Human mesenchymal stromal cell sheets induce macrophages predominantly to an anti-inflammatory phenotype

Tissue healing is a highly complex process involving a cascade of biochemical and cellular events. Excessive inflammation can impair the healing response. Previous in vitro studies have shown that mesenchymal stromal cells can modulate macrophage-induced inflammation and therefore are promising candidates for cell-based therapies aimed at promoting tissue repair. Recently, cell sheets were introduced as a new method of delivering stromal cells to the repair-site. The goal of the current study was to compare the effect of different types of stromal cell sheets on the inflammatory state of macrophages <i>in vitro</i>. We compared the effects of adipose tissue-derived stromal cell (ASC) sheets, bone marrow derived stromal cell (BMSC) sheets and fibroblast sheets on macrophage functional phenotype using flow cytometric analysis, gene expression as well as cell sheet protein secretion. This was evaluated with and without inflammatory stimulation. Viability and senescence for the different types of sheet were also evaluated. Macrophages cultured in ASC sheet conditioned medium (CM) displayed a higher fluorescence intensity of the anti-inflammatory CD206 surface marker than when cultured in BMSC sheet CM, and expressed more <i>CCL18</i> and <i>IL1RA</i> than when cultured in fibroblast sheet CM. Moreover, ASC sheets had higher cell viability and less senescent cells than BMSC sheets and fibroblast sheets. Taken together, ASC and BMSC can stimulate the anti-inflammatory macrophage (M2) phenotype to a better extent than fibroblasts. It is suggested, that ASC sheets might outperform BMSC sheets in an inflammatory situation since ASC sheet CM induced-macrophages have more M2 characteristics and ASC in the sheet were more viable.