CD40 pathway blockade as an approach to immunotherapy

Toward Small-Molecule Inhibition of Protein-Protein Interactions: General Aspects and Recent Progress in Targeting Costimulatory and Coinhibitory (Immune Checkpoint) Interactions

Protein-Protein Interactions (PPIs) that are part of the costimulatory and coinhibitory (immune checkpoint) signaling are critical for adequate T cell response and are important therapeutic targets for immunomodulation. Biologics targeting them have already achieved considerable clinical success in the treatment of autoimmune diseases or transplant recipients (e.g., abatacept, belatacept, and belimumab) as well as cancer (e.g., ipilimumab, nivolumab, pembrolizumab, atezolizumab, durvalumab, and avelumab). In view of such progress, there have been only relatively limited efforts toward developing small-molecule PPI inhibitors (SMPPIIs) targeting these cosignaling interactions, possibly because they, as all other PPIs, are difficult to target by small molecules and were not considered druggable. Nevertheless, substantial progress has been achieved during the last decade. SMPPIIs proving the feasibility of such approaches have been identified through various strategies for a number of cosignaling interactions including CD40-CD40L, OX40-OX40L, BAFFR-BAFF, CD80-CD28, and PD-1-PD-L1s. Here, after an overview of the general aspects and challenges of SMPPII-focused drug discovery, we review them briefly together with relevant structural, immune-signaling, physicochemical, and medicinal chemistry aspects. While so far only a few of these SMPPIIs have shown activity in animal models (DRI-C21045 for CD40-D40L, KR33426 for BAFFR-BAFF) or reached clinical development (RhuDex for CD80-CD28, CA-170 for PD-1-PD-L1), there is proof-of-principle evidence for the feasibility of such approaches in immunomodulation. They can result in products that are easier to develop/ manufacture and are less likely to be immunogenic or encounter postmarket safety events than corresponding biologics, and, contrary to them, can even become orally bioavailable.

Small-Molecule Inhibitors of the CD40-CD40L Costimulatory Protein-Protein Interaction

Costimulatory interactions are required for T cell activation and development of an effective immune response; hence, they are valuable therapeutic targets for immunomodulation. However, they, as all other protein-protein interactions, are difficult to target by small molecules. Here, we report the identification of novel small-molecule inhibitors of the CD40-CD40L interaction designed starting from the chemical space of organic dyes. For the most promising compounds such as DRI-C21045, activity (IC50) in the low micromolar range has been confirmed in cell assays including inhibition of CD40L-induced activation in NF-κB sensor cells, THP-1 myeloid cells, and primary human B cells as well as in murine allogeneic skin transplant and alloantigen-induced T cell expansion in draining lymph node experiments. Specificity versus other TNF-superfamily interactions (TNF-R1-TNF-α) and lack of cytotoxicity have also been confirmed at these concentrations. These novel compounds provide proof-of-principle evidence for the possibility of small-molecule inhibition of costimulatory protein-protein interactions, establish the structural requirements needed for efficient CD40-CD40L inhibition, and serve to guide the search for such immune therapeutics.

CDP7657, an anti-CD40L antibody lacking an Fc domain, inhibits CD40L-dependent immune responses without thrombotic complications: an in vivo study

INTRODUCTION

CD40 ligand (CD40L) blockade has demonstrated efficacy in experimental autoimmune models. However, clinical trials of hu5c8, an anti-human CD40L IgG1 antibody, in systemic lupus erythematosus (SLE) were halted due to an increased incidence of thrombotic events. This study evaluated CDP7657, a high affinity PEGylated monovalent Fab' anti-CD40L antibody fragment, to assess whether an Fc-deficient molecule retains efficacy while avoiding the increased risk of thrombotic events observed with hu5c8.

