|The Vacantis (from bottom) Jay, Chuck, Marty, and Frank are tissue engineering's preeminent scientific siblings.|
|Among their many breakthroughs: lab-grown cartilage. The Vacanti solution for injured or malformed ears: Grow new ones. Here, a piece of biodegradable polymer that has been molded into the shape of an ear's underlying cartilage, down to the fleshy lobe, before it is impregnated with a patient's own cells.|
The doctor they call Chuck stands over the body with an electric blade, ready to make the first incision. The knife whirs, peeling crisp brown skin off the breast and digging into the firm white flesh below. The doctor wields the knife confidently, humming to himself, as if he finds pleasure in severing muscle from bone. His two brothers, Marty the pathologist and Frank the anesthesiologist, stand nearby, ready to offer advice. (Jay, the oldest brother, is on call.)
It is the last Thursday in November and the patient is dead, a 23-pound turkey roasted to feed the assembled Vacanti family. As Chuck buzzes away, slicing white meat and dark, the grown-ups sip Riesling, the kids and Uncle Frank gulp cola. The table is groaning with side dishes. All in all, the scene is about average for Thanksgiving Day.
Still, it does not take long to discover that there is little or nothing average about the Vacanti brothers. Joseph (Jay), Charles, Martin, and Francis Vacanti work together as researchers in the new field of tissue engineering, a discipline they practically invented. What they are trying to create is nothing less than lab-grown human organs, produced from a patient's own tissue. Their work is urgently needed roughly 100,000 patients in this country die each year because not enough people donate organs, and many of those who are saved by transplantation ultimately die because donor organs are rejected.
In the new world the Vacantis hope to build, an infant born without intestines and destined to die will get a new gut grown from a clutch of her own cells. As the fruit of the child, that new intestine will never be rejected. Imagine a world, say the Vacantis, in which diseased pancreases, lungs, and spinal cords can be replaced as easily as the transmission in an old Chevy. Imagine a world in which salvation grows in an incubator. Imagine a world in which hope is a given.
So far, artificial skin and cartilage are the only lab-grown tissues available to surgeons. But that is about to change so quickly that even doctors familiar with the research will find it difficult to comprehend the possibilities. It was only in 1996 that Chuck and Jay Vacanti held the first conference of their fledgling Tissue Engineering Society. Today two of their former colleagues, Anthony Atala, a pediatric urologist at Children's Hospital in Boston, and Laura Niklason, a Duke University researcher, have already performed what seem like miracles Atala successfully implanting lab-grown bladders in beagles and Niklason growing fresh pig arteries in her lab. This year there are more than 50 laboratories in the United States alone racing to create people-made people parts. And the researchers in all of those labs are indebted to five breakthroughs made by the four Vacanti brothers.
Breakthrough #1: How Do We Make a Scaffold?
The brothers grew up in Omaha, born to a dentist father and a mother who stopped six credit hours shy of a premed degree to marry. There were eight children, and money was always tight. Jay, the oldest son, longed to go to Harvard. His father pulled him aside one day and told him that he could work his way through the Ivy League school or go to Creighton, where Dad was on the faculty, for free. Jay reluctantly chose Creighton but soon made it to Harvard as a surgical intern. His brothers got the same speech, also attended Creighton, and eventually followed Jay to Massachusetts.
Meanwhile, working at Massachusetts General Hospital, the largest teaching hospital for Harvard Medical School, Jay witnessed an endless parade of gurneys delivering children who could not be saved. "I have always thought that being a pediatric surgeon was the most gratifying kind of surgery," he says. "You start with the most helpless and vulnerable of humans, diagnose a potentially harmful condition, definitively manage it, oftentimes with surgical intervention, and return the child to his family and to possibly another 80 years of life." But too many children Jay saw needed new livers, bladders, intestines. There weren't enough organs to go around; there wasn't nearly enough hope. Jay Vacanti determined to fix that.
He knew that in 1979 Eugene Bell, an engineer at the Massachusetts Institute of Technology, had grown skin cells in flat sheets of tissue. Jay, along with his colleague Robert Langer, a chemical engineer at MIT, became obsessed with figuring out how to extend Bell's work beyond two dimensions.
