Among high-concept forms of medicine, few approaches have as much intuitive appeal as cellular therapy. The idea is disarmingly simple-remove homegrown cells from the patient's body, grow them to vast numbers in the lab and then give them back as medicine. It has already been attempted in a few instances against cancer. Remember the TIL cell-"tumor infiltrating lymphocytes"-craze of the 1980s?

But perhaps the most interesting cellular therapy to date, and the only one to receive the blessings of the Food and Drug Administration as a bona fide biologic intervention, involves not one of the body's vaunted cellular paladins, such as lymphocytes or neurons, but rather a blue-collar cell known as the chondrocyte. These cells provide the cushion known as cartilage between joints, and for the past three years, orthopedic surgeons in this country and Europe have been using them to rebuild knee joints denuded of cartilage by acute or repetitive trauma.