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Letters to The Lancet

These letters were published in The Lancet on June 29, 2002.



Sir-The association between simian virus 40 (SV40) and tumours, especially
lymphoma, are highlighted in the report of Regis Vilchez and colleagues
(March 9, p 817).1 This animal-derived virus seems to have infected millions
of people through inadvertent contamination of poliovirus vaccines between
1955 and 1963. However, people born after 1963 have also been infected,
which implies human-to-human transmission.2

What we now know about SV40 should serve as an important warning. We need to
be extremely vigilant so that a similar situation does not arise with other
animal viruses. Such vigilance is particularly relevant to xenografts.

The SV40 experience shows that viruses in animal tissue can be transmitted
to human beings via medical procedures, can cause disease that manifests
many decades after initial infection, and have the potential to be spread
from person to person. Viruses can be part of an animal's genome, such as
porcine endogenous retrovirus, and, therefore, impossible to remove. Other
viruses, including some currently undiscovered, are probably likely to be
present in xenografts. SV40 was not known to be present in the early
poliovirus vaccines when they were manufactured.

Xenografts have a poor record of success to date, yet many are vigorously
espousing the potential benefits of this procedure. We need to remember that
many of the epidemic infections that cause continuing difficulties to human
beings were initially derived from animals (eg, HIV, hepatitis B,
influenza).2 We should, therefore, be very circumspect before embarking on
procedures such as xenografts anywhere in the world.

Some proponents of xenografts are trying to circumvent the regulations in
countries such as New Zealand by doing xenografts in the Cook Islands.3 If a
new infection developed in underresourced countries, the infection would
probably not be identified and constrained if human to human transmission
occurred.

People carrying a new infection can easily move around the world. Therefore,
what happens with xenografts and especially in a remote corner of the globe
should be a concern to us all.

Peter Collignon

Infectious Disease Unit and Microbiology Department, Canberra Hospital,
ACTPathology, Canberra Clinical School, Sydney University, PO Box 11, Woden,
Australian Capital Territory 2606, Australia

1 Vilchez RA, Madden CR, Kozinetz CA, et al. Association between simian
virus 40 and non-Hodgkin lymphoma. Lancet 2002; 359:817-23.

2 Collignon P, Purdy L. Xenografts: are the risks so great that we should
not proceed? Microbes Infect 2001; 3: 341-48.

3 Archer K, McLellan F. Controversy surrounds proposed xenograft trial.
Lancet 2002; 359: 949.

Xenotransplantation trials

Sir-At the 6th Congress of the International Xenotransplantation Association
held in Chicago, October, 2001, a presentation was made on a clinical trial
involving the treatment of diabetic children in Mexico City using pig islets
introduced into the peritoneal cavity. The islets had been prepared in New
Zealand and transported to Mexico for the clinical trial.

Transnational clinical trials raise an important issue. We believe that
effective national and international regulation of clinical trials of
xenotransplantation need to be developed. If clinical xenotransplantation
trials are done without rigorous regulations, they could be brought into
disrepute in the view of the general public. We are not aware that this
trial was perceived as being inadequately regulated. However, we see a trend
for future clinical trials being planned in a similar way.

Questions have been raised about the potential for the transfer of porcine
infectious agents into the human population. Porcine endogenous retroviruses
have perhaps received most attention, but there are several other
micro-organisms that are of potential concern. In the absence of regulatory
authorities, clinical trials may place patients at risk, and raise the
possibility of risk to the general population.

Although such trials may provide a limited amount of information on the
outcome of xenografts, we suggest that clinical trials done outside an
internationally accepted regulatory framework will prove harmful to the
development of xenotransplantation as a treatment.

We believe that organisers of transplantation meetings and editors of
journals should, before acceptance, insist on presentation or publication of
verification of adherence to internationally acceptable guidelines. We urge
academic centres and companies involved in xenotransplantation research not
to pursue clinical trials unless supervised by a nationally or
internationally recognised regulatory body.

Ian F C McKenzie, Anthony J F d'Apice, *David K C Cooper

Austin Research Institute, Austin, and Repatriation Hospital, Heidelberg,
Melbourne, Victoria, Australia; Department of Clinical Immunology, St
Vincent's Hospital, Fitzroy, Melbourne; *Transplantation Biology Research
Center, Massachusetts General Hospital, Harvard Medical School, 13th Street,
Boston, MA 02129, USA

(e-mail: David.Cooper@tbrc.mgh.harvard.edu)