To that end, several mammalian cell lines with defined NHEJ-deficiency were employed including: (i) hamster cell lines with defects in either Ku80 (xrs5) or XRCC4 (XR-1) as well as their respective control cell line CHO-K1; (ii) the human glioblastoma DNA-PK-deficient MO59J cells and their wildtype cells MO59K and (iii) the human fibroblast line 180BR deficient in LIGIV together with a normal human fibroblast strain NFHH1. The gene discussed is PRKDC; the disease is glioblastoma.