IL-36γ promotes a local immune response via the formation of tertiary lymphoid structures in colorectal carcinoma.

Abstract Tertiary lymphoid structures (TLS) form at sites of chronic inflammation, and locally prime the immune system independently of secondary lymphoid organs. The intratumoral presence of TLS has been associated with a positive prognostic outcome for patients with solid tumors, including colorectal carcinoma. Thus, the therapeutic induction of TLS would be hypothesized to confer clinical benefit to patients. Indeed, the therapeutic introduction of the IL-1 family cytokine IL-36 gamma into the tumor microenvironment (TME) of murine MC38 colon carcinoma leads to delayed tumor progression and the development of TLS at 5 days post-treatment. The TLS present with characteristics of secondary lymphoid organs, including PNAd+ high endothelial venules (HEV) surrounded by CD3+ T cells and CD11c+ dendritic cells, but are considered as "non-classical" due to the absence of a defined B cell zone. The formation of TLS is dependent upon the adaptive immune response, as IL-36 gamma-treated tumors grown in Rag2−/− animals fail to present with PNAd+ vasculature within the tumor. Thus, crosstalk between the immune system and cells of the vasculature is key to the efficacy of the IL-36 gamma-induced anti-tumor immune response. In human colorectal carcinoma, IL-36 gamma was also observed to promote the local anti-tumor immune response. Expression of IL-36 gamma by vascular endothelial cells of HEV was associated with an increased density of CD20+ B cells in TLS. Specific IL-36 gamma production by CD68+ macrophages was associated with an increased infiltration of CD4+ central memory T cells into the TME. Therefore, IL-36 gamma is a pro-inflammatory mediator involved in the anti-tumor immune response in both murine and human colorectal cancer.