Clinical significance of IgG Fc receptors and Fc gamma R-directed immunotherapies

Cerium End-Deposited Gold Nanorods-Based Photoimmunotherapy for Boosting Tumor Immunogenicity

BACKGROUND

Triple-negative breast cancer (TNBC) was closely related to high metastatic risk and mortality and has not yet found a targeted receptor for targeted therapy. Cancer immunotherapy, especially photoimmunotherapy, shows promising potential in TNBC treatment because of great spatiotemporal controllability and non-trauma. However, the therapeutic effectiveness was limited by insufficient tumor antigen generation and the immunosuppressive microenvironment.

METHODS

We report on the design of cerium oxide (CeO₂) end-deposited gold nanorods (CEG) to achieve excellent near-infrared photoimmunotherapy. CEG was synthesized through hydrolyzing of ceria precursor (cerium acetate, Ce(AC)₃) on the surface of Au nanorods (NRs) for cancer therapy. The therapeutic response was first verified in murine mammary carcinoma (4T1) cells and then monitored by analysis of the anti-tumor effect in xenograft mouse models.

RESULTS

Under near-infrared (NIR) light irradiation, CEG can efficiently generate hot electrons and avoid hot-electron recombination to release heat and form reactive oxygen species (ROS), triggering immunogenic cell death (ICD) and activating part of the immune response. Simultaneously, combining with PD-1 antibody could further enhance cytotoxic T lymphocyte infiltration.

CONCLUSIONS

Compared with CBG NRs, CEG NRs showed strong photothermal and photodynamic effects to destroy tumors and activate a part of the immune response. Combining with PD-1 antibody could reverse the immunosuppressive microenvironment and thoroughly activate the immune response. This platform demonstrates the superiority of combination therapy of photoimmunotherapy and PD-1 blockade in TNBC therapy.

Mace-Like Plasmonic Au-Pd Heterostructures Boost Near-Infrared Photoimmunotherapy

Photoimmunotherapy, with spatiotemporal precision and noninvasive property, has provided a novel targeted therapeutic strategy for highly malignant triple-negative breast cancer (TNBC). However, their therapeutic effect is severely restricted by the insufficient generation of tumor antigens and the weak activation of immune response, which is caused by the limited tissue penetration of light and complex immunosuppressive microenvironment. To improve the outcomes, herein, mace-like plasmonic AuPd heterostructures (Au Pd HSs) have been fabricated to boost near-infrared (NIR) photoimmunotherapy. The plasmonic Au Pd HSs exhibit strong photothermal and photodynamic effects under NIR light irradiation, effectively triggering immunogenic cell death (ICD) to activate the immune response. Meanwhile, the spiky surface of Au Pd HSs can also stimulate the maturation of DCs to present these antigens, amplifying the immune response. Ultimately, combining with anti-programmed death-ligand 1 (α-PD-L1) will further reverse the immunosuppressive microenvironment and enhance the infiltration of cytotoxic T lymphocytes (CTLs), not only eradicating primary TNBC but also completely inhibiting mimetic metastatic TNBC. Overall, the current study opens a new path for the treatment of TNBC through immunotherapy by integrating nanotopology and plasmonic performance.

ADCC enhancement: A conundrum or a boon to mAb therapy?

The ability of antibodies to distinctly identify the antigens is an important feature exploited by the scientific community for the treatment of various diseases. The therapeutic action of monoclonal antibodies (mAbs) is mediated along with the cells of the immune system, such as natural killer cells, T cells and macrophages. The two major mechanisms that govern the therapeutic efficacy of mAbs are the antibody dependent cell mediated cytotoxicity (ADCC) and the complement dependent cytotoxicity (CDC). Consequently, much of the research dedicated to improving their action is focussed on enhancing either of these mechanisms. This manuscript focuses on the strategies to enhance ADCC, for providing more efficacious mAb therapeutics. These approaches essentially bring about changes in the elements of ADCC mechanism, such as the effector cell or the antibody itself and thus favour an enhanced therapeutic response. Several technologies of ADCC enhancement have been developed, based on the success of various strategies advanced by the researchers. These technologies show success with a few antibody therapeutics while they do not work with others. This review presents a detailed overview on these strategies and presents perspectives regarding the same.

