Ex-vivo CS1-OKT3 dual specific bivalent antibody-armed effector T cells mediate cellular immunity against multiple myeloma

Bispecific T cell engaging antibodies (bsAbs) have emerged as novel and powerful therapeutic agents for redirecting T cells towards antigen-specific tumor killing. The cell surface glycoprotein and SLAM family member, CS1, exhibits stable and high-level expression on malignant plasma cells including multiple myeloma, which is indicative of an ideal target for bsAb therapy. Here, we developed a CS1 bsAb (CS1-dbBiTE) using Click chemistry to conjugate intact anti-CS1 antibody (Elotuzumab) and anti-huOKT3 antibody at their respective hinge regions. Using a cellular therapy approach, human T cells were armed ex-vivo with CS1-dbBiTE prior to examining effector activity. Our data indicates that arming T cells with CS1-dbBiTE induced T cell activation and expansion and subsequent cytotoxic activity against CS1-bearing MM tumors, demonstrated by significant CD107a expression as well as inflammatory cytokine secretion. As expected, CS1-dbBiTE armed T cells showed significantly reduced effector activity in the absence of CS1 expression. Similarly, in MM mouse xenograft studies, armed T cells exhibited effective anti-tumor efficacy highlighted by reduced tumor burden in MM.1S tumor-bearing mice compared to controls. On the basis of these findings, the rationale for CS1 targeting by human T cells armed with CS1-dbBiTE presents a potentially effective therapeutic approach for targeting MM.

EGF-Receptor against Amphiregulin (AREG) Influences Costimulatory Molecules on Monocytes and T Cells and Modulates T-Cell Responses

Amphiregulin (AREG) is a ligand of the epidermal growth factor receptor (EGFR) and has been shown to regulate the phagocytosis-induced cell death of monocytes in peripheral blood. AREG-dependent apoptotic signaling engages factors of the intrinsic and extrinsic apoptotic pathway, such as BCL-2, BCL-XL, and death ligand/receptor CD95/CD95L. Here, we tested the hypothesis that AREG influences costimulatory monocyte functions, which are crucial for T-cell responses. We found a stronger expression of AREG and EGFR in monocytes compared to lymphocytes. As a novel function of AREG, we observed reduced T-cell proliferation following polyclonal T-cell stimulation with OKT3. This reduction of proliferation occurred in the presence of monocytes as well as in their absence, monocyte signaling being replaced by crosslinking of OKT3. Increasing concentrations of AREG down-modulated the concentration of costimulatory B7 molecules (CD80/CD86) and HLA-DR on monocytes. In proliferation assays, CD28 expression on T cells was down-modulated on the application of OKT3 but unaltered by AREG. LcK activation, following OKT3-stimulation, was reduced in T cells that had been coincubated with AREG. The effects of AREG on T-cell phenotypes were also present when monocytes were depleted and OKT3 was crosslinked. The rearranged expression of immunological synapse proteins was accompanied by an alteration of T-cell polarization. Although the proportion of regulatory T cells was not shifted by AREG, IL-17-expressing T cells were significantly enhanced, with a bias toward TH1-polarization. Taken together, these results suggest that AREG acts as an immunoregulatory molecule at the interface between antigen-presenting cells and T cells.

Development of a flow cytometry-based potency assay for prediction of cytokine storms induced by biosimilar monoclonal antibodies

Cytokine release syndrome (CRS) is an undesired immune reaction that may cause dangerous side effects after the administration of novel biological therapies. In vitro cytokine release assays (CRA) are used for preclinical safety assessment prior to first-in-man dose administration of therapeutic monoclonal antibodies (mAbs). A variety of CRA platforms has been developed where the analysis of secreted cytokines is performed. Analysis of T cell activation markers is not performed routinely in CRA platforms and few studies have described intracellular cytokine levels after stimulation with therapeutic mAbs. In the present study, we performed a CRA using intracellular cytokine staining and assessment of extracellular T cell activation markers by flow cytometry. We used commercially available reference mAbs for the stimulation of peripheral blood mononuclear cells (PBMCs). We found that stimulation using solid phase (SP) dry coating with two different CD28 antibodies and muromonab-CD3 increased the percentage of IFN-ɣ + CD4+ and CD8+ T cells as well as of CD3-CD56+ NK cells compared to stimulation with antibodies in aqueous phase (AP). Expression of the T cell activation markers CD25 and CD69 on CD4+ and CD8+ T cells was also increased upon SP muromonab-CD3 stimulation. Using multiplex cytokine assessment, we showed that stimulation in AP using ANC28.1, CD28.2 and muromonab-CD3 led to an increase of IFN-ɣ, GM-CSF, TNF-α, and IL-2 secretion. Stimulation of PBMCs preincubated at high-density culture led to an increase in IFN-ɣ production but not in the expression of activation markers compared to low-density culture. Our findings demonstrated that flow cytometry analyses for assessing relevant T cell and NK cell markers may be used as a supplement to multiplex cytokine analysis in CRAs. The approach may be a valuable addition that enables a more precise description of the mechanisms leading to CRS.

