Cloned Pigs Open Possibility of Organ Farms. Two scientific studies published this week report success with cloning pigs in different ways. Interest in this effort has been spurred by the potential it presents for a source of organs for human transplant, given pigs’ similarities in size and physiology with humans. Perhaps genetic engineering could create a strain of pig whose tissues lacks factors that so far stimulate rejection.

Yet another study raises alarm about this prospect. Apparently, all pig cells are infected with endogenous retroviruses which, it is revealed, might infect human cells via transplanted tissue — these porcine endogenous retroviruses (PERVs) were recently shown to infect immunocompromised mice which received porcine grafts. Although the mice infected with the PERVs did not become ill in any way, recall that many recently emerging devastating human diseases including HIV have arisen through cross-species jumps. Viruses tolerated in one species and co-existing with their hosts can cause devastating illness in an alien species; the major protection appears to be the relative improbability of the cross-species infection. Is this a bridge we want to be building, especially given that human recipients are highly immunosuppressed to prevent transplant rejection and thus present no resistance to colonization with the alien virus? Many months ago, I posted a blink to the Campaign for Responsible Transplantation, which has raised exactly these concerns. The new study is empirical evidence that their worries are well-founded.