Dr Zavos claimed in an interview with The Independent that he had created 14 cloned human embryos and transferred 11 of them into the wombs of the four women, who wanted to give birth to cloned babies, although none of them had become pregnant.
Leading figures in the fertility world, including Lord Winston of Imperial College London, poured scorn on Dr Zavos's claims, saying he had not produced any scientific evidence to support his statements, which critics said can only be done by publishing the work in a peer-reviewed scientific journal.
"I do not know of any credible evidence that suggests Dr Zavos can clone a human being. This seems to be yet another one of his claims to get publicity," said Lord Winston, who was the head of a fertility clinic at Hammersmith Hospital in London.
Alastair Kent, director of the Genetic Interest Group, a charity dedicated to helping families affected with inherited disorders, said that Dr Zavos claimed to have mastered a technology that other scientists had been struggling with for years.
"Once again he claims to have used it for purposes widely condemned as unsafe and dangerous. And he has done this in secret, using the hopes of couples desperate to create or to recreate a child as a springboard for his vaulting ambition," he said.
"For his claims to have credibility, and to prevent the unethical exploitation of grieving or desperate couples Dr Zavos must throw open his work to peer review. He must demonstrate openness and allow scrutiny by experts, not just by the media. If he is as good as he claims then he has nothing to fear. If he is not, then vulnerable women and couples need protection from his activities," Dr Kent said.
Dr Zavos also revealed that he has created human-animal "hybrid" clones by fusing the cells of dead people with the empty egg cells of cows. These hybrid embryos were created to study the cloning process, rather than being used for embryo transfer, Dr Zavos said.
Professor Azim Surani of the University of Cambridge said that Dr Zavos had breached the taboo on creating human clones with the intention of transferring them into the wombs of women in order to achieve a pregnancy – a procedure that is a criminal offence in Britain.
"This affair shows a complete lack of responsibility. If true, Zavos has again failed to observe the universally-accepted ban on human cloning, which was agreed because most of the resulting embryos from such animal experiments are abnormal," Professor Surani said.
"This is yet another episode designed to gain maximum publicity without performing rigorous animal experiments or presenting it for peer review in a scientific journal. He has the opportunity to do this for his claim on making animal-human hybrid embryos in culture," he said.
Dr Zavos said that much of his work has in fact been published in peer-reviewed journals but that some publications have rejected his manuscripts out of hand because it is their editorial policy not to publish what they say are illegal and unethical attempts at human reproductive cloning.
In support of his claims, an independent documentary-maker, Peter Williams, has been filming Dr Zavos's cloning attempts over the past six years. The documentary, broadcast last night on the Discovery Channel, showed human clones being created in a secret laboratory outside Europe and interviews with couples who were willing to have them transferred to the womb.
"The interesting thing here is that for the first time these cloning attempts appear to have been documented," said Professor Wolf Reik, an expert in reproductive biology at the Babraham Institute in Cambridge, yesterday.
"We have no reason to think that human cloning will not work – it works in primates – but it may take many, many attempts.
"But to say it is substantially safer now, with new technical developments, is nonsense; the available techniques are still very inefficient, and the great majority of embryos die in utero, or are born with abnormalities. This is why, in my opinion, it remains problematical for it to be carried out on humans," Professor Reik added.
Dr Zavos: On ethics, his motives and technology
The doctor at the centre of the cloning row yesterday answered readers' questions on The Independent's website. This is a selection of his answers. To see the full exchanges go to www.independent.co.uk/pzavos
How do you justify the use of cloning technology in this way? For you, what is the ultimate goal and what drives your desire to clone people?
Zavos: I am a fertility doctor and I have been creating children to thousands of people for the last 30 years. I consider reproductive cloning as a modality to assist infertile couples to become parents via this technique. This is a very small group of people that have exhausted all possibilities of becoming parents via any other way. However, I am interested also in developing similar technologies in using embryonic stem cells that are derived from cloned embryos to treat a variety of diseases and possibly creating body parts in vitro but not creating human beings for spare parts. If all of those technologies are developed and applied properly this can make it a better world for all of us.
To what extent do you think people like yourself should be involved in ethical dialogue? Do you feel you should have a say in the process, or do you see yourself as simply providing a service which others have to deal with?
As a fertility doctor for 30 years I have assisted thousands of couples, straight, lesbian, gay and single, in becoming parents. During the consultation I assist those people to make the best decision as they attempt to become parents. I am definitely not the person to make the ultimate decision for them but advise them in the best possible way in using treatments. I do get involved in such ethical dialogues at all times but I cannot dictate to those people my feelings about their decisions.
Would you consider fertilising eggs with the genomes of two women?
This technology can only help 3 to 4 per cent of infertile couples that have exhausted all possibilities of having a child. Helping a distressed mother that missed her daughter is not very high on my agenda at the moment. As to me helping same-gender couples to have children, I do that every day via sexual reproduction. At the moment, the cloning technology cannot assist either two men or two women in having a biological child of their own. However, the future may allow us to do that. I remain optimistic.
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