Macrophage-based assays for the in vitro testing of the anti-inflammatory activity of mesenchymal stem cell-based products

Therapies based on mesenchymal stromal cells (MSCs) have high potential in the field of regenerative medicine due mainly to their immunomodulatory properties. However, their clinical translation is hampered by a lack of sufficiently standardised potency tests. Since macrophages comprise key mediators of the effects of MSCs, macrophage-based assays potentially provide a relevant in vitro tool for the evaluation of the activity of MSC products. This study involved the coculturing of canine adipose-derived mesenchymal stem cells (ASCs) with macrophages derived from human THP-1 and U937 monocyte cell lines, murine RAW264.7 macrophages and primary human macrophages. The M2 polarisation was assessed following stimulation with IL-4/IL-13. The mRNA expression of the pro- and anti-inflammatory markers was analysed applying qPCR. The ASC secretome acted to reduce the pro-inflammatory mRNA expression across all the macrophage models, albeit with a certain degree of model-dependent variability. Only the U937 macrophages responded consistently to the M2-polarising stimuli, while the RAW264.7 cells provided practical advantages in terms of routine screening. The results thus provided support for the application of macrophage-based potency assays as a suitable platform for the testing of MSC products; the U937 cells were found to be particularly suitable for the study of polarisation and the RAW264.7 cells for standardised screening.