A Porcine Dolly

Two different research teams -- reporting in the current issue of the journals Science and Nature --have successfully cloned pigs.

One of the teams promises to produce an "ultimate pig" for human transplantation studies in 4 years. Even as these studies race off the press, a third report -- its publication also expedited by Nature -- finds that porcine endogenous retroviruses (PERV) can be transmitted across species. These viruses cause no disease in their host or, so far, in mice or men. But cause for concern comes from their close relation to other type C retroviruses that cause leukemia in various species -- and from the fact that another type of retrovirus, harmless in its original host species, causes AIDS in humans. Every cell in a pig's body carries some 50 copies of PERV. Even so, this does not necessarily mean the end of pig-organ transplantation. Indeed, PERV-infected mice remain as healthy as immunosuppressed animals can be. Needles to say that the jury is still out on using pigs as a granary for much need organs for transplant.