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M J Robertson

Publications and source records attributed to M J Robertson.

At least 19 recordsLinked to original sources
PubMed1995

A triplet of nuclease proteins (NP42-50) is activated in human Jurkat cells undergoing apoptosis.

Activation of a triplet of nuclear proteins (NP42-50) was observed in human Jurkat T cell line following treatment with an antibody to CD95 (Fas/Apo-1), a cell surface molecule involved in apoptotic cell death. The nuclease activity, corresponding to a triplet of proteins observed at approximately 42, 45, and 50 kDa in size, was extractable, heat-stable, and detected by sodium dodecyl sulfate-polyacrylamide gel electrophoresis containing deoxyribonucleic acids (SDS-PAGE-DNA) assay. The NP42-50 activity requires the presence of Mg2+/Ca2+ and is insensitive to inactivation by heating at 80 degrees C for 5 min. Zinc effectively inhibited the enzymatic activity of NP42-50 on SDS-PAGE-DNA and also protected Jurkat cells from the CD95-mediated apoptosis in cell cultures. The nuclease activation, however, was not a unique pathway for the CD95-mediated cell death. The apoptosis induced by arabinofuranosyl cytosine, a chemotherapeutic agent, also activated the NP42-50 nuclease activity in Jurkat cells, suggesting that a similar cascade of subsequent events in apoptosis may occur in most instances although many different signals can initiate apoptotic cell death in various cell types. The nuclease identified by this study appears to be distinguishable from DNase I or DNase II by its molecular characteristics and its enzymatic requirements. The NP42-50, with respect to the nuclease activity closely associated with apoptotic cell death, may serve as a candidate for the endonuclease(s) involved in the cleavage of DNA into fragments during apoptosis.

Amino Acid Sequence↗
PubMed1995

Phosphorylation of src family lck tyrosine kinase following interleukin-12 activation of human natural killer cells.

Interleukin-12 (IL-12) is a heterodimeric cytokine that augments the cytolytic activity of human NK cells and T cells but has little mitogenic activity on resting lymphocytes. The intracellular signaling pathways involved in NK cell activation by IL-12 have not been fully characterized. In the present studies we found that IL-12 induces tyrosine phosphorylation of a 56-kDa protein, identified in Western blot experiments as p56lck, in resting NK cells. IL-12 was active in the range of 0.1 to 1000 U/ml, with maximal activity between 10 and 100 U/ml (30 and 300 pM). The maximal effect was noted 5 min after stimulation and was almost completely inhibited by genistein. IL-12 induced similar effects in resting and IL-2 activated NK cells. Following IL-12 stimulation of resting NK cells, immunoprecipitated lck kinase exhibited increased in vitro autophosphorylation activity 5 and 10 min after activation. Several additional substrates were phosphorylated in vitro following IL-12 stimulation, including proteins of 70 and 110 kDa. These studies indicate that lck tyrosine kinase is involved in the IL-12 signaling pathway in human NK cells. As the primary functional effect of IL-12 on resting NK cells is the enhancement of cytolytic activity and secretory function rather than cell proliferation, these findings suggest that lck tyrosine kinase is involved in these signaling pathways in human NK cells.

Animals↗
PubMed1995

Interleukin 2 signaling involves the phosphorylation of Stat proteins.

One of the most important cytokines involved in immune response regulation is interleukin 2 (IL-2), a potent activator of the proliferation and function of T lymphocytes and natural killer cells. The mechanisms by which the effects of IL-2 are propagated within cells are not understood. While the binding of IL-2 to its receptor was recently shown to lead to the activation of two kinases, Jak-1 and Jak-3, subsequent steps in the signaling pathway to the nucleus that lead to the activation of specific genes had not been characterized. Since many cytokines that activate Jak kinases also lead to the tyrosine phosphorylation and activation of members of the Stat family of transcription factors, the ability of IL-2 to trigger Stat phosphorylation was examined. Exposure of activated human T lymphocytes or of a natural killer cell line (NKL) to IL-2 leads to the phosphorylation of Stat1 alpha, Stat1 beta, and Stat3, as well as of two Stat-related proteins, p94 and p95. p94 and p95 share homology with Stat1 at the phosphorylation site and in the Src homology 2 (SH2) domain, but otherwise are immunologically distinct from Stat1. These Stat proteins were found to translocate to the nucleus and to bind to a specific DNA sequence. These findings suggest a mechanism by which IL-2 binding to its receptor may activate specific genes involved in immune cell function.

