ARG1 and lung cancer: Previously, we showed that tumor cell-derived MPs induce an immunosuppressive M2 phenotype that promotes tumor progression in macrophages.16 Consistent with these results, the treatment of macrophages with HCC827 (a human lung cancer cell line)-derived MPs (L-MPs) resulted in the upregulation of VEGF, IL-10 and arginase 1 expression and the downregulation of IL-12, iNOS and TNF-α expression (Fig. 1a, supplementary Fig. 1).