A cow implanted with cells taken from a cloned embryo didn´t reject the tissue, showing the potential of much-debated therapeutic cloning, researchers say. Some scientists who oppose cloning humans say they believe therapeutic cloning should be pursued because it could supply healthy new tissue to fix a variety of illnesses. Doctor Anthony Atala, director of tissue engineering at Children´s Hospital Boston, co-authored the cow embryo study published in the June issue of Nature Biotechnology. He says more works needs to be done, but therapeutic cloning method shows potential. Cloning technology is controversial and opposed by many, including President Bush and Pope John Paul II, because it requires creating and destroying embryos.