iCaspase 9 Suicide Gene System

Although cellular therapies may be effective in cancer treatment, their potential for expansion, damage of normal organs, and malignant transformation is a source of concern. The ability to conditionally eliminate aberrant cells in vivo would ameliorate these concerns and broaden the application of cellular therapy. We devised an inducible T-cell safety switch that can be stably and efficiently expressed in human T cells without impairing phenotype, function, or antigen specificity. This system is based on the fusion of human caspase 9 to a modified human FK-binding protein, allowing conditional dimerization using a small-molecule drug. When exposed to a synthetic dimerizing drug, the inducible caspase 9 (iC9) becomes activated and leads to the rapid apoptosis of cells expressing this construct. We have demonstrated the clinical feasibility and efficacy of this approach after haploidentical hematopoietic stem cell transplant (haplo-HSCT). A single dose of a small-molecule drug (AP1903) eliminated more than 90 % of the modified T cells within 30 min after administration and symptoms resolved without recurrence. This system has the potential to broaden the clinical applications of cellular therapy.

Impact of antidepressants on cytokine production of depressed patients in vitro

The interplay between immune and nervous systems plays a pivotal role in the pathophysiology of depression. In depressive episodes, patients show increased production of pro-inflammatory cytokines such as interleukin (IL)-1β and tumor necrosis factor (TNF)-α. There is limited information on the effect of antidepressant drugs on cytokines, most studies report on a limited sample of cytokines and none have reported effects on IL-22. We systematically investigated the effect of three antidepressant drugs, citalopram, escitalopram and mirtazapine, on secretion of cytokines IL-1β, IL-2, IL-4, IL-6, IL-17, IL-22 and TNF-α in a whole blood assay in vitro, using murine anti-human CD3 monoclonal antibody OKT3, and 5C3 monoclonal antibody against CD40, to stimulate T and B cells respectively. Citalopram increased production of IL-1β, IL-6, TNF-α and IL-22. Mirtazapine increased IL-1β, TNF-α and IL-22. Escitalopram decreased IL-17 levels. The influence of antidepressants on IL-2 and IL-4 levels was not significant for all three drugs. Compared to escitalopram, citalopram led to higher levels of IL-1β, IL-6, IL-17 and IL-22; and mirtazapine to higher levels of IL-1β, IL-17, IL-22 and TNF-α. Mirtazapine and citalopram increased IL-22 production. The differing profile of cytokine production may relate to differences in therapeutic effects, risk of relapse and side effects.

A proteomic view at T cell costimulation

The "two-signal paradigm" in T cell activation predicts that the cooperation of "signal 1," provided by the T cell receptor (TCR) through engagement of major histocompatility complex (MHC)-presented peptide, with "signal 2″ provided by costimulatory molecules, the prototype of which is CD28, is required to induce T cell effector functions. While the individual signalling pathways are well understood, little is known about global changes in the proteome pattern during TCR/CD28-mediated activation. Therefore, comparative 2-DE-based proteome analyses of CD3(+) CD69(-) resting T cells versus cells incubated with (i) the agonistic anti-CD3 antibody OKT3 mimicking signal 1 in absence or presence of IL-2 and/or with (ii) the agonistic antibody 15E8 triggering CD28-mediated signaling were performed. Differentially regulated spots were defined leading to the identification of proteins involved in the regulation of the metabolism, shaping and maintenance of the cytoskeleton and signal transduction. Representative members of the differentially expressed protein families, such as calmodulin (CALM), glyceraldehyde-3-phosphate dehydrogenase (GAPDH), L-lactate dehydrogenase (LDH), Rho GDP-dissociation inhibitor 2 (GDIR2), and platelet basic protein (CXCL7), were independently verified by flow cytometry. Data provide a detailed map of individual protein alterations at the global proteome level in response to TCR/CD28-mediated T cell activation.

