The realization that human cancers can be responsive to the manipulation of the immune system has only recently been documented. The immune approaches to the treatment of malignancy can be broadly classified into either active or passive immunotherapies. With active immunotherapy, treatment relies on the in vivo stimulation of the endogenous host immune system to react against tumors with the administration of biological response-modifying agents (ie, bacterial adjuvants, cytokines, tumor vaccines). With passive immunotherapy, treatment involves the delivery of biologic reagents with established tumor-immune reactivity (ie, antibodies or cells) that can directly or indirectly mediate antitumor effects and does not necessarily depend on an intact host immune system. Cellular therapy of malignancy has become more feasible with increased understanding of the interactions between immune cells and tumors. This article will review our current understanding of the principles underlying these interactions.
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