Regulation by anti-CD2 monoclonal antibody of the activation of a human T cell clone induced by anti-CD3 or anti-T cell receptor antibodies

In this study the effect of anti-cluster designation (CD) 2 monoclonal antibodies (mAb) on the activation of a cloned human T cell line, HY837, after triggering the CD3/T cell receptor (TcR) complex by anti-CD3 or anti-TcR mAb is described. HY837, which reacts with a series of mAb directed at different epitopes on the TcR, could be induced to proliferation and interleukin 2 (IL-2) production by soluble mAb directed at the CD3/TcR complex in the absence of accessory cells. mAb directed at the CD2 epitope T11-1 were shown to block the IL-2 production by HY837, as well as the expression of the IL-2 receptor, induced by anti-CD3 mAb, resulting in the inhibition of the proliferative response. The effect of anti-CD2 mAb on the proliferative response of HY837, induced by anti-CD3 mAb, was not due to a competition for Fc binding sites. In contrast, the proliferative responses and IL-2 production of HY837, induced by mAb directed at the TcR, were shown to be enhanced by the action of the anti-CD2 mAb. These results indicate that effects mediated by anti-CD3/TcR mAb cannot always be extrapolated to antigen-mediated effects and show that anti-CD2 mAb may regulate the T cell response, induced by mAb directed at the CD3/TcR complex, depending on which part of this complex is triggered during activation.     

Highly active antiretroviral therapy drug combination induces oxidative stress and mitochondrial dysfunction in immortalized human blood-brain barrier endothelial cells

The era of highly active antiretroviral therapy (HAART) has controlled AIDS and its related disorders considerably; however, the prevalence of HIV-1-associated neurocognitive disorders has been on the rise in the post-HAART era. In view of these developments, we investigated whether a HAART drug combination of 3'-azido-2',3'-deoxythymidine (AZT) and indinavir (IDV) can alter the functionality of the blood-brain barrier (BBB) endothelial cells, thereby exacerbating this condition. The viability of hCMEC/D3 cells (in vitro model of BBB) that were exposed to these drugs was significantly reduced after 72h treatment, in a dose-dependent manner. Reactive oxygen species were highly elevated after the exposure, indicating that mechanisms that induce oxidative stress were involved. Measures of oxidative stress parameters, such as glutathione and malondialdehyde, were altered in the treated groups. Loss of mitochondrial membrane potential, as assessed by fluorescence microscopy and decreased levels of ATP, indicated that cytotoxicity was mediated through mitochondrial dysfunction. Furthermore, AZT+IDV treatment caused apoptosis in endothelial cells, as assessed by the expression of cytochrome c and procaspase-3 proteins. Pretreatment with the thiol antioxidant N-acetylcysteine amide reversed some of the pro-oxidant effects of AZT+IDV. Results from our in vitro studies indicate that the AZT+IDV combination may affect the BBB in HIV-infected individuals treated with HAART drugs.     

TDP1 repairs nuclear and mitochondrial DNA damage induced by chain-terminating anticancer and antiviral nucleoside analogs

Chain-terminating nucleoside analogs (CTNAs) that cause stalling or premature termination of DNA replication forks are widely used as anticancer and antiviral drugs. However, it is not well understood how cells repair the DNA damage induced by these drugs. Here, we reveal the importance of tyrosyl–DNA phosphodiesterase 1 (TDP1) in the repair of nuclear and mitochondrial DNA damage induced by CTNAs. On investigating the effects of four CTNAs—acyclovir (ACV), cytarabine (Ara-C), zidovudine (AZT) and zalcitabine (ddC)—we show that TDP1 is capable of removing the covalently linked corresponding CTNAs from DNA 3′-ends. We also show that Tdp1^−/− cells are hypersensitive and accumulate more DNA damage when treated with ACV and Ara-C, implicating TDP1 in repairing CTNA-induced DNA damage. As AZT and ddC are known to cause mitochondrial dysfunction, we examined whether TDP1 repairs the mitochondrial DNA damage they induced. We find that AZT and ddC treatment leads to greater depletion of mitochondrial DNA in Tdp1^−/− cells. Thus, TDP1 seems to be critical for repairing nuclear and mitochondrial DNA damage caused by CTNAs.     

