Differential effects of IL-2 and IL-15 on expression of IL-2 receptor alpha

IL-2 and IL-15 have overlapping functions since they share the IL-2Rbetagamma receptor complex. However, each cytokine has a private alpha receptor namely IL-2Ralpha for IL-2 and IL-15Ralpha for IL-15. As a consequence the effects of the two cytokines may differ. We describe the differential effects of the two cytokines regarding the induction of cell surface expression of the IL-2Ralpha subunit on YT-l cells. Both cytokines induced transcription of the IL-2Ralpha gene. Furthermore translation of IL-2Ralpha leading to intracellular expression of the receptor was observed following either IL-2 or IL-15 addition. However, only IL-15 was associated with the induction of cell surface expression of IL-2Ralpha. With IL-2 there appears to be an impediment to the translocation of IL-2Ralpha to the cell membrane. Since surface expression of IL-2Ralpha is a key element in the formation of the high affinity IL-2 receptor, translocation of IL-2Ralpha to the membrane represents another level of control of the immune response in addition to regulation of IL-2Ralpha transcription and translation.

Comparative assessment of virulence of recombinant vaccinia viruses expressing IL-2 and IL-15 in immunodeficient mice

IL-2 and -15 belong to the four alpha-helix bundle family of cytokines and display a spectrum of overlapping immune functions because of shared signal transducing receptor components of the IL-2 receptor complex. However, recent evidence suggests a nonredundant unique role for IL-15 in the establishment and perhaps maintenance of peripheral natural killer (NK) cell populations in vivo. To explore the contribution of locally released IL-15 on peripheral NK-cell-mediated innate immune responses, we generated a recombinant vaccinia virus that expresses IL-15 and evaluated the course of vaccinial disease in athymic nude mice. Coexpression of IL-15 resulted in the attenuation of virulence of vaccinia virus, and mice inoculated with 10(5) plaque-forming units or less resolved the infection successfully. In contrast, mice inoculated with a similar dose of the control vaccinia virus failed to eliminate the virus and died of generalized vaccinial disease. Enhanced expression of IL-12 and IFN-gamma as well as induction of chemokines were evident in the mice inoculated with IL-15-expressing vaccinia virus in addition to an increase in NK cells in the spleen. However, in this model system, the degree of attenuation in viral virulence attained with coexpression of IL-15 was much less than that achieved with coexpression of IL-2, suggesting that the peripheral NK-cell-mediated events are more responsive to IL-2 than to IL-15.

IL-2Ralpha-Directed monoclonal antibodies provide effective therapy in a murine model of adult T-cell leukemia by a mechanism other than blockade of IL-2/IL-2Ralpha interaction

Adult T-cell leukemia (ATL) develops in a small proportion of human T-cell lymphotrophic virus-I infected individuals. The leukemia consists of an overabundance of activated T cells, which are characterized by the expression of CD25, or IL-2Ralpha, on their cell surface. Presently, there is not an accepted curative therapy for ATL. We developed an in vivo model of ATL in non-obese diabetic/severe combined immunodeficient (NOD/ SCID) mice by introducing cells from an ATL patient (MET-1) into the mice. The leukemic cells proliferated in these mice that lack functional T, B, and natural killer (NK) cells. The MET-1 leukemic cells could be monitored by measurements of both serum soluble Tac (IL-2Ralpha) and soluble human beta2-microglobulin (beta2mu) by ELISA. The disease progressed to death in the mice after approximately 4-6 weeks. The mice developed grossly enlarged spleens and a leukemia involving ATL cells that retained the phenotype and the T-cell receptor rearrangement and human T-cell lymphotrophic virus-I integration pattern of the patient's ATL leukemia cells. This model is of value for testing the efficacy of novel therapeutic agents for ATL. The administration of humanized anti-Tac (HAT), murine anti-Tac (MAT), and 7G7/B6, all of which target IL-2Ralpha, significantly delayed the progression of the leukemia and prolonged the survival of the tumor-bearing mice. In particular, HAT induced complete remissions in 4 of 19 mice and partial remissions in the remainder. It appears that the antibodies act by a mechanism that had not been anticipated. The prevailing view is that antibodies to the IL-2Ralpha receptor have their effective action by blocking the interaction of IL-2 with its growth factor receptor, thereby inducing cytokine deprivation apoptosis. However, although both HAT and MAT block the binding of IL-2 to IL-2Ralpha of the high affinity receptor, the 7G7/B6 monoclonal antibody binds to a different epitope on the IL-2Ralpha receptor, one that is not involved in IL-2 binding. This suggested that the antibodies provide an effective therapy by a mechanism other than induction of cytokine deprivation. In accord with this view, the MET-1 cells obtained from the spleens of leukemic mice did not produce IL-2, nor did they express IL-2 mRNA as assessed by reverse transcription-PCR. Another possible conventional mechanism of action involves complement-mediated killing. However, although MAT and 7G7/B6 fix rabbit complement, HAT does not do so. Furthermore, in the presence of NOD/SCID mouse serum, there was no complement-mediated lysis of MET-1 cells. In addition, the antibodies did not manifest antibody-dependent cellular cytotoxicity with NOD/SCID splenocytes that virtually lack NK cells as the effector cells as assessed in an in vitro chromium-release assay. However, in contrast to the efficacy of intact HAT, the F(ab')2 version of this antibody was not effective in prolonging the survival of mice injected with MET-1 ATL cells. In conclusion, in our murine model of ATL, monoclonal antibodies, HAT, MAT, and 7G7/B6, appear to delay progression of the leukemia by a mechanism of action that is different from the accepted mechanism of IL-2 deprivation leading to cell death. We consider two alternatives: the first, antibody-dependent cellular cytotoxicity mediated by FcRI- or FcRIII-expressing cells other than NK cells, such as monocytes or polymorphonuclear leukocytes. The second alternative we consider involves direct induction of apoptosis by the anti-IL-2R antibodies in vivo. It has been shown that the IL-2R is a critical element in the peripheral self-tolerance T-cell suicide mechanism involved in the phenomenon of activation-induced cell death.

A mechanism for modulation of cellular responses to VEGF: activation of the integrins

Many similarities exist in the cellular responses elicited by VEGF and governed by integrins. Here, we identify a basis for these interrelationships: VEGF activates integrins. VEGF enhanced cell adhesion, migration, soluble ligand binding, and adenovirus gene transfer mediated by alphavbeta3 and also activated other integrins, alphavbeta5, alpha5beta1, and alpha2beta1, involved in angiogenesis. Certain tumor cells exhibited high spontaneous adhesion and migration, which were attributable to a VEGF-dependent autocrine/paracrine activation of integrins. This activation was mediated by the VEGFR2 receptor and regulated via phosphatidylinositol-3-kinase, Akt, and the PTEN signaling axis. Thus, integrin activation provides a mechanism for VEGF to induce a broad spectrum of cellular responses.

Treatment of noninfectious intermediate and posterior uveitis with the humanized anti-Tac mAb: a phase I/II clinical trial

To evaluate the safety and potential therapeutic activity of humanized anti-IL-2 receptor mAb (Daclizumab) therapy in the treatment of patients with severe, sight-threatening, intermediate and posterior noninfectious uveitis, a nonrandomized, open-label, pilot study was performed. Patients with uveitis were treated with a minimum of 20 mg of prednisone, cyclosporine, antimetabolites, or any combination of these agents were eligible. Patients were weaned off their systemic immunosuppressive agents according to a standardized schedule, while ultimately receiving Daclizumab infusions every 4 weeks. Anti-IL-2 receptor antibody therapy, given intravenously with intervals of up to 4 weeks in lieu of standard immunosuppressive therapy, appeared to prevent the expression of severe sight-threatening intraocular inflammatory disease in 8 of 10 patients treated over a 12-month period, with noted improvements in visual acuity. One patient met a primary endpoint with a loss of vision of 10 letters or more from baseline in one eye and another patient discontinued therapy because of evidence of increased ocular inflammation. All patients were able to tolerate the study medications without the need for dose reduction. We report effective long-term use of anti-IL-2 therapy for an autoimmune indication. These initial findings would suggest that anti-IL-2 receptor therapy may be an effective therapeutic approach for uveitis and, by implication, other disorders with a predominant Th1 profile.

IL-15 induces the expression of chemokines and their receptors in T lymphocytes

IL-15 is a T cell growth factor that shares many biological activities with IL-2 and uses the same beta/gamma polypeptides of the IL-2R complex for signal transduction. Accumulating evidence implicates an important role for this cytokine in the inflammatory response of the host. Consistent with such a role, IL-15 has been shown to be a chemoattractant for T lymphocytes, NK cells, and neutrophils. Extending these observations, we now show that IL-15 is a potent inducer of CC-, CXC-, and C-type chemokines in T lymphocytes. In addition, we demonstrate that IL-15 induces CC chemokine receptors, but not CXC chemokine receptors, in a dose-dependent manner. Thus, our findings suggest that the proinflammatory effects of IL-15 at least in part may be due to the induction of chemokines and their receptors in T cells. Furthermore, we demonstrate that IL-15 promotes entry and replication of macrophage-tropic HIV in T lymphocytes and suggest a plausible mechanism by which IL-15, a cytokine that is elevated in HIV-infected individuals, may promote the transition of HIV displaying the M-tropic phenotype primarily associated with the initial transmission into the T cell-tropic phenotype that predominates as the disease progresses.