Ex vivo expansion of human CD8+ T cells using autologous CD4+ T cell help

Background

Using in vivo mouse models, the mechanisms of CD4⁺ T cell help have been intensively investigated. However, a mechanistic analysis of human CD4⁺ T cell help is largely lacking. Our goal was to elucidate the mechanisms of human CD4⁺ T cell help of CD8⁺ T cell proliferation using a novel in vitro model.

Methods/Principal Findings

We developed a genetically engineered novel human cell-based artificial APC, aAPC/mOKT3, which expresses a membranous form of the anti-CD3 monoclonal antibody OKT3 as well as other immune accessory molecules. Without requiring the addition of allogeneic feeder cells, aAPC/mOKT3 enabled the expansion of both peripheral and tumor-infiltrating T cells, regardless of HLA-restriction. Stimulation with aAPC/mOKT3 did not expand Foxp3⁺ regulatory T cells, and expanded tumor infiltrating lymphocytes predominantly secreted Th1-type cytokines, interferon-γ and IL-2. In this aAPC-based system, the presence of autologous CD4⁺ T cells was associated with significantly improved CD8⁺ T cell expansion in vitro. The CD4⁺ T cell derived cytokines IL-2 and IL-21 were necessary but not sufficient for this effect. However, CD4⁺ T cell help of CD8⁺ T cell proliferation was partially recapitulated by both adding IL-2/IL-21 and by upregulation of IL-21 receptor on CD8⁺ T cells.

Conclusions

We have developed an in vitro model that advances our understanding of the immunobiology of human CD4⁺ T cell help of CD8⁺ T cells. Our data suggests that human CD4⁺ T cell help can be leveraged to expand CD8⁺ T cells in vitro.

Photo-activated affinity-site cross-linking of antibodies using tryptophan containing peptides

Affinity-based conjugation methods for antibodies can produce defined and reproducible conjugates. This requires that the target antibody has an affinity site for the ligand and that the ligand has a reactive site. These requirements are critical for the conjugation of antibodies designed for diagnostic and therapeutic application. Our laboratory has discovered a novel affinity of antibodies for the amino acid tryptophan using an azido derivative of tryptophan. Here we show that tryptophan without the azido group can be photo-cross-linked to antibodies. Biotinylated tryptophan peptides are photolysed into monoclonal and polyclonal antibodies and such biotinylated antibodies are used in avidin-based ELISA. With the simple and gentle tryptophan-affinity photo-conjugation of peptides, antibodies can be conjugated with peptides to enhance their potency and expand their targeting range.

[Eukaryotic expression of anti-CD3 single chain Fv antibody gene and the characterization of its bioactivities]

AIM

To express anti-CD3 scFv in Hela cells and investigate its biological activity.

METHODS

DNA fragment encoding anti-CD3 scFv was inserted into eukaryotic expression vector pDisplay. The recombinant expression vector was sequenced and then transfected into Hela cells by electroporation method. The expression of anti-CD3 scFv was identified by in situ hybridization. In-vitro T lymphocyte activation was then detected by (3)H-TdR incoporation method. Anti-CD3 scFv gene-transfected Hela cells were co-cultured with T cells and cytotoxicity was measured by MTT colorimetry.

RESULTS

Anti-CD3 scFv gene was correctly inserted into pDisplay and expressed in Hela cells. The secreted anti-CD3 scFv was able to activate T lymphocytes in the presence of anti-CD28 mAb. Cytotoxicity could be observed when anti-CD3 scFv gene-transfected Hela cells were mixed and co-cultured with T lymphocytes.

CONCLUSION

Anti-CD3 scFv expressed by Hela cells can activate T lymphocytes.

Crystal structure of the human T cell receptor CD3 epsilon gamma heterodimer complexed to the therapeutic mAb OKT3

The CD3 epsilon gamma heterodimer is essential for expression and function of the T cell receptor. The crystal structure of the human CD3 epsilon gamma heterodimer is described to 2.1-A resolution complexed with OKT3, a therapeutic mAb that not only activates and tolerizes mature T cells but also induces regulatory T cells. The mode of CD3 epsilon gamma dimerization provides a general structural basis for CD3 assembly and maps candidate T cell antigen receptor docking sites, including a duplicated linear region rich in acidic residues that is unique to human CD3 epsilon. OKT3 binds to an atypically small area of CD3 epsilon and has a low affinity for the isolated CD3 epsilon gamma heterodimer. The structure of the OKT3/CD3 epsilon gamma complex has implications for T cell signaling and therapeutic design.