The number one challenge in tissue engineering is to get the specimen cells to grow at all. Freshly plucked from a human, a batch of cells hasn't got long to live. They need oxygen, a temperature of about 98 degrees Fahrenheit, and nutrients. So a tissue engineer doesn't waste time. He places the cells in a petri dish with liquid nutrients carbohydrates and amino acids do nicely then tucks them away in an incubator. With a little luck they multiply and in a few days produce enough cells to be considered tissue. As amazing as the process is up to this point, it's relatively useless, because clumps of tissue are of little use to a patient. The tissue engineer must convince cells to morph from a meaningless jumble of flesh into a functioning organ.
Jay and Langer's vision was radical build a scaffold out of plastic on which the cells could build a three-dimensional organ. "The original organ we had in mind was the liver," Jay recalls. "I thought degradable plastics would make an ideal scaffold. I knew from my work in cell biology that cells adhere to plastic dishes for in vitro culture, secreting their own scaffold as they settle to the bottom of the plate. I also knew you could treat the surfaces of plastics so they would be more likely to cause cell adherence."
But Eugene Bell was already on the record: Plastic polymers simply wouldn't work as a scaffold. He dismissed the idea as fatuous. That word stuck in Jay's craw.
In the summer of 1986 Jay took his family to Cape Cod. As his children played in the surf, he perched on a jetty, mulling the problem. You could get cells to populate the exterior of a hunk of polymer, where they had easy access to oxygen and nutrition, but the interior was another story you might as well try to grow a houseplant inside a basketball. Out of the corner of his eye, Jay saw a sheet of seaweed bobbing in the water. Then it hit him. Nature, the original tissue engineer, had already solved the problem. Under the seaweed's rubbery skin lies a network of fine, hollow branches that pipe fresh oxygen into the organism while pumping out expended gases. Jay shot an entire roll of film of that seaweed and phoned Langer before the day was out. Their scaffold interior had to be light and airy, like spun candy, they decided. Build the branches, and the cells would do the rest.
Today that's the game plan in labs everywhere. Tissue engineers build a porous, three-dimensional polymer model of an organ, squirt a soup of nutrients and living cells over the structure, incubate, and wait. "It makes sense," says Jay, "that cells thrive best in this environment because they are designed to live and function in three-dimensional space." In time the biodegradable framework dissolves in the body's water through the process of hydrolysis, until what is left is wholly alive.
Now when Jay talks to young tissue engineers, he sometimes slaps a transparency on the overhead projector that displays Webster's
definition of the word fatuous:
"smugly or foolishly stupid." His intention is to encourage his successors to trust their instincts and go forward, ignoring criticism that might hold them back.
Breakthrough #2:The First Human Experiments
|Top: Living cells have colonized a rigid framework to become a fully functional trachea, later implanted in a sheep's body. Middle: Because cells need a structure to inhabit before they can grow into part of the body, the Vacantis carved a piece of surgical coral into the shape of a patient's thumb bone (left), used molds to cast ear scaffolds, and stuffed broken spinal cords with cottony, biodegradable polymer fiber (bottom).|
In 1989 Chuck and his team, then also based at Mass General, submitted a paper to a top journal announcing they'd grown a piece of human cartilage. It was rejected outright: "No practical implications," the reviewers wrote.
Chuck was stunned. No practical implications? He saw it as a challenge. So he quizzed plastic surgeons: What's the toughest cartilaginous structure to repair? The human ear, they answered, no question. Every day infants are born with underdeveloped ears; children and adults lose ears in car accidents. Somewhere between bone and skin, cartilage is a tricky substance to work with, and the ear is the body's most intricately shaped and visible piece of it.
So Chuck and his team decided to build one. They needed a living host that wasn't human, so they implanted an ear scaffold under the wrinkled skin of a hairless lab mouse they nicknamed Auriculosaurus.
