This study is testing a new treatment called **IPS101A** for people with **Parkinson's disease**. Parkinson's is a condition that affects the brain and can make it hard to move or do daily activities. The treatment uses a special type of gene therapy, which involves introducing new genetic material into the body to help fight the disease. The study will check if IPS101A is safe and see how well it works for patients with severe symptoms. Participants must be between 50 and 80 years old, have had Parkinson's for at least 10 years, and still have severe symptoms even after trying other treatments. People with dementia or certain other conditions cannot join. **Key Points:** - The study will help determine if the new treatment is safe and effective. - Participants will need to meet specific criteria and undergo various tests. - The study is designed to learn more about the treatment's effects and how the body processes it. This is an opportunity to try a new treatment that might help with severe Parkinson's symptoms. However, there may be risks involved, and only those who meet the study's criteria can participate. Compensation details are not specified.