CRISPR-Cas9 gene editing is based on a tactic bacteria developed to protect themselves from viruses. Research shows that the countermeasure viruses came up with—inhibitory proteins referred to as anti-CRISPRs—can be used to improve CRISPR-Cas9 as a gene-therapy tool, decreasing off-target gene editing that could cause unwanted side effects.

The study demonstrated that one particular anti-CRISPR protein called AcrIIA4 reduced by four-fold the off-target effects of a CRISPR-Cas9 molecule that uses a guide RNA to find, snip and replace the mutated hemoglobin gene responsible for sickle cell disease. It does this without significantly reducing the desired on-target gene-editing.