By Jennifer Stastny
In February this year, a South Korean research team led by Dr Wook Suk Hwang made medical history by announcing that they had successfully used nuclear transfer - the same process used to create Dolly the sheep in 1996 - to generate 30 human embryos. It was the first confirmed report of human cloning.
It's hard to exaggerate the importance of this announcement. For one thing, it confirmed the practicability of nuclear transfer, which involves removing the nucleus of an egg and replacing it with one from a live donor cell before jolting it to life with electricity. The process, it was clear, could be used on humans as well as sheep. For better or worse, the announcement also opened the door to therapeutic cloning, in which the resulting embryo is not implanted into a womb, but harvested for stem cells.
And harvest the Koreans did. When the embryos were five or six days old, at which time they consisted of about 200 cells each and became known as blastocysts, Hwang and his team sucked out their stem cells, destroying them in the process. Transferring the stem cells into petri dishes, the researchers then exposed them to various chemical and electrical stimuli, coaxing them to form ectoderm, mesoderm and endoderm cell layers. These layers have the capacity to further differentiate into, respectively, the skin and nerves; the internal organs, blood and bones; and the linings of the respiratory and digestive tracts.
Again, this was an important step for medical science, being the first time cloned human stem cells had differentiated in laboratory conditions. Four years ago, scientists working on non-cloned human stem cells managed to further differentiate these three layers into functional neurons and beating cardiac muscles. Not quite a fully functional test-tube organ, perhaps, but nonetheless healthy tissue of the kind that is being used in international clinical trials to treat ailments such as Parkinson's disease.
Embryonic stem cells are the closest thing to immortal that human tissue can be. Unlike muscle or nerve cells, which don't usually replicate, embryonic stem cells can divide and renew themselves almost indefinitely. They also have unlimited potential: being the most basic, undifferentiated cells in the human body, they can grow into anything from kidneys to corneas.
Learning how to provide the correct catalysts at the correct times to steer this differentiation predictably is the fundamental aim of therapeutic cloning and stem-cell research. "The simpler the tissue, the more likely we will be able to engineer it," says Professor Sue Kidson, a molecular biologist with the University of Cape Town.
"There are still, however, many years of research ahead to deal with the basic science questions, such as how the cell lines differ, how to induce them and how to put them back in the body so that they become part of the cellular architecture."
Although stem cell research is by no means new, obtaining the cells from cloned human embryos is. Stem cells are found in a variety of human tissue. For years, researchers worked almost exclusively on stem cells sourced from umbilical-cord blood after birth or adult tissues, particularly the bone marrow. So why, with an alternative source, should therapeutic cloning be permitted?
Because not all stem cells are created equal, it seems. Adult and umbilical-cord stem cells are only found in small quantities and are not as flexible, or "plastic", as embryonic stem cells. Whereas the latter can differentiate into any kind of tissue, bone marrow stem cells, for example, can only be cultivated into fat, bone, cartilage, nerve tissue or muscle.
Another source of stem cells are "spare" embryos produced during in vitro fertilisation. These stem cells certainly are created equal. Being embryonic, they are able to differentiate into any of the 200 tissue types in the human body. The drawback is they have their own DNA, raising the problem of tissue rejection if ever they are used in clinical trials.
Add to this the fact that researchers will need to obtain permission from each and every couple undergoing in vitro fertilisation, and there is little to commend IVF embryos above those formed by therapeutic cloning.
So science is left with cloning as the preferred source of stem cells, as ethically dubious as it is to create an embryo for the sole purpose of destroying it five days later. Indeed, deciding whether or not to allow therapeutic cloning has proven to be a difficult call for any country.
Although South Africa's Human Tissues Act currently prohibits any form of cloning, the pending National Health Bill, which should be passed soon and will repeal the Human Tissues Act, permits therapeutic cloning under strict guidelines.
Professor Ames Dhai, the head of Bioethics, Medical Law and Research Ethics at the University of KwaZulu-Natal, is part of the group of lawyers and scientists that have been asked to specify these guidelines. One of the group's main concerns has been determining when an embryo starts feeling pain.
"The National Health Bill prevents stem cells from being harvested from embryos older than 14 days because at day 14 the embryo shows the first sign of neuronal development," explains Professor Dhai. "So, although embryos and foetuses have no rights under South African law until they are born, the Bill errs on the side of caution when it comes to stem-cell research."
