Targeted Integration of Inducible Caspase-9 in Human iPSCs Allows Efficient in vitro Clearance of iPSCs and iPSC-Macrophages

Induced pluripotent stem cells (iPSCs) offer great promise for the field of regenerative medicine, and iPSC-derived cells have already been applied in clinical practice. However, potential contamination of effector cells with residual pluripotent cells (e.g., teratoma-initiating cells) or effector cell-associated side effects may limit this approach. This also holds true for iPSC-derived hematopoietic cells. Given the therapeutic benefit of macrophages in different disease entities and the feasibility to derive macrophages from human iPSCs, we established human iPSCs harboring the inducible Caspase-9 (iCasp9) suicide safety switch utilizing transcription activator-like effector nuclease (TALEN)-based designer nuclease technology. Mono- or bi-allelic integration of the iCasp9 gene cassette into the AAVS1 locus showed no effect on the pluripotency of human iPSCs and did not interfere with their differentiation towards macrophages. In both, iCasp9-mono and iCasp9-bi-allelic clones, concentrations of 0.1 nM AP20187 were sufficient to induce apoptosis in more than 98% of iPSCs and their progeny—macrophages. Thus, here we provide evidence that the introduction of the iCasp9 suicide gene into the AAVS1 locus enables the effective clearance of human iPSCs and thereof derived macrophages.