by ecancer reporter Janet Fricker

For the first time Spanish researchers report in ‘Nature’ that it is now possible to generate induced pluripotent stem cells (iPS cells) directly within tissues of a living organism (in vivo).

The landmark study suggests that selective laboratory culture conditions are no longer essential for reprogramming to pluripotency, and that the in vivo environment can substitute.

“We believe that in principal our approach has the advantage of not requiring the engraftment of cells from in vitro to in vivo which is usually a very inefficient process. Cells are already integrated into the tissue in the right position,” said Manuel Serrano, the senior author of the study, in a telephone press briefing.

In the study investigators from the Spanish National Research Center, Madrid, Spain, report that a ‘recipe’ of four defined factors (Oct4, Sox2, Klf4 and c-Myc) could be used to induce pluripotency in a variety of cell types within living mice.

These factors, added Serrano, were the exact same factors used by Shinya Yamanaka in his Nobel Prize winning work which generated iPS cells from adult mouse fibroblasts in vitro.

For the current study, the team generated mice carrying a drug-inducible ‘gene cassette’ of the four cell reprogrammable factors, with expression of transcription factors induced by adding the drug doxycycline to the animal’s drinking water.

After several weeks teratomas emerged in multiple organs.

Teratomas are a particular class of tumours that originate from pluripotent cells after a process of expansion and disorganized differentiation.

Their presence is seen as indicating reprogramming into full pluripotency.

Analyses of the stomach, intestine, pancreas and kidney furthermore revealed groups of dedifferentiated cells expressing the pluripotency marker NANOG.

“These observations support the concept that reprogramming occurs in situ,” wrote the authors.

The team went on to show that iPS cells could be isolated from the blood of reprogrammable mice.

In two out of a total of 77 induced reprogrammable mice, the presence of small cysts in the thoracic and abdominal cavities were found, which were shown to be ‘embryo like’ structures.

Additionally, in a small number of cases intraperitoneal injections of the in vivo iPS cells into wild type mice generated embryo like structures, containing an ectoderm, mesoderm, and endoderm.

No such structures could be indentified in wild type mice injected with in vivo iPS cells.

The in vivo structures were surprisingly sophisticated and even had yolk sacs with markers associated with blood formation. “Although not totipotent, the cells had features of totipotency and we have to work to see if we can find the right conditions to achieve totipotency,” said Serrano.

From such observations the investigators believe that in vivo reprogramming fixes iPS cells in a ‘more pristine, totipotent’ state, than in vitro derived cells.

In an accompanying editorial, Alejandros De Los Angeles and George Daley, from the Dana Farber Cancer Institute, write, “The growing parallels between reprogramming and regeneration should inspire the application of reprogramming technologies in living organisms for regenerative ends.”

Serrano stressed that in any eventual human trials safety will be an issue.

“Pluripotent cells have the potential to produce teratomas, which is obviously not a desirable effect in patients. For in vivo reprogramming we have to find the conditions that are sufficient to improve regeneration without producing tumours,” he said.

The reprogrammable mice, Serrano added, will be available to the scientific community so that experts in different fields, organs and regeneration processes can explore the therapeutic possibilities of these models in greater.

Reference

M Abad, L Mosteiro, C Pantoja, et al. Reprogramming in vivo produces teratomas and iPS cells with totipotency features. Nature. Doi:10.1038/nature12586

A De Los Angeles, G Daley. Reprogramming in situ. Nature doi:101.1038/nature 12559