The Safety and Tolerability of XS411CN Injection in Treatment of Primary Parkinson's Disease

This study is testing the safety and tolerability of an injection called XS411CN — a type of cell therapy — as a treatment for Parkinson's disease that has been present for at least 5 years and whose symptoms (especially "off" periods when medication is not working well) are no longer well controlled by current medications. **You may be eligible if...** - You are between 50 and 75 years old and have had established Parkinson's disease for at least 5 years - You experience at least 2.5 hours per day of "off" time (when your medication stops working and symptoms worsen) - Your Parkinson's medications have worked in the past but are no longer as effective, or cause movement side effects - Your blood counts, liver, and kidney function meet required levels **You may NOT be eligible if...** - You have a different type of Parkinson's-like condition (not classic Parkinson's disease) - You have severe cognitive impairment, severe depression, or hallucinations - You have had brain surgery (such as deep brain stimulation) in the past - You have serious heart disease, active infection, cancer history, or uncontrolled autoimmune disease - You are pregnant or breastfeeding Talk to your doctor to see if this trial is right for you.