For the first time, a team of scientists say they have successfully converted human skin cells into embryonic stem cells, a move that could help quiet the ethical debate surrounding stem cell research.

Researchers at Oregon Health & Science University say they were able to implant the nucleus from a skin cell into a donated human egg cell with its nucleus removed, creating an embryo-like cell that has the genetic makeup of the patient who donated the skin cell.

Since 2007, scientists have had successes with the procedure using monkeys and other mammals but not with human subjects.

"Every species is a little different biologically," says Shoukrat Mitalipov, lead author of the study, which was published Wednesday in Cell. "We've been using a good model in primates, but we've now finally been able to optimize it in humans."

The embryonic stem cells created by Mitalipov can be differentiated into many types of human cell, including nerve cells, liver cells and heart cells. Scientists have suggested that stem cells may one day be used to treat brain and nerve damage and diseases such as Parkinson's and multiple sclerosis.

Mitalipov's method has several benefits over using standard embryonic stem cells, which are created from fertilized eggs: Because the cells contain a patient's genetic material, the body is unlikely to reject the cells after implantation. The method also only uses a donor egg instead of a donor embryo, which some anti-abortion advocates may be more willing to tolerate ethically.

During monkey trials of the process, the team attempted to implant the newly-created embryo-like cells into a female monkey to see if it'd lead to a viable pregnancy.

"We never tried that in humans and it's not our intention," he says. "But in monkeys we wanted to see if the embryo was viable, but it wasn't. It's unlikely the technique we described could be used for cloning."

Though Mitalipov is hopeful that his new method will be more palatable for people ethically opposed to embryonic stem cell research, he says it might raise new concerns.

"We believe there are big differences in the methods. We're not destroying fertilized embryos," he says. "We think it's more ethically acceptable, but you never know. Some people my say now they're trying to use cloned embryos."

There have been several recent breakthroughs in cell conversions. Last month, researchers in California were able to use stem cells taken from an adult human's bone marrow and turn them into brain cells. But many scientists agree that embryonic stem cells are likely the best cells to use for therapies because they are "fresher" than adult stem cells.

When using adult stem cells, Mitalipov says that newly-created cells still contain some signs of aging that have built up in a cell's mitochondria, or power center.

"If you take a cell from a 90-year-old patient, its battery is kind of drained. You could make new cells by reprogramming it, but the energy is gone," he says. "The idea behind using egg cells is that you're fully recharging the battery and making cells that could probably live another 90 years. We're taking you back to having young cells."