Capillary leak syndrome, which is seen in more than 50% of patients receiving IL-2 therapy, occurs both directly as a result of interaction with endothelial cells via CD25 [24] and indirectly via LAK cell-stimulated production of vasoactive lymphokines, which increase capillary permeability and decrease vascular tone [23,25,26]. Here, IL2 is linked to capillary leak syndrome.