Tumours from multiple cancer types can be infiltrated by CD8+ T cells (TILs)(Spranger et al, 2016). TILs are thought to be suppressed by multiple immune inhibitory molecules in the tumour microenvironment, and this suppression has been associated with tumour progression (Gajewski et al, 2013). Therefore, despite tumour infiltration, almost all tumours containing TILs will progress if not treated. While several immune inhibitory mechanisms have been identified, immune inhibitory receptors expressed on activated T cells, like CTLA-4 and PD-1, have received the most attention over recent years owing to the immense clinical success of PD-1 and CTLA-4 neutralising antibodies (Hodi et al, 2010; Topalian et al, 2012). The engagement of inhibitory receptors expressed by TILs is thought to render TILs dysfunctional. However, evidence from both human tumour samples and mouse models has suggested that, despite inhibitory receptor expression, TILs are not functionally inert and actually retain the ability to proliferate, produce IFN-γ (Daud et al, 2016;