Induced pluripotent stem cell clones reprogrammed via recombinant adeno-associated virus-mediated transduction contain integrated vector sequences.

Fibroblasts can be reprogrammed into induced pluripotent stem cells (iPSC) by ectopic expression of key transcription factors. Current methods for the generation of integration-free iPSC are limited by the low efficiency of iPSC generation and by challenges in reprogramming methodology. Recombinant adeno-associated virus (rAAV) is a potent gene delivery vehicle capable of efficient transduction of transgenic DNA into cells. rAAV stays mainly as an episome in nondividing cells, and the extent of integration is still poorly defined for various replicating cells. In this study, we aimed to induce iPSC from mouse and human fibroblasts by using rAAV vector-mediated transient delivery of reprogramming factors. We succeeded in deriving induced pluripotent stem cells from mouse but not human fibroblasts. Unexpectedly, the rAAV vector-mediated reprogramming led to frequent genomic integration of vector sequences during the reprogramming process, independent of the amount of virus used, and to persistent expression of reprogramming factors in generated iPSC clones. It thus appears that rAAV vectors are not compatible with the derivation of integration-free iPSC.