GDNF and Parkinson disease: Thus, probably hUC‐MSCs should overexpress or be co‐encapsulated with GDNF to potentiate their therapeutic effects, which is supported by the positive outcome of a study in which hUC‐MSCs overexpressing hepatocyte growth factor (HGF), a survival factor for motor neurons, were used to treat a cell model of PD (Liu et al., 2014).