Human mesenchymal stem cells are thought to be multipotent cells, which are present in adult marrow, that can replicate as undifferentiated cells and that have the potential to differentiate to lineages of mesenchymal tissues, including bone, cartilage, fat, tendon, muscle, and marrow stroma. Cells that have the characteristics of human mesenchymal stem cells were isolated from marrow aspirates of volunteer donors. These cells displayed a stable phenotype and remained as a monolayer in vitro. These adult stem cells could be induced to differentiate exclusively into the adipocytic, chondrocytic, or osteocytic lineages. Individual stem cells were identified that, when expanded to colonies, retained their multilineage potential.

Mesenchymal stem cells (MSCs) are multipotent cells found in several adult tissues. Transplanted allogeneic MSCs can be detected in recipients at extended time points, indicating a lack of immune recognition and clearance. As well, a role for bone marrow-derived MSCs in reducing the incidence and severity of graft-versushost disease (GVHD) during allogeneic transplantation has recently been reported; however, the mechanisms remain to be investigated. We examined the immunomodulatory functions of human

Background-Cellular cardiomyoplasty has been proposed as an alternative strategy for augmenting the function of diseased myocardium. We investigated the potential of human mesenchymal stem cells (hMSCs) from adult bone marrow to undergo myogenic differentiation once transplanted into the adult murine myocardium. Methods and Results-A small bone marrow aspirate was taken from the iliac crest of healthy human volunteers, and hMSCs were isolated as previously described. The stem cells, labeled with lacZ, were injected into the left ventricle of CB17 SCID/beige adult mice. At 4 days after injection, none of the engrafted hMSCs expressed myogenic markers. A limited number of cells survived past 1 week and over time morphologically resembled the surrounding host cardiomyocytes. Immunohistochemistry revealed de novo expression of desmin, ␤-myosin heavy chain, ␣-actinin, cardiac troponin T, and phospholamban at levels comparable to those of the host cardiomyocytes; sarcomeric organization of the contractile proteins was observed. In comparison, neither cardiac troponin T nor phospholamban was detected in the myotubes formed in vitro by MyoD-transduced hMSCs. Conclusions-The purified hMSCs from adult bone marrow engrafted in the myocardium appeared to differentiate into cardiomyocytes. The persistence of the engrafted hMSCs and their in situ differentiation in the heart may represent the basis for using these adult stem cells for cellular cardiomyoplasty.

The terms MSC and MSCs have become the preferred acronym to describe a cell and a cell population of multipotential stem/progenitor cells commonly referred to as mesenchymal stem cells, multipotential stromal cells, mesenchymal stromal cells, and mesenchymal progenitor cells. The MSCs can differentiate to important lineages under defined conditions in vitro and in limited situations after implantation in vivo. MSCs were isolated and described about 30 years ago and now there are over 55,000 publications on MSCs readily available. Here, we have focused on human MSCs whenever possible. The MSCs have broad anti-inflammatory and immune-modulatory properties. At present, these provide the greatest focus of human MSCs in clinical testing; however, the properties of cultured MSCs in vitro suggest they can have broader applications. The medical utility of MSCs continues to be investigated in over 950 clinical trials. There has been much progress in understanding MSCs over the years, and there is a strong foundation for future scientific research and clinical applications, but also some important questions remain to be answered. Developing further methods to understand and unlock MSC potential through intracellular and intercellular signaling, biomedical engineering, delivery methods and patient selection should all provide substantial advancements in the coming years and greater clinical opportunities. The expansive and growing field of MSC research is teaching us basic human cell biology as well as how to use this type of cell for cellular therapy in a variety of clinical settings, and while much promise is evident, careful new work is still needed.