The Economist

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(May 25, 2005) -- The past week saw more progress in the study of human stem cells, bringing closer the day when replacement tissues -- and perhaps even entire organs -- can be grown in laboratories for patients who need them. But such research remains controversial -- so much so that President George Bush has promised to veto a bill, passed this week by the House of Representatives, which increases government funding for stem cells.

AMERICA'S loss is South Korea's gain. Unlike many Americans, up to and including the president, Korean scientists -- and the authorities that support them -- do not wring their hands in agony about experimenting on tiny clusters of cells that might, in other circumstances, grow into people. They just get on with it. The latest paper in the field, published last week in SCIENCE, has 25 authors. They were led by Woo Suk Hwang of Seoul National University, and all but two of them work in South Korea.

The tiny clusters of cells in question are known as blastocysts. A blastocyst is the precursor to an embryo. It contains a number of so-called stem cells that are capable of differentiating into many different types of tissue. Optimists hope stem cells might be used to generate replacement tissues -- and even entire organs -- for those who have lost their originals to disease. But not just any old stem cells. Using stem cells derived by cloning from the very patients who need the transplants might get around the problem of rejection by the immune system that bedevils transplant techniques at the moment.

This hope, combined with the ethical fears about such research that some people have and -- inevitably -- the suggestion that cloning blastocysts might lead to cloned people, meant that when Dr. Hwang published a paper last year describing the creation of the first cloned human blastocyst, the announcement was accompanied by a lot of excitable comment in the media and denunciations from anti-cloning quarters. Opposition to such research remains strong, and President George Bush has pledged to veto a bill, passed this week by the House of Representatives, which increases government funding for the study of embryonic stem cells.

Dr. Hwang's paper of last year, however, was merely a proof of principle (and a proof that has been contested by some other researchers). Last week's paper addresses the concerns of the sceptics who questioned whether Dr. Hwang had actually cloned anything, rather than simply stimulated unfertilised eggs to start dividing and growing by themselves (a process known as parthenogenesis). It also moves things on a little towards the point where the technique might be useful.

EMBRYONIC IDEAS

Clones come in many varieties. Some, such as identical twins, are formed when an embryo divides. Others, such as plant cuttings, start with part of an adult. The form of cloning Dr. Hwang uses is known as nuclear transfer. This involves taking the nucleus out of an unfertilised egg and replacing it with one from an adult cell.

The reason for this convoluted procedure is that adult mammal cells are set in their ways. Once they have specialised into a particular type of tissue (skin, muscle or whatever), they cannot easily be induced to go backwards. But the isolated nuclei of such cells can sometimes be persuaded to revert by exposing them to the inside of an egg. In effect, this creates a fertilised egg without going through the process of fertilisation. This egg, though, has the same genetic complement as the adult from which the nucleus came. Anything that grows from it is thus a clone.

In last year's paper, Dr. Hwang described transplanting human nuclei this way, but only from the adult cells of the women who provided the eggs. Such "auto-cloning" would be of limited therapeutic use. The main advance reported in the new paper is therefore that human nuclear-transfer cloning works whether or not the nucleus donor and the egg donor are the same person.

At least as important for half of humanity is that it works even when the two individuals are of opposite sexes. Nor does age appear to be a factor. Nuclei from people as young as two, and as old as 56, were successfully transplanted. And in a move that might spike the guns of some critics of the ethics of the whole procedure, all of the nuclear donors suffer from conditions such as diabetes and spinal-cord injuries that successful cloning might help to treat.

Altogether, Dr. Hwang and his colleagues managed to create 31 cloned blastocysts, and to establish 11 self-perpetuating cultures (known as cell lines) from stem cells they extracted from these blastocysts. By combining nuclei and eggs from different people, they showed that the eggs were not merely dividing and growing by themselves with a bit of prodding. And they also managed to grow their blastocysts and cell lines on so-called feeder cells derived from humans, rather than relying on mouse feeder cells as they had done previously. That will make the cloned stem cells safer to use by eliminating the risk of transferring mouse viruses to patients.

That there is still a long road from this work to transplantable tissues is denied by no one. But Dr. Hwang and his team are striding boldly down it. Who will follow in their footsteps remains to be seen.