METHODS

The potency and cross-reactivity of CDP7657 was assessed in in vitro assays employing human and non-human primate leukocytes, and the capacity of different antibody formats to activate platelets in vitro was assessed using aggregometry and dense granule release assays. Given the important role CD40L plays in regulating humoral immunity, in vivo efficacy was assessed by investigating the capacity of Cynomolgus monkeys to generate immune responses to the tetanus toxoid antigen while the potential to induce thrombotic events in vivo was evaluated after repeat dosing of antibodies to Rhesus monkeys. A PEGylated anti-mouse CD40L was generated to assess efficacy in the New Zealand Black/White (NZB/W) mouse model of SLE.

RESULTS

CDP7657 dose-dependently inhibited antigen-specific immune responses to tetanus toxoid in Cynomolgus monkeys, and in contrast to hu5c8, there was no evidence of pulmonary thrombovasculopathy in Rhesus monkeys. Aglycosyl hu5c8, which lacks Fc receptor binding function, also failed to induce thrombotic events in Rhesus monkeys. In vitro experiments confirmed that antibody constructs lacking an Fc, including CDP7657, did not induce human or monkey platelet activation. A PEGylated monovalent Fab' anti-mouse CD40L antibody also inhibited disease activity in the NZB/W mouse model of SLE after administration using a therapeutic dosing regimen where mice received antibodies only after they had displayed severe proteinuria.

CONCLUSIONS

These findings demonstrate for the first time that anti-CD40L antibodies lacking a functional Fc region do not induce thrombotic events in Rhesus monkeys and fail to activate platelets in vitro but, nevertheless retain pharmacological activity and support the investigation of CDP7657 as a potential therapy for systemic lupus erythematosus and other autoimmune diseases.

TNF superfamily protein-protein interactions: feasibility of small- molecule modulation

The tumor necrosis factor (TNF) superfamily (TNFSF) contains about thirty structurally related receptors (TNFSFRs) and about twenty protein ligands that bind to one or more of these receptors. Almost all of these cell surface protein-protein interactions (PPIs) represent high-value therapeutic targets for inflammatory or immune modulation in autoimmune diseases, transplant recipients, or cancers, and there are several biologics including antibodies and fusion proteins targeting them that are in various phases of clinical development. Small-molecule inhibitors or activators could represent possible alternatives if the difficulties related to the targeting of protein-protein interactions by small molecules can be addressed. Compounds proving the feasibility of such approaches have been identified through different drug discovery approaches for a number of these TNFSFR-TNFSF type PPIs including CD40-CD40L, BAFFR-BAFF, TRAIL-DR5, and OX40-OX40L. Corresponding structural, signaling, and medicinal chemistry aspects are briefly reviewed here. While none of these small-molecule modulators identified so far seems promising enough to be pursued for clinical development, they provide proof-of-principle evidence that these interactions are susceptible to small-molecule modulation and can serve as starting points toward the identification of more potent and selective candidates.

Critical role of lipid rafts in CD154-mediated T cell signaling

Although signal pathways triggered via the CD40 molecule are well characterized, those induced via CD154 are less known. This study demonstrates that engagement of CD154 in Jurkat D1.1 cells with soluble CD40 leads to PKC alpha and delta activation, calcium mobilization, and phosphorylation of the Map kinases ERK1/2 and p38. Such response is accompanied by significant recruitment of CD154 into lipid rafts. Disruption of lipid rafts integrity with nystatin or methyl beta-cyclodextrin abrogated PKCalpha PKCdelta and p38 phosphorylation, but had no effect on ERK1/2 phosphorylation. Inhibition of PKC activation completely abolished p38 phosphorylation but had no effect on ERK1/2 phosphorylation, suggesting that localization of CD154 within lipid rafts is an absolute requirement for CD154-induced PKCalpha- and PKCdelta-dependent p38 phosphorylation. Furthermore, CD154 acts as co-stimulator for the production of IL-2 in an APC-superantigen-T-cell activation model. The results obtained demonstrate for the first time, that lipid rafts are of immunological relevance for CD154-triggered signals, and reinforce the importance of CD154 in T-cell activation.

