The tumor-bearing state induces augmented responses of organ-associated lymphocytes to high-dose interleukin-2 therapy in mice

A high-dose bolus regimen for interleukin(IL)-2 administration to cancer patients frequently causes serious side-effects in which various organs are involved. In order to reveal the mechanism of toxicities associated with this regimen, we compared the augmenting effect of high-dose IL-2 on murine organ-associated lymphocytes between neoplastic and non-neoplastic states. Intraperitoneal administration of IL-2 at a dose of 105 JRU (Japanese Reference Units) twice daily for 3 days led to the death of all the syngeneic MH134-hepatoma- or X5563-myeloma-bearing mice, whereas it had no lethal effect on non-tumor-bearing mice. Histological and morphometric analyses demonstrated that tumor-bearing mice displayed more extensive infiltration of large granular lymphocytes and agranular lymphocytes in the liver and lungs than did the non-tumor-bearing mice. Large granular lymphocytes had the ultrastructural characteristics of lymphokine-activated killer cells. Lymphocytes often underwent extravasation into the interstitial space and exhibited local proliferation without causing any direct injury to apposed parenchymal cells. Flow-cytometric analysis of hepatic mononuclear cells demonstrated that IL-2-receptor-β(IL-2Rβ)-bearing lymphocytes, i.e., natural killer cells and intermediate CD3 cells, were increased in number in the neoplastic state before the IL-2 injection. The present study indicates that the tumor-bearing state increases the number of organ-associated IL-2Rβ+ lymphocytes, which are then greatly amplified by the challenge of high-dose IL-2, leading to the functional disturbance of organs. We have further demonstrated here that an intermittent low-dose IL-2 regimen has a potential therapeutic effect on tumor regression without causing lethal side-effects.