An integration-defective lentivirus-based resource for site-specific targeting of an edited safe-harbour locus in the human genome

Optimized gene transfer into human cells are still challenging the promise of human stem and induced pluripotent stem cells as resources for disease models, diagnostic screens and personalized cell therapy. These potential applications require precise control of the spatio-temporal action of gene switches and the coordinated regulation of modulators, effectors and differentiation factors during pluripotency, differentiation and homeostasis. Most studies require identical transgene environments for comparable analysis; however, this cannot be achieved by standard methods for transgenesis in human cells because of unintended epigenetic modifications, genetic instability, dose-dependent effects, and disruption or activation of host genes. Although gene targeting can circumvent these problems, human cells have proved difficult to target, and there is therefore a need to develop tools for targeted transgenesis at efficiencies similar to those achieved in mice. We present a simple strategy, KASTRINA 2.0, for reliable transgenesis in human cells, based on targeted recombinase-mediated cassette exchange and the safe episomal status conferred by integrase-deficient lentivirus (IDLV). By driving limited cre recombinase expression, the IDLV yields single site-specific recombination of a selectable donor cassette (TRINA) at the 'safe-harbour' AAVS1 locus previously edited by zinc-finger nuclease to contain an acceptor site (KAS2.0).