Figure 2. Cytokines and growth factors produced by tumor cells impair host anti-tumor immunity by activating STAT3 signaling in both tumor cells and professional antigen-presenting cells. Tumor cells expressing constitutively active NFB and STAT3 produce greatly reduced levels of RANTES and IP-10, thereby impairing T-cell infiltration and migration to the sites of tumor growth. In addition, several tumor-derived cytokines and growth factors activate STAT3 in immature dendritic cells, which blocks DC differentiation and expression of co-stimulatory molecules such as CD80 and CD86. High levels of immature DCs (iDC) can actively induce T-cell tolerance to tumor antigens and promote cancer progression.