Regulation of vascular endothelial growth factor secretion in human meningioma cells

Previously, we induced vascular endothelial growth factor/vascular permeability factor (VEGF/VPF) secretion in glioma cell lines by using physiologic concentrations of epidermal growth factor (EGF), basic fibroblast growth factor (bFGF), or platelet-derived growth factor-BB (PDGF-BB). We hypothesized that VEGF/VPF might enhance the blood supply required for the unregulated growth of tumors, and that it acts as the central mediator of tumor angiogenesis. The objective of this study was to determine whether the expression of VEGF/VPF by meningiomas is regulated by growth factors or sex hormones. By means of an enzyme-linked immunosorbent assay of CH-157MN meningioma cell supernatants, we demonstrated that EGF and bFGF similarly induce VEGF secretion by CH-157MN meningioma cells. At the maximum concentrations of EGF (50 ng/mL) and bFGF (50 ng/mL) used in this study, VEGF secretion was induced to 140% to 160% above baseline constitutive secretion. PDGF-BB homodimer did not enhance VEGF secretion significantly. Estradiol (up to 10(-7) mol/L), progesterone (up to 10(-5) mol/L), or testosterone (up to 10(-5) mol/L) did not stimulate or inhibit VEGF secretion in CH-157MN meningioma cells (p > 0.05). Furthermore, we demonstrated that dexamethasone decreased VEGF secretion to 32% of baseline constitutive secretion. This might explain the effect of corticosteroids in alleviating peritumoral brain edema in meningiomas. These results suggest that VEGF secretion in CH-157MN meningioma cells is mainly regulated by growth factors and corticosteroids, but not by sex hormones. Understanding the regulation of VEGF/VPF secretion in meningiomas might contribute to the development of a new therapeutic strategy.

Paracrine expression of a native soluble vascular endothelial growth factor receptor inhibits tumor growth, metastasis, and mortality rate

Vascular endothelial growth factor (VEGF) is a potent and selective vascular endothelial cell mitogen and angiogenic factor. VEGF expression is elevated in a wide variety of solid tumors and is thought to support their growth by enhancing tumor neovascularization. To block VEGF-dependent angiogenesis, tumor cells were transfected with cDNA encoding the native soluble FLT-1 (sFLT-1) truncated VEGF receptor which can function both by sequestering VEGF and, in a dominant negative fashion, by forming inactive heterodimers with membrane-spanning VEGF receptors. Transient transfection of HT-1080 human fibrosarcoma cells with a gene encoding sFLT-1 significantly inhibited their implantation and growth in the lungs of nude mice following i.v. injection and their growth as nodules from cells injected s.c. High sFLT-1 expressing stably transfected HT-1080 clones grew even slower as s.c. tumors. Finally, survival was significantly prolonged in mice injected intracranially with human glioblastoma cells stably transfected with the sflt-1 gene. The ability of sFLT-1 protein to inhibit tumor growth is presumably attributable to its paracrine inhibition of tumor angiogenesis in vivo, since it did not affect tumor cell mitogenesis in vitro. These results not only support VEGF receptors as antiangiogenic targets but also demonstrate that sflt-1 gene therapy might be a feasible approach for inhibiting tumor angiogenesis and growth.

Adenovirus-mediated p16 gene transfer prevents drug-induced cell death through G1 arrest in human glioma cells

This study examined the effects of full-length p16 gene transfer by recombinant adenovirus on cell growth and on sensitivity to CDDP or ACNU chemotherapies. We developed a recombinant adenovirus expressing the full-length human p16 gene (AxCA-hp16) by the COS-TPC method. AxCA-hp16 was infected into the p16-null human glioma cell line, U251MG. AxCA-hp16 infection inhibited proliferation of U251MG cells. A proliferation assay employing MTT showed that AxCA-hp16 infection induced chemoresistance, preventing CDDP-induced cell death (11- to 15-fold) and ACNU-induced cell death (80- to 92-fold). In the absence of AxCA-hp16, cell death was induced with CDDP or ACNU at 3 to 5 days after treatment, as demonstrated by Trypan-blue exclusion. Flow-cytometric analysis showed that CDDP or ACNU arrested cells in the G2 phase on day 1 and that cells re-entered the cycle on day 3. However, the cells infected with AxCA-hp16 after CDDP or ACNU treatment showed G1 arrest on day 5 after re-entering the cycle from G2 arrest on day 3. The cells infected with AxCA-hp16 before CDDP or ACNU treatment showed G1 arrest over the 5 days after the infection. This study demonstrated that G1 arrest induced with p16-gene expression prevents ACNU- or CDDP-induced cell death. The cell death induced by ACNU and CDDP therefore appears to occur in the phase after the G1/S check point.

Endothelial cell vehicles for delivery of cytotoxic genes as a gene therapy approach for carcinoma of the ovary

Human umbilical vein endothelial cells (HUVECs) were evaluated for utility as a vector to achieve a bystander effect and killing of ovarian carcinoma cell lines. After demonstrating that HUVECs could be transduced with the reporter gene LacZ encoded by an adenoviral vector, appropriate cell killing of the AdCMVHSV-TK-transduced HUVECs was exhibited after treatment with 20 microM ganciclovir. Mixing experiments were then performed to determine whether the transduced HUVECs would demonstrate a bystander effect with the ovarian cancer cell lines. When 50% AdCMVHSV-TK-transduced HUVECs were mixed with untransduced ovarian cancer cells, > 70% of all cells were killed. Finally, s.c. and i.p. injections of herpes simplex-thymidine kinase-expressing HUVECs and SKOV3ip1 tumor cells were performed to evaluate the effects of HUVECs in in vivo models. These studies showed a decrease in tumor growth s.c. as well as a statistically significant survival prolongation (P < 0.05) in the i.p. model. These findings suggest that endothelial cells may be used as a vehicle for the delivery of cytotoxicity (bystander effect) in molecular chemotherapy.

Preassembly of interleukin 2 (IL-2) receptor subunits on resting Kit 225 K6 T cells and their modulation by IL-2, IL-7, and IL-15: a fluorescence resonance energy transfer study

Assembly and mutual proximities of alpha, beta, and gamma(c) subunits of the interleukin 2 receptors (IL-2R) in plasma membranes of Kit 225 K6 T lymphoma cells were investigated by fluorescence resonance energy transfer (FRET) using fluorescein isothiocyanate- and Cy3-conjugated monoclonal antibodies (mAbs) that were directed against the IL-2R alpha, IL-2R beta, and gamma(c) subunits of IL-2R. The cell-surface distribution of subunits was analyzed at the nanometer scale (2-10 nm) by FRET on a cell-by-cell basis. The cells were probed in resting phase and after coculture with saturating concentrations of IL-2, IL-7, and IL-15. FRET data from donor- and acceptor-labeled IL-2R beta-alpha, gamma-alpha, and gamma-beta pairs demonstrated close proximity of all subunits to each other in the plasma membrane of resting T cells. These mutual proximities do not appear to represent mAb-induced microaggregation, because FRET measurements with Fab fragments of the mAbs gave similar results. The relative proximities were meaningfully modulated by binding of IL-2, IL-7, and IL-15. Based on FRET analysis the topology of the three subunits at the surface of resting cells can be best described by a "triangular model" in the absence of added interleukins. IL-2 strengthens the bridges between the subunits, making the triangle more compact. IL-7 and IL-15 act in the opposite direction by opening the triangle possibly because they associate their private specific alpha receptors with the beta and/or gamma(c) subunits of the IL-2R complex. These data suggest that IL-2R subunits are already colocalized in resting T cells and do not require cytokine-induced redistribution. This colocalization is significantly modulated by binding of relevant interleukins in a cytokine-specific manner.

Stable in vivo gene transduction via a novel adenoviral/retroviral chimeric vector

Gene therapy to correct defective genes requires efficient gene delivery and long-term gene expression. The available vector systems have not allowed the simultaneous achievement of both goals. We have developed a chimeric viral vector system that incorporates favorable aspects of both adenoviral and retroviral vectors. Adenoviral vectors induce target cells to function as transient retroviral producer cells in vivo. The progeny retroviral vector particles are then able to stably transduce neighboring cells. In this system, the nonintegrative adenoviral vector is rendered functionally integrative via the intermediate generation of a retroviral producer cell. The chimeric vectors may allow realization of the requisite goals for specific gene-therapy applications.

Brain edema in meningiomas is associated with increased vascular endothelial growth factor expression

OBJECTIVE

Vascular permeability factor/vascular endothelial growth factor (VPF/VEGF), an endothelial cell-specific cytokine, induces proliferation of endothelial cells and increases vascular permeability dramatically. All gliomas secrete significant amounts of VEGF, whereas meningiomas are variable in expression. Thus, we sought to determine whether the extent of VPF/VEGF expression in meningiomas correlated with differences in brain edema associated with these tumors.