Blotting, Western↗
PubMed1995

Renal pharmacology of GR138950, a novel non-peptide angiotensin AT1 receptor antagonist.

This paper describes the renal pharmacology of the novel, specific, non-peptide angiotensin AT1 receptor antagonist, GR138950 (1-[[3-bromo-2-[2-[[(trifluoromethyl) sulphonyl] amino] phenyl]-5-benzofuranyl] methyl]-4-cyclopropyl-2-ethyl-1H-imidazole-5- carboxamide). When administered to anaesthetised salt-replete dogs, GR138950 caused renal vasodilatation and significant increases in sodium and urine excretion. No change in glomerular filtration rate was observed indicating that the natriuresis was a consequence of inhibition of tubular sodium reabsorption. Qualitatively similar but less marked changes in renal function were observed in response to the angiotensin converting enzyme inhibitor, captopril, although in contrast to GR138950, captopril also caused a small but significant fall in mean blood pressure. Intra-renal artery infusion of exogenous angiotensin II resulted in dose-related renal vasoconstriction and decreases in urine excretion, sodium excretion, fractional excretion of sodium and glomerular filtration rate. These renal effects of angiotensin II were all markedly antagonised by GR138950. We conclude that GR138950 is an effective antagonist of the renal haemodynamic and excretory actions of endogenous and exogenous angiotensin II.

Angiotensin I↗
PubMed1995

Inhibition of selective signaling events in natural killer cells recognizing major histocompatibility complex class I.

Many studies have characterized the transmembrane signaling events initiated after T-cell antigen receptor recognition of major histocompatibility complex (MHC)-bound peptides. Yet, little is known about signal transduction from a set of MHC class I recognizing receptors on natural killer (NK) cells whose ligation dramatically inhibits NK cell-mediated killing. In this study we evaluated the influence of MHC recognition on the proximal signaling events in NK cells binding tumor targets. We utilized two experimental models where NK cell-mediated cytotoxicity was fully inhibited by the recognition of specific MHC class I molecules. NK cell binding to either class I-deficient or class I-transfected target cells initiated rapid protein tyrosine kinase activation. In contrast, whereas NK cell binding to class I-deficient targets led to inositol phosphate release and increased intracellular free calcium ([Ca2+]i), NK recognition of class I-bearing targets did not induce the activation of these phospholipase C-dependent signaling events. The recognition of class I by NK cells clearly had a negative regulatory effect since blocking this interaction using anti-class I F(ab')2 fragments increased inositol 1,4,5-trisphosphate release and [Ca2+]i and increased the lysis of the targets. These results suggest that one of the mechanisms by which NK cell recognition of specific MHC class I molecules can block the development of cell-mediated cytotoxicity is by inhibiting specific critical signaling events.

Antibodies, Monoclonal↗
PubMed1995

Functional consequences of APO-1/Fas (CD95) antigen expression by normal and neoplastic hematopoietic cells.

Murine monoclonal antibody (mAb) 7C11 binds to the same cell surface epitope as anti-APO-1 and anti-Fas and reacts specifically with cells transfected with a cDNA encoding the human Fas antigen. Furthermore, incubation with 7C11 causes death of hematopoietic cell lines that express APO-1/Fas but not APO-1/Fas-negative cell lines. 7C11 therefore recognizes the human APO-1/Fas (CD95) antigen, a 40 to 50 kDa cell surface glycoprotein that can trigger apoptosis or programmed cell death. Expression of APO-1/Fas antigen by normal and neoplastic hematopoietic cells was determined by flow cytometry using 7C11. APO-1/Fas is expressed by approximately 30 to 40% of resting peripheral blood T cells, B cells, and monocytes and by approximately 5% of resting NK cells and thymocytes. It was not detected on granulocytes, erythrocytes, or platelets. Approximately 80 to 90% of activated T cells, B cells, and thymocytes express APO-1/Fas, as do the majority of activated NK cells. Perturbation of APO-1/Fas by 7C11 does not affect the viability of resting lymphocytes or monocytes. In contrast, activated T cells and NK cells undergo apoptosis within 3 hours of exposure to 7C11. Other mAb that stimulate T cells or NK cells do not cause rapid induction of programmed cell death. APO-1/Fas antigen is expressed by many cell lines of lymphoid and myeloid lineage. However, this antigen was detected on neoplastic cells from only one of 69 patients with acute myeloid leukemia, acute lymphoblastic leukemia, chronic myelogenous leukemia, chronic lymphocytic leukemia, or multiple myeloma. Only 3 out of 25 tumor samples from patients with non-Hodgkin's lymphoma were found to express APO-1/Fas. All three of these lymphomas harbored the bcl-2-Ig fusion gene associated with the chromosomal translocation t (14;18). Conversely, only 27% of lymphomas that possessed the bcl-2-Ig gene were found to express the APO-1/Fas antigen. Like normal activated lymphocytes, leukemia and lymphoma cells that expressed APO-1/Fas antigen were found to undergo apoptosis in vitro after incubation with 7C11. The APO-1/Fas antigen appears to regulate the growth of normal hematopoietic cells, and the marked upregulation of this antigen on activated normal lymphocytes contrasts sharply with the absence of APO-1/Fas on neoplastic cells of hematopoietic lineage. Defects in the apoptotic signal delivered through this antigen might contribute to the pathogenesis of hematopoietic neoplasms. Thus, the gene encoding APO-1/Fas can be considered a novel type of tumor suppressor gene, just as bcl-2 can be considered a cellular proto-oncogene.

