When cultured with native or recombinant interleukin 2 (IL 2), human lymphoid cells proliferate and acquire the ability to lyse both NK-sensitive and NK-resistant tumor targets. Such IL 2-activated killer (IAK) cells generally do not destroy nonmalignant nontransformed cells. Due to their apparent specificity for tumor cells, adoptive immunotherapeutic trials of IAK cells and IL 2 have been initiated, with promising results. However, infusion of high doses of IL 2 causes systemic toxicity in patients and experimental animals resulting in the development of a vascular leakage syndrome. Certain aspects of such toxicity suggest IL 2-induced, cell-mediated destruction of normal tissue. This study examines the interaction between IL 2-induced human lymphoid cells and endothelial cells (EC). IL 2, in a dose-dependent manner, causes lymphocytes to strongly adhere to EC, but not to tumor cells, fibroblasts, or epithelial cells. In addition, these IL 2-activated lymphocytes were highly cytotoxic not only to NK-resistant Daudi cells but also to vascular and corneal EC. The IAK cells caused lysis of not only human EC but also bovine EC. Although IAK cells did not display significant adherence to normal human fibroblasts or epithelial cells, when brought together by 50 X G centrifugation, these targets were lysed by IAK cells. The ability to lyse EC was not confined to any single subpopulation of IL 2-activated lymphocytes. The lysis of EC was mediated by both IL 2-activated large granular lymphocytes and small agranular lymphocytes. Furthermore, cells within both CD4+ and CD8+ sublineages of T cells, and also non-T subpopulations, mediated IL 2-induced cytolysis of EC. The destruction of EC by IAK cells may contribute in part to the systemic toxicity associated with infusions of high doses of IL 2.

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