Stem cell therapy for human brain disorders.

Transplantation of stem cells or their derivatives, and mobilization of endogenous stem cells in the adult brain, have been proposed as future therapies for various brain disorders such as Parkinson's disease and stroke. In support, recent progress shows that neurons suitable for transplantation can be generated from stem cells in culture, and that the adult brain produces new neurons from its own stem cells in response to injury. However, from a clinical perspective, the development of stem cell-based therapies for brain diseases is still at an early stage. Many basic issues remain to be solved and we need to move forward with caution and avoid scientifically ill-founded trials in patients. We do not know the best stem cell source, and research on embryonic stem cells and stem cells from embryonic or adult brain or from other tissues should therefore be performed in parallel. We need to understand how to control stem cell proliferation and differentiation into specific cell types, induce their integration into neural networks, and optimize the functional recovery in animal models closely resembling the human disease. All these scientific efforts are clearly justified because, for the first time, there is now real hope that we in the future can offer patients with currently intractable diseases effective cell-based treatments to restore brain function.