Signals involved in T cell activation. T cell proliferation induced through the synergistic action of anti-CD28 and anti-CD2 monoclonal antibodies

Loading of Primary Human T Lymphocytes with Citrate-Coated Superparamagnetic Iron Oxide Nanoparticles Does Not Impair Their Activation after Polyclonal Stimulation

For the conversion of immunologically cold tumors, characterized by a low T cell infiltration, into hot tumors, it is necessary to enrich T cells in the tumor area. One possibility is the use of magnetic fields to direct T cells into the tumor. For this purpose, primary T cells that were freshly isolated from human whole blood were loaded with citrate-coated superparamagnetic iron oxide nanoparticles (SPION^Citrate). Cell toxicity and particle uptake were investigated by flow cytometry and atomic emission spectroscopy. The optimum loading of the T cells without any major effect on their viability was achieved with a particle concentration of 75 µg Fe/mL and a loading period of 24 h. The cellular content of SPION^Citrate was sufficient to attract these T cells with a magnet which was monitored by live-cell imaging. The functionality of the T cells was only slightly influenced by SPION^Citrate, as demonstrated by in vitro stimulation assays. The proliferation rate as well as the expression of co-stimulatory and inhibitory surface molecules (programmed cell death 1 (PD-1), lymphocyte activation gene 3 (LAG-3), T cell immunoglobulin and mucin domain containing 3 (Tim-3), C-C motif chemokine receptor 7 (CCR7), CD25, CD45RO, CD69) was investigated and found to be unchanged. Our results presented here demonstrate the feasibility of loading primary human T lymphocytes with superparamagnetic iron oxide nanoparticles without influencing their viability and functionality while achieving sufficient magnetizability for magnetically controlled targeting. Thus, the results provide a strong fundament for the transfer to tumor models and ultimately for new immunotherapeutic approaches for cancer treatment.

Genetic Modification of T Cells with Chimeric Antigen Receptors: A Laboratory Manual

Redirected T cells genetically modified with a chimeric antigen receptor (CAR) have induced spectacular remissions of refractory leukemia/lymphoma in early phase trials, attracting interest to use CAR T cells in a variety of other applications including solid cancer and nonmalignant diseases. However, extensive preclinical explorations demand highly effective and robust procedures for the genetic modification of blood T cells; the same applies for engineering with a recombinant T cell receptor. We present laboratory procedures in a step-by-step protocol to engineer human and mouse T cells with a CAR by γ-retro- or lentiviral transduction for further preclinical testing.

Cytokine production by leukocytes of military personnel with depressive symptoms after deployment to a combat-zone: a prospective, longitudinal study

Major depressive disorder (MDD) is frequently diagnosed in military personnel returning from deployment. Literature suggests that MDD is associated with a pro-inflammatory state. To the best of our knowledge, no prospective, longitudinal studies on the association between development of depressive symptomatology and cytokine production by peripheral blood leukocytes have been published. The aim of this study was to investigate whether the presence of depressive symptomatology six months after military deployment is associated with the capacity to produce cytokines, as assessed before and after deployment. 1023 military personnel were included before deployment. Depressive symptoms and LPS- and T-cell mitogen-induced production of 16 cytokines and chemokines in whole blood cultures were measured before (T0), 1 (T1), and 6 (T2) months after return from deployment. Exploratory structural equation modeling (ESEM) was used for data reduction into cytokine patterns. Multiple group latent growth modeling was used to investigate differences in the longitudinal course of cytokine production between individuals with (n = 68) and without (n = 665) depressive symptoms at T2. Individuals with depressive symptoms after deployment showed higher T-cell cytokine production before deployment. Moreover, pre-deployment T-cell cytokine production significantly predicted the presence of depressive symptomatology 6 months after return. There was an increase in T-cell cytokine production over time, but this increase was significantly smaller in individuals developing depressive symptoms. T-cell chemokine and LPS-induced innate cytokine production decreased over time and were not associated with depressive symptoms. These results indicate that increased T-cell mitogen-induced cytokine production before deployment may be a vulnerability factor for development of depressive symptomatology in response to deployment to a combat-zone. In addition, deployment to a combat-zone affects the capacity of T-cells and monocytes to produce cytokines and chemokines until at least 6 months after return.

The carriage of the type 1 diabetes-associated R262W variant of human LNK correlates with increased proliferation of peripheral blood monocytes in diabetic patients

OBJECTIVE

Lymphocyte adaptor protein (LNK) plays a pivotal role as a suppressor of T-cell receptor-mediated immune signaling and negative regulator of lymphopoiesis and early hematopoiesis. Recently, association between the R262W (c.784T>C) variant of the SH2B3 gene (rs3184504) encoding human LNK and type 1 diabetes (T1D) was found in several populations. In this study, we aimed to check whether this marker is associated with T1D in a Russian population.

METHODS

Using a Taqman allele discrimination assay, we genotyped 1062 unrelated Russian individuals with diabetes at childhood and adolescence onset and 1020 healthy controls. T-cell proliferation assay based on the measurement of incorporation of bromo-2'-deoxyuridine incorporation into newly synthesized DNA was used to evaluate whether carriage of SH2B3 784T>C correlates with T-cell proliferation in patients' peripheral mononuclear blood cells (PMBCs) stimulated with anti-CD28 and anti-CD3 antibodies.

RESULTS

The allele 784C of SH2B3 was related to a higher risk of T1D (odds ratio of 1.52, p = 1.2 × 10(-12)). A correlation between the carriage of the predisposing C/C variant of LNK and increased proliferation of T lymphocytes was shown in PMBCs of both diabetic [C/C vs. C/T vs.T/T = optical density at 450 nm (OD(450)) 6.3 ± 0.8 vs. 4.4 ± 0.7 vs. 2.7 ± 0.5, p = 0.0007] and non-diabetic (C/C vs. C/T vs.T/T = OD(450) 2.9 ± 0.6 vs. 2.2 ± 0.4 vs. 1.7 ± 0.4, p = 0.022) patients.

CONCLUSIONS

The SH2B3 784T>C variant could contribute to the pathogenesis of T1D through impaired immune response that promotes activation and expansion of self-reactive lymphocytes in susceptible individuals.

CD7(-) T cells are late memory cells generated from CD7(+) T cells

CD7(-) T cells constitute a distinct subset within the CD4(+) and CD8(+) T cell populations; their developmental and functional relationship to the majority of CD7(+) T cells, however, remained so far unresolved. We here elucidate that CD7(-) cells represent aging T cells in late memory cell development characterized by a high activation threshold, low effector capacities, and high sensitivity to activation-induced cell death (AICD). In this regard, CD7(-) T cells highly express killer cell lectin-like receptor G1 (KLRG-1), harbor telomeres of shorter lengths, a decreased telomerase expression per cell, and less amounts of T cell receptor rearrangement excision circles (TRECs) compared to CD7(+) cells. CD7(-) T cells are generated in vitro from naive CD7(+) T cells upon repetitive TCR/CD28 engagement, a process that is unidirectional and requires multiple cell divisions. Consequently, clonal expansions of CD7(-) T cells in vivo are less frequent than of CD7(+) T cells, the former can be traced back to those of CD7(+) T cells.

Intravenous immunoglobulin (IVIG) treatment for modulation of immune activation in human immunodeficiency virus type 1 infected therapy-naive individuals

We evaluated the ability of intravenous immunoglobulin (IVIG) to diminish immune hyperactivation, which is considered a major cause of CD4+ T cell loss during chronic HIV-1 infection and whether this affected CD4+ T cell counts and plasma HIV-1 RNA (pVL). Therefore, we treated six chronically HIV-1-infected, antiretroviral-therapy-naive patients with IVIG (0.4 g/kg) at weeks 0 and 4, with a follow-up of 12 weeks after the second dosage during which pVL, T cell numbers, and T cell activation were measured. At baseline median CD4+ T cell counts were 300 (range 200-460) x 10(6)/liter and median pVL was 5.0 (range 3.2-5.2) log10 copies/ml. IgG plasma levels peaked during the first days after administration. We observed a decrease in the percentage of activated (CD38+ HLA-DR+) CD4+ and CD8+ T cells [3.5% (range 1-7%) and 5% (1-10%), respectively (p = 0.027)], but no effect on the fraction of proliferating CD4+ or CD8+ T cells as measured by Ki67 expression. CD4+ T cell counts were significantly increased on day 4 (median +55 cells, range 0-150, p = 0.043). pVL was significantly increased on day 1 after IVIG infusion (median +0.13 log10, range 0.01-0.55, p = 0.028). All these parameters returned to baseline levels within 1 week after infusion. In conclusion, administration of IVIG caused a temporary decrease in T cell activation and an increase in CD4+ T cell counts, despite an increase in pVL. Our results support the hypothesis that T cell activation, rather than direct HIV-1 infection, mediates the loss of CD4+ T cells and suggest that immunomodulating therapy in HIV-1 infection could indeed be effective.

