Cool accidental discovery of useful building blocks for science.

A great deal of stem cell research focuses on new ways to make and use pluripotent stem cells. Pluripotent stem cells can be created by reactivating embryonic genes to “reprogram” mature adult cells. Reprogramming mature cells into induced pluripotent stem cells, or iPS cells, allows them to become malleable building blocks that can morph into any cell in the body.

For example, if a patient has a defective liver, healthy cells could be taken from the patient, reprogrammed into iPS cells, which could then be used to help regenerate the person’s failing organ. Taking cells from the same patient may greatly reduce the chance of the body rejecting the new treatment, Parenti said.

Prior to the discovery of reprogramming, scientists developed pluripotent stem cells from embryos. However, the embryo produces not only pluripotent stem 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.