MIP-1β (macrophage inflammatory protein-1β; CCL4) is one of four members of the MIP-1 CC chemokine subfamily along with MIP-1α (CCL3), MIP-1δ (CCL15), and MIP-1γ (CCL9). Chemokines are 8 -12 kD proteins characterized by 3 to 4 conserved cysteine residues, with the C-C subfamily having the first 2 cysteines adjacent to each other. Chemokine signals are transduced through GPCRs, and MIP-1β is bound by the CCR5 member of this superfamily. The cardinal feature of chemokines is to recruit leukocytes to the site of inflammation; however their full physiological role is more complex. Chemokines have been found to have therapeutic potential in anti-tumor immune-therapy. MIP-1β can inhibit tumor growth and prolong survival of tumor-bearing mice, presumably through chemoattraction of T-Cells and NK cells to the tumor site. MIP1-β was one of the top up-regulated genes in patients that responded to anti-CLA4 (iplimumab) treatment, and immune responsiveness in patients appears to correlate with favorable prognosis. In this context, MIP-1B can help function as a prognostic marker for anti-tumor therapy.