Tumor progression is accompanied by an altered myelopoiesis that causes the accumulation of cells inhibiting anti-tumor T lymphocytes. We previously reported that immunosuppressive cells can be generated in vitro from bone marrow cells (BM) after four days GM-CSF and IL-6 treatment. Here, we describe that miR-142-3p down-regulation directs macrophage differentiation and determines the acquisition of their immunosuppressive function in cancer. Enforced miR over-expression impaired monocyte to macrophage transition both in vitro and in vivo. Conversely, forced miR down-regulation promoted the generation of immunosuppressive macrophages even during G-CSF-induced granulocytic differentiation. To identify how miR-142-3p regulates MDSC generation and activity, we analyze the gene expression of BM cultures transfected with either CTRL- or miR 142-3p mimic oligo -transfected before four days GM-CSF and IL-6 treatment. Keywords: Expression profiling by array Overall design: BM cells were transfected either CTRL- or miR 142-3p mimic oligo before GM-CSF and IL-6 treatment to generate in vitro MDSCs during enforced miR over-expression. A triplicate of each sample was considered.Total RNA from obtained in vitro BM-differentiated MDSCs was isolated by Trizol reagent, and cRNA samples were hybridized to the Affymetrix GeneChip MOE430 2.0.