Cells therapy for Parkinson's disease--so close and so far away.

One of the strategies of treating Parkinson's disease (PD) is the replacement of lost neurons in the substantia nigra with healthy dapamingergic cells. Potential sources for cells range from autologous grafts of dopamine secreting cells, fetal ventral mesencephalon tissue, to various stem cell types. Over the past quarter century, many experimental replacement therapies have been tried on PD animal models as well as human patients, yet none resulted in satisfactory outcomes that warrant wide applications. Recent progress in stem cell biology has shown that nuclear transfer embryonic stem cells (ntES) or induced pluripotent stem cells (iPS) derived cells can be used to successfully treat rodent PD models, thus solving the problem of immunorejection and paving the way for future autologous transplantations for treating PD. Meanwhile, however, post mortem analysis of patients who received fetal brain cell transplantation revealed that implanted cells are prone to degeneration just like endogenous neurons in the same pathological area, indicating long-term efficacy of cell therapy of PD needs to overcome the degenerating environment in the brain. A better understanding of neurodegeneration in the midbrain appeared to be a necessary step in developing new cell therapies in Parkinson's disease. It is likely that future cell replacement will focus on not only ameliorating symptoms of the disease but also trying to slow the progression of the disease by either neuroprotection or restoring the micro-environment in the midbrain.