Orthogonal transcriptional modulation and gene editing using multiple CRISPR-Cas systems

CRISPR-Cas-based transcriptional activation (CRISPRa) and interference (CRISPRi) enable transient programmable gene regulation by recruitment or fusion of transcriptional regulators to nuclease-deficient Cas (dCas). Here, we expand on the emerging area of transcriptional engineering and RNA delivery by benchmarking combinations of RNA-delivered dCas and transcriptional modulators. We utilize dCas9 from Staphylococcus aureus and Streptococcus pyogenes for orthogonal transcriptional modulation to upregulate one set of genes while downregulating another. We also establish trimodal genetic engineering by combining orthogonal transcriptional regulation with gene knockout by Cas12a (Acidaminococcus; AsCas12a) ribonucleoprotein delivery. To simplify trimodal engineering, we explore optimal parameters for implementing truncated single guide RNAs (sgRNAs) to make use of SpCas9 for knockout and CRISPRa. We find the Cas9 protein/sgRNA ratio to be crucial for avoiding sgRNA cross-complexation and for balancing knockout and activation efficiencies. We demonstrate high efficiencies of trimodal genetic engineering in primary human T cells while preserving basic T cell health and functionality. This study highlights the versatility and potential of complex genetic engineering using multiple CRISPR-Cas systems in a simple one-step process yielding transient transcriptome modulation and permanent DNA changes. We believe such elaborate engineering can be implemented in regenerative medicine and therapies to facilitate more sophisticated treatments.