Pigs as a Source for New Organs

By Kendall K. Morgan

The statistics on organ transplantation are startling. According to the U.S. Department of Health and Human Services, someone will have been added to the waiting list by the time you finish reading this blog post; on average, the list grows by one every 10 minutes. Every day, an average of 79 people receive an organ transplant, and 18 people die waiting.

There just aren’t enough human organs available. And that’s why there is excitement about a convergence of news on the use of pigs as a ready organ source. A team led by Muhammad Mohiuddin at the National Heart, Lung, and Blood Institute drew considerable attention after announcing at a conference late last month that pig hearts have kept six baboons alive for a period going on two years.

“The developments may instill a new ray of hope for thousands of patients waiting for human donor organs,” Mohiuddin told the Telegraph.

Stories about pig organs in baboons were in the news back in the 1990s, but problems related to rejection apparently slowed the work back then. While those concerns remain, another recent announcement of a deal between Synthetic Genomics, a company founded by Craig Venter, and United Therapeutics’ Lung Biotechnology to develop humanized pig organs brings more promising news. (Venter is most famous for his role in sequencing the first reference human genome.)

“The goal is to go in and edit, and where necessary, rewrite using our synthetic genomic tools, the pig genes that seem to be associated with immune responses,” Venter told Reuters in a story about the new research collaboration. “We want to get it so there is no acute or chronic rejection.”

While the whole idea still sounds a lot like science fiction, the basic notion of sourcing organs from other species goes way, way back, as described in “A brief history of cross-species organ transplantation,” written by David K.C. Cooper of the University of Pittsburgh. In the 1960s, chimpanzee kidneys and a heart were transplanted into people, without much success.

“With the advent of genetic engineering and cloning technologies, pigs are currently available with a number of different manipulations that protect their tissues from the human immune response, resulting in increasing pig graft survival in nonhuman primate models,” Cooper wrote in that 2012 historical review. “Genetically modified pigs offer hope of a limitless supply of organs and cells for those in need of a transplant.”

Of course, there is hope that stem cells might one day offer another ready source for new organs, without any fear of rejection. Discover magazine put “Scientists Make Progress in Growing Organs From Stem Cells” at No. 5 on its list of the top 100 stories of 2013, based in part on the transplantation of 5-millimeter human liver buds into mice.

A human would need many thousands of those buds, according to the lead researcher of that work, and getting there successfully could take awhile. Clinical trials of humanized pig organs are likely still a ways off, too. But, with these latest advances, it looks like there’s reason for hope.