The mouse grew an ear on its back. The image was beamed into newsrooms all over the world. Facing hard questions from the public and colleagues about his motives, Chuck had to explain that he'd only intended to show the medical world what could be done.
In April 1994 Chuck and Jay got a chance to prove what could be done in a human. They met Sean McCormack, 12, who had been born with a protruding sternum and no cartilage or bone under the skin of his left torso. Unprotected, his heart could be seen beating just below the skin. As a Little League pitcher, he badly needed a chest wall. Boston's Children's Hospital let the Vacantis conduct a procedure so bizarre the Food and Drug Administration had no regulations to cover it. The doctors harvested cartilage cells from Sean's sternum to seed a flat, round scaffold about the size of a compact disc. Awash in nutrients, the cells multiplied and permeated the polymer. Weeks later the construct was inserted in Sean's chest. As his body grew, it incorporated the shield for his heart; seven years later, he's a star BMX bicycle racer.
In 1998, Raul Murcia, a machinist, crushed and severed his left thumb in a cargo elevator. Chuck and his team, now at the University of Massachusetts in Worcester, leaped to the challenge: Think we can grow this guy a new distal phalanx? Chuck carved a piece of surgical coral into the shape of a thumb, seeded Murcia's bone cells onto it, and in a few weeks he had a thumb digit ready for implanting. By then newspapers were screeching "test-tube thumb," and Chuck was fielding a call from the FDA: What are you guys doing up there?
Since Sean McCormack's operation, the FDA had developed a set of regulations governing cultured cells. The surgical coral was FDA approved, and the FDA had decided that one could implant autologous cells those grown from a patient's own cells without approval. However, if a doctor combined two FDA-approved technologies, the technique required separate approval. You can implant the new bone, they told Chuck, but you absolutely cannot implant any tissue-engineered cartilage. "I asked what to do, and they suggested I apply for retroactive approval, which I did," Chuck says.
In the end Murcia got a new thumb-tip, but Chuck was not allowed to attach cartilage or tendons to it. In a paper published in May 2001 in The New England Journal of Medicine,
Chuck and his colleagues report the case, including the happy results of Murcia's recent biopsy: Much of the coral still exists, but its pores have filled in with Murcia's own cells. More surprising, the new cells are intelligently transforming the coral, remodeling it to look more like a human thumb bone.
Today researchers in tissue labs all over the world have moved beyond thumbs and ears, as they struggle to grow more important and complex tissue structures. In the search for foolproof methods, they play with variables: What's the best polymer for arteries? For tracheae? They jet to symposia, deliver papers, send e-mails to find out what other labs are up to. Such encounters are civil, even genteel, but an undercurrent of rivalry often fills the air.
Breakthrough #3: The Miracle Cells
|Before the Vacantis repaired his chest, Sean McCormack says, "I never took my shirt off in front of friends. Now I wash my car without a shirt. Even the little stuff means a lot."|
The Vacanti brothers have raised sibling rivalry to an art form. Jay knows, for example, that if he's courting an applicant for residency at Mass General, chances are the would-be tissue engineer has already visited Chuck and Marty at the University of Massachusetts, who told him: "If you're offered a position at Harvard, you should consider it just because it's Harvard. If you're offered a position in tissue engineering at UMass, you should accept it because we're better."
Chuck says the brothers are "very competitive" with each other but not destructive. They needle each other in the same delighted way they always have, but they know they are safe. "It's absolutely better to work with your own brother. You trust your own brother in a way you can never trust someone else," says Chuck, who adds, laughing, "If one of us does something to break that trust, we can always go tell our mom."
Their rivalry is balanced by an intimacy few scientists will ever enjoy. "You don't have to go into the dance that you would if you were sharing an idea with a colleague," says Jay, "where both of you are trying to be polite. If you're dealing with your brother, he can say, 'You know, that's really stupid.' It's an efficient way to problem-solve. On the other hand, if he says, 'That's really smart,' you know it's genuine."
That dynamic engendered their most startling breakthrough, which was announced last fall.
