I don't want to be negative, but I don't see GDNF as a cure for Parkinson's disease. At least not by itself. Why ? 1 or 2 years ago there was research published about neurotrophic factors. Neurotrophic factors don't work in an environment with misfolded alpha-synuclein. The misfolded alpha-synuclein blocks the creation of new neurons. I don't remember anymore why, but I do remember this was the case. Therefore, I see GDNF as a cure for people with stroke or brain damage, but not for people with neurodegenerative diseases. If the misfolded alpha-synuclein can be removed or get its original form back, then I think GDNF might help people to regenerate lost neurons. Therefore, I think GDNF by itself cannot cure this disease.
What strikes me is that I am 100 % sure that scientist are very well aware about the research done about misfolded alpha-synuclein blocking the brain's plasticity, but despite that, they are hyping GDNF. They are very well aware that people with PD have misfolded alpha-synuclein and before continuing testing this on human with PD, they should first demonstrate it works on an animal model with misfolded alpha-synuclein ... something which was already done with no succes. So I guess they just want to do some experiments on human lab rats.
Oh wait, I just got a new insight about the result of this experiment. My guess is that this will be the result of this experiment: "Unfortunately, GDNF hasn't show to cure PD. But the used delivery method has been shown to be safe and effective and can be used in future on human beings."