Mechanisms underlying B-cell tolerance induction by antigen-immunoglobulin G gene transfer

Previous studies on the mechanisms underlying tolerance induction in diabetes have mainly focused on T cells, however B cells also have an important role in diabetes. Based on our previous studies that splenocytes, transduced with glutamic acid decarboxylase (GAD) 65 fused to immunoglobulin (Ig) G carrier, reduced antibody-mediated response in non-obese diabetic (NOD) mice, here we examined the mechanisms underlying B-cell tolerance in this system. We found that GAD-IgG-transduced splenocytes did not reduce CD40 expression on B-cells in NOD mice, but they did downregulate CD40 ligand (CD40L) expression. Furthermore, anti-CD40L injection reduced autoantibody levels in NOD mice and in vitro experiments demonstrated that CD40L blockade reduced the antigenpresenting capability of B-cells. In conclusion, the results of this study suggest that downregulation of CD40L may be one mechanism underlying the induction of B-cell tolerance in GAD-IgG-treated NOD mice.

CD44v7 ligation downregulates the inflammatory immune response in Crohn's disease patients by apoptosis induction in mononuclear cells from the lamina propria

Deletion of exon CD44v7 abrogates experimental colitis by apoptosis induction in intestinal mononuclear cells. Here we show that CD44v7 expression was upregulated upon CD40 ligation in human mononuclear cells, and examined whether ligation of CD44v7 also affects activation and apoptosis in lamina propria mononuclear cells (LPMC) from Crohn's disease (CD) patients. Thirty five patients with chronic inflammatory bowel disease (IBD), fourteen controls and four patients with diverticulitis were evaluated. CD44v7 was upregulated predominantly in the inflamed mucosa of CD patients. Furthermore, incubation with an anti-CD44v7 antibody induced apoptosis in LPMC isolated from inflamed mucosa of CD patients, but not from non-inflamed mucosa, from patients with ulcerative colitis (UC) or from normal controls. CD40 ligation and simultaneous incubation with anti-CD44v7 significantly downregulated CD80 in dendritic cells, thus inhibiting a critical second signal for naive T-cell activation. The apoptotic signal was mediated via the intrinsic mitochondrial pathway with decreased Bcl-2 and increased 7A6 (a mitochondrial membrane protein) expression. It was Fas independent and required caspases-3 and -9 activation. The process is highly specific for macrophage activation via CD40. These findings point to a novel mechanism of apoptosis induction in CD patients mediated by CD44v7 ligation.

New reagents on the horizon for immune tolerance

Recent advances in immunology and a growing arsenal of new drugs are bringing the focus of tolerance research from animal models into the clinical setting. The conceptual framework for therapeutic tolerance induction has shifted from a "sledgehammer" approach that relies solely on cellular depletion and cytokine targeting, to a strategy directed toward restoring a functional balance across the immune system, namely the different populations of naive cells, effector and memory cells, and regulatory cells. Unlocking the key to tolerance induction in the future will likely depend on our ability to harness the functions of T regulatory cells. Also, dendritic cells are strategically positioned at the interface between innate and adaptive immunity and may be subject to deliberate medical intervention in a way that can control a chronic inflammatory response. Many reagents with tolerance-inducing potential are currently undergoing clinical testing in transplantation, autoimmune diseases, and allergic diseases, and even more that are on the horizon promise to offer enormous benefits to human health.

Costimulatory molecules as immunotherapeutic targets in systemic lupus erythematosus

T cells undergo full and productive activation when they traffic to lymph nodes where they encounter dendritic cells displaying foreign antigen in the context of MHC molecules on their surface. Recognition of these antigen-MHC complexes by the T cell's receptor for antigen, or T cell receptor, provides the first of two obligate signals needed to drive cell proliferation. The second antigen-independent signal is provided by the costimulatory receptor, CD28, as it engages its ligand on the antigen-presenting cells. Failure of the T cell to receive this second signal after antigen recognition leaves the T cell in a state of anergy. Understanding the role of T cell costimulatory receptors in T cell activation has led to the development of novel approaches for regulating immune responses in subjects with cancer or autoimmune disease by experimentally triggering or blocking costimulatory receptor signaling. In this review, we will discuss, first, several costimulatory pathways known to participate or regulate the progression of autoimmune disease, and, second, how manipulation of T cell costimulation and/or costimulation blockade has been used to treat systemic lupus erythematosus.

