In vitro multipotentiality and characterization of human unfractured traumatic hemarthrosis-derived progenitor cells: A potential cell source for tissue repair.

Mesenchymal progenitor cells (MPCs) are a very attractive tool in the context of repair and regeneration of musculoskeletal tissue damaged by trauma. The most common source of MPCs to date has been the bone marrow, but aspirating bone marrow from the patient is an invasive procedure. In an attempt to search for alternative sources of MPCs that could be obtained with minimal invasion, we looked into traumatic hemarthrosis of the knee. In this study, we determined whether a population of multipotent MPCs could be isolated from acute traumatic knee hemarthrosis in the absence of intra-articular fractures. Mononuclear cells were isolated from the aspirated hemarthrosis by density gradient separation, and cultured. We were able to obtain plastic adherent fibroblast-like cells from the mononuclear cell fractions. Flow cytometry analysis revealed that the adherent fibroblast-like cells were consistently positive for CD29, CD44, CD105, and CD166, and were negative for CD14, CD34, and CD45. These were similar to control bone marrow stromal cells. These cells could differentiate in vitro into osteogenic, adipogenic, and chondrogenic cells in the presence of lineage-specific induction factors. In conclusion, acute unfractured traumatic hemarthrosis of the knee contains MPCs with multipotentiality. Because knee hemarthrosis is easy to harvest with minimal pain and without unnecessary invasion, we regard hemarthrosis-derived cells as an additional progenitor cell source for future tissue engineering and cell-based therapy in knee injuries.