Minimal cross-linking and epitope requirements for CD40-dependent suppression of apoptosis contrast with those for promotion of the cell cycle and homotypic adhesions in human B cells

Quantifying biomolecular organisation in membranes with brightness-transit statistics

Cells crucially rely on the interactions of biomolecules at their plasma membrane to maintain homeostasis. Yet, a methodology to systematically quantify biomolecular organisation, measuring diffusion dynamics and oligomerisation, represents an unmet need. Here, we introduce the brightness-transit statistics (BTS) method based on fluorescence fluctuation spectroscopy and combine information from brightness and transit times to elucidate biomolecular diffusion and oligomerisation in both cell-free in vitro and in vitro systems incorporating living cells. We validate our approach in silico with computer simulations and experimentally using oligomerisation of EGFP tethered to supported lipid bilayers. We apply our pipeline to study the oligomerisation of CD40 ectodomain in vitro and endogenous CD40 on primary B cells. While we find a potential for CD40 to oligomerize in a concentration or ligand depended manner, we do not observe mobile oligomers on B cells. The BTS method combines sensitive analysis, quantification, and intuitive visualisation of dynamic biomolecular organisation.

Cell targeting and immunostimulatory properties of a novel Fcγ-receptor-independent agonistic anti-CD40 antibody in rhesus macaques

Targeting CD40 by agonistic antibodies used as vaccine adjuvants or for cancer immunotherapy is a strategy to stimulate immune responses. The majority of studied agonistic anti-human CD40 antibodies require crosslinking of their Fc region to inhibitory FcγRIIb to induce immune stimulation although this has been associated with toxicity in previous studies. Here we introduce an agonistic anti-human CD40 monoclonal IgG1 antibody (MAB273) unique in its specificity to the CD40L binding site of CD40 but devoid of Fcγ-receptor binding. We demonstrate rapid binding of MAB273 to B cells and dendritic cells resulting in activation in vitro on human cells and in vivo in rhesus macaques. Dissemination of fluorescently labeled MAB273 after subcutaneous administration was found predominantly at the site of injection and specific draining lymph nodes. Phenotypic cell differentiation and upregulation of genes associated with immune activation were found in the targeted tissues. Antigen-specific T cell responses were enhanced by MAB273 when given in a prime-boost regimen and for boosting low preexisting responses. MAB273 may therefore be a promising immunostimulatory adjuvant that warrants future testing for therapeutic and prophylactic vaccination strategies.

The CD40 agonist HERA-CD40L results in enhanced activation of antigen presenting cells, promoting an anti-tumor effect alone and in combination with radiotherapy

Introduction

The ability to modulate and enhance the anti-tumor immune responses is critical in developing novel therapies in cancer. The Tumor Necrosis Factor (TNF) Receptor Super Family (TNFRSF) are potentially excellent targets for modulation which result in specific anti-tumor immune responses. CD40 is a member of the TNFRSF and several clinical therapies are under development. CD40 signaling plays a pivotal role in regulating the immune system from B cell responses to myeloid cell driven activation of T cells. The CD40 signaling axis is well characterized and here we compare next generation HERA-Ligands to conventional monoclonal antibody based immune modulation for the treatment of cancer.

Methods & results

HERA-CD40L is a novel molecule that targets CD40 mediated signal transduction and demonstrates a clear mode of action in generating an activated receptor complex via recruitment of TRAFs, cIAP1, and HOIP, leading to TRAF2 phosphorylation and ultimately resulting in the enhanced activation of key inflammatory/survival pathway and transcription factors such asNFkB, AKT, p38, ERK1/2, JNK, and STAT1 in dendritic cells. Furthermore, HERA-CD40L demonstrated a strong modulation of the tumor microenvironment (TME) via the increase in intratumoral CD8+ T cells and the functional switch from pro-tumor macrophages (TAMs) to anti-tumor macrophages that together results in a significant reduction of tumor growth in a CT26 mouse model. Furthermore, radiotherapy which may have an immunosuppressive modulation of the TME, was shown to have an immunostimulatory effect in combination with HERA-CD40L. Radiotherapy in combination with HERA-CD40L treatment resulted in an increase in detected intratumoral CD4+/8+ T cells compared to RT alone and, additionally, the repolarization of TAMs was also observed, resulting in an inhibition of tumor growth in a TRAMP-C1 mouse model.

Discussion

Taken together, HERA-CD40L resulted in activating signal transduction mechanisms in dendritic cells, resulting in an increase in intratumoral T cells and manipulation of the TME to be pro-inflammatory, repolarizing M2 macrophages to M1, enhancing tumor control.

An optimally designed anti-human CD40 antibody with potent B cell suppression for the treatment of autoimmune diseases

Antibodies targeting the CD40-CD40L pathway have great potential for treating autoimmune diseases like rheumatoid arthritis, systemic lupus erythematosus (SLE), lupus nephritis (LN), and inflammatory bowel diseases (IBD). However, in addition to the known difficulty in generating a purely antagonistic CD40 antibody, the presence of CD40 and CD40L on platelets creates additional unique challenges for the safety, target coverage, and clearance of antibodies targeting this pathway. Previously described therapeutic antibodies targeting this pathway have various shortcomings, and the full therapeutic potential of this axis has yet to be realized. Herein, we describe the generation and characterization of BI 655064, a novel, purely antagonistic anti-CD40 antibody that potently neutralizes CD40-CD40L-dependent B-cell stimulation without evidence of impacting platelet functions. This uniquely optimized antibody targeting a highly challenging pathway was obtained by applying stringent functional and biophysical criteria during the lead selection process. BI 655064 has favorable target-mediated drug disposition (TMDD)-saturation pharmacokinetics, consistent with that of a high-quality therapeutic monoclonal antibody.

The Hexavalent CD40 Agonist HERA-CD40L Induces T-Cell-mediated Antitumor Immune Response Through Activation of Antigen-presenting Cells

CD40 ligand (TNFSF5/CD154/CD40L), a member of the tumor necrosis factor (TNF) superfamily is a key regulator of the immune system. The cognate receptor CD40 (TNFRSF5) is expressed broadly on antigen-presenting cells and many tumor types, and has emerged as an attractive target for immunologic cancer treatment. Most of the CD40 targeting drugs in clinical development are antibodies which display some disadvantages: their activity typically depends on Fcγ receptor-mediated crosslinking, and depletion of CD40-expressing immune cells by antibody-dependent cellular cytotoxicity compromises an efficient antitumor response. To overcome the inadequacies of antibodies, we have developed the hexavalent receptor agonist (HERA) Technology. HERA compounds are fusion proteins composed of 3 receptor binding domains in a single chain arrangement, linked to an Fc-silenced human IgG1 thereby generating a hexavalent molecule. HERA-CD40L provides efficient receptor agonism on CD40-expressing cells and, importantly, does not require FcγR-mediated crosslinking. Strong activation of NFκB signaling was observed upon treatment of B cells with HERA-CD40L. Monocyte treatment with HERA-CD40L promoted differentiation towards the M1 spectrum and repolarization of M2 spectrum macrophages towards the M1 spectrum phenotype. Treatment of in vitro co-cultures of T and B cells with HERA-CD40L-triggered robust antitumor activation of T cells, which depended upon direct interaction with B cells. In contrast, bivalent anti-CD40 antibodies and trivalent soluble CD40L displayed weak activity which critically depended on crosslinking. In vivo, a murine surrogate of HERA-CD40L-stimulated clonal expansion of OT-I-specific murine CD8 T cells and showed single agent antitumor activity in the CD40 syngeneic MC38-CEA mouse model of colorectal cancer, suggesting an involvement of the immune system in controlling tumor growth. We conclude that HERA-CD40L is able to establish robust antitumor immune responses both in vitro and in vivo.

