Using signaling pathways to overcome immune tolerance to tumors.

The ability of tumors to evade the immune system is thought to result from the inability of T lymphocytes to recognize and respond to tumor antigens. This lack of T cell response may depend on a failure of dendritic cells to present antigen in the proper context so that T cells become tolerant to tumor antigens rather than primed to undergo an immune response. The inability of tumor-associated dendritic cells to effectively present antigen may in turn depend on inhibitory factors in the tumor milieu. Recent experiments suggest that the administration of toll-like receptor ligands stimulate dendritic cell activation and maturation and may thus help overcome T cell tolerance to tumor antigens. Whether or not such an approach is clinically feasible remains to be seen.