Durable tumor regression and potential cures of metastatic solid cancers can be achieved by a variety of cellular immunotherapy strategies, including cytokine therapy, dendritic cell–based vaccines, and immune-activating antibodies, when used in so-called immune-sensitive cancers such as melanoma and renal cell carcinoma. However, these immunotherapy strategies have very low tumor response rates, usually in the order of 5% to 10% of treated patients. We propose that the antitumor activity of adequately stimulated tumor antigen–specific T cells is limited by local factors within the tumor milieu and that pharmacologic modulation of this milieu may overcome tumor resistance to immunotherapy. By understanding the mechanisms of cancer cell immune escape, it may be possible to design rational combinatorial approaches of novel therapies able to target immunosuppressive or antiapoptotic molecules in an attempt to reverse resistance to immune system control. We term this mode of treatment “immunosensitization.” Ideal candidates for immunosensitizing drugs would be targeted drugs that block key oncogenic mechanisms in cancer cells resulting in a proapoptotic cancer cell milieu and at the same time do not negatively interfere with critical lymphocyte functions.