Cutting Edge: Extracellular Signal-Regulated Kinases 1/2 Function as Integrators of TCR Signal Strength

Altered signaling through the TCR is currently showing promise for immunotherapy. However, the molecular mechanisms are not completely understood. Therefore, we investigated whether varying the strength of TCR engagement in various human T cells would yield different second messenger responses. The kinetics and duration of extracellular signal-regulated kinase (ERK) activation, central to multiple cellular responses, are distinctly dependent on the T cell activation state (naive vs effector), strength of TCR cross-linking, and input from the phosphatidylinositol-3 kinase pathway, which is regulated by cytokines and growth factors. Moreover, the duration of ERK activation affects c-Fos expression, a component of the AP-1 transcription complex. Thus, the character of ERK activation, transient or sustained, acts as a signal integrator to quantify the strength of TCR engagement and direct the cellular response.

The CD43 coreceptor molecule recruits the zeta-chain as part of its signaling pathway

CD43 is an abundant cell surface sialoglycoprotein implicated in hemopoietic cell adhesion and activation. Cell stimulation through CD43 results in recruitment of different signaling proteins, including members of the Src family kinases, Syk, phospholipase Cgamma2, the adapter protein Shc, the guanine nucleotide exchange factor Vav, and activation of protein kinase C. In this study, we report that in human T lymphocytes, the zeta-chain is part of the CD43 signaling pathway. Upon CD43 engagement, the zeta-chain was tyrosine-phosphorylated, generating docking sites for tyrosine-phosphorylated zeta-associated protein of 70 kDa and Vav. In vitro kinase assays suggested that zeta-associated protein of 70 kDa could account for the kinase activity associated with the zeta-chain following CD43 engagement. Cross-linking CD43 on the surface of the Lck-deficient JCaM.1 cells failed to phosphorylate the zeta-chain and associated proteins, suggesting that Lck is a key element in the CD43 signaling pathway leading to zeta phosphorylation. CD43 engagement with beads coated with anti-CD43 mAb resulted in concentration of the zeta-chain toward the bead attachment site, but interestingly, the distribution of the T cell Ag receptor complex remained unaffected. Recruitment of the zeta-chain through CD43-mediated signals was not restricted to T lymphocytes because phosphorylation and redistribution of the zeta-chain was also observed in NK cells. Our results provide evidence that the zeta-chain functions as a scaffold molecule in the CD43 signaling pathway, favoring the recruitment and formation of downstream signaling complexes involved in the CD43-mediated cell activation of T lymphocytes and other leukocytes such as NK cells.

Analysis of the mobility of signaling molecules in lymphocytes using fluorescence photobleaching techniques

The earliest biochemical events at the plasma membrane that lead to gene activation appear to depend not only on the local concentration of signaling molecules, but also on the mobility of these molecules at the site of signaling. To elucidate the process of signal transduction after receptor engagement in the immune system, it is important to analyze the mobility of signaling molecules in living lymphocytes. Current knowledge of the changes in intracellular localization and dynamic movements of signaling molecules during lymphocyte activation is limited. Here, we describe a method for known as fluorescence recovery after photobleaching, used to measure the diffusion mobility of a signaling molecule in a T cell line after T cell receptor stimulation. This method is a useful tool in studies of spatiotemporal regulation in immunoreceptor signaling.

Lipid raft distribution of CD4 depends on its palmitoylation and association with Lck, and evidence for CD4-induced lipid raft aggregation as an additional mechanism to enhance CD3 signaling

By mutagenesis, we demonstrated that the palmitoylation of the membrane-proximal Cys(396) and Cys(399)of CD4, and the association of CD4 with Lck contribute to the enrichment of CD4 in lipid rafts. Ab cross-linking of CD4 induces an extensive membrane patching on the T cell surface, which is related to lipid raft aggregation. The lipid raft localization of CD4 is critical for CD4 to induce the aggregation of lipid rafts. The localization of CD4 in lipid rafts also correlates to the ability of CD4 to enhance receptor tyrosine phosphorylation. Thus, our data suggest that CD4-induced aggregation of lipid rafts may play an additional role in CD4 signaling besides its adhesion to MHC molecules and association with Lck.

