Differences in IgG autoantibody Fab glycosylation across autoimmune diseases.

BACKGROUND: Increased prevalence of autoantibody Fab glycosylation has been demonstrated for several autoimmune diseases. OBJECTIVES: To study whether elevated Fab glycosylation is a common feature of autoimmunity, this study investigated Fab glycosylation levels on serum IgG and its subclasses for autoantibodies associated with a range of different B cell-mediated autoimmune diseases, including rheumatoid arthritis, myasthenia gravis subtypes, pemphigus vulgaris, antineutrophil cytoplasmic antibody-associated vasculitis, systemic lupus erythematosus, anti-glomerular basement membrane glomerulonephritis, thrombotic thrombocytopenic purpura, and Guillain-Barré syndrome. METHODS: The level of Fab glycosylated IgG antibodies was assessed by lectin affinity chromatography and autoantigen-specific immunoassays. RESULTS: In 6 of 10 autoantibody responses, in 5 of 8 diseases, the investigators found increased levels of Fab glycosylation on IgG autoantibodies that varied from 86% in rheumatoid arthritis to 26% in systemic lupus erythematosus. Elevated autoantibody Fab glycosylation was not restricted to IgG4, which is known to be prone to Fab glycosylation, but was also present in IgG1. When autoimmune diseases with a chronic disease course were compared with more acute autoimmune illnesses, increased Fab glycosylation was restricted to the chronic diseases. As a proxy for chronic autoantigen exposure, the investigators determined Fab glycosylation levels on antibodies to common latent herpes viruses, as well as to glycoprotein 120 in individuals who are chronically HIV-1-infected. Immunity to these viral antigens was not associated with increased Fab glycosylation levels, indicating that chronic antigen-stimulation as such does not lead to increased Fab glycosylation levels. CONCLUSIONS: These data indicate that in chronic but not acute B cell-mediated autoimmune diseases, disease-specific autoantibodies are enriched for Fab glycans.

Endothelial and Inflammation Biomarker Profiles at Diagnosis Reflecting Clinical Heterogeneity and Serving as a Prognostic Tool for Treatment Response in Two Independent Cohorts of Patients With Juvenile Dermatomyositis.

OBJECTIVE: Juvenile dermatomyositis (DM) is a heterogeneous systemic immune-mediated vasculopathy. This study was undertaken to 1) identify inflammation/endothelial dysfunction-related biomarker profiles reflecting disease severity at diagnosis, and 2) establish whether such biomarker profiles could be used for predicting the response to treatment in patients with juvenile DM. METHODS: In total, 39 biomarkers related to activation of endothelial cells, endothelial dysfunction, and inflammation were measured using multiplex technology in serum samples from treatment-naive patients with juvenile DM from 2 independent cohorts (n = 30 and n = 29). Data were analyzed by unsupervised hierarchical clustering, nonparametric tests with correction for multiple comparisons, and Kaplan-Meier tests with Cox proportional hazards models for analysis of treatment duration. Myositis-specific antibodies (MSAs) were measured in the patients' serum using line blot assays. RESULTS: Severe vasculopathy in patients with juvenile DM was associated with low serum levels of intercellular adhesion molecule 1 (Spearman's rho [rs ] = 0.465, P = 0.0111) and high serum levels of endoglin (rs = -0.67, P < 0.0001). In the discovery cohort, unsupervised hierarchical clustering analysis of the biomarker profiles yielded 2 distinct patient clusters, of which the smaller cluster (cluster 1; n = 8) exhibited high serum levels of CXCL13, CCL19, galectin-9, CXCL10, tumor necrosis factor receptor type II (TNFRII), and galectin-1 (false discovery rate <0.0001), and this cluster had greater severity of muscle disease and global disease activity (each P < 0.05 versus cluster 2). In the validation cohort, correlations between the serum levels of galectin-9, CXCL10, TNFRII, and galectin-1 and the severity of global disease activity were confirmed (rs = 0.40-0.52, P < 0.05). Stratification of patients according to the 4 confirmed biomarkers identified a cluster of patients with severe symptoms (comprising 64.7% of patients) who were considered at high risk of requiring more intensive treatment in the first 3 months after diagnosis (P = 0.0437 versus other cluster). Moreover, high serum levels of galectin-9, CXCL10, and TNFRII were predictive of a longer total treatment duration (P < 0.05). The biomarker-based clusters were not evidently correlated with patients' MSA serotypes. CONCLUSION: Results of this study confirm the heterogeneity of new-onset juvenile DM based on serum biomarker profiles. Patients with high serum levels of galectin-9, CXCL10, TNFRII, and galectin-1 may respond suboptimally to conventional treatment, and may therefore benefit from more intensive monitoring and/or treatment.

