CXCL12 and neoplasm: CXCL12 in the tumor microenvironment is mostly produced by CAF and plays a crucial function in attracting myeloid cells and supporting an immunosuppressive phenotype; inhibition of CXCL12 or its receptor CXCR4 lowers the amount of MDSC in the tumor (Obermajer et al., 2011; Feig et al., 2013).