The action of interleukin 6 on lymphoid populations

We have analysed the role of IL-6 in activation of human lymphocytes isolated from peripheral blood. We found little effect of IL-6 on proliferation of T cells. IL-6 did stimulate production of IgM by B cells. However, it did not behave as a terminal differentiation factor and was required only during the first two days of the culture. Under most conventional stimulation conditions T cells themselves produce little or no IL-6. High IL-6 production could be induced by stimulating the cells with a combination of phorbol-12-myristate 13-acetate (PMA) and anti-CD28 antibodies.

Molecular construction and characterization of a novel exotoxin fusion protein that selectively blocks the B7:CD28 costimulatory signal system

An important strategy for specifically preventing and treating graft-versus-host and host-versus-graft diseases is to selectively block the B7:CD28/cytotoxic T-lymphocyte A4 costimulatory signal system for induced immune tolerance. In this study, a novel recombinant B7-2-L-PE40KDEL fusion protein was created to target the B7:CD28 system. We used a flexible linker sequence (Gly4Ser)4 and overlapping sequence extension to link the cDNAs encoding a human B7-2 extracellular domain and a mutant truncated form of Pseudomonas exotoxin A (PE), PE40KDEL. This B7-2-L-PE40KDEL fusion gene was then inserted into the pTYB4 expression vector, expressed in Escherichia coli, and purified through Ni-NTA mealty affinity-->MonoQ anion exchange-->Superdex75 gel filtration chromatography 3-step purification protocols. Western blotting demonstrated that the B7-2-L-PE40KDEL fusion protein specifically bound antihuman B7-2 monoclonal antibody and anti-pseudomonas exotoxin A antiserum. We used the Antheprot nucleic acid and protein analyzing software to predict the characteristics of this fusion protein, and showed that the fusion did not confer new antigenicities to the fusion protein. 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide tests demonstrated that at doses ranging from 0.2 to 2 microg/mL, this fusion protein specifically killed CD28-overexpressing Jurkat cells but even at doses of 2 microg did not kill CD28-negative Hut28 cells. The results of a one-way mixed lymphocyte reaction demonstrated that the fusion protein has a range of suppressive effects on HLA class I and II matched related donors and recipients, and HLA class I and II mismatched unrelated donors. Taken together, these results demonstrate that we have developed a novel recombinant human B7-2-L-PE40KDEL exotoxin fusion protein that specifically blocks the B7:CD28 costimulatory signal system in a manner that may be of significant importance in preventing and treating graft-versus-host or host-versus-graft diseases.

B7-1-HSA (CD80-CD24), a recombinant hybrid costimulatory molecule retains ligand binding and costimulatory functions

Optimal activation of naïve T lymphocyte requires two signals; an antigen-specific signal initiated by engagement of TCR with the antigen-MHC complex and a costimulatory signal independent of the antigen receptor complex. Without the costimulatory signal, T cells become anergic. Various adhesion molecules, such as B7-1 (CD80) and heat stable antigen (HSA, CD24), expressed on antigen presenting cells have been demonstrated to provide costimulatory signals to T cells. It was reported that the combinations of different adhesion molecules could induce even stronger immune response. In this study, we made a hybrid costimulatory molecule, B7-1-HSA, and tested its T cell stimulatory function. Chinese hamster ovary (CHO) cells expressing this hybrid molecule bound both anti-CD80 and anti-CD24 monoclonal antibodies, and induced stronger T cell proliferation than CHO cells expressing B7-1 or HSA alone. These results suggest that the B7-1-HSA hybrid molecule can deliver two costimulatory signals simultaneously that can synergize in inducing T cell proliferation. The purified B7-1-HSA protein reacted with both anti-B7-1 and anti-HSA mAbs in Western blotting and specifically mediated adhesion of Jurkat cells. Furthermore, purified B7-1-HSA molecule spontaneously incorporated onto cell membrane through its glycolipid anchor suggesting that this hybrid costimulatory molecule can be used in protein transfer to develop effective cancer vaccines.

Activation of V gamma 9V delta 2 T cells by NKG2D

Human Vgamma9 Vdelta2 T cells recognize phosphorylated nonpeptide Ags (so called phosphoantigens), certain tumor cells, and cells treated with aminobisphosphonates. NKG2D, an activating receptor for NK cells, has been described as a potent costimulatory receptor in the Ag-specific activation of gammadelta and CD8 T cells. This study provides evidence that Vgamma9 Vdelta2 T cells may also be directly activated by NKG2D. Culture of PBMC with immobilized NKG2D-specific mAb or NKG2D ligand MHC class I related protein A (MICA) induces the up-regulation of CD69 and CD25 in NK and Vgamma9 Vdelta2 but not in CD8 T cells. Furthermore, NKG2D triggers the production of TNF-alpha but not of IFN-gamma, as well as the release of cytolytic granules by Vgamma9 Vdelta2 T cells. Purified Vgamma9 Vdelta2 T cells kill MICA-transfected RMA mouse cells but not control cells. Finally, DAP10, which mediates NKG2D signaling in human NK cells, was detected in resting and activated Vgamma9 Vdelta2 T cells. These remarkable similarities in NKG2D function in NK and Vgamma9 Vdelta2 T cells may open new perspectives for Vgamma9 Vdelta2 T cell-based immunotherapy, e.g., by Ag-independent killing of NKG2D ligand-expressing tumors.

Baseline T cell reactivity in multiple sclerosis is correlated to efficacy of interferon-beta

BACKGROUND

Measuring proliferative responses of T lymphocytes is a simple, reproducible and widely used assay of immune competence. Evidence suggests a role of T cell reactivity in autoimmune diseases. Interferon (IFN)-beta blocks in vitro proliferation of human T cells.

OBJECTIVES

To assess (i) the relation between T cell proliferation and disease characteristics of MS patients, (ii) differences in T cell proliferation between subgroups and HC, and (iii) the predictive value of T cell proliferation for efficacy of IFN-beta.

METHODS

Proliferative responses were measured in phytohaemagglutinin (PHA), anti-CD2/CD28 and anti-CD3 stimulated whole blood of 189 MS patients and 249 healthy controls (HC). Forty-eight patients started treatment with IFN-beta. Based on EDSS progression, number of relapses and steroid interventions, patients were classified as either clinical responder or nonresponder to IFN-beta.

RESULTS

Significant differences between MS subgroups and HC were found in T cell responses upon both PHA stimulation (RR>HC: p=0.001 and SP>HC: p=0.001) and CD2/CD28 stimulation (RR>HC, SP>HC and PP>HC: all p values <0.001). No significant differences were found between the MS subgroups. A probability of 88% (95% CI, 71-95%) for a favorable response to IFN-beta was found with increased baseline proliferative T cell responses to PHA; a probability of only 16% (95% CI, 7-33%) with decreased values.

CONCLUSION

Our results suggest that the level of T cell proliferation in whole blood predicts efficacy of IFN-beta in MS.