Analytical validation of the Hevylite assays for M-protein quantification.

BACKGROUND: The heavy/light chain (HLC) immunoassay quantifies the different heavy chain/light chain combinations of each immunoglobulin (Ig) class. This makes the HLC assay suited to quantify monoclonal immunoglobulins (M-protein) and for monitoring of patients with monoclonal gammopathies. This method is particularly advantageous for those samples in which electrophoretic quantification of the M-protein is not possible. METHODS: In this study we tested the analytical performance of the HLC assay in 166 routine clinical samples and in 27 samples derived from the Dutch external quality assessment (EQA) for M-protein diagnostics (74 participating laboratories). Analytical accuracy was assessed by verification that the sum of the HLC-pairs equaled total Ig concentration. Sensitivity of the HLC assay was determined in a direct method comparison with immunofixation electrophoresis (IFE). RESULTS: Comparison of HLC data with routine Ig diagnostics in 27 EQA samples showed very good correlation for both the quantification of polyclonal and monoclonal IgG, IgA and IgM (Pearson correlations [r] were 0.94, 0.99 and 0.99, respectively; slopes were 0.94, 1.07 and 0.98, respectively). The overall concordance between IFE and the HLC ratio was high (93%) with a Cohen κ coefficient of 0.84. Discrepancies between both assays were mainly caused by the higher sensitivity of IFE to detect monoclonality. CONCLUSIONS: We conclude that the HLC assay is an accurate method to quantify M-proteins that can improve monitoring of M-proteins in the beta fraction that cannot be quantified using electrophoretic techniques.

Increased IgA glycoprotein-2 specific antibody titres in refractory celiac disease.

BACKGROUND & AIMS: In most cases celiac disease (CD) is successfully treated with a gluten-free diet (GFD). However, some patients become refractory to the GFD. Refractory CD (RCD) patients have an increased risk for developing enteropathy associated T-cell lymphoma and early diagnosis is therefore of importance. Currently, RCD diagnosis relies on endoscopy and adequate serological markers are lacking. Antibodies against glycoprotein-2 (GP2A) were described in Crohn's disease (CrD) and active CD but not in ulcerative colitis (UC), suggesting this is a specific marker for small intestinal lesions. METHODS: Sera obtained from patients visiting our outpatient clinic for routine serological tests for diagnosis and/or follow-up of inflammatory bowel disease (n=78), active CD (n=45), GFD (n=34) and RCD (n=15) were analysed for GP2A titres. RESULTS: Increased GP2A-IgA levels in CrD and active CD as compared to controls (p<0.001) and lack thereof in UC was confirmed. However, we could not confirm the association with small bowel localization within the CrD patient group. Within CD patients, we demonstrated a significant decrease of GP2A-IgA titres upon a GFD and increased levels in RCD patients as compared to patients on a GFD. Although GP2A-IgA was not associated with the degree of villous atrophy, GP2A-IgA levels were able to distinguish RCD patients from GFD patients (ROC AUC=0.79, p=0.002). CONCLUSION: Follow-up of GP2A-IgA titres in CD patients on a GFD may help to identify patients at risk for developing RCD.

The NOX2-mediated ROS producing capacity of recipient cells is associated with reduced T cell infiltrate in an experimental model of chronic renal allograft inflammation.

