New York, Mar 4 (IANS): Scientists have discovered a new kind of stem cell -- one that could lead to advances in regenerative medicine as well as offer new ways to study birth defects and other reproductive problems.

The researchers unearthed the new cells - induced XEN cells, or iXEN - in a cellular trash pile, of sorts.

"Other scientists may have seen these cells before, but they were considered to be defective, or cancer-like," said study lead author Tony Parenti from Michigan State University in the US.

"Rather than ignore these cells that have been mislabelled as waste byproducts, we found gold in the garbage," Parenti noted.

The findings were reported in the journal Stem Cell Reports.

A great deal of stem cell research focuses on new ways to make and use pluripotent stem cells that can be created by reactivating embryonic genes to "reprogramme" mature adult cells.

The embryo produces not only pluripotent stem cells, or iPS cells, but also XEN cells, a stem cell type with unique properties. While pluripotent stem cells produce cells in the body, XEN cells produce extraembryonic tissues that play an essential but indirect role in fetal development.

Parenti and his team speculated that if the embryo produces both pluripotent and XEN cells, this might also occur during reprogramming.

The eureka moment came when Parenti discovered colonies of iXEN cells popping up like weeds in his iPS cell cultures.

Using mice models, the team spent six months proving that these genetic weeds are not cancer-like, as previously suspected, but in fact, a new kind of stem cell with desirable properties.

Even more surprising, the team found that by inhibiting expression of XEN genes during reprogramming, they could decrease production of iXEN cells and increase production of iPS cells.

The next steps of this research will involve seeing if this process occurs in human cells.