Specific and effective targeting cancer immunotherapy with a combination of three bispecific antibodies

For the purpose of establishing a new adoptive immunotherapy for bile duct carcinoma (BDC), we previously constructed two kinds of bispecific antibodies (bsAbs), anti-MUC1 x anti-CD3 (M x 3) and anti-MUC1 x anti-CD28 (M x 28), which activate T cells and form bridges between them and MUC1-expressing tumor cells. In our previous studies [Cancer Res. 56 (1996) 4205] specific targeting therapy (STT) consisting of i.v. administration of lymphokine activated killer cells with a T cell phenotype (T-LAK) sensitized with two kinds of bsAbs to human BDC-grafted severe combined immunodeficient (SCID) mice demonstrated remarkable inhibition of tumor growth. However, complete cures could not be obtained. In order to improve antitumor efficacy, we have paid attention to anti-CD2 monoclonal antibodies (mAbs), thought to play an important roles in signal transduction in T cell activation or control of T cell receptor (TCR)-driven activation. Therefore, we developed another bsAb, anti-MUC1 x anti-CD2 (M x 2), in order to examine if this would show synergism with the two previously described bsAbs. The combination of the three bsAbs (M x 3, M x 28 and M x 2 bsAbs) showed highest cytotoxicity against MUC1-expressing BDC cells when given simultaneously with peripheral blood mononuclear cells (PBMCs) or T-LAK cells in vitro. When 2 x 10(7) T-LAK cells sensitized with different combinations of bsAbs were administered four times i.v. to BDC-grafted SCID mice, the best therapeutic result was obtained with a combination of all three bsAbs. These results indicate usefulness of combination of three bsAbs for targeting cancer immunotherapy.

Regulation of IL-13 synthesis in human lymphocytes: implications for asthma therapy

1. IL-13 is an important mediator in inflammatory diseases such as asthma. IL-13 is mainly produced by T cells. However, signalling pathways leading to induction of this cytokine are not well-characterized. We analysed the regulation of IL-13 in human peripheral blood mononuclear cells and CD4(+) T cells. 2. Cyclosporine (CsA) and FK-506 inhibited IL-13 synthesis, when cells were stimulated by TPA/ionomycin. However, stimulation by alpha-CD3/alpha-CD28 led to an enhanced IL-13 synthesis. 3. NF-kappa B inhibitor N-tosyl-L-lysine chloromethylketone (TLCK) inhibited IL-13 synthesis more effectively after TPA/ionomycin stimulation. After alpha-CD3/alpha-CD28 stimulation, only 300 microM TLCK inhibited IL-13 synthesis. Dexamethasone inhibited IL-13 equally effective after alpha-CD3/alpha-CD28 and TPA/ionomycin stimulation. 4. p38 MAPK inhibitor SB203580 inhibited IL-13 synthesis only partially. MEK inhibitor U0126 inhibited TPA/ionomycin induced IL-13 synthesis very effectively, whereas alpha-CD3/alpha-CD28 stimulated IL-13 induction was resistant to this drug. 5. These results were confirmed in purified CD4(+) T cells. In difference to PBMCs alpha-CD3/alpha-CD28 stimulated IL-13 synthesis was effectively inhibited by CsA, FK-506 and U0126. 6. Therefore U0126 was tested in an animal model of allergic asthma. We could demonstrate for the first time that inhibition of the MEK - ERK cascade is a therapeutic option for asthma. Intraperitoneal administration of 10 mg kg(-1) U0126 reduced lung eosinophilia in ovalbumin-challenged Brown Norway rats by 44%. 7. These results demonstrate that different signalling pathways are involved in regulating IL-13 synthesis in primary human T cells. Characterizing highly potent inhibitors of IL-13 synthesis can be exploited to identify new drugs to treat immunological diseases such as asthma.

CD80 (B7-1) and CD86 (B7-2) are functionally equivalent in the initiation and maintenance of CD4+ T-cell proliferation after activation with suboptimal doses of PHA

Effective activation of T cells requires engagement of two separate T-cell receptors. The antigen-specific T-cell receptor (TCR) binds foreign peptide antigen-MHC complexes, and the CD28 receptor binds to the B7 (CD80/CD86) costimulatory molecules expressed on the surface of antigen-presenting cells (APC). The simultaneous triggering of these T-cell surface receptors with their specific ligands results in an activation of this cell. In contrast, CTLA-4 (CD152) is a distinct T-cell receptor that, upon binding to B7 molecules, sends an inhibitory signal to T cell activation. Many in vitro and in vivo studies demonstrated that both CD80 and CD86 ligands have an identical role in the activation of T cells. Recently, functions of B7 costimulatory molecules in vivo have been investigated in B7-1 and/or B7-2 knockout mice, and the authors concluded that CD86 could be more important for initiating T-cell responses, while CD80 could be more significant for maintaining these immune responses. In this study, we directly compared the role of CD80 and CD86 in initiating and maintaining proliferation of resting CD4(+) T cells in an in vitro mode system that allowed to provide the first signal-to-effector cells through the use of suboptimal doses of PHA and the second costimulatory signal through cells expressing CD80 or CD86, but not any other costimulatory molecules. Using this experimental system we demonstrate that the CD80 and CD86 molecules can substitute for each other in the initial activation of resting CD4(+) T cells and in the maintenance of their proliferative response.

Biased activation of human T lymphocytes due to low extracellular pH is antagonized by B7/CD28 costimulation

As T cell response to tumor-associated antigens may be impaired by the acidic microenvironment typical of solid tumors, we assessed the effect of extracellular pH (pH(e)) on the activation and proliferation of human T lymphocytes and generation of the cytotoxic response. T lymphocytes stimulated with anti-CD3 mAb or PHA at low pH(e) were unable to secrete IL-2 and IFN-gamma and their ability to progress through the cell cycle was impaired. T lymphocytes also displayed up-regulation of IFN-gammaR2 chain and CTLA-4 expression, rendering them sensitive to negative regulatory signals. Agonistic mAb against CD28, but not against CD2, completely restored cytokine production and cell cycle progression, but down-regulated IFN-gammaR2 and CTLA-4 expression. The anti-CD28mAb rescued the CTL response of allogeneic anti-tumor cultures generated at low pH(e). Following anti-CD28 mAb treatment, T cells synthesized cyclooxygenase-2 (Cox-2) protein, which is involved in the early phases of T cell activation. This rescue of T cell activation was independent of the inducible 6-phosphofructo-2-kinase (iPFK-2) pathway, which stimulates proliferation in hypoxic and acidic conditions. The restoration of proliferative and cytotoxic T cell responses by CD28-triggering provides insight into the mechanisms by which B7 enhances the T cell anti-tumor response in vivo.

In vitro analysis of CD40-CD154 and CD28-CD80/86 interactions in the primary T-cell response to allogeneic "nonprofessional" antigen presenting cells

BACKGROUND

Recently, several ligand interactions have been examined in detail as potential mediators of costimulatory signaling. The CD154/CD40 and CD28/B7 interactions have been highlighted as being among the more-significant contributors to proper activation of unprimed T lymphocytes. Human keratinocytes (HK) and human dermal fibroblasts (HF) are capable of expressing Class II HLA and CD40 antigens after interferon-gamma exposure, yet neither express significant levels of B7. HK and HF have been characterized as "nonprofessional" antigen presenting cells (APC) and their poor APC function has been partially attributed to deficient costimulatory activity.

METHODS

In this study, we examined whether substituting for costimulatory signaling events through the addition of cross-linked monoclonal antibodies against the T-cell ligand/s (CD28 and/or CD154) could restore allostimulation. Mixed lymphocyte reactions were performed combining enriched human peripheral blood T cells and allogeneic HK or HF with or without stimulatory anti-CD28 and/or anti-CD154 antibodies.

RESULTS

The results show that the addition of anti-CD28 alone permitted HF but not HK to present alloantigen effectively. In contrast, addition of both anti-CD154 and anti-CD28 was required to generate even a moderate proliferative response to allogeneic HK. Further, adding a monomorphic anti-HLA-DR antibody substantially inhibited these responses. Additional experiments suggest that signaling through CD40/CD154 directs HK to produce TGF-beta, which would adversely affect T-cell activation.

CONCLUSIONS

The data presented highlight significant differences in signaling capacities for HK versus HF and provide evidence for a partial mechanism by which allogeneic human skin equivalents might be immunologically null upon engraftment.

