ERBB2 and glioblastoma: Ahmed and collaborators successfully administered 1 × 108 HER2-specific CAR-T cells with a CD28ζ endodomain without dose-limiting toxic effects in glioblastoma patients [291], while other preclinical data revealed that co-stimulation with CD137 displayed lower cytokine production and better anti-tumor efficacy compared to co-stimulation with CD28 [292].