Effects of a ceramic biomaterial on immune modulatory properties and differentiation potential of human mesenchymal stromal cells of different origin

The aim of this study was to assess the immune modulatory properties of human mesenchymal stromal cells obtained from bone marrow (BM-MSCs), fat (ASCs), and cord blood (CB-MSCs) in the presence of a hydroxyapatite and tricalcium-phosphate (HA/TCP) biomaterial as a scaffold for MSC delivery. In resting conditions, a short-term culture with HA/TCP did not modulate the anti-apoptotic and suppressive features of the various MSC types toward T, B, and NK cells; in addition, when primed with inflammatory cytokines, MSCs similarly increased their suppressive capacities in the presence or absence of HA/TCP. The long-term culture of BM-MSCs with HA/TCP induced an osteoblast-like phenotype with upregulation of OSTERIX and OSTEOCALCIN, similar to what was obtained with dexamethasone and, to a higher extent, with bone morphogenetic protein 4 (BMP-4) treatment. MSC-derived osteoblasts did not trigger immune cell activation, but were less efficient than undifferentiated MSCs in inhibiting stimulated T and NK cells. Interestingly, their suppressive machinery included not only the activation of indoleamine-2,3 dioxygenase (IDO), which plays a central role in T-cell inhibition, but also cyclooxygenase-2 (COX-2) that was not significantly involved in the immune modulatory effect of human undifferentiated MSCs. Since COX-2 is significantly involved in bone healing, its induction by HA/TCP could also contribute to the therapeutic activity of MSCs for bone tissue engineering.