We previously showed that anti-inflammatory Mph (Mph2) can both in vitro and in vivo induce regulatory T cells (Tregs) in a reactive oxygen species (ROS)-dependent fashion. As influx of Mph is an important characteristic of chronic inflammatory responses, we investigated the impact of NOX2-mediated ROS production by recipient cells in an experimental model of chronic allograft inflammation. We used a kidney transplantation (Tx) model with Lewis (Lew) rats as donor and congenic DA.Ncf1(DA/DA) (low ROS) and DA.Ncf1(E3/E3) (normal ROS) rats as recipients. At day 7 the contralateral kidney was removed, and the animals were sacrificed four weeks after Tx. Renal function and injury were monitored in serum and urine and the composition of the infiltrate was analyzed by immunohistochemistry. Four weeks after Tx, large leukocyte clusters were observed in the allograft, in which signs of ROS production could be demonstrated. These clusters showed no difference regarding composition of myeloid cells or the number of FoxP3 positive cells. However, T cell infiltrate was significantly reduced in the DA.Ncf1(E3/E3) recipients having normal ROS production. Therefore, this study suggests a regulatory effect of ROS on T cell infiltration, but no effect on other inflammatory cells in the allograft.

Subsets of human type 2 macrophages show differential capacity to produce reactive oxygen species.

Reactive oxygen species (ROS) produced by macrophages have recently been shown to have immunosuppressive properties and induce regulatory T cells. Here we investigated the ROS producing capacity of well-defined human Mph2 subsets and studied the contribution of ROS in the Mph-T cell interaction. Mph were generated from monocytes using M-CSF (Mph2), IL-4 (Mph2a), or IL-10 (Mph2c). Upon PMA stimulation, Mph2 and Mph2c showed a high ROS producing capacity, whereas this was low for Mph2a. Mph2 and Mph2c displayed a reduced T cell stimulatory capacity compared to Mph2a. Addition of the ROS inhibitor DPI decreased the T cell proliferation and IFN-γ production. When testing directly on Mph, DPI dose-dependently decreased the IL-10 and IL-12p40 production of CD40L-stimulated Mph2 subsets. In conclusion, the ROS producing capacity is different among human Mph type-2 subsets. In all cases, DPI suppressed T cell proliferation and cytokine production, indicating a ROS-dependent mechanism of T cell activation.

Differential IL-13 production by small intestinal leukocytes in active coeliac disease versus refractory coeliac disease.

A small fraction of coeliac disease (CD) patients have persistent villous atrophy despite strict adherence to a gluten-free diet. Some of these refractory CD (RCD) patients develop a clonal expansion of lymphocytes with an aberrant phenotype, referred to as RCD type II (RCDII). Pathogenesis of active CD (ACD) has been shown to be related to gluten-specific immunity whereas the disease is no longer gluten driven in RCD. We therefore hypothesized that the immune response is differentially regulated by cytokines in ACD versus RCDII and investigated mucosal cytokine release after polyclonal stimulation of isolated mucosal lymphocytes. Secretion of the T(H)2 cytokine IL-13 was significantly higher in lamina propria leukocytes (LPLs) isolated from RCDII patients as compared to LPL from ACD patients (P = 0.05). In patients successfully treated with a gluten-free diet LPL-derived IL-13 production was also higher as compared to ACD patients (P = 0.02). IL-13 secretion correlated with other T(H)2 as well as T(H)1 cytokines but not with IL-10 secretion. Overall, the cytokine production pattern of LPL in RCDII showed more similarities with LPL isolated from GFD patients than from ACD patients. Our data suggest that different immunological processes are involved in RCDII and ACD with a potential role for IL-13.

Dexamethasone increases ROS production and T cell suppressive capacity by anti-inflammatory macrophages.

