The International Society for Stem Cell Research has published guidelines for human embryonic stem cell research in the latest edition of the U.S. magazine “Science.”

The guidelines stipulate that research lacking an evident scientific basis or raising ethical controversies like human cloning, must not be allowed.

They also ban crossbreeding between humans and animals, and research activities using embryos more than two weeks' old.

With regard to human egg donation, the guidelines require researchers to compensate donors only for direct costs like medical expenses incurred in egg collection. According to the new rules, stem cell researchers must receive written consent from egg or sperm donors.