METHODS

Meningioma tissue samples from 37 patients (15 men, average age 65 +/- 13 yr; 22 women, average age 60 +/- 10 yr) who underwent surgery at or were referred to the University of Alabama Hospital were examined retrospectively for the extent of expression of immunoreactive VPF/VEGF. Additionally, peritumoral edema was assessed on a blinded basis radiographically from preoperative magnetic resonance imaging scans. Selected specimens were examined by in situ hybridization to document the source of VPF/VEGF.

RESULTS

The predominant meningioma subclassifications were transitional (57%) or meningothelial (27%) subtypes. VPF/VEGF immunoreactivity ranged from 0 to 3.5, with a median value of 2 on a subjective 5-point scale; magnetic resonance imaging-assessed edema ranged in extent from 0 to 4 (subjective 5-point scale), with a median value of 2.5. The correlation of determination (R2) of magnetic resonance imaging-assessed tumor edema rating and VPF/VEGF staining intensity rating was 0.6087 (r = 0.78; P = 0.0001). In situ hybridization localized VPF/VEGF messenger ribonucleic acid in meningioma cells and not in normal parenchymal brain cells.

CONCLUSION

These data suggest that meningioma-associated edema may be a result of the capacity of meningioma cells to produce VPF/VEGF locally, leading to increased tumor neovascularization and enhanced vascular permeability.

In vitro and in vivo gene delivery mediated by a synthetic polycationic amino polymer

A synthetic polyamino polymer with a glucose backbone was used for gene transfer in vitro and in vivo. Gene transfer in vitro to various human carcinoma cell lines was achieved with an efficiency superior to a commercially available cationic liposome preparation. The polymer was resistant to inhibition by serum, which allowed for efficient gene transfer in vivo. Direct Intracranial tumor injection using this reagent resulted in reporter gene expression levels comparable to those achieved by a recombinant adenoviral vector. Thus, this compound represents a new class of agent that may have broad utility for gene transfer and gene therapy applications.

Targeted gene delivery to Kaposi's sarcoma cells via the fibroblast growth factor receptor

Kaposi's sarcoma (KS) is a major AIDS-related malignancy associated with significant morbidity and mortality. Current chemotherapeutic regimens are associated with a dismal prognosis. In an effort to develop a new approach to KS treatment, we devised a gene therapy-based adenovirus retargeting schema that redirects the adenovirus to fibroblast growth factor receptors endogenously present on the cell surface of KS cells. By using a bifunctional conjugate consisting of a blocking antiadenoviral knob Fab linked to basic fibroblast growth factor, FGF2, the gene transduction of KS cells was enhanced 7.7-44 fold; recombinant adenoviruses encoding either the firefly luciferase reporter gene, or the herpes simplex thymidine kinase gene, demonstrated quantitative enhancement of expression in the KS cell lines. In this regard, two KS cell lines that were previously refractory to native adenovirus transduction could be successfully transduced by the addition of the conjugate. This study thus addresses the utility of adenoviral retargeting to the FGF receptor in KS cells that are ordinarily transduction refractory to standardized approaches and allows practical development of gene therapy approaches for the treatment of human KS.

Radioimmunotherapy of interleukin-2R alpha-expressing adult T-cell leukemia with Yttrium-90-labeled anti-Tac

Adult T-cell leukemia (ATL) is a malignancy of mature lymphocytes caused by the retrovirus human T-cell lymphotropic virus-I. It is an aggressive leukemia with a median survival time of 9 months; no chemotherapy regimen appears successful in inducing long-term disease-free survival. The scientific basis of the present study is that ATL cells express high-affinity interleukin-2 receptors identified by the anti-Tac monoclonal antibody, whereas normal resting cells do not. To exploit this difference, we administered anti-Tac armed with Yttrium-90 (90Y) to 18 patients with ATL initially (first 9 patients) in a phase I dose-escalation trial and subsequently (second group of 9 patients) in a phase II trial involving a uniform 10-mCi dose of 90Y-labeled anti-Tac. Patients undergoing a remission were permitted to receive up to eight additional doses. At the 5- to 15-mCi doses used, 9 of 16 evaluable patients responded to 90Y anti-Tac with a partial (7 patients) or complete (2 patients) remission. The responses observed represent improved efficacy in terms of length of remission when compared with previous results with unmodified anti-Tac. Clinically meaningful (> or = grade 3) toxicity was largely limited to the hematopoietic system. In conclusion, radioimmunotherapy with 90Y anti-Tac directed toward the IL-2R expressed on ATL cells may provide a useful approach for treatment of this aggressive malignancy.

Vascular endothelial growth factor in human glioma cell lines: induced secretion by EGF, PDGF-BB, and bFGF

Vascular endothelial growth factor/vascular permeability factor (VEGF/VPF) is an endothelial cell-specific mitogen that is structurally related to platelet-derived growth factor (PDGF). Vascular endothelial growth factor/vascular permeability factor induces angiogenesis in vivo and may play a critical role in tumor angiogenesis. Using immunohistochemical analysis, the authors demonstrated the presence of VEGF/VPF protein in surgical specimens of glioblastoma multiforme and cultured glioma cells. By means of an enzyme-linked immunosorbent assay (ELISA) of cell supernatants, the authors showed that VEGF/VPF is variably secreted by all nine cultured human malignant glioma cell lines (CH-235MG, D-37MG, D-54MG, D-65MG, U-87MG, U-105MG, U-138MG, U-251MG, U-373MG) and by a single meningioma cell line (CH-157MN). An immunocytochemical survey of these cell lines revealed a cytoplasmic and cell-surface distribution of VEGF/VPF. In the U-105MG glioma cell line, VEGF/VPF secretion was induced with physiological concentrations of epidermal growth factor, PDGF-BB, or basic fibroblast growth factor, but not with PDGF-AA. Moreover, it was observed that activation of convergent growth factor signaling pathways led to increased glioma VEGF secretion. Similar results were obtained using these growth factor combinations in the D-54MG glioma cell line. The data obtained suggest a potential role for VEGF/VPF in tumor hypervascularity and peritumoral edema. These observations may lead to development of new therapeutic strategies.

Physiologic responses of REVC, a continuous rabbit endothelial vascular cell

Endothelial cells (EC) are fastidious in their growth requirements in vitro and will not survive extensive passages. We have partially characterized a continuous cell line (> 40 passages) established in culture from New Zealand White rabbit vena cava endothelium (REVC). REVC cells resemble typical EC, but remain hardy when grown on uncoated plastic in DMEM/F12 + 10% FBS. REVC cells have typical cobblestone appearance, are contact-inhibited in monolayers and express factor VIII-related antigen. Weibel-Palade bodies were not seen by electron microscopy. REVC cells grown in 2% FBS on plastic demonstrate dose-dependent increases in [3H]thymidine uptake in response to acidic FGF (10-100 ng/ml), basic FGF (3-100 ng/ml), EGF (10-50 ng/ml), and ECGS (10-100 micrograms/ml). Heparin (5-100 micrograms/ml) potentiates proliferation induced by aFGF and lowered the ED50 for aFGF. REVC cells did not show an increased proliferative rate in response to vascular endothelial growth factor. Transforming growth factor beta 1 and beta 2 profoundly inhibited thymidine uptake at doses as low as 100 pg/ml. When grown on a collagen I substratum, REVC cells became larger, more polygonal and assumed a sheet-like appearance upon reaching confluence. REVC cells plated on fibronectin, laminin or poly-L-lysine demonstrated increases in pericellular granularity and pronounced spreading, especially on fibronectin. Phorbol myristate acetate produced profound morphological changes characterized by swirling whorls of bipolar cells surrounding patches of polygonal cells and multilayered overgrowth. When plated on EHS (Engelbreth-Holm-Swarm) tumor extracellular matrix (Matrigel), REVC cells became quiescent and underwent morphological changes reminiscent of differentiation with elongated cytoplasmic extensions. Chromosomal examination of REVC cells revealed a normal diploid karyotype (2n = 44). This continuous cell line is undergoing further characterization and may be quite useful in investigating many aspects of endothelial cell biology in vitro.

