Revisiting the pigs

By Massie Santos Ballon

MANILA, Philippines —- Five years ago, I wrote about the notion of using pigs as the organ donors for humans. Researchers in Europe and the United States were hyping this as a means of reducing the long lists of organ transplant patients around the world. Five years later, xenotransplantation doesn’t seem to have moved much beyond the realm of possibility into practical application.

“The experimental development of xenotransplantation has been slower than anticipated,” admitted David Cooper of the University of Pittsburgh’s Thomas E. Starzl Transplantation Institute and his colleagues in their recent review on the topic.

Making headlines

Though the idea had actually been around for a couple of decades, xenotransplantation didn’t really make headlines until 2002. At the time, a group of Scottish researchers at PPL Therapeutics (best known for their work on Dolly the sheep) had turned their attention to pigs. They introduced piglets that lacked a gene which would have made the human body reject the animal’s transplanted organ.

Not to be outdone, Novartis partially funded a biotech company in the United States that planned to offer organs from smaller pigs as better (sizewise) human matches.

Five years later, Novartis seems to have quietly shut down its spin-off project and PPL Therapeutics is gone. The Scottish company closed in 2004, and its American branch was bought out by a number of investors, among them the University of Pittsburgh Medical Center.

Research

Currently known as Revivicor, the company is still involved in xenotransplantation research, though this topic has faded once more from the public eye. Regular reports from stem cell researchers helped people forget about the pigs.

Fears about pig diseases being transferred to humans have been eclipsed by avian flu. And though organ donations from both the living and the dead have increased worldwide, there are still people selling their kidneys. (One memorable Inquirer article last year had Health Undersecretary Jade del Mundo protesting that Filipino donors were being “shortchanged,” receiving only P50,000 for their kidneys because of middlemen.) And there are still people dying while waiting for a transplant.

GT-Knockout pigs

The clinical trials for xenotransplantation didn’t happen two years ago as expected; that date has since shifted. Still, progress has been made. Pigs have been genetically engineered to remove the gene which would lead to immediate organ rejection in the event of a pig-to-human transplant.

Organs from these so-called GT-knockout pigs have been transplanted into baboons that survived for several months after. And, Cooper et al. note with satisfaction, while the baboons had medications to prevent organ rejection, the dosages were lower than expected.

Cooper et al.’s review in the July 15 issue of the journal Transplantation asked what the next step should be, and a few researchers gave their own opinions on the future of GT-knockout pigs in the same issue.

Genetic modifications

More genetic modifications are planned, but there is no consensus yet on what these will be. There were also concerns then about the safety of using animal organs in humans. Questions were raised about whether or not viruses could and/or would cross the species barrier.

Cooper et al. say that studies have somewhat alleviated some of those concerns. And, of course, there was the question of whether or not people would even consider, much less accept, having animal organs replace their own to stay alive. That may not be taken seriously until xenotransplantation becomes a viable alternative.

In short, xenotransplantation still remains something more sci-fi than scientific. Clinical trials might happen by 2012, but how long it would take from that moment to people being on a (possibly) shorter waiting list for a new heart, kidney, or liver is anyone’s guess. “The potential benefits… remain immense,” say Cooper et al. in closing. These are still pig promises waiting to be kept.

Copyright © 2007 Inquirer.

This article posted October 15, 2007.