Immune escape of colorectal tumours via local LRH‐1/Cyp11b1‐mediated synthesis of immunosuppressive glucocorticoids

Control of tumour development and growth by the immune system critically defines patient fate and survival. What regulates the escape of colorectal tumours from destruction by the immune system remains currently unclear. Here, we investigated the role of intestinal synthesis of glucocorticoids in the tumour development during an inflammation‐induced mouse model of colorectal cancer. We demonstrate that the local synthesis of immunoregulatory glucocorticoids has dual roles in the regulation of intestinal inflammation and tumour development. In the inflammation phase, LRH‐1/Nr5A2‐regulated and Cyp11b1‐mediated intestinal glucocorticoid synthesis prevents tumour development and growth. In established tumours, however, tumour‐autonomous Cyp11b1‐mediated glucocorticoid synthesis suppresses anti‐tumour immune responses and promotes immune escape. Transplantation of glucocorticoid synthesis‐proficient colorectal tumour organoids into immunocompetent recipient mice resulted in rapid tumour growth, whereas transplantation of Cyp11b1‐deleted and glucocorticoid synthesis‐deficient tumour organoids was characterized by reduced tumour growth and increased immune cell infiltration. In human colorectal tumours, high expression of steroidogenic enzymes correlated with the expression of other immune checkpoints and suppressive cytokines, and negatively correlated with overall patients' survival. Thus, LRH‐1‐regulated tumour‐specific glucocorticoid synthesis contributes to tumour immune escape and represents a novel potential therapeutic target.