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Feb. 18, 2000 (Atlanta) -- Growth factors, substances naturally produced by the body that promote the growth of specific tissues, may be the wave of the future for treating musculoskeletal injuries, according to a report in the February issue of The Physician and Sportsmedicine. But doctors say that more studies are needed before gene therapy and tissue engineering are used in clinical practice.

Because ligaments, tendons, and cartilage have a limited blood supply, injuries to these tissues are often slow to heal. For this reason, the use of growth factors in generating cells and tissue is an active area of research. The authors say that both gene therapy and tissue engineering hold great promise in treating slow-healing injuries, severe fractures, and arthritis.

"Gene therapy delivers corrected genetic material to cells and tissues through vectors, or carrier cells," says Johnny Huard, PhD, associate director of the Pittsburgh Tissue Engineering Initiative and assistant professor of orthopaedic surgery, molecular genetics, and biochemistry at the University of Pittsburgh. "And viruses make ideal vectors because of their ability to invade cells." Huard tells WebMD that illness-causing viral genes must first be replaced with growth factors.

"Once the corrected genetic material is delivered to the injured area, it serves as a template for cellular production of growth hormones in muscle, ligament, or bone," says Huard. "But there's a potential for overproduction and mutation of these transferred genes. That's why it's only used to treat cancer, muscular dystrophy, and cystic fibrosis." Huard says that regulatory enhancements in gene therapy will allow for use in combination with tissue engineering.

"Tissue engineering involves using biological substitutes to reconstruct musculoskeletal tissue. And recently, genetic modifications have been combined with these substitutes to optimize the healing process," says Huard. "In large injuries or when blood supply is inadequate, genetically engineered tissue acts as scaffolding for rebuilding injured cartilage." Huard tells WebMD that tendons from cows have been used to rebuild human knee tissue, and other research in this area is underway.

"This summer, we're beginning the second phase of a gene therapy trial for rheumatoid arthritis in conjunction with Harvard," says Paul Robbins, PhD, a professor of molecular genetics and biochemistry at the University of Pittsburgh. "And similar studies are getting underway at the University of Michigan and in the Netherlands." But Robbins tells WebMD that gene research has already shown that joint spaces are an effective route of administration.

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