In conclusion, these data demonstrate for the first time in vivo that the absence of the mMGL1 receptor restrains MDSC expansion; reduces the infiltration of inflammatory mediators such as Mφs, NKs, iNOS and arginase 1; and increases the percentage of CD4+ and CD8+ T cells in colon tumors, thereby reducing tumor growth in the colonic mucosa. The gene discussed is ARG1; the disease is neoplasm.