Decoding the effects of neural transplantation in patients with Parkinson's disease: a multimodal imaging study

Parkinson's disease (PD) is a common incurable neurodegenerative disease, clinically characterised by the development of bradykinesia, rigidity and tremor. These clinical features are linked to progressive loss of the dopaminergic input from the substantia nigra to the striatum. Thus the management of PD can initially be highly successful using dopaminergic drugs, however these agents do not re-establish normal tonic /phasic signalling, and with time lead to disabling side-effects, such as "ON-OFF" fluctuations and uncontrollable involuntary movements (dyskinesias). These side effects relate not only to the non physiological delivery of dopamine (DA), but also to drug actions that are off target. One way to combat these problems is using targeted DA cell based therapies placed in the putamen, the site of the brain with greatest DA loss in PD. This has been done with greatest success when the grafted tissue is derived from the developing human ventral mesencephalon. Over the last 25 years it has been shown (including by our group) that this approach can lead to long term survival of cells, with physiological DA release and re-activation of relevant cortical motor areas. However, while some patients have responded extremely well to this intervention with significant relief of symptoms to the extent that they could come off their anti-PD medications, others showed only modest clinical improvements while some developed severe, off-state graft-induced dyskinesias (GID). Nonetheless, the potential for this therapy to provide considerable benefit is clear and led to a gathering of international experts to examine the reasons behind the variable outcomes. This resulted in a successful application to the EU, and a new trial (Transeuro) in which patient selection, immunosuppressive regime, method of transplant and tissue dissection were re-appraised and optimized (including new pre-clinical studies) to increase the rate of success.
This project has now evolved to the point that by the end of this year 15 patients will have been grafted out of an observational cohort of 150 patients, who have had extensive imaging pre transplantation. From November 2015 to date we have performed 13 surgeries, and we aim to complete 15 patients by December 2016.
We now wish to follow up this unique cohort of grafted patients using the same extensive multimodal battery of neuroimaging techniques that we have already employed pre transplantation.
This study that we are now proposing will:
1. Accurately quantify any changes to the metabolism and transport of DA, particularly in the putamen at the graft site.
2. Examine whether the grafted tissue contains significant serotonin neurons which in the past have been linked to the development of GIDs.
3. Identify which brain alterations are most important at predicting a positive clinical outcome post grafting, as well as those associated with any side effects such as GIDs.
4. Define the degree to which functional activation in cortical motor regions is restored, and whether there are improvements in specific frontostriatal circuits which are impacted on by the transplant.
5. Combine imaging analysis with the extensive motor, cognitive, neuropsychological and quality of life data, in order to ascertain the direct links between brain and behaviour.
6. Define those imaging parameters pre and post grafting that best predict clinical response to dopamine cell transplants.
While human fetal mesencephalic tissue transplants will never become a mainline therapy for PD given the logistical and ethical problems that they engender, they will lay the foundations for the next generation of stem cell derived dopamine therapies for PD. STEM-PD is currently is in the final stages of pre clinical development, with a projected time to a first in human trial in 2019. As such the outcome of this study will inform us as to how to deliver the best imaging protocol for this first in human clinical trial with stem cells.

Early trials of human fetal mesencephalic tissue (hfVM) in Parkinson's disease (PD) provided evidence that such grafted cells can survive, restore dopamine release and cortical motor function, enabling dramatic clinical improvements in motor symptoms and quality of life with the cessation of their PD drugs in some cases. While later double-blind trials failed to confirm such efficacy and even generated dyskinesias, patients still exhibited significant increases in dopaminergic function and partial relief of symptoms, indicating that outcome heterogeneity thus far had resulted from inconsistent and sub-optimal protocols.
In 2006 we set up an international working group that sought to collate and analyse the data from all the existing hfVM trials with the aim of identifying how best to take this therapy forward, especially as we enter an era of stem cell treatments. This led to the funding of TRANSEURO (EU FP7 programme). Unlike previous trials patients in this programme are younger with less advanced disease and no significant LIDs, they were transplanted with more standardised tissue preparations, and have undergone a novel extensive multimodal imaging protocol thus providing a uniquely well-characterized cohort.
In this new project we propose to study 15 grafted patients and 15 matched PD patients from TRANSEURO using a comprehensive clinical and multimodal imaging battery in order to understand the complex underlying neural networks related to this cell repair strategy and to develop optimal imaging assessments for future stem cell transplants. In this regard, while hfVM based therapies will never become mainline therapies for PD for logistical and ethical reason, they nevertheless will pave the way for the next generation of stem cell treatments. These therapies are now approaching first in human clinical trials and as such the study proposed in this application, will be vital in the testing of this new exciting restorative therapy.

The focus of this project is on the investigation of how putaminal transplantation of human fetal ventral mesencephalic dopaminergic cells may modify the otherwise progressive neurodegenerative disease course of Parkinson's disease using a range of objective in vivo imaging techniques and which alterations best map on to clinical outcome. The results of this project will have significant impact upon the following:
- Healthcare - Cell therapy in Parkinson's disease has the potential to combat rising healthcare costs and increase the quality of life for affected individuals and their families. The costs of treating PD with conventional drugs and newer innovative therapies, such as DBS and/or Apomorphine or DuoDopa pumps, amounts to between 8,000 and 40,000 Euro a year per patient. Indeed, in the UK alone, the total cost of PD is estimated to be between 449 million and 3.3 billion pounds annually. It is anticipated that cell therapies will not only reduce the costs of care in the short term but also in the long term; in contrast to current "gold standard" approaches whereby progressively worsening symptoms are managed continually, cell therapy approaches target the repair of the underlying neural network, hence altering the natural history of treated disease for the better. Over a 5-10 year period it is probable that engrafted cell therapies will significantly lessen the need for patients to use drug therapies and may obviate the need for them to have other expensive treatments. The results of this study will provide information necessary to accelerate the development of cell therapies for use in the clinic.
- Cell research - The use of human fetal ventral mesencephalic cells is not feasible for future routine clinical use. Instead the results of this study are expected to offer guidance for the development of the next generation of reparative therapies using stem cells. While clinical observations are necessary to establish the polarity of these changes they are not informative as to the mode by which they have occurred. In fact, progress in the field has been stunted by the lack of comprehensive post-graft investigations outside of 18F-DOPA PET in previous trials. By establishing causal links between resultant symptoms and alterations within the brain through the use of multiple in vivo imaging techniques we will be able to pinpoint factors responsible for improvements and the origin of potential side effects. This objective information will be of great value to the way in which stem cells are developed for engraftment in PD patients and to refine surgical protocols and post-graft care. It will also provide the evidence needed to generate commercial investment given the heightened clarity of directions worth pursuing towards a one-off and unique reparative therapy.
- Post-graft monitoring - We anticipate that our exhaustive multimodal imaging protocol will be informative for the standard of post-graft monitoring in future trials. It is likely that novel radioligands and updated MRI sequences will emerge in years to come, however the methods and analytical strategies that will encompass multiple imaging metrics conceived here will likely be used as a basis from which future methodological approaches for all regenerative medicine therapies in PD approaching clinical translation are developed.
- Validity of the approach to protocol design - All aspects of the procedure from mode of engraftment, immunosuppressive regime, DA/5HT ratio of implanted cells and patient selection have been interrogated and fine-tuned with the hope that doing so will increase the rate of positive outcomes whilst minimising its potential side effects. Our findings will conclude 15 years' of work on how best to use cell therapies in PD, either validating the approaches taken in the re-appraisal and design phases or at the very least provide further considerations that will shape the future of regenerative trials in PD.