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Much of the meeting yesterday focused on controversial research being conducted by the New Zealand-based company Diatranz, Ltd., which transplanted pig islet cells into 12 diabetic children in Mexico and plans to perform other human experiments in the Cook Islands. The company's genetically modified pigs have tested positive for three classes of porcine endogenous retroviruses (PERVs). Though Diatranz claims that its patients have remained free of infection after one year - not long in the life of a retrovirus - one patient was found to have pig DNA circulating in his/her blood, suggesting a potential infection.
Diatranz's experiments were condemned by the New Zealand Ministry of Health, which enacted a moratorium on clinical xeno trials last year and issued a "xenotransplantation research warning" in a media release on March 7th. The release stated that: studies on the benefits to Diatranz's patients were inadequate and did not counterbalance the risks of transferring animal viruses to humans. Moreover, jurisdictions like Mexico and the Cook Islands did not have the appropriate regulatory mechanisms in place to safeguard public health or monitor patients and their contacts for viruses on a long term basis.
What are the risks of xenotransplantation to the wider community?
Xenotransplantation carries some risks for the wider community. The major concern for public health is that xenotransplantation might transmit an infectious agent (such as a virus) from animals to humans. Retroviruses are the chief concern, because there are many examples of such viruses moving from one species to become infectious in another.
However, retroviruses do not always cause obvious signs of disease initially. If a retrovirus present in a xenotransplant were to infect the recipient of the transplant, it may spread to close contacts, carers and even the general population before it became obvious that an infection had occurred.
What viruses are we most concerned about in xenotransplantation?
Nonhuman primates (apes and monkeys) are not being considered as the source for animal-to-human transplants because their close relationship to humans increases the risk of a virus being transmitted across species.
The virus that is of most concern in xenotransplantation using pigs as the donor species is the porcine endogenous retrovirus (PERV). PERV is present in almost all strains of pigs and cannot be removed by raising pigs in sterile conditions. Although PERV is inactive, and therefore harmless, in pigs, there are concerns that transplantation into humans may activate the virus, creating a new human disease that could spread to those close to the transplant recipient and eventually to the wider community. PERV can infect human cells in the laboratory, suggesting that it could infect humans through xenotransplantation. However, studies of around 150 people worldwide who have been transplanted with pig tissue or had their blood pass through pig cells have shown no evidence of infection with a virus or any other infectious agent originating from pigs.
Approval of an animal-to-human trial would depend on there being an appropriate policy for testing the xenotransplant recipient and their close contacts for PERV and any other organisms that may emerge as a result of the transplant.
Dr. David White joined The John P. Robarts Research Institute from the biotechnology company, Imutran, in Cambridge, England, where he was Director of Research. Dr. White is a Fellow of the Royal College of Pathologists and has a PhD from the University of Cambridge.
Ethically, such an experiment cannot be balanced by control data. For example, it is not possible to remove the device and show that diabetes returns. For this reason the community is pressuring the group to test the approach in non-human primates, dog or rabbit. Valdes has agreed, but has also begun trials in a further 24 patients.
The book documents the episode in which the Cook Islands nearly became the site for the world's first transplantation of pig cells into living humans (xenotransplantation) as a cure for diabetes in 2002. Pacific Islanders in general suffer from very high rates of Type-2 diabetes, and some researchers claimed transplanting pancreas cells from pigs into diabetics offered a potential cure. The New Zealand government had banned such xenotransplants as too risky in 2001.
Had the experiments gone forward, the US might have branded the Cook Islands and its 14,000 inhabitants a "rogue nation," writes Cook Islands’ Traditional Chief Te Tika Mataiapo - Dorice Reid. Panicked US government health officials threatened to bar admission into the US of anyone from the islands as potential carriers of dangerous retroviruses from the pig cells.
After initially agreeing to the xenotransplants in 2002, the Cook Islands’ government reversed its decision after protests from tribal leaders like Reid and the world medical community.