British scientists say they have taken human embryonic stem cells and turned them into sperm-like cells that have moving tails.
Researchers at Newcastle University and the NorthEast England Stem Cell Institute say the work is in its early stages and the end result, while containing all the essential qualities for creating life, is not perfect.
Newcastle research leader Karim Nayernia said in a statement Wednesday that the technique they used could some day help develop treatments for infertile couples, although current British law forbids the use of lab-created sperm or egg cells in fertility treatments.
Some U.K. experts say they are unconvinced by the research. They also say the cells created were clearly abnormal.
Dr. Allan Pacey, a sperm biologist from the University of Sheffield, told the BBC he did not think the sperm were fully developed.
"They are early sperm, but functional tests would be needed to know exactly what has been achieved," he said.
Nayernia acknowledged both the shape of the new cells and their movement were "not quite normal" and more investigation would be needed.
The team isolated stem cells that had XY chromosomes. The cells were permitted to undergo meiosis, a type of division, reducing the number of chromosomes in each cell by half. Though the genetic code of a human being is contained within 46 chromosomes, only half this number exists within the cell of a sperm or an egg.
Stem cells are immature cells that can develop into different cell types.
The results of the experiment were published in the Stem Cells and Development journal. Nayernia and his team say they hope their work can at least be used as an experimental model to study male infertility.