Fc-gamma IIIa-V158F receptor polymorphism contributes to the severity of Guillain-Barré syndrome

Objective

Guillain‐Barré syndrome (GBS) is a rare, life‐threatening disorder of the peripheral nervous system. Immunoglobulin G Fc‐gamma receptors (FcγRs) mediate and regulate diverse effector functions and are involved in the pathogenesis of GBS. We investigated whether the FcγR polymorphisms FcγRIIa H/R131 (rs1801274), FcγRIIIa V/F158 (rs396991), and FcγRIIIb NA1/NA2, and their haplotype patterns affect the affinity of IgG‐FcγR interactivity and influence GBS susceptibility and severity.

Methods

We determined FcγR polymorphisms in 303 patients with GBS and 302 ethnically matched healthy individuals from Bangladesh by allele‐specific polymerase chain reaction. Pairwise linkage disequilibrium and haplotype patterns were analyzed based on D ´statistics and the genotype package of R statistics, respectively. Logistic regression analysis and Fisher’s exact test with corrected P (Pc) values were employed for statistical comparisons.

Results

FcγRIIIa‐V158F was associated with the severe form of GBS compared to the mild form (P = 0.005, OR = 2.24, 95% CI = 1.28–3.91; Pc = 0.015); however, FcγR genotypes and haplotype patterns did not show any association with GBS susceptibility compared to healthy controls. FcγRIIIa‐V/V158 and FcγRIIIb‐NA2/2 were associated with recent Campylobacter jejuni infection (P ≤ 0.001, OR = 0.36, 95% CI = 0.23–0.56; Pc ≤ 0.003 and P = 0.004, OR = 1.70, 95% CI = 1.18–2.44; Pc ≤ 0.012, respectively). Haplotype 1 (FcγRIIa‐H131R‐ FcγRIIIa‐V158F‐ FcγRIIIb‐NA1/2) and the FcγRIIIb‐NA2/2 genotype were more prevalent among anti‐GM1 antibody‐positive patients (P = 0.031, OR = 9.61, 95% CI = 1.24–74.77, Pc = 0.279; P = 0.027, OR = 1.62, 95% CI = 1.06–2.5, Pc = 0.081, respectively).

Interpretation

FcγR polymorphisms and haplotypes are not associated with susceptibility to GBS, though the FcγRIIIa‐V158F genotype is associated with the severity of GBS.

Combined Magnetic Hyperthermia and Immune Therapy for Primary and Metastatic Tumor Treatments

Cancer immunotherapy shows promising potential in future cancer treatment but unfortunately is clinically unsatisfactory due to the low therapeutic efficacy and the possible severe immunotoxicity. Here we show a combined magnetic hyperthermia therapy (MHT) and checkpoint blockade immunotherapy for both primary tumor ablation and mimetic metastatic tumor inhibition. Monodispersed, high-performance superparamagnetic CoFe₂O₄@MnFe₂O₄ nanoparticles were synthesized and used for effective MHT-induced thermal ablation of primary tumors. Simultaneously, numerous tumor-associated antigens were produced to promote the maturation and activation of dendritic cells (DCs) and cytotoxic T cells for effective immunotherapy of distant mimetic metastatic tumors in a tumor-bearing mice model. The combined MHT and checkpoint blockade immunotherapy demonstrate the great potentials in the fight against both primary and metastatic tumors.

Effects of complement and serum IgG on rituximab-dependent natural killer cell-mediated cytotoxicity against Raji cells

Accumulating evidence indicates that the anti-CD20 monoclonal antibody rituximab significantly improves the clinical prognosis of patients with non-Hodgkin lymphoma and chronic lymphocytic leukemia. However, a number of patients relapse or fail to respond to rituximab. To further understand the cause of this, polymorphisms of FcγRIIIa were initially detected in healthy volunteers. Subsequently, the rituximab-dependent natural killer (NK) cell-mediated cytotoxicity of different FcγRIIIa genotypes was assessed by a cytotoxicity assay in vitro. Ultimately, the effect of human serum immunoglobulin (Ig) G and complement on rituximab-dependent NK cell-mediated cytotoxicity was evaluated in vitro. It was revealed that FcγRIIIa polymorphisms were associated with the antibody-dependent cell-mediated cytotoxicity (ADCC) of NK cells. In addition, the ADCC of NK cells with FcγRIIIa-158 V/V was increased compared with that of FcγRIIIa-158 V/F. The serum IgG and rituximab Fc segment was able to bind competitively with NK cell FcγRIIIa. It was observed that serum IgG inhibited, whereas complement enhanced rituximab-induced NK-cell mediated ADCC. Therefore, various agents administered synchronously with rituximab may modulate the efficacy of this agent and ultimately its toxicity against tumor cells.