Complex Interplay between Epitope Specificity and Isotype Dictates the Biological Activity of Anti-human CD40 Antibodies

Anti-CD40 monoclonal antibodies (mAbs) that promote or inhibit receptor function hold promise as therapeutics for cancer and autoimmunity. Rules governing their diverse range of functions, however, are lacking. Here we determined characteristics of nine hCD40 mAbs engaging epitopes throughout the CD40 extracellular region expressed as varying isotypes. All mAb formats were strong agonists when hyper-crosslinked; however, only those binding the membrane-distal cysteine-rich domain 1 (CRD1) retained agonistic activity with physiological Fc gamma receptor crosslinking or as human immunoglobulin G2 isotype; agonistic activity decreased as epitopes drew closer to the membrane. In addition, all CRD2-4 binding mAbs blocked CD40 ligand interaction and were potent antagonists. Thus, the membrane distal CRD1 provides a region of choice for selecting CD40 agonists while CRD2-4 provides antagonistic epitopes.

B-cell activation with CD40L or CpG measures the function of B-cell subsets and identifies specific defects in immunodeficient patients

Around 65% of primary immunodeficiencies are antibody deficiencies. Functional tests are useful tools to study B-cell functions in vitro. However, no accepted guidelines for performing and evaluating functional tests have been issued yet. Here, we report our experience on the study of B-cell functions in infancy and throughout childhood. We show that T-independent stimulation with CpG measures proliferation and differentiation potential of memory B cells. Switched memory B cells respond better than IgM memory B cells. On the other hand, CD40L, a T-dependent stimulus, does not induce plasma cell differentiation, but causes proliferation of naïve and memory B cells. During childhood, the production of plasmablasts in response to CpG increases with age mirroring the development of memory B cells. The response to CD40L does not change with age. In patients with selective IgA deficiency (SIgAD), we observed that switched memory B cells are reduced due to the absence of IgA memory B cells. In agreement, IgA plasma cells are not generated in response to CpG. Unexpectedly, B cells from SIgAD patients show a reduced proliferative response to CD40L. Our results demonstrate that functional tests are an important tool to assess the functions of the humoral immune system.

A redox state-dictated signalling pathway deciphers the malignant cell specificity of CD40-mediated apoptosis

CD40, a member of the tumour necrosis factor receptor (TNFR) superfamily, has the capacity to cause extensive apoptosis in carcinoma cells, while sparing normal epithelial cells. Yet, apoptosis is only achieved by membrane-presented CD40 ligand (mCD40L), as soluble receptor agonists are but weakly pro-apoptotic. Here, for the first time we have identified the precise signalling cascade underpinning mCD40L-mediated death as involving sequential TRAF3 stabilisation, ASK1 phosphorylation, MKK4 (but not MKK7) activation and JNK/AP-1 induction, leading to a Bak- and Bax-dependent mitochondrial apoptosis pathway. TRAF3 is central in the activation of the NADPH oxidase (Nox)-2 component p40phox and the elevation of reactive oxygen species (ROS) is essential in apoptosis. Strikingly, CD40 activation resulted in down-regulation of Thioredoxin (Trx)-1 to permit ASK1 activation and apoptosis. Although soluble receptor agonist alone could not induce death, combinatorial treatment incorporating soluble CD40 agonist and pharmacological inhibition of Trx-1 was functionally equivalent to the signal triggered by mCD40L. Finally, we demonstrate using normal, ‘para-malignant' and tumour-derived cells that progression to malignant transformation is associated with increase in oxidative stress in epithelial cells, which coincides with increased susceptibility to CD40 killing, while in normal cells CD40 signalling is cytoprotective. Our studies have revealed the molecular nature of the tumour specificity of CD40 signalling and explained the differences in pro-apoptotic potential between soluble and membrane-bound CD40 agonists. Equally importantly, by exploiting a unique epithelial culture system that allowed us to monitor alterations in the redox-state of epithelial cells at different stages of malignant transformation, our study reveals how pro-apoptotic signals can elevate ROS past a previously hypothesised ‘lethal pro-apoptotic threshold' to induce death; an observation that is both of fundamental importance and carries implications for cancer therapy.

Differential Downstream Effects of Cd40 Ligation Mediated by Membrane or Soluble CD40L and Agonistic Ab: A Study on Purified Human B Cells

With the addition of various cytokines, the CD40-CD40 ligand (CD40L) system can act as a T-helper cell surrogate to permit B lymphocytes to produce large amounts of polyclonal Ig. In the present study, we tested six CD40-CD40L stimulation models: (i, ii) soluble agonistic 89 and G28.5 mAbs; (iii, iv) ‘89’ and ‘G28.5’ bound via their Fc fragments on CDw32-transfected mouse fibroblasts; (v) purified, soluble, trimeric human CD40L molecules (sCD40L); and (vi) human CD40L expressed by a CD40L-transfected mouse fibroblastic cell line (LCD40L). Target B cells consisted of purified blood and tonsillar CD19+ lymphocytes cultured in the presence of CD40 stimuli and IL-2 and IL-10, added at the onset of each B cell culture. A) There was differential expression of CD69, CD80 and CD86 exposure to sCD40L and LCD40L was ensued by the strongest % MFI changes over control. B) In blood B cells, mAbs and sCD40L induced IgA, IgM and IgG production almost equally well; LCD40L proved less efficient. In contrast, in tonsil B cells, LCD40L induced significantly more IgA, IgG 1, IgG3and IgM production than other signals. Using certain CD40/CD40L stimuli to model in vitro Ig production, a system used regularly in many laboratories, may affect the interpretation based on the cell type and on the CD40/CD40L system used.

Functional Antagonism of Human CD40 Achieved by Targeting a Unique Species-Specific Epitope

Current clinical anti-CD40 biologic agents include both antagonist molecules for the treatment of autoimmune diseases and agonist molecules for immuno-oncology, yet the relationship between CD40 epitope and these opposing biological outcomes is not well defined. This report describes the identification of potent antagonist domain antibodies (dAbs) that bind to a novel human CD40-specific epitope that is divergent in the CD40 of nonhuman primates. A similarly selected anti-cynomolgus CD40 dAb recognizing the homologous epitope is also a potent antagonist. Mutagenesis, biochemical, and X-ray crystallography studies demonstrate that the epitope is distinct from that of CD40 agonists. Both the human-specific and cynomolgus-specific molecules remain pure antagonists even when formatted as bivalent Fc-fusion proteins, making this an attractive therapeutic format for targeting hCD40 in autoimmune indications.

