How Safe is Organ Transplantation?

Organ failure has killed many people and incidences of organ failure, kidneys, heart and liver are on the increase. For patients who suffer from organ failure, organ transplantation is their only hope, but sadly such organs are in short supply. Some have proposed xenotransplantation as a potential solution. This idea is to transplant organs, tissues or cells from a closely-related species into human patients. Xenotransplantation between species has been around for the last 95 years (Mayo Clinic, 2007). Attempts at xenotransplanation in humans have reported preliminary success (Michler, 1996). Despite such positive results, the practice of xenotransplantation is not without danger. Opponents of xenotransplantation at the Transplantation Society of Australia and New Zealand warn in their online report (2007) that the risk of infections being introduced from animals to humans is a key issue in xenografts. A comparison of the potential of xenotransplantation and issues associated with it will show that the risks are too real to be ignored and there is no compelling reason to resort to xenotransplanation as a temporary or long-term solution for organ failure.

The potential of xenotransplantation has been discussed in Michler (1996). He highlighted that preliminary successes of heart, kidney and liver xenografts in extending life has stimulated researchers to exploit xenotransplantation as a temporary strategy to sustain and stabilize patients so that they can eventually receive organs from human donors. Acknowledging that xenotransplantation is currently only an experimental procedure, he holds the view that xenotransplantation as such a temporary strategy can be explored to test its feasibility as a long-term solution. Admittedly, xenotransplantation may give the patient more time to wait for an organ from a suitable human donor, but to argue that those preliminary successes show the potential of xenotrasnplantation as a long-term solution to the problem of organ shortage would be premature in view of the possible risks of rejection and infection from animal viruses arising from xenotransplantation.

One of the major argument against organ transplantation as well as xenotransplantation is the risk of organ rejection. Transplanted organs triggers an automatic immune response. Patients who receive organs from close relatives, like parents and siblings, will have better matched organ tissue and therefore the risk of rejection can be reduced. However, in most cases, organs are from unknown donors and so the issue of organ rejection is very real. In the case of xenotransplantation, where animal organs are used, one can safely conclude that the risk of rejection will be greater. The solution to this is to load the patient with immunosuppression drugs (Michler, 1996). However, loading the patient with such drugs will lead to a weakened immunity system and this would put the patient in danger of developing other infections and complications (Transplantation Society of Australia and New Zealand, 2007). Although there are ongoing studies to genetically engineer pig organs so that the immune response will not be triggered, such studies are merely exploratory (Mayo Clinic, 2007). Thus we need to bear in mind that using organs of genetically engineered animals may pose long-term dangers that we are unaware of at this stage.

The key concern is risks associated with animal viruses and several problems have been highlighted by the Transplantation Society of Australia and New Zealand (2007). First, while it may be possible to manage zoonotic viruses (infectious agents transmitted by animals to humans under natural conditions) through careful screening of donor animals, xenozoonotic viruses (those transmitted to humans through xenogenetic tissue) are far more dangerous. The latter is a real threat because they may not be identifiable using existing tests. Second, latent animal viruses may develop the ability to infect humans or cause cancers and the behavior of the viruses may change because of immunosuppression drugs that transplant patients have to take. Thirdly, as pointed out by the Society, if the patient should succumb to lethal infections from animal viruses due to inadequate screening of xenograft organs, others in contact with him would also be at risk. The Society believes that isolation and treatment procedures can restrict the spread of such infections. However, the costs and risks are too high when we weigh them against the limited success of xenotransplantation achieved to date.

In conclusion, there is really no compelling reason to resort to a risky procedure as xenotransplantation. The failure rates for human-to-human organ donation are significant and the risks are amplified in xenografts. More importantly, we cannot overlook the risk of infection from animal viruses in xenograft patients due to their weakened immune system. The costs of clinical research on xenotransplantation are high, and in view of the risks and limited success of xenografts so far, researchers should be cautioned against presenting xenograft as a standard temporary procedure for patients awaiting human organ transplants.

Reference: Keeping Human Tissue Transplant Safe, http://www.fda.gov/fdac/features/2005/305_tissue.html