A connective tissue cell that normally gives rise to other cells that are organized as three-dimensional masses. In humans, this cell type is CD73-positive, CD90-positive, CD105-positive, CD45-negative, CD34-negative, and MHCII-negative. They may further differentiate into osteoblasts, adipocytes, myocytes, neurons, or chondroblasts in vitro. Originally described as residing in the bone marrow, this cell type is now known to reside in many, if not all, adult organs.

Many but not all mesenchymal cells derive from the mesoderm. MSCs are reportedly CD3-negative, CD4-negative, CD5-negative, CD8-negative, CD11a-negative, CD11b-negative, CD14-negative, CD19-negative, CD29-positive, CD31-negative, CD34-negative, CD38-negative, CD40-negative, CD44-positive, CD45-negative, CD49-positive, CD54-positive, CD66b-negative, CD79a-negative, CD80-negative, CD102-positive, CD106-positive, CD117-positive, CD121a-positive, CD121b-positive, CD123-positive, CD124-positive, CD133-negative, CD146-positive, CD166-positive, CD271-positive, B220-negative, Gr1-negative, MHCI-positive, MHCII-negative, SSEA4-negative, sca1-positive, Ter119-negative, and glycophorin A-negative. Cultured MSCs are capable of producing stem cell factor, IL7, IL8, IL11, TGF-beta, cofilin, galectin-1, laminin-receptor 1, cyclophilin A, and MMP-2.