Extensive temporally regulated reorganization of the lipid raft proteome following T-cell antigen receptor triggering

Signalling by immunoreceptors is orchestrated at specific plasma membrane microdomains, referred to as lipid rafts. Here we present a proteomics approach to the temporal analysis of protein association with lipid rafts following T-cell antigen receptor (TCR) triggering. We show that TCR engagement promotes the temporally regulated recruitment of proteins participating in the TCR signalling cascade to lipid rafts. Furthermore, TCR triggering results in profound modifications in the composition of lipid rafts involving a number of proteins associated either directly or indirectly with both plasma and intracellular membranes. Raft-associated proteins can be clustered according to their temporal profile of raft association. The data identify lipid rafts as highly dynamic structures and reveal a dramatic impact of surface TCR triggering not only on components of the TCR signalling machinery but also on proteins implicated in a number of diverse cellular processes.

Evidence for protein kinase C-dependent and -independent activation of mitogen-activated protein kinase in T cells: potential role of additional diacylglycerol binding proteins

Activation of mitogen-activated protein kinases (MAPK) is a critical signal transduction event for CTL activation, but the signaling mechanisms responsible are not fully characterized. Protein kinase C (PKC) is thought to contribute to MAPK activation following TCR stimulation. We have found that dependence on PKC varies with the method used to stimulate the T cells. Extracellular signal-regulated kinase (ERK) activation in CTL stimulated with soluble cross-linked anti-CD3 is completely inhibited by the PKC inhibitor bisindolylmaleimide (BIM). In contrast, only the later time points in the course of ERK activation are sensitive to BIM when CTL are stimulated with immobilized anti-CD3, a condition that stimulates CTL degranulation. Surprisingly, MAPK activation in response to immobilized anti-CD3 is strongly inhibited at all time points by the diacylglycerol (DAG)-binding domain inhibitor calphostin C implicating the contribution of a DAG-dependent but PKC-independent pathway in the activation of ERK in CTL clones. Chronic exposure to phorbol ester down-regulates the expression of DAG-responsive PKC isoforms; however, this treatment of CTL clones does not inhibit anti-CD3-induced activation of MAPK. Phorbol ester-treated cells have reduced expression of several isoforms of PKC but still express the recently described DAG-binding Ras guanylnucleotide-releasing protein. These results indicate that the late phase of MAPK activation in CTL clones in response to immobilized anti-CD3 stimulation requires PKC while the early phase requires a DAG-dependent, BIM-resistant component.

Non-Fc receptor-binding humanized anti-CD3 antibodies induce apoptosis of activated human T cells

Human trials in organ allografts have demonstrated that murine anti-CD3 mAbs are immunosuppressive. By mimicking Ag, anti-CD3 can produce T cell activation, anergy, or death. Activation of resting T cells in vivo results in dose-limiting cytokine release and is caused by Ab-mediated cross-linking of T cells and Fcgamma receptor (FcR)-bearing cells. With the goal of minimizing cytokine-induced toxicity, anti-CD3 have been engineered to lower Fc binding avidity. Preclinical murine studies have indicated that non-FcR-binding anti-CD3 can induce apoptosis of Ag-activated T cells. Since induction of T cell apoptosis may be an important mechanism of immunosuppression by anti-CD3, we tested whether Fc mutations affect the ability of anti-human CD3 to induce apoptosis of activated T cells. We compared wild-type murine anti-CD3, M291, and OKT3 and their humanized, FcR- and non-FcR-binding structural variants in quantitative assays of T cell apoptosis. Non-FcR-binding variants produced more sustainable phosphorylation of extracellular signal-regulated kinase-2, greater release of IFN-gamma, and more effectively caused activation-dependent T cell apoptosis. Non-FcR-binding variants dissociated more quickly from the T cell surface and caused less internalization of the TCR, which then remained available in greater abundance on the cell surface for signaling. Cross-linking of non-FcR-binding variants by antiglobulin enhanced TCR internalization and minimized induction of T cell apoptosis. We conclude that non-FcR-binding, humanized anti-CD3 have improved ability to induce apoptosis of activated T cells, presumably by allowing durable expression of the TCR and sustained signaling.

