Highly efficient RNA-guided genome editing in human cells via delivery of purified Cas9 ribonucleoproteins

TLDR

CRISPR/Cas RGENs enable genome editing in human cells but suffer from off‑target mutations and plasmid‑derived DNA integration. The study aims to deliver purified Cas9 protein and guide RNA as ribonucleoproteins into cultured human cells, including hard‑to‑transfect fibroblasts and pluripotent stem cells. Purified Cas9 RNPs are introduced into cells, cleave chromosomal DNA almost immediately, and are rapidly degraded, thereby limiting off‑target effects. RNP delivery achieves up to 79 % site‑specific mutation efficiency, markedly reduces off‑target mutations at sites differing by one or two nucleotides, and yields at least twice as many colonies in human embryonic stem cells compared to plasmid transfection.

Abstract

RNA-guided engineered nucleases (RGENs) derived from the prokaryotic adaptive immune system known as CRISPR (clustered, regularly interspaced, short palindromic repeat)/Cas (CRISPR-associated) enable genome editing in human cell lines, animals, and plants, but are limited by off-target effects and unwanted integration of DNA segments derived from plasmids encoding Cas9 and guide RNA at both on-target and off-target sites in the genome. Here, we deliver purified recombinant Cas9 protein and guide RNA into cultured human cells including hard-to-transfect fibroblasts and pluripotent stem cells. RGEN ribonucleoproteins (RNPs) induce site-specific mutations at frequencies of up to 79%, while reducing off-target mutations associated with plasmid transfection at off-target sites that differ by one or two nucleotides from on-target sites. RGEN RNPs cleave chromosomal DNA almost immediately after delivery and are degraded rapidly in cells, reducing off-target effects. Furthermore, RNP delivery is less stressful to human embryonic stem cells, producing at least twofold more colonies than does plasmid transfection.