E. Montesoro

Interleukin-2 bolus therapy induces immediate and selective disappearance from peripheral blood of all lymphocyte subpopulations displaying natural killer activity: role of cell adhesion to endothelium.

As early as 10-15 min after the start of a 30 min interleukin-2 (IL-2) infusion, a rapid, virtually complete disappearance of all natural killer (NK) lymphocyte subpopulations (including both CD3- CD56+ and CD3+ CD56+ cells with either alpha/beta or gamma/delta T-cell receptor) was observed from peripheral blood. In contrast, the number of T lymphocytes (CD3+ CD56-) was unmodified for at least 2 h after IL-2 injection. The IL-2-induced, rapid disappearance from peripheral blood of NK and NK-like lymphocytes may be related to their massive adherence to the activated endothelium. In this regard, IL-2 infusion caused a very rapid rise of tumour necrosis factor-alpha (TNF-alpha) plasma concentration, whereas other cytokines, such as interferon-gamma (IFN-gamma), were induced only at later times. In vitro experiments indicated that IL-2, either alone or better combined with TNF-alpha, exerts a rapid and selective stimulatory effect on NK adhesion to endothelial cells. On the basis of these findings, we suggest that the activation of NK lymphocytes induced by IL-2, alone or combined with TNF-alpha, plays a key role in mediating the massive and selective adherence of NK and NK-like cells following IL-2 bolus infusion.

Interleukin-2-dependent long-term cultures of low-density lymphocytes allow the proliferation of lymphokine-activated killer cells with natural killer, Tiγ/δ or TNK phenotype

SummaryWe have developed a culture system for “longterm” growth of human lymphokine-activated killer (LAK) cells exhibiting an elevated, wide-spectrum antitumor cytotoxicity. The system allows the exponential growth of monocyte-depleted low-density lymphocytes in the presence of human serum and recombinant human interleukin-2 (103 U/ml), alone or in combination with interleukin-1 α or β (both at 10 U/ml). Eighteen cultures were established from 18 normal adult donors. The membrane phenotypes of the final LAK cell population, assessed by a panel of monoclonal antibodies (mAb), consist of three main types: (a) NKH-1+, Tiα/β−, Tiγ/δ−, and CD3− lymphocytes; (b) NKH-1+, Tiα/β−, Tiγ/δ+, and CD3+ lymphocytes and (c) NKH-1+, Tiα/β+, Tiγ/δ− and CD3+ lymphocytes. Northern blot analysis showed that all these cell populations express relatively high levels of perforin RNA, particularly cells exhibiting the first phenotype. This culture system may provide a tool for cellular and molecular studies on the mechanisms of antitumor cytotoxicity, as well as the basis for new adoptive immunotherapy protocols in advanced cancer.

Expression of transferrin receptors: differential regulatory mechanisms in monocytes-macrophages versus other hemopoietic cells.

Interaction of a cell membrane receptor with its ligand induces either activation of a specific biological process or cellular uptake of an essential nutrient. On this basis, receptors have been classified in two categories:’ class I receptors transmit a specific piece of information (e.g., epidermal and platelet-derived growth factor receptors modulate the growth of a variety of cell types); class I1 receptors interact with and internalize glycoproteins carrying essential metabolic factors (e.g., low-densitylipoproteins (LDL) and transferrin (Trf) receptors allow respectively the uptake of cholesterol and iron). Upon exposure to ligand, class I receptors are rapidly downregulated. In contrast, binding of ligand with class I1 receptors does not usually lead to modulation of their number. A paradigmatic class I1 receptor is the human receptor for LDL.’ Incubation of cells with cholesterol-saturated LDL results in a decrease in the number of receptors. Conversely, incubation in the absence of LDL causes a rise in their number. Both phenomena are mediated by modulation of receptor synthesis, which is in turn controlled by the intracellular concentration of free cholesterol.2 Recent studies suggest that the Trf receptor may similarly represent a typical class I1 receptor: the level of intracellular iron apparently modulates the rate of Trf receptor synthesis,’ thus resembling the regulation of LDL receptors via cholesterol. All types of cells require iron to sustain essential metabolic pathways. Additionally, actively dividing cells need iron for their growth, presumably because the metal is

IL-2 induces the release of secondary cytokines which stimulate the cytotoxic activity of either NK or CD8(+) lymphocytes.

The therapeutic potential of interleukin-2 (IL-2) for the treatment of human cancer has been extensively investigated (cfr. 1). In cell cultures IL-2 activates not only the lymphocytes which mediate MHC-restricted recognition of specific target cells, but also the natural killer (NK) lymphocytes which lyse in vitro particular tumor targets, The lymphokine-activated killer (lAK) cells, obtained by culturing peripheral blood lymphocytes (PBL) with IL-2 (2) exhibit the capacity of lysing a wide range of fresh and cultured malignant cells and virally-transformed normal tissues with minimal destruction of normal cells (2). Clinical trials have shown that significant anti-tumor responses are observed in a minority of patients with disseminated malignancies following infusion of large dosages of 11-2, combined or not with IAK cells (3). However severe toxicity is associated with high-dose IL-2 therapy (3). The administration of IL-2 results in a series of typical modifications of circulating blood cells. Thus IL-2 has a pronounced effects on the number of circulating lymphocytes: lymphopenia develops early after initiation of bolus IL-2 infusion and persists during the entire period of IL-2 administration. Within 24-48 h after discontinuance of IL-2, a marked rebound lymphocytosis develops (4); the level of rebound is doseand schedule-related (4). Furthermore, IL-2 infusion also elicits a series of secondary effects on the hematopoietic system: i) a progressive anemia may develop, which often requires blood transfusion; ii) thrombocytopenia is occasionally monitored; iii) eosinophilia often occurs, particularly after prolonged IL-2 administration (5). Prelimirary studies suggested that these hematological changes were associated with a decline in circulating erythroid (BFU-E) and granulocyte-macrophage (CFU-GM) progenitors (5). In the present study we have investigated the mechanisms responsible for IL-2-induced hematological modifications and the possible role of secondary IL-2-induced cytokines in the activation of cytotoxic lymphocytes.