In 1996 Chuck had convinced Marty, the pathologist, to leave Nebraska and join him in Worcester. Chuck had grown increasingly frustrated with the fragile adult-tissue cells he had been working with. Most cannot last more than 30 minutes without an oxygen supply. Fetal stem cells are hardier, but harvesting them is controversial.
Chuck told Marty to find an alternative: "Look for stem cells in adult tissue."
He instantly replied: "They don't exist."
"They have to exist," Chuck insisted, intent on driving his point home. "If the human body is constantly trying to repair itself, it must have immature cells somewhere. Find them."
"You're nuts," Marty told him.
"Just do it."
"If I had talked like that to anyone other than a family member," Chuck says, "he would have gone home and told his wife I had an attitude problem."Instead, Marty decided to give it a try. For 15 months he drew cells from living animals, only to watch them die. He scrounged lab animals other researchers had sacrificed for their work. He scraped flesh with scalpels and dissolved it in enzymes. He peered into the resulting broth, magnified 200 times, to no avail. At every staff meeting, Marty had nothing to report. It became embarrassing.
Then one day, peering through the microscope, he spotted tiny circular shapes. Adult-tissue cells are about 15 micrometers wide. Marty saw cells only 3 micrometers wide. He began showing them around. They're too small to be stem cells, everyone said. Just debris. Junk.
Tired and depressed, Marty stood in his lab staring at flasks of the cell soup, thinking, "Wastebasket or incubator?" For reasons he does not comprehend, he stuck them in the incubator. Three days later, those little specks of junk had multiplied. What's more, they had gone without oxygen for more than an hour before he put them in the incubator, an ordeal adult stem cells could not have survived.
At staff meetings Marty took center stage. Eventually someone asked: What do you call these cells? Privately, Marty had begun to call them "sporelike cells." They had a faintly prokaryotic, sporelike look about them. Until 2.5 billion years ago, life on this planet was limited to bacteria and algae that reproduced through the agency of single-celled bodies called spores, which lay dormant until called upon to create new life. In time prokaryotes morphed into eukaryotes, multicelled creatures. Marty's mind reeled when he thought about it: What if the most primitive process of evolution and self-repair was still going on inside our bodies? At one large meeting, on Jay's turf at Mass General, his concentration was broken by Jay chanting sotto voce: "Fungus, fungus, yeast, yeast!"
Weeks later, Chuck phoned with a suggestion, but Marty cut him off. Obsessed now, he had been examining every scrap of tissue he could lay his hands on and had isolated sporelike cells in every one. He'd bought a tray of chicken livers at the grocery. Even there, he found them.
Chuck was agog but, being Chuck, couldn't wait to up the ante. Freeze 'em and cook 'em, he said. Marty took them down to -121 degrees Fahrenheit. The cells survived. He left them at 187 degrees Fahrenheit for 30 minutes. They were still alive.
Marty tried to keep a lid on his excitement. He'd learned early that it was prudent to get the data in the bag before you crowed over a new discovery. His confidence soared the day he showed his work to Guido Manjo, an eminent Italian-born pathologist who lectures at UMass. Manjo's advice: Test those cells for DNA and publish as soon as possible. Then came the ultimate compliment: "Dr. Vacanti," said the senior scientist, "you may have discovered a fundamental process of nature that has not yet been described."
Manjo was correct. DNA was present in the cells, and no one in the history of biology had ever identified such minuscule formations living in mammalian tissue. They were the kind of cells that the Vacantis had been dreaming about: They could live in the body without oxygen for days until blood vessels grew to supply them. Marty's most recent research shows the cells may actually be able to differentiate into tissues other than those of the organs from which they originated.
Properly incubated, they grow like grass on a prairie. The team in the lab at Worcester has used them to grow everything from retinal rods and cones to liver, bone, fascia, skin, and heart tissue. They have pulled sporelike cells out of a diabetic pancreas and grown insulin-producing islets in 12 weeks. They have cut a golf-ball-sized section from a living sheep's lung, stuffed the wound with a scaffold seeded with pulmonary sporelike cells, and watched as the lung incorporated the new tissue in eight weeks. Everyone was in awe: A lung is perhaps the most complex organ in the body, possessing at least half a dozen different types of tissue.