Anti-TWEAK monoclonal antibodies reduce immune cell infiltration in the central nervous system and severity of experimental autoimmune encephalomyelitis

TWEAK is a member of the TNF family, constitutively expressed in the central nervous system (CNS), with pro-inflammatory, proliferative or apoptotic effects depending upon cell types. Its receptor, Fn14, is expressed in CNS by endothelial cells, reactive astrocytes and neurons. We showed that TWEAK and Fn14 mRNA expression increased in spinal cord during experimental autoimmune encephalomyelitis (EAE). We investigated the role of TWEAK during EAE using neutralizing anti-TWEAK antibody in myelin oligodendrocyte glycoprotein (MOG) induced EAE in C57BL/6 mice. We observed a reduction of disease severity and leukocyte infiltration when mice were treated after the priming phase.

B-cell subsets in blood and lymphoid organs in Macaca fascicularis

BACKGROUND

Cynomolgus monkeys (Macaca fascicularis) are widely used animal models in biomedical research. However, the phenotypic characteristics of cynomolgus monkey (CM) B cells in peripheral blood (PB) and lymphoid organs are poorly understood.

METHODS

FACS analyses of PB-, spleen-, lymph node (LN)-, and bone marrow (BM)-derived B cells were performed.

RESULTS

CM peripheral blood B cells have a smaller fraction of CD27(-) (naive) cells ( approximately 40%), as compared to human blood samples ( approximately 70%). Similar to humans, an early activation marker, CD23, is expressed more on CD27(-) CM naive B cells, as compared to CD27(+) B cells. The mean fraction of B cells exhibiting a memory phenotype is similar to that seen in human blood. Unlike humans, CM blood contains a subset of CD20(++)CD80(+)CD21(-)IgM(+/-)CD27(+)CD19(+)FSC(++)BAFF-R(low) B cells that are likely of germinal center origin. Thus, CM blood contains (i) a higher percentage of B cells that express the co-stimulatory molecule CD80, and (ii) a lower fraction of B cells that are CD21(+), as compared to human blood. Due to the relative paucity of information on B-cell subsets in organs of healthy humans, a direct comparison between human and CM lymphoid organ data is limited. The fraction of CD27(+) and CD23(+) B cells appears to be similar, while the fraction of CD80(+) B cells appears to be higher than that seen in human lymphoid organs. CM spleens and to some extent lymph nodes have a distinct subset of CD21(++) cells that are also CD80(+/-)CD23(low)IgM(++)CD27(+/-)FSC(++). This subset is phenotypically similar to the marginal zone B cells present in human spleen and LN samples. We also provide detailed analyses on the fraction of lymphoid organ B cells that express CD21, CD23, CD32, and/or CD80 B-cell markers.

CONCLUSIONS

In general, cynomolgus monkey B-cell subsets are similar to those seen in humans, as well as to those seen in other nonhuman primates. However, there are some clear differences between human and cynomolgus monkey B-cell subsets. These findings have direct implications for a variety of in vivo studies in cynomolgus monkeys, ranging from basic research on primate B-cell differentiation to models of infectious diseases and trials of new B-cell targeting therapeutic agents.

Depletion of B Cells by a Humanized Anti-CD20 Antibody PRO70769 in Macaca Fascicularis