Zidovudine (AZT) treatment suppresses granulocyte-monocyte colony stimulating factor receptor type alpha (GM-CSFR alpha) gene expression in murine bone marrow cells

In vitro exposure of murine bone marrow cells to increasing concentrations of zidovudine (AZT, 0.1-50 microM) had a concentration dependent suppressive effect on the growth of granulocyte-monocyte colony forming unit (CFU-GM) derived colonies. In our previous published study, the mechanism of AZT-induced suppression of erythroid colony forming unit (CFU-E) derived colonies was linked to a decrease in erythropoitin receptor (Epo-R) gene expression. In this study, we have observed that AZT exposure also induced a concentration dependent suppressive effect (35-90%) on GM-CSF receptor type alpha (GM-CSFR alpha) gene expression. The suppression of GM-CSFR alpha mRNA expression was specific, since AZT caused a much lower decrease (15-22%) on the IL-3 receptor type alpha (IL-3R alpha) message level, and had an insignificant effect on glyceraldehyde 3-phosphate dehydrogenase (GAPDH) and c-myc message levels. Erythropoietin (Epo) therapy has been used for reversal of AZT induced erythroid toxicity. Exposure to increasing concentrations (10-500 U/ml) of GM-CSF was unable to override the suppressive effect of AZT on CFU-GM derived colonies, however, treatment in combination with IL-3 (10-250 U/ml) ameliorated the suppressive effects of AZT on CFU-GM and on GM-CSFR alpha and IL-3R alpha gene expression. These findings suggest a mechanism via which AZT may suppress granulocyte-monocyte specific differentiation in murine bone marrow cells. These data also suggest that a combination of GM-CSF and IL-3 may be a superior therapeutic intervention for AZT-induced neutropenia.     

Potentiation of interleukin-2 production and its binding by monoclonal antibodies to the gangliosides GD3 and GD2

Summary Previous studies have shown that monoclonal antibodies (mAbs) against certain gangliosides, which induced remissions in patients with melanoma, also potentiated the response of lymphocytes to a variety of stimuli, including lectins, interleukin-2 (IL-2) and antigens. The present studies have investigated the mechanism of these effects on lymphocytes. Although the mAbs potentiated phytohemagglutinin (PHA)-induced IL-2 production at high concentrations of mAbs and of PHA, this did not appear to explain their potentiation of the proliferative responses of lymphocytes. Hence, although IL-2 production was minimal or absent from the CD8⁺ subset the latter showed the highest degree of augmentation. Furthermore, addition of IL-2 to PHA-stimulated cultures did not produce similar augmentation of mitogenic responses to that produced by the mAb to GD3 or GD2. The augmented and normal mitogenic responses were, however, dependent on IL-2, as shown by their inhibition with mAbs against IL-2. The antiganglioside mAbs did not have significant effects on IL-2 receptor expression measured by mAbs to Tac. However, the mAbs appeared to increase the affinity of binding of radiolabelled IL-2 to IL-2 receptor and increased internalization of the latter. These results suggest that the effects of the mAbs on IL-2 production may be distinguished from their effects on the proliferative responses of T cells and that the latter were associated with changes in affinity and internalization of ¹²⁵I-IL-2. Whether the latter is a direct cause of the increased proliferative response remains unknown. The ability of mAbs to GD2 and GD3 to increase IL-2 production and to enhance IL-2-dependent proliferative responses suggests the may have valuable clinical roles as immunopotentiating agents.     

Transport of antiviral 3'-deoxy-nucleoside drugs by recombinant human and rat equilibrative, nitrobenzylthioinosine (NBMPR)-insensitive (ENT2) nucleoside transporter proteins produced in Xenopus oocytes.