Pharmacology of Epidermal Growth Factor Inhibitors

Research into the molecular bases of malignant diseases has yielded the development of many novel agents with potential antitumor activity. Evidence for a causative role for the epidermal growth factor receptor (EGFR), which is now regarded as an excellent target for cancer chemotherapy in human cancer, leads to the development of EGFR inhibitors. Two classes of anti-EGFR agents are currently in clinical use: monoclonal antibodies directed at the extracellular domain of the receptor, and the low-molecular-weight receptor tyrosine kinase inhibitors acting intracellularly by competing with adenosine triphosphate for binding to the tyrosine kinase portion of the EGFR. The effect on the receptor interferes with key biological functions including cell cycle arrest, potentiation of apoptosis, inhibition of angiogenesis and cell invasion and metastasis. Cetuximab, a monoclonal antibody, and the receptor tyrosine kinase inhibitors gefitinib and erlotinib are currently approved for the treatment of patients with cancer. New agents with clinical activity are entering the clinic, and new combinatorial approaches are being explored with the aim of improving the potency and pharmacokinetics of EGFR inhibition, to increase the synergistic activity in combination with chemotherapy and overcome resistance to the EGFR inhibitors.

CD89-mediated recruitment of macrophages via a bispecific antibody enhances anti-tumor efficacy

Since tumors are often infiltrated by macrophages, it would be advantageous to turn these types of cells into cytotoxic effector cells. Here, we have designed a novel bispecific antibody (BsAb) that targets both tumor antigen (CD20) and the FcαRI receptor (CD89). This antibody could be used to lyse tumors by connecting tumor cells to CD89-expressing immune effector cells such as macrophages and neutrophils. Previously there were very limited attempts to exploit FcαRI-expressing cells as effector cells for tumor cell-killing, largely due to the lack of an appropriate in vivo model, since mice do not express a human CD89 homolog. In this study, we used a transgenic mouse strain with specific expression of CD89 on macrophages and monocytes. In this transgenic mouse model, the CD89 bispecific antibody showed significant anti-tumor activities, demonstrating that bispecific antibodies can redirect macrophages, including M2 macrophages, to mediate additional effector function in the tumor microenvironment. This approach realized the full potential of the innate immune system and could be applied to other tumor-associated antigens especially the solid tumors, thus has potential to translate into clinical benefits in human cancers.

Anti-Ganglioside Antibodies Induce Nodal and Axonal Injury via Fcγ Receptor-Mediated Inflammation

Guillain-Barré syndrome (GBS) is a postinfectious autoimmune neuropathy and anti-ganglioside antibodies (Abs) are strongly associated with this disorder. Several studies have implied that specific anti-ganglioside Abs induce neuropathy in patients with axonal forms of GBS. To study the mechanisms of anti-ganglioside Abs-induced neuropathy, we established a new passive transfer mouse model by L5 spinal nerve transection (L5SNT; modified Chung's model) and systemic administration of anti-ganglioside Abs. L5SNT causes degeneration of a small proportion of fibers that constitute sciatic nerve and its branches, but importantly breaks the blood-nerve barrier, which allows access to circulating Abs and inflammatory cells. Our studies indicate that, in this mouse model, anti-ganglioside Abs induce sequential nodal and axonal injury of intact myelinated nerve fibers, recapitulating pathologic features of human disease. Notably, our results showed that immune complex formation and the activating Fc gamma receptors (FcγRs) were involved in the anti-ganglioside Abs-mediated nodal and axonal injury in this model. These studies provide new evidence that the activating FcγRs-mediated inflammation plays a critical role in anti-ganglioside Abs-induced neuropathy (injury to intact nerve fibers) in GBS.

