Animal Organs into Humans

The transplant techniques have advanced substantially, but not so the number of donors.

Due to the huge shortage of donor organs, researchers have been looking for methods of transplanting animal organs across different species (a method named "xenotransplantation"), with the main goal of employing animal organs for humans. "The major stumbling block is that the immune system in the animal receiving the organ tends to reject the transplant," said Dr Muhammad Mohiuddin (US National Heart, Lung, and Blood Institute).

But the recent advances in genetic engineering and the achievement of genetically modified pigs that are more compatible with humans, "has reinstated hope for the success of xenotransplantation," he said.

In his survey, Dr Mohiuddin points the reasons why xenotransplantation comes with higher potential than other methods for replacing impaired organs.

One example are the ventricular mechanical devices for treating heart failure that are prone to induce blood clotting and are still not proven suitable for replacing transplantation. "And while the idea of growing organs in culture dishes has fascinated scientists for years, there have been no major success stories yet," he said.

But there are some encouraging studies pointing that xenotransplantation could eventually be of benefit to humans.

In one approach, insulin-producing cells from pigs were transplanted into monkeys with diabetes, inducing the complete reversal of diabetes for over 100 days. "But such research is still a long way off from being relevant to humans. For example, in the pig-to-monkey studies, very large doses of drugs called "immunosuppresants" were needed to stop the monkeys' immune system from rejecting the pig islet cells--such doses would be unacceptable in humans," explained Mohiuddin.

Besides immune rejection, another risk of the xenotransplantation is the transmission of viruses from animals to humans. "Whether the risk of transmission of these pathogens will increase with xenotransplantation is not yet known. But the risk can be anticipated, and thus prepared for. A long-term careful follow-up of transplanted patients will be required to monitor for infection by latent viruses and other pathogens. A timely intervention would be important to treat the infection and control its spread to other individuals."