Scientists at the heart of one of the greatest scandals in modern science made a dramatic leap forward in stem cell research without realising it, an investigation into their work revealed yesterday. Hwang Woo-suk, a leading stem cell scientist, from South Korea, fell from grace last year when an official inquest found he had faked data on human cloning. The fraud severely dented hopes for treatments based on embryonic stem cells, which in principle can grow into any tissue in the body. But it appears he has inadvertently achieved a world first, according to researchers who studied his work.

Dr Hwang's team had succeeded in extracting stem cells from human eggs forced to undergo parthenogenesis, where eggs develop into early-stage embryos despite not being fertilised by sperm. The feat has been a much sought goal for stem cell scientists, since it paves the way for the creation of human tissues that are genetically identical to those of the egg donor. Replacement organ tissues or nerve fibres grown from a woman's stem cells could be used to treat serious diseases or injuries without fear of rejection from the immunity system of the recipient.

A team of experts, including researchers at Harvard and Cambridge universities, analysed stem cells created by Dr Hwang's group, and found that some stem cells must have come from an unfertilised human egg alone, and not from a cloned embryo as Dr Hwang originally claimed. Some animals, such as Komodo dragons and hammerhead sharks, can deliver healthy offspring via virgin births, the outcome of unfertilised eggs becoming embryos. Very rarely human eggs divide without being fertilised, but the embryos are flawed so rejected in the womb.

The latest study, led by George Daley at the Harvard Stem Cell Institute, clears up the mystery of how Dr Hwang's stem cells were created. Details of the study appear in the journal Cell Stem Cell. Dr Daley noted: "They might represent a favourable source for tissue replacement therapies."

Last month, a team of US and Russian researchers said they had derived embryonic stem cells from unfertilised eggs.

Miodrag Stojkovic, the professor who, in 2005, created Britain's first cloned human embryo, said stem cells from eggs could make a substantial impact on medicine. "They offer hope for patient-specific stem cells because they contain only the woman's DNA so are genetically identical to [her]," he said.