Purpose: High levels of circulating myeloid-derived suppressor cells (MDSCs) in various cancer types, including melanoma, were shown to correlate with poor survival. We investigated whether frequencies of circulating CD33 þ

Bone regeneration achieved using mesenchymal stem cells (MSCs) and nonviral gene therapy holds great promise for patients with fractures seemingly unable to heal. Previously, MSCs overexpressing bone morphogenetic proteins (BMPs) were shown to differentiate into the osteogenic lineage and induce bone formation. In the present study, we evaluated the potential of osteogenic differentiation in porcine adipose tissue- and bone marrow-derived MSCs (ASCs and BMSCs, respectively) in vitro and in vivo when induced by nucleofection with rhBMP-2 or rhBMP-6. Our assessment of the in vivo efficiency of this procedure was made using quantitative micro-computed tomography (micro-CT). Nucleofection efficiency and cell viability were similar in both cell types; however, the micro-CT analyses demonstrated that in both ASCs and BMSCs, nucleofection with rhBMP-6 generated bone tissue faster and of higher volumes than nucleofection with rhBMP-2. RhBMP-6 induced more efficient osteogenic differentiation in vitro in BMSCs, and in fact, greater osteogenic potential was identified in BMSCs both in vitro and in vivo than in ASCs. On the basis of our findings, we conclude that BMSCs nucleofected with rhBMP-6 are superior at inducing bone formation in vivo than all other groups studied.

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Nonunion fractures present a challenge to orthopedics with no optimal solution. In-vivo DNA electroporation is a gene-delivery technique that can potentially accelerate regenerative processes. We hypothesized that in vivo electroporation of an osteogenic gene in a nonunion radius bone defect site would induce fracture repair. Nonunion fracture was created in the radii of C3H/HeN mice, into which a collagen sponge was placed. To allow for recruitment of host progenitor cells (HPCs) into the implanted sponge, the mice were housed for 10 days before electroporation. Mice were electroporated with either bone morphogenetic protein 9 (BMP-9) plasmid, Luciferase plasmid or injected with BMP-9 plasmid but not electroporated. In vivo bioluminescent imaging indicated that gene expression was localized to the defect site. Microcomputed tomography (µCT) and histological analysis of murine radii electroporated with BMP-9 demonstrated bone formation bridging the bone gap, whereas in the control groups the defect remained unbridged. Population of the implanted collagen sponge by HPCs transfected with the injected plasmid following electroporation was noted. Our data indicate that regeneration of nonunion bone defect can be attained by performing in vivo electroporation with an osteogenic gene combined with recruitment of HPCs. This gene therapy approach may pave the way for regeneration of other skeletal tissues.

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