FcγR gene copy number in Kawasaki disease and intravenous immunoglobulin treatment response

OBJECTIVE

Kawasaki disease (KD), response to intravenous immunoglobulin (IVIG) therapy, and associated coronary artery disease progression have been associated with genetic polymorphisms in Fc gamma receptor (FcγR) genes. However, it is not known whether the existing gene copy number (GCN) variability relates to KD treatment response, susceptibility, or associated sequelae.

METHODS

The copy number of individuals with KD (n=510) and their family members (n=808) for three variable FcγRs was assessed using pyrosequencing. We performed the transmission disequilibrium test to examine the association of GCN for FcγRs (FcγR2C, FcγR3A, and FcγR3B) with susceptibility and used logistic regression models to determine its association with IVIG treatment outcomes.

RESULTS

FcγR2C and FcγR3B GCN were significantly associated with KD susceptibility. IVIG response was associated with GCN variations of FcγR3B in Whites and FcγR2C in Hispanics, and gene risk score based on single nucleotide polymorphism and GCN in FcγRs were significantly different between IVIG responders and nonresponders among Whites. We found no significant associations between coronary artery disease and any of the FcγR copy numbers.

CONCLUSION

GCN of FcγR2C and FcγR3B influences IVIG treatment response and predisposes individuals to KD, providing potential insights into understanding the mechanism of the FcγR gene family in the IVIG pathway.

Knobs-into-holes antibody production in mammalian cell lines reveals that asymmetric afucosylation is sufficient for full antibody-dependent cellular cytotoxicity

Knobs-into-holes is a well-validated heterodimerization technology for the third constant domain of an antibody. This technology has been used to produce a monovalent IgG for clinical development (onartuzumab) and multiple bispecific antibodies.^1,2 The most advanced uses of this approach, however, have been limited to E. coli as an expression host to produce non-glycosylated antibodies. Here, we applied the technology to mammalian host expression systems to produce glycosylated, effector-function competent heterodimeric antibodies. In our mammalian host system, each arm is secreted as a heavy chain-light chain (H-L) fragment with either the knob or hole mutations to allow for preferential heterodimer formation in vitro with low levels of homodimer contaminants. Like full antibodies, the secreted H-L fragments undergo Fc glycosylation in the endoplasmic reticulum. Using a monospecific anti-CD20 antibody, we show that full antibody-dependent cell-mediated cytotoxicity (ADCC) activity can be retained in the context of a knobs-into-holes heterodimer. Because the knobs-into-holes mutations convert the Fc into an asymmetric heterodimer, this technology was further used to systematically explore asymmetric recognition of the Fc. Our results indicate that afucosylation of half the heterodimer is sufficient to produce ADCC-enhancement similar to that observed for a fully afucosylated antibody with wild-type Fc. However, the most dramatic effect on ADCC activity is observed when two carbohydrate chains are present rather than one, regardless of afucosylation state.

Detection of the FCGR3a polymorphism using a real-time polymerase chain reaction assay

The fragment crystallizable (Fc) region of the immunoglobulin G, low affinity III A receptor (FCGR3a, also known as CD16) belongs to the Fc gamma receptor family (FCGR), which plays an important role in immunoinflammatory processes. It is a low affinity, transmembrane receptor that is mainly expressed in monocytes, natural killer cells, and macrophages. It has been implicated in various inflammatory conditions, and recently a polymorphism (rs396991) in this gene has been shown to influence response to rituximab (anti-CD20) therapy in various disorders. We evaluated two molecular methods to genotype this polymorphism. Archived, formalin-fixed, paraffin-embedded samples from 26 biopsies of diffuse large B-cell lymphoma were retrieved and DNA was extracted. The samples were tested for the FCGR3a polymorphism using real-time polymerase chain reaction (PCR) followed by melt curve analysis or by a standard TaqMan allelic discrimination assay using the ABI 7500 FAST real-time PCR instrument. With the TaqMan allelic discrimination assay, we found that 16 cases were the wild type genotype, homozygous phenylalanine (F/F), for the FCGR3a receptor, whereas two cases had the homozygous valine (V/V) polymorphism and eight cases were heterozygous with a V/F genotype. Results with the real-time PCR followed by melt curve analysis were similar for 25 cases; however, four samples did not have sufficient DNA for the melt curve analysis method, and the result from one sample was discordant. The new TaqMan assay offers several advantages over previously published assays, such as faster turnaround time and ease of interpretation. These performance characteristics make it highly suitable for use in a clinical laboratory.

