Xeno by David Cooper and Robert Lanza, Oxford, 拢18.99/$30, ISBN
0195128338
A NEW 鈥渋nfectious Chernobyl鈥� threatens us. 鈥淭he entire human population on
this planet is put at risk鈥� if animal organs are transplanted into humans, says
the Campaign for Responsible Transplantation. Yet the Islet Foundation, whose
mission is 鈥淎 Final Push in the Cure for Diabetes鈥� takes the opposite point of
view: 鈥淭oday we have a situation in which some totally unproved and speculative
risks are being used to prevent the elimination of the very real risks of
diabetes.鈥� The foundation hopes that transplanted insulin-generating 鈥渋slets鈥�
will provide a cure: 鈥淚t is an absurd situation in which the horrors of diabetes
are allowed to continue in the face of opposition that is more superstition than
蝉肠颈别苍肠别.鈥�
So what is to be done? Transplantating foreign cells, tissues or organs from
one animal species to another鈥攛enotransplantation鈥攃learly raises
strong feelings. The reasons are not hard to fathom. On the one hand lies the
danger of introducing new diseases into the human population. On the other is
the promise of immense therapeutic benefit.
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To understand the background to this conflict, there is no better place to
start than by reading Xeno. David Cooper and Robert Lanza describe the
three scientific challenges of xenotransplantation: preventing the host鈥檚 immune
system rejecting the transplant; ensuring that the transplanted tissue or organ
is physiologically compatible and does its job; and guaranteeing safety from
infectious diseases.
Xeno also touches on a host of legal, economic and ethical
questions. What are the ethics of genetically modifying animals as sources of
transplant material? How would xenotransplantation affect healthcare spending or
the donation of human organs? How should or could it be regulated? The result is
remarkably up-to-date and accurate in its description of the science and
medicine.
As revealed by Xeno鈥檚 subtitle, The promise of transplanting animal
organs into humans, the book gives an optimistic perspective. The authors are
enthusiasts, active researchers in the field who have no qualms about blowing
their own trumpets.
Remarkable progress has certainly been made in overcoming graft rejection, at
least in its initial phase. But much remains to be done. Unfortunately, in many
areas research has reached its limit in animal models. Further progress hinges
on clinical trials in humans鈥攁nd this raises the spectre of diseases
crossing from the donor species into our own.
How great are these risks? The authors describe how donor pigs could be
raised free from bacterial infections and conventional viruses. But they devote
just two-and-a-half pages to what most of the opposition sees as the serious
risk: the so-called 鈥減orcine endogenous retroviruses鈥� or PERVs. These viruses
have incorporated themselves into the pig genome, as HIV and the T-cell
leukaemia viruses do in people. PERVs seem harmless to pigs: but what if they
cross the species barrier? Those directly involved in the field seem to be
reaching consensus that the PERV threat is probably not as great as was once
feared. But this, if correct, means that the hazard is potentially very serious,
albeit with a very low probability of occurring: probably the hardest case of
all to evaluate.
The benefits are also rather poorly defined, and are still more potential
than assured. Risk-benefit analysis is difficult. To evaluate the benefits
properly means moving from lab bench to hospital bed鈥攚hich invokes the
risk. Limited, closely monitored clinical trials, in which efficacy and safety
are assessed simultaneously, seem to me to represent the best chance of
progress. Approval of such trials is now entering the political arena. But will
a climate clouded with fears of BSE, HIV and genetic modification permit such
work to go ahead?