Human amniotic fluid stem cells do not differentiate into dopamine neurons in vitro or after transplantation in vivo

Although embryonic stem (ES) cells can generate dopamine (DA) neurons that are potentially useful as a cell replacement therapy in Parkinson's disease (PD), associated ethical and practical concerns remain major stumbling blocks to their eventual use in humans. In this study, we examined human amniotic fluid stem (hAFS) cells derived from routine amniocenteses for their potential to give rise to DA neurons in vitro and following transplantation into the 6-hydroxydopamine-lesioned rat brain. We show that undifferentiated hAFS cells constitutively expressed mRNAs and proteins typical of stem cells but also cell derivatives of all three germ layers, including neural progenitors/neurons (nestin, beta-tubulin III, neurofilament). Additionally, these cells expressed mRNAs of an immature DA phenotype (Lmx1a, Pitx-3, Nurr1, Aldh1a1) but not the corresponding proteins. Importantly, treatment with DA differentiation factors using a variety of protocols did not further promote the development of fully differentiated DA neurons from hAFS cells. Thus, Lmx1a, Aldh1a1, AADC, TH, and DAT proteins were not detected in hAFS cells in culture or after transplantation into the PD rat brain. Moreover, by 3 weeks after implantation, there were no surviving AFS cells in the graft, likely as a result of an acute immunorejection response, as evidenced by the abundant presence of CD11+ macrophage/microglia and reactive GFAP+ astrocytes in the host brain. Taken together, these results suggest that further studies will be needed to improve differentiation procedures in culture and to prolong cell survival in vivo if hAFS cells are to be useful as replacement cells in PD.