Tumors may escape immune detection through a variety of mechanisms that create a local microenvironment unfavorable for effective tumor immunity. Local DCs may be immature and unable to take up, process, or present antigens. These DCs may also be inhibited from migrating to regional lymph nodes or may actually induce tolerance, especially when presenting self-antigens. The tumor site may also be infiltrated with regulatory T cells that are able to mediate suppression of antigen-primed T cells. The helper CD4 T cell response may also be skewed toward a Th2 phenotype, which inhibits the initiation of Th1 T cells and effective cellular immunity. The tumor cells may express aberrant MHC class I molecules or β2-microglobulin, resulting in inadequate antigen presentation and, thus, inefficient recognition of tumors by effector T cells. Finally, tumor cells and the surrounding stroma may release a number of suppressive cytokines, such as IL-6, IL-10, and TGF-β. This creates an environment that is not conducive to local immunity, which allows tumor cells to escape.