The postischemic environment differentially impacts teratoma or tumor formation after transplantation of human embryonic stem cell-derived neural progenitors.

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. CONCLUSIONS: 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.

Human induced pluripotent stem cells improve stroke outcome and reduce secondary degeneration in the recipient brain.

Human induced pluripotent stem cells (hiPSCs) are a most appealing source for cell replacement therapy in acute brain lesions. We evaluated the potential of hiPSC therapy in stroke by transplanting hiPSC-derived neural progenitor cells (NPCs) into the postischemic striatum. Grafts received host tyrosine hydroxylase-positive afferents and contained developing interneurons and homotopic GABAergic medium spiny neurons that, with time, sent axons to the host substantia nigra. Grafting reversed stroke-induced somatosensory and motor deficits. Grafting also protected the host substantia nigra from the atrophy that follows disruption of reciprocal striatonigral connections. Graft innervation by tyrosine hydoxylase fibers, substantia nigra protection, and somatosensory functional recovery were early events, temporally dissociated from the slow maturation of GABAergic neurons in the grafts and innervation of substantia nigra. This suggests that grafted hiPSC-NPCs initially exert trophic effects on host brain structures, which precede integration and potential pathway reconstruction. We believe that transplantation of NPCs derived from hiPSCs can provide useful interventions to limit the functional consequences of stroke through both neuroprotective effects and reconstruction of impaired pathways.