Breakthrough #4:Seeking to Heal the Spine
|The Vacanti brothers not only work together they also play. They visit back and forth, taking turns entertaining one another on holidays; they talk on the phone constantly; they fish together on a lake near Chuck's house; they even help one another repair their cars.|
Marty's discovery paved the way for the most astounding experiment at Worcester to date. In the late summer of 1998, the Vacanti team inserted scaffolds seeded with sporelike cells into the severed spinal cords of eight lab rats. They hoped new tissue would bridge the gap. But first, the team cut themselves a big break. Scarring of nerve ends in severed spinal cords interferes with healing. So they put the scaffolds in place immediately after the cords were cut and before scarring set in. The cells quickly stitched themselves into the fibers of the existing cords, and the paralyzed rats regained a significant degree of feeling and movement in their previously paralyzed limbs. "After 10 days," Chuck recalls, "you could see little twitches in their toes . . . In three months, some rats could stand on their hind legs and eat what you fed them." After several months a few of them walked.
Meanwhile, in Jay's lab at Mass General, Frank, an anesthesiologist and the youngest of the brothers, was building an interest in the same problem. Frank had started out in stroke research, where he made several breakthroughs. He was, for example, the first to realize that slightly lowering the body temperature of a patient at risk for a stroke, such as during an operation, could minimize complications. That interest in neurology developed into a fascination with spinal-cord repair.
Frank suspected the severed fibers in a spinal cord wouldn't be able to resist an easy pathway along which they could grow back toward each other. So he used a laser to drill tiny tunnels through his scaffolds, which he implanted into the cords of rats immediately after he severed them.
The procedure fits his personality. Frank loves building things, so much so that he almost didn't become a doctor like his brothers. As a teenager he wanted to be an engineer but noticed that engineers were having a hard time finding work after Nixon decimated the space program. He craved a job where he could work with gadgetry. A medical lab appealed to him, but shifting gears from a technician's mind-set to that of a biologist would be a challenge. Nonetheless, he harnessed his inner Vacanti and plowed through academia, taking the Hippocratic oath at 23.
Now a seasoned mechanic, he labors away in the lab on weekends, drilling his 2-millimeter holes in solitude, which he prefers. At first, it looked as if his idea was headed for success. After just six weeks spinal-cord tissue appeared to have nearly replaced the scaffold. Sadly, the effects on the rats ranged from mixed to negligible. Some of them died; others lived to barely wiggle their toes. "Not enough," says Frank. "I wanna see them jump rope."
Analyzing his failure, he saw that he could improve life-support systems for the recovering rats. Redesigning the study got him thinking about salamanders: "If a salamander damages his spinal cord, he can repair it. They don't scar. But in mammals the cords form scars . . . At some point, the ability to scar must have been an evolutionary advantage."
As organisms became more complex, tissues required more oxygen to function. And that, Frank thinks, hurts us in the regeneration department. If a human spine is damaged, the cells cannot tolerate being torn away from blood and oxygen. Scar tissue sweeps in to obscure the damage. If we once had the ability to heal, Frank reasons, we must be able to restore it, and he intends to find out how.
His imagination and curiosity have taken him beyond medicine. He has begun writing physics essays, one of which has been published in a prestigious journal. "You can't advance science unless you take a risk," he says. "It's like fixing a spinal cord. Most people think you're crazy. But to have any success you have to let your mind wander. You have to look for relationships, see how things fit. It's beautiful. But it's not the scientific method."
Breakthrough #5: A Heart of Foam
|When living cells are dropped onto this silicon-wafer scaffold, they grow into 3-D capillaries, the smallest of which are just one tenth the size of a human hair in diameter.|
Sooner or later, all tissue engineers are haunted by the body's need for oxygen. It was no accident that the earliest successes in tissue engineering came in hatching skin, bone, and cartilage, which can survive for hours in the body until blood vessels mosey over to attach themselves. "Now we're getting into organs like livers and hearts that are too thick to work that way," Jay says. "To survive, they need oxygen, they need nutrition, they need to dump waste." They need a circulatory system. But how does one coax cells to grow into something as complex as a network of capillaries?
