Pseudotype Infection and Luciferase Assay for GBM Cells

U87 cells were cultivated in DMEM/10% FBS, while cells from grade 4 GBM tumors were cultivated in 50% hCSF, 45% DMEM, and 5% FBS in 96-well plates (Cell+™, Sarstedt, Nümbrecht, Germany). Infection of cells with pseudotypes was carried out as described previously [29 (link)]. Briefly, cell culture supernatants from COS-1-transfected cells were given to tumor cells at a 70–80% density. After 3 h, 100 µL of medium was added, and the cultures were incubated at 37 °C for 3 days. For luciferase detection, the cells were washed three times on day three, and 100 µL of the BrightGlow™ luciferase assay reagent (Luciferase Assay System, Promega E1483, Walldorf, Germany) was added. The plates were incubated for 5 min, and bioluminescence was measured using a 96-well plate reader (Luminometer Centro LB960, Berthold Technologies, Bad Wildbad, Germany). The green fluorescence of HIVgfp-infected cells was monitored using an EVOS M7000 Imaging System (Thermo Fisher Scientific, Braunschweig, Germany).