CD2 and CD3 associate independently with CD5 and differentially regulate signaling through CD5 in Jurkat T cells

In T lymphocytes, the CD2 and CD5 glycoproteins are believed to be involved in the regulation of signals elicited by the TCR/CD3 complex. Here we show that CD2 and CD3 independently associate with CD5 in human PBMC and Jurkat cells. CD5 coprecipitates with CD2 in CD3-deficient cells and, conversely, coprecipitates with CD3 in cells devoid of CD2. In unstimulated CD2+ CD3+ Jurkat cells, CD5 associates equivalently with CD2 and CD3 and is as efficiently phosphorylated in CD2 as in CD3 immune complexes. However, upon activation the involvement of CD5 is the opposite in the CD2 and CD3 pathways. CD5 becomes rapidly tyrosine phosphorylated after CD3 stimulation, but is dephosphorylated upon CD2 cross-linking. These opposing effects correlate with the decrease in the activity of the SH2 domain-containing protein phosphatase 1 (SHP-1) following CD3 activation vs an enhanced activity of the phosphatase after CD2 triggering. The failure of CD5 to become phosphorylated on tyrosine residues in the CD2 pathway has no parallel with the lack of use of zeta-chains in CD2 signaling; contrasting with comparable levels of association of CD2 or CD3 with CD5, zeta associates with CD2 only residually and is nevertheless slightly phosphorylated after CD2 stimulation. The modulation of CD5 phosphorylation may thus represent a level of regulation controlled by CD2 in signal transduction mechanisms in human T lymphocytes.

Apoptosis of a human melanoma cell line specifically induced by membrane-bound single-chain antibodies

CD28 is a key regulatory molecule in T cell responses. Ag-TCR/CD3 interactions without costimulatory signals provided by the binding of B7 ligands to the CD28R appear to be inadequate for an effective T cell activation. Indeed, the absence of B7 on the tumor cell surface is probably one of the factors contributing to the escape of tumors from immunological control and destruction. Therefore, to increase the immunogenicity of tumor cell vaccines, we have expressed anti-CD3 and anti-CD28 single-chain Abs (scFv) separately on the surface of a human melanoma SkMel63 cell line (HLA-A*0201). A mixture of cells expressing anti-CD3 with cells expressing anti-CD28 resulted in a marked activation of allogeneic human PBL in vitro. The apparent induction of a Th1 differentiation pathway was accompanied by the proliferation of MHC-independent NK cells and MHC-dependent CD8+ T cells. PBL that had been cultured together with transfected SkMel63 tumor cells were able to specifically induce apoptosis in untransfected SkMel63 cells. In contrast, three other tumor cell lines expressing HLA-A*0201, including two melanoma cell lines, showed no significant apoptosis. These results provide valuable information for both adoptive immunotherapy and the generation of autologous tumor vaccines.

Laminin 5 promotes activation and apoptosis of the T cells expressing alpha3beta1 integrin

By introducing an alpha3 gene-containing plasmid into a human T cell line Jurkat, we prepared the T cells, which express a high level of the alpha3beta1 integrin, to assess the role of laminin 5 in the skin immune system. The alpha3beta1-expressing T cells adhered to laminin 5 and exhibited spreading. These adhered T cells showed a significant tyrosine phosphorylation of intracellular proteins including p59(fyn) upon T-cell receptor (TCR) stimulation. Six hours after cross-linking TCR, these cells on laminin 5 secreted a three times higher level of IL-2 than those on a BSA-coated plate. Twenty hours after the stimulation, 48% of the alpha3beta1-expressing T cells on laminin 5 caused apoptosis. The protein level of cyclin D3 and E decreased, while that of p53 increased in these T cells. These data suggest that laminin 5 may play at least two regulatory roles for T cell functions: augmentation of IL-2 production by antigen-stimulated T cells and induction of apoptosis in these T cells.

Human IgG2 variants of chimeric anti-CD3 are nonmitogenic to T cells

The mouse anti-human CD3 mAb OKT3 is a potent immunosuppressive agent used for the treatment of acute transplant rejection. OKT3 therapy is associated with acute toxicity resulting from in vivo T cell activation and systemic cytokine release, and a human anti-mouse Ab response. T cell activation is thought to be triggered by CD3 cross-linking mediated by the Abs bridging T cells and Fc receptor-bearing cells. Recent studies in a mouse model indicate that anti-mouse CD3 Abs with low affinity for Fc receptors can achieve immunosuppression without T cell activation, toxicity, or an anti-Ab response. To obtain an analogous Ab to improve the current anti-human CD3 therapy, a humanized Ab with low affinity for Fc receptors is needed. In this study, we introduced mutations into the upper CH2 region of IgG2 and expressed the altered Fc as chimeric OKT3 Abs. Compared with chimeric OKT3 IgG1, IgG2, IgG3, and IgG4, the IgG2 mutants were less mitogenic to T cells, and they did not induce the release of TNF-alpha, IFN-gamma, or IL-2. In parallel, we observed no functional interaction of the IgG2 mutant Abs with K562 cells, which express the IgG2-binding Fc receptor on their surface. Despite no measurable T cell activation, the mutant Abs could still modulate the CD3 complex. When coupled to a humanized anti-CD3, the IgG2 variant may provide a drug with less acute toxicity and immunogenicity, but may still retain potent immunosuppressive properties.

