Antigenic differences between normal and malignant cells of the cancer patient form the rationale for clinical immunotherapeutic strategies. One emerging strategy in the treatment of tumors involves stimulation of an immunologic response against the neoplastic cells. 吀e hope is that the immune system can be called into play to destroy malignant cells. However, in most instances, proliferating tumors do not provoke anti-tumor cellular immune responses. 吀e precise mechanisms that enable antigenic neoplasms to escape host immunity are incompletely understood. 吀e cells appear to escape recognition by the immune system in spite of the fact that neoplastic cells form weakly immunogenic tumor associated antigens.