Residual type 1 immunity in patients genetically deficient for interleukin 12 receptor beta1 (IL-12Rbeta1): evidence for an IL-12Rbeta1-independent pathway of IL-12 responsiveness in human T cells

Genetic lack of interleukin 12 receptor beta1 (IL-12Rbeta1) surface expression predisposes to severe infections by poorly pathogenic mycobacteria or Salmonella and causes strongly decreased, but not completely abrogated, interferon (IFN)-gamma production. To study IL-12Rbeta1-independent residual IFN-gamma production, we have generated mycobacterium-specific T cell clones (TCCs) from IL-12Rbeta1-deficient individuals. All TCCs displayed a T helper type 1 phenotype and the majority responded to IL-12 by increased IFN-gamma production and proliferative responses upon activation. This response to IL-12 could be further augmented by exogenous IL-18. IL-12Rbeta2 was found to be normally expressed in the absence of IL-12Rbeta1, and could be upregulated by IFN-alpha. Expression of IL-12Rbeta2 alone, however, was insufficient to induce signal transducer and activator of transcription (Stat)4 activation in response to IL-12, whereas IFN-alpha/IFN-alphaR ligation resulted in Stat4 activation in both control and IL-12Rbeta1-deficient cells. IL-12 failed to upregulate cell surface expression of IL-18R, integrin alpha6, and IL-12Rbeta2 on IL-12Rbeta1-deficient cells, whereas this was normal on control cells. IL-12-induced IFN-gamma production in IL-12Rbeta1-deficient T cells could be inhibited by the p38 mitogen-activated protein kinase (MAP) kinase inhibitor SB203580 and the MAP kinase kinase (MEK) 1/2 inhibitor U0126, suggesting involvement of MAP kinases in this alternative, Stat4-independent, IL-12 signaling pathway.Collectively, these results indicate that IL-12 acts as a partial agonist in the absence of IL-12Rbeta1. Moreover, the results reveal the presence of a novel IL-12Rbeta1/Stat4-independent pathway of IL-12 responsiveness in activated human T cells involving MAP kinases. This pathway is likely to play a role in the residual type 1 immunity in IL-12Rbeta1 deficiency.

Functional Fv fragment of an antibody specific for CD28: Fv-mediated co-stimulation of T cells

The most predominant co-stimulation pathway, which is critical for T cell activation and proliferation, is the CD28-B7 pathway. The anti-CD28 monoclonal antibody (mAb) also provides a co-stimulatory signal to T cells. In order to construct a functional Fv fragment (complex of VH and VL domains) of anti-CD28 antibody using a bacterial expression system, cDNA encoding the variable regions of immunoglobulin from 15E8 hybridoma cells was cloned and expressed in Escherichia coli. The Fv fragment was obtained as a soluble protein from the periplasmic fraction and showed a binding pattern similar to parental IgG. The Fv fragment induced proliferation of peripheral blood mononuclear cells in the presence of anti-CD3 or anti-CD2 mAb and enhanced anti-tumor activity of anti-MUC1x(anti)-CD3 bispecific antibody when tested with lymphokine-activated killer cells with T cell phenotype. Thus, the anti-CD28 Fv fragment will be promising not only for the study of co-stimulation, but also for cancer immunotherapy.

Nonradioactive techniques for measurement of in vitro T-cell proliferation: alternatives to the [(3)H]thymidine incorporation assay

T-cell proliferation is an important in vitro parameter of in vivo immune function and has been used as a prognostic marker of human immunodeficiency virus type 1 (HIV-1) disease progression. The proliferative capacity of T cells in response to various stimuli is commonly determined by a radioactive assay based on incorporation of [(3)H]thymidine ([(3)H]TdR) into newly generated DNA. In order to assess techniques for application in laboratories where radioactive facilities are not present, two alternative methods were tested and compared to the [(3)H]TdR assay as a "gold standard." As an alternative, T-cell proliferation was measured by flow cytometric assessment of CD38 expression on T cells and by an enzyme-linked immunosorbent assay (ELISA) based on bromo-2'-deoxyuridine (BrdU) incorporation. Peripheral blood mononuclear cells (PBMCs), either in whole blood or Ficoll-Isopaque separated, from a total of 26 HIV-1-positive and 18 HIV-1-negative Dutch individuals were stimulated with CD3 monoclonal antibody (MAb) alone, a combination of CD3 and CD28 MAbs, or phytohemagglutinin. BrdU incorporation after 3 days of stimulation with a combination of CD3 and CD28 MAbs correlated excellently with the [(3)H]TdR incorporation in both study groups (HIV-1 positives, r = 0.96; HIV-1 negatives, r = 0.83). A significant correlation of absolute numbers of T cells expressing CD38 with [(3)H]TdR incorporation, both in HIV-1-positive (r = 0.96) and HIV-1-negative (r = 0.84) individuals, was also observed under these conditions. The results of this study indicate that determination of both the number of CD38-positive T cells and BrdU incorporation can be used as alternative techniques to measure the in vitro T-cell proliferative capacity. The measurement of CD38 expression on T cells provides the additional possibility to further characterize the proliferating T-cell subsets for expression of other surface markers.

Signal transduction by the major histocompatibility complex class I molecule

Ligation of cell surface major histocompatibility class I (MHC-I) proteins by antibodies, or by their native counter receptor, the CD8 molecule, mediates transduction of signals into the cells. MHC-I-mediated signaling can lead to both increased and decreased activity of the MHC-I-expressing cell depending on the fine specificity of the anti-MHC-I antibodies, the context of CD8 ligation, the nature and cell cycle state of the MHC-I-expressing cell and the presence or absence of additional cellular or humoral stimulation. This paper reviews the biochemical, physiological and cellular events immediately after and at later intervals following MHC-I ligation. It is hypothesized that MHC-I expression, both ontogenically and in evolution, is driven by a cell-mediated selection pressure advantageous to the MHC-I-expressing cell. Accordingly, in addition to their role in T-cell selection and functioning, MHC-I molecules might be of importance for the maintenance of cellular homeostasis not only within the immune system, but also in the interplay between the immune system and other organ systems.

Specific targeting immunotherapy of cancer with bispecific antibodies

In order to enhance cell mediated cytotoxicity, bispecific antibodies (BsAbs), molecules combining two or more antibodies with different antigenic specificities, have been developed as new agents for immunotherapy. Our recent studies revealed that simultaneous administration of two kinds of BsAbs (anti-tumor x anti-CD3 plus anti-tumor x anti-CD28) together with lymphokine activated killer cells with a T cell phenotype (T-LAK cells) inhibited growth of human xenotransplanted tumors in severe combined immunodeficient (SCID) mice, while single BsAb was without effect. Three kinds of BsAbs (anti-tumor x anti-CD3, anti-tumor x anti-CD28, anti-tumor x anti-CD2) showed the highest cytotoxicity against tumor cells when given simultaneously with T-LAK cells or peripheral blood mononuclear cells in vitro and in vivo. BsAbs can be preserved for immediate application, while cytotoxic T lymphocytes (CTLs) must be made-to-order, and are time-consuming to prepare. Tumor associated antigens, such as MAGE antigens, SART antigens, MUC1 antigen, c-erbB 2 antigen or cancer/testis antigens can be served to target antigens for BsAb production. By conjugation with antibodies to effector cells (anti-CD3, anti-CD28, anti-CD16, anti-CD64, anti-CD89 or anti-CD2), many kinds of BsAbs can be produced to cover most types of cancers from different organs. Therefore this strategy might be ubiquitously applicable to most malignancies.

T-Cell Receptor-Independent Activation of Clonal Th2 Cells Associated With Chronic Hypereosinophilia

We recently observed a clonal expansion of CD3−CD4+ T cells secreting Th2-type cytokines in patients presenting chronic hypereosinophilia. As clonal T cells isolated from such patients did not spontaneously secrete cytokines in vitro, we reasoned that costimulatory signals delivered by antigen-presenting cells might be required to induce their full activation. To address this question, we investigated in two such patients the responses of CD3−CD4+ T cells to dendritic cells (DC). DC elicited proliferation and production of interleukin-5 (IL-5) and IL-13 by clonal cells from patient 1 and upregulated their expression of CD25 (IL-2R-). These effects were abolished when blocking monoclonal antibodies (MoAbs) against IL-2R- and IL-2 were added to cocultures, indicating critical involvement of an autocrine IL-2/IL-2R pathway. Cells from patient 2 were stimulated by DC to produce Th2 cytokines only when rIL-2 or rIL-15 was added to cocultures. In both patients, addition of inhibitory MoAbs against B7-1/B7-2 or CD2 to cocultures resulted in dramatic reduction of cytokine production and inhibited CD25 upregulation. Thus, TCR/CD3-independent activation of clonal Th2 cells by DC is an IL-2–dependent process, which requires signaling through CD2 and CD28.

