IL-10 dampens antitumor immunity and promotes liver metastasis via PD-L1 induction.

BACKGROUND & AIMS: The liver is one of the organs most commonly affected by metastasis. The presence of liver metastasis is reported to be responsible for an immunosuppressive microenvironment and diminished immunotherapy efficacy. Here, we aimed to investigate the role of IL-10 in liver metastasis formation and decipher its therapeutic potential in affecting immunotherapy effectiveness.

METHODS: To induce spontaneous or forced liver metastasis in mice, murine cancer cells (MC38) or colon tumor organoids were injected into the cecum or the spleen, respectively. Mice with complete and cell-type specific deletion of IL-10- and IL-10Ra were used to identify the source and the target of IL-10 during metastasis formation. Programmed death ligand 1 (PD-L1)-deficient mice were used to test the role of this checkpoint. Flow cytometry was applied to characterize the regulation of IL-10 on PD-L1.

RESULTS: We found that Il10-deficient mice and mice treated with IL-10Ra antibodies were protected against liver metastasis formation. Furthermore, by using IL-10 reporter mice, we demonstrated that Foxp3+ regulatory T cells (Tregs) were the major cellular source of IL-10 in liver metastatic sites. Accordingly, deletion of IL-10 in Tregs, but not in myeloid cells, led to reduced liver metastasis. Mechanistically, IL-10 acted on Tregs in an autocrine manner, thereby further amplifying IL-10 production. Furthermore, IL-10 acted on myeloid cells, i.e., monocytes, and induced the upregulation of the immune checkpoint protein PD-L1. Finally, the PD-L1/PD-1 axis attenuated CD8-dependent cytotoxicity against metastatic lesions.

CONCLUSIONS: Treg-derived IL-10 upregulates PD-L1 expression in monocytes, which in turn reduces CD8+ T-cell infiltration and related antitumor immunity in the context of colorectal cancer (CRC)-derived liver metastasis. These findings provide the basis for future monitoring and targeting of IL-10 in CRC-derived liver metastasis.

IMPACT AND IMPLICATIONS: Liver metastasis diminishes the effectiveness of immunotherapy and increases the mortality rate in CRC patients. We investigate the role of IL-10 in liver metastasis formation and decipher its therapeutic potential in affecting immunotherapy effectiveness. Our data identify IL-10 as a pro-metastatic factor in liver metastasis formation and characterize this cytokine as a regulator of PD-L1. This provides the basis for future monitoring and targeting of IL-10 in CRC-derived liver metastasis.