Cas9 goes into stealth-mode

Written by Francesca Lake

A new method has set out to tackle one of the limitations of CRISPR, promising to make gene-editing with CRISPR-Cas9 more reliable and “stealthy”.

CRISPR techniques for gene editing have been labeled a scientific breakthrough and opened up a whole new world for research; however, they have been dogged by problems. While CRISPR techniques could help treat genetic diseases and transform ecosystems, potential limitations of CRISPR such as off-target effects and the ethical debates raised by changing our DNA have stalled progress.

One such problem is the potential for CRISPR-Cas9 to trigger an immune response, resulting in toxicity. However, new research has seen a team of researchers describe a method to render CRISPR-Cas9 “immunosilent”, potentially fixing this problem.



“Being as much a societal revolution as a technological revolution, many researchers have started to look into ethical, societal, safety and regulatory considerations related to CRISPR usage,” explained Samira Kiani, one of the study authors (Arizona State University, AZ, USA). “Safety engineering to address controllability, specificity and side effects of CRISPR treatments have gained significant momentum and ethical debates have arisen to ensure correct use of technology.”

Cas9 is derived from Streptococcus pyogenes, which affects 700 million people annually across the globe. As a result, many people have pre-existing immunity to its proteins.

“That’s the unique part of what we’ve done. We took those dominant epitopes and tried to silence them – just by doing one or two mutations in the Cas9 gene. But we rebuilt it, so the gene was still functional.”

The new study confirmed Cas9’s immunogenicity, showing that pre-existing exposure to S. pyogenes results in a T-cell response to the protein. The team then went on to show that two mutations in epitope anchor residues resulted in a functional version of the protein with a 25—30-fold reduction in T-cell reactivity.

“That’s the unique part of what we’ve done,” commented Karen Andersen (Arizona State University). “We took those dominant epitopes and tried to silence them – just by doing one or two mutations in the Cas9 gene. But we rebuilt it, so the gene was still functional. It’s not immunologically silent, but its more quiet.”

The team believes that the new Cas9 could be combined with other strategies to improve CRISPR safety and reduce the need for immunosuppressants.

“We are hoping that this study is the beginning of many efforts that when combined can address the immunogenicity of CRISPR for clinical trials,” concluded Kiani.