Impact of lithium alone and in combination with antidepressants on cytokine production in vitro

Lithium is an important psychopharmacological agent for the treatment of unipolar as well as bipolar affective disorders. Lithium has a number of side effects such as hypothyroidism and aggravation of psoriasis. On the other hand, lithium has pro-inflammatory effects, which appear beneficial in some disorders associated with immunological deficits, such as human immunodeficiency virus (HIV) infection and systemic lupus erythematosus (SLE). Therefore, immunological characteristics of lithium may be an important consideration in individualized therapeutic decisions. We measured the levels of the cytokines interleukin (IL)-1ß, IL-2, IL-4, IL-6, IL-22, IL-17 and tumour necrosis factor (TNF)-α in the stimulated blood of thirty healthy subjects supplemented with lithium alone, the antidepressants citalopram, escitalopram or mirtazapine alone, the combination of each antidepressant with lithium, and a no drug control. These drugs were tested under three blood stimulant conditions: murine anti-human CD3 monoclonal antibody OKT3 and the 5C3 monoclonal antibody (OKT3/5C3), phytohemagglutinin (PHA), and unstimulated blood. Lithium, alone and in combination with any of the tested antidepressants, led to a consistent increase of IL-1ß, IL-6 and TNF-α levels in the unstimulated as well as the stimulated blood. In the OKT3/5C3- and PHA-stimulated blood, IL-17 production was significantly enhanced by lithium. Lithium additionally increased IL-2 concentrations significantly in PHA-stimulated blood. The data support the view that lithium has pro-inflammatory properties. These immunological characteristics may contribute to side effects of lithium, but may also explain its beneficial effects in patients suffering from HIV infection or SLE.

The human agonistic CD40 antibody ADC-1013 eradicates bladder tumors and generates T-cell-dependent tumor immunity

PURPOSE

Local administration of immune-activating antibodies may increase the efficacy and reduce the immune-related adverse events associated with systemic immunotherapy of cancer. Here, we report the development and affinity maturation of a fully human agonistic CD40 antibody (IgG1), ADC-1013.

EXPERIMENTAL DESIGN

We have used molecular engineering to generate an agonistic antibody with high affinity for CD40. The functional activity of ADC-1013 was investigated in human and murine in vitro models. The in vivo effect was investigated in two separate bladder cancer models, both using human xenograft tumors in immune deficient NSG mice and using a syngeneic bladder cancer model in a novel human CD40 transgenic mouse.

RESULTS

Activation of dendritic cells (DC) by ADC-1013 results in upregulation of the costimulatory molecules CD80 and CD86, and secretion of IL12. ADC-1013 also activates DCs from human CD40 transgenic mice, and peptide-pulsed and ADC-1013-stimulated DCs induce antigen-specific T-cell proliferation in vitro. In vivo, treatment with ADC-1013 in a syngeneic bladder cancer model, negative for hCD40, induces significant antitumor effects and long-term tumor-specific immunity. Furthermore, ADC-1013 demonstrates significant antitumor effects in a human bladder cancer transplanted into immunodeficient NSG mice.

CONCLUSIONS

Our data demonstrate that ADC-1013 induces long-lasting antitumor responses and immunologic memory mediated by CD40 stimulation. To the best of our knowledge, ADC-1013 represents the first immunomodulatory antibody developed for local immunotherapy of cancer.

Anti-human CD40 monoclonal antibody therapy is potent without FcR crosslinking

Antibody agonists targeting tumor necrosis factor (TNF) superfamily receptors, including CD40, are being tested therapeutically as anticancer agents. Studies in mice have shown that anti-CD40 monoclonal antibody (mAb) requires Fc-receptor (FcR) engagement to activate antitumor immunity. In contrast, we have reported that clinically active anti-human CD40 mAb CP-870,893 does not require FcR crosslinking, a finding with translational implications.

Modulation of cytokine production by drugs with antiepileptic or mood stabilizer properties in anti-CD3- and anti-Cd40-stimulated blood in vitro

Increased cytokine production possibly due to oxidative stress has repeatedly been shown to play a pivotal role in the pathophysiology of epilepsy and bipolar disorder. Recent in vitro and animal studies of valproic acid (VPA) report antioxidative and anti-inflammatory properties, and suppression of interleukin (IL)-6 and tumor necrosis factor (TNF)-α. We tested the effect of drugs with antiepileptic or mood stabilizer properties, namely, primidone (PRM), carbamazepine (CBZ), levetiracetam (LEV), lamotrigine (LTG), VPA, oxcarbazepine (OXC), topiramate (TPM), phenobarbital (PB), and lithium on the production of the following cytokines in vitro: interleukin (IL)-1β, IL-2, IL-4, IL-6, IL-17, IL-22, and TNF-α. We performed a whole blood assay with stimulated blood of 14 healthy female subjects. Anti-human CD3 monoclonal antibody OKT3, combined with 5C3 antibody against CD40, was used as stimulant. We found a significant reduction of IL-1 and IL-2 levels with all tested drugs other than lithium in the CD3/5C3-stimulated blood; VPA led to a decrease in IL-1β, IL-2, IL-4, IL-6, IL-17, and TNF-α production, which substantiates and adds knowledge to current hypotheses on VPA's anti-inflammatory properties.

High molecular weight complex analysis of Epstein-Barr virus Latent Membrane Protein 1 (LMP-1): structural insights into LMP-1's homo-oligomerization and lipid raft association

LMP-1 is a constitutively active Tumor Necrosis Factor Receptor analog encoded by Epstein-Barr virus. LMP-1 activation correlates with oligomerization and raft localization, but direct evidence of LMP-1 oligomers is limited. We report that LMP-1 forms multiple high molecular weight native LMP-1 complexes when analyzed by BN-PAGE, the largest of which are enriched in detergent resistant membranes. The largest of these high molecular weight complexes are not formed by purified LMP-1 or by loss of function LMP-1 mutants. Consistent with these results we find a dimeric form of LMP-1 that can be stabilized by disulfide crosslinking. We identify cysteine 238 in the C-terminus of LMP-1 as the crosslinked cysteine. Disulfide crosslinking occurs post-lysis but the dimer can be crosslinked in intact cells with membrane permeable crosslinkers. LMP-1/C238A retains wild type LMP-1 NF-κB activity. LMP-1's TRAF binding, raft association and oligomerization are associated with the dimeric form of LMP-1. Our results suggest the possibility that the observed dimeric species results from inter-oligomeric crosslinking of LMP-1 molecules in adjacent core LMP-1 oligomers.

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.

