Recently, there has been growing interest in developing blood-derived or serum-derived predictive biomarkers of ICI response across a variety of cancer types,38–40 especially on-therapy biomarkers.41 We analyzed the early on-therapy change in peripheral serum cytokines and circulating T cell levels and found that a higher percentage of baseline CD3+ cells and a decrease in IL-2, IL-18, sFasL and CCL2 levels in peripheral blood could predict a better outcome of ICI-based combination therapy. Here, CCL2 is linked to cancer.