Standardisation and quality assurance of lymphocyte proliferation assays for use in the assessment of immune function. European Concerted Action on Immunological and Virological Markers of HIV Disease Progression

Lymphocyte proliferation is a widely used technique to assess immune competence. However, the technique is subject to a large degree of variation, some biological and some technical. In this study, the components of variation in whole blood proliferation assays were analysed over time, using both antibody and mitogenic stimulants. The levels of variation within individual samples, between individuals and between groups of individuals over time were examined. A method of transforming the data is proposed which reduces the coefficients of variation to an acceptable level, and which expresses individual results as a standardised count. This method overcomes the problem of different levels of absolute counts, it corrects for time sensitive errors and allows data from multiple laboratories to be pooled.

T cell activation by monoclonal antibodies bound to tumor cells by a cell surface displayed single-chain antibody

Tumor cells often lack the costimulatory molecules necessary for T cell activation. However, the transformation of cells with more than one stimulatory molecule is a difficult procedure. We therefore developed a retroviral vector for the expression of a cell membrane anchored single-chain antibody fragment (scFv) directed against the hapten 4-ethoxymethylene-2-phenyl-2-oxazoline-5-one (phOx). Proteins and peptides can be readily modified with this hapten, thus, enabling them to be bound to cells with the cell surface displayed anti-phOx scFv. To test combinations of surface-bound stimulatory molecules on T cell activation, SK-Mel63 human melanoma cells expressing the membrane anchored anti-phOx scFv were incubated with phOx-labeled mAbs against CD3, CD28 and CD5. Cells presenting a given mixture of modified anti-CD3 and anti-CD28 molecules stimulated T cell activation better than any single antibody and a given mixture of anti-CD3, anti-CD28 and anti-CD5 provided a stimulatory response higher than the best double combination. However, the relative concentrations are very important and must be carefully chosen. Concentrations of antibodies giving good T cell responses when used alone can block synergistic effects.

Kinetics of intracytoplasmic Th1 and Th2 cytokine production assessed by flow cytometry following in vitro activation of peripheral blood mononuclear cells

BACKGROUND

Standard cytokine detection methods are unable to determine which cells are the producing cells. We report on the extent and under which conditions the multilabeling capability of flow cytometry (FCM) can bring new advances into the field.

METHODS

Five different cytokines, interleukin-2 (IL-2), -4, -5, -10 and interferon-gamma (IFN-gamma), were assessed simultaneously under five ex vivo stimulation conditions in peripheral blood mononuclear cells from five healthy volunteers in a 5-day kinetic study. A second group of 35 volunteers was assessed for IFN-gamma and IL-2 production.

RESULTS

This study showed that (a) intracytoplasmic cytokines were almost undetectable within unstimulated cells, (b) intracytoplasmic cytokines were detected only in CD69(+) T lymphocytes, and (c) intracytoplasmic IL-2 and IFN-gamma were dramatically upregulated after stimulation with phorbol myristate acetate (PMA)-ionomycin in a biphasic response or with PMA-phytohemagglutinin (one major peak only at 18 h) but to a lesser extent with other stimuli such as monoclonal antibodies. Th2 cytokines were detected at a later time point and at lower levels. PMA/ionomycin stimulation after 4 h and 18 h of culture in 35 other volunteers individualized several subgroups according to the frequency of IFN-gamma- or IL-2-producing cells--IFN-gamma delayed producers (n = 10/35), IFN-gamma low producers (n = 8/35), and IL-2 delayed producers (n = 16/35)--as opposed to IFN-gamma or IL-2 normal producers.

CONCLUSIONS

FCM appears to be a good tool to examine cell cytokine status in pathology (allergy, autoimmune disease, etc.) provided that optimal stimulation conditions and multiple time-point cultures are used. It also seems to be a relevant method to define new Th subsets further.

CD99 Engagement on Human Peripheral Blood T Cells Results in TCR/CD3-Dependent Cellular Activation and Allows for Th1-Restricted Cytokine Production

We have assessed the functional effect of CD99 engagement on resting human peripheral blood (PB) T cells. CD99, as detected by the mAb 3B2/TA8, is constitutively expressed on all PB T cells and becomes further up-regulated upon cellular activation. In this study we demonstrate that cross-linking of the CD99 molecule with the agonistic mAb 3B2/TA8 cooperates with suboptimal TCR/CD3 signals, but not with phorbol ester, ionomycin, or CD28 mAb stimulation, to induce proliferation of resting PB T cells. Comparable stimulatory effects were observed with the CD99 mAb 12E7. Characterization of the signaling pathways involved revealed that CD99 engagement leads to the elevation of intracellular Ca2+, which is dependent on the cell surface expression of the TCR/CD3 complex. No CD99 mAb-induced calcium mobilization was observed on TCR/CD3-modulated or TCR/CD3-negative T cells. To examine the impact of CD99 stimulation on subsequent cytokine production by T cells, we cross-linked CD99 molecules in the presence of a suboptimal TCR/CD3 trigger followed by determination of intracellular cytokine levels. Significantly, T cell lines as well as Th1 and Th0 clones synthesized TNF-α and IFN-γ after this treatment. In contrast, Th2 clones were unable to produce IL-4 or IFN-γ when stimulated in a similar fashion. We conclude that CD99 is a receptor that mediates TCR/CD3-dependent activation of resting PB T cells and specifically induces Th1-type cytokine production in polyclonally activated T cell lines, Th1 and Th0 clones.

Low T-cell responses to CD3 plus CD28 monoclonal antibodies are predictive of development of AIDS

OBJECTIVE

Decreased T-cell reactivity in vitro is strongly associated with progression to AIDS and low CD4+ T-cell numbers. Low T-cell responses in vitro induced by CD3 monoclonal antibody (mAb) are predictive for progression to AIDS independent of low CD4+ T-cell counts and high HIV-1 RNA levels. We developed a whole-blood lymphocyte culture system in which T cells were stimulated by a combination of CD3 and CD28 mAb. Combined stimulation of CD28, a costimulatory molecule, and CD3 considerably enhances T-cell responses in vitro and reduces variation coefficients, which may increase the prognostic power of T-cell responses.

DESIGN

A prospective study of HIV-1-infected homosexual men followed for 35 months.

METHODS

The predictive value of low T-cell responses to CD3 plus CD28 mAb relative to low CD4+ T-cell counts, high HIV-1 RNA levels and the presence of syncytium-inducing (SI) HIV-1 variants was evaluated longitudinally in 202 HIV-1-infected homosexual men followed for 35 months.

RESULTS

In multivariate analysis, decreased T-cell responses at baseline were predictive of development of AIDS, independent of low CD4+ T-cell numbers and high HIV-1 RNA levels. In a time-dependent model, HIV-1 RNA levels lost their predictive value, whereas low T-cell responses, low CD4+ T-cell numbers and the presence of SI HIV-1 variants independently predicted AIDS.

CONCLUSIONS

These data demonstrate that combined use of virological and immunological markers may be useful in monitoring disease progression and response to antiretroviral therapy.

Severe mycobacterial and Salmonella infections in interleukin-12 receptor-deficient patients

Interleukin-12 (IL-12) is a cytokine that promotes cell-mediated immunity to intracellular pathogens by inducing type 1 helper T cell (TH1) responses and interferon-gamma (IFN-gamma) production. IL-12 binds to high-affinity beta1/beta2 heterodimeric IL-12 receptor (IL-12R) complexes on T cell and natural killer cells. Three unrelated individuals with severe, idiopathic mycobacterial and Salmonella infections were found to lack IL-12Rbeta1 chain expression. Their cells were deficient in IL-12R signaling and IFN-gamma production, and their remaining T cell responses were independent of endogenous IL-12. IL-12Rbeta1 sequence analysis revealed genetic mutations that resulted in premature stop codons in the extracellular domain. The lack of IL-12Rbeta1 expression results in a human immunodeficiency and shows the essential role of IL-12 in resistance to infections due to intracellular bacteria.

