US scientists at biotech company Stemagen Corporation in La Jolla, California, allege they made the first cloned human embryos using DNA extracted from skin cells. This is not a very important advance in the field, because they did not manage to extract stem cell lines.

Infamous Korean scientist Hwang Woo-suk claimed a few years ago that he created such stem cell lines, but it was later proven he forged the research.

"We're the first in the world to take adult human cells and then document that in fact we were able to clone embryos from them," lead researcher Dr Samuel Wood told BBC News.

This small advance in the cloning field is basically technical. The other approach to obtaining stem cells, the so-called nuclear reprogramming technique, is much more interesting in the long term. While "therapeutic" cloning produces stem cells, the technology involves the creation and destruction of embryos, which is ethically unsound. The stem cells created also run the high risk of being rejected by the recipient's body. In turn, nuclear reprogramming, creates stem-like cells from the patient's own cells, avoiding both medical and ethical problems.

Researchers in Japan and the US were able to successfully "rewind" adult cells back to their embryonic state using the nuclear reprogramming technique. However, it will take many years for the process to be deemed safe for actual use of the resulting stem cells in humans.

Two research groups managed to obtain stem cells without the ethical problems posed by destroying human embryos. Through different techniques, they managed to turn human skin cells into cvasi-stem cells which appear to be pluripotent, having theoretically the ability to develop into any cell type.

Both experiments essentially replaced four genes in adult cells to make them behave like they were still embryonic stem cells. The two teams used viruses to force these genes into the cells' DNA and reprogram them. These results which used human tissue are a big step up from similar breakthroughs in mice, separately reported last summer by Dr. Yamanaka's group and two other research teams in the U.S.

Dolly's cloner also endorsed this technique and declared last year he abandoned human cloning in favor of nuclear reprogramming.

In November last year, researchers at the Oregon Health & Science University have created for the first time cloned embryos of monkeys from which they extracted stem cells. Despite the apparent success, the technique had a very high rate of failure: of 304 eggs from 14 rhesus macaque monkeys, only two stem cell lines resulted.