Sivasubramaniyan K, Koevoet WJLM, Hakimiyan AA, et al. - Experts recognized primary synovial multipotent progenitor/stromal cells (MPCs) and characterized them in regards to cartilage regeneration. In the synovium, a combination of CD45, CD31, CD73, and CD90 could isolate two different MPC-subsets. These MPC-subsets, newly separated from synovium, did not express CD45 or CD31 though it expressed CD73. Moreover, CD90 was also expressed by a subpopulation of CD73⁺ cells. In the presence of TGFβ1, CD45^-CD31^-CD73⁺CD90^- cells were significantly more chondrogenic in comparison with CD45^-CD31^-CD73⁺CD90⁺ cells. Interestingly, the decreased chondrogenic ability of CD73⁺CD90⁺ cells could be reversed by adding BMP2, revealing discrete chondrogenic factor wants by distinct cell-subsets. Furthermore, these MPCs had different anatomical localization and in the intimal and sub-intimal regions, CD73 was expressed both while CD90 was improved in the sub-intimal region. A further illustration that these subsets were also there in healthy synovium was done. Thus, suggestions that primary MPCs in synovial intima and sub-intima are phenotypically and functionally different, with various chondrogenic properties, were provided.