Grow your own body parts

It took only 15 seconds. Bob Emerson was working as an electrician in a power plant when a co-worker 4 feet away accidentally touched a "live" electrical contact. Suddenly, fire filled the room and Emerson was engulfed in flames. When doctors saw the burns covering more than 85 percent of his body -- so deep that the skin would never grow back -- they thought Emerson would die.

But by the next day, Emerson's skin was growing. A miracle? Perhaps. Emerson's skin was growing in a laboratory, 900 miles from his Kalamazoo, Michigan, hospital bed. The idea was to grow enough skin in the lab so Emerson could receive a transplant of his own skin.

Scientists experimenting with this technique, called tissue engineering, say one day it may be used to replace other body parts that can't grow back on their own -- like ears, livers, and heart valves. Researchers say these transplants, for which the donor and recipient are the same person, could save thousands of lives.

TALE OF A TRANSPLANT

Typically, when an organ is damaged and can't be surgically repaired, doctors have few choices. They can replace it with a new organ from another person or an animal. Or they can use artificial organs made from metal, plastic, or some other material.

But most organs can't be created from artificial parts -- their functions are just too complex to duplicate. And real organs from human donors are few and far between. For example, every year, 40,000 people wait on hospital transplant lists to receive new hearts. Only about 2,300 get them.

But the biggest problem with using someone else's organs is that your body might reject, or destroy, the transplant. That's because your body has special blood cells that recognize and attack cells that don't belong to you -- like harmful bacteria. These blood cells make up your immune system -- the body's mechanism for fighting disease.

Rejection can't happen, however, when you donate your own tissues. So, when Emerson first arrived at the hospital, doctors searched his body to find some unburned skin. They carefully removed two patches, each smaller than a quarter, and sent them to a tissue-engineering lab in Cambridge, Massachusetts. With the addition of sugars and other growth-boosting nutrients, the skin cells started to multiply to form flat sheets.

"The next two to three weeks were a blur," Emerson recalled recently. Under heavy painkillers, he waited. By the end of three weeks, the lab had grown enough of the paper-thin skin to completely cover Emerson's body -- about 1.7 square meters (18 square feet).

Technicians packed up the new skin and flew it to Kalamazoo, where surgeons applied it to Emerson's legs, arms, and chest in small rectangular pieces. His immune system instantly recognized the skin as his own. And eventually, the pieces grew together to form one seamless sheet.

THE REAL THING?

Compared to other organs, skin's structure is pretty simple -- which is why the researchers who first experimented with tissue engineering in the 1970s tackled this organ first. Natural skin consists of two layers of cells: the flat epidermis, or upper layer, and the dermis, which lies underneath (see diagram, right). Such flat sheets of tissue are easier to grow in a lab tray than, say, a three-dimensional liver would be.

Even so, lab-grown skin can't ever completely mimic the real thing. One reason is that real skin has so many complex jobs to do: It forms a protective shield between your innards and the world outside. It prevents water and other body liquids from leaking and evaporating, so you don't dry up into a giant prune. It contains sweat glands and blood vessels to help maintain a constant body temperature. And it contains nerve cells that sense changes in pressure, heat, cold, and pain.

For burn patients like Emerson, who had virtually no skin left, the most urgent need is to replace the protective, moisture-sealing layer -- even if it means doing without some of skin's other functions. That's why the technicians growing Emerson's skin chose to isolate and grow keratinocytes, the main type of epidermal cells. Keratinocytes produce keratins, proteins that help give skin its protective properties, says Dr. Howard Green, one of the doctors who created this process for growing, or culturing, skin cells.

Emerson's new epidermis looked pretty strange at first. "Initially it looked almost like plastic wrap," he says. "Shiny, wrinkly, and very smooth." The skin had very few melanocytes, the pigment-producing cells normally found in the epidermis, that give skin its color. It also didn't have sweat glands, which are located in the dermis. So, Emerson has to be careful not to let his body overheat.

VIRTUALLY NO SCARS

Luckily, though, Emerson's new skin was also lacking fibroblasts, the cells that make scar tissue. So, his skin patches healed together without scars at the borders.

In time, the few melanocytes that were in Emerson's epidermis have multiplied to give his skin some color. Plus, a type of skin cell that originates in the bone marrow (called Langerhans cells) eventually migrated through Emerson's blood to his epidermis. Now the epidermis has started to regenerate Emerson's dermis. "My skin continues to get more and more natural every year," he says.