Macrophages have been demonstrated to suppress T cell responses by producing reactive oxygen species (ROS) leading to the subsequent induction of T regulatory cells in a ROS-dependent manner. Macrophages may therefore be instrumental in downregulating T cell responses in situations of exacerbated immune responses. Here we investigated the effect of immunosuppressive drugs on ROS production by macrophage subsets and the subsequent effects on T cell activation. Macrophage types 1 and 2 were differentiated with GM-CSF or M-CSF, in presence or absence of dexamethasone, cyclosporine A, FK506, rapamycin, or mycophenolic acid. The ROS producing capacity of fully differentiated Mph was highest in anti-inflammatory Mph2 and not affected by exposure to immunosuppressive drugs. However, presence of rapamycin during Mph2 differentiation decreased the ROS production of these cells. In contrast, other immunosuppressive drugs, with dexamethasone being the most potent, increased the ROS producing capacity of Mph2. Intriguingly although the ROS producing ability of Mph1 was unaffected, dexamethasone strongly increased the ROS producing capabilities of dendritic cells. Both at the mRNA and protein level we found that dexamethasone enhanced the expression of NOX2 protein p47(phox). Functionally, dexamethasone further enhanced the capacity of Mph2 to suppress T cell mediated IFN-γ and IL-4 production. In vivo, only in rats with normal ROS production (congenic DA.Ncf1(E3/E3)) it was observed that dexamethasone injection resulted in long-lasting upregulation of ROS production by macrophages and induced higher levels of Treg in a ROS-dependent manner. In conclusion, we show that the anti-inflammatory drug dexamethasone increases the ROS producing capacity of macrophages.

CD68-expressing cells can prime T cells and initiate autoimmune arthritis in the absence of reactive oxygen species.

It is widely believed that DC, but not macrophages, prime naïve T cells in vivo. Here, we investigated the ability of CD68-expressing cells (commonly defined as macrophages) in priming autoreactive T cells and initiating collagen-induced arthritis (CIA) in the mouse. For this purpose, a transgenic mouse was developed (MBQ mouse) where macrophages exclusively expressed the MHC class II H2-A(q) (A(q)) on an H2-A(p) (A(p)) background. A(q), but not A(p) expression mediates susceptibility to CIA through presentation of type II collagen (CII) to T cells. CIA severity is enhanced by a mutation in the Ncf1 gene, impairing reactive oxygen species (ROS) production by the phagocyte NADPH oxidase (NOX2) complex. Expression of functional Ncf1 on macrophages was previously shown to protect from severe CIA. To study the effect of ROS on macrophage-mediated priming of T cells, the Ncf1 mutation was introduced in the MBQ mouse. Upon CII immunization, Ncf1-mutated MBQ mice, but not Ncf1 wild-type MBQ mice nor Ncf1-mutated A(p) mice, activated autoreactive T cells and developed CIA. These findings demonstrate for the first time that macrophages can initiate arthritis and that the process is negatively regulated by ROS produced via the NOX2 complex.

In vitro-generated DC with tolerogenic functions: perspectives for in vivo cellular therapy.

Dendritic cells (DCs) have a central role in immune regulation and serve as an essential link between innate and adaptive immunity. Their broad range of powerful immune stimulatory as well as regulatory functions has made DCs a target for vaccine development strategies. One approach to promote the tolerogenicity of DCs is to suppress their maturation by pharmacological agents, including the glucocorticoid dexamethasone. In this chapter, we describe methods to generate tolerogenic Dex-DC derived from either human peripheral blood monocytes or rat bone marrow cells.

Induction of regulatory T cells by macrophages is dependent on production of reactive oxygen species.

