CD28 and central nervous system cancer: The GCT02 and 2173 CD8+ CAR and EV T cells from three independent PBMC donors were cocultured with positive control (TCR) ligand anti‐CD3/CD28 coated Dynabeads®, parental or EGFRvIII‐expressing U87 and U251 glioma cells for 18 h and the coculture supernatant probed for secretion of key effector cytokines IFN‐γ, IL‐2 and TNF‐α (Figure 3g–i).