Highly efficient generation of isogenic pluripotent stem cell models using prime editing
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Curated by eLife
Evaluation Summary:
In this manuscript, Li et al directly compare different editing strategies for human pluripotent stem cells. They demonstrate that prime editing is more efficient and precise, compared with double-strand break-based methods. They also confirm the suitability of prime editing for the introduction of different mutations related to Parkinson's disease as a model.
(This preprint has been reviewed by eLife. We include the joint public review from the reviewers here; the authors also receive private feedback with suggested changes to the manuscript. Reviewer #1 agreed to share their name with the authors.)
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Abstract
The recent development of prime editing (PE) genome engineering technologies has the potential to significantly simplify the generation of human pluripotent stem cell (hPSC)-based disease models. PE is a multicomponent editing system that uses a Cas9-nickase fused to a reverse transcriptase (nCas9-RT) and an extended PE guide RNA (pegRNA). Once reverse transcribed, the pegRNA extension functions as a repair template to introduce precise designer mutations at the target site. Here, we systematically compared the editing efficiencies of PE to conventional gene editing methods in hPSCs. This analysis revealed that PE is overall more efficient and precise than homology-directed repair of site-specific nuclease-induced double-strand breaks. Specifically, PE is more effective in generating heterozygous editing events to create autosomal dominant disease-associated mutations. By stably integrating the nCas9-RT into hPSCs we achieved editing efficiencies equal to those reported for cancer cells, suggesting that the expression of the PE components, rather than cell-intrinsic features, limit PE in hPSCs. To improve the efficiency of PE in hPSCs, we optimized the delivery modalities for the PE components. Delivery of the nCas9-RT as mRNA combined with synthetically generated, chemically-modified pegRNAs and nicking guide RNAs improved editing efficiencies up to 13-fold compared with transfecting the PE components as plasmids or ribonucleoprotein particles. Finally, we demonstrated that this mRNA-based delivery approach can be used repeatedly to yield editing efficiencies exceeding 60% and to correct or introduce familial mutations causing Parkinson’s disease in hPSCs.
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Evaluation Summary:
In this manuscript, Li et al directly compare different editing strategies for human pluripotent stem cells. They demonstrate that prime editing is more efficient and precise, compared with double-strand break-based methods. They also confirm the suitability of prime editing for the introduction of different mutations related to Parkinson's disease as a model.
(This preprint has been reviewed by eLife. We include the joint public review from the reviewers here; the authors also receive private feedback with suggested changes to the manuscript. Reviewer #1 agreed to share their name with the authors.)
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Joint Public Review:
While prime editing has been successfully implemented for hPSCs, its use for the generation of disease models is comparatively less explored. In this manuscript, Hanqin Li et al. set out to identify the most efficient methodology for correcting heterozygous mutations in human iPSC. For this purpose, the authors tested several known gene editing methods, including TALENs, conventional CRISPR/Cas9, and prime editing (PE) and, not surprisingly, found that PE resulted in the best balance of correct versus unwanted editing events.
In this process, the authors noted a lower editing efficiency of hPSCs, compared with tumour cell lines, and explored ways to improve it. Nucleofection of in vitro-transcribed mRNA-based delivery approach significantly increased the editing efficiency, without the need to select for targeted …
Joint Public Review:
While prime editing has been successfully implemented for hPSCs, its use for the generation of disease models is comparatively less explored. In this manuscript, Hanqin Li et al. set out to identify the most efficient methodology for correcting heterozygous mutations in human iPSC. For this purpose, the authors tested several known gene editing methods, including TALENs, conventional CRISPR/Cas9, and prime editing (PE) and, not surprisingly, found that PE resulted in the best balance of correct versus unwanted editing events.
In this process, the authors noted a lower editing efficiency of hPSCs, compared with tumour cell lines, and explored ways to improve it. Nucleofection of in vitro-transcribed mRNA-based delivery approach significantly increased the editing efficiency, without the need to select for targeted clones. The authors optimise the delivery of prime editing components and demonstrate that their optimised method can achieve >60% editing efficiency in hPSCs and be used for Parkinson's disease modelling.
Finally, they demonstrate that multiple rounds of mRNA-based prime editing can yield near complete editing of hPSCs, and extend their findings to disease-causing mutations.
Perhaps the major weakness of the manuscript is the relative lack of perceived novelty, since the different gene editing and delivery methods used in these studies have all been reported and tested in contexts that are not so distant to the one explored here. As a matter of fact, most findings in the paper (with the notable exception of mRNA delivery outperforming RNPs -but then again, the specific activity of the homemade recombinant nCas9-RT protein could be an issue and is not appropriately benchmarked) would have arguably been the best guess by researchers familiar with the literature on the topic.
At any rate, the study methodology is sound and the results are presented in a clear manner and strongly support the authors' conclusions. In combination with a streamlined workflow (or 'platform'), the optimized PE protocol described in this manuscript could very well be the go-to reference for editing heterozygous mutations in human iPSC. Additional strengths of this paper include having validated the most critical findings across genomic loci (4 different loci in 3 different genes) and 2 independent iPSC lines.
Although the utility of this method for more complex genetic editing needs to be investigated, the current platform paves the way for future prime editing methods for hPSCs.
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