The phagocyte NAPDH-oxidase complex consists of several phagocyte oxidase (phox) proteins, generating reactive oxygen species (ROS) upon activation. ROS are involved in the defense against microorganisms and also in immune regulation. Defective ROS formation leads to chronic granulomatous disease (CGD) with increased incidence of autoimmunity and disturbed resolution of inflammation. Because regulatory T cells (Tregs) suppress autoimmune T-cell responses and are crucial in down-regulating immune responses, we hypothesized that ROS deficiency may lead to decreased Treg induction. Previously, we showed that in p47(phox)-mutated mice, reconstitution of macrophages (Mph) with ROS-producing capacity was sufficient to protect the mice from arthritis. Now, we present evidence that Mph-derived ROS induce Tregs. In vitro, we showed that Mph ROS-dependently induce Treg, using an NADPH-oxidase inhibitor. This finding was confirmed genetically: rat or human CGD Mph with mutated p47(phox) or gp91(phox) displayed hampered Treg induction and T-cell suppression. However, basal Treg numbers in these subjects were comparable to those in controls, indicating a role for ROS in induction of peripheral Tregs. Induction of allogeneic delayed-type hypersensitivity with p47(phox)-mutated Mph confirmed the importance of Mph-derived ROS in Treg induction in vivo. We conclude that NAPDH oxidase activity in Mph is important for the induction of Tregs to regulate T cell-mediated inflammation.

Handbook of experimental pharmacology "dendritic cells": the use of dexamethasone in the induction of tolerogenic DCs.

Dendritic cells (DCs) have a central role in immune regulation, ranging from tolerance induction to the induction of specific immune responses. DCs serve as an essential link between innate and adaptive immunity. This broad range of powerful immune stimulatory as well as regulatory functions has made DCs as targets for vaccine development strategies. One approach to promote the tolerogenicity of DCs is to suppress their maturation by pharmacological agents, including glucocorticoids (GCs). In the present chapter we will review GCs used in vitro with cultured DCs, applied in vivo, or used to generate tolerogenic DCs for cellular therapy.

Complement production and regulation by dendritic cells: molecular switches between tolerance and immunity.

In recent years it has become clear that the innate and adaptive immune systems are highly integrated and interact at several levels. Dendritic cells (DCs) are on the one hand instrumental for directing and controlling adaptive immunity and on the other hand are specialized in detecting and integrating signals from the microenvironment. In view of the strong link between deficiencies in certain complement components and the development of autoimmunity, interaction between complement and DCs seems to be of fundamental importance. We will discuss the role of C1q, C3, as well as complement regulators in DC biology.

Generation and characterization of a novel anti-rat CD40L antibody with inhibitory activities in vitro and in vivo.

The CD40-CD40L interaction plays a critical role in cell-mediated immune responses. Blocking this interaction has been shown to be beneficial in the treatment of various diseases studied in murine models. Although rats are widely used to test therapeutic strategies in several disease models, a monoclonal antibody (mAb) to block the CD40-CD40L interaction in rats is not broadly available. In the present study we generated Armenian hamster fibroblasts expressing rat CD40L and used these to generate a novel anti-rat CD40L mAb (AS1). In vitro studies showed that AS1 was able to block CD40L-induced DC maturation and B cell proliferation. Most importantly, in vivo, AS1 inhibited B cell responses in a dose-dependent fashion, as measured by the production of OVA specific antibodies after subcutaneous immunization with OVA. AS1 was shown to be a powerful tool to modulate Ag presentation in vitro and in vivo. Elucidating the effect of AS1 in various rat models for human diseases will provide more insight into blocking the CD40-CD40L interaction as a therapeutic strategy to prevent human diseases.

Macrophages suppress T cell responses and arthritis development in mice by producing reactive oxygen species.

Reduced capacity to produce ROS increases the severity of T cell-dependent arthritis in both mice and rats with polymorphisms in neutrophil cytosolic factor 1 (Ncf1) (p47phox). Since T cells cannot exert oxidative burst, we hypothesized that T cell responsiveness is downregulated by ROS produced by APCs. Macrophages have the highest burst capacity among APCs, so to study the effect of macrophage ROS on T cell activation, we developed transgenic mice expressing functional Ncf1 restricted to macrophages. Macrophage-restricted expression of functional Ncf1 restored arthritis resistance to the level of that of wild-type mice in a collagen-induced arthritis model but not in a T cell-independent anti-collagen antibody-induced arthritis model. T cell activation was downregulated and skewed toward Th2 in transgenic mice. In vitro, IL-2 production and T cell proliferation were suppressed by macrophage ROS, irrespective of T cell origin. IFN-gamma production, however, was independent of macrophage ROS but dependent on T cell origin. These effects were antigen dependent but not restricted to collagen type II. In conclusion, macrophage-derived ROS play a role in T cell selection, maturation, and differentiation, and also a suppressive role in T cell activation, and thereby mediate protection against autoimmune diseases like arthritis.

