TP53 and infection: To confirm whether the effect of Ax-hp16 infection plus irradiation was specific for human glioma cell lines, we also performed the clonogenic assay for other p16-null human cancer cell lines infected with Ax-hp16: the non-small-cell lung cancer cell line A549 (p21, undetectable protein expression; p53, wild type), and the gastric cancer cell line MKN45 (p21 and p53, wild type).