Correlation of ADCC activity with cytokine release induced by the stably expressed, glyco-engineered humanized Lewis Y-specific monoclonal antibody MB314

A major limitation to the application of therapeutic monoclonal antibodies (mAbs) is their reduced in vivo efficacy compared with the high efficacy measured in vitro. Effector functions such as antibody-dependent cell-mediated cytotoxicity (ADCC) are dramatically reduced in vivo by the presence of high amounts of endogenous IgG in the serum. Recent studies have shown that modification of the glycosylation moieties attached to the Fc part of the mAb can enhance binding affinity to FcγRIIIα receptors on natural killer cells and thus may counteract the reduced in vivo efficacy. In the present study, a humanized IgG1/κ monoclonal antibody recognizing the tumor-associated carbohydrate antigen Lewis Y was stably produced in a moss expression system that allows glyco-engineering. The glyco-modified mAb (designated MB314) showed a highly homogeneous N-glycosylation pattern lacking core-fucose. A side-by-side comparison to its parental counterpart produced in conventional mammalian cell-culture (MB311, formerly known as IGN311) by fluorescence-activated cell sorting analysis confirmed that the target specificity of MB314 is similar to that of MB311. In contrast, ADCC effector function of MB314 was increased up to 40-fold whereas complement dependent cytotoxicity activity was decreased 5-fold. Notably, a release of immunostimulatory cytokines, including interferon γ, monocyte chemotactic protein-1 (MCP-1), interleukin-6 and tumor necrosis factor (TNF) was particularly induced with the glyco-modified antibody. TNF release was associated with CD14 (+) cells, indicating activation of monocytes.

Involvement of Stat1 in the phagocytosis of M. avium

Mycobacterium avium is an intracellular pathogen preferentially infecting human macrophages where they activate the JAK/STAT1 pathway. This activation enhances the survival of infected cells, but, at the same time, makes macrophages optimal targets for drugs development against p-tyr₇₀₁stat1. In this study, we demonstrate that the fast and transient activity of the JAK/STAT1 pathway occurs immediately after macrophages internalization of heat-killed M. avium or inert particles. Furthermore, we show that a persistent Stat1 pathway activation occurs only when an intracellular M. avium infection is established in macrophages. These results strongly indicate different mechanisms of p-tyr₇₀₁Stat1 activation. In particular, here we report findings aiming at explaining the short-time enhancement of p-tyr₇₀₁Stat1 and shows its predominant relationship with FcγRs engagement during the internalization process. Furthermore, we demonstrate that opsonized live M. avium is phagocytosed by macrophages involving membrane receptors not related with JAK/STAT1 signalling pathway. On the contrary, heat-inactivated bacilli or latex particles seem to be internalized only after involvement of FcγRs and subsequent Stat1 phosphorylation.

The effect of TNF-alpha, FcγR and CD1 polymorphisms on Guillain-Barré syndrome risk: evidences from a meta-analysis

BACKGROUND AND OBJECTIVES

The findings on the associations between potential genetic variants and risk of Guillain-Barré syndrome (GBS) are controversial. We conducted a meta-analysis for candidate genes to provide the evidences for the current understanding of the genetic association with GBS.

METHODS

We searched relevant studies without language restriction in PubMed, Embase and Cochrane library through May 2011. The strengths of the associations between genetic variants and GBS risk were estimated by odds ratios (ORs) with 95% confidence intervals (CIs). Random-effects models or fixed effects model was applied based on the heterogeneity test.

