再浏览了Nature medicine另外一篇文章，上一篇文章测试的是人正常体细胞（视网膜色素上皮），这篇用的则是人多能干细胞（hPSCs）。主要结论是CRISPR/Cas9会引起hPSCs毒性，造成hPSCs死亡。和上一篇文章一致，这种毒性也是因为DNA双链断裂激活p53通路，同时也降低同源重组效率。这篇文章认为，对hPSCs进行基因编辑时，有可能会筛选到p53突变的克隆，从而增加致癌风险，因此建议如果使用CRISPR编辑hPSCs时，因仔细监测p53位点。这篇文章带来的问题是，在其他细胞类型中（比如造血干细胞）：1.CRIPSR引发的细胞毒性有多大？2. 是否因为筛选到p53突变克隆而增加致癌风险。我认为，对于体外编辑，这些风险是可控的；而对于体内编辑来说，则可能需要更多的数据来证明其安全性。相信这些天，学术界和几家公司会对此展开讨论。

“The toxic response to Cas9 activity has important implications for hPSC-based therapies. P53 inhibition could alleviate toxicity but has the potential to increase off-target mutations and poses a risk for cancer. For ex vivo engineering, Cas9 toxicity combined with clonal expansion could potentially select for P53 mutant cells more tolerant of DNA damage. Although the mutation rate of P53 remains to be determined for other clinically relevant cell types, this is a serious concern for hPSCs. The basal P53 mutation rate in hESCs is significant, and in ref. 14it was found that 3.5% of independent hESC lines and up to 29% of hESCs commonly used in RNA-seq databases have P53 mutations. Before engineering patient cells, the risks and benefits must be fully evaluated. It will be imperative to determine the spontaneous mutation rate of P53 in engineered cells as well as the mutational burden associated with transient P53 inhibition. As hPSC-based cell therapies using genome-edited cells move into the clinic, it will be critical to ensure that patient cells have a functional P53 before and after engineering.”

$CRISPR Therapeutics AG(CRSP)$ $Editas Medicine, Inc.(EDIT)$ $Intellia Therapeutics, Inc.(NTLA)$