白细胞介素-33 是一种新型免疫抑制因子，通过巨噬细胞介导的脱落机制保护肿瘤细胞逃避 TIL 杀伤

Recognition of specific antigens expressed in cancer cells is the initial process of cytolytic T cell-mediated cancer killing.

However, this process can be affected by other non-cancerous cellular components in the tumor microenvironment.

Here, it is shown that interleukin-33 (IL-33)-activated macrophages protect melanoma cells from tumor-infiltrating lymphocyte-mediated killing.

Mechanistically, IL-33 markedly upregulates metalloprotease 9 (MMP-9) expression in macrophages, which acts as a sheddase to trim NKG2D, an activating receptor expressed on the surface of natural killer (NK) cells, CD8+ T cells, subsets of CD4+ T cells, iNKT cells, and T cells.

Further, MMP-9 also cleaves the MHC class I molecule, cell surface antigen-presenting complex molecules, expressed in melanoma cells. Consequently, IL-33-induced macrophage MMP-9 robustly mitigates the tumor killing-effect by T cells. Genetic and pharmacological loss-of-function of MMP-9 sheddase restore T cell-mediated cancer killing.

Together, these data provide compelling in vitro and in vivo evidence showing novel mechanisms underlying the IL-33-macrophage-MMP-9 axis-mediated immune tolerance against cancer cells. Targeting each of these signaling components, including IL-33 and MMP-9 provides a new therapeutic paradigm for improving anticancer efficacy by immune therapy.