Evasion of Pre-Existing Immunity to Cas9: a Prerequisite for Successful Genome Editing In Vivo?

Purpose of Review CRISPR-Cas9-mediated genome editing holds promise for the future correction of congenital defects in vivo, providing potentially curative interventions for numerous intractable diseases. Nevertheless, the bacterial origin of the Cas9 endonuclease raises the spectre of pre-existing immunity that threatens to undermine the success of this powerful technology, necessitating a careful assessment of the potential risks involved.