TP53 and Ewing sarcoma: Indeed, using the same CRISPR mediated gene targeting approach as performed on parental RPE cells that failed to produce knockout clones (Fig. 1a, b), we were able to produce STAG2 knockout clones at high efficiency in p53-depleted RPE cells and multiple Ewing sarcoma cell lines harboring inactivating TP53 mutations (Fig. 5d–g).