Stem cell strategies for treating neurodegenerative diseases. We propose that a multifaceted stem cell transplant approach would provide the most significant benefit for patients suffering from neurodegenerative disease. In the case of Parkinson's disease, halting the degeneration of substantia pars compacta (SNpc) neurons could prevent further degradation of motor ability. Augmenting the signal in remaining circuitry could improve the motor symptoms associated with the disease. Finally, regenerating lost circuitry could abolish disease symptomology.

Human stem cells grown from different tissue sources have properties that each may be advantageous for different therapeutic strategies. (a) Human embryonic stem cells (hESCs) derived from excess blastocysts that have been donated by women who have undergone in vitro fertilization (IVF) generate millions of cells with unlimited potential (they can generate all cells in the body). In their primitive form, hESCs can be easily engineered to secrete neurotransmitter or growth factors to stop disease progression or to augment intact circuitry, respectively. When hESCs are differentiated into neural progenitors, they can then make neurons, astrocytes and oligodendroctyes, the precursors of which could potentially be used to regenerate dying circuitry. (b) Foetal neural progenitors harvested from the brain tissue of discarded foetuses can be expanded for use in thousands of patients. They readily generate neurons and astrocytes in vitro and generate neurons when transplanted into neurogenic areas of the adult brain. (c) Adult neural progenitors can be harvested from post-mortem tissue or even from patient biopsies to generate immunologically matched transplants. These cells generate neurons, astrocytes and oligodendrocyte precursors in culture and neurons when transplanted into neurogenic regions of the adult brain. The biggest limitation with adult neural progenitors is that they rapidly senesce in culture preventing large-scale expansion.