Bone Marrow Mesenchymal Stem Cells

Abstract

The term mesenchymal stem cell (MSC) refers to adult mesenchymal progenitor cells with the potential to produce progeny that differentiate to produce a variety of mesenchymal cell types (e. g., fibroblasts, muscle, bone, tendon, ligament adipose tissue). It is not known if these cells actually have the capacity to self-renew, which is a property of stem cells. MSCs may be found in muscle, skin, and adipose tissue, as well as in the bone marrow. MSCs in the bone marrow may be identified by colony-forming units that produce fibroblasts and make up a very small percentage of the total marrow population. The ability of MSCs in the bone marrow to form bone and cartilage has been known for more than 100 yr. MSCs or their progeny in the bone marrow provide a stromal microenvironment for hematopoiesis. During development, MSCs in the bone marrow may derive from the developing vessels (pericytes) or from circulating precursors. MSCs also produce osteoclasts and osteoblasts responsible for remodeling of bone and adipocytes, which make up a major portion of the bone marrow. MSCs may be isolated from bone marrow, peripheral blood, fat, skin, vasculature, and muscle, where they most likely are responsible for normal tissue renewal, as well as for a response to injury. Bone marrow MSCs are negative for primitive hematopoietic cell markers but express antibody-defined markers: SH2 (type III TGF receptor), SH3 and SH4 (ecto-5′-nucleotidase), and STRO-1. Individual clones of cell lines derived from MSCs have different potentials for differentiation, indicating different stages of determination and levels of plasticity. Transplanted MSCs have been shown to enhance bone, tendon, cartilage, and nerve repair in experimental models. Systemic transplantation of MSCs has not always led to functional results in tissue repair but has tremendous potential. The use of MSCs for gene therapy for hematopoietic, metabolic, and neurological disorders is currently under investigation.