To clone or not to clone?
Recent medical advances have led to a situation in which the demand for tissues and organs for transplantation is outstripping supply. There is therefore considerable interest in xenotransplantation, in which suitable animals (such as pigs) might provide tissue for transplantation into humans.
Although xenotransplantation is attractive in principle, it raises issues of ethics and safety. This week's issue of Nature [Vol. 406, Issue 6797, August 17, 2000] includes an editorial and a brief news item addressing some of the safety questions posed by current scientific work in the area. Two research papers linked to the debate are also being released in electronic form, and will appear in a future printed edition of the journal.
In one paper, Alan Colman and colleagues, from PPL Therapeutics, report the generation of a litter of five female pigs cloned from cultured cells by a new 'double nuclear transfer' procedure. [Cloned pigs produced by nuclear transfer from adult somatic cells. IRINA A. POLEJAEVA, SHU-HUNG CHEN, TODD D. VAUGHT, RAY L. PAGE, JUNE MULLINS, SUYAPA BALL, SHAWN WALKER, DAVE L. AYARES, ALAN COLMAN & KEITH H. S. CAMPBELL.]
In the future, this should allow the production of pigs that have been genetically engineered so that their organs may evade rejection by the human immune system.
Meanwhile, Daniel Salomon from the Scripps Institute in La Jolla, California, and co-workers elsewhere, describe work on the 50 or so 'porcine endogenous retroviruses' (PERVs) which are found in pigs. [Infection by porcine endogenous retrovirus after islet xenotransplantation in SCID mice. LUC J.W. VAN DER LAAN, CHRISTOPHER LOCKEY, BRADLEY C. GRIFFETH, FRANCINE S. FRASIER, CAROLYN A. WILSON, DAVID E. ONIONS, BERNHARD J. HERING, ZHIFENG LONG, EDWARD OTTO, BRUCE E. TORBETT & DANIEL R. SALOMON.]
PERVs have not been found to be pathogenic to date, but related viruses are associated with leukaemia in other species. Salomon and colleagues show that PERVs can infect isolated human cells. When pig pancreatic cells are transplanted into immunodeficient mice, moreover, the viruses are found to be active and can infect various mouse tissues away from the site of transplantation.
These studies indicate that rapid progress is being made towards the goal of making xenotransplantation of pig tissue into human subjects feasible. At the same time, however, while PERVs have not been shown to infect human subjects, their spread in a mouse suggests that concerns about the safety of xenotransplantation in humans may be justified.
The trials of xenotransplantation.
While some researchers report progress towards the goal of producing pig organs for human transplantation, others have revealed new causes for worry about the potential consequences. For Full Text, click here.
Roslin backs off pig organ work [LONDON]. The future of efforts at the Roslin Institute in Edinburgh to create transgenic pigs as a source of organs for transplant to humans appears to be in doubt.
For Full Text, click here.
The Campbell et al., and Salomon et al. letters will be published in a future issue of Nature. In the meantime, please cite these papers as "In press" until full publication details are available.
(C) Nature press release.
Message posted by: Trevor M. D'Souza