
<ArticleTitle>Effect of <prot>bone morphogenetic protein-2</prot>-expressing muscle-derived cells on healing of critical-sized bone defects in mice.</ArticleTitle>
<AbstractText>BACKGROUND: Cells that express <prot>bone morphogenetic protein-2</prot> (<prot>BMP-2</prot>) can now be prepared by transduction with adenovirus containing <prot>BMP-2</prot> cDNA. Skeletal muscle tissue contains cells that differentiate into osteoblasts on stimulation with <prot>BMP-2</prot>. The objectives of this study were to prepare <prot>BMP-2</prot>-expressing muscle-derived cells by transduction of these cells with an adenovirus containing <prot>BMP-2</prot> cDNA and to determine whether the <prot>BMP-2</prot>-expressing muscle-derived cells would elicit the healing of critical-sized bone defects in mice. METHODS: Primary cultures of muscle-derived cells from a normal male mouse were transduced with adenovirus encoding the recombinant human <prot>BMP-2</prot> gene (<prot>adBMP-2</prot>). These cells (5 yen 10(5)) were implanted into a 5-mm-diameter critical-sized skull defect in female SCID (severe combined immunodeficiency strain) mice with use of a collagen sponge as a scaffold. Healing in the treatment and control groups was examined grossly and histologically at two and four weeks. Implanted cells were identified in vivo with use of the Y-chromosome-specific fluorescent in situ hybridization (FISH) technique, and their differentiation into osteogenic cells was demonstrated by osteocalcin immunohistochemistry. RESULTS: Skull defects treated with muscle cells that had been genetically engineered to express <prot>BMP-2</prot> had 85% closure within two weeks and 95% to 100% closure within four weeks. Control groups in which the defect was not treated (group 1), treated with <prot>collagen</prot> only (group 2), or treated with <prot>collagen</prot> and muscle cells without <prot>adBMP-2</prot> (group 3) showed at most 30% to 40% closure of the defect by four weeks, and the majority of the skull defects in those groups showed no healing. Analysis of injected cells in group 4, with the Y-chromosome-specific FISH technique showed that the majority of the transplanted cells were located on the surfaces of the newly formed bone, but a small fraction (approximately 5%) was identified within the osteocyte lacunae of the new bone. Implanted cells found in the new bone stained immunohistochemically for <prot>osteocalcin</prot>, indicating that they had differentiated in vivo into osteogenic cells. CONCLUSIONS: This study demonstrates that cells derived from muscle tissue that have been genetically engineered to express <prot>BMP-2</prot> elicit the healing of critical-sized skull defects in mice. The cells derived from muscle tissue appear to enhance bone-healing by differentiating into osteoblasts in vivo. Clinical Relevance: Ex vivo gene therapy with muscle-derived cells that have been genetically engineered to express <prot>BMP-2</prot> may be used to treat nonhealing bone defects. In addition, muscle-derived cells appear to include stem cells, which are easily obtained with muscle biopsy and could be used in gene therapy to deliver <prot>BMP-2</prot>.</AbstractText>
