No abstract

Efficient and precise genome editing is crucial for realizing the full research and therapeutic potential of human induced pluripotent stem cells (iPSCs). Engineered nucleases including CRISPR/Cas9 and transcription activator like effector nucleases (TALENs) provide powerful tools for enhancing gene-targeting efficiency. In this study, we investigated the relative efficiencies of CRISPR/Cas9 and TALENs in human iPSC lines for inducing both homologous donor-based precise genome editing and nonhomologous end joining (NHEJ)-mediated gene disruption. Significantly higher frequencies of NHEJ-mediated insertions/deletions were detected at several endogenous loci using CRISPR/Cas9 than using TALENs, especially at nonexpressed targets in iPSCs. In contrast, comparable efficiencies of inducing homologous donor-based genome editing were observed at disease-associated loci in iPSCs. In addition, we investigated the specificity of guide RNAs used in the CRISPR/Cas9 system in targeting disease-associated point mutations in patient-specific iPSCs. Using myeloproliferative neoplasm patient-derived iPSCs that carry an acquired JAK2-V617F point mutation and α1-antitrypsin (AAT) deficiency patient-derived iPSCs that carry an inherited Z-AAT point mutation, we demonstrate that Cas9 can specifically target either the mutant or the wild-type allele with little disruption at the other allele differing by a single nucleotide. Overall, our results demonstrate the advantages of the CRISPR/Cas9 system in allele-specific genome targeting and in NHEJ-mediated gene disruption.

Large-scale production of human induced pluripotent stem cells (hiPSCs) by robust and economic methods has been one of the major challenges for translational realization of hiPSC technology. Here we demonstrate a scalable culture system for hiPSC expansion using the E8 chemically defined and xeno-free medium under either adherent or suspension conditions. To optimize suspension conditions guided by a computational simulation, we developed a method to efficiently expand hiPSCs as undifferentiated aggregates in spinner flasks. Serial passaging of two different hiPSC lines in the spinner flasks using the E8 medium preserved their normal karyotype and expression of undifferentiated state markers of TRA-1–60, SSEA4, OCT4, and NANOG. The hiPSCs cultured in spinner flasks for more than 10 passages not only could be remained pluripotent as indicated by in vitro and in vivo assays, but also could be efficiently induced toward mesodermal and hematopoietic differentiation. Furthermore, we established a xeno-free protocol of single-cell cryopreservation and recovery for the scalable production of hiPSCs in spinner flasks. This system is the first to enable an efficient scale-up bioprocess in completely xeno-free condition for the expansion and cryopreservation of hiPSCs with the quantity and quality compliant for clinical applications.