All lines of human embryonic stem cells approved for research by the federal government are useless for medical treatments, according to a recent study published in the journal Nature Medicine.

Embryonic stem cells are harvested from fertilized eggs and can be used to make many different tissues in the human body. Because of their versatility, scientists hope to use them to treat various health conditions.

An animal protein found in the 22 lines approved for research and not normally found in human cells could be recognized as foreign and attacked by human antibodies, according to the study.

The lines have, until recently, been grown with the help of “feeder layers” of animal cells that support the growth of human cells. As a result, the lines express an animal protein not normally found in human cells, the study said.

Dan Kaufman, professor of medicine and faculty member at the University’s Stem Cell Institute, said the results are “somewhat expected” but had not been formally proven before.

Despite what the study found, Kaufman said he has heard officials from the Food and Drug Administration say growing existing human embryonic stem cell lines with animal cells does not make them completely ineligible for clinical trials.

He said researchers could have an easier time working with the human cells if they knew what could contaminate them.

The University receives federal and private funding to finance its stem cell research. Kaufman said scientists might have to seek more private funds if the approved lines present problems.

“This type of study brings up reasons to explore deriving new cell lines,” he said. “And that would have to be privately funded.”

Tony Kriesel, Pro-Life Law Society president, said he has been “uncomfortable” with the federally approved lines.

While he supports adult stem cell research, Kriesel said, he disapproves of embryonic stem cell research.

“Embryonic stem cell research has effectively done nothing for treating any human diseases,” he said.