The interleukin (IL) 2 receptor beta chain is shared by IL-2 and a cytokine, provisionally designated IL-T, that stimulates T-cell proliferation and the induction of lymphokine-activated killer cells

Late-phase human T-cell lymphotropic virus I-associated adult T-cell leukemia cells express IL-2 receptors (IL-2R) but no longer produce IL-2. We have reported that the IL-2-independent adult T-cell leukemia line HuT-102 secretes a cytokine, provisionally designated IL-T, that stimulates T-cell proliferation and lymphokine-activated killer cell activity. Stimulation of proliferation of the cytokine-dependent human T-cell line Kit-225 mediated by HuT-102-conditioned medium or by 3200-fold-purified IL-T was not blocked by the addition of antibodies against IL-2 or IL-2R alpha subunit. However, IL-T-mediated stimulation of this human T-cell line was inhibited by addition of Mik-beta 1, an antibody that binds specifically to IL-2R beta subunit. In addition, the activation of large granular lymphocytes to lymphokine-activated killer cells mediated by IL-T-containing conditioned medium was not blocked by antibodies directed toward IL-2 or IL-2 alpha but was inhibited by an antibody to IL-2R beta, suggesting the requirement of this receptor subunit for IL-T action. This conclusion was confirmed using an IL-3-dependent murine myeloid precursor cell line, 32D, that expresses IL-2R alpha and IL-2R gamma, but not IL-2R beta. Neither IL-2 nor IL-T stimulated 32D cell proliferation. However, after transfection with the gene encoding human IL-2R beta, 32D beta cells proliferated on addition of either cytokine. The IL-T-mediated stimulation of 32D beta proliferation was inhibited by an anti-IL-2R beta antibody but not by an anti-IL-2 antibody. Thus, the IL-T-mediated stimulation of T-cell and lymphokine-activated killer cell activation requires the expression of the IL-2R beta subunit.

A lymphokine, provisionally designated interleukin T and produced by a human adult T-cell leukemia line, stimulates T-cell proliferation and the induction of lymphokine-activated killer cells

In early phases of human T-cell lymphotrophic virus I-induced adult T-cell leukemia (ATL), the malignant cell proliferation is associated with an autocrine process involving coordinate expression of interleukin (IL) 2 and its receptor. However, during late-phase ATL, leukemic cells no longer produce IL-2 yet continue to express high-affinity IL-2 receptors. During studies to define pathogenic mechanisms that underlie this IL-2-independent proliferation, we demonstrated that the ATL cell line HuT-102 secretes a lymphokine, provisionally designated IL-T, that stimulates T-cell proliferation and the induction of lymphokine-activated killer cells. Conditioned medium from HuT-102, when added to the IL-2-dependent CTLL-2 line, yielded a stimulation index of 230. Since CTLL-2 was purported to be IL-2-specific, we performed a number of studies to exclude IL-2 production by HuT-102. Stimulation of CTLL-2 cells by HuT-102-conditioned medium was not meaningfully inhibited by addition of an antiserum to IL-2. Furthermore, uninduced HuT-102 cells did not express mRNA encoding IL-2 as assessed by Northern blot analysis. No biological activity on CTLL-2 cells was mediated by purified IL-1, IL-3, IL-4, IL-5, IL-6, IL-7, IL-9, IL-10, IL-12, IL-13, or granulocyte/macrophage colony-stimulating factor, thus differentiating these factors from IL-T. Based on preliminary biochemical data, IL-T is a protein with a pI value of 4.5 and a molecular mass in SDS gels of 14 kDa. In addition to its action on CTLL-2 cells, 3200-fold-purified IL-T stimulated proliferation of the human cytokine-dependent T-cell line Kit-225. Furthermore, addition of IL-T enhanced cytotoxic activity of large granular lymphocytes (i.e., induced lymphokine-activated killer cells). Thus, IL-T is a lymphokine that plays a role in T-cell proliferation and induction of lymphokine-activated killer cells. Furthermore, IL-T may contribute to IL-2-independent proliferation of select ATL cells and lines.

The interleukin-2 receptor: a target for monoclonal antibody treatment of human T-cell lymphotrophic virus I-induced adult T-cell leukemia

Adult T-cell leukemia (ATL) is a malignancy of mature lymphocytes caused by the retrovirus human T-cell lymphotrophic virus-I (HTLV-I). It is an aggressive leukemia with an overall mortality rate of 50% within 5 months; no conventional chemotherapy regimen appears successful in inducing long-term disease-free survival in ATL patients. However, ATL cells constitutively express high-affinity interleukin-2 receptors (IL-2Rs) identified by the anti-Tac monoclonal antibody, whereas normal resting cells do not. To exploit this difference in receptor expression, we administered anti-Tac intravenously (IV) to 19 patients with ATL. In general the patients did not suffer untoward reactions, and in 18 of 19 cases did not have a reduction in normal formed elements of the blood. Seven patients developed remissions that were mixed (1 patient), partial (4 patients), or complete (2 patients), with partial and complete remissions lasting from 9 weeks to more than 3 years as assessed by routine hematologic tests, immunofluorescence analysis, and molecular genetic analysis of T-cell receptor gene rearrangements and of HTLV-I proviral integration. Furthermore, remission was associated with a return to normal serum calcium levels and an improvement of liver function tests. Remission was also associated in some cases with an amelioration of the profound immunodeficiency state that characterizes ATL. Thus the use of a monoclonal antibody that blocks the interaction of IL-2 with its receptor expressed on ATL cells provides a rational approach for treatment of this aggressive malignancy.

APO-1-induced apoptosis of leukemia cells from patients with adult T-cell leukemia

The 48-Kd cell-surface protein APO-1 is a new member of the nerve growth factor (NGF)/tumor necrosis factor (TNF) receptor superfamily. APO-1 is expressed on various cells, including activated T and B cells and some lymphoid and nonlymphoid cell lines. Triggering of APO-1 by the monoclonal antibody anti-APO-1 induces programmed cell death (apoptosis) in APO-1-expressing cells. APO-1 is also present on T-cell lines derived from patients with adult T-cell leukemia (ATL). Therefore, we investigated APO-1 expression and APO-1-mediated induction of apoptosis ex vivo in cells from patients with ATL. Fresh leukemic cells from nine patients with ATL were assayed for APO-1 expression by two-color immunofluorescence. The leukemic cells from all patients strongly expressed APO-1. Incubation of ATL cells with anti-APO-1 in vitro inhibited spontaneous and cytokine-mediated DNA synthesis. Furthermore, DNA isolated from cells treated with anti-APO-1 exhibited polynucleosomal DNA fragmentation (DNA ladder) characteristic for apoptotic cell death. The analysis of APO-1-mediated apoptosis may represent a new approach to the study of growth control in lymphoid malignancies. In addition, induction of apoptosis by administration of anti-APO-1 may represent a new therapeutic approach for aggressive T-cell malignancies such as ATL.

Epidermal growth factor stimulates vascular endothelial growth factor production by human malignant glioma cells: a model of glioblastoma multiforme pathophysiology

Hypervascularity, focal necrosis, persistent cerebral edema, and rapid cellular proliferation are key histopathologic features of glioblastoma multiforme (GBM), the most common and malignant of human brain tumors. By immunoperoxidase and immunofluorescence, we definitively have demonstrated the presence of vascular endothelial growth factor (VEGF) and epidermal growth factor receptor (EGFr) in five out of five human glioma cell lines (U-251MG, U-105MG, D-65MG, D-54MG, and CH-235MG) and in eight human GBM tumor surgical specimens. In vitro experiments with glioma cell lines revealed a consistent and reliable relation between EGFr activation and VEGF production; namely, EGF (1-20 ng/ml) stimulation of glioma cells resulted in a 25-125% increase in secretion of bioactive VEGF. Conditioned media (CM) prepared from EGF-stimulated glioma cell lines produced significant increases in cytosolic free intracellular concentrations of Ca2+ ([Ca2+]i) in human umbilical vein endothelial cells (HUVECs). Neither EGF alone or CM from glioma cultures prepared in the absence of EGF induced [Ca2+]i increases in HUVECs. Preincubation of glioma CM with A4.6.1, a monoclonal antibody to VEGF, completely abolished VEGF-mediated [Ca2+]i transients in HUVECs. Likewise, induction by glioma-derived CM of von Willebrand factor release from HUVECs was completely blocked by A4.6.1 pretreatment. These observations provide a key link in understanding the basic cellular pathophysiology of GBM tumor angiogenesis, increased vascular permeability, and cellular proliferation. Specifically, EGF activation of EGFr expressed on glioma cells leads to enhanced secretion of VEGF by glioma cells. VEGF released by glioma cells in situ most likely accounts for pathognomonic histopathologic and clinical features of GBM tumors in patients, including striking tumor angiogenesis, increased cerebral edema and hypercoagulability manifesting as focal tumor necrosis, deep vein thrombosis, or pulmonary embolism.