A new arthritis therapy with oxidative burst inducers.

BACKGROUND: Despite recent successes with biological agents as therapy for autoimmune inflammatory diseases such as rheumatoid arthritis (RA), many patients fail to respond adequately to these treatments, making a continued search for new therapies extremely important. Recently, the prevailing hypothesis that reactive oxygen species (ROS) promote inflammation was challenged when polymorphisms in Ncf1, that decrease oxidative burst, were shown to increase disease severity in mouse and rat arthritis models. Based on these findings we developed a new therapy for arthritis using oxidative burst-inducing substances. METHODS AND FINDINGS: Treatment of rats with phytol (3,7,11,15-tetramethyl-2-hexadecene-1-ol) increased oxidative burst in vivo and thereby corrected the effect of the genetic polymorphism in arthritis-prone Ncf1(DA) rats. Importantly, phytol treatment also decreased the autoimmune response and ameliorated both the acute and chronic phases of arthritis. When compared to standard therapies for RA, anti-tumour necrosis factor-alpha and methotrexate, phytol showed equally good or better therapeutic properties. Finally, phytol mediated its effect within hours of administration and involved modulation of T cell activation, as injection prevented adoptive transfer of disease with arthritogenic T cells. CONCLUSIONS: Treatment of arthritis with ROS-promoting substances such as phytol targets a newly discovered pathway leading to autoimmune inflammatory disease and introduces a novel class of therapeutics for treatment of RA and possibly other chronic inflammatory diseases.

Cross-linking tumor cells with effector cells via CD55 with a bispecific mAb induces beta-glucan-dependent CR3-dependent cellular cytotoxicity.

Complement (C) regulatory proteins decrease the effectiveness of immunotherapeutic anti-cancer antibodies. Bispecific mAb (bi-mAb) that target a tumor antigen and simultaneously inhibit a C regulator increase the effectiveness of such a therapy. Here we investigated the mechanism by which bi-mAb increase tumor cell lysis. Apart from C-dependent cytotoxicity, C activation can lead to complement receptor 3 (CR3)-dependent cellular cytotoxicity (CR3-DCC) by CR3-positive effector cells in the presence of beta-glucan. Here we show that an anti-Ep-CAM*anti-CD55 bi-mAb induced more than threefold higher CR3-DCC (71%) of human colorectal cancer cells compared with anti-Ep-CAM alone (20%). This CR3-DCC was dependent on the binding of the anti-CD55 arm of tumor-bound anti-Ep-CAM*anti-CD55 bi-mAb to effector cell CD55, CR3 priming by beta-glucan and the presence of iC3b on the target cell. Comparable lysis could be obtained in the absence of iC3b, when CR3 and CD55 were cross-linked on the effector cells, suggesting cooperation between CD55 and CR3 in signal transduction. Tumor cells with low antigen expression were effectively lysed via this mechanism in contrast to direct C-dependent cytotoxicity. These data imply that the effectiveness of mAb immunotherapy can be improved using anti-tumor antigen*anti-CD55 bi-mAb and beta-glucan, thereby initiating CR3-DCC as an additional effector mechanism that is efficient for eradication of tumor cells with lower antigen expression.

Inhibiting complement regulators in cancer immunotherapy with bispecific mAbs.

