CD4 and neoplasm: CD27 is expressed mainly by naive and subsets of memory CD4+ and CD8+ T cells, as well as Treg cells.113 CD70 can be expressed by antigen‐presenting cells, but also by tumour‐infiltrating Treg and effector T cells.129 Engagement of CD27 with CD70 within tumours is important for expansion of Treg cells within tumours.129 Intriguingly, it was proposed that this activity is indirect, and acts through the ability of CD27‐CD70 signalling to drive IL‐2 production by Tconv cells, although evidence supporting this hypothesis was derived from in vitro experiments.