RESULTS

We identified 12 case-control studies involving 1,590 GBS cases and 2,154 controls for the analysis. Because of limited eligible data, our meta-analysis specifically focused on 6 genetic variants of 3 candidate genes, TNF-α, FcγR and CD1. We found that TNF-α 308 G/A polymorphism was significantly associated with the risk of GBS in the overall population (GG+GA vs. AA: OR=0.32, 95%CI=0.16-0.62; GG vs. AA: OR=0.36, 95%CI=0.19-0.68). Subgroup analysis further provided evidence of significant association between TNF-α 308 G/A and risk of the GBS in Asian population (GG+GA vs. AA: OR=32, 95%CI=0.11-0.93; GG vs. AA: OR=0.32, 95%CI=0.15-0.68). In addition, we did not observe significant associations between FcγRIIA R/H, FcγRIIIA F/V, FcγRIIIB NA1/NA2, CD1A 1/2 and CD1E 1/2 polymorphisms and susceptibility for developing GBS.

CONCLUSIONS

Our findings showed that TNF-α 308A allele might be a moderate risk factor for GBS. However, the results should be interpreted with caution due to the limited number of studies available.

Brucella abortus inhibits IFN-γ-induced FcγRI expression and FcγRI-restricted phagocytosis via toll-like receptor 2 on human monocytes/macrophages

The strategies that allow Brucella abortus to persist for years inside macrophages subverting host immune responses are not completely understood. Immunity against this bacterium relies on the capacity of IFN-γ to activate macrophages, endowing them with the ability to destroy intracellular bacteria. We report here that infection with B. abortus down-modulates the expression of the type I receptor for the Fc portion of IgG (FcγRI, CD64) and FcγRI-restricted phagocytosis regulated by IFN-γ in human monocytes/macrophages. Both phenomena were not dependent on bacterial viability, since they were also induced by heat-killed B. abortus (HKBA), suggesting that they were elicited by a structural bacterial component. Accordingly, a prototypical B. abortus lipoprotein (L-Omp19), but not its unlipidated form, inhibited both CD64 expression and FcγRI-restricted phagocytosis regulated by IFN-γ. Moreover, a synthetic lipohexapeptide that mimics the structure of the protein lipid moiety also inhibited CD64 expression, indicating that any Brucella lipoprotein could down-modulate CD64 expression and FcγRI-restricted phagocytosis. Pre-incubation of monocytes/macrophages with anti-TLR2 mAb blocked the inhibition of the CD64 expression mediated by HKBA and L-Omp19. These results, together with our previous observations establish that B. abortus utilizes its lipoproteins to inhibit the monocytes/macrophages activation mediated by IFN-γ and to subvert host immunonological responses.

Analysis of MIF, FCGR2A and FCGR3A gene polymorphisms with susceptibility to pulmonary tuberculosis in Moroccan population

In order to investigate the influence of functional polymorphisms of macrophage migration inhibitory factor (MIF), Fcg receptors CD16A (FCGR3A) and CD32A (FCGR2A) genes on susceptibility to pulmonary tuberculosis (PTB) in the Moroccan population, we analyzed 123 patients with PTB and 154 healthy controls. The genotyping for MIF-173 (G/C) (rs755622), FCGR2A-131H/R (rs1801274) and FCGR3A-158V/F (rs396991) was carried out using TaqMan SNP Genotyping Assay method. We found a statistically significant increase of the MIF -173CC homozygote genotype and MIF -173*C allele frequencies in PTB patients compared with healthy controls (17.07%versus 5.84%, P = 0.003; and 35.37%versus 26.30%, P = 0.02; respectively). In contrast, no association was observed between FCGR2A-131H/R and FCGR3A-158V/F polymorphisms and tuberculosis disease. Our finding suggests that MIF -173*C variant may play an important role in the development of active tuberculosis.

The influence of IgG density and macrophage Fc (gamma) receptor cross-linking on phagocytosis and IL-10 production

