Griffin, K. H.; Sagheb, I. S.; Coonan, T. P.; Wu, L. A.; Rowland, D. J.; Arzi, B.; Lewis, J.; Leach, K.

Mesenchymal stromal cells (MSCs) are a promising cell-based therapy for bone healing, contributing to tissue regeneration through direct differentiation or immunomodulatory factor secretion. However, diseases that feature chronic or dysregulated inflammation, such as non-union fractures and osteonecrosis of the jaw (ONJ), have proven difficult to treat with current MSC-based approaches. Here, we investigated whether controlled delivery of immunomodulatory factors would allow MSCs to simultaneously undergo osteogenic differentiation and modulate inflammation. We first used a Design of Experiments approach to identify the type and concentrations of immunomodulatory factors (IMFs) that most effectively induce concurrent pro-regenerative macrophages and MSC osteogenic differentiation, then loaded these IMFs into polymeric microparticles for controlled release. Through our in vitro models, we demonstrated that microparticles releasing IL-10 and IL-4 promote naive MSC osteogenesis and modulate immune response, even in chronic, physiologically relevant, inflammatory conditions. We then applied this approach to an in vivo rat model of ONJ as a clinically relevant example of such conditions. We observed clinically relevant sex-based differences in inflammation and bone formation that have not yet been reported. These data represent key findings that will facilitate the reversal of diseases that are linked to chronic bone loss and inflammation, such as ONJ.