Scientists in Britain claimed a first Tuesday, saying they have created a human embryo using DNA from one man and two women, which they say could help provide treatment for genetic diseases.
Researchers from Newcastle University in northeast England used 10 embryos which were unsuitable for in vitro fertilisation (IVF), and replaced faulty mitochondria cells from the mother with undamaged cells from a female donor.
The research was disclosed last week in parliament's upper House of Lords but has not yet been published officially in scientific journals, the university said Tuesday.
The embryos were developed for five days and the transplant on one of them was deemed a success.
Mitochondria play a vital role in the body's energy supply. However, if they are damaged they can cause a series of serious neuro-muscular diseases, liver failure, blindness, deafness or strokes.
"The research aims to tackle and prevent a group of relatively uncommon but really severe diseases which affect the nervous system and muscles," said Professor Patrick Chinnery, a Newcastle University neurogenetic expert.
"Ultimately in many ... cases they are fatal and there is no treatment. The aim is to develop ways of preventing them from being passed on from the mother to her offspring."
In five to 10 years' time, transplanting "good" mitochondria could be done within days of a routine IVF, he said.
The baby would only inherit the mother and father's characteristics, as the transplanted mitochondria from the donor would not have any effect on the child's personality or appearance, the scientists said.
Josephine Quintavelle, of the pro-life group Comment on Reproductive Ethics, said: "We should not be messing around with the building blocks of life.
"To experiment on a human child in this way is absolutely unforgivable."