We have previously demonstrated that the addition of immune complexes (IC) to stimulated macrophages could profoundly influence cytokine production. In the present work we sought to determine the density of IgG on immune complexes necessary to mediate phagocytosis, inhibit IL-12 production and induce IL-10 production from stimulated macrophages. We developed immune complexes with predictable average densities of surface-bound immunoglobulin. We show that a threshold amount of IgG was necessary to mediate attachment of IC to macrophages. At progressively higher densities of IgG, Fc receptor-mediated phagocytosis resulted in an inhibition of IL-12 production and then an induction of IL-10. The reciprocal alterations in these two cytokines occurred when as little as one optimally opsonized SRBC was bound per macrophage. Macrophage IL-10 induction by immune complexes was associated with the activation of the MAP kinase, ERK, which was progressively increased as a function of IgG density. We conclude that signal transduction through the macrophage Fcγ receptors vary as a function of signal strength. At moderate IgG densities, especially in the presence of complement, efficient phagocytosis occurs in the absence of cytokine alterations. At slightly higher IgG densities IL-12 production is shut off and eventually IL-10 induction occurs. Thus, the myriad events emanating from FcγR ligation depends on the density of immune complexes, allowing the Fc receptors to fine-tune cellular responses depending on the extent of receptor cross-linking.

Characterization of porcine CD205

Dendritic cells express a type cell-surface receptor, CD205 that plays a role in antigen capture and delivery to the endocytic pathway. Besides DCs, high CD205 expression is also detected on thymic epithelial cells but B cells, macrophages, and T cells have limited or no expression. CD205 has been characterized in several animal species except swine. The aim of this work was to characterize porcine CD205 and mRNA expression on different cells and tissues involved in immune responses. A complete porcine CD205 sequence of 5175bp was obtained from porcine thymus cDNA by PCR gene-walking strategy and this gene encoded a protein of 1723 amino acids. The multi-domain structure reported for murine, human, and bovine CD205 was also conserved in porcine with an overall amino acid identity of 74, 81, and 85%, respectively. Quantitative RT-PCR analysis of the CD205 mRNA profiles in normal porcine tissues and cells showed that thymus and Langerhans cells expressed the highest levels. Further characterization of porcine CD205 will lead to better understanding of the role of this receptor and development of contemporary strategies for antigen targeting to DCs in swine.

Immunoglobulin IgG Fc-receptor polymorphisms and HLA class II molecules in Guillain-Barré syndrome

OBJECTIVE

To analyze host genetic factors immunoglobulin G Fc receptors (FcgammaRs) and human leukocyte antigen (HLA) class II in GBS patients.

METHODS

FcgammaRIIA, IIIA and IIIB polymorphisms were studied in 80 each GBS patients and healthy controls by allele specific PCR. HLA class II DRbeta1 and DQbeta1 typing was performed at the two-digit level by PCR in randomly selected 54 GBS patients and 202 controls.

RESULTS

FcgammaRIIA-H/H (56% vs 9%; P < 0.0001) and FcgammaRIIIA-V/V (40% vs 13%; P < 0.0001) genotypes, H131 allele frequencies (0.73 vs 0.26, P < 0.0001) and HLA DQbeta1*060x (OR, 1.96; 95% CI, 1.26-3.04; P < 0.01) were significantly increased in GBS than controls. DRbeta1*0701 alone (OR, 10; 95% CI, 45.90-2.25; P < 0.001) and together with FcgammaRIIA-H/H (OR, 11.03; 95% CI, 2.63-46.20; P < 0.001) was significantly associated with GBS patients having microbiological evidence of recent infection.

CONCLUSIONS

The study indicates that homozygous FcgammaRIIA and FcgammaRIIIA genotypes and FcgammaRIIA H131 allele are associated with GBS. HLA class II molecule DRbeta1*0701 is identified as novel genetic risk factor for development of GBS in patients with preceding infection.

A versatile bifunctional dendritic cell targeting vaccine vector

We have developed an efficient versatile in vivo dendritic cell (DC) targeting vector for delivering different classes of antigens such as proteins, peptide, glycolipids and naked DNA for vaccine applications. A single chain antibody (scFv) that recognizes DEC-205 receptor of DC was fused with a core-streptavidin domain and expressed in Escherichia coli using the T7 expression system. The bifunctional fusion protein (bfFp) was expressed as a periplasmic soluble protein and affinity-purified in its monomeric form. The bifunctional activity against DEC-205 and biotin was characterized by ELISA and Western blot. In vivo DC targeting of a diverse group of biotinylated antigens such as viral and bacterial proteins, a cancer peptide, gangliosides and DNA of certain infectious diseases was conducted in mice. Results show that in the presence of bfFp and costimulatory anti-CD40 mAb, both humoral and cell-mediated responses were augmented in either the single antigen or multiple antigen targeting strategy. Lastly, bfFp based DC targeting of antigens in low doses may be a useful strategy for the design of monovalent or polyvalent vaccines for the masses.

