IL21 and glioblastoma: Although the NK cells that were expanded by using K562-OX40L-mb-IL-18/IL-21 feeder cells showed cytotoxic effects against GBM cells in vitro and no therapeutic effects on single treatment with s.c and i.c U87 GBM models, the combination of NK cells with Bev and Iri enhanced cytotoxic effects against GBM cells in vitro and delayed tumor progression during early-stage treatment.