FcγRΙΙB controls the potency of agonistic anti-TNFR mAbs

Isotype plays a crucial role in therapeutic monoclonal antibody (mAb) function, mediated in large part through differences in Fcγ receptor (FcγR) interaction. Monoclonal Abs such as rituximab and alemtuzumab, which bind target cells directly, are designed for efficient recruitment of immune effector cells through their activatory FcγR engagement to mediate maximal target cell killing. In this setting, binding to inhibitory FcγRIIB is thought to inhibit function, making mAbs with high activatory/inhibitory (A/I) FcγR binding ratios, such as mouse IgG2a and human IgG1, the first choice for this role. In contrast, exciting new data show that agonistic mAbs directed against the tumour necrosis factor receptor superfamily member CD40 require interaction with FcγRIIB for in vivo function. Such ligation activates antigen-presenting cells, promotes myeloid and CTL responses and potentially stimulates effective anti-cancer immunity. It appears that the role of FcγRIIB is to mediate mAb hyper-crosslinking to allow CD40 downstream intracellular signalling. Previous work has shown that mAbs directed against other TNFR family members, Fas and death receptor 5 and probably death receptor 4, also require FcγRIIB hyper-crosslinking to promote target cell apoptosis, suggesting a common mechanism of action. In mouse models, IgG1 is optimal for these agents as it binds to FcγRIIB with tenfold higher affinity than IgG2a and hence has a relatively low A:I FcγR binding ratio. In contrast, human IgG isotypes have a universally low affinity for FcγRIIB, but in the case of human IgG1, engineering the Fc to increase its affinity for FcγRIIB can potentially overcome this problem. Thus, modifying the A/I binding ratio of human IgG Fc can be used to optimise different types of therapeutic activity by enhancing cytotoxic or hyper-crosslinking function.

T-cell-independent antitumor effects of CD40 ligation

CD40 ligation has been shown to induce antitumor effects in mice and cancer patients. Most of the studies have focused on the ability of an agonistic anti-CD40 mAb to either directly kill CD40-positive tumor cells or activate T-cell immune responses. In this review the authors focus on the ability of CD40 ligation to activate antitumor effector mechanisms of the cells of innate immunity such as macrophages and NK cells.

Interaction with FcγRIIB is critical for the agonistic activity of anti-CD40 monoclonal antibody

A high activatory/inhibitory FcγR binding ratio is critical for the activity of mAb such as rituximab and alemtuzumab that attack cancer cells directly and eliminate them by recruiting immune effectors. Optimal FcγR binding profiles of other anti-cancer mAb, such as immunostimulatory mAb that stimulate or block immune receptors, are less clear. In this study, we analyzed the importance of isotype and FcγR interactions in controlling the agonistic activity of the anti-mouse CD40 mAb 3/23. Mouse IgG1 (m1) and IgG2a (m2a) variants of the parental 3/23 (rat IgG2a) were engineered and used to promote humoral and cellular responses against OVA. The mouse IgG1 3/23 was highly agonistic and outperformed the parental Ab when promoting Ab (10-100-fold) and T cell (OTI and OTII) responses (2- to >10-fold). In contrast, m2a was almost completely inactive. Studies in FcγR knockout mice demonstrated a critical role for the inhibitory FcγRIIB in 3/23 activity, whereas activatory FcγR (FcγRI, -III, and -IV) was dispensable. In vitro experiments established that the stimulatory effect of FcγRIIB was mediated through Ab cross-linking delivered in trans between neighboring cells and did not require intracellular signaling. Intriguingly, activatory FcγR provided effective cross-linking of 3/23 m2a in vitro, suggesting the critical role of FcγRIIB in vivo reflects its cellular distribution and bioavailability as much as its affinity for a particular Ab isotype. In conclusion, we demonstrate an essential cross-linking role for the inhibitory FcγRIIB in anti-CD40 immunostimulatory activity and suggest that isotype will be an important issue when optimizing reagents for clinical use.

Different molecular behavior of CD40 mutants causing hyper-IgM syndrome

CD40/CD40 ligand (CD40L) cross-talk plays a key role in B-cell terminal maturation in the germinal centers. Genetic defects affecting CD40 cause a rare form of hyper-immunoglobulin M (IgM) syndrome, a disorder characterized by low or absent serum IgG and IgA, associated with recurrent infections. We previously reported on a few patients with homozygous CD40 mutations resulting in lack or severe reduction of CD40 cell surface expression. Here we characterize the 3 CD40 mutants due to missense mutations or small in-frame deletions, and show that the mutated proteins are synthesized but retained in the endoplasmic reticulum (ER), likely due to protein misfolding. Interestingly, the intracellular behavior and fate differ significantly among the mutants: progressive accumulation of the P2 mutant causes endoplasmic reticulum stress and the activation of an unfolded protein response; the mutant P4 is rather efficiently disposed by the ER-associated degradation pathway, while the P5 mutant partially negotiates transport to the plasma membrane, and is competent for CD40L binding. Interestingly, this latter mutant activates downstream signaling elements when overexpressed in transfected cells. These results give new important insights into the molecular pathogenesis of HIGM disease, and suggest that CD40 deficiency can also be regarded as an ER-storage disease.

CD40/CD40L signaling and its implication in health and disease

CD40, a transmembrane receptor of the tumor necrosis factor gene superfamily is expressed on a variety of cells, such as monocytes, B-cells, antigen presenting cells, endothelial, smooth muscle cells, and fibroblasts. The interaction between CD40 and CD40 ligand (CD40L) enhances the expression of cytokines, chemokines, matrix metalloproteinases, growth factors, and adhesion molecules, mainly through the stimulation of nuclear factor kappa B. The aim of this review is to summarize the molecular and cellular characteristics of CD40 and CD40L, the mechanisms that regulate their expression, the cellular responses they stimulate and finally their implication in the pathophysiology of inflammatory and autoimmune diseases.

Therapeutic interventions targeting CD40L (CD154) and CD40: the opportunities and challenges

CD40 was originally identified as a receptor on B-cells that delivers contact-dependent T helper signals to B-cells through interaction with CD40 ligand (CD40L, CD154). The pivotal role played by CD40-CD40L interaction is illustrated by the defects in B-lineage cell development and the altered structures of secondary lymphoid tissues in patients and engineered mice deficient in CD40 or CD40L. CD40 signaling also provides critical functions in stimulating antigen presentation, priming of helper and cytotoxic T-cells and a variety of inflammatory reactions. As such, dysregulations in the CD40-CD40L costimulation pathway are prominently featured in human diseases ranging from inflammatory conditions to systemic autoimmunity and tissue-specific autoimmune diseases. Moreover, studies in CD40-expressing cancers have provided convincing evidence that the CD40-CD40L pathway regulates survival of neoplastic cells as well as presentation of tumor-associated antigens to the immune system. Extensive research has been devoted to explore CD40 and CD40L as drug targets. A number of anti-CD40L and anti-CD40 antibodies with diverse biological effects are in clinical development for treatment of cancer and autoimmune diseases. This chapter reviews the role of CD40-CD40L costimulation in disease pathogenesis, the characteristics of therapeutic agents targeting this pathway and status of their clinical development.

The Germinal centre-derived lymphomas seen through their cellular microenvironment

The human lymph node is a complex tissue resulting from the microenvironmental organisation of different cell populations linked by topographical and/or functional relationships. Germinal centres (GCs) of lymphoid follicles contain a meshwork of follicular dendritic cells in addition to B-cells and some CD4(+) T cells. Moreover, there is a sharp demarcation around the whole follicle centre, which is highlighted by fibroblastic reticulum cells. On the whole, GC exerts a role in B cell physiology and malignancy. In GC-derived lymphomas, gene expression profiling studies have raised the possibility that survival of the affected patients may be associated with signatures preferentially expressed in non-malignant T cells and macrophages and/or dendritic cells. Immunohistological analyses in lymphoma biopsy samples have confirmed that the biological behaviour and tumour progression may be influenced by the tumour microenvironment. This review will examine GC-derived lymphomas, including follicular lymphomas, Hodgkin lymphomas and angioimmunoblastic T-cell lymphoma, through their integrated cellular microenvironment, highlighting those findings which may serve as a useful surrogate marker for tumour diagnosis or tumour progression, together with key molecules involved in tumour development.

