IFNB1 and infection: In addition, Hep3B cells, which had undergone stringent in vitro selection to escape VSV-IFNβ oncolysis (Hep3B-VSV-IFNβ-ESC), and which contain the CSDE1C-T mutation at very high frequency (Supplementary Fig. 1), produced significantly less M protein when infected with VSV-IFNβ compared to infection with VSV-IFNβ–IGR P/MC-U (Fig. 3D, lanes 7 vs. 9).