Substitutive cell therapy using fetal striatal grafts has demonstrated preliminary clinical success in patients with Huntington's disease, but the logistics required for accessing fetal cells preclude its extension to the relevant population of patients. Human embryonic stem (hES) cells theoretically meet this challenge, because they can be expanded indefinitely and differentiated into any cell type. We have designed an in vitro protocol combining substrates, media, and cytokines to push hES cells along the neural lineage, up to postmitotic neurons expressing striatal markers. The therapeutic potential of such hES-derived cells was further substantiated by their in vivo differentiation into striatal neurons following xenotransplantation into adult rats. Our results open the way toward hES cell therapy for Huntington's disease. Long-term proliferation of human neural progenitors leads, however, to xenograft overgrowth in the rat brain, suggesting that the path to the clinic requires a way to switch them off after grafting.cell therapy ͉ Huntington's disease ͉ striatum ͉ cell differentiation ͉ overgrowth

Wnt-ligands are among key morphogens that mediate patterning of the anterior territories of the developing brain in mammals. We qualified the role of Wnt-signals in regional specification and subregional organization of the human telencephalon using human pluripotent stem cells (hPSCs). One step neural conversion of hPSCs using SMAD inhibitors leads to progenitors with a default rostral identity. It provides an ideal biological substrate for investigating the role of Wnt signaling in both anteroposterior and dorso-ventral processes. Challenging hPSCneural derivatives with Wnt-antagonists, alone or combined with sonic hedgehog (Shh), we found that Wntinhibition promote both telencephalic specification and ventral patterning of telencephalic neural precursors in a dose-dependent manner. Using optimal Wnt-antagonist and Shh-agonist signals we produced human ventraltelencephalic precursors, committed to differentiation into striatal projection neurons both in vitro and in vivo after homotypic transplantation in quinolinate-lesioned rats. This study indicates that sequentially organized Wntsignals play a key role in the development of human ventral telencephalic territories from which the striatum arise. In addition, the optimized production of hPSCderived striatal cells described here offers a relevant biological resource for exploring and curing Huntington disease.

Background and Purpose-Risk of tumorigenesis is a major obstacle to human embryonic and induced pluripotent stem cell therapy. Likely linked to the stage of differentiation of the cells at the time of implantation, formation of teratoma/tumors can also be influenced by factors released by the host tissue. We have analyzed the relative effects of the stage of differentiation and the postischemic environment on the formation of adverse structures by transplanted human embryonic stem cell-derived neural progenitors. Methods-Four differentiation stages were identified on the basis of quantitative polymerase chain reaction expression of pluripotency, proliferation, and differentiation markers. Neural progenitors were transplanted at these 4 stages into rats with no, small, or large middle cerebral artery occlusion lesions. The fate of each transplant was compared with their pretransplantation status 1 to 4 months posttransplantation. Results-The influence of the postischemic environment was limited to graft survival and occurrence of nonneuroectodermal structures after transplantation of very immature neural progenitors. Both effects were lost with differentiation. We identified a particular stage of differentiation characterized in vitro by a rebound of proliferative activity that produced highly proliferative grafts susceptible to threaten surrounding host tissues. Conclusion-The effects of the ischemic environment on the formation of teratoma by transplanted human embryonic stem cell-derived neural progenitors are limited to early differentiation stages that will likely not be used for stem cell therapy. In contrast, hyperproliferation observed at later stages of differentiation corresponds to an intrinsic activity that should be monitored to avoid tumorigenesis. (Stroke. 2010;41:153-159.)

Huntington's disease (HD) is characterized by a late clinical onset despite ubiquitous expression of the mutant gene at all developmental stages. How mutant huntingtin impacts on signalling pathways in the pre-symptomatic period has remained essentially unexplored in humans due to a lack of appropriate models. Using multiple human embryonic stem cell lines derived from blastocysts diagnosed as carrying the mutant huntingtin gene by pre-implantation genetic diagnosis, we explored early developmental changes in gene expression using differential transcriptomics, combined with gain and loss of function strategies. We demonstrated a down-regulation of the HTT gene itself in HD neural cells and identified three genes, the expression of which differs significantly in HD cells when compared with wild-type controls, namely CHCHD2, TRIM4 and PKIB. Similar dysregulation had been observed previously for CHCDH2 and TRIM4 in blood cells from patients. CHCHD2 is involved in mitochondrial function and PKIB in protein kinase A-dependent pathway regulation, which suggests that these functions may be precociously impacted in HD.

Cell therapy products (CTP) derived from pluripotent stem cells (iPSCs) may constitute a renewable, specifically differentiated source of cells to potentially cure patients with neurodegenerative disorders. However, the immunogenicity of CTP remains a major issue for therapeutic approaches based on transplantation of non-autologous stem cell-derived neural grafts. Despite its considerable side-effects, long-term immunosuppression, appears indispensable to mitigate neuro-inflammation and prevent rejection of allogeneic CTP. Matching iPSC donors’ and patients’ HLA haplotypes has been proposed as a way to access CTP with enhanced immunological compatibility, ultimately reducing the need for immunosuppression. In the present work, we challenge this paradigm by grafting autologous, MHC-matched and mis-matched neuronal grafts in a primate model of Huntington’s disease. Unlike previous reports in unlesioned hosts, we show that in the absence of immunosuppression MHC matching alone is insufficient to grant long-term survival of neuronal grafts in the lesioned brain.