Identification of a strongly activating human anti-CD40 antibody that suppresses HIV type 1 infection

We characterized the functional properties of a novel set of human anti-CD40 monoclonal antibodies originating from a human phage display library and identified an antibody that strongly activates cells via the CD40 receptor for potential use in HIV therapy. The anti-CD40 antibodies were converted from a single chain antibody fragment format (scFv) to an IgG format and produced in HEK293 cells, and the binding characteristics were evaluated. Next, their ability to (1) rescue a human B cell line from induced apoptosis, (2) stimulate B cell proliferation, and (3) block the CD40-CD40L interaction was determined. Finally, the most activating anti-CD40 antibody was tested for its ability to block HIV-1 infection in a monocyte-derived cell line. The different anti-CD40 antibodies, A24, B44, E30, F33, and A2-54, displayed a wide variety of binding and functional properties. In particular, B44 showed a very strong ability to activate normal human B cells and, in addition, did not block the CD40-CD40L interaction. This antibody was able to suppress HIV-1 infection in a human cell line (MonoMac 1) and may be a potential therapeutic candidate in HIV infection.

CD154 tone sets the signaling pathways and transcriptome generated in model CD40-pluricompetent L3055 Burkitt's lymphoma cells

Activated B cells reacting to small amounts of CD40L (CD154) maintain homeostasis by suppressing default apoptosis. Additional outcomes, particularly differentiation, demand higher CD40 occupancy. Here, focusing on survival, we compared changes in the transcriptome of pleiotropically competent, early passage L3055 Burkitt's lymphoma cells confronted with low (picomolar) and high (nanomolar) concentrations of CD154 to gain insight into how a single receptor sets these distinct phenotypes. Of 267 genes altering transcriptional activity in response to strong CD154 tone, only 25 changed coordinately on low receptor occupancy. Seven of the top nine common up-regulated genes were targets of NF-kappaB. Direct measurement and functional inhibition of the NF-kappaB pathway revealed it to be central to a CD40-dependent survival signature. Although the canonical NF-kappaB axis was engaged by both signaling strengths equally, robust alternative pathway activation was a feature selective to a strong CD40 signal. Discriminatory exploitation of the two separate arms of NF-kappaB activation may indicate a principle whereby a cell senses and reacts differentially to shifting ligand availability. Identifying components selectively coupling CD40 to each axis could indicate targets for disruption in B cell pathologies underpinned by ectopic and/or hyper-CD154 activity such as neoplasia and some autoimmunities.

CD40-mediated death and cytokine secretion in colorectal cancer: a potential target for inflammatory tumour cell killing

CD40, a member of the tumour necrosis factor family, is expressed in a variety of epithelial cells. Although soluble CD40 agonists are growth-inhibitory, membrane-presented CD40 ligand (CD40L) induces extensive apoptosis in carcinoma cells. This study investigated whether CD40 is expressed in human colorectal carcinoma (CRC) cells and explored the functional consequences of CD40 ligation. CD40 expression in a panel of CRC lines was assessed by flow cytometry and in resected human CRCs by immunohistochemistry. CRC cells were treated in vitro with soluble CD40 agonists or cocultured with fibroblasts expressing membrane-bound CD40 ligand. Apoptosis was determined by flow cytometry using Annexin V/propidium iodide labelling and by a DNA fragmentation assay. Cytokine secretion induced by CD40 ligation was quantified by a multiplex-bead array approach. We show that CD40 is expressed in a proportion of established CRC lines in culture and that receptor expression is functional. Activation of CD40 by membrane-presented CD40L, but not soluble agonists, causes high levels of death in CD40-positive CRC cells and induces secretion of proinflammatory cytokines. In agreement with our in vitro observations, immunohistochemical studies demonstrated that CD40 is highly expressed in a proportion of colorectal cancer specimens. The high level of susceptibility of CRC cells to CD40-killing combined with the ability of CD40 to induce concomitant secretion of proinflammatory cytokines suggest that CD40 ligation may represent a novel mechanism for elimination of CRC cells and render CD40 a promising therapeutic target for the eradication of colorectal tumours.

C4b binding protein binds to CD154 preventing CD40 mediated cholangiocyte apoptosis: a novel link between complement and epithelial cell survival

Activation of CD40 on hepatocytes and cholangiocytes is critical for amplifying Fas-mediated apoptosis in the human liver. C4b-Binding Protein (C4BP) has been reported to act as a potential surrogate ligand for CD40, suggesting that it could be involved in modulating liver epithelial cell survival. Using surface plasmon resonance (BiaCore) analysis supported by gel filtration we have shown that C4BP does not bind CD40, but it forms stable high molecular weight complexes with soluble CD40 ligand (sCD154). These C4BP/sCD154 complexes bound efficiently to immobilised CD40, but when applied to cholangiocytes they failed to induce apoptosis or proliferation or to activate NFkB, AP-1 or STAT 3, which are activated by sCD154 alone. Thus C4BP can modulate CD40/sCD154 interactions by presenting a high molecular weight multimeric sCD154/C4BP complex that suppresses critical intracellular signalling pathways, permitting cell survival without inducing proliferation. Immunohistochemistry demonstrated co-localisation and enhanced expression of C4BP and CD40 in human liver cancers. These findings suggest a novel pathway whereby components of the complement system and TNF ligands and receptors might be involved in modulating epithelial cell survival in chronic inflammation and malignant disease.

Generation of a multimeric form of CD40L with potent immunostimulatory activity using streptavidin as a chaperon

Effective aggregation of cell surface immune receptors with their ligands is critical in promoting humoral and cellular immune responses. Simulation of these interactions using soluble multimeric ligands having potent adjuvant effects may prove an effective alternative to agonistic antibodies as immunotherapeutics. Multimeric ligands may effectively engage their receptors, leading to aggregation and effective signal transduction. We exploited the structural characteristics of streptavidin (SA) for the generation of multimeric chimeric proteins. Streptavidin forms stable tetramers and oligomers under physiological conditions, and, as such, chimeric molecules with SA are expected to possess similar features. Two chimeric molecules consisting of the extracellular domains of human and mouse CD40L and a modified form of core streptavidin were generated. These proteins form stable oligomers that could only be dissociated into monomers by heating at 100 degrees C, but not 60 degrees C, under denaturing conditions. The chimeric proteins vigorously stimulated B cells, monocytes, and dendritic cells for the production of cytokines and chemokines and upregulation of immunostimulatory molecules. The use of SA as a chaperon presents a novel approach to generate multimeric immunological molecules with potent activities and their use as potential therapeutics for the treatment of cancer and other immune-based disorders.