In the present study, one has determined the relative role of plasma membrane equilibrative (Na+-independent) ENT nucleoside transport proteins (particularly ENT2) in the uptake of antiviral nucleoside analogues for comparison with the previously reported drug transport properties of concentrative (Na+-dependent) CNT nucleoside transport proteins. The human and rat nucleoside transport proteins hENT1, rENT1, hENT2 and rENT2 were produced in Xenopus oocytes and investigated for their ability to transport three 3'-deoxy-nucleoside analogues, ddC (2'3'-dideoxycytidine), AZT (3'-azido-3'-deoxythymidine) and ddI (2'3'-dideoxyinosine), used in human immunodeficiency virus (HIV) therapy. The results show, for the first time, that the ENT2 transporter isoform represents a mechanism for cellular uptake of these clinically important nucleoside drugs. Recombinant h/rENT2 transported ddC, ddI and AZT, whilst h/rENT1 transported only ddC and ddI. Relative to uridine, h/rENT2 mediated substantially larger fluxes of ddC and ddI than h/rENT1. Transplanting the amino-terminal half of rENT2 into rENT1 rendered rENT1 transport-positive for AZT and enhanced the uptake of both ddC and ddI, identifying this region as a major site of 3'-deoxy-nucleoside drug interaction.     

Stimulation of AIDS lymphocytes with calcium ionophore (A23187) and phorbol ester (PMA): studies of cytoplasmic free Ca, IL-2 receptor expression, IL-2 production, and proliferation

We have studied whether the decreased lymphocyte proliferative responses of AIDS lymphocytes to stimulation by mitogens and antigens may be overcome when challenged with a combination of calcium ionophore A23187 and phorbol ester PMA. Comparison of the proliferative response of lymphocytes from nine patients with AIDS with the response of lymphocytes from nine control subjects showed that the response of AIDS lymphocytes was severely decreased when stimulated with PHA and no further response could be achieved by stimulation with A23187/PMA. On the other hand, no significant difference between the PHA-induced rise of cytoplasmic free calcium concentration ([Ca2+]1) in normal and AIDS lymphocytes was observed. The percentage of cells expressing IL-2 receptors (CD25) was also normal both after addition of PHA and after addition of A23187/PMA and the expression was normal on both CD4 and CD8 cells. The production of IL-2 in normal lymphocytes stimulated with A23187/PMA was 33 times higher than that after stimulation with PHA. In AIDS lymphocytes the production of IL-2 induced by all activators was severely decreased compared to control subjects, although the production of IL-2 after stimulation with A23187/PMA was higher than that in control lymphocytes after stimulation with PHA. The present study shows that a direct activation of protein kinase C combined with mobilization of cytoplasmic calcium does not overcome the lymphocyte proliferative deficiency of AIDS lymphocytes.     

Inhibition of antigen-specific proliferation of type 1 murine T cell clones after stimulation with immobilized anti-CD3 monoclonal antibody

The effect of stimulating normal type 1 murine T cell clones with anti-CD3 antibody was examined in vitro. In the absence of accessory cells, anti-CD3 antibody immobilized on plastic plates stimulated inositol phosphate production, suboptimal proliferation, IL-2 and IL-3 production, and maximal IFN-gamma production. Addition of accessory cells augmented lymphokine production and proliferation when the effects of "high-dose suppression" were relieved by removing the T cells from the antibody-coated plates. Exposure of type 1 T cell clones to immobilized anti-CD3 antibody alone rapidly induced long-lasting proliferative unresponsiveness (anergy) to Ag stimulation that could be prevented by accessory cells. This anergic state was characterized by a lymphokine production defect, not a failure of the T cells to respond to exogenous IL-2 or to express surface Ti/CD3 complexes. In addition, anergy could not be induced in the presence of cyclosporine A. These results suggest that under certain conditions anti-CD3 antibodies may have potent immunosuppressive effects independent of Ti/CD3 modulation. Furthermore, our results support a two-signal model of type 1 T cell activation in which Ti/CD3 occupancy alone (signal 1) induces anergy, whereas Ti/CD3 occupancy in conjunction with a costimulatory signal (signal 2) induces a proliferative response.     