Prolongation of graft survival in primate allograft transplantation by yttrium-90-labeled anti-Tac in conjunction with granulocyte colony-stimulating factor

High-affinity IL-2 receptors are expressed by T cells activated in response to foreign histocompatibility antigens but not by normal resting T cells. To exploit this difference in IL-2R expression, anti-Tac, a murine monoclonal antibody specific for the IL-2R alpha subunit, was used to inhibit organ allograft rejection. To enhance its effector function, anti-Tac was armed by chelation with yttrium-90, a pure beta-emitting radionuclide. Animals received no immunosuppression (n = 5, group I, controls), unmodified anti-Tac (n = 5, 1 mg/kg q.o.d., group II), or 90Y-anti-Tac (n = 5, 1.6 mCi/kg divided into four doses, group III). The animals in group IV (n = 4) were treated identically to those in group III with the exception that 5 micrograms/kg/dose of granulocyte colony-stimulating factor was administered intramuscularly on the days when the yttrium-90 was given and on postoperative days 12 through 35 in order to reduce hematopoietic toxicity. Mean graft survival +/- S.E.M. for the control group was 8.2 +/- 0.5 days as compared with 13.8 +/- 2.1 days (P < 0.05) for those monkeys treated with unmodified anti-Tac. Graft survival was further prolonged in animals of group III that received 90Y-anti-Tac, with a mean graft survival of 45.0 +/- 11.8 days; however, three of the five monkeys retained viable grafts within this group but died secondary to bone marrow suppression. In comparison, the monkeys in group IV that were treated with G-CSF in conjunction with 90Y-anti-Tac had a mean graft survival of 49.2 +/- 2.9 days. In contrast to group III there were no deaths in the group (IV) receiving G-CSF. Furthermore, animals in group IV had a reduced magnitude and shortened duration of irradiation-induced neutropenia when compared with that observed in group III animals that did not receive G-CSF. Thus, treatment with 90Y-anti-Tac in conjunction with G-CSF may have potential applications in organ transplantation and the treatment of IL-2 receptor-expressing neoplastic diseases.

Anti-Tac-H, a humanized antibody to the interleukin 2 receptor, prolongs primate cardiac allograft survival

High-affinity interleukin 2 receptors (IL-2Rs) are expressed by T cells activated in response to foreign histocompatibility antigens but not by normal resting T cells. To exploit this difference in IL-2R expression, anti-Tac-M, a murine monoclonal antibody specific for the IL-2R alpha chain, was used to inhibit organ allograft rejection. However, the use of murine anti-Tac as an immunosuppressive agent was limited by neutralization by human anti-murine antibodies and by weak recruitment of effector functions. To circumvent these difficulties, a humanized antibody to the IL-2R, anti-Tac-H, was prepared. This molecule is human with the exception of the hypervariable segments, which are retained from the mouse. In vivo survival of anti-Tac-H is 2.5-fold longer than simultaneously administered anti-Tac-M (terminal t1/2, 103 hr vs. 38 hr). In addition, anti-Tac-H is less immunogenic than anti-Tac-M when administered to cynomolgus monkeys undergoing heterotopic cardiac allografting. Specifically, all monkeys treated with anti-Tac-M developed measurable anti-anti-Tac-M levels by day 15 (mean onset, 11 days). In contrast, none of the animals receiving anti-Tac-H produced measurable antibodies to this monoclonal antibody before day 33. Finally, there was a prolongation of graft survival in the cynomolgus heterotopic cardiac allograft model in animals receiving anti-Tac. In animals that received anti-Tac-M, the allograft survival was prolonged compared to that of the control group (mean survival, 14 +/- 1.98 days compared to 9.2 +/- 0.48 days; P less than 0.025). Graft survival was further prolonged by anti-Tac-H with a mean survival of 20.0 +/- 0.55 days (compared to controls, P less than 0.001; compared to anti-Tac-M, P less than 0.02). There was no toxicity attributable to the administration of either form of anti-Tac. Thus, anti-Tac-H significantly prolonged allograft survival in primates, without toxic side effects, and may be of value as an adjunct to standard immunosuppressive therapy in humans.

Use of yttrium-90-labeled anti-Tac antibody in primate xenograft transplantation

The high-affinity interleukin-2 receptor (IL-2R) is expressed by T cells activated in response to foreign histocompatibility antigens but not by normal resting cells. Thus, blockade of the interaction of IL-2 with its receptor could achieve selective immunosuppression. Accordingly, anti-Tac, a murine IgG2a class monoclonal antibody specific to the IL-2R, was used alone or in a chelated form with yttrium-90 (90Y), a pure beta emitter, to inhibit rejection of cardiac xenografts from Macaca fascicularis (cynomolgus) donors transplanted to the cervical or abdominal region of Macaca mulatta (rhesus) recipients (n = 20). Animals received no immunosuppression (n = 3, group I, controls), unmodified anti-Tac (n = 5, 2 mg/kg q.o.d., group II), or 90Y-anti-Tac (n = 5, 16 mCi, group III). To distinguish the nonspecific immunosuppressive effect of radiation, 90Y was administered bound to UPC-10 (n = 4, 16 mCi, group IV), another murine monoclonal antibody that does not specifically recognize activated immunoresponsive cells. All immunosuppression was administered in divided doses during the first 2 weeks posttransplant. Group I animals rejected their grafts at 6.7 +/- 1 days and demonstrated a rise in soluble IL-2R levels at the time of rejection, indicating the generation of Tac-expressing and -releasing cells. Graft survival in group II was not prolonged compared with controls (mean survival 6.2 +/- 1 days; P greater than 0.05). In contrast, graft survival in animals that received the designed dosage of 90Y-anti-Tac was significantly prolonged to an average of 38.4 +/- 5 days compared with groups I and II (P less than 0.005 and P les sthan 0.0005, respectively). Prolongation of graft survival occurred in animals that received 90Y-UPC-10 (mean survival 21.3 +/- 5 days, P less than 0.05 versus group I, P less than 0.01 versus group II). However, 90Y-UPC-10 was significantly less effective in prolonging graft survival than 90Y-anti-Tac, in which one-half the per-kilogram dosage of radioactivity was delivered in specific fashion via anti-Tac (P less than 0.025). Reversible nonlethal bone marrow suppression occurred without associated nephro- or hepatotoxicity, and virtually all animals developed antibodies to the murine monoclonal. Thus, the approach used in the present study, IL-2R-directed therapy with 90Y-anti-Tac, may have potential applications in organ transplantation and in the treatment of Tac-expressing neoplastic diseases.

Selective elimination in vitro of alloresponsive T cells to human transplantation antigens by toxin or radionuclide conjugated anti-IL-2 receptor (Tac) monoclonal antibody

The human allogeneic mixed lymphocyte reaction is the in vitro correlate of graft rejection. Cytotoxic effector cells generated during an allogeneic mixed lymphocyte reaction were previously shown to express the human p55 IL-2 receptor subunit, whereas resting cells do not express this receptor peptide. In this study, we asked whether Pseudomonas exotoxin or bismuth-212 (an alpha-particle emitting radionuclide) coupled to the anti-IL-2 receptor mAb, anti-Tac, were able to selectively eliminate alloresponsive cells generated during an allogeneic mixed lymphocyte reaction. After assembly, anti-Tac immunoconjugates retained their binding integrity, specificity, and selectivity. Deletion of alloresponsive cells was shown by the removal of alloproliferating cells as assessed by quantitating cell recovery and by measurement of thymidine incorporation into newly synthesized DNA. Both toxin and radionuclide immunoconjugates eliminated established cytotoxic effector cells generated in an allogeneic mixed lymphocyte reaction, while leaving intact the PHA-inducible mitogenic response of the nonactivated cells. The addition of excess anti-Tac blocked all of the effects of these cytotoxic reagents. The therapeutic reagents in vitro were most effective when added just prior to the peak of the alloproliferative response, when receptor expression would be close to maximum. Thus, anti-Tac conjugated either with toxin or radionuclide is effective in vitro in specifically eliminating cytotoxic effector cells.

Selective elimination in vitro of alloresponsive T cells to human transplantation antigens by toxin or radionuclide conjugated anti-IL-2 receptor (Tac) monoclonal antibody

The human allogeneic mixed lymphocyte reaction is the in vitro correlate of graft rejection. Cytotoxic effector cells generated during an allogeneic mixed lymphocyte reaction were previously shown to express the human p55 IL-2 receptor subunit, whereas resting cells do not express this receptor peptide. In this study, we asked whether Pseudomonas exotoxin or bismuth-212 (an alpha-particle emitting radionuclide) coupled to the anti-IL-2 receptor mAb, anti-Tac, were able to selectively eliminate alloresponsive cells generated during an allogeneic mixed lymphocyte reaction. After assembly, anti-Tac immunoconjugates retained their binding integrity, specificity, and selectivity. Deletion of alloresponsive cells was shown by the removal of alloproliferating cells as assessed by quantitating cell recovery and by measurement of thymidine incorporation into newly synthesized DNA. Both toxin and radionuclide immunoconjugates eliminated established cytotoxic effector cells generated in an allogeneic mixed lymphocyte reaction, while leaving intact the PHA-inducible mitogenic response of the nonactivated cells. The addition of excess anti-Tac blocked all of the effects of these cytotoxic reagents. The therapeutic reagents in vitro were most effective when added just prior to the peak of the alloproliferative response, when receptor expression would be close to maximum. Thus, anti-Tac conjugated either with toxin or radionuclide is effective in vitro in specifically eliminating cytotoxic effector cells.

