 Cryonics Institute |
 Contents Comparing About
Cryonics
FAQ
Links News &
Views |
|
|
From wire service reports:
Baxter International's Nextran subsidiary, located in Princeton, N.J., concluded trials late last year in which specially engineered pig livers were used as filters outside the body to perform human liver functions, Baxter spokeswoman Deborah Spak said in an interview.
"The results were very encouraging," she said. "There were several patients who bridged." That is, they stayed alive on the pig liver apparatus until a human organ was available.
Spak said this so-called "ex vivo" trial involved a handful of patients, but the researchers have enough data to publish results in a major scientific journal within a few months. She also expects the firm, in the next 18 months, will request FDA permission for "in vivo" trials, with the organ actually transplanted into the body.
Nextran hopes to provide a viable alternative when no human organ is available -- a sad and all-too-common event for those on transplant lists.
"The whole reason that we're doing this stuff that may seem so crazy to people is that there are just not enough organs to go around and the number of people who are waiting and dying is absolutely staggering," said Dr. Marlon Levy, a transplant surgeon at Baylor University Medical Center in Dallas.
Levy performed the two "ex vivo" liver trials that have taken place at Baylor and said both patients -- who were near death -- were doing quite well. "This is, on our part, an act of desperation to try to solve the crisis in organ availability," he said.
According to data from the United Network for Organ Sharing, there is a critical shortage of human donor organs. As of January, more than 67,000 patients in the United States were on its waiting list for organs -- nearly 44,000 for kidneys; another 4,000 for hearts; 3,600 for lungs. Thousands of people die waiting. Another 100,000 never even qualify to get on the list in the first place.
Baxter sees this need as a logical fit with its own leading position in kidney dialysis. In the mid 1990s, the company began to study xenotransplantation -- or transplant of organs between species -- as a possible alternative.
According to Marvin Miller, Nextran CEO, there would be 125,000 organ transplants yearly in the United States if everyone who could benefit actually got one. In 1998 only 21,000 people were lucky enough -- most of them kidney recipients. Furthermore, Baxter says, the demand for transplants increases 15 percent each year while the supply of organs is static.
Research into using animals for transplant purposes started as far back as the late 1960s. In the early 1990s, worldwide attention focused on two patients in Pittsburgh who received baboon livers but eventually died. Use of pig-tissue heart valves is common today, but unlike organs, the pig cells are killed first.
Dr. Goran Klintmalm, another Baylor transplant surgeon, said critical new information was learned in each attempt of animal-to-human transplantation. Only now are specially engineered animals being studied, a whole new realm.
Unlike the "ex vivo" trials, Nextran's trials of fully transplanted organs will involve hearts and kidneys, he said. That is because if the transgenic kidneys or hearts do not work, doctors can turn to other alternatives like kidney dialysis or a heart device called a left-ventricular assist device to keep patients alive. For livers, there is simply no alternative.
Also, the liver acts like a biochemical factory, performing numerous complex functions that may be hard to replicate. But doctors said what has been learned about rejection in livers can readily be applied to other organ systems.
The chief obstacles are immunological in nature, according to John Logan, vice president of research and development at Nextran.
First is preventing what is called hyperacute rejection -- the process by which foreign tissue is turned into a pulpy mess almost immediately by a human's immune system.
Nextran is engineering pig organs to express a human gene that prevents this rapid rejection. Even with the transgenic organs, however, patients still need to take special immunosuppressive drugs every day for the rest of their lives.
Researchers are also very concerned with a certain virus contained by most if not all pigs -- the porcine endogenous retroviruses (PERV). They pose no threat to pigs and, at least so far, seem not to infect humans who have undergone pig tissue transplants. But concerns linger.
"The results so far cause us to be cautiously optimistic," Levy said. "Two or three years ago, everybody was ready to bring these trials to a screeching halt because of the concern that PERV viruses could infect human cells in a tissue culture. Now, just a short two years later, we've got data on my two patients that show no PERV infectability in serial sampling over time."
In addition, Levy pointed to a recent study conducted by Imutran, the unit of Swiss pharmaceutical giant Novartis AG <NOVZn.S>, and the only other major company studying xenotransplantation of whole organs. Imutran studied 160 people who had some form of pig tissue transplant and found no evidence of PERV infection.
To Dr. Klintmalm, tremendous progress has been made to date with the transgenic animals. "Just the fact that we've tried is progress," he said. "We have much, much more to do than we've done, but we've started."