Some Transplant Patients may Not Need Anti Rejection Drugs
2007-08-31 20:44:51Some Transplant Patients may Not Need Anti Rejection Drugs
Scientist have given hope to some organ transplant patient by suggesting that
they may not need the anti rejection drugs to which they are otherwise resigned
to for a life time.
Researchers at Lucile Packard Children's Hospital and the Stanford University
School of Medicine used simple blood sample to identify a pattern of gene
expression shared by a small group of patients who remained healthy without
medication. This group who beat the odd have given many a hope of respite from
the anti rejection drugs.
The findings suggest that transplant recipients who share the same pattern of
genes but are still on conventional medication may be able to reduce or
eliminate their lifelong dependence on immunosuppressive drugs. The study may
also help physicians determine how best to induce acceptance, or tolerance, of
donor organs in all transplant patients, regardless of their gene expression
profiles.
"We're very excited by the findings," said Minnie Sarwal, MD, PhD, a pediatric
nephrologist at Packard Children's. "Most transplant patients who stop taking
their medications will reject their organ. But now we have the chance of telling
someone committed to a lifetime of drugs that it may be possible to minimize
their exposure to the drugs."
Although the anti-rejection medications, known as immunosuppressants, tamp down
the immune system enough to permit lifesaving organ transplants, their benefits
come at a price. They also quash the body's natural response to dangerous
invaders, such as bacteria and viruses, and to rogue cancer cells.
Transplant physicians prescribing immunosuppressants to their patients walk a
fine line between avoiding organ rejection and increasing the risk of infection
and cancer.
Sarwal, associate professor of pediatrics at the medical school, is the senior
author of the research, which will be published Aug. 20 in the advance online
edition of the Proceedings of the National Academy of Sciences. She collaborated
with physicians at Stanford and Packard Children's, as well as with colleagues
from the Veterans Affairs Palo Alto Health Care System and several institutions
in France, China and the Netherlands.
The researchers used microarray, or gene chip, technology to compare gene
expression patterns in blood samples from 16 healthy volunteers with those from
three groups of adult kidney transplant recipients from the United States,
Canada and France: 22 people on anti-rejection medications who had healthy donor
kidneys, 36 people who were taking their medications but who were still
rejecting their organs and 17 "tolerant" people who had successfully stopped
taking their medications without rejecting their donated kidneys.
Sarwal and her collaborators found that the expression pattern of just 33 genes
in a random sampling of peripheral blood could be used to accurately pick out
more than 90 percent of the tolerant patients. What's more, one out of 12
stable, fully medicated patients and five out of 10 patients on a modified,
low-dose immunosuppressant regimen shared very similar expression patterns.
The findings imply that patients regularly taking immunosuppressants who have a
strong matching pattern for the tolerance genes may be able to safely reduce or
even eliminate their dependence on the medication. Equally important, it
suggests that patients who don't share the gene pattern, even if on very
low-dose medication, should be particularly vigilant about continuing to take
their immunosuppressants.
"For the first time, we now have evidence that will help us say to the five out
of 10 patients without this expression pattern, 'Please, please don't think
about changing your medications'," said Sarwal. "At the same time, we may be
able to say a different patient, 'We'd like to try to cut back your drugs.'"
Although it's not known exactly how the 33 genes identified by the researchers
affect the development of tolerance, the expression and function of nearly
one-third are controlled by a regulatory molecule called TGFbeta. Sarwal and her
colleague speculate that the genes somehow affect the development of immune
cells responsible for distinguishing self from non-self.
But they caution that even long-term tolerance may not last forever; immune
challenges such as severe infection can sometimes cause rejection of a donated
organ years after anti-rejection medication was successfully stopped.
"The real value of this technology is the ability to easily and repeatedly
monitor patients over long periods of time," said Sarwal. "We can keep an eye on
this genetic signature and watch for changes that might indicate the beginning
of rejection before any clinical signs are apparent. This could be a very
exciting advance for both patients and physicians as it can lead to the ability
to, for the first time, safely customize immunosuppression for an individual
patient."
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