The multichain interleukin-2 receptor: a target for immunotherapy of patients receiving allografts

Antigen-induced activation of resting T cells induces the synthesis of interleukin-2 (IL-2) as well as the expression of specific cell surface high-affinity receptors for this lymphokine. There are at least two forms of the cellular receptors for IL-2, one with a very high affinity and the other with a lower affinity. Two IL-2 binding peptides, a 55-kd peptide reactive with the anti-Tac monoclonal antibody and a 75-kd, non-Tac IL-2-binding peptide, were identified. A multichain model for the high-affinity receptor in which an independently existing p55 or p75 peptide would represent low-or intermediate-affinity receptors, respectively, and high-affinity receptors would be expressed when both of these receptors are expressed and associated in a receptor complex, is proposed. An additional 95 - to 105-kd peptide may also participate in the multisubunit, high-affinity form of the IL-2 receptor. The p75 peptide is receptor for IL-2 on large granular lymphocytes and is sufficient for the IL-2 activation of these cells. In contrast to resting T cells, the T cells of patients with certain neoplasias of mononuclear cells and of patients with select autoimmune disorders, as well as T cells participating in organ allograft rejections, express the Tac antigen. To exploit the fact that IL-2 receptors are present on abnormally activated T cells but no on normal resting T cells, clinical trials have been initiated involving patients with neoplastic or autoimmune disorders as well as those receiving organ allografts. These patients are being treated with unmodified anti-Tac, with isotopic (212 Bi and 90Y) chelates of anti-Tac, with truncated Pseudomonas toxin conjugates of anti-Tac or IL-2, and with recombinant chimeric "humanized" anti-Tac.

The interaction of interleukin 2 with its receptor in the generation of suppressor T cells in antigen-specific and antigen-nonspecific systems in vitro

The role of interleukin-2 (IL-2) in the activation of suppressor T cells was investigated using the monoclonal antibody anti-Tac, which blocks the binding of IL-2 to the 55-kDa IL-2-binding peptide. The addition of anti-Tac during a preculture period inhibited the generation of Epstein-Barr virus (EBV)-induced suppressor T cells and of suppressor T cells induced in an antigen-specific system by a high antigen (sheep red blood cell) concentration. The cells activated by a short 2- or 7-day preculture period with EBV to become suppressor effectors were of the T8, Tac-positive phenotype. However, the T8-positive T cells obtained from peripheral blood mononuclear cells precultured with EBV for 14 days continued to manifest suppressor function, even though they were no longer Tac positive. In summary, our studies indicate that anti-Tac, by producing a functional blockade of human IL-2 receptors, inhibits the generation of suppressor T cells in antigen-specific as well as antigen-nonspecific systems and that cells that no longer express the Tac antigen may also function as suppressors.

Therapy of patients with human T-cell lymphotrophic virus I-induced adult T-cell leukemia with anti-Tac, a monoclonal antibody to the receptor for interleukin-2

Human T-cell lymphotropic virus I (HTLV-I)-induced adult T-cell leukemia (ATL) cells constitutively express interleukin-2 (IL-2) receptors identified by the anti-Tac monoclonal antibody (MoAb), whereas normal resting cells do not. This observation provided the scientific basis for a trial of intravenous anti-Tac in the treatment of nine patients with ATL. The patients did not suffer untoward reactions and did not have a reduction in the normal formed elements of the blood, and only one of the nine produced antibodies to the anti-Tac MoAb. Three patients had transient mixed, partial, or complete remissions lasting from 1 to more than 8 months after anti-Tac therapy, as assessed by routine hematologic tests, immunofluorescence analysis of circulating cells, and molecular genetic analysis of HTLV-I provirus integration and of the T-cell receptor gene rearrangement. The precise mechanism of the antitumor effects is unclear; however, the use of a MoAb that prevents the interaction of IL-2 with its receptor on ATL cells provides a rational approach for the treatment of this malignancy.

Flow cytometric resonance energy transfer measurements support the association of a 95-kDa peptide termed T27 with the 55-kDa Tac peptide

Two monoclonal antibodies (OKT27 and OKT27b) have been produced that react with distinct epitopes of a 95-kDa peptide. The T27 antigen is widely distributed, being expressed on B lymphocytes, monocytes, and adult T-leukemic cells but not on polymorphonuclear leukocytes or platelets. There was a low level of T27 expression on resting T cells that increased on T-cell activation. In preliminary studies, the OKT27b antibody coprecipitated a 55-kDa peptide, as well as the 95-kDa peptide, from the radiolabeled cells of the HuT 102B2 cell line. Preclearance with anti-Tac, a monoclonal antibody to the 55-kDa peptide of the multichain interleukin 2 receptor, removed the 55-kDa but not the 95-kDa peptide from subsequent OKT27b immunoprecipitates of HuT 102B2 extracts, suggesting the possibility that the T27 peptide was associated with the Tac peptide. However, the precipitation of the p55 Tac peptide by OKT27b was quite inconsistent. Thus, additional information was sought using a flow cytometric energy transfer technique to provide a physical estimation of the proximity between the Tac and the T27 peptides. The flow cytometric version of the fluorescence resonance energy transfer technique permits the determination of inter- and intramolecular distances at 2- to 10-nm levels on a cell-by-cell basis. Using this approach, there was a mean energy transfer of 7.3% with HuT 102B2 cells when fluorescein isothiocyanate anti-Tac served as the donor and tetramethylrhodamine isothiocyanate OKT27 served as the acceptor. In contrast, there was no energy transfer in comparable studies observed when fluorescein anti-Tac and rhodamine anti-transferrin receptor antibodies were used. These observations support the conclusion that there is a close nonrandom proximity in HuT 102B2 cells between the 95-kDa peptide identified by the OKT27 monoclonal antibody and the p55 Tac peptide of the multichain interleukin 2 receptor.

The p75 peptide is the receptor for interleukin 2 expressed on large granular lymphocytes and is responsible for the interleukin 2 activation of these cells

There are at least two interleukin 2 (IL-2) binding peptides: one is the Mr 55,000 peptide (p55) reactive with the anti-Tac monoclonal antibody, and the other is a Mr 75,000 non-Tac IL-2 binding peptide (p75). Independently existing Tac or p75 peptides represent low-affinity IL-2 receptors, whereas high-affinity IL-2 receptors are expressed when both peptides are present and associated in a receptor complex. It has long been known that normal large granular lymphocytes (LGL) or leukemic cells from the patients with abnormal expansions of LGL can be activated by IL-2 not only to more-potent natural killer cells but also to effectors of lymphokine-activated killer (LAK) activity, although they do not express the Tac peptide. In the present study, using cross-linking methodology, we found that normal LGL and leukemic LGL from all individuals tested expressed the p75 IL-2 binding peptide but did not express the Tac peptide. These LGL leukemia cells made proliferative responses to IL-2 but required a much higher concentration than that required for the proliferation of normal phytohemagglutinin-stimulated T lymphoblasts that express high-affinity receptors. Furthermore, the addition of IL-2 to Tac-negative LGL leukemic cells augmented transcription of the Tac gene and induced the Tac peptide. Neither the IL-2-induced proliferation nor the up-regulation of Tac gene expression was inhibited by the addition of anti-Tac. These results strongly suggest that the p75 peptide is responsible for IL-2-induced activation of LGL and that the p75 peptide alone can mediate an IL-2 signal. Thus, the p75 peptide may play an important role in the IL-2-mediated immune response not only by participating with the Tac peptide in the formation of the high-affinity receptor complex on T cells but also by contributing to the initial triggering of LGL activation so that these cells become efficient natural killer and lymphokine-activated killer cells.

Contribution of a p75 interleukin 2 binding peptide to a high-affinity interleukin 2 receptor complex

There are at least two forms of cellular receptors for interleukin 2 (IL-2); one with a very high affinity and the other with a lower affinity. We identified a non-Tac IL-2 binding peptide with a relative molecular weight of 75,000 (p75). Cell lines bearing either the p55 Tac or the p75 peptide alone manifested low-affinity IL-2 binding, whereas a cell line bearing both peptides manifested both high- and low-affinity receptors. After the internalization of labeled IL-2 through high-affinity receptors, the p75 peptide could not be detected by cross-linking studies. Furthermore, fusion of cell membranes from low-affinity IL-2 binding cell lines bearing the Tac peptide alone with membranes from a cell line bearing the p75 peptide alone generated hybrid membranes bearing high-affinity receptors. These results suggest a multichain model for the high-affinity IL-2 receptor in which high-affinity receptors would be expressed when both Tac and p75 IL-2 binding peptides are present and associated in a receptor complex.

Expression of functional IL 2 receptors by lipopolysaccharide and interferon-gamma stimulated human monocytes

Human peripheral blood monocytes were stimulated with lipopolysaccharide (LPS) and interferon-gamma (IFN-gamma) alone or in combination. Stimulated but not resting monocytes displayed the Tac peptide of the interleukin 2 (IL 2) receptor within 24 hr as measured by immunofluorescence staining and [3H] Tac binding. The total number of anti-Tac binding sites on co-stimulated monocytes was 13,700. By using scatchard analysis with radiolabeled IL 2, the activated cells were shown to express low numbers (below 100 sites/cell) of high affinity binding sites with a KD of approximately 15 pM. LPS and IFN-gamma were additive in augmenting the number of IL 2 and anti-Tac binding sites. By using an ELISA assay specific for the soluble released form of the Tac peptide we identified 112 U/ml of IL 2 receptors in the supernatant of monocytes stimulated for 24 hr with IFN-gamma, 233 U/ml after stimulation with LPS, and 519 U/ml after the addition of both stimulating agents. Both the membrane form (55,000 daltons), as well as the soluble form (45,000 to 50,000 daltons) of the Tac, IL 2 receptor, peptide from monocytes were shown by immunoprecipitation and gel electrophoresis to be similar size to the comparable forms of these receptors derived from activated T cells. In addition, monocytes stimulated for 8 hr contained mRNA specifically hybridizing to a cDNA probe coding for the Tac peptide. Finally, activated monocytes responded to the addition of recombinant IL 2 by an increase in H2O2 production that was measured by using fluorescent indicator 2,7-dichlorofluorescein. This response as well as the observed induction of monocytic IL 2 receptors by LPS may point to a functional role for this receptor during monocyte/macrophage responses to microbial infections.