Animals↗
PubMed1995

Pharmacological effects of GR138950, a novel angiotensin AT1 receptor antagonist.

The antagonist activity of GR138950 (1-[[3-bromo-2-[2-[[(trifluoromethyl)sulphonyl]amino]phenyl]-5- benzofuranyl]methyl]-4-cyclopropyl-2-ethyl-1H-imidazole-5-carboxamide) was investigated at angiotensin AT1 receptors and AT2 receptors in vitro and on blood pressure in conscious rats. GR138950 suppressed and displaced angiotensin II (AII) concentration-effect curves in the rabbit isolated aorta (pKb approximately 9.0-9.7) but had no effect against phenylephrine or serotonin induced-contractions. GR138950 competed with [3H]-AII for angiotensin AT1 receptors in rat liver membranes (pKi = 9.09). GR138950 had no apparent affinity for angiotensin AT2 receptors (bovine cerebellum; pKi < 6.0). GR138950 (1 mg/kg i.a. and p.o.) inhibited pressor responses to AII, but not phenylephrine, in conscious normotensive rats. Parallel displacements in AII dose-response curves occurred without any reduction in the maximum response to AII. The antagonist activity of GR138950 lasted for up to 24 h. GR138950 (> 0.03 mg/kg i.a., > 0.3 mg/kg p.o.) significantly reduced diastolic blood pressure (DBP) in renal artery ligated hypertensive rats. DBP was reduced maximally, 5 to 7 h after administration and the antihypertensive effect of GR138950 lasted for up to 48 h. Daily administration (5 days) of GR138950 to renal artery ligated hypertensive rats produced a sustained reduction in DBP. Acute administration of GR138950 (1 mg/kg i.a.) also significantly reduced DBP in spontaneously hypertensive rats but not in normotensive rats. Heart rate was little changed in renal artery ligated hypertensive rats, normotensive rats and spontaneously hypertensive rats. These experiments demonstrate that GR138950 is a potent, selective and specific angiotensin AT1 receptor antagonist that is orally active and reduces DBP in conscious hypertensive rats.(ABSTRACT TRUNCATED AT 250 WORDS)

Angiotensin II↗
PubMed1994

Interleukin 2 receptor gamma chain expression on resting and activated lymphoid cells.

The interleukin 2 receptor (IL-2R) is known to be comprised of at least three genetically distinct subunits termed alpha, beta, and gamma. These chains can be expressed individually or in various combinations resulting in distinct receptors with different affinities for IL-2. In contrast to alpha and beta, the cell surface expression of the gamma chain protein previously has not been well-characterized. To examine cell surface expression of IL-2R gamma on hematopoietic cells, we developed two new monoclonal antibodies (mAbs) specific for this protein. Both 1A11 (immunoglobulin [IgG1]) and 3G11 (IgM) specifically reacted with murine cells transfected with IL-2R gamma cDNA, and immunoprecipitation studies indicated that both antibodies precipitated a protein of approximately 62-65 kD. Scatchard analysis of IL-2 binding to murine cells transfected with cDNA-encoding combinations of IL-2R components demonstrated that neither beta nor gamma chain bind IL-2 with measurable affinity, but coexpression of both beta and gamma is sufficient to form an intermediate affinity receptor. In the absence of gamma chain, beta chain interacts with alpha chain to form a "pseudo-high" affinity receptor. In contrast, gamma chain does not appear capable of interacting with alpha in the absence of beta chain. Thus, gamma chain appears to interact only with beta, but beta chain is capable of interacting with both alpha and gamma. Using the newly developed mAbs to examine cell surface expression by immunofluorescence, resting T cells were found to express low levels of gamma chain without detectable alpha or beta. Early after mitogen stimulation, T cells expressed higher levels of alpha, beta, and gamma. However, at later time points, T cells expressed alpha and gamma in marked excess over beta. Thus, formation of high affinity IL-2R on activated T cells was primarily limited by beta chain expression. In contrast, resting natural killer (NK) cells constitutively expressed IL-2R beta without detectable alpha or gamma. After activation with either IL-2 or IL-12, expression of both alpha and gamma transiently increased and then returned to very low levels. Expression of functional IL-2R on resting and activated NK cells, therefore, appeared to be primarily limited by the expression of gamma chain. IL-2 binding studies with resting NK cells confirmed the results of immunofluorescence studies indicating the presence of very low numbers of intermediate affinity (beta gamma) receptors for IL-2 on these cells.(ABSTRACT TRUNCATED AT 400 WORDS)

