Examples include studies investigating the neuroprotective effects of encapsulated cells delivering glial cell line-derived neurotrophic factor (GDNF) to the brain [7,8], l-dopa-secreting cells for Parkinson’s disease [9,10], and Nerve Growth Factor (NGF) for Alzheimer’s disease [11,12]. The gene discussed is GDNF; the disease is early-onset autosomal dominant Alzheimer disease.