Expression of functional IL 2 receptors by lipopolysaccharide and interferon-gamma stimulated human monocytes

Human peripheral blood monocytes were stimulated with lipopolysaccharide (LPS) and interferon-gamma (IFN-gamma) alone or in combination. Stimulated but not resting monocytes displayed the Tac peptide of the interleukin 2 (IL 2) receptor within 24 hr as measured by immunofluorescence staining and [3H] Tac binding. The total number of anti-Tac binding sites on co-stimulated monocytes was 13,700. By using scatchard analysis with radiolabeled IL 2, the activated cells were shown to express low numbers (below 100 sites/cell) of high affinity binding sites with a KD of approximately 15 pM. LPS and IFN-gamma were additive in augmenting the number of IL 2 and anti-Tac binding sites. By using an ELISA assay specific for the soluble released form of the Tac peptide we identified 112 U/ml of IL 2 receptors in the supernatant of monocytes stimulated for 24 hr with IFN-gamma, 233 U/ml after stimulation with LPS, and 519 U/ml after the addition of both stimulating agents. Both the membrane form (55,000 daltons), as well as the soluble form (45,000 to 50,000 daltons) of the Tac, IL 2 receptor, peptide from monocytes were shown by immunoprecipitation and gel electrophoresis to be similar size to the comparable forms of these receptors derived from activated T cells. In addition, monocytes stimulated for 8 hr contained mRNA specifically hybridizing to a cDNA probe coding for the Tac peptide. Finally, activated monocytes responded to the addition of recombinant IL 2 by an increase in H2O2 production that was measured by using fluorescent indicator 2,7-dichlorofluorescein. This response as well as the observed induction of monocytic IL 2 receptors by LPS may point to a functional role for this receptor during monocyte/macrophage responses to microbial infections.

Demonstration of a non-Tac peptide that binds interleukin 2: a potential participant in a multichain interleukin 2 receptor complex

The interleukin 2 (IL-2) receptor system plays a key role in the T-cell immune response. Although IL-2 binding was reported to be restricted to the Tac peptide, we have identified an IL-2 binding peptide that does not react with anti-human IL-2 receptor monoclonal antibodies, including anti-Tac on MLA 144, a gibbon ape T-cell line. The MLA 144 cell line expressed 6800 IL-2 binding sites per cell with a low (Kd = 14 nM) affinity for human recombinant IL-2. Using cross-linking methodology, we demonstrated that the IL-2 binding peptide on MLA 144 is larger (Mr 75,000) than the Tac peptide, which has a Mr of 55,000. An IL-2 binding peptide of similar size (Mr 75,000) was also identified in addition to the Tac peptide (Mr 54,000-57,000) on Hut 102, a human T-cell lymphotrophic virus I-induced T-cell leukemia line, and phytohemagglutinin-activated normal human and gibbon ape lymphoblasts. Anti-Tac antibody did not block the binding of 125I-labeled IL-2 to MLA 144 cells. However, this antibody abolished the binding of 125I-labeled IL-2 not only to the Tac peptide on Hut 102 cells and normal lymphoblasts but also to the Mr 75,000 IL-2 binding peptide, suggesting that this latter peptide is associated with the Tac peptide to form the high-affinity IL-2 receptor complex.

Postsynaptic alpha 2-noradrenergic receptors mediate feeding induced by paraventricular nucleus injection of norepinephrine and clonidine

This study examines the feeding response induced by hypothalamic noradrenergic stimulation, in terms of the type and synaptic position of its mediating receptor. Tests with norepinephrine or the alpha 2 receptor agonist clonidine, injected into the area of the paraventricular nucleus (PVN), revealed a potent feeding response in satiated animals. This response by either agonist was blocked, in a dose-dependent fashion, by local injection of the alpha 2-noradrenergic antagonists, rauwolscine and yohimbine. It was also blocked by the general antagonist, phentolamine. In contrast, it was unaffected by hypothalamic injection of the alpha 1-noradrenergic antagonists, prazosin and corynanthine. These results indicate that feeding elicited by noradrenergic stimulation in the region of the PVN is mediated through alpha 2-type receptors. These alpha 2 receptors appear to be located postsynaptically, since the effectiveness of clonidine in eliciting eating was undisturbed by prior injection of the catecholamine synthesis inhibitor, alpha-methyl-p-tyrosine.

Interleukin 2 receptor (Tac antigen) expression in HTLV-I-associated adult T-cell leukemia

Interleukin-2 (IL-2) is a lymphokine synthesized by some T-cells following activation. Resting T-cells do not express IL-2 receptors, but receptors are rapidly expressed on T-cells following interaction of antigens, mitogens, or monoclonal antibodies with the antigen-specific T-cell receptor complex. Using anti-Tac, a monoclonal antibody that recognizes the IL-2 receptor, the receptor has been purified and shown to be a Mr 33,000 peptide that is posttranslationally glycosylated to a Mr 55,000 mature form. Normal resting T-cells and most leukemic T-cell populations do not express IL-2 receptors; however, the leukemic cells of the 11 patients examined who had human T-cell lymphotropic virus-associated adult T-cell leukemia expressed the Tac antigen. In human T-cell lymphotropic virus-I infected cells, the Mr 42,000 long open reading frame protein encoded in part by the pX region of this virus may act as a transacting transcriptional activator that induces IL-2 receptor gene transcription, thus providing an explanation for the constant association of IL-2 receptor expression with adult T-cell lymphotropic virus-I infection of lymphoid cells. The constant expression of large numbers of IL-2 receptors which may be aberrant may play a role in the uncontrolled growth of adult T-cell leukemia cells. Two patients with Tac-positive adult T-cell leukemia have been treated with the anti-Tac. One of the patients had 6- and 3-mo remissions of his leukemia following two courses of therapy with this monoclonal antibody directed toward this growth factor receptor.

Expression of interleukin 2 receptors on activated human B cells

Using anti-Tac, a monoclonal anti-interleukin 2 (IL-2) receptor antibody, we have explored the possibility that certain activated B cells display receptors for IL-2. Resting normal B cells and unselected B cell lines established from normal individuals were Tac antigen negative. In contrast, the cell surface Tac antigen expression was demonstrable on 6 of 10 B cell lines from patients with Burkitt's lymphoma, 5 of 6 B cell lines derived from patients with HTLV-I-associated adult T cell leukemia (including all four that had integrated HTLV-I into their genome), and on certain normal B cells activated with pokeweed mitogen. Furthermore, cloned Epstein-Barr virus-transformed B cell lines derived from Tac-positive normal B cells continued to express the Tac antigen in long-term cultures and manifested high affinity IL-2 receptors identified in binding studies with purified radiolabeled IL-2. The line 5B4 developed in the present study could be induced with purified JURKAT-derived or recombinant IL-2 to express a larger number of IL-2 receptors. Furthermore, the addition of IL-2 to the 5B4 B cell line augmented IgM synthesis, which could be blocked by the addition of anti-Tac. The size of the IL-2 receptors expressed on the cloned normal B cell lines was similar (53,000-57,000 daltons) to that of receptors on phytohemagglutinin-stimulated T cell lymphoblasts. Thus, certain malignant and activated normal B cells display the Tac antigen and manifest high affinity receptors for IL-2. These data suggest that IL-2 may play a role in the differentiation of activated B cells into immunoglobulin-synthesizing and -secreting cells.

Functional and phenotypic comparison of human T cell leukemia/lymphoma virus positive adult T cell leukemia with human T cell leukemia/lymphoma virus negative Sézary leukemia, and their distinction using anti-Tac. Monoclonal antibody identifying the human receptor for T cell growth factor

Adult T cell leukemia (ATL) and Sézary leukemia are malignant proliferations of T lymphocytes that share similar cell morphology and clinical features. ATL is associated with HTLV (human T cell leukemia/lymphoma virus), a unique human type C retrovirus, whereas most patients with the Sézary syndrome do not have antibodies to this virus. Leukemic cells of both groups were of the T3, T4-positive, T8-negative phenotype. Despite the similar phenotype, HTLV-negative Sézary leukemic cells frequently functioned as helper cells, whereas some HTLV-positive ATL and HTLV-positive Sézary cells appeared to function as suppressors of immunoglobulin synthesis. One can distinguish the HTLV-positive from the HTLV-negative leukemias using a monoclonal antibody (anti-Tac) that appears to identify the human receptor for T cell growth factor (TCGF). Resting normal T cells and most HTLV-negative Sézary cells were Tac-negative, whereas all ATL cell populations were Tac-positive. The observation that ATL cells manifest TCGF receptors suggests the possibility that an abnormality of the TCGF-TCGF receptor system may partially explain the uncontrolled growth of these cells.

