Loss of ACKR4 in tumor cells dysregulates dendritic cell migration to tumor-draining lymph nodes and T-cell priming

Abstract

Colorectal cancer (CRC) is one of the most common malignancies in both morbidity and mortality. Immune checkpoint blockade (ICB) treatments have been successful in a portion of mismatch repair-deficient (dMMR) CRC patients but failed in the mismatch repair-proficient (pMMR) CRC patients. Atypical Chemokine Receptor 4 (ACKR4) is known for regulating dendritic cell (DC) migration. However, the roles of ACKR4 in CRC development and immunoregulation are unclear. By analyzing human CRC tissues, transgenic animals, and genetically modified CRC cells lines, our study revealed an important function of ACKR4 in maintaining CRC immune response. Loss of ACKR4 in CRC is associated with poor immune infiltration in the tumor microenvironment. More importantly, loss of ACKR4 in CRC tumor cells, rather than stromal cells, restrains the DC migration and antigen presentation to the tumor-draining lymph nodes (TdLNs). Tumors with ACKR4 knockdown become less sensitive to immune checkpoint blockades. Finally, we identified that microRNA-552 negatively regulates ACKR4 expression in human CRC. Taken together, our work identifies a critical mechanism for the maintenance of the DC-mediated T-cell priming in the TdLNs. These new findings demonstrate a novel mechanism leading to immunosuppression and ICB treatment resistance in CRC tumors. LAY SUMMARY Our study demonstrated that Atypical Chemokine Receptor 4 (ACKR4) is downregulated in human colorectal cancer (CRC) tissues compared with normal colon tissues. Loss of ACKR4 in human CRC tissues is associated with a weak anti-tumor immune response. Knockdown of ACKR4 in tumor cells impairs the dendritic cell migration from the tumor tissue to the tumor-draining lymph nodes (TdLNs), causing inadequate tumor-specific T-cell expanding and insensitivity to immune checkpoint blockades. However, loss of ACKR4 in tumor stromal cells does not significantly affect anti-tumor immunity. In human CRC tumors, high expression of microRNA-552 is a mechanism leading to ACKR4 downregulation. Our study revealed a novel mechanism that leads to the poor immune response in a subset of CRC tumors and will contribute to the framework for identifying new therapies against this deadly tumor.