Two teams of UK and Canadian researchers have been able to induce pluripotent stem cells without using viral vectors.

The teams used the piggyBac transposon, first discovered in a moth, which can integrate transgenes into host cell genomes.

In two papers published today in Nature, researchers led by Keisuke Kaji from the University of Edinburgh and Andras Nagy from the University of Toronto combined the coding sequences of the four “Yamanaka” genes – c-Myc, Klf4, Oct4 and Sox2 – into a single multi-protein expression vector.

They showed that the vector could reprogram mouse fibroblasts into a pluripotent state and then used the Cre enzyme to excise the transgene. While this worked, they decided to combine the vector with a piggyBac transposon to deliver the genes to embryonic fibroblasts.

PiggyBac transposons are removable from their integration sites without DNA modification, and the researchers conclude that this is the most efficient method.