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Thursday, March 16, 2000

Cell engineering expands rapidly

Cell and tissue engineering is a young yet vigorous field that is ripe with opportunity, Rocky S. Tuan, MD, said yesterday in a AAOS/ORS symposium.

"This field, because of its interdisciplinary nature, can accommodate a tremendous amount of innovation," said Dr. Tuan of the Department of Orthopaedic Surgery at Thomas Jefferson University in Philadelphia. "I invite all of you to get involved."

Yet, the unexpected twists and turns in this rapidly evolving field could dramatically alter the stan-dard of care for orthopaedic surgery. "When they invented the automobile, the horseshoe makers took a big pay cut," Dr. Tuan said.

While some of the key concepts in the field were established decades ago, it is only within the past five to 10 years that cell and tissue engineering has captured the imagination of basic scientists and orthopaedic surgeons alike.

The field is growing by leaps and bounds, judging from the volume of medical literature available. Dr. Tuan performed a simple MEDLINE search on the term "tissue engineering" and found no references prior to 1989, followed by only a few papers in the early 1990s, and "exponential growth" to more than 200 papers in 1999. And just three months into 2000, the number of literature references for "tissue engineering" has already exceeded more than half the number of papers published the previous year.

The field is so nascent that its boundaries are still being defined; today, it spans a wide range of cell and tissue aspects, from stem cell technology to tissue-organ substitutes to bioimaging and computer-assisted digital technology.

Currently, some of the most prominent technologies involve stem cells. Embryonic stem cells have a variety of applications in the modeling of gene mutations and the generation of transgenic animals, though Dr. Tuan noted that a variety of technical and ethical issues remain to be resolved.

Adult stem cells, on the other hand, derive from marrow stroma and connective tissues. In particu-lar, Dr. Tuan said, work with stromal mesenchymal stem cells represents "one of the most exciting areas in connective tissue research," Dr. Tuan said.

In the same symposium, Daniel R. Marshak, PhD, Chief Scientific Officer of Osiris Therapeutics, Inc. described some of his company's basic and pre-clinical investigations into mesenchymal stem cells for regeneration of bone.

"This is a very exciting field that goes hand-in-hand with tissue engineering," said Dr. Marshak, adjunct professor with the Johns Hopkins University School of Medicine in Baltimore, Md.

Initial studies of an autologous preparation of mesenchymal stem cells in canine femur showed callus formation, resorption and formation of bony bridge over 16 weeks in an active treatment group, while controls had no observed periosteal reaction.

A preparation of allogeneic mesenchymal stem cells has been studied in preclinical models of canine, rat and baboon. In all cases, fully-mismatched cells produced bone generation with no evidence of lymphocytic infiltration or immune response.

"There is no apparent rejection, and the amount of bone formed is quite similar (across studies)," Dr. Marshak said.

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Last modified 16/March/2000 by IS