Toward therapeutic applications using mesenchymal stem cells : bone defect repair and immunoregulation

Abstract

This motivated the development of cell-free approaches to employ the therapeutic qualities of the MSC secretome sans the challenges associated with cell-based approaches. In these contexts, the overarching goals of this thesis are to: (1) evaluate the osteoinductive capacity of novel material-based approaches to bone defect repair; and (2) assess a pharmacologic strategy to enhance the immunoregulatory function of the MSC secretome towards the development of cell-free therapies. Towards the first goal, we evaluate and demonstrate the intrinsic osteoinductive capacity of two novel materials using bone marrow-derived human MSCs (h-MSCs): (1) poly(ε-caprolactone)-diacrylate (PCL-DA) shape memory polymers incorporating thermoplastic poly-L-lactic acid (PLLA) in a semi-interpenetrating design, and (2) incorporation of a phosphonated-siloxane macromer in a templated poly(ethylene glycol)-diacrylate hydrogel scaffolds. Towards the second goal, we expand on the array of immune markers beyond what is typically measured from proinflammatory macrophages following treatment with native and cytokine-primed h-MSC conditioned-medium (CM). In addition, we demonstrate a combinatorial treatment modality utilizing purinergic P2 receptor antagonist suramin and h-MSC CM for transitioning macrophages towards a pro-regulatory and wound healing phenotype.Mesenchymal stem cells (MSCs) are an ideal cell type for tissue engineering and regenerative medicine applications owing to their ability to differentiate down osteogenic, chondrogenic and adipogenic lineages as well as their immunological properties through regulation of functions within the immune system. Over the last three decades, preclinical investigations have harnessed MSCs’ attributes to evaluate material-guided strategies for bone defect repair applications and to develop cell therapies for several inflammatory disorders. With respect to bone repair, assessment of MSC differentiation towards the abovementioned lineages has guided the identification and refinement of materials with inherent osteogenic properties. Likewise, the production of several bioactive factors from MSCs has been associated with immunomodulatory functions in macrophages – the primary communicators of inflammatory responses and mediators of tissue regeneration. While MSC’s have demonstrated themselves to be potent immunomodulators, several challenges pertaining to utilization of cell-based treatment modalities such as low survival rates in vivo and immunogenicity partially contributed to the observed heterogenous outcomes.