Note: A path to efficient gene editing

Note: A path to efficient gene editing

Doi: 10.1038/s41591-018-0110-y

Gene editing in human pluripotent stem cells (hPSCs) and iPSC -- the efficiency is very low compared to the other cell types.

Kaykas and colleagues and Taipale and colleagues

• finding p53 antagonizing efficient genome editing using Cas9 in hPSC and immortalized human retinal pigment epithelial cells

• Editing gene that is silent in hPSCs -- > same result as editing one that active

• Single DSB induced by Cas9 in the genome of hPSC -- > reduces their survival

• Cas9 screens in transformed cells

• Copy number of gene target (rather than nature of individual genes) -- > drive phenotype of edited cells

• Thus -- clinical applications -- this could cause undesired side effects

Kaykas and colleagues 

• Study transcriptional response of hPSC using gene editing with Cas9

• Even one single strand break -- > increases expression of genes involved in programmed cell death

• Cas9-induced toxicity is mediated by p53

• Reduced the levels, or function, of p53 in the cells and found that this dramatically reduced Cas9-induced toxicity and—more importantly—increased the number of hPSCs with an edited genome that survived

Taipale and colleagues

• Precise edits in the genome of hPSCs is antagonized by p53, and they also observed an increased efficiency of editing in hRPE cells in which p53 function was reduced.

For gene editing which used DSB-based

• Transient suppression of p53is well-tolerated by hPSCs, and, on the basis of the provided data, it clearly could be an option for experiments in which efficient DSB-based engineering of their genome is required.

ZFN and TAL

• Safety is good

ZFN-edited human hematopoietic stem and progenitor cells

• NCT02500849 and NCT03432364 -- underway

Important point

• Transient suppression of p53 -- > cause accumulation of mutations -- > later on causing unk side effect