Although published reports would not suggest that this might be due to reduced expression of PD-1 or CTLA-4, as these are often observed to increase with ageing (36, 37), this was not the case in our experimental setting (Supplementary Figure 7) where we observed decreased levels of PD-1 and CTLA-4 on CD8+ T cells within the tumor. Here, CTLA4 is linked to neoplasm.