Sequential factor delivery enables efficient workflow for universal gene editing in clinical grade iPS cells

Human induced pluripotent stem cells (iPSCs) are gaining momentum as a powerful starting material in cell therapy. To fully harness their potential, CRISPR technology permits endogenous gene modifications as well as the introduction of advanced features, to increase the immune compatibility of the cells or insert suicide genes for enhancing therapeutic safety, for instance. However, genetic manipulation of iPSCs, in particular the generation of knock-in lines, remains relatively inefficient. Conventional mitigation strategies, such as enriching for positive cells using antibiotic selection or complex instrumentation, may, however, cause conflicts with good manufacturing practice (GMP) requirements. To address this challenge, we have systematically optimized a basic gene editing procedure using both Cas9 and Cas12a-based ribonucleoprotein (RNP) complexes. Based on the sequential delivery of RNPs and donor plasmids as a critical hallmark, this virus-free approach permits knock-ins of full-length transgenes at above 30% efficiency, while readily identifying positive clones through random screening at small scale. We exemplify these advances by creating and characterizing homozygous iPSC lines depleted of HLA class I and carrying an inducible caspase-9 suicide gene. Isolated clones from independent GMP iPSC lines retained genomic integrity, differentiation capability, and functionality of the safety switch in the differentiated state. This improved methodology will form a flexible platform for custom gene editing universally applicable both in basic iPSC research and therapy.