Although monoclonal antibody (mAb)-mediated immunotherapy of cancer has been proven to be feasible for clinical use, success rates until now have been disappointing. One reason for this might be the overexpression of membrane-bound complement regulatory proteins (mCRPs) by tumour cells. As complement activation is an important effector mechanism induced by therapeutic mAbs, inhibition of complement activation by tumour cells might reduce therapeutic efficacy by decreasing direct complement-mediated lysis as well as complement-dependent cellular cytotoxicity. Modulation of the function of these mCRPs might be achieved with therapeutic bispecific (bi-)mAbs that target a tumour antigen and simultaneously block a major mCRP. Clinical results will probably increase with such bi-mAbs compared with monovalent antitumour mAbs. In this review the feasibility of this approach is discussed.

Tumor-specific inhibition of membrane-bound complement regulatory protein Crry with bispecific monoclonal antibodies prevents tumor outgrowth in a rat colorectal cancer lung metastases model.

Membrane-bound complement regulatory proteins (mCRP) inhibit complement-mediated tumor cell eradication in vitro and in vivo. Immunotherapy of cancer with monoclonal antibodies (mAbs) that activate complement might be hampered by expression of mCRP on tumor cells. An important strategy to improve mAb immunotherapy can be blocking or overwhelming mCRP at the tumor cells surface in a tumor-specific manner. In our study, we investigated the feasibility of this approach in vivo using bispecific mAbs (bi-mAbs). This study, performed in a syngeneic lung metastases model of rat (WAG/Rij) colorectal cancer, showed that modulation of mCRP on tumor cells resulted in significantly decreased tumor outgrowth. Opsonization of tumor cells with a bi-mAb directed against a tumor-associated antigen and rat mCRP Crry (MG4(2a)*5I2) almost completely prevented the outgrowth of lung tumors (0-7 tumors/rat; n = 17). Opsonization with mAb-cobra venom factor conjugates significantly reduced the number of lung tumors (23-59 tumors; n = 12) compared with the unconjugated MG4(2a) (175-246 tumors; n = 17; P = 0.008 and 0.014, respectively). The effect of MG4(2a)*5I2 was shown to be caused by increased complement activation due to inhibition of Crry. Moreover, prophylactic treatment with MG4(2a)*5I2 or MG4(2a) showed comparable results (3-24 and 215-472 tumors, P = 0.02; n = 6) as observed with pre-opsonized tumor cells without noticeable side effects, despite binding of MG4(2a)*5I2 to endothelium and leukocytes. These results demonstrate that Crry inhibits complement-mediated tumor cell eradication by immunotherapeutic mAbs and show that tumor-specific inhibition of complement regulatory proteins using bi-mAbs can significantly improve mAb-mediated immunotherapy.

Beta-glucan enhanced killing of renal cell carcinoma micrometastases by monoclonal antibody G250 directed complement activation.

Metastases from renal cell carcinomas (RCC) are resistant to radiation and chemotherapy but are relatively immunogenic. We have investigated the possibility to eliminate human RCC micrometastases using MAb G250. G250 penetrates human micrometastases completely in a spheroid model and induces complement deposition rapidly on the outmost cell layers. However, complement dependent cytotoxicity (CDC) was barely detected using either (51)chromium release assays or confocal microscopy, due to relatively low expression of the G250 antigen and the effect of membrane bound complement regulatory proteins. Addition of blocking anti-CD59 MAbs enhanced formation of C5b-9 and consequently complement mediated lysis (13%). Complement assisted cellular cytotoxicity (CACC) was not detectable, although the iC3b ligand and CR3 receptor were present on respectively target and effector cells. Addition of soluble beta-glucan induced the killing of MAb and iC3b opsonized spheroids by effector cells (6-21%). Despite a lower affinity for G250 antigen, a bispecific anti-G250*anti-CD55 MAb enhanced cell killing in spheroids comparable to the parental G250 MAb. Our results suggest that complement-activating G250 in combination with anti-mCRP MAbs is able to kill human RCC cells in micrometastasis in vitro. For CACC the presence of CR3-priming beta-glucan seems to be obligatory. In vivo, bi-MAb may be more effective as therapeutic agent due to its increased C5a generating properties.