Countries scrambling to draft guidelines for xenotransplantation human clinical trials.
Clinical trials have focused primarily on pig products. Fetal pig brain cells, for example, are being evaluated as a treatment for severe neurologic diseases, such as Parkinsons and Huntingtons. Pigs livers have been used ex vivo (outside the body) as a bridge to remove toxins from the blood of patients in fulminant liver failure, until a human liver becomes available. And encapsulated pig pancreatic islet cells may one day provide a cure for patients with insulin-dependent diabetes. However, most pigs, carry a virus that though generally harmless to them, could be dangerous to humans. Pig endogenous retrovirus (PERV) is one of many known and unknown infectious agents that may be transferred via animal-to-human transplants. The risk of such transmission and subsequent infection in transplant patients may be facilitated by long-term immunosuppressive therapy, necessary to prevent rejection of animal organs or tissue.
To limit the spread of zoonotic (non-human) infections from animals to transplant recipients and from transplant recipients to the general public, all experiments using animal tissues must be cleared through the FDA. To further reduce the risk to public health, last February, the agencys Center for Biologics Evaluation and Research (CBER) drafted a guidance document recommending that the nations blood collection centers modify their blood donor questionnaire and defer recipients of transplanted animal organs and tissues, as well as those who have had intimate contact with the recipients.
CBERs recommendations have received a lukewarm response from representatives of the blood banking community, which, among other things, worries that the definition of xenotransplant contacts casts too broad a net and could defer many perfectly safe blood donors. Nonetheless, the guidelines likely will be finalized, said Linda Chambers, MD, a senior medical officer of the American Red Cross, which collects half of the nations blood supply.
In contrast to the stringent US regulations, clinical trials and folk treatments using xenotransplantation are being offered in Mexico under weak safety rules, according to members of a federal advisory committee. That could open the door for international xenotourism, where desperate Americans go to Mexico or other countries for the procedures, they said.
For years, US citizens have traveled to Mexican border towns like Tijuana to receive injections of cells from rabbits, sheep, and shark fetuses, all touted as rejuvenating treatments. But the committee members were particularly alarmed that a New Zealand company called Diatranz, Ltd is conducting a trial in Mexico using pancreatic and testicular cells from fetal pigs to treat diabetes in children. The company reportedly is preparing to launch a similar trial in the Cook Islands. According to a statement on its Web site, Diatranz says that 12 children have been injected with the cells in the Mexico trials, and that no adverse reactions, including infection with pig viruses of any sort, has occurred.
A scientific group called the International Xenotransplantation Association sent a letter to the New Zealand government asking it to look into the Diatranz trials. The risks [of xenotransplantation] can only be regarded as manageable if proper monitoring of recipients and family contacts can be undertaken on a long-term basis, the letter stated. Jurisdictions like Mexico and the Cook Islands do not have appropriate regulatory authorities to develop appropriate guidelines to safeguard the patients and their contacts.
New Zealands Ministry of Healthy released a statement saying that a substantially more informed debate on xenotransplantation is needed, and that the countrys parliament is considering changing the law to tighten safety requirements.
Ultimately, there probably is little the US can do about controversial trials in other nations. I dont think were going to be able to police the whole world, said Eda Bloom, PhD, an FDA virologist who represents the agency on the committee.
Daniel Salomon, PhD, a molecular researcher at the Scripps Research Institute in La Jolla, CA and another committee member, agreed that US authorities could do little to stop the treatments in Mexico. But Salomon said that officials should reach out to other countries to help them develop stricter rules. We should take a global societal view of this. At least respect the general overarching premise that there should be some form of regulation.
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|Title Annotation:||Diatranz Ltd. investigating use of fetal pig cells to treat human diabetes causes concern by the U.S. and the International Xenotransplantation Association|
|Author:||Correspondent, Michele Grygotis Transplant News Special|
|Article Type:||Brief Article|
|Date:||Apr 28, 2002|
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