Role of endogenously produced interleukin-6 as a second signal in murine thymocyte proliferation induced by multiple cytokines: regulatory effects of transforming growth factor-beta

Previous studies have demonstrated that murine thymocytes proliferate in the presence of submitogenic concentrations of phytohemagglutinin-P (PHA-P) and various cytokines such as interleukin-1 (IL-1), interleukin-4 (IL-4), tumor necrosis factor-alpha (TNF-alpha), and interleukin-6 (IL-6). We report that C3H/HeJ thymocytes stimulated with PHA-P and IL-1, IL-4, or TNF-alpha secrete significant levels of IL-6 as determined on B9 hybridoma cells. The possibility that thymocyte proliferation induced by these cytokines was mediated through IL-6 was investigated utilizing a neutralizing monoclonal antibody against murine IL-6, MP5 20F3.1. The results demonstrate that MP5 20F3.1 inhibited the proliferative response of thymocytes and B9 hybridoma cells to recombinant MuIL-6 (but not HuIL-6) and neutralized the endogenous IL-6 produced in the thymocyte cultures, but did not have any measurable effects on the proliferative responses induced by IL-1, IL-4, or TNF-alpha. Although the level of endogeneously produced IL-6 did not play a measurable role in the proliferative response induced by TNF-alpha, the addition of higher concentrations of IL-6 augmented the proliferation of murine thymocytes induced by rMu TNF-alpha. In addition, recombinant human transforming growth factor-beta 1 (rHu TGF-beta 1) significantly inhibited thymocyte proliferation induced by HuIL-1, rMuIL-4, rMuIL-6, and rMuTNF-alpha. The studies suggest that IL-1, IL-4, or TNF-alpha mediate a proliferative signal on murine thymocytes independent of IL-6 and that the proliferative signals provided by these cytokines as well as IL-6 are inhibitable by rHu TGF-beta 1.     

Transport of antiviral 3'-deoxy-nucleoside drugs by recombinant human and rat equilibrative,nitrobenzylthioinosine (NBMPR)-insensitive (ENT2) nucleoside transporter proteins produced in Xenopus oocytes

In the present study, one has determined the relative role of plasma membrane equilibrative (Na⁺-independent) ENT nucleoside transport proteins (particularly ENT2) in the uptake of antiviral nucleoside analogues for comparison with the previously reported drug transport properties of concentrative (Na⁺-dependent) CNT nucleoside transport proteins. The human and rat nucleoside transport proteins hENT1, rENT1, hENT2 and rENT2 were produced in Xenopus oocytes and investigated for their ability to transport three 3'-deoxy-nucleoside analogues, ddC (2' 3'-dideoxycytidine), AZT (3'-azido-3'-deoxythymidine)and ddI (2' 3'-dideoxyinosine), used in human immunodeficiency virus (HIV) therapy. The results show, for the first time, that the ENT2 transporter isoform represents a mechanism for cellular uptake of these clinically important nucleoside drugs. Recombinant h/rENT2 transported ddC, ddI and AZT, whilst h/rENT1 transported only ddC and ddI. Relative to uridine, h/rENT2 mediated substantially larger fluxes of ddC and ddI than h/rENT1. Transplanting the amino-terminal half of rENT2 into rENT1 rendered rENT1 transport-positive for AZT and enhanced the uptake of both ddC and ddI, identifying this region as a major site of 3'-deoxy-nucleoside drug interaction.     

Modulation of ex vivo cytokine production by splenocytes using in vitro combined therapeutics in murine retroviral model.

Altered levels of Type 1 and Type 2 cytokines are important in retrovirus-induced immunosuppression. The combination of immunostimulatory agents with antiviral drugs alters the course of murine retroviral infections. Previously, it was demonstrated that in vitro treatment of noninfected splenocytes and in vivo treatment of Friend leukemia virus (FLV)-infected mice with the combination of azidothymidine (AZT) and methionine enkephalin (MENK) significantly increases Type 1 cytokine levels and decreases Type 2 cytokines compared with treatment with only AZT. In order to study the effect of the time of initiation of immunomodulation on the course of retroviral infections, we examined the kinetics of cytokine production by isolated splenocytes from infected mice. BALB/c mice were infected with FLV, and spleen cells were removed at specified times postinfection (days 1, 3, 7, 10, and 14). Interleukin (IL)-2, interferon (IFN-gamma, IL-4, and IL-10 production by unstimulated or ConA-stimulated splenocytes treated in vitro with AZT, MENK, or AZT + MENK was determined after 48 h. The capacity of the isolated splenocytes to produce the Type 1 cytokines IL-2 and IFN-gamma in response to stimulation with ConA and combination therapy decreased over the course of infection. These results suggest that MENK treatment initiated later in the course of infection is unable to modulate the cytokine profile and would likely be ineffective in altering the course of FLV induced-disease. The results indicate the necessity to initiate antiretroviral therapy early in infection. Such information may be applicable in designing future regimens for HIV-1 infections in humans.     

