Giuseppe Maria de Peppo

Commercially-pure titanium (cp-Ti) and the titanium-aluminum-vanadium alloy (Ti6Al4V) are widely used as reconstructive implants for skeletal engineering applications, due to their good mechanical properties, biocompatibility and ability to integrate with the surrounding bone. Electron beam melting technology (EBM) allows the fabrication of customized implants with tailored mechanical properties and high potential in the clinical practice. In order to augment the interaction with the biological tissue, stem cells have recently been combined with metallic scaffolds for skeletal engineering applications. We previously demonstrated that human embryonic stem cell-derived mesodermal progenitors (hES-MPs) hold a great potential to provide a homogeneous and unlimited supply of cells for bone engineering applications. This study demonstrates the effect of EBM-fabricated cp-Ti and Ti6Al4V porous scaffolds on hES-MPs behavior, in terms of cell attachment, growth and osteogenic differentiation. Displaying different chemical composition but similar surface properties, EBM-fabricated cp-Ti and Ti6Al4V scaffolds supported cell attachment and growth, and did not seem to alter the expression of genes involved in osteogenic differentiation and affect the alkaline phosphatase activity. In conclusion, interfacing hES-MPs to EBM-fabricated scaffolds may represent an interesting strategy for design of third-generation biomaterials, with the potential to promote implant integration in clinical conditions characterized by poor bone quality.

Introduction: Human mesenchymal stem cells (hMSCs) are promising candidates for bone engineering and regeneration with a considerable number of experimental successes reported over the last years. However, hMSCs show several limitations for tissue engineering applications, which can be overcome by using human embryonic stem cell-derived mesodermal progenitors (hES-MPs). The aim of this study was to investigate and compare the osteogenic differentiation potential of hMSCs and hES-MPs. Materials and Methods: The osteogenic differentiation and mineralization behavior of both cell types were evaluated at passage 5, 10, 15, and 20. Expression of COL1A1 , RUNX2 , OPN , and OC was evaluated by reverse transcription (RT)-polymerase chain reaction, whereas mineralization was examined by photospectrometry, von Kossa staining, and time-of-flight secondary ion mass spectrometry. The immunoprofile of both cell types was investigated by flow cytometry. Results: We demonstrated that, under proper stimulation, hES-MPs undergo osteogenic differentiation and exhibit significantly increased mineralization ability compared to hMSCs after protracted expansion. hES-MPs were also found to express lower amount of human leukocyte antigens class II proteins. Conclusions: The high osteogenic ability of hES-MPs, together with low expression of human leukocyte antigens class II, makes these cells an attractive alternative for bulk production of cells for bone engineering applications.

Adult stem cells, such as human mesenchymal stem cells (hMSCs), show limited proliferative capacity and, after long-term culture, lose their differentiation capacity and are therefore not an optimal cell source for tissue engineering. Human embryonic stem cells (hESCs) constitute an important new resource in this field, but one major drawback is the risk of tumor formation in the recipients. One alternative is to use progenitor cells derived from hESCs that are more lineage restricted but do not form teratomas. We have recently derived a cell line from hESCs denoted hESC-derived mesodermal progenitors (hES-MPs), and here, using genome-wide microarray analysis, we report that the process of hES-MPs derivation results in a significantly altered expression of hESC characteristic genes to an expression level highly similar to that of hMSCs. However, hES-MPs displayed a significantly higher proliferative capacity and longer telomeres. The hES-MPs also displayed lower expression of HLA class II proteins before and after interferon-γ treatment, indicating that these cells may somewhat be immunoprivileged and potentially used for HLA-incompatible transplantation. The hES-MPs are thus an appealing alternative to hMSCs in tissue engineering applications and stem-cell-based therapies for mesodermal tissues.