Animals↗
PubMed1994

Agonist-antagonist interactions at angiotensin receptors: application of a two-state receptor model.

Interactions between agonists and antagonists at angiotensin receptors are characterized by a number of features: variation of antagonist dynamics between apparent simple competition, insurmountable antagonism and, occasionally, augmentation; the tendency for insurmountable antagonism to be saturable; slow recovery of agonist responses following agonist-induced tachyphylaxis; and the ability of competitive antagonists to accelerate recovery from the latter intervention. Some of these phenomena have also been observed in studies of 5-HT2 receptors where they were attributed to the operation of a two-state model with an allosteric site. In this article, Mark Robertson and colleagues propose that the properties of angiotensin AT1 receptors may be explained by a similar model, but without the need to evoke an allosteric site.

Angiotensin II↗
PubMed1994

Cardiovascular effects of GR117289, a novel angiotensin AT1 receptor antagonist.

1. The effect of GR117289, an angiotensin AT1 receptor antagonist, on diastolic blood pressure (DBP) was determined in angiotensin-dependent and angiotensin-independent models of hypertension in rats. In addition, the antagonist profile of GR117289 at angiotensin AT1 receptors was determined in conscious renal hypertensive rats and conscious normotensive rats, dogs and marmosets. 2. Intra-arterial and oral administration of GR117289 (0.3-3 mg kg-1, i.a.; 1-10 mg kg-1, p.o.) to 6-day left renal artery ligated hypertensive (RALH) rats (DBP > 140 mmHg) produced significant, dose-related reductions in DBP with little apparent effect on heart rate (< 15%). The antihypertensive effect of GR117289 developed progressively over several hours and with some doses persisted for 24-48 h after administration. 3. Administration of GR117289 (1 mg kg-1, i.a.) on 5 consecutive days to RALH rats reduced DBP on each day. The antihypertensive effect of GR117289 was not cumulative as DBP had almost returned to base-line values, 24 h after administration of each dose. 4. A dose of GR117289 (3 mg kg-1, i.a.), which produced a substantial reduction in DBP (about 70 mmHg) in RALH rats, was administered to rats in which blood pressure was elevated either by unilateral renal artery clipping, sustained infusion of angiotensin II (AII), DOCA-salt administration or genetic inbreeding. GR117289 reduced DBP in rats in which the renin-angiotensin system was activated by renal artery clipping or AII infusion but had little effect in normotensive rats, DOCA-salt rats and SHR. 5. Systemic administration of All to RALH rats and to normotensive rats, dogs and marmosets elicited reproducible pressor responses in all species. Systemic or oral administration of GR1 17289 (3 mg kg-1)inhibited the pressor responses produced by All, resulting in parallel, rightward displacements of All dose-response curves.6. Maximal displacements of All dose-response curves occurred 1 h and 1-7 h after systemic and oral administration, respectively. GR1 17289 produced a 32-246 fold displacement after systemic administration and a 4-12 fold displacement after oral administration. The effect in dogs was short lasting after systemic administration but the effect of GRI17289 lasted for up to 24 h in rats and marmosets and for up to 24 h after oral administration in all species. The antagonist activity appeared specific for angiotensin receptors as GRi17289 did not inhibit pressor responses to phenylephrine or vasopressin.7. These experiments demonstrate that GRI 17289 reduces blood pressure in conscious hypertensive rats after both systemic and oral administration, and is an effective antagonist at angiotensin AT1 receptors in conscious rats, dogs and marmosets.

