Laboratory production of T cells-immune cells that grow naturally in the thymus gland-could provide new therapies against cancer, autoimmune disorders and organ transplant rejection. But they're hard to grow in culture dishes; current methods yield too few cells of too little variety. Researchers from Massachusetts General Hospital in Boston and the Woburn, MA, biotechnology firm Cell Science Therapeutics have developed an artificial thymus that solves both problems. Constructed from a porous metal-and-carbon material typically used for bone repair and arranged in a three-dimensional matrix, the structure mimics the functions of a living-tissue thymus, generating a bumper crop of T cells that can adjust to new threats. Clinical trials start in 2002, with commercial availability expected a few years later. -M. Wortman