For example, excess cholesterol in the tumour microenvironment can drive the expression of checkpoint inhibitors through the induction of X-box binding protein 1 (XBP1)-dependent ER stress in T cells36; however, CD8+ T cells treated with ACAT inhibitors showed no consistent change in PD-1 expression (Supplementary Fig. 4a). This evidence concerns the gene XBP1 and neoplasm.