Introduction

Abstract

The immune system has long been linked with the natural homeostatic regulation of the growth of malignant cells. Moreover, immunotherapeutic approaches have been sought to control cancer because of the inherent specificity of the immune system. The majority of these immunotherapeutic approaches has relied on specific or nonspecific activation of immune effector cells. Recently, however, interest has centered on leukolysins, the term recently adopted by the Reticuloendothelial Society to denote the soluble cytotoxic molecules secreted by activated leukocytes with anticancer activities. This specialized class of immunologic hormones is rapidly being brought to the clinic as a result of genetic engineering. A typical pattern has emerged in the clinical development of these cytotoxic molecules. Initially, a biologic “activity” is described, generally the growth inhibition or cytolysis of some type of tumor cell by the soluble product of an activated leukocyte. The “activity” is biochemically characterized and purified. Because these molecules are difficult to isolate in large quantities, only limited clinical trials have been performed with native materials. Hence, genetically engineered molecules are being used clinically. The leukolysins represent a whole new type of therapeutic agent, and much new research needs to be done to determine their best methods of use.