GREM1 and neoplasm: GREM1 expression in macrophages (F4/80+) of liver infiltrating tumor tissues was enhanced in Exo-scramble-treated mice compared with PBS-treated mice, and GREM1 expression in macrophages of liver metastases was significantly reduced in mice pre-treated with Exo-KD 1# and Exo-KD 2# (Fig. 6E).