In short
MSC are connective-tissue stem cells found in bone marrow, adipose tissue and umbilical cord. Their most studied properties are immunomodulation and secretion of factors supporting tissue repair, not conversion into new organs.
How MSC are identified
Academic criteria include plastic adherence, surface marker expression such as CD73, CD90 and CD105 without CD45 or CD34, and the ability to differentiate into bone, fat and cartilage cells in the laboratory.
Mechanisms studied
MSC secrete growth factors, cytokines and exosomes that may reduce inflammation and fibrosis and promote new blood-vessel formation. These paracrine effects are why many studies focus on secreted factors rather than the cells themselves.
Limitations to understand
MSC properties vary with tissue source, donor age, culture passage number and preparation method, which makes studies hard to compare and is a key reason manufacturing standards matter so much.