British scientists said on Wednesday that they created human sperm from embryonic stem cells for the first time, an accomplishment they say may someday help infertile men father children. The technique could in 10 years allow researchers to use the basic knowledge of how sperm develop to design treatments to enable infertile men the chance to have biological children, said lead researcher Karim Nayernia, of Newcastle University, whose team earlier produced baby mice from sperm derived in a similar way. The research, published in the journal Stem Cells and Development, was conducted by scientists at Newcastle and the NorthEast England Stem Cell Institute. Stem cells can become any cell in the body, and scientists have previously turned them into a variety of new entities, including cells from the brain, pancreas, heart and blood vessels. Some experts challenged the research, saying they weren't convinced Nayernia and his colleagues had actually produced sperm cells. Several critics also said the sperm cells they created were clearly abnormal. "I am unconvinced from the data presented in this paper that the cells produced by Professor Nayernia's group from embryonic stem cells can be accurately called 'spermatazoa," said Allan Pacey, a senior lecturer in andrology at the University of Sheffield. Pacey said in a statement that the sperm created by Nayernia did not have the specific shape, movement and function of real sperm. Azim Surani, a professor of physiology and reproduction at the University of Cambridge said the sperm produced by the Newcastle team were "a long way from being authentic sperm cells." Nayernia said the cells "showed all the characteristics of sperm," but his group's intention was simply to "open up new avenues of research" with their early findings, rather than using the sperm to fertilize eggs. Robin Lovell-Badge, a stem cell expert at the National Institute of Medical Research said that despite the questions raised, Nayernia and colleagues may have made some progress in obtaining human sperm from embryonic cells. Nayernia said creating embryos from lab-manufactured sperm is banned by British law. He said they only plan to produce sperm to study the reasons behind infertility, and will not fertilize any eggs. Some lawmakers said provisions should be made to allow sperm derived from stem cells to be tested as part of potential fertility treatments.