Targeting IRG1 in tumor-associated macrophages for cancer therapy

Immune-responsive gene 1 (IRG1) is a mitochondrial aconitate decarboxylase and can produce the immunomodulatory metabolite itaconic acid (ITA). However, its role in modulating the function of tumor-associated macrophages (TAMs) remains elusive. Here, we show that IRG1 is expressed in TAMs in human tumors and mouse models of cancer. Tumor cells induce Irg1 expression in macrophages which dampens the inflammatory response and restricts M1-like TAM polarization. In contrast, Irg1-deficent macrophages acquire more proinflammatory M1-like features, promote immunogenic antigen presentation, and enhance cytotoxic T cell infiltration into tumor sites. Consequently, Irg1 deficiency suppresses the growth of mouse syngeneic tumors, including melanoma, colorectal cancer, breast cancer, and pancreatic cancer. Irg1-deficient macrophages not only dictate the tumoricidal effect but enhance the efficacy of anti-PD(L)1 immunotherapy. In conclusion, our data identify IRG1 as a myeloid immune check point gene and foster the development of genetic or pharmacologic targeting of IRG1 for skewing macrophages toward an anti-tumor phenotype to treat a broad spectrum of cancer. Overall design: We performed single-cell RNA sequencing on Irg1+/+ and Irg1-/- mice and obtained CD45+ cells from B16-F10 melanoma tumors.