| Abstract: | Pluripotent cells represent a powerful tool for tissue regeneration, but their clinical utility is limited by their propensity to form teratomas. Little is known about their interaction with the surrounding niche following implantation and how this may be applied to promote survival and functional engraftment. In this study, we evaluated the ability of an osteogenic microniche consisting of a hydroxyapatite-coated, bone morphogenetic protein-2–releasing poly-l-lactic acid scaffold placed within the context of a macroenvironmental skeletal defect to guide in vivo differentiation of both embryonic and induced pluripotent stem cells. In this setting, we found de novo bone formation and participation by implanted cells in skeletal regeneration without the formation of a teratoma. This finding suggests that local cues from both the implanted scaffold/cell micro- and surrounding macroniche may act in concert to promote cellular survival and the in vivo acquisition of a terminal cell fate, thereby allowing for functional engraftment of pluripotent cells into regenerating tissue.Pluripotent stem cells hold significant promise for the treatment of tissue deficiencies and other human diseases (1, 2). Both human induced pluripotent stem cells (h-iPSCs) and embryonic stem cells (h-ESCs) are capable of differentiating into a multitude of cell types from each of three germ layers, allowing investigators to devise novel platforms for research and therapeutic drug screening (3, 4). This same property has also made these cells a much more powerful tool compared with mesenchymal stromal cells for regenerative medicine. In addition, as h-iPSCs can be reprogrammed from a patient’s own somatic cells, they have the added potential of mitigating some of the concerns over immunogenic sequelae that are raised with other cell types, yet simultaneously enabling development of patient-specific disease modeling (5–7).Despite dramatic progress made over recent years, widespread application of pluripotent cells in clinical medicine has been hampered by several challenges, chief among which is the propensity for both h-iPSCs and h-ESCs to form tumors in vivo (8). As recent studies have shown development of teratomas to directly correlate with the number of residual undifferentiated cells implanted, several strategies have been proposed to eliminate these persistent pluripotent cells before injection (8–10). It is still unknown, however, if they can be completely successful in the context of the number of cells required for in vivo tissue regeneration. Furthermore, few reports have also demonstrated engraftment and functional integration of pluripotent cells into the surrounding tissue, and little is known about how transplanted cells truly interact with the endogenous niche following implantation. These niches may in fact play significant roles in stabilizing fully pluripotent cells and guiding acquisition of cell fate, while also minimizing teratoma formation (11).In this study, we evaluated how a skeletal defect macroniche combined with a pro-osteogenic biomimetic scaffold microniche could provide cues affecting survival and differentiation of implanted cells lacking in a developmental program. In response to such an environment, not only did we find a high degree of survival, but the transplanted pluripotent cells were also shown to acquire a fully differentiated osteogenic state, integrating into the surrounding bone without the formation of a teratoma. Our data thus suggest that the surrounding niche is capable of not only supporting cellular viability, but can also guide differentiation of pluripotent cells for functional engraftment into regenerating tissue. |
