In patients with advanced melanoma, the persistence of high levels of monocytic MDSCs has been reported to be associated with disease progression, poor survival, and poor response to checkpoint inhibitor therapy targeting PD-1 and CTLA-4.18, 19In this experiment, the spleen of tumor-bearing mice and the control group were taken for flow cytometry, and the results showed that the proportion of MDSCs in tumor-bearing mice was significantly higher than that in normal mice, which was consistent with previous reports. Here, CTLA4 is linked to melanoma.