Patterns of T-cell repopulation, virus load reduction, and restoration of T-cell function in HIV-infected persons during therapy with different antiretroviral agents

The effect of antiretroviral therapy on both T-cell numbers and T-cell function in peripheral blood was studied. CD4+ and CD8+ T-cell numbers, T-cell reactivity to CD3 monoclonal antibodies (mAb), and viral RNA load date were obtained from patients treated for at least 28 weeks with either the HIV-1 protease inhibitor ritonavir, the nonnucleoside HIV-1 reverse transcriptase (RT) inhibitor nevirapine, or the nucleoside-analogue RT inhibitor zidovudine. Compared with both RT inhibitors, treatment with the protease inhibitor ritonavir resulted in the most significant and persistent elevation of CD4+ and CD8+ T-cell counts. However, in vitro T-cell functional improvement was of limited duration in the ritonavir-treated group and was inversely correlated with viral RNA load changes during the entire follow-up period. Thus, despite what can be assumed of responses during RT inhibitor therapy, quantitative responses on therapy did not necessarily correlate with qualitative immunologic responses, as can be seen during treatment with ritonavir. For optimal immune reconstitution, both numeric and functional immunologic improvements are essential. During antiretroviral therapy, measurement of in vitro improvement in immune function will be useful as a correlate for transient drug-induced alteration of immunodeficiency.

Decrease in peripheral type 1 over type 2 T cell cytokine production in patients with rheumatoid arthritis correlates with an increase in severity of disease

OBJECTIVES

To compare peripheral type 1 (T1) and type 2 (T2) T cell activities in rheumatoid arthritis (RA) patients with that found for osteoarthritic (OA) patients and healthy controls and to correlate peripheral T1/T2 cell activity in RA with parameters of the disease.

METHODS

Peripheral blood mononuclear cells were isolated from patients with RA (n = 66), OA (n = 19), and healthy controls (n = 15). Primary T cell activity in these mononuclear cells was enhanced by means of anti-CD3/anti-CD28, which mimicks stimulation of T cells by activation of the T cell receptor and a major co-stimulatory signal. Interferon gamma (IFN gamma) production and interleukin 4 (IL4) production in the three groups were quantified as measures of T1 and T2 cell activity, respectively, and compared. Serum tumour necrosis factor alpha (TNF alpha), erythrocyte sedimentation rate (ESR), C reactive protein (CRP), and joint destruction assessed radiographically of RA patients were determined as parameters of disease activity and correlated with T1/T2 cell activity.

RESULTS

Peripheral T cells from RA patients produced significantly less IFN gamma and more IL4 than T cells from both age and sex matched OA patients and healthy controls. Moreover, in RA patients both a decrease in IFN gamma and an increase in IL4 production correlated with an increase in serum TNF alpha, ESR, CRP, and joint destruction.

CONCLUSIONS

These results suggest a role for differential T cell activity in RA. In view of the intra-articular T1 cell predominance the results might be explained by selective T1 cell migration into the joint or peripheral suppression of T1 cell activity.

Immunity aging. I. The chronic perduration of the thymus acute involution at puberty? Or the participation of the lymphoid organs and cells in fatal physiologic decline?

The author has focused the subject on the perduration of puberty thymus involution as a cause of immunity aging, a term in which he does not include senescence. The decrease between immune reactions against HIV1 at 25 years of age and those at 35 is considerable; the decrease is also indirectly revealed by spontaneous tumor exponentially growing incidence after 40 years in man and its equivalent, 16 months in mice: the immunity parameters indicate a regression correlated with this incidence growth. He regrets the neglect of suppressor cell and anti-idiotype problems by the basic immunologic research. Given the role of cofactors non specifically related to the antigen, such as that CD28 and its ligands, he suggests the interest to approach immunology via the science of chaos and fractals, which would be more appropriate than classical methodology to study highly complex phenomena on which apparently minimal interventions may induce considerable effects.

On the interaction between agalactosyl IgG and Fc gamma receptors

One of the serum abnormalities observed in autoimmune diseases such as rheumatoid arthritis (RA) and systemic lupus erythematosus (SLE) is the occurrence of IgG that lacks the terminal galactose on asparagine-linked biantennary complex type oligosaccharides [Gal(0)-IgG] located in the CH2 domain. Additionally, IgG without glycosylation is known to be defective in several effector functions due to a reduced ability to bind to its specific receptors (Fc gamma R). It has thus been speculated that, by analogy with unglycosylated IgG, Gal(0)-IgG may also be functionally impaired or exert altered effector mechanisms. If this were true, Gal(0)-IgG could contribute to the phenotype of above-mentioned autoimmune diseases, like impaired immune complex clearance and defective down-regulation of activated B cells. Here, we show by three different methods that the interaction of Gal(0)-IgG and normally glycosylated IgG with the low-affinity Fc gamma RII (CD32) is indistinguishable with respect both to binding and receptor-mediated signalling. These data argue against a prominent role for Fc gamma R-dependent Gal(0)-IgG interactions in the etiology or pathogenesis of autoimmune diseases.

Specific T cell unresponsiveness in human filariasis: diversity in underlying mechanisms

In an attempt to overcome T cell unresponsiveness to filarial antigens, 65 individuals belonging to the three clinical groups of elephantiasis patients, microfilaraemics, and asymptomatic amicrofilaraemics who exhibited unresponsiveness to Brugia malayi adult worm antigen (BmA) were studied. Peripheral blood mononuclear cells were cocultured with antigen and one of the following reagents that have been reported to be effective in reconstituting T cell proliferation: interleukin-2 (IL-2), interleukin-7 (IL-7), anti-interleukin-4, anti-interleukin-10, anti-CD2, anti-CD27, anti-CD28, indomethacin, phorbol myristate acetate (PMA), or calcium ionophore (A23187). We were able to overcome antigen-specific unresponsiveness in only a minority of the individuals studied. Co-culture with IL-2, IL-7, indomethacin and PMA were the only conditions which resulted in enhanced proliferation to BmA in these individuals. In general, unresponsiveness in elephantiasis patients was easier to reverse than in other clinical groups: in 50% of elephantiasis patients, in 12.5% of microfilaraemics and in 20% of asymptomatic amicrofilaraemics. The results indicate that more than one distinct immunological mechanism may account for the antigen-specific unresponsiveness in individuals exposed to and infected with brugian filariasis.

Construction, purification, and functional incorporation on tumor cells of glycolipid-anchored human B7-1 (CD80)

To generate a potent cell-mediated immune response, at least two signals are required by T cells. One is engagement of the T-cell receptor with peptide-bearing major histocompatibility complex molecules. The other signal can be delivered by various molecules on the antigen-presenting cell, such as B7-1 (CD80). Many tumor cells escape immune recognition by failing to express these costimulatory molecules. Transfection of the B7 gene into some murine tumor cells allows for immune recognition and subsequent rejection of the parental tumor. We have studied an alternative approach for the introduction of B7-1 onto the surface of tumor cells. This method involves purified glycosyl-phosphatidylinositol (GPI)-anchored proteins which can spontaneously incorporate their lipid tail into cell membranes. We have created and purified a GPI-anchored B7-1 molecule (called GPI-B7) which is able to bind its cognate ligand, CD28, and incorporate itself into tumor cell membranes after a short incubation. Tumor cells that have been reconstituted with GPI-B7 can provide the costimulatory signal needed to stimulate T cells. These findings suggest an approach for the introduction of new proteins onto cell membranes to create an effective tumor vaccine for potential use in human immunotherapy.

