Embryonic stem cells have been taken from a cloned human embryo for the first time, opening new doors and countless possibilities in regenerative medicine.

A team of international scientists have accomplished a medical first and possibly put us on our way to making new cells of any type, including heart, bone, and brain.

"We have now refined the steps to come up with a process for generating these cells that is pretty efficient,” head of the cell cloning study Shoukhrat Mitalipov said.

But the researchers are worried that the method in which they got the embryonic stem cells may be too controversial, difficult, and expensive.

"There is no one trick to making this work. It is like winning the lottery, all the numbers have to line up the right way to win,” Mitalipov said.

At first the study was perfected on monkeys before the team could move on to human donors. Women volunteers donated eggs for the scientists to implant chromosomes, taken from skin cells, into the eggs.

This causes the egg to start growing and dividing, thus creating a human embryo. The cells of the embryos were genetic copies of the cells of the three subjects who donated their skin cells. Human clones.

It marks the first time that cloned embryos made it past eight cells. In fact, they had hundreds of embryonic stem cells within them.

But where does this take the study ethically?

Dr. David King of the Human Genetics Alert campaign group is not so keen on the idea.

"Scientists have finally delivered the baby that would-be human cloners have been waiting for: a method for reliably creating cloned human embryos,” he said.

"This makes it imperative that we create an international legal ban on human cloning before any more research like this takes place. It is irresponsible in the extreme to have published this research."

The study was published in the journal Cell.