BERLIN, April 13 (Xinhua) -- German researchers announced Friday that they have turned stem cells taken from human bone marrow into primitive sperm cells in a first step towards creating artificial sperm cells.

If researchers succeeded in turning the primitive sperm cells into mature sperm, it could provide new and better treatments for infertility.

A team led by Dr. Karim Nayernia at the University of Gottingenin Germany reported that they obtained the bone marrow stem cells from four adult men who were about to undergo bone marrow transplants. The researchers mixed these cells with proteins that promote cell growth and vitamin A, which appears to play an important role in sperm development. This mixture converted the cells into sperm stem cells, called spermatogonium cells.

Sperm stem cells are normally found in the testes, where they divide to help provide a continuous supply of sperm. Nayernia said his ongoing experiments have suggested that sperm cells derived from the bone stem cells of mice can undergo the first two of three divisions necessary to become mature sperm capable of fertilizing eggs. He said that his team would work to achieve all the necessary divisions in mice before trying similar manipulations with human cells.

According to Nayernia, developing the spermatogonial stem cells into mature sperm in the laboratory should take around three to five years of experiments.

Some experts, however, cautioned that turning sperm stem cells derived from bone marrow into functioning sperm would be extremely challenging, so it is premature to talk about a new form of infertility treatment.

Stem cell biologist Harry Moore at the University of Sheffield in Britain has expressed the worry that sperm created from bone stem cells could have undetectable abnormalities that could cause disease in offspring.