RelA is a potent transcriptional activator of the CD28 response element within the interleukin 2 promoter

T-cell activation requires two different signals. The T-cell receptor's recognition of a specific antigen on antigen-presenting cells provides one, and the second signal comes from costimulatory molecules such as CD28. In contrast, T cells that are stimulated with antigen in the absence of the CD28 costimulatory signal can become anergic (nonresponsive). The CD28 response element (CD28RE) has been identified as the DNA element mediating interleukin 2 (IL-2) gene activation by CD28 costimulation. Our previous work demonstrates that the Rel/NF-kappa B family proteins c-Rel, RelA (p65), and NFKB1 (p50) are involved in the complex that binds to the CD28RE. We also showed that c-Rel, but not NFKB1 (p50), can bind to the CD28RE and activate CD28RE-driven transcription in cotransfection assays. However, the role of RelA (p65) in CD28 signaling has not yet been addressed. We provide evidence that RelA (p65) itself bound directly to the CD28RE of the IL-2 promoter and other lymphokine promoters. In addition, RelA (p65) was a potent transcriptional activator of the CD28RE in vivo. We show that a RelA (p65)-c-Rel heterodimer bound to the CD28RE and synergistically activated the CD28RE enhancer activity. We also demonstrate that activated Raf-1 kinase synergized with RelA (p65) in activating the CD28RE enhancer activity. Interestingly, a soluble anti-CD28 monoclonal antibody alone, in the absence of other stimuli, also synergized with RelA (p65) in activating the CD28RE. Furthermore, we show that RelA (p65) activated expression of the wild-type IL-2 promoter but not the CD28RE-mutated IL-2 promoter. A combination of RelA (p65) and NFKB1 (p50) also activated the IL-2 promoter through the CD28RE site. These results demonstrate the functional regulation of the CD28RE, within the IL-2 promoter, by Rel/NF-kappa B transcription factors.

Expression of Epstein-Barr virus nuclear antigen-2 (EBNA2) induces CD21/CR2 on B and T cell lines and shedding of soluble CD21

Stable transfection of Epstein-Barr virus (EBV) nuclear antigen 2 (EBNA2) expressed as a fusion protein with the hormone-binding domain of the estrogen receptor was used to study expression of CD21 and other surface markers in different cell lines. Special emphasis was placed on cell lines with a normally low expression of CD21, especially on T cell lines. After induction of EBNA2, a substantial increase in CD21 mRNA was observed, as well as increased production of membrane CD21. This was found not only in cell lines of B cell origin, but also in the T cell line Jurkat. The amount of CD21 was quantitated by means of a fluorescence immunoassay, and found to correlate with the presence of EBNA2 protein. A decrease in EBNA2 abundance was associated with complete loss of cell-associated CD21. As we could also detect large amounts of soluble CD21 (sCD21) in the supernatant of the transfected cell lines, which exceeded the total amount contained in the respective cell lysates, this indicates considerable shedding of the newly synthesized receptor molecules induced by EBNA2, comparable to the situation described for CD23. It further provides an explanation of the recent findings of increased sCD21 levels in sera of patients with EBV-associated disease, and suggests a possible additional function of EBNA2 in vivo.

Accessory signalling by B7-1 for T cell activation induced by anti-CD2: evidence for IL-2-independent CTL generation and CsA-resistant cytokine production

Resting T cells can be activated by selected pairs of anti-CD2 MoAb. Activation is dependent on the presence of accessory cells, which can be replaced by either anti-CD28, or by the combination of IL-1 beta and IL-6. The present study was undertaken to investigate accessory signalling by B7-1, the natural ligand of CD28, in this pathway of T cell activation. 3T6 mouse fibroblasts were transfected with human B7-1 and used as accessory cells in cultures of purified resting human T cells. In the presence of a stimulating pair of anti-CD2 MoAb, T cell proliferation, production of cytokines (IL-2, IL-4, IL-10, GM-CSF, IFN-gamma and TNF-alpha), and generation of cytotoxic T lymphocytes were all supported by B7-1(+) 3T6 cells but not by control 3T6 cells. Blocking studies with anti-IL-2 + anti-IL-2R MoAb revealed both IL-2-dependent and IL-2-independent CTL generation after B7-1-mediated costimulation. Moreover, a partial or complete resistance to inhibition with CsA was observed for IL-2 production and CTL generation respectively in the presence of the costimulatory signal derived from B7-1-CD28 interaction. Anti-CD2 MoAb with B7-1 costimulation could directly induce proliferation, IL-2 production and generation of CTL activity in highly purified CD8+ T cells without the help of CD4+ T cells. We conclude that CD28 ligation with the natural ligand B7-1 provides a strong accessory signal for CD4 and CD8 cell activation through CD2.

Inhibition of activation of transcription factor AP-1 by CD28 signalling in human T-cells

Co-stimulation of T-lymphocytes by T-cell receptor (TcR) occupancy and activation of the CD28 surface molecule results in enhanced proliferation and interleukin 2 (IL-2) production. The increase in IL-2 gene expression triggered by CD28 involves a kappa B-like sequence in the 5'-regulatory region of the IL-2 promoter, called CD28-responsive element. Stimulation of T-cells by agonistic anti-CD28 antibodies in conjunction with phorbol 12-myristate 13-acetate (PMA)- or TcR-derived signals induces the enhanced activation of the transcription factor NF-kappa B. Here we report that CD28 engagement, however, exerts opposite effects on the transcription factor AP-1. Whereas anti-CD28 together with PMA increased the DNA binding and trans-activation activity of NF-kappa B, PMA-induced activation of AP-1 was significantly suppressed. The inhibitory effect exerted by anti-CD28 was observed at the level of DNA binding as well as in functional reporter-gene assays. These results suggest that the two transcription factors are independently regulated and may perform different functions during T-cell activation.

IgE production in atopic patients is not related to IL-4 production

To analyse whether there is a general defect in T or B cell function in atopic individuals we have measured cytokine and IgE production by peripheral blood lymphocytes, isolated from 19 atopic donors (17 asthma/rhinitis and two dermatitis patients) in comparison with 19 non-atopic controls. After stimulation of lymphocytes with anti-CD2 and anti-CD28, we found no significant difference in IL-2, IL-4 and interferon-gamma (IFN-gamma) production. To examine the correlation between the production of IgE and IL-4, we stimulated lymphocytes with anti-CD2 and rIL-2. Under this condition both T cell IL-4 and B cell IgE production can be measured. No significant difference was found for the amount of IgE and IL-4 produced between the two groups (P > 0.05). The non-atopic donors showed a good correlation between IL-4 and IgE production (r = 0.70). Surprisingly, within the atopic group there was no correlation between IgE and IL-4 production at all (r = -0.04). The ratio of IgE to IL-4 was higher (although not significantly) in the atopic group. Our data suggest that in atopic donors IgE production is less dependent on IL-4, and that other cytokines are involved.

Functional defects in peripheral blood T cells of multiple sclerosis patients. Diminished in vitro responsiveness in accessory cell dependent activation systems

Function and phenotype of peripheral blood (PB) T cells in multiple sclerosis (MS) patients were analyzed. In whole blood cultures, T cell proliferation of multiple sclerosis (MS) patients, using soluble CD3 mAb and CD2 mAb as stimulants, was reduced in comparison to healthy controls. A similar difference was seen when isolated PBMC were tested after stimulation with soluble CD3 mAb. However, in accessory cell-independent activation systems, i.e. after stimulation of PBMC with immobilized CD3 mAb or after co-stimulation with CD28 mAb, both patients and controls responded equally well. Phenotypical analysis of the circulating T cell population showed that there were no differences in the percentage of CD26+, 'memory' (CD45R0+) or 'effector' (CD4+CD45R0+CD27-) cells between MS patients and healthy controls. Finally, although MS patients did show an enhanced proportion of 'naive' (CD4+CD45RA+) T cells, this did not correlate with the observed functional defects.

Interleukin 12 synergizes with B7/CD28 interaction in inducing efficient proliferation and cytokine production of human T cells

Several receptors and counter-receptor pairs on T cells and on antigen-presenting cells (APCs) deliver costimulatory signals to T cells during antigen presentation. The CD28 receptor on T cells with its ligand B7 represents one of the best characterized and most important examples of this costimulation. We show here that interleukin 12 (IL-12), a cytokine also produced by APCs (monocyte/macrophages and B cells) and active on T and natural killer cells, has a strong synergistic effect with the B7/CD28 interaction in inducing proliferation and cytokine production in both mitogen-activated and freshly isolated peripheral blood T cells. Together with anti-CD28 antibodies, IL-12 induces proliferation of T cells to levels higher than those obtained with IL-2 stimulation and it is effective at IL-12 concentrations 100- to 1,000-fold lower than effective concentrations of IL-2. The proliferative effect of anti-CD28 and IL-12 is resistant to moderate doses of cyclosporin A and is largely independent of endogenous IL-2, IL-12, in synergy with anti-CD28 or B7-transfected cells, is most effective in inducing interferon gamma (IFN-gamma) production, but production of tumor necrosis factor alpha and granulocyte/macrophage colony-stimulating factor is also observed. IL-12-induced IFN-gamma production in peripheral blood mononuclear cells is inhibited by the chimeric molecule CTLA-4 immunoglobulin, which prevents binding of CD28 to B7, suggesting that endogenous B7 on the mononuclear cells and IL-12 cooperate in inducing IFN-gamma production. IL-10 inhibits both IL-12 production and B7 expression on monocytes. These two effects are largely responsible for the ability of IL-10, acting on accessory cells, to inhibit IFN-gamma production by lymphocytes, because anti-CD28 antibodies and IL-12 can reverse the inhibitory effect of IL-10 on IFN-gamma production. Our results in vitro suggest that the synergy between B7 and IL-12, a surface antigen and a soluble product of APCs, respectively, plays a role in regulating T cell activation and immune response in the microenvironment of inflamed tissues.

