SUNDAY, June 29 (HealthDay News) -- More than 98,000 Americans are clinging to life this very second, and their only chance for survival is a dead person's generosity.

The science of organ transplantation has improved by leaps and bounds. But despite the advances, almost 7,200 Americans died in 2005, waiting for a replacement organ that never arrived, according to the U.S. Health Resources and Services Administration.

"The success of the clinical side is phenomenal," said David Fleming, executive director of Donate Life America, a nonprofit alliance of national and local organizations dedicated to promoting organ donation. "Unfortunately, it's not a medical problem we're looking to solve. It's truly a matter of just not having the supply that we need."

The waiting list for donated kidneys is longest. Almost 75,000 patients are waiting for a kidney, or about three of every four people waiting for an organ.

That's generally because a person without a kidney can be kept alive longer, Fleming said. Dialysis can sustain them, while patients in need of such vital organs as hearts or lungs often die quickly.

However, the nation's diabetes epidemic is expected to make kidney failure much more prevalent in the future, leading to even greater demand for donated kidneys, Fleming added.

The waiting list for livers is next longest, with more than 16,000 patients awaiting help. More than 2,600 people are waiting for a heart, while an estimated 2,100 people need a lung, and around 1,600 patients are waiting for a pancreas.

The main problem with supply is that donors must die in a very specific way for their organs to be useful to others.

"In order to donate a solid organ, you have to die a brain death," Fleming said. "It's a very small percentage of the population that die in a way that leaves them brain dead," he said, about 1 percent of deaths annually, between 20,000 to 30,000 people.

Of those who die under optimal conditions, only about 60 percent have consented to donate their organs, he said.

"Realistically, if 100 percent of the people consented to donate their organs, we still wouldn't be able to save everybody," Fleming said. "The need continues to outstrip the supply. But if we can get everyone to consent to transplant, that's nearly twice the number of people who can be saved."

But supply isn't the only obstacle facing transplant recipients. To keep their bodies from rejecting donated organs, patients must take a variety of medications that suppress the immune system. Unfortunately, those drugs often come with a range of severe side effects. By suppressing the immune system, they also leave patients open to infection.

In the latest wave of innovation, researchers have discovered therapies that allow transplant recipients to stop taking the powerful drugs that keep their bodies from rejecting the new organ.

"We hope this will improve the quality of life for someone who receives a transplant from another human being," said Dr. David Sachs, director of the Transplantation Biology Research Center at Massachusetts General Hospital in Boston, who published his findings in a recent edition of the New England Journal of Medicine. "We think this tolerance also will help reduce the amount of chronic rejection of organs.

"That's the main disadvantage of immunosuppression, that it increases the risk of a wide range of infections, and even cancer," he added.

And that's why the new research -- in which patients can be taken off the anti-rejection drugs -- is important, said Sachs, who heads one of the research teams that have had success.

The method being investigated involves a procedure that partially destroys a transplant recipient's bone marrow. This is done to reduce the level of T-cells, the part of the immune system most responsible for organ rejection.

When the bone marrow regenerates, the new T-cells it produces tend to accept the new organ as part of the body.

"We start the immune system over, so to speak, so the new T-cells that form are eliminated if they react too strongly to either the self or the new organ," Sachs said.

The promise of the research doesn't end there. Taking it further, Sachs believes these methods could end the dire demand for organs by creating a new supply.

"We believe this same kind of tolerance can be induced for a xenograft" -- or a grafted organ donated from an animal rather than a human, Sachs said. "We've been working very hard on that, too, and we're working on pigs as a potential donor."

"Tolerance can be even more important there, because the amount of immunosuppression needed is even greater when the donor is from outside the species," he added.

Such a breakthrough could end the frustration that organ donation experts feel on a daily basis, as more lives that could have been saved are instead lost.

Until then, calls for organ donation will continue to ring out.

"We have lots of national heath-care crises in this country that we don't have a solution for," Fleming said. "We actually know the solution for this one, for a big part of it. It's very frustrating when you know the cure for something, but you can't get someone to do it."

More information

To learn more about organ donation, visit Donate Life America.