These days Jay, along with researchers at the Massachusetts Institute of Technology and the Draper Laboratory, has embarked on a radical protocol: They are etching blood vessels onto silicon wafers. Cells are then deposited onto the wafers, where they grow into circuits just micrometers in diameter and shaped like branching vessels. In time the entire fragile sheet can be lifted from the wafer and the vessels rolled like cigars or stacked like checkers to build a circulatory structure. They work: Jay and his team enjoy showing visitors a video of blood cells coursing through the man-made vessels like water in a stream. This project has taken them one step closer to meeting their greatest challenge yet.
In a corner of the lab lies a polymer cast of a sheep's heart. To build it, Jay and his team took a real sheep's heart, pumped its vessels full of liquid plastic, then dissolved the tissue in a bath of flesh-eating enzymes. When Jay saw the first cast, it looked like a ball of Styrofoam. "I thought they had made a mistake," he says. "Then we looked at it under a microscope and saw: These are all capillaries. It showed us where we're headed. In organs like the heart, circulation is structure." MIT engineers have used the specs from the cast to design a scaffold, another big step down this road.
Someday, Jay and his team will implant cells on a scaffold and try to grow them into a heart. But that is still a good while off. In the meantime, Jay's lab is working on smaller projects such as building an esophagus for children who are born without one or with a portion missing. Before 1938 this condition, called esophageal atresia, was always fatal. Then doctors began using skin to fashion a replacement. In the 1950s they hit upon the technique used today of replacing the missing part with a section of the colon. However, a high incidence of esophageal cancer is associated with this technique. A grown-to-order organ would be a godsend.
The Vacantis can't rest.
"It was a driving motivation for me to specialize in the surgical care of children," Jay says. "I'm certain that our Sicilian-American cultural tradition imprinted on us the primacy of caring for and nurturing children. We were reared in a family of eight children with a large extended family, including grandparents, great-grandparents, and many cousins."
Growing up in Omaha, the four brothers could not help but pick up that lesson and more. From their parents, Joanne and Charles, they learned that no theory, no question, no design of theirs was too ridiculous to explore. They grew to manhood knowing in their bones that they did not labor solely for themselves. They've lost their father, who taught them this lesson through a life devoted to his family, students, patients, and science. He died of a heart attack in 1994, and those who gather each year at the table on Thanksgiving miss him. But their mother is still around and does not hesitate to remind them they were put on this Earth to work for the good of others.
Chuck's own heart has led him to an even deeper understanding of the values his parents instilled. Nine years ago chest pains led to an angiogram for Chuck. It showed that his left coronary artery had completely occluded. He exercised and shed 30 pounds. Life looked good. Then one day five years ago his heart sounded another alarm as he sat in his office. Despite crushing pain, he calmly instructed his secretary to cancel appointments for six weeks and call the emergency room while he paged his cardiologist.
"I think I need to come in," Chuck told him.
"I can see you in two or three days."
"Maybe I haven't made clear the severity of the problem," Chuck said. "I believe I'm infarcting as we speak."
He wasn't scared. Denial chased danger from his mind. After another angiogram, doctors told him that three coronary arteries had occluded. Interesting, thought Chuck: My diagnosis was correct. You need a bypass immediately, they said. He stalled, enumerating other procedures. Can you try this or that? Uh, yeah, we can try all those things, but you'll be dead. We're doing this now.
So it came down to the healer's own cells rebelling, his sternum sawed and spread, his heart exposed to the glare of lights. Before he went under, he was still curious: I wonder whether I'm going to die.
That's when it hit him. Even in your most desperate hour, it is not just about you. No life ever is.
"When you're gone," he says now, "what you really have is what you're remembered for. I realized I would like people to say, 'He did something good for man. For mankind.'"
The journal Tissue Engineering publishes the latest cutting-edge research. Its home on the Web is www.liebertpub.com/TEN/default1.asp