PRO70769 is a humanized IgG1 monoclonal antibody against the CD20 molecule that is present on normal and malignant B cells. PRO70769 is being evaluated for treatment of B-cell-mediated diseases and is in a phase 1 trial for rheumatoid arthritis. As part of the preclinical toxicology evaluation, B-cell depletion profiles and safety of PRO70769 were assessed in cynomolgus monkeys. Animals were administered drug (IV) on days 1 and 15 with 10, 50, or 100 mg/kg PRO70769 and killed 2 weeks after the second dose and after a 3-month recovery period. In a parallel study, animals were not necropsied but instead were retreated with a second cycle of PRO70769 administered under an identical regimen. PRO70769 suppressed B cells in the blood to undetectable levels and significantly reduced B cells in lymphoid tissues. Splenic B cells were depleted to a greater extent compared with lymph node B cells. A second cycle of treatment resulted in a greater extent of depletion in lymphoid tissues compared with the depletion observed after one cycle of treatment; however, residual B cells in lymphoid tissues were still detectable, even at the highest dose. The rate of B-cell recovery in peripheral blood appeared similar between one and two cycles of treatment. Upon depletion there was a change in the profile of lymph node B-cell subsets. After recovery, B-cell subsets were reconstituted to normal levels. Depletion of CD20-expressing cells and lymphoid follicular atrophy were the only treatment-related effects.

Future therapeutic options for celiac disease

Celiac disease is a disorder of the small intestine caused by an inappropriate immune response to wheat gluten and similar proteins of barley and rye. At present, the only available treatment is a strict gluten-exclusion diet; hence the need for alternative treatments. Recent advances have improved our understanding of the molecular basis for this disorder and there are several attractive targets for new treatments. Oral enzyme supplementation is designed to accelerate gastrointestinal degradation of proline-rich gluten, especially its proteolytically stable antigenic peptides. Complementary strategies aiming to interfere with activation of gluten-reactive T cells include the inhibition of intestinal tissue transglutaminase activity to prevent selective deamidation of gluten peptides, and blocking the binding of gluten peptides to the HLA-DQ2 or HLA-DQ8 molecules. Other possible treatments include cytokine therapy, and selective adhesion molecule inhibitors that interfere with inflammatory reactions, some of which are already showing promise in the clinic for other gastrointestinal diseases.

The contribution of Fc effector mechanisms in the efficacy of anti-CD154 immunotherapy depends on the nature of the immune challenge

Blockade of the CD154-CD40 co-stimulatory pathway with anti-CD154 mAbs has shown impressive efficacy in models of autoimmunity and allotransplantation. Clinical benefit was also demonstrated in systemic lupus erythematosus (SLE) and idiopathic thrombocytopenia patients with the humanized anti-CD154 mAb, 5C8 (hu5C8). However, thromboembolic complications that occurred during the course of the hu5C8 clinical trials have proven to be a major setback to the field and safe alternative therapeutics targeting the CD154-CD40 pathway are of great interest. Recently, effector mechanisms have been shown to play a part in anti-CD154 mAb-induced transplant acceptance in murine models, while this issue remains unresolved for humoral-mediated models. Herein, aglycosyl anti-CD154 mAbs with reduced binding to FcgammaR and complement were used as a novel means to test the role of effector mechanisms in non-human primate and murine models not amenable to gene knockout technology. While aglycosyl hu5C8 mAb was relatively ineffective in rhesus renal and islet allotransplantation, it inhibited primary and secondary humoral responses to a protein immunogen in cynomolgus monkeys. Moreover, an aglycosyl, chimeric MR1 mAb (muMR1) prolonged survival and inhibited pathogenic auto-antibody production in a murine model of SLE. Thus, the mechanisms required for efficacy of anti-CD154 mAbs depend on the nature of the immune challenge.

CD40/CD154 interactions at the interface of tolerance and immunity

Development of the acquired immune response is dependent on the signaling of CD40 by its ligand, CD154. These molecules govern both the magnitude and quality of humoral- and cell-mediated immunity. A litany of studies have conclusively documented that blockade of this ligand-receptor pair can prevent, and also intervene in, the progression of antibody- and cell-mediated autoimmune diseases, and can instill long-lived allogeneic and xenogeneic graft tolerance. Many effector mechanisms of inflammation are abolished as a result of CD154 blockade, but we are now beginning to understand that CD154 blockade may, in some instances, engender long-lived, antigen-specific tolerance. In the context of transplantation tolerance, we present a hypothesis that alpha CD154 blockade is most effective at inducing long-lived allospecific tolerance if anergy and regulation can be elicited prior to the onslaught of inflammation that is induced by grafting (preemptive tolerance). This facet of alpha CD154-induced tolerance appears to co-opt the normal processes of peripheral tolerance induced by immature DCs and can be exploited to induce long-lived antigen-specific tolerance. The underlying science and the prospects for inducing long-lived antigen-specific tolerance in a model of allograft tolerance through CD154 blockade are presented and discussed.

