Hundreds of thousands of people worldwide desperately need organ transplants. Unfortunately, organs aren't always available, and recipients win a second chance at life only through luck-of-the-draw tissue compatibility. New research raises hopes that someday this problem could be skirted with customized organs grown from the recipient's own stem cells.
Embryonic stem cells can transform into any cell type--from liver to brain to lung. Researchers have been able to grow the cells in petri dishes, and have even successfully stimulated stem cells to begin building different kinds of tissue. But after a certain point, the stem cells don't seem to know what to do; they can't evolve into complex configurations such as organs.
Reasoning that stem cells might need a more natural, three-dimensional environment in which to grow and differentiate, Massachusetts Institute of Technology biomedical engineers Robert Langer, Shulamit Levenberg, and colleagues created an artificial scaffold to give the miracle cells enough physical support to aggregate and organize into larger structures. Using biodegradable polymers, the team created a spongelike scaffold with micrometer-sized pores, dosed it with growth hormones in different places, and seeded it with stem cells. Within days the stem cells reproduced and began to differentiate. The team detected neural tissue, cartilage, and liver cells in the areas of the scaffold where corresponding hormones had been applied.
They then implanted the engineered tissue scaffolds just under the skin of mice with disabled immune systems. After two weeks, the team was surprised to find that blood vessels riddled the tissue, linking it to the mouse vasculature system. Even more encouraging, the engineered tissues still continued to produce human neural, cartilage, and liver cell proteins, the team reports online this week in the Proceedings of the National Academy of Sciences. Meanwhile, the scaffolds themselves were slowly breaking down. This is a crucial advance toward creating viable human transplant tissues, says Levenberg.
But there's still a long way to go, says tissue engineer David Mooney of the University of Michigan, Ann Arbor. "Clearly this is a significant step in understanding early tissue development," he says. "Now we need to see whether these engineered cell structures remain stable over time, and if they can function appropriately as organ tissues."