Does this make it more acceptable to create an embryo, knowing that you plan to destroy it? It does, says Professor Dhai. "Historically, sacrifice of developing human life has been accepted to benefit others," she argues in an article she co-authored.
In obstetrics, for example, it's common practice to deliver a baby prematurely, despite a good chance that it will die, if the pregnancy is causing life-threatening hypertension in the mother. And in cases of multiple foetuses, it's all right to kill off some of the foetuses to optimise the chance of survival of the others.
Of greater legal concern to the group than the embryo's legal rights are those of the women who donate their egg cells, or oocytes (pronounced oh-uh-sites). To create 30 blastocytes, the Korean team went through 242 oocytes from 16 female volunteers. That's a lot of broken eggs, especially if you consider the health risks to the women whose eggs were harvested.
It's no fun donating an oocyte. Because a woman can only produce one egg per menstrual cycle, donors are put on special hormones to speed things up.
This hormonal treatment can, if left unmonitored, cause serious imbalances leading to hyperstimulation syndrome and, in severe cases, death. Then comes the actual harvesting of the egg, which involves inserting a wide-bore needle into the vagina and aspirating the oocyte directly from the ovaries. If done repeatedly, egg aspiration may leave ovarian scar tissue that could impair future fertility.
Because of these dangers, Professor Dhai believes it is of the utmost importance to outline stringent procedures for harvesting oocytes, including the close monitoring of stimulated cycles, full disclosure of the risks to the donor, and - perhaps most importantly - prohibiting commercial trade in egg cells.
"Women should donate their oocytes out of a sense of altruism or because it will benefit them directly, for example, if their eggs will be used for therapeutic cloning to treat a condition they themselves have. They should not be given improper financial incentives," she argues.
Professor Udo Schuklenk, the head of bioethics at Wits University's faculty of health sciences, disagrees. As long as the egg harvesting is well monitored and done under the strictest clinical standards, he feels it is safer than most daily activities and bordering on undue paternalism to prevent needy women from selling their oocytes. "The reality is that most of these women could use this money to buy much-needed food, shelter and medical attention," he writes in a past issue of the South African Medical Journal.
"Assuming that most potential volunteers are rational agents who can make decisions on their own, why should the government endorse paternalistic legislation that decides for them, effectively mandating the closure of a financial opportunity that would otherwise benefit them greatly?"
It is difficult to believe that desperate people are necessarily rational agents. Arguably, it is basic human nature to ignore inconvenient facts if motivated by financial reward: just look at the contestants on the reality television show Survivor, who risk malnutrition and miscellaneous ailments for a million measly dollars.
Similarly, an unemployed woman with children to feed and clothe may well be tempted to sell her eggs, time and again, until the damage is irreversible. As it stands, the National Health Bill will probably not allow trade in oocytes or stem cells, or their import or export, for that matter. (This is probably to prevent exploitation by countries like Germany, where it is illegal to extract stem cells from embryos, but legal - and explicitly encouraged - to import them.)
Despite this divergence of opinion, Schuklenk and Dhai do agree on one thing: that South Africa can't afford to be left behind when it comes to therapeutic cloning and stem-cell research.
Not only will legalising therapeutic cloning be of possible benefit to South Africans living with debilitating or terminal diseases when the research starts paying off, they argue, but it will also lead to an influx of research funding and a reverse brain drain as international scientists eager to work in the field emigrate to South Africa.
But isn't therapeutic cloning just the first step on a slippery slope to reproductive cloning? Probably not. Reproductive cloning carries high levels of genetic mutation and tumour growth. Despite the much-heralded successes in animal reproductive cloning, the complete procedure, including the gestation process, has a very low success rate.
Indeed, it took 276 unsuccessful attempts to create Dolly the sheep. And cloned foetuses are usually much larger than average at birth, which could be risky for the mother. In all, there is good reason for the World Health Organisation to call reproductive cloning "ethically unacceptable" in humans. It has, however, received a warm welcome in the animal sciences.
On 19 April 2003, the North West Province became the birthplace of Africa's first cloned farm animal. Futhi the calf weighed 32 kilograms at birth and is the genetic duplicate of a cow that used to break records by producing 78 litres of milk a day.
