The low conversion efficiency by Ascl1 was not due to low expression of Ascl1 in GBM cells, because we confirmed the overexpression of Neurog2, NeuroD1, or Ascl1 using immunohistochemistry (Supplementary Figure S2A), as well as by using RT-qPCR (Supplementary Figure S2B), which actually found an increase of Ascl1 mRNA level among Ascl1-infected GBM cells (20 dpi). Here, NEUROD1 is linked to glioblastoma.