A Trial to Determine the Safety and Tolerability of Transplanted Stem Cell Derived Dopamine Neurons to the Brains of Individuals With Parkinson's Disease

Inclusion Criteria: * Have given written informed consent to participate in the trial * Diagnosed with PD as defined using Queens Square Brain Bank criteria * Moderate disease as defined by having Hoehn and Yahr stage 2-3 in OFF state * Disease duration \> 10 years * Male or female, aged between 50 and 75 years (inclusive) * Have a significant response to dopamine therapies as judged by the PI or other delegated clinician * Have symptoms that are not appropriately controlled by existing oral anti-PD medications, as judged by the PI or other delegated clinician * Ability to travel to Lund for surgery * Followed up for at least 12 months prior to inclusion in this trial in the TransEUro observational study * Be fluent in English/Swedish to enable completion of questionnaires as assessed by the PI or other delegated clinician at Cambridge/Lund, respectively * Be approved by the TMG clinical sub-group for trial participation Exclusion Criteria: * Tremor dominant disease, as assessed by the PI or other delegated clinician * Significant drug induced dyskinesias as defined by a score of \> 2 in the Abnormal Involuntary Movement Scale (AIMS) dyskinesias rating scale, in any body part in the ON state * Ongoing major medical or psychiatric disorders, including depression (MADRS \> 20) and psychosis, that make participation unsuitable, as judged by the PI or other delegated clinician * Any contraindication to neurosurgery * Unable to be imaged using MRI * Extensive ventral striatal loss or normal findings on F-DOPA PET at screening * Significant cognitive impairment indicative of an incipient dementia/established dementia or values consistent with MoCA score of ≤ 24 * Unable to perform normal copying of interlocking pentagons and/or a semantic fluency score for naming animals of less than 20 over 90 seconds * Other concomitant treatment with neuroleptics (including atypical neuroleptics) and/or cholinesterase inhibitors * Previous neurosurgery to the brain, or cell or organ transplantation, or recipient of repeated blood transfusions * Any contraindication to immunosuppressive therapy, prophylactic antibiotics, and/or osteoporosis prophylaxis (refer to STEM-PD Trial Immunosuppressant Manual) * High levels of pre-formed specific anti-HLA antibodies to the cell product * Severely reduced TPMT activity (less than half of the lower normal TPMT activity level) * History of documented severe/significant allergy requiring treatment * Female who is pregnant or breastfeeding * Received an investigational drug (including investigational vaccines) or used an invasive investigational medical device within 4 weeks of the screening visit, or is currently enrolled in an interventional investigational trial * Female of childbearing potential or male unwilling to follow contraception requirements (see protocol section 12.15) * Any other condition which, in the opinion of the investigator, makes the patient inappropriate for entry into the trial