Administration, Oral↗
PubMed1993

Developmental regulation of a mucinlike glycoprotein selectively expressed on natural killer cells.

Natural killer (NK) cells are CD3:TCR-, CD16+, CD56+ large granular lymphocytes capable of recognizing and eliminating a variety of virus-infected, malignant, and antibody-coated target cells. Two functionally distinct populations of peripheral blood NK cells can be differentiated by their surface expression of an isoform of the neural cell adhesion molecule (CD56). CD56bright NK cells have the attributes of an undifferentiated cell, in that they proliferate in response to exogenous cytokines, but exert poor cytolytic activity. CD56dim NK cells have the attributes of a more differentiated cell, in that they proliferate poorly in response to exogenous cytokines, but are potent cytolytic effector cells. Here we describe the molecular characterization of a NK cell restricted epitope (PEN5) that is selectively expressed on the functionally differentiated CD56dim NK cells. PEN5+ NK cells proliferate poorly in response to interleukin 2 (IL-2), but are potent cytolytic effectors, whereas PEN5- NK cells proliferate in response to IL-2, but are poor cytolytic effectors. Biochemical and immunochemical analyses reveal the PEN5 epitope to be an unusual sulfated poly-N-lactosamine carbohydrate related to keratan sulfate glycosaminoglycans. Immunoprecipitates prepared using a monoclonal antibody reactive with PEN5 include two polydisperse membrane-bound glycoproteins, PEN5 alpha (120-170 kD) and PEN5 beta (210-245 kD). Enzymatic deglycosylation reduces the apparent molecular weight of both PEN5 isoforms by 80-90%, and classifies PEN5 beta as a mucinlike glycoprotein. The surface expression of the PEN5 epitope is downmodulated by stimuli that induce NK cell proliferation, and it is absent from leukemic NK cells of patients with granular lymphocyte proliferative disorder. Taken together, these results indicate that PEN5 is a developmentally regulated poly-N-lactosamine epitope associated with a mucin-type glycoprotein, whose expression is restricted to the population of nonproliferative NK cells fully committed to cytolytic effector function.

Amino Sugars↗
PubMed1993

Prediction of graft-versus-host disease by phenotypic analysis of early immune reconstitution after CD6-depleted allogeneic bone marrow transplantation.

Graft-versus-host disease (GVHD) is a major cause of morbidity and mortality following allogeneic bone marrow transplantation (BMT). Because GVHD is frequently refractory to treatment, the early identification of high-risk patients could have significant clinical value. To identify such patients, we examined early immunologic recovery in 136 patients with hematologic malignancies who received anti-T12 (CD6)-purged allogeneic bone marrow over a 9-year period. The majority of patients received marrow from HLA-matched sibling donors after ablation with cyclophosphamide and total body irradiation. No patients received any immune suppressive medications for GVHD prophylaxis. The fraction and absolute numbers of peripheral blood lymphocytes (PBL) expressing the CD3, CD4, CD8, and CD56 surface antigens were determined weekly by immunofluorescence analysis in patients beginning 8 to 14 days (week 2) after marrow infusion. Results in patients who did or did not subsequently develop GVHD post-BMT were compared. Within 2 weeks of marrow infusion, patients who developed grades 2-4 GVHD had significantly higher percentages and absolute numbers of CD8+ T cells and a lower fraction of CD56+ natural killer (NK) cells than individuals who remained free of GVHD. Thirty-five percent of patients whose PBL were greater than 25% CD8+ in the second posttransplant week developed GVHD, compared with only 3% of patients who had < or = 25% CD8+ cells (odds ratio 37.8; 95% confidence interval [CI] 4.1 to 397). A subgroup of patients at very high risk for GVHD could be identified based on the combined frequency of CD8+ T cells and NK cells in blood. Seventy-five percent of patients with greater than 25% CD8+ cells and < or = 45% CD56+ cells during week 2 post-BMT developed GVHD, compared with only 11% of the remaining patients (odds ratio 24.9; 95% CI, 5.3 to 117.0). None of the 23 patients with both less than 25% CD8+ cells and greater than 45% CD56+ cells in the second posttransplant week developed grades 2-4 GVHD. Our findings indicate that CD8+ T cells play an important role in the pathogenesis of GVHD in humans. Analysis of immune reconstitution early after BMT is useful in predicting the onset of GVHD and can help direct the implementation of treatment strategies before the appearance of clinical manifestations. Such interventions may decrease the morbidity and mortality associated with allogeneic BMT and ultimately improve overall survival.

