Of note, repeated attempts to establish KO-Y235T cells or other p53-positive KO-cell lines (e.g. RT4 bladder cancer cell line) failed, likely due to strong apoptotic response caused by endonucleolytic DNA cleavage by the constitutive Cas9 enzyme activity in ureter/bladder cells (unpublished observations). The gene discussed is TP53; the disease is urinary bladder cancer.