Hematopoietic changes induced by a single injection of anti-CD3 monoclonal antibody into normal mice

The present study evaluates hematopoietic modifications consecutive to in vivo treatment of mice with anti-CD3 monoclonal antibodies (mAb). The hamster mAb 145-2C11, administered in a single i.v. injection of 10 micrograms, induced the release of both interleukin 3 (IL-3) and GM-CSF into the circulation. IL-3 could be detected in the serum within 1 h, attained maximal levels after 4 h and had disappeared after 24 h. Three days later, treated mice exhibited a two- to threefold rise in blood neutrophil levels and increased spleen cell counts. Concomitantly, the incidence of nucleated erythroid cells in these spleens increased around 10-fold, relative to controls having received hamster Ig. At the same time point, clonogenic progenitor frequencies were 10-fold higher in spleens from treated mice than in those from control mice. Furthermore, the responsiveness of these splenocytes to IL-3, in terms of histamine synthesis, was enhanced. In contrast, bone marrow cell populations were only slightly affected by anti-CD3 injection. All hematopoietic changes required multivalent crosslinking of the mAb for induction, since F(ab')2 fragments lacked this activity. A return to normal occurred 7-10 days after treatment. Two i.v. injections of recombinant murine IL-3 together with recombinant murine GM-CSF on a single day had a less pronounced effect on progenitor cell frequencies in the spleen than treatment with anti-CD3. This difference is probably due to the amplification of growth factor-induced hematopoiesis by the interaction with other cytokines generated in response to anti-CD3.

Side-effects of a monoclonal antibody, muromonab CD3/orthoclone OKT3: bibliographic review

Orthoclone OKT3 is a very powerful immunosuppressive drug marketed by Laboratory Cilag and the first monoclonal murine antibody to become available for therapy in humans. It is indicated in acute allograft rejection treatment and its side-effects are strongly linked with its mechanism of action, ORT/OKT3 is an Ig2a immunoglobulin produced by hybridoma technique that recognizes, binds and blocks the CD3 complex of the T-cell receptor. Two types of side-effects may occur that are either the consequences of overimmunosuppression or activation of immune system, since ORT/OKT3 behaves as a foreign antigen. This report is a bibliographic review of the suspected side-effects of this product.

Identification of sites of degradation in a therapeutic monoclonal antibody by peptide mapping

A peptide mapping procedure was developed to locate regions of a monoclonal antibody, OKT3, that undergo chemical modification as the molecule degrades upon storage. The structures of these peptide degradation products were investigated. Deamidation at specific asparagine residues and oxidation of a cysteine and several methionines were found to be major routes of OKT3 degradation. A unique chain cross-linked degradation product was also observed and characterized. Changing the storage conditions of the antibody affected the relative distribution of degradation products. These results were useful in the development of more stable formulations for OKT3, and the methods can be used in the characterization of other monoclonal antibodies intended for therapeutic use.

The pharmacokinetics and pharmacodynamics of immunosuppressive agents

Designing immunosuppressive regimens for the pediatric transplant patient is challenging because one must balance the need to provide adequate immunosuppression without interfering with normal growth processes or causing long-term adverse consequences. To optimize immunosuppressive therapy and minimize toxicity, it is necessary for the nurse to be knowledgeable of the pharmacokinetic and pharmacodynamic characteristics of the various agents. It is also important to understand which drugs interact with immunosuppressive agents and how to manage these interactions.

