Administration of agonistic reagents demonstrates that OX40‐signalling reduces Treg cell suppressive function in vitro and in vivo;117 however, other studies suggest that Treg cells are not impaired.118 One potential explanation is that the context of OX40 ligand (OX40L) expression can have different effects on Treg cells.113 In the context of cancer, OX40L is expressed by glioblastoma, especially under hypoxic conditions. Here, TNFRSF4 is linked to cancer.