Activation of human T lymphocytes by bryostatin

The immunologic effects of bryostatin (Bryo), a PKC activator with antineoplastic activity, were assessed and compared to PMA. Bryo induced IL-2R expression on CD4+ and CD8+ human T lymphocytes with a dose response comparable to PMA. However, Bryo induced only a marginal proliferative response as compared with the vigorous response induced by PMA. Bryo mediated functional receptor expression because the proliferative response was enhanced by addition of rIL-2. Furthermore, the proliferative response was inhibited by the relatively specific Ca+, phospholipid-dependent protein kinase (PKC) inhibitor, H-7, indicating a role of PKC in Bryo-induced activation. Addition of the calcium ionophore, ionomycin, to Bryo-stimulated lymphocytes resulted in the production and secretion of IL-2 with a concomitant proliferative response. This effect of the calcium ionophore could be inhibited by cyclosporine with identical results obtained in PMA-stimulated cultures. A most intriguing finding was that Bryo could effectively antagonize PMA-induced T cell proliferation. Although this mechanism of inhibition is unclear, a discussion with respect to differential effects on potential intracellular PKC isoforms is provided. These studies indicated that Bryo has potent immunopotentiating properties that share some similar effects of the phorbol ester, PMA, but offers the additional property of modulating other phorbol ester effects on proliferation.     

Analysis of Antiretroviral Nucleosides by Electrospray Ionization Mass Spectrometry and Collision Induced Dissociation

Abstract

Antiretroviral nucleoside drugs used against the human immunodeficiency virus (HIV) infection have been analyzed using negative ion electrospray ionization (ESI) mass spectrometry and collision-induced dissociation (CID-MS/MS). Mass fragmentation of azidothymidine (AZT), didanosine (ddI), dideoxycytidine (ddC) and dideoxythiacytidine (3TC) were obtained at different cone voltages and collision energies. Fragmentation of purines and pyrimidines occurred by different pathways. For purines (ddI), the fragmentation was similar to those found in endogenous nucleosides; mainly the pseudo molecular ion is present (M-H) and a cleavage through the glycosidic bond forming (B) was observed. For pyrimidines (AZT, ddC, 3TC), the fragmentation pathways were different from endogenous nucleosides; for AZT, the fragmentation occurred primarily through the elimination of the azido group in the 3′-position (M-H₂-N₃), whereas ddC and 3TC presented more complex fragmentation patterns. For ddC, fragmentation appeared to be dominated by a retro Diels-Alder mechanism (M-CONH). For 3TC, the sulfur atom in the sugar moiety provided greater stability to the charge, producing fragments where the charge resided initially in the dideoxyribose (M-C₂O₂H₆).     

The absence of IL-6 does not affect Th2 cell development in vivo, but does lead to impaired proliferation, IL-2 receptor expression, and B cell responses

The role of IL-6 in Th2 cell differentiation and response development after the injection of eggs from Schistosoma mansoni was investigated using wild-type (WT) and IL-6-/- mice. IL-6 was induced in the lymph nodes (LN) of WT mice within 24 h of egg injection, and IL-4 production by WT LN cells and CD4 T cells isolated 24 h after egg injection and stimulated in vitro was observed. In the absence of IL-6, this early production of IL-4 by LN cells and purified CD4 T cells was not abolished; although the level of IL-4 produced by IL-6-/- LN cells was similar to WT, IL-4 production by purified IL-6-/- CD4 T cells was reduced compared with WT. Despite the difference in CD4 T cell production of IL-4, the development of egg-specific Th2 cells 7 days after egg injection was not affected by the absence of IL-6. Nevertheless, Ab production was impaired and the in vitro proliferative response of whole LN cell populations, CD4 and CD8 T cells, and B cells from IL-6-/- mice was poor compared with WT. The proliferative defect in the IL-6-/- cells correlated with decreased IL-2R expression, and addition of exogenous IL-6 enhanced IL-2R expression as well as proliferation of LN cells from IL-6-/- mice. These studies demonstrate that Th2 differentiation and response development in vivo is not dependent on IL-6, but that Th-dependent and independent B cell responses are. Our results also emphasize the importance of IL-6 for lymphoproliferation, possibly through induction of IL-2R expression.     