C3-symmetric peptide scaffolds are functional mimetics of trimeric CD40L

Interaction between CD40, a member of the tumor necrosis factor receptor (TNFR) superfamily, and its ligand CD40L, a 39-kDa glycoprotein, is essential for the development of humoral and cellular immune responses. Selective blockade or activation of this pathway provides the ground for the development of new treatments against immunologically based diseases and malignancies. Like other members of the TNF superfamily, CD40L monomers self-assemble around a threefold symmetry axis to form noncovalent homotrimers that can each bind three receptor molecules. Here, we report on the structure-based design of small synthetic molecules with C3 symmetry that can mimic CD40L homotrimers. These molecules interact with CD40, compete with the binding of CD40L to CD40, and reproduce, to a certain extent, the functional properties of the much larger homotrimeric soluble CD40L. Architectures based on rigid C3-symmetric cores may thus represent a general approach to mimicking homotrimers of the TNF superfamily.

Preclinical antilymphoma activity of a humanized anti-CD40 monoclonal antibody, SGN-40

SGN-40 is a humanized IgG1 antihuman CD40 that is currently in a phase I clinical trial for the treatment of multiple myeloma. As surface CD40 expression on B-lineage cells is maintained from pro-B cells to plasma cells, SGN-40 may be applicable to treatment of other B-cell neoplasias, including non-Hodgkin's lymphoma. In this study, we examined potential in vitro and in vivo anti-B-lineage lymphoma activity of SGN-40. Recombinant SGN-40 was expressed and purified from Chinese hamster ovary cells and characterized based on binding affinity, specificity, and normal B-cell stimulation. The ability of SGN-40 to target neoplastic B cells was examined in vitro by proliferation inhibition, cytotoxicity, and antibody-dependent cell cytotoxicity assays and in vivo by human lymphoma xenograft models. Recombinant SGN-40 showed high affinity, Kd of approximately 1 nmol/L, and specific binding to CD40. Whereas SGN-40 was a weak agonist in stimulating normal B-cell proliferation in the absence of IL-4 and CD40L, it delivered potent proliferation inhibitory and apoptotic signals to, and mediated antibody-dependent cytotoxicity against, a panel of high-grade B-lymphoma lines. These in vitro antilymphoma effects were extended to disseminated and s.c. xenograft CD40 tumor models. In these xenograft models, the antitumor activity of SGN-40 was comparable with that of rituximab. The preclinical in vitro and in vivo antilymphoma activity of SGN-40 observed in this study provides a rationale for the clinical testing of SGN-40 in the treatment of CD40+ B-lineage lymphomas.

K+ channel expression during B cell differentiation: implications for immunomodulation and autoimmunity

Using whole-cell patch-clamp, fluorescence microscopy and flow cytometry, we demonstrate a switch in potassium channel expression during differentiation of human B cells from naive to memory cells. Naive and IgD(+)CD27(+) memory B cells express small numbers of the voltage-gated Kv1.3 and the Ca(2+)-activated intermediate-conductance IKCa1 channel when quiescent, and increase IKCa1 expression 45-fold upon activation with no change in Kv1.3 levels. In contrast, quiescent class-switched memory B cells express high levels of Kv1.3 ( approximately 2000 channels/cell) and maintain their Kv1.3(high) expression after activation. Consistent with their channel phenotypes, proliferation of naive and IgD(+)CD27(+) memory B cells is suppressed by the specific IKCa1 inhibitor TRAM-34 but not by the potent Kv1.3 blocker Stichodactyla helianthus toxin, whereas the proliferation of class-switched memory B cells is suppressed by Stichodactyla helianthus toxin but not TRAM-34. These changes parallel those reported for T cells. Therefore, specific Kv1.3 and IKCa1 inhibitors may have use in therapeutic manipulation of selective lymphocyte subsets in immunological disorders.

CD40/CD40 homodimers are required for CD40-induced phosphatidylinositol 3-kinase-dependent expression of B7.2 by human B lymphocytes

Preformed CD40/CD40 homodimers were initially observed on human Burkitt lymphoma cell lines, normal B cells, and transitional bladder carcinoma cell lines. However, the nature and the biological relevance of these homodimers have not yet been investigated. In the present study, we demonstrated that Epstein-Barr virus-transformed B cells and CD40-transfected HEK 293 cells constitutively expressed disulfide-linked CD40/CD40 homodimers at low levels. Oligomerization of CD40 leads to a rapid and significant increase in the disulfide-linked CD40/CD40 homodimer formation, a response that could be prevented using a thiol-alkylating agent. Formation of CD40/CD40 homodimers was found to be absolutely required for CD40-mediated activation of phosphatidylinositol 3-kinase, which, in turn regulated B7.2 expression. In contrast, CD40 monomers provided the minimal signal emerging from CD40, activating p38 MAP kinase and inducing homotypic B cell adhesion. CD40/CD40 homodimer formation was totally independent of TRAF1/2/3/5 associations with the threonine at position 254 in the cytoplasmic tail of the CD40 molecules. This finding may be vital to better understanding the molecular mechanisms that govern cell signaling triggered by CD40/CD154 interactions.

Affinity and epitope profiling of mouse anti-CD40 monoclonal antibodies

The CD40-CD40L interaction plays a critical role in both humoral and cellular immune responses and interfering antibodies have been suggested as an effective approach for the treatment of lymphomas and autoimmune diseases. In this study we have profiled a panel of mouse antihuman CD40 monoclonal antibodies (MoAbs), regarding their CD40 binding affinity and epitope-specificity relative to the CD40L binding in relation to their cellular activating potential. Despite a rather similar domain-recognition profile, the MoAbs blocked the CD40L binding to a varying degree, with MoAb 5C3 being the poorest inhibitor. There was no correlation between affinity and cellular activation potential. In contrast, a correlation between the ability to block CD40L-binding and activation potential could be seen. We believe that this analysis of several mouse anti-CD40 antibodies can be used to develop strategies for producing new human anti-CD40 antibodies that can more effectively induce or block B-cell proliferation.

Pre-assembly of the extracellular domains of CD40 is not necessary for rescue of mouse B cells from anti-immunoglobulin M-induced apoptosis

CD40 is a tumour necrosis factor receptor (TNFR) family member of central importance for the adaptive immune system. To elucidate the functional role of the different extracellular domains of CD40, we have created a set of truncated CD40 molecules where domains, or parts of domains, have been removed. These CD40 proteins, which contain a peptide tag in the N-terminal end, have been expressed in a murine B-cell line, WEHI 231. It was found that ligation of these engineered CD40 proteins via the peptide tag, was sufficient to rescue as well as to promote proliferation of apoptotic WEHI 231 cells, even when all the extracellular domains of CD40 were absent. Our results suggest that pre association of CD40 in the cell membrane plays no critical role for the CD40 signalling pathway. Furthermore, our data imply that conformational changes initiated in the extracellular domains of CD40 are not essential for signal transduction.