Cure of xenografted human tumors by bispecific monoclonal antibodies and human T cells

Tumor immunotherapy should increase both the number of T cells that kill the tumor and the likelihood that those cells are activated at the tumor site. Bispecific monoclonal antibodies (Bi-mAbs) were designed that bound to a Hodgkin's tumor-associated antigen (CD30) on the tumor and to either CD3 or CD28 on the T cell. Immunodeficient mice were cured of established human tumors when mice were treated with both the CD3-CD30 and the CD28-CD30 Bi-mAbs and then given human peripheral blood lymphocytes that had been incubated with the CD3-CD30 Bi-mAb and cells that expressed CD30. The enrichment of human T cells within the tumor and the fact that established tumors can be cured may indicate in situ activation of both the T cell receptor and the costimulatory pathway.

Reduced expression of distinct T-cell CD molecules by collagenase/DNase treatment

DNase/collagenase treatments are widely used to obtain single-cell suspensions of tumour cells and tumour-infiltrating T lymphocytes (TIL) from solid tumours. Since the functional integrity of such cells has been questioned, we have studied whether treatments with commonly used preparations of these enzymes could affect the expression of lymphocyte surface molecules and lymphocyte proliferative responsiveness. With peripheral-blood-derived T cells as a model, flow-cytometric analysis revealed strongly reduced expression of distinct CD molecules for each enzyme, notably CD2, CD4, CD8 and CD44 for DNase, and CD4, CD14, CD16, and CD56 for collagenase. The effects were found to be due to protease contaminations present in all but the purest enzyme preparations tested. Addition of serum or trypsin inhibitor abolished the effects. Since serum-free media are widely used to expand tumour-infiltrating T cells for clinical therapeutic use, data from early phenotypic analyses can be strongly misleading. Even after an 18-h rest period following the enzyme treatments, re-expression of the affected membrane markers was still far from complete. On the other hand, despite strongly reduced expression of CD2 molecules on the lymphocyte membrane, anti-CD2-induced proliferation was not affected, showing the redundancy of this signal molecule. Since other important T cell activation molecules (TCR, CD3, CD28) were not affected by enzymatic treatment, the use of expensive, highly purified collagenase/DNase preparations does not seem to be mandatory in clinical studies with expanded TIL.

Helper effector function of human T cells stimulated by anti-CD3 mAb can be enhanced by co-stimulatory signals and is partially dependent on CD40-CD40 ligand interaction

In this study we have investigated whether anti-CD3-induced human T cell help for immunoglobulin production could be enhanced by co-stimulation of the T cells via other T cell surface molecules, and the contribution of CD40-CD40 ligand interaction to the execution of T helper effector function induced by these different stimulatory signals. In a system in which irradiated tonsillar T cells were stimulated with immobilized anti-CD3 monoclonal antibody (mAb), it was found that ligation of CD2 with a mitogenic pair of mAb considerably enhanced anti-CD3-induced T cell help for immunoglobulin production. Likewise, ligation of CD28 with mAb enhanced T helper activity, although to a lesser extent. Upon addition of anti-CD28 and anti-CD2 mAb together, an even higher immunoglobulin production was observed. This combination resulted in a four- to fivefold increase in immunoglobulin production as compared to cultures in which T cells were stimulated with anti-CD3 mAb alone. The effect of ligation with B7, the natural ligand of CD28, was studied in a system which utilizes the presentation of anti-CD3 mAb on human Fc gamma RII-expressing mouse fibroblasts which were co-transfected with human B7. It appeared that B7 could stimulate help for immunoglobulin production much more efficiently than ligation of CD28 with mAb did. Physical separation of B cells from T cells led to complete abrogation of immunoglobulin production. Blocking of CD40 with specific mAb, which have no intrinsic B cell stimulatory properties, or the CD40 ligand with a soluble CD40-human IgM fusion protein, resulted in dose-dependent, but only partial, inhibition of T cell-dependent immunoglobulin production with all modes of T cell activation tested. A clear correlation was found between the induction of CD40 ligand expression on the T cells by the different modes of co-stimulation and subsequent immunoglobulin production by the B cells. It is concluded that ligation of CD28 and/or CTLA-4, and of CD2 can generate co-stimulatory signals for T cell help for immunoglobulin production, which was found to be only partially dependent on the CD40-CD40 ligand interaction.

Co-stimulation with anti-CD28 (Kolt-2) enhances DNA synthesis by defective T cells in common variable immunodeficiency

In normal T cells, an anti-CD28 MoAb (Kolt-2) will synergize with the mitogenic stimuli phytohaemagglutinin (PHA), anti-CD3 (OKT3) or a combination of anti-CD2 antibodies (OKT11 and GT2) in the induction of DNA synthesis. A subgroup of patients with common variable immunodeficiency (CVID) show a defect in DNA synthesis by T cells stimulated in vitro with the above mitogens. We have now investigated whether anti-CD28 will correct the defect. This strategy partially restored DNA synthesis, providing evidence that the CD28 co-stimulatory pathway in CVID T cells is normal. Ligation of CD28 acts through co-stimulating IL-2 secretion. The natural ligand (B7) for CD28 on antigen-presenting cells from CVID patients is expressed normally. We conclude that the defect in CVID T cells lies in pathways that lead to transcription of the IL-2 gene other than that induced by ligation of CD28 with Kolt-2.

Functional expression of human CD28 in murine T cell hybridomas

CD28 is a 44 kDa Ig superfamily cell surface molecule expressed on most mature T cells. Through its interaction with the recently identified B7/BB1 counter-receptor, it is believed to play an important role as a co-stimulator of T cells along with the TCR-CD3 complex. Activation of T cells with CD28 mAbs synergizes with TCR-CD3 and CD2 stimulation, resulting in long term T cell proliferation, differentiation of cytotoxic T cells and production of large amounts of cytokines. In order to further delineate the role of CD28 in signal transduction and T cell activation, human CD28 was transfected into CD3+ murine T cell hybridomas. High levels of cell surface CD28 expression was achieved by protoplast fusion. The transfected molecule retained all the native CD28 mAb epitopes found on human T cells. In these transfectants, CD28 mAbs, similarly to CD3 mAbs, were able to induce Ca2+ mobilization, IL-2 promoter induction (measured as beta-galactosidase activity in T cells hybridomas pre-transfected with the IL-2-lac Z reporter gene), IL-2 secretion, TNF alpha production and apoptosis (observed as growth arrest and genome fragmentation). The parental host cells, or cells transfected with vector alone, responded only to mAbs to CD3. IL-2 secretion in the transfectants was obtained using either an IgM mAb to CD28 or IgG mAbs presented on the surface of IgG-FcR+ B lymphoma cells. Optimal activation via CD28 was inhibited by suboptimal concentrations of soluble CD3 mAb, suggesting an interaction between the two pathways. The immunosuppressive drugs Cyclosporin A and FK506 completely blocked CD28 and CD3 mediated IL-2 production in these transfectants whereas rapamycin had only a partial inhibitory effect. Finally, since the transfected human CD28 molecule confers full functional responsiveness to the murine T cell hybridomas without the need for costimulators such as PMA, this model is ideal for studying the structure-function relationships of the CD28 molecule as well as the transmembrane and cytoplasmic associations implied in CD28 signaling.