Rituximab-mediated depletion of cynomolgus monkey B cells in vitro in different matrices: possible inhibitory effect of IgG

The mechanism of rituximab-mediated depletion of nonmalignant CD20+B cells remains to be clarified. In this report, we examine contributions of complement- and cell-dependent killing to the rituximab-mediated depletion of cynomolgus monkey B cells in the in vitro assay. B cell depletion was assessed in whole blood, buffer, autologus plasma (plasma), heat-inactivated plasma (H/I plasma), and cobra venom factor (CVF)-treated plasma matrices in cynomolgus monkey and human samples. Rituximab-mediated B cell depletion in buffer appeared to be greater than that in whole blood or in autologus plasma. Heat inactivation of plasma resulted in the degree of B cell depletion closer to that seen in buffer, whereas CVF treatment of plasma had no effect on B cell depletion. Addition of IgG to the buffer decreased the degree of B cell depletion. The results of these studies imply that (i) plasma components (including complement) are not the mediators of the rituximab-triggered B cell depletion in the in vitro assay, suggesting that cell-mediated mechanisms are likely to be responsible for in vitro killing of normal B cells, and that (ii) some plasma components appear to inhibit rituximab-mediated B cell depletion in the in vitro assay, with IgG identified as a possible inhibitor component.

Cutting edge: T cells trigger CD40-dependent platelet activation and granular RANTES release: a novel pathway for immune response amplification

Platelets, in addition to exerting hemostatic activity, contribute to immunity and inflammation. The recent report that platelets express CD40 led us to hypothesize that CD40 ligand (CD40L)-positive T cells could bind to platelets, cause their activation, and trigger granular RANTES release, creating a T cell recruitment feedback loop. Platelets were cocultured with resting or activated autologous T cells and their activation was assessed by P-selectin expression. RANTES binding to endothelial cells was assessed by confocal microscopy, and its biological activity was demonstrated by a T cell adhesion assay. CD40L-positive T cells induced platelet activation through a contact-mediated, CD40-dependent pathway resulting in RANTES release, which bound to endothelial cells and mediated T cell recruitment. Soluble CD40L induced the same events via p38, but not extracellular signal-regulated kinase, phosphorylation. These results show the existence of a novel platelet-dependent pathway of immune response amplification which brings these nonimmune cells close to the level of pathogenic relevance traditionally attributed to classical immune cells.

Mutations of CD40 ligand in two patients with hyper-IgM syndrome

Two patients with the X-linked form of the hyper-IgM syndrome have been studied. Both patients present: 1. Mutations in the CD40L gene (a nonsense point mutation that introduces a termination codon at the extracellular domain of the protein, and a deletion that eliminates exon 4 as consequence of an abnormal splicing). 2. Lack of CD40L expression on the lymphocyte surface after stimulation with ionomycin and PMA. 3. Altered lymphocytic proliferation in response to anti-CD3. 4. Hyper IgM, low IgG and IgA levels and neutropenia. One of the patients shows, in addition, low Natural Killer cell numbers and severe herpetic infections, which distinguishes this case from the common hyper-IgM syndrome phenotype. Finally, a hyper-IgM stable phenotype has been immortalized by Herpes virus Saimiri for the first time.

