Pig Organ Transplants May Be Safer than Thought

Risk of transmitting viruses to humans appears low

By Gabe Romain

Betterhumans Staff

September 1, 2004

Pigs may be a safer source of organs and tissues for transplantation than previously thought, according to a new study that found a low risk of viruses jumping from pig to human cells.

Researcher Yong-Guang Yang and colleagues from Massachusetts General Hospital in Boston have shown that the danger of transmitting pig-derived viruses called porcine endogenous retroviruses (PERVs) to humans through transplantation may be extremely low.

"Our results demonstrate, we believe for the first time, that human and pig cells can coexist long-term (up to 25 weeks) without direct PERV infection of human cells," say the researchers.

Dangerous PERVs

Xenotransplantation-- the transplantation of cells, tissues or organs between species, usually from nonhumans to humans --could alleviate the worldwide shortage of donor organs such as livers, kidneys and hearts. There are fears, however, that transplanted tissue may carry unknown dormant infections that, once introduced into a recipient, could be activated and jump species barriers.

Particular attention with pigs has been paid to PERVs because they have the potential to replicate in human cells. PERVs have been found to infect human cells in test tubes, however, no evidence of continued viral replication or disease has been found.

Until now, the actual frequency of PERV transmission within a living organism had not been tested in either people or animal models under circumstances where human cells are exposed over a long period of time to similar amount of pig tissue.

Long-Term coexistence

For their study, Yong-Guang Yang and colleagues developed a new xenotransplantation model in which human cells coexist with large numbers of pig cells in a transgenic mouse.

They found that the cells could in fact coexist long-term without PERV infection in the human cells.

The researchers did find that human cells in the mice contained PERV sequences, but further investigation showed that this was caused by a mouse retrovirus infecting the pig cells and then transmitting PERV sequences from there to human cells.

This may account for previous observations of PERV transmission into human cells in other mouse studies, and indicates the importance of developing robust models that do not contain additional replication capable viruses.

"The absence of direct human cell infection following long-term in vivo coexistence with large numbers of porcine cells provides encouragement regarding the potential safety of using pigs that do not produce human-tropic PERV as source animals for transplantation to humans," say the researchers.

The research is reported in the Journal of Clinical Investigation.

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This article posted October 2, 2004.