CD4 and neoplasm: Tumor cell-derived LCN2 cooperates with C-C Motif Chemokine Ligand 2 (CCL2) to suppress immune cells by decreasing the costimulatory molecule HLA-DR and increasing expression of immunosuppressive programmed death ligand 1 (PD-L1) on CD11c+ regulatory dendritic cells, which is followed by induction of CD4+/FOXP3+ regulatory T cells and tumor escape (167).