Other kinds of implants have also shown that the seeded cells can act as beacons that summon cells from the recipient's body, said William Wagner, director of the McGowan Institute for Regenerative Medicine at the University of Pittsburgh. Sometimes that works out fine, but other times it can lead to scarring or inflammation instead, he said. Controlling what happens when an engineered implant interacts with the body is a key challenge, he said.
So far, the lab-grown parts implanted in people have involved fairly simple structures — basically sheets, tubes and hollow containers, notes Anthony Atala of Wake Forest University whose lab also has made scaffolds for noses and ears. Solid internal organs like livers, hearts and kidneys are far more complex to make.
His pioneering lab at Wake Forest is using a 3-D printer to make miniature prototype kidneys, some as small as a half dollar, and other structures for research. Instead of depositing ink, the printer puts down a gel-like biodegradable scaffold plus a mixture of cells to build a kidney layer by layer. Atala expects it will take many years before printed organs find their way into patients.
Another organ-building strategy used by Atala and maybe half a dozen other labs starts with an organ, washes its cells off the inert scaffolding that holds cells together, and then plants that scaffolding with new cells.
"It's almost like taking an apartment building, moving everybody out ... and then really trying to repopulate that apartment building with different cells," says Dr. John LaMattina of the University of Maryland School of Medicine. He's using the approach to build livers. It's the repopulating part that's the most challenging, he adds.
One goal of that process is humanizing pig organs for transplant, by replacing their cells with human ones.
"I believe the future is ... a pig matrix covered with your own cells," says Doris Taylor of the Texas Heart Institute in Houston. She reported creating a rudimentary beating rat heart in 2008 with the cell-replacement technique and is now applying it to a variety of organs.
Ott's lab and the Yale lab of Laura Niklason have used the cell-replacement process to make rat lungs that worked temporarily in those rodents. Now they're thinking bigger, working with pig and human lung scaffolds in the lab. A human lung scaffold, Niklason notes, feels like a handful of Jell-O.
Cell replacement has also worked for kidneys. Ott recently reported that lab-made kidneys in rats didn't perform as well as regular kidneys. But, he said, just a "good enough organ" could get somebody off dialysis. He has just started testing the approach with transplants in pigs.
Ott is also working to grow human cells on human and pig heart scaffolds for study in the laboratory.
There are plenty of challenges with this organ-building approach. One is getting the right cells to build the organ. Cells from the patient's own organ might not be available or usable. So Niklason and others are exploring genetic reprogramming so that, say, blood or skin cells could be turned into appropriate cells for organ-growing.
Others look to stem cells from bone marrow or body fat that could be nudged into becoming the right kinds of cells for particular organs. In the near term, organs might instead be built with donor cells stored in a lab, and the organ recipient would still need anti-rejection drugs.
How long until doctors start testing solid organs in people? Ott hopes to see human studies on some lab-grown organ in five to 10 years. Wagner calls that very optimistic and thinks 15 to 20 years is more realistic. Niklason also forecasts two decades for the first human study of a lung that will work long-term.
But LaMattina figures five to 10 years might be about right for human studies of his specialty, the liver.
"I'm an optimist," he adds. "You have to be an optimist in this job."
Michael Rubinkam in Lewisburg, Pa., and Allen Breed in Winston-Salem, N.C., contributed to this story.