 2018.
Please introduce yourself and your home institution
I am a professor at the Center for iPS Cell Research and Application (CiRA), Kyoto University. I graduated from the Kyoto University Faculty of Medicine with my MD in 1986, and started my career as a neurosurgeon at Kyoto University Hospital thereafter. After I earned my PhD, also from the Kyoto University Graduate School of Medicine, in 1993, I did a postdoctoral fellowship at the Salk Institute (Dr. Fred Gage’s laboratory; CA, USA) where I started research work on neural stem cells. Since returning to Kyoto University Hospital in 1997, I have been investigating functional neurosurgery including deep brain stimulation and cell-based therapies for Parkinson’s disease (PD). In 2010, I moved to CiRA to develop new regenerative medicine for PD using iPSC technologies.
In 2017, you reported success in an animal trial for this intervention. How much has the study design changed for this human trial?
The monkey study published in 2017 (Kikuchi et al. Nature 548: 592-596, 2017) was not just a scale up from the rodent studies, but a simulation of the planned clinical trial. In fact, the protocol was almost the same as the clinical trial, and the study confirmed the efficacy and safety of iPSC-derived dopaminergic (DA) progenitors. The results verified important details about the clinical trial such as the number of donor cells to be injected, the method of brain imaging, the observation period and the number of the patients to be included.
Differences between the monkey study and the clinical trial can be summarized in two main points. First is the use of research grade iPSC lines vs. clinical grade iPSC lines, which were established from the peripheral blood cells of an HLA-homozygous healthy individual at CiRA. Second are the differences between MPTP-treated monkey PD models and human PD patients.
(Editor: MPTP is a neurotoxin that was used to induce PD in the monkeys used in the 2017 trial)
You will be using cells from the iPS Cell Stock for Regenerative Medicine. How will the quality of the banked cells be assured?
As mentioned above, we will use an iPSC line derived from the peripheral blood cells of an HLA-homozygous healthy individual. The HLA haplotype being used is the most frequent in Japan and covers 17% of the population. The details of the iPSC line can be found in Donor Recruitment and Eligibility Criteria for HLA-Homozygous iPS Cell Bank in Japan (Stem Cell Banking, Springer).
Of course, the quality of the clinical grade iPSCs and their derivatives must be evaluated before starting a clinical trial. We discussed with a Japanese regulatory agency (Pharmaceutical and Medical Devices Agency) and performed safety tests including tumorigenicity, toxicity, distribution and genomic stability. We also confirmed the efficacy of the clinical grade cells in 6-OHDA-treated rat models.
(Editor: 6-OHDA is another neurotoxin that can be used to induce PD in animal models)
How will the iPS cells be differentiated into dopaminergic progenitor cells?
The differentiation method is described in the article by Doi et al. (Stem Cell Rep. 2: 337-350, 2014). Briefly, neural cells are induced from human iPSC by inhibiting BMP and activin signals and specified to ventral midbrain identity by adding Wnt and Shh signals. We succeeded to do this at large scale on xeno-free laminin fragments. In addition, DA progenitor cells are enriched by sorting the cells expressing CORIN, a cell surface marker for the floor plate where midbrain DA neurons originate.
Why have you chosen not to treat patients with the most severe Parkinson’s disease in this trial?
The mode of action of this treatment is that the grafted cells secrete dopamine and stimulate striatal neurons in the brain. In the severe stage of PD, the striatal neurons and their innervating cortical neurons are already degenerated to the point that they show little response to dopamine. Therefore, it is too late for these patients even if the grafted cells survive and secrete dopamine in the brain. In fact, previous studies of fetal cell transplantation for PD patients showed that the treatment had little effect for severe cases. Considering these results, we will choose patients in the middle stage of PD for our clinical trial.
How will you monitor and reduce the risk of tumorigenesis?
As mentioned above, we will sort CORIN+ cells in our manufacturing protocol. This process not only enriches DA progenitor cells but also eliminates immature cells which may proliferate in the brain. Further, the use of CORIN+ cells reduces the risk of tumorigenesis by the donor cells. Indeed, we have confirmed that our cells are not tumorigenic in rodent and non-human primate brains. In the clinical trial, we will monitor the graft size by MRI and the cell proliferation by [18F]FLT-PET studies.
What are the trial’s primary endpoints and how were these chosen?
This is the first clinical trial using human iPSCs. So, the primary endpoints are related to safety, especially tumorigenicity. Specifically, we will be observing 1) the incidence and severity of adverse events, and 2) the presence or absence of graft expansion in the brain 24 months after the transplantation. The details can be found in the clinical trial listing.
Japan is often thought of as leading the way in iPSC research and translation. Why do you think this is?
The most important reason is that because iPSC were discovered by Prof. Shinya Yamanaka, they are viewed as a Japanese invention and thus receive exceptional support from the Japanese government. As an example, CiRA was established in 2010 to promote the research and application of iPSC technology. Furthermore, the clinical application of embryonic stem cells was prohibited until recently and there were no translational projects using embryonic stem cells in Japan. Therefore, regenerative medicine in Japan is heavily tilted toward iPSC compared to the other countries such as the USA and UK.
This is an investigator-led trial. Why did you decide not to work with an industry partner?
I am working with a pharmaceutical company. However, as a physician-scientist, I think I am responsible for the cells and wanted to watch this initial trial carefully: that’s the reason.
Why did you choose Parkinson’s disease at a target for this therapy? Are neurological diseases more amenable to treatment with cell therapies?
There are several reasons. The pathology is relatively simple: a single type of neuron (dopaminergic neuron) in a small area is degenerated. In addition, the method to induce dopaminergic neurons from mouse ES cells was known; when the late Dr. Yoshiki Sasai discovered this method, which was published in Neuron in 2000, we started a collaboration. There are also a large, but not huge, number of patients and there is evidence that fetal cell transplantation can improve the motor symptoms of the Parkinson’s disease patients.
What has been the biggest challenge in developing this therapy and bringing it to clinical trial?
Every step is important, but the biggest challenge and our unique point is a sorting of CORIN-positive cells. It can enrich dopaminergic progenitors and eliminate unwanted (or dangerous) cells, which increases the safety, efficacy and quality stability of the donor cells.
Financial & competing interests disclosure
Collaboration and partly funded by Sumitomo Dainppon Pharma (Osaka, Japan).