Genetically modified il-4 over-expressing mscs enhance bone healing

Abstract

Background & Aim Healing of large critical size bone defects is challenging in cases of fracture non-union, wear particle disease, osteonecrosis etc. Traditionally, substantial amounts of autologous bone are harvested from the patient's iliac crest for grafting. However, this procedure has substantial potential morbidity; furthermore, bone graft may be insufficient in quantity or quality due to local or systemic factors (e.g. chronic diseases, antagonistic medications, advanced age etc.). New approaches have been devised including the use of autologous concentrated cells harvested from the iliac crest, together with an osteoinductive or osteoconductive carrier. We developed lentivirus-transduced Interleukin-4 (IL-4) over-expressing MSCs (IL-4 MSCs) that continuously produce the anti-inflammatory, pro-regenerative cytokine IL-4, for healing of long bone defects. We report the potential of IL-4 MSCs for healing of large bone defects. Methods, Results & Conclusion Methods: MSCs encapsulated in a unique microribbon (μRB) hydrogel scaffold (Sc) were tested in an established murine femoral critical sized defect model. Ten-week-old male BALB/c mice were fitted with MouseExFix devices (RISystem AG, Switzerland) and a 2 mm bone defect was made in the femoral diaphysis. The three treatments included Sc only, Sc + (unmodified) MSCs, and Sc + IL-4 MSCs. In the Sc only and the Sc + MSC groups, μRB-Sc were placed immediately after the bone defects were made; in the Sc + IL-4 MSCs group, μRB-Sc with IL-4 MSCs were placed 3 days after the defect was created in a second surgery, to allow for the initial mandatory inflammatory response for optimal bone healing to occur. 1.0 × 107 MSCs/mL were used in the scaffold. MicroCT, immune and histomorphometric analyses of the defect were performed 6 weeks after surgery. Results The Sc + IL-4 MSC group had significantly decreased defect size at 6 weeks, compared to the other two groups (Figs. 1 and 2). Histological analysis showed more trabecular bone and M2 macrophages in the defect area in Sc + IL-4 MSCs group, compared to the other 2 groups. Conclusion IL-4 has been shown to promote osteogenesis and M2 macrophage polarization, after an initial mandatory period of acute inflammation lasting 48-72 hours. IL-4 overexpressing MSCs in a unique microribbon hydrogel scaffold, when delivered at the appropriate time and dosage, appears to be a promising strategy to treat critical size long bone defects.