Effect of a single amino acid mutation on the activating and immunosuppressive properties of a "humanized" OKT3 monoclonal antibody

The binding specificity of the murine OKT3 has been transferred into a human antibody framework to reduce its immunogenicity. This "humanized" anti-CD3 mAb (gOKT3-5) was previously shown to retain, in vitro, all the properties of native OKT3, including T cell activation, which has been correlated, in vivo, with the severe side effects observed in transplant recipients after the first administration of the mAb. T cell activation is thought to be triggered by the cross-linking mediated by the antibodies between T cells and Fc receptor-bearing cells. In this study, we introduced a single amino acid mutation from a leucine to a glutamic acid at position 235 in the Fc receptor binding segment of the gOKT3-5 mAb to produce Glu-235 mAb. This mutation generated a 100-fold decrease in the affinity of the antibody for the Fc receptor on U937 cells, without affecting Ag binding. In parallel, we observed a marked reduction in the T cell activation triggered by the mAb (proliferation, cell surface expression of early activation markers including Leu 23 and IL-2R, and release of TNF-alpha, IFN-gamma, and granulocyte macrophage-CSF). In contrast, the mutated mAb retained suppressive properties similar to the gOKT3-5 mAb, as assessed by significant modulation of the T cell receptor complex and suppression of Ag-specific CTL activity. We conclude that this anti-CD3 mAb bearing a single amino acid mutation in its Fc portion retains important immunosuppressive properties, while exhibiting significantly less T cell activation than OKT3 in vitro. This drug might achieve potent immunosuppression while minimizing acute toxicity in vivo and thus be useful in transplantation as well as in autoimmune diseases.

Anti-CD3 monoclonal antibody treatment of patients with CD3-negative tumors: a phase IA/B study

Anti-CD3 monoclonal antibodies induce the proliferation of human T-cells in vitro and activate specific and nonspecific cytolysis by human T-cell clones and human peripheral blood lymphocytes. In vivo administration of anti-CD3 prevents tumor growth of a UV-induced mouse fibrosarcoma. We conducted a phase I trial to determine the toxicity and immunomodulatory properties of low doses of anti-CD3 in 36 patients with cancer. In 23 patients, anti-CD3 was given i.v. over 3 h at 1, 10, 30, and 100 mcg/patient. Five other patients received anti-CD3 at 30 mcg by i.v. bolus. Patients were treated every 3 days for a total of four doses. An additional eight patients received anti-CD3 daily for 14 days at 3 mcg by i.v. bolus, 3-h infusion, or 24-h infusion. Dose-limiting toxicity was headache. Headache was often accompanied by signs and symptoms of meningeal irritation leading to performance of a lumbar puncture in nine patients. The opening pressure was usually elevated, and six patients had a cerebrospinal fluid lymphocytosis with an elevated protein. Increased levels of interleukin 6 were identified in the cerebrospinal fluid. The maximum tolerated dose by 3-h infusion was 30 mcg. There were no objective tumor responses. There was a dose-related increase in the number of peripheral blood lymphocytes expressing the T-cell activation antigen CD69 (Leu 23), but no changes were seen in CD25 (interleukin 2 receptor) expression, and no changes were observed in the serum levels of the soluble interleukin 2 receptor. Even at these low doses of anti-CD3, 8 of 16 patients tested developed human anti-mouse antibodies.

Modulation of calcium fluxes in Jurkat T cells by myristic acid. Inhibition is independent of membrane potential and intracellular pH

Treatment of T lymphocytes with mitogenic antibodies against the T-cell receptor/CD3 complex induces within seconds a rise in the concentration of intracellular free Ca2+. We recently reported that free myristic acid, but not its methyl ester, inhibits both the anti-CD3-induced Ca2+ influx across the cell membrane and the Ca2+ release from intracellular stores in Jurkat T cells. Here we show that myristic acid induced a rapid hyperpolarization of the cell membrane potential and a decrease in intracellular pH in Jurkat cells. Lauric acid and palmitic acid caused minor hyperpolarization, whereas other saturated non-esterified fatty acids tested were without effect. Hyperpolarization of the membrane potential in Jurkat cells with valinomycin did not, however, inhibit the anti-CD3-induced Ca2+ signal, and the blocking effect on the Ca2+ signal in myristic acid-treated Jurkat cells was not reversed after normalization of the cell membrane potential by treatment with gramicidin. The inhibitory effect of myristic acid on the Ca2+ fluxes thus cannot be explained by changes in membrane potential. We also present evidence that the blocking effect of myristic acid on the receptor-operated Ca2+ flux is not due to the myristic acid-induced decrease in intracellular pH. Moreover, we demonstrate that myristic acid does not prevent the release of Ca2+ triggered by inositol 1,4,5-trisphosphate from intracellular pools in permeabilized cells. Our findings indicate that myristic acid blocks anti-CD3-induced Ca2+ traffic in Jurkat cells by interfering with the regulation of Ca2+ mobilization, apparently by blocking an early step in signal transduction from the T-cell-antigen receptor/CD3 complex.