Adult↗
PubMed1993

Costimulatory signals are required for optimal proliferation of human natural killer cells.

CD56dim NK cells, which comprise approximately 90% of human peripheral blood NK cells, respond to IL-2 with cytokine production, up-regulation of functionally relevant surface molecules, and augmented cytolytic activity. Nevertheless, CD56dim NK cells proliferate poorly in response to IL-2 alone. We found that other NK cell mitogens, including IL-4, IL-7, and IL-12, also induced little proliferation of CD56dim NK cells. Indeed, IL-2 stimulated at least 10-fold more NK cell proliferation than did IL-4, IL-7, or IL-12. In contrast, leukocyte-conditioned medium (LCM) induced two- to threefold greater proliferation of CD56dim NK cells than did optimal concentrations of IL-2. Although the calcium ionophore ionomycin did not stimulate proliferation by itself, it markedly augmented LCM-induced proliferation of CD56dim NK cells. Proliferation in response to either LCM alone or LCM together with ionomycin was almost completely abrogated by anti-IL-2R antibodies. Thus, IL-2 appears to be necessary but not sufficient for optimal proliferation of CD56dim NK cells. LCM-induced proliferation of ionomycin-activated CD56dim NK cells was inhibited 24% by anti-IL-1 heteroantisera and 57% by anti-TNF antisera; a combination of both antisera inhibited proliferation by 73%. Furthermore, although rIL-1 and TNF did not induce proliferation by themselves, both cytokines could augment IL-2-induced proliferation of resting or ionomycin-activated NK cells. Hence IL-1 and TNF do not appear to be primary NK cell mitogens, but rather accessory factors that can enhance IL-2-dependent NK cell proliferation. Stimulation through CD2 or CD16 Ag did not enhance LCM-induced NK cell proliferation. However, stimulation with NK-sensitive K562 cells strongly augmented CD56dim NK cell proliferation to LCM or to IL-2, IL-1, and TNF in combination. NK-resistant Daudi cells did not promote the proliferation of highly purified NK cells. Thus, NK cell proliferation may be enhanced by triggering through putative receptors for natural killing, and ionomycin may mimic such triggering. Although IL-2 by itself can induce NK cell proliferation, most NK cells resemble T and B lymphocytes in that they require multiple signals for optimal proliferation.

Animals↗
PubMed1993

Selective modulation of human natural killer cells in vivo after prolonged infusion of low dose recombinant interleukin 2.

The immunologic consequences of prolonged infusions of rIL-2 in doses that produce physiologic serum concentrations of this cytokine were investigated. rIL-2 in doses of 0.5-6.0 x 10(6) U/m2 per d (3.3-40 micrograms/m2 per d) was administered by continuous intravenous infusion for 90 consecutive days to patients with advanced cancer. IL-2 concentrations (25 +/- 25 and 77 +/- 64 pM, respectively) that selectively saturate high-affinity IL-2 receptors (IL-2R) were achieved in the serum of patients receiving rIL-2 infusions of 10 micrograms/m2 per d and 30 micrograms/m2 per d. A gradual, progressive expansion of natural killer (NK) cells was seen in the peripheral blood of these patients with no evidence of a plateau effect during the 3 mo of therapy. A preferential expansion of CD56bright NK cells was consistently evident. NK cytotoxicity against tumor targets was only slightly enhanced at these dose levels. However, brief incubation of these expanded NK cells with IL-2 in vitro induced potent lysis of NK-sensitive, NK-resistant, and antibody-coated targets. Infusions of rIL-2 at 40 micrograms/m2 per d produced serum IL-2 levels (345 +/- 381 pM) sufficient to engage intermediate affinity IL-2R p75, which is constitutively expressed by human NK cells. This did not result in greater NK cell expansion compared to the lower dose levels, but did produce in vivo activation of NK cytotoxicity, as evidenced by lysis of NK-resistant targets. There was no consistent change in the numbers of CD56- CD3+ T cells, CD56+ CD3+ MHC-unrestricted T cells, or B cells during infusions of rIL-2 at any of the dosages used. This study demonstrates that prolonged infusions of rIL-2 in doses that saturate only high affinity IL-2R can selectively expand human NK cells for an extended period of time with only minimal toxicity. Further activation of NK cytolytic activity can also be achieved in vivo, but it requires concentrations of IL-2 that bind intermediate affinity IL-2R p75. Clinical trials are underway attempting to exploit the differing effects of various concentrations of IL-2 on human NK cells in vivo.

Antibody-Dependent Cell Cytotoxicity↗