We developed a method for the efficient generation of functional dopaminergic (DA) neurons from human embryonic stem cells (hESCs) on a large scale. The most unique feature of this method is the generation of homogeneous spherical neural masses (SNMs) from the hESC-derived neural precursors. These SNMs provide several advantages: (i) they can be passaged for a long time without losing their differentiation capability into DA neurons; (ii) they can be coaxed into DA neurons at much higher efficiency than that from previous reports (86% tyrosine hydroxylase-positive neurons/total neurons); (iii) the induction of DA neurons from SNMs only takes 14 days; and (iv) no feeder cells are required during differentiation. These advantages allowed us to obtain a large number of DA neurons within a short time period and minimized potential contamination of unwanted cells or pathogens coming from the feeder layer. The highly efficient differentiation may not only enhance the efficacy of the cell therapy but also reduce the potential tumor formation from the undifferentiated residual hESCs. In line with this effect, we have never observed any tumor formation from the transplanted animals used in our study. When grafted into a parkinsonian rat model, the hESC-derived DA neurons elicited clear behavioral recovery in three behavioral tests. In summary, our study paves the way for the large-scale generation of purer and functional DA neurons for future clinical applications.is a neurodegenerative disorder characterized by progressive and selective loss of dopaminergic (DA) neurons in the midbrain substantia nigra (1). Currently, the prevailing strategy for the treatment of PD is pharmacological. However, pharmacological treatment with L-DOPA works initially, but over time, the effectiveness of L-DOPA wanes and side effects develop (2). An alternative approach may be the transplantation of DA-synthesizing cells. One source of DA-synthesizing cells is embryonic stem cells (ESCs). ESCs are pluripotent and capable of self-renewal (3-5). For the purpose of applying the ESCs to PD, many researchers have tried to develop protocols by which ESCs from some species can differentiate into DA neuronal phenotypes (6-11). Although some progress has been made in the generation of DA neurons from human ESCs (hESCs) (12-22), there are still many technical improvements to be made before the application of hESCs to treat PD. Examples include increasing the purity of DA neurons, supplying a sufficient quantity of DA neurons for clinical applications, decreasing tumor formation after transplantation, and clearly demonstrating the functionality of hESC-derived DA neurons in a parkinsonian animal model.Here, we introduce a method that allows us to differentiate hESCs into functional tyrosine hydroxylase-positive (TH ϩ ) neurons up to near 86% of the total hESC-derived neurons, which is the highest purity ever reported. Achieving high efficiency of DA neuronal derivation is an important issue in cell therapy, because it would not only increase the effica...

The UT is the major site of late aneurysmal dilation. A large UT false lumen diameter on the initial CT portends late aneurysm and adverse outcome warranting early intervention.