The IL-33/ST2 axis and tissue Treg maintains epithelial homeostasis in the skin and restrains cancer development

IL-33 is constitutively expressed in many epithelial tissues at steady state and signals through the receptor, ST2. IL-33 is released upon tissue injury and functions as an endogenous danger signal to alert the immune system to tissue damage. Here we investigate the physiological role of the IL-33/ST2 axis in skin homeostasis and cancer development. We show that expression of IL-33 differentiates malignant from normal/benign human tissues and that in mouse models of cutaneous squamous cell carcinoma the IL-33/ST2 axis protects against carcinogenesis. Tissue Treg are the predominant cells expressing ST2 in the skin and localise around the hair follicle and IL-33+ epithelial cells (EC). Adoptive transfer experiments demonstrate that skin Treg regulate EC differentiation, minimizes mutational load and retrains cancer development following exposure to an environmental carcinogen. Our findings indicate an important role for direct EC-Treg cross-talk as an early checkpoint to contain tissue damage and carcinogenesis.