Select Committee on Science and Technology Written Evidence

Memorandum by the Department of Health on Xenotransplantation and infection


  1.  Xenotransplantation is the transplantation of tissue and organs between different species, and in particular the transplantation of animal tissue into humans. The formal definition currently used in the UK is:

    any procedure that involves the use of live cells, tissues and organs from a non-human animal source, transplanted or implanted into a human or used for ex-vivo perfusion.

  Ex-vivo perfusion is a means of partially taking over the function of a failing organ by passing the patient's blood through substitute tissues or organs outside the body.

  2.  There is currently, and will continue to be, a shortage of human organs and tissue for transplantation. Xenotransplantation is a potential solution to this shortage. More likely, however, is the potential benefit from cell transplant therapies in the treatment of conditions such as Parkinson's Disease, Huntingdon's Disease, stroke, epilepsy, spinal injury and diabetes.

  3.  Before xenotransplantation can become an accepted treatment, three major obstacles have to be overcome:

    —  the risk of transmission of disease from the donor animal to humans has to be minimal;

    —  rejection of the "foreign" tissue has to be prevented; and

    —  there has to be evidence that the animal organ or cells would function effectively in humans.

  4.  Recent scientific developments, including genetic modification of source animals, may mean that the problem of rejection of tissue transplanted between species can be overcome. This increases the possibility of using animals to increase the supply of organs and tissue to meet medical demand. However, it also raises complex ethical and other issues, including safety—both of the individual and of the wider public, the efficacy of such procedures and considerations of animal welfare.

  5.  The Government is advised on these issues by the United Kingdom Xenotransplantation Interim Regulatory Authority (UKXIRA), established in 1997 following the Government's acceptance of the recommendations made in Animal Tissue into Human, the report of the Advisory Group on the Ethics of Xenotransplantation (the Kennedy report). The UKXIRA's role is to:

    —  provide a focal point for xenotransplantation activity in the UK;

    —  provide a means of regulating xenotransplantation and, in particular, to provide a process through which applications to undertake xenotransplantation in humans can be considered; and

    —  consider the underlying evidence about xenotransplantation developments and to consider whether clinical trials can be justified.


  6.  All xenotransplantation procedures raise similar safety issues, and uncertainty about the safety of xenotransplantation continues to be a significant obstacle to its therapeutic use. The potential for infectious agents to be passed from a source animal, via a transplant (organ or cell), to a human recipient and from the patient to the wider population is still a major concern. The breeding of source animals in appropriate bio-secure facilities can eliminate many of the obvious agents of concern, but the question of, as yet, unknown infectious agents remains, as does the question of agents which cannot be bred out of source animals—in particular the porcine endogenous retrovirus (PERV).

  7.  Since the establishment of the UKXIRA much new evidence regarding infectious risk has emerged. Various study groups have in the last couple of years reported evidence of cross-species transmission of PERV using small animal (mice, guinea pigs) models. The significance of these findings remains unclear. Whether the same risk of infectious agent transmission applies to all forms of xenotransplantation remains a matter of debate. It may seem logical to suppose that a permanent whole-organ xenotransplant represents a greater potential for infectious agent transmission than, for example, the temporary passage of fluid through a barrier-protected membrane. However, a single cell, or a single viral particle, may present an infection risk. Until further evidence comes to light, the UKXIRA considers it prudent to assume that all xenotransplantation procedures carry a risk of some degree.

  8.  Campaigning groups opposed to xenotransplantation have called for a moratorium on clinical trials, one reason being because of infectious risk. Until clear evidence becomes available on the infection risks posed by any particular xenotransplant technique, the UKXIRA will assess the level of risk posed by each procedure balanced against the potential benefits on a case by case basis. Account will be taken not only of the infection risks involved, but also of evidence of efficacy and the ethical and animal welfare considerations involved.


  9.  There has been considerable international debate about the precise definition of xenotransplantation and in particular whether certain procedures (both pre-existing and newly emerging) require the same ethical and medico-scientific framework as other forms of xenotransplantation.

  10.  In 2001, the Secretary of State for Health accepted the UKXIRA's recommendation that the definition of xenotransplantation currently used in the UK (see paragraph 1) should be changed—as soon as was practicable—to bring it into line with the revised, broader, definition adopted in the USA in 2000 (and which the Council of Europe is expected to recommend for adoption by Member States):

    any procedure that involves the transplantation, implantation, or infusion into a human recipient of either (a) live cells, tissues or organs from a non-human animal source, or (b) human body fluids, cells, tissues or organs that have had ex vivo contact with live non-human cells, tissues or organs.

  11.  The US definition encompasses a wider range of possible products and procedures. Examples would include procedures that involve the culturing of cells for transplant through contact with a feeder layer of viable animal cells derived from cell lines. Treatments using this type of process are already in use and include the culturing of replacement skin for the treatment of serious burns victims and for other forms of plastic surgery.

  12.  The UKXIRA had to consider the extent of the risk of infectious agent transmission from these processes. In skin replacement therapies, well-established mouse cell lines are usually used and they have been used for a variety of scientific and medical purposes for more than twenty years. There was, however, considered to be a theoretical risk of infectious disease transmission, albeit small.

  13.  The Department of Health commissioned Professor George Griffin (a Member of the UKXIRA) and Dr Gee Yen Shin, both of St George's Hospital Medical School, to assess the possible infection risks to patients associated with this skin culturing procedure and to produce recommendations to minimise them. Professor Griffin's and Dr Shin's final report is expected shortly. The use of such mouse cells for cell culture has also been reviewed by the Advisory Committee on Dangerous Pathogens, which concluded that the risk of transmission of mouse infectious agents was very small.


  14.  In 2001, the UKXIRA commissioned an assessment of the feasibility of developing a national infection surveillance scheme for xenotransplantation purposes for public health for the UK. It was to be based on the draft guidance from the UKXIRA Infection Surveillance Steering Group (see paragraph 16) and to allow for future international surveillance requirements. Recommendations for a scheme to be contracted to the Public Health Laboratory Service (PHLS) have been submitted to the UKXIRA and are under consideration. Any arrangement being developed with the PHLS would be taken forward with the new Health and Protection Agency from 1 April 2003.


  15.  The UKXIRA has published a number of reports and literature reviews which are available from its website at

    —  First Annual Report, May 1997—August 1998 (1998).

    —  Second Annual Report, September 1998—August 1998 (1999).

    —  Third Annual Report, September 1999—November 2000 (2001).

    —  Fourth Annual Report, December 2000—December 2001 (2002).

    —  Guidance on making proposals to conduct xenotransplantation on human subjects (1998).

    —  Report of the workshop on porcine endogenous retroviruses, 6 August 1998 (1998).

    —  Infection Risks in Xenotransplantation (2001).

    —  The Physiology of Xenotransplantation (2002).

  16.  Two draft reports are also available from the UKXIRA website:

    —  Draft Report of the Biosecurity Steering Group of the UKXIRA: guidance notes on the biosecurity considerations in relation to xenotransplantation.

    —  Draft Report of the Infection Surveillance Steering Group of the UKXIRA: further guidance on infection surveillance aspects of xenotransplantation.

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