KIT and rheumatoid arthritis: C-kit is expressed by a subpopulation of MSC in the highly vascularized adipose tissue showing increased proliferative activity and self-renewal capacity (Blazquez-Martinez et al., 2014), and in vivo vascular niches of synovial tissues from patients with RA and OA contain STRO-1 positive MSC found in clusters together with EPC as demonstrated by our group previously (Rüger et al., 2004).