Control of receptor-induced signaling complex formation by the kinetics of ligand/receptor interaction

Tumor necrosis factor (TNF) exists both as a membrane-integrated type II precursor protein and a soluble cytokine that have different bioactivities on TNFR2 (CD120b) but not on TNFR1 (CD120a). To identify the molecular basis of this disparity, we have investigated receptor chimeras comprising the cytoplasmic part of Fas (CD95) and the extracellular domains of the two TNF receptors. The membrane form of TNF, but not its soluble form, was capable of inducing apoptosis as well as activation of c-Jun N-terminal kinase and NF-kappaB via the TNFR2-derived chimera. In contrast, the TNFR1-Fas chimera displayed strong responsiveness to both TNF forms. This pattern of responsiveness is identical to that of wild type TNF receptors, demonstrating that the underlying mechanisms are independent of the particular type of the intracellular signaling machinery and rather are controlled upstream of the intracellular domain. We further demonstrate that the signaling strength induced by a given ligand/receptor interaction is regulated at the level of adaptor protein recruitment, as shown for FADD, caspase-8, and TRAF2. Since both incidents, strong signaling and robust adapter protein recruitment, are paralleled by a high stability of individual ligand-receptor complexes, we propose that half-lives of individual ligand-receptor complexes control signaling at the level of adaptor protein recruitment.

Modulation of the CD40-CD40 ligand interaction using human anti-CD40 single-chain antibody fragments obtained from the n-CoDeR phage display library

CD40 plays a central regulatory role in the immune system and antibodies able to modulate CD40 signalling may consequently have a potential in immunotherapy, in particular for treatment of lymphomas and autoimmune disease like multiple sclerosis. As a first step to achieve this goal, we describe the selection and characterization of a novel set of fully human anti-CD40 antibody fragments (scFv) from a phage display library (n-CoDeR). In order to determine their biological potential, these antibody fragments have been analysed for their ability to promote B-cell activation, rescue from apoptosis and to block the CD40-CD40 ligand (CD40L) interaction. The selected cohort of human scFv could be subcategorized, each expressing a distinct functional signature. Thus scFv were generated that induced B-cell proliferation, rescued B cells from apoptosis and blocked the CD40-CD40L interaction to different extents. In particular, one of the scFv clones (F33) had the ability to abrogate completely this interaction. The epitope recognition patterns as well as individual rate constants were also determined and the affinity was shown to vary from low to high nanomolar range. In conclusion, this panel of human anti-CD40 scFv fragments displays a number of distinct properties, which may constitute a valuable source when evaluating candidates for in vivo trials.

CD40 ligation downregulates EBNA-2 and LMP-1 expression in EBV-transformed lymphoblastoid cell lines

Epstein-Barr virus (EBV) drives the proliferation of human B cells in vitro and during primary infection in vivo. The transformed immunoblasts express nuclear proteins EBNA1-6, transcribed from the Cp/Wp promoter, and the membrane proteins LMP-1, -2A and -2B (lymphoblastoid type of latency). EBV persists through life in resting memory B cells with a restricted type of latency in the absence of the Cp/Wp promoter activity. Since CD40 crosslinking can reportedly inhibit the growth of EBV-transformed lymphoblastoid cell lines (LCLs), we have examined the effect of CD40 ligation on the expression of EBNAs and LMP-1 and on Cp EBV promoter activity together with several phenotypic markers. CD40 crosslinking led to a partial downregulation of EBNA-2, EBNA3-6 and LMP-1 in LCLs, paralleled by downregulation of Cp promoter activity. It also induced upregulation of the germinal center marker CD77 on the LCL cells. Our findings suggest that the encounter of proliferating EBV-transformed immunoblasts with CD40L, as would occur when normal B cells generate memory cells in germinal centers, may switch the viral transcription program from the full lymphoblastoid to a more restricted latency program in a proportion of cells. This would permit virus persistence in the B-cell memory compartment.

Population depletion activates autonomous CD154-dependent survival in biopsylike Burkitt lymphoma cells

Population size is governed through cells reacting to a variety of intrinsic and extrinsic cues. Tumors, while liberated from many of the homeostatic constraints placed on physiologic counterparts, can nonetheless remain subject to both social and environmental control. Burkitt lymphoma cells faithful to the biopsy phenotype were used to model the reliance of the colony, if any, on an inbuilt population sensor. Below a normally suicidal threshold number of cells, low picomolar quantities of exogenous CD40 ligand (CD40L/CD154) were found to sustain the clone without the discernible shift in phenotype that accompanies high CD40L encounter. Although CD154 was undetectable in populous cultures, message was induced as numbers became limiting. Correspondingly, attempts to neutralize endogenous CD40L activity failed to perturb cells at optimal densities but resulted in their marked decline as the critical threshold was approached. These data reveal an auto-inducible survival mechanism seemingly regulated through the monitoring of population size, a process somewhat akin to that of "quorum sensing" among gram-negative bacteria in which diffusible molecules provide a means of communication to coordinate gene expression with population density. This process could be activated as cells discern depletions in their community or when deprived of signals otherwise furnished within an appropriate environmental niche.

Analysis of the oligomeric requirement for signaling by CD40 using soluble multimeric forms of its ligand, CD154

We describe the construction of a novel soluble dodecameric form of CD154 (CD40 ligand) that is more effective than trimeric tCD154 in triggering B cell activation. Dodecameric surfactant protein (SP)-D-CD154 was more potent than tCD154 in inducing B cell proliferation over a wide range of concentrations. At saturating concentrations, the level of proliferation triggered by SP-D-CD154 was fourfold higher than that achieved with tCD154. Moreover, stimulation with dodecameric CD154 induced higher levels of the costimulatory molecules ICAM-1 and CD86. The higher activity of dodecameric CD154 when compared to trimeric CD154 is unlikely to be due to differences in their avidity for CD40, since both forms bound to CD40 strongly. Therefore, the extent of receptor clustering directly regulates signaling by CD40.

Functional activity of CD40 antibodies correlates to the position of binding relative to CD154

In this study we describe the characterization of a panel of 12 anti-mouse CD40 monoclonal antibodies (mAb). Characterization was performed in terms of antibody-binding site relative to the CD154 ligand, and the relationship between position and functional outcome of binding. The antibodies divided into three groups. The first were strong inhibitors of CD154 binding, and induced strong proliferative and activation signals to B cells. Two antibodies gave intermediary inhibition and comparable levels of activation. The remaining antibodies were found to bind outside the CD154 binding site and were poor inducers of B-cell activation. Data presented show a strong correlation between location of mAb binding and the resultant activation signal delivered. This correlation is shown to be independent of the isotype of the antibody involved and of its affinity. Implications of these findings are discussed.

