**4. Molecular mechanism of MSC-based cytotherapy for OA management**

Generally, MSCs function mainly via orchestrating a series of mode of action including compositional microenvironment, immunoregulation, autocrine, paracrine, and direct- or trans-differentiation into functional cells [15, 62, 63]. In particular, the unique immunomodulatory property and paracrine manner have prompted the enthusiasm for allogenic transplantation of the "off-the-shelf" MSC products in both preclinical and clinical practices in the field of regenerative medicine.