Disorders of B cells and helper T cells in the pathogenesis of the immunoglobulin deficiency of patients with ataxia telangiectasia

The pathogenesis of the immunoglobulin deficiency of 20 patients with ataxia telangiectasia was studied using an in vitro immunoglobulin biosynthesis system. 10 patients had no detectable IgA in their serum as assessed by radial diffusion in agar and 3 had a reduced serum IgA concentration. The peripheral blood mononuclear cells of 17 of the patients and 17 normal controls were cultured with pokeweed mitogen for 12 d and the immunoglobulin in the supernatants measured. The immunoglobulin synthesis was below the lower limit of the normal 95% confidence interval for IgM in 5 patients, for IgG in 8, and for IgA in 14. The mononuclear cells from 9 of the 10 patients with a serum IgA concentration less than 0.1 mg/ml failed to synthesize IgA in vitro. None of the patients manifested excessive suppressor cell activity. All patients had reduced but measurable helper T cell activity for immunoglobulin synthesis by co-cultured normal pokeweed mitogen-stimulated B cells (geometric mean 22% of normal). Furthermore, the addition of normal irradiated T cells to patient peripheral blood mononuclear cells led to an augmentation of IgM synthesis in 15 of 17 and to increased IgG synthesis in 9 of the 17 patients studied, including 9 of the 12 patients who had synthesized IgG before the addition of the irradiated T cells. In addition, IgA synthesis was increased in all eight patients examined that had serum IgA concentrations greater than 0.1 mg/ml. These studies suggest that a helper T cell defect contributes to the diminished immunoglobulin synthesis. However, a helper T cell defect does not appear to be the sole cause since there was no IgA synthesis by the peripheral blood mononuclear cells of 9 of the 10 patients with a profoundly reduced serum IgA even when co-cultured with normal T cells. Furthermore, the cells of the nine patients with profoundly reduced IgA levels examined also failed to produce IgA when stimulated with the relatively helper T cell-independent polyclonal activators, Nocardia water soluble mitogen or Epstein-Barr virus. Taken together these data support the view that the reduced immunoglobulin synthesis of these patients is due to defects of both B cells and helper T cells. Such a broad defect in lymphocyte maturation taken in conjunction with our demonstration of persistent alpha fetoprotein production by ataxia telangiectasia patients provides support for the proposal that these patients exhibit a generalized defect in tissue differentiation.

Normal human B cells display ordered light chain gene rearrangements and deletions

Human kappa-producing B cell lines and leukemias retain their excluded lambda light chain genes in the germ line configuration, whereas transformed lambda-producing B cells uniformly rearrange or delete their kappa genes (12). Whether the unexpected lambda gene recombinations within malignant lambda-producing B cells reflect a normal developmental process or are secondary to transformation and specific chromosomal translocations was uncertain. To resolve this issue, we purified circulating lambda-bearing B cells from a normal individual to 97% purity by using a series of negative selection steps and a final positive selection on a cell sorter. Over 95% of the collective kappa genes in these lambda B cells were no longer in their germ line form, with the majority (60%) deleted and the remainder present but in a rearranged state. The chromosomal loss of the germ line kappa genes included the joining (J kappa) segments as well as the constant (C kappa) region, yet the particular variable (V kappa) gene family studied was spared. In addition, the incidence of kappa gene deletions was higher in long-term than in freshly transformed lambda B cell lines. This implies that the deletion of aberrantly rearranged kappa genes may occur as a second event. Such a mechanism would serve to eliminate aberrant transcripts and light chain fragments that might interfere with the synthesis and assembly of effective immunoglobulin molecules. Thus, despite the nearly equal usage of kappa and lambda light chain genes in man, there appears to be a sequential order to their expression during normal B cell ontogeny in which kappa gene rearrangements precede those of lambda.

B cell, helper T cell, and suppressor T cell abnormalities contribute to disordered immunoglobulin synthesis in patients following bone marrow transplantation

The pathogenic mechanisms responsible for the hypogammaglobulinemia that occurs in patients who have undergone bone marrow transplantation were studied using peripheral blood lymphocytes in an in vitro immunoglobulin biosynthesis assay. None of the nine marrow recipients between 2 and 15 months after transplantation produced normal amounts of IgG, IgA, or IgM in response to pokeweed mitogen (a T cell-dependent activator). However, three of these same patients responded to Epstein-Barr virus (a helper T cell- independent activator), suggesting that these three possessed responsive B cells. Cocultures of the marrow recipients' lymphocytes with lymphocytes from their respective donors or other normal subjects documented excessive suppressor cell activity in five cases. These suppressor cells frequently had profound activity (greater than 80% suppression of the immunoglobulin synthesis of cocultured normal cells), were predominantly radioresistant, and were T cells in the cases where analyzed. Helper T cell activity for immunoglobulin synthesis was not demonstrable in seven of the nine cases. In addition, four of the patients apparently possessed defective B cells. Although most patients had combined defects of several lymphocyte subpopulations, it appeared that either an isolated helper T cell or isolated B cell deficiency was sufficient to result in altered Ig synthesis. In this regard, two patients had demonstrable helper T cell defects with partially responsive B cells and no excessive suppressor activity. Interestingly, these two patients were experiencing a recurrence of their hypogammaglobulinemia following a period of normalized immunoglobulin levels. Thus, defects within all lymphocytic elements involved in the response and regulation of immunoglobulin synthesis were identified and may contribute to the humoral immunodeficiency which follows marrow transplantation.

Stimulation of immunoglobulin biosynthesis in human B cells by wheat germ agglutinin. I. Evidence that WGA can produce both a positive and negative signal for activation of human lymphocytes

Wheat germ agglutinin (WGA), previously regarded strictly as a nonmitogenic or anti-mitogenic lectin, can under appropriate conditions markedly stimulate in vitro synthesis and secretion of immunoglobulin (Ig) by human B lymphocytes. Stimulation of Ig production by WGA is 1) confined to a narrow lectin dose range (2 to 10 micrograms/ml; 2) abrogated by the simple sugar N-acetyl-D-glucosamine but not by a variety of other monosaccharides; 3) effective only after early additions of WGA within the initial 72 hr of 12-day cultures; 4) detected in the presence of B and T cells but not B cells alone; and 5) polyisotypic in nature, as indicated by augmented synthetic rates of Ig in each of 3 major classes (IgG, IgA, and IgM). With few exceptions, WGA produces equivalent or greater rates of Ig production as obtained in cultures activated with pokeweed mitogen (PWM), a well-recognized T-dependent polyclonal activator of human B cells. Furthermore, periperal blood lymphocytes from select individuals that respond weakly to PWM are markedly stimulated with WGA. In contrast to these stimulatory effects of WGA on Ig production by lymphocytes exposed to low lectin concentrations, addition of WGA in amounts greater than 15 micrograms/ml to PWM-stimulated human lymphocyte cultures produces marked suppression of the expected level of Ig synthesis. These data indicate that varying doses of WGA can produce contrasting stimulatory and inhibitory effects on human B cell metabolism.

Stimulation of immunoglobulin biosynthesis in human B cells by wheat germ agglutinin. I. Evidence that WGA can produce both a positive and negative signal for activation of human lymphocytes

Wheat germ agglutinin (WGA), previously regarded strictly as a nonmitogenic or anti-mitogenic lectin, can under appropriate conditions markedly stimulate in vitro synthesis and secretion of immunoglobulin (Ig) by human B lymphocytes. Stimulation of Ig production by WGA is 1) confined to a narrow lectin dose range (2 to 10 micrograms/ml; 2) abrogated by the simple sugar N-acetyl-D-glucosamine but not by a variety of other monosaccharides; 3) effective only after early additions of WGA within the initial 72 hr of 12-day cultures; 4) detected in the presence of B and T cells but not B cells alone; and 5) polyisotypic in nature, as indicated by augmented synthetic rates of Ig in each of 3 major classes (IgG, IgA, and IgM). With few exceptions, WGA produces equivalent or greater rates of Ig production as obtained in cultures activated with pokeweed mitogen (PWM), a well-recognized T-dependent polyclonal activator of human B cells. Furthermore, periperal blood lymphocytes from select individuals that respond weakly to PWM are markedly stimulated with WGA. In contrast to these stimulatory effects of WGA on Ig production by lymphocytes exposed to low lectin concentrations, addition of WGA in amounts greater than 15 micrograms/ml to PWM-stimulated human lymphocyte cultures produces marked suppression of the expected level of Ig synthesis. These data indicate that varying doses of WGA can produce contrasting stimulatory and inhibitory effects on human B cell metabolism.