Soluble CD40 ligand induces selective proliferation of lymphoma cells in primary mantle cell lymphoma cell cultures

Interaction between CD40 and the CD40 ligand (CD40L) is critical for the survival and proliferation of B cells during immunopoiesis. However, the role of CD40L in the pathogenesis of malignant lymphomas is ambiguous. Primary mantle cell lymphoma (MCL) cells were cultured in the presence of recombinant human CD40L trimer (huCD40LT), and a significant time- and dose-dependent induction of DNA synthesis was observed in thymidine incorporation assays (n = 7,P < .04). The maximal rate of DNA synthesis was reached at huCD40LT doses of 100 ng/mL and above after 4 days of culture, but a significant increase of DNA synthesis was detected already at doses of 1 ng/mL (P = .03). HuCD40LT never inhibited the basal level of DNA synthesis. These findings established 400 ng/mL of huCD40LT for 4 days as standard conditions in the system. Under these conditions, huCD40LT significantly increased the proportion of cells in the S/G2/M phases of the cell cycle in 4 of 7 studied cases, while the fraction of apoptotic cells remained unchanged (n = 7). HuCD40LT also induced expression of CD80/B7-1, CD86/B7-2, and CD95/Fas and up-regulated the expression of HLA-DR (n = 6). With the use of bromodeoxyuridine incorporation in triple-color flow cytometric analysis, it was found that huCD40LT induced cell-cycle progression in light chain–restricted cells only, of which a median of 14% (range, 0.5% to 29%; n = 4) returned to G0/1 phase DNA content after bromodeoxyuridine incorporation, demonstrating completion of at least one cell cycle in the presence of huCD40LT. Thus, primary clonal MCL cells are activated and can proliferate in the presence of huCD40LT as a single agent.

Soluble CD40 ligand induces selective proliferation of lymphoma cells in primary mantle cell lymphoma cell cultures

Interaction between CD40 and the CD40 ligand (CD40L) is critical for the survival and proliferation of B cells during immunopoiesis. However, the role of CD40L in the pathogenesis of malignant lymphomas is ambiguous. Primary mantle cell lymphoma (MCL) cells were cultured in the presence of recombinant human CD40L trimer (huCD40LT), and a significant time- and dose-dependent induction of DNA synthesis was observed in thymidine incorporation assays (n = 7,P < .04). The maximal rate of DNA synthesis was reached at huCD40LT doses of 100 ng/mL and above after 4 days of culture, but a significant increase of DNA synthesis was detected already at doses of 1 ng/mL (P = .03). HuCD40LT never inhibited the basal level of DNA synthesis. These findings established 400 ng/mL of huCD40LT for 4 days as standard conditions in the system. Under these conditions, huCD40LT significantly increased the proportion of cells in the S/G2/M phases of the cell cycle in 4 of 7 studied cases, while the fraction of apoptotic cells remained unchanged (n = 7). HuCD40LT also induced expression of CD80/B7-1, CD86/B7-2, and CD95/Fas and up-regulated the expression of HLA-DR (n = 6). With the use of bromodeoxyuridine incorporation in triple-color flow cytometric analysis, it was found that huCD40LT induced cell-cycle progression in light chain–restricted cells only, of which a median of 14% (range, 0.5% to 29%; n = 4) returned to G0/1 phase DNA content after bromodeoxyuridine incorporation, demonstrating completion of at least one cell cycle in the presence of huCD40LT. Thus, primary clonal MCL cells are activated and can proliferate in the presence of huCD40LT as a single agent.

The indispensable role of microenvironment in the natural history of low-grade B-cell neoplasms

Follicular lymphoma (FL) and B-cell chronic lymphocytic leukemia (B-CLL) are paradigmatic examples of lymphoid malignancies in which the relevant biological mechanisms are alterations in the control of apoptosis rather than an exaggerated proliferation. This explains why low-grade B-cell neoplasms still fail to be cured with current approaches. It is becoming increasingly clear that the defective apoptosis of FL and B-CLL has to be ascribed not only to intrinsic defects of the neoplastic cells, but also to extrinsic factors that influence their behavior. Malignant B cells retain the capacity to respond to microenvironmental signals, but have devised a monothematic responsiveness. They have a specific sensitivity to anti-apoptotic signals that favor their survival, whereas they seem to have become insensitive to pro-apoptotic signals. Bystander, nontumoral cells play a fundamental (though not sufficient) role both in the onset and in the progression of these diseases. The survival of leukemic cells appears to be dependent on direct cell-cell contacts. The localization of malignant B cells in bone marrow or neoplastic follicles is not a passive adhesion phenomenon but a crucial step for their survival. Bidirectional malignant lymphocyte-nontumoral cell interactions may lead to the amplification of a microenvironment able to inhibit the apoptosis of neoplastic B cells. The pressure of antigenic selection and the role of the tumor necrosis factor receptor family through the functional survival signal provided by CD40 together with the crippled death signal exerted by CD95 are new prominent characters on the stage.

The extrafollicular-to-follicular transition of human B lymphocytes: induction of functional globotriaosylceramide (CD77) on high threshold occupancy of CD40

Amongst lymphocytes, expression of CD77 (globotriaosylceramide, Gb3) is exclusive to B cells of the germinal center (GC). Its acquisition by extrafollicular B cells may thus herald their commitment to a follicular response. Here we show that high threshold occupancy of CD40 by its cognate ligand (CD40L) promotes rapid induction of CD77 expression in non-GC (CD38(lo)) B cells. The kinetics of CD77 acquisition mirrored those of GC-related markers CD95 and CD86 but contrasted with the more delayed increase in CD38 expression. Induction of CD77 was not a simple consequence of cell cycle entry: other conditions of stimulation equally capable of driving proliferation failed to promote CD77 expression. CD77 was functional in that cells were now sensitive to Verotoxin-1, an Escherichia coli-derived ligand of Gb3. These data indicate that acquisition by extrafollicular B cells of CD77 results from high threshold occupancy of CD40, a situation that should be reached physiologically only once a critical level of T cell priming has been achieved.

Epitope-dependent synergism and antagonism between CD40 antibodies and soluble CD40 ligand for the regulation of CD23 expression and IgE synthesis in human B cells

BACKGROUND

The induction of IgE synthesis in naive B cells requires two T-cell-derived signals: one delivered through CD40 and the other via interleukin-4 (IL-4). The natural counterstructure to CD40 is the CD40 ligand (CD40L). We have asked about the interplay between CD40L and CD40 mAb that recognize distinct epitopes in delivering signals for regulating IL-4-dependent IgE synthesis and the expression of CD23, the low-affinity IgE receptor, in resting B cells.

METHODS

After culture of purified human tonsillar B cells with CD40 agonists and IL-4, surface CD23 was determined by flow cytometric analysis. CD23 levels in cell lysates and supernatants were quantified by ELISA, as were those of secreted IgE.

RESULTS

With regard to both induction of CD23 and IgE production, soluble CD40L trimer (sCD40LT) showed synergistic interaction with two mAb to CD40 which bind to epitopes located outside the ligand binding site (EA5 and 5C3), but not with a mAb (G28-5) which effectively competes for CD40L binding to CD40. Each of the two noncompeting mAb to CD40 was able to cooperate strongly with sCD40LT in promoting high-level induction of CD23 even in the absence of IL-4, an effect mirrored in the promotion of strong homotypic clustering and high-rate DNA synthesis. G28-5, uniquely, induced a down-regulation in IL-4-induced CD23 expression with time, a change that was accompanied by an increase in the amount of soluble CD23 detected. While the two noncompeting mAb consistently synergized with sCD40LT for the promotion of IL-4-dependent IgE synthesis, sCD40LT and G28-5 (which, by itself, was the most potent of the CD40 mAb at inducing IL-4-dependent IgE production) exhibited mutual antagonism in this regard, the level of which could be quite profound.

CONCLUSIONS

This study demonstrates that appropriate targeting of CD40 can modulate IgE synthesis either positively or negatively.