For example, in the case of stem cell transplantation in a Parkinson’s disease model, <300 tyrosine hydroxylase (TH)-positive neurons survived after transplanting 100,000–400,000 ES cells, and <4.3% of neural stem cell (NSC)-derived TH positive neurons survived after transplantation; these survival rates remain low even at present [34]. The gene discussed is TH; the disease is Parkinson disease.