Prevention of CD40-triggered dendritic cell maturation and induction of T-cell hyporeactivity by targeting of Janus kinase 3

Pharmacological targeting of Janus kinase 3 (JAK3) has been employed successfully to control allograft rejection and graft-vs.-host disease (GVHD). Recent evidence suggests that in addition to its involvement in common-gamma chain (cgamma) signaling of cytokine receptors, JAK3 is also engaged in the CD40 signaling pathway of peripheral blood monocytes. In this study, we assessed the consequences of JAK3 inhibition during CD40-induced maturation of myeloid dendritic cells (DCs), and tested the impact thereof on the induction of T-cell alloreactivity. Dendritic cells triggering through CD40 induced JAK3 activity, the expression of costimulatory molecules, production of IL-12, and potent allogeneic stimulatory capacity. In contrast, JAK3 inhibition with the rationally designed JAK3 inhibitor WHI-P-154 prevented these effects arresting the DCs at an immature level. Interestingly, DCs exposed to the JAK3-inhibitor during CD40-ligation induced a state of hyporeactivity in alloreactive T cells that was reversible upon exogenous IL-2 supplementation to secondary cultures. These results suggest that immunosuppressive therapies targeting the tyrosine kinase JAK3 may also affect the function of myeloid cells. This property of JAK3 inhibitors therefore represents a further level of interference, which together with the well-established suppression of cgamma signaling could be responsible for their clinical efficacy.

Effect of anti-CD20 monoclonal antibody, Rituxan, on cynomolgus monkey and human B cells in a whole blood matrix

BACKGROUND

Cynomolgus monkeys are widely used animal models in biomedical research. The differences between cynomolgus monkey and human B cells are not completely understood. However, these differences are of crucial importance for interpretation of data from studies on new therapeutic agents aimed at B-cell depletion, such as anti-CD20 monoclonal antibodies.

METHODS

Multicolor fluorescence-activated cell sorting analysis of peripheral blood B cells was performed on samples treated ex vivo with the anti-CD20 therapeutic monoclonal antibody, Rituxan, in a whole blood matrix.

RESULTS

In contrast to humans, cynomolgus monkeys had two distinct B-cell subsets, CD20highCD40lowCD21- and CD20lowCD40highCD21+. These B-cell subsets had a 2.5-fold difference in the EC50 for Rituxan binding and differed significantly in their in vitro susceptibility to Rituxan depletion. Human B cells were similar to the CD20lowCD40highCD21+ cynomolgus monkey B cells with regard to their EC50 for Rituxan and response to Rituxan in a whole blood matrix assay. CD21 was upregulated, whereas CD40 was downregulated at incubation with Rituxan in the CD20lowCD40highCD21+ monkey and human B cells in a concentration-dependent manner.

CONCLUSIONS

These findings have direct implications for in vivo studies of therapeutic agents that target B cells in cynomolgus monkeys and for extrapolation of the results to humans. In addition, our data are consistent with the model in which CD20, CD21, and CD40 exist in a supramolecular complex that is affected by anti-CD20 monoclonal antibodies.

TNF ligands and receptors in autoimmunity: an update

Over two decades of research have increased the interest in factors from the tumor necrosis factor family. The vast majority of these factors are powerful modulators of critical immune functions and participate in pathogenic mechanisms leading to autoimmune disease. This field constantly evolves with the addition of new family members and the discovery of their function. During the past few years several additional factors from this family, such as BAFF, RANKL, TRAIL and GITRL, have emerged with novel functions that regulate both T and B cell immune tolerance and participate in tissue destruction in autoimmunity. These new findings revealed exciting innovative strategies for the treatment of autoimmune diseases.

Variation in the ordered structure of complexes between CD154 and anti-CD154 monoclonal antibodies

The cell surface co-stimulatory protein CD154 (CD40L) is a target for monoclonal antibody (mAb) inhibitors of T-cell mediated immune diseases. This protein, like most other members of the TNF ligand family, forms homotrimeric complexes on the cell surface and in solution, with a three-fold axis of symmetry. We find that several different anti-CD154 monoclonal antibodies form distinctive complexes with soluble CD154. These soluble complexes have been analyzed using size exclusion chromatography, static and dynamic light scattering, and electron microscopy and shown to consist of caged structures of various geometries. The cell surface complexes have been analyzed by confocal microscopy and, depending on the mAb, remain as small, separate complexes or form large aggregates. The formation of these complexes in solution is likely to have an impact on measures of affinity, while the cell surface complexes could affect binding potency and provoke other biological effects.