Table 1 Advantages and disadvantages of different stem cell types for use in Parkinson's disease

Embryonic Stem Cells (ESCs)

Pluripotent stem cells derived from the inner cell mass of the blastocyst that are able to differentiate into cells of the three germ layers and show an extensive capability for self-renewal without differentiation, both in vivo and in vitro

(a) Highly proliferative/retain pluripotency after in vitro expansion

(b) Can generate DA-ergic neurons

(c) Shown to survive transplantation and generate some degree of functional recovery

(a) Risk of tumor formation

Induced pluripotent Stem Cells (iPSCs)

Reprogrammed adult murine fibroblasts into ESC-like cells

(a) Generation of unlimited PD patient-specific cells/autologous transplantation

(b) Shown to survive transplantation and generate some degree of functional recovery

(c) Could minimize immune reactions and ethical issues

Risk of tumor formation

(b) Autologous transplantation - risk of susceptibility to the original pathology of the patient

Bone marrow-derived stromal cells and mesenchymal Stem Cells (MSCs)

Small population of cells in the bone marrow that can differentiate into adipocytes, chondrocytes and osteoblasts, both in vivo and in vitro

(a) Improve motor performance in mice

(b) No adverse effects in humans at 12 months following transplantation

(a) Modest clinical improvement in humans

Fetal brain neural Stem Cells (NSCs)

Multipotent stem cells that are able to differentiate into neurons, astrocytes and oligodendrocytes

(a) Lower risk of tumor formation and immune rejection than ESCs

(a) Shown only limited differentiation in vivo

(b) Shown only partial effect in PD-like symptoms