Now nearly a year and a half old, Futhi is happily living out her days at the Embrio Plus Centre in Brits, waiting for the day when she will pit her milk-production skills against those of her prodigious donor cow.
The cloning procedure that was used to produce Futhi differed slightly from that used to create Dolly the sheep. Instead of replacing the nucleus of a single oocyte, two eggs were halved in such a way that their nuclei ended up in one half, whereas the other half contained only cytoplasm. These nucleus-free halves were then fused to create a single egg, into which the nucleus from the donor cow was introduced.
But why clone a cow when scientists have already successfully cloned sheep, goats, cats, mice, donkeys and pigs? "To see if we could. Why else?" jokes Dr Morné de la Rey of Embrio Plus.
Certainly, the centre has enjoyed little financial gain from the venture, since the low success rate of current methods makes reproductive cloning economically impractical. There may come a time, however, when the technology will be reliable enough to cost-effectively replicate exceptionally productive and invaluable livestock. When that happens, the Centre will be able to say it was the first in Africa.
Although not commercially viable, cloning could prove to be most useful in reviving the numbers of critically endangered species. It would certainly have been a useful tool in 1985, when conservationists had to take dramatic action to save North America's black-footed ferret from complete extinction.
With no time to lose, conservationists herded up the wild population, which had dwindled to 18, conducted tests to see which individuals were genetically related and instituted a captive breeding programme. Some breeding pairs got along like a house on fire, and for those that didn't, there was impregnation by the romantic means of artificial insemination. By 2000, the first group of ferrets were ready for reintroduction into the wild.
If reproductive cloning had been an option, the conservationists could also have bred those ferrets that were beyond their reproductive best to add genetic variety - that all-important aspect of species survival - to the population. It would have been even better if conservationists could have cloned ferrets using the DNA of animals from previous
generations, when the population was still large and genetically diverse. Unfortunately, there was neither the technology, initially, nor the live tissue samples from bygone generations to
do this.
In South Africa, the Endangered Wildlife Trust's Wildlife Biological Resource Centre is responsible for collecting and banking biological materials from indigenous species. "Our aim is to secure South Africa's genetic resources for the future," says Dr Paul Bartels, the head of the Resource Centre. To date, the Centre has collected tissues from nearly 30 local species; even common animals like lions and buffalo have been banked down in case disease, habitat destruction or the widespread use of toxins unexpectedly crashes their populations.
These banked tissues can be used for anything from research into animal diseases and migration patterns to, should the need arise, assisted reproduction techniques such as artificial insemination, in vitro fertilisation and, of course, cloning. "Cloning is, theoretically, the only way to bring back biodiversity in a critically low population," says Dr Bartels. "If you banked tissues from a big group of animals 20 years ago, the (genetic) diversity that you thought you lost could be revived."
Cloning is especially useful because ooctyes don't freeze well. "If you were in a situation where you wanted to introduce new genetic material into an animal population, you would in all likelihood have to use a fresh oocyte from one of the remaining females and frozen sperm, which means you would only get half a complement of new genes," explains Bartels. "With cloning, however, you don't need to use an oocyte from the endangered species; you can use one from a closely related animal." So if you are trying to clone a bontebok, for example, you could use the denucleated oocyte of a blesbok and still end up with a genetically complete bontebok.
Interestingly, although cloning is by no means a perfect science - "we're still at the infancy of cloning," says Dr Bartels, with a knack for the unintended pun - neither is in vitro fertilisation. "Each animal has a specific protocol that must be followed with in vitro fertilisation, and we haven't yet worked out the protocols for all species," he explains. "Cloning is in many ways easier because it shortcuts the fertilisation stage and goes straight into embryo development."
As for resurrecting species that are already extinct by cloning them from a scrap of hair or bone, it simply isn't plausible since nuclear transfer requires a live nucleus from a live cell. When a cell dies, the DNA soon degenerates, and until we can figure out how to piece this DNA back together we won't be able to use it for cloning, let alone identification of the animal.
"Besides, even if you did manage to reconstruct the DNA, you wouldn't be recreating the same animal, you'd be making a new one," warns Dr De la Rey. "It's probably a better idea to bank animal tissues, before it's too late."
- This article orignally appeared in the July 2004 issue of the South African edition of Popular Mechanics magazine.