Non-classical Monocytes Enhance the Efficacy of Immune Checkpoint Inhibitors on Colon Cancer in a Syngeneic Mouse Model

Background/Aim: The response rate to immune checkpoint inhibitors (ICIs) is approximately 10%-30% and only in a few cancer types. In the present study, we determined whether non-classical monocytes (NCMs) could enhance ICI efficacy in colon cancer using a syngeneic mouse model. Materials and Methods: The MC38 C57BL/6 mouse colon cancer model was used. Cells collected from the bone marrow of C57BL/6 mice were cultured, and NCMs were fractionated by cell sorting and administered via the tail veins to the mice implanted with MC38 cells. The anti -mouse PD-L1 antibody was administered three times, and tumor volume and overall survival were observed. Results: More tumors were eradicated and more complete response occurred, after cotreatment with ICIs and NCMs than after treatment with ICIs alone. Moreover, no efficacy was observed when NCMs were administered alone. Conclusion: NCMs enhance ICI efficacy. The underlying mechanisms and clinical applications will be studied in the future.