Lymphocytic choriomeningitis virus-induced immunodepression: inherent defect of B and T lymphocytes.

Infection of mice with lymphocytic choriomeningitis virus (LCMV) produces a rapidly induced immuno-suppression manifested by low lymphocyte proliferation in response to lipopolysaccharide (LPS) and concanavalin A (ConA). Analysis of the mechanisms underlying the unresponsiveness to these mitogens was undertaken at the cellular and molecular levels 7 days after infection. The selective elimination of CD8+ T cells and the results of coculture experiments demonstrated that unresponsiveness was not due to suppressor cells. Similarly, the role of inhibitory factors such as prostaglandins was excluded, since indomethacin, which inhibits their production, did not reverse the unresponsiveness. Analysis of different cytokines secreted by ConA-activated macrophages or T cells revealed that interleukin-1 (IL-1), synthesized during the T-dependent activation of macrophages by ConA, was normally produced by cells from LCMV-infected mice. In contrast, IL-2, which is produced by activated CD4+ T cells, was undetectable. Addition of exogenous IL-2 did not restore the proliferative response, although the p55-kilodalton protein of the IL-2 receptor was induced by ConA on CD4+ cells from LCMV-infected mice. Our results can be interpreted as showing that (i) unresponsiveness to mitogens of cells from LCMV-infected mice is not due to altered functions of the macrophages with respect to IL-1 production; (ii) CD4+ cells are activated, since the p55 chain of the IL-2 receptor is induced; (iii) the lack of IL-2 production cannot explain T-cell unresponsiveness, since addition of exogenous IL-2 did not restore the proliferative response. Taken together, these data suggest that T-lymphocyte unresponsiveness should be related to an inherent proliferative defect subsequent to T-cell activation and IL-2 receptor expression.     

Investigation of the immunostimulatory properties of oxihumate

A unique process has been developed to convert bituminous coal by controlled wet oxidation followed by base treatment to a water-soluble humate called oxihumate. The effects of oxihumate on the proliferative response of lymphocytes has been studied in vitro and ex vivo. Oxihumate increased the proliferative response of phytohaemagglutinin-stimulated human lymphocytes, from a concentration of 20 microg/ml and upwards. This response was even more striking in the case of lymphocytes from HIV-infected patients and was not limited to the in vitro setting since similar effects were observed ex vivo following administration of a non-toxic dosage of 4 g oxihumate per day to HIV-positive individuals for two weeks. Mechanistic studies revealed that stimulation of the proliferative response of lymphocytes by oxihumate is associated with an increased production of IL-2, as well as expression of the IL-2 receptor in the setting of decreased production of IL-10. Oxihumate therefore holds promise for the treatment of immunocompromized patients.     

Human immunodeficiency virus type 1 pol gene mutations in an AIDS patient treated with multiple antiretroviral drugs.

Multiple mutations were found in the human immunodeficiency virus pol gene following treatment of an AIDS patient with antiretroviral drugs. After approximately 2.5 years of monthly alternating therapy with 3'-azido-3'-deoxythymidine (AZT) and 2',3'-dideoxycytidine (ddC), most of the pol sequences amplified from the patient's peripheral blood mononuclear cell DNA contained known AZT resistance mutations at codons 41, 67, and 215 and a putative ddC resistance mutation at codon 69 as well as other novel mutations. These mutations persisted for 6 months after the patient was switched to 2',3'-dideoxyinosine monotherapy. Mutations known to be associated with 2',3'-dideoxyinosine resistance did not occur during this time. Antiviral susceptibility testing of point mutants, introduced into the genetic background of laboratory strain NL4-3, showed that the codon 41 mutation antagonized ddC resistance when present with the codon 69 mutation. However, this antagonism was not found with a chimeric mutant containing the patient's pol gene sequence from codons 25 to 218, implying that other mutations compensated for the antagonism. Thus, alternating therapy with AZT and ddC resulted in the selection of viruses resistant to both drugs.