FFAR2 deficiency restricted tumor growth was eliminated by depletion of MDSCs (Fig. 4B) and the infiltration of MDSCs, CD4, CD8, DCs, NKs and macrophages in LLC tumor-bearing mouse upon isotype and anti-Gr-1 antibody treatment was shown in Additional file 1: Fig. S5A–F, implying the dominant role of FFAR2 in the protumoral phenotypes of MDSCs. The gene discussed is CD4; the disease is neoplasm.