Figure 1.

A Model System of Pre-existing Immunity to Cas9

Systemic AAV delivery of CRISPR-Cas9 and gRNA is a well-established method to achieve stable genome editing in the livers of mice. However, the stability of that editing is unknown in the context of pre-existing immunity to Cas9. Li et al.⁹ found that when mice are immunized with Cas9 protein prior to AAV-CRISPR treatment, the initial genome editing is followed by a T cell response that results in loss of the edited cells.