Recombinant interleukin-2 directly augments the cytotoxicity of human monocytes

Recombinant interleukin-2 limits the replication of Mycobacterium lepraemurium and Mycobacterium bovis BCG in mice

BALB/c mice were infected with Mycobacterium lepraemurium in the footpad or with Mycobacterium bovis BCG intravenously with 5 x 10(7) bacilli. Recombinant interleukin-2 (IL-2) was injected intraperitoneally as a single dose (20,000 U), as a single course of five injections (400 U each), or as a 6-month course starting 3 days after the M. lepraemurium infection. BCG-infected mice received a single dose (1,000 U) or five daily injections of 100 or 1,000 U each. IL-2 significantly reduced the total bacterial counts in the footpad, lymph nodes, and liver of M. lepraemurium-infected mice (50 to 85%) by 6 months and viable counts in the spleen (30 to 50%) by 60 days after BCG infection. The courses of IL-2 started at 60 days were more effective than those started at 3 days after M. lepraemurium infection (P less than 0.05 to 0.001), and for BCG, 100 U of IL-2 was better than 1,000 U (P less than 0.05 to 0.01). These results indicate that IL-2 limits mycobacterial infections in mice and raise the question of its possible use in humans.

Role of interleukin 2, interleukin 4, and alpha, beta, and gamma interferon in stimulating macrophage antibody-dependent tumoricidal activity

Pretreatment of murine peritoneal exudate macrophages with 1-5 U/ml rIFN-gamma or rIL-2, or higher concentrations of IFN-alpha or IFN-beta greatly stimulated ADCC to Rl lymphoma targets. The assay was direct counting of viable target cells after 9 and 24 h using an E/T ratio of 5:1. 2d of pretreatment was optimal for enhancing ADCC. rIL-4 was inactive and IL-4-depleted Con A-induced spleen lymphokine retained its ADCC-stimulating activity. Antibody to IFN-gamma blocked the ADCC-promoting effect of the lymphokine, suggesting a major role for this factor.

Effect of recombinant human interleukin-2 on the course of experimental chronic respiratory tract infection caused by Klebsiella pneumoniae in mice

The effect of recombinant human interleukin-2 (rIL-2) on the course of experimental chronic respiratory tract infection caused by Klebsiella pneumoniae in mice was examined. rIL-2 was administered subcutaneously once a day for 7 or 14 days, starting 2 weeks after the mice were infected. Administration of 2 or 20 micrograms of rIL-2 per mouse daily for 7 days reduced bacterial counts in the lungs dose dependently. At a dose of 0.2 microgram per day, proliferation of bacteria in the lungs was suppressed after 14 days of administration. Agglutinin titers in serum were not affected by rIL-2 treatment. Monocyte and lymphocyte counts in peripheral blood were increased by administration of 20 micrograms of rIL-2 daily for 14 days but not by treatment for 7 days. In addition, clearance of bacteria from the lungs after aerosol exposure was enhanced by treatment for 7 days before infection. Thus, rIL-2 acted therapeutically or prophylactically in the presence or absence, respectively, of a specific antigen. These effects were not abolished by anti-asialo GM1 antibody. This suggests that activation of natural killer cells does not play a critical role in the therapeutic and prophylactic effects of rIL-2.

Nonrestricted cytotoxicity mediated by interleukin 2-expanded leukocytes is inhibited by anti-LFA-1 monoclonal antibodies (MoAb) but potentiated by anti-CD3 MoAb

Previous results have shown that in addition to their ability to kill tumor cell lines, peripheral blood leukocytes (PBL) expanded in interleukin 2 (IL-2) can also destroy normal PBL targets. Cold target competition results show that PBL and tumor cells can be destroyed by the same population of IL-2-expanded leukocytes (IEL), with better killing observed for tumor cell targets. Since cytolytic activity of IEL is nonspecific, differential binding of target cells by IEL could determine how well each target cell type can be killed. The binding affinity of IEL, in turn, could be influenced by the accessory molecules expressed on effector and target cells. We tested the effect of MoAb to LFA-1, CD2, CD3, CD4, CD8, and HLA molecules on killing mediated by IEL. Anti-LFA-1 inhibited strongly the killing of normal PBL and to a lesser extent the killing of tumor cells. Anti-CD2, CD3, CD4, CD8, and HLA class I molecules did not inhibit the nonspecific killing; rather, anti-CD3 potentiated the killing of PBL, K562, and Daudi cells. These results support the notion that qualitative and quantitative variations in LFA-1-mediated binding of target cells by IEL could result in differential killing of targets. The possibility of using anti-CD3 to selectively potentiate the killing of tumor cells is discussed.

Interleukin 2 and its receptor: structure, function and therapeutic potential

In this review, salient molecular, biochemical and functional features of human interleukin 2 (IL-2), its membrane receptor, and its clinical relevance are outlined. We also describe experimental systems, where observed biological or pharmacological effects of IL-2 could be applied to corresponding clinical situations. In particular, IL-2 has been intensively studied in the context of cancer therapy. We discuss the rationale for the use of IL-2 in cancer treatment and our experience in this area. A better understanding of the IL-2 system and, specifically, the nature of signals transduced through it will allow us to manipulate the immune response in a variety of different ways, resulting in new approaches to investigation of immune responsiveness in general. This may have a profound impact on clinical medicine.

Endothelial cell lysis induced by lymphokine-activated human peripheral blood mononuclear cells

In vitro exposure of human peripheral blood mononuclear cells (PBMC) to interleukin 2 results in the generation of lymphokine-activated killer (LAK) cells. Such LAK cells exhibit cytotoxicity against a spectrum of tumor target cell lines whereas they apparently do not affect normal tissues. In this report we show that PBMC that have been activated with T cell growth factor lyse trypsinized human umbilical cord venous endothelial cells as well as endothelial cell monolayers in a dose-dependent manner. Microscopic analysis showed that during the 4-h incubation period cell clumps containing detached endothelial cells and LAK cells were formed. When these clumps were evaluated with trypan blue the endothelial cells stained positive whereas LAK cells excluded the dye. No lysis occurred when fresh PBMC were added to target endothelial cells. The endothelial cell kill could not be blocked with an anti-LFA-1 antibody nor with intact OKT3 or F(ab')2 fragments of WT32. We conclude that lymphokine-activated PBMC exhibit cell-mediated endothelial cell detachment and lysis.