Induction of anti-tumor immunity by trifunctional antibodies in patients with peritoneal carcinomatosis

Peritoneal carcinomatosis (PC) from epithelial tumors is a fatal diagnosis without efficient treatment. Trifunctional antibodies (trAb) are novel therapeutic approaches leading to a concerted anti-tumor activity resulting in tumor cell destruction. In addition, preclinical data in mouse tumor models demonstrated the induction of long lasting tumor immunity after treatment with trAb. We describe the induction of anti-tumor specific T-lymphocytes after intraperitoneal administration of trAb in patients with PC.

9 patients with progressive PC from gastric (n = 6) and ovarian cancer (n = 2), and cancer of unknown primary (n = 1) received 3 escalating doses of trAb after surgery and/or ineffective chemotherapy. The trAb EpCAM × CD3 (10, 20, 40 μg) or HER2/neu × CD3 (10, 40, 80 μg) were applicated by intraperitoneal infusion. Four weeks after the last trAb application, all patients were restimulated by subdermal injection of trAb + autologous PBMC + irradiated autologous tumor cells. Immunological reactivity was tested by analyzing PBMC for specific tumor reactive CD4+/CD8+ T lymphocytes using an IFN-γ secretion assay.

In 5 of 9 patients, tumor reactive CD4+/CD8+ T-lymphocytes increased significantly, indicating specific anti-tumor immunity. A clinical response (stable disease, partial regression) has been observed in 5 of 9 patients, with a mean time to progression of 3.6 months. Follow-up showed a mean survival of 11.8 months (median 8.0 months) after trAb therapy.

TrAb are able to induce anti-tumor immunity after intraperitoneal application and restimulation. The induction of long-lasting anti-tumor immunity may provide an additional benefit of the intraperitoneal therapy with trAb and should be further elevated in larger clinical trials.

Selective expression of inhibitory Fcgamma receptor by metastatic melanoma impairs tumor susceptibility to IgG-dependent cellular response

During melanoma progression, patients develop anti-tumor immunity including the production of anti-tumor antibodies. Although the strategies developed by malignant cells to escape anti-tumor cellular immunity have been extensively investigated, little is known about tumor resistance to humoral immunity. The main effect of IgG antibodies is to activate the immune response by binding to host Fc gamma receptors (FcgammaR) expressed by immune cells. We previously reported in a limited study that some human metastatic melanoma cells ectopically express the FcgammaRIIB1, an inhibitory isoform of FcgammaR. By analyzing a large panel of different types of human primary and metastatic solid tumors, we report herein that expression of FcgammaRIIB is restricted to melanoma and is acquired during tumor progression. We show that FcgammaRIIB expression prevents the lysis of human metastatic melanoma cells by NK cell-mediated antibody-dependent cellular cytotoxicity (ADCC) in vitro, independently of the intracytoplasmic region of FcgammaRIIB. Using experimental mouse models, we demonstrate that expression of FcgammaRIIB protects B16F0 melanoma tumors from the ADCC induced by monoclonal and polyclonal anti-tumor IgG in vivo. Thus, our results identify FcgammaRIIB as a marker of human metastatic melanoma that impairs the tumor susceptibility to FcgammaR-dependent innate effector responses.

Expression of FcgammaRs and mCD14 on polymorphonuclear neutrophils and monocytes may determine periodontal infection

Variance in expression of receptors for immunoglobulin G (FcgammaRs), complement (CR3) and lipopolysaccharide (mCD14) on polymorphonuclear neutrophils (PMNs) and monocytes might affect susceptibility for infection with certain pathogens in periodontitis, a chronic infectious disease of tooth-supportive tissues. Levels of FcgammaRI, IIa, III, CR3 and mCD14 on PMNs and monocytes were measured in 19 periodontitis patients and 18 healthy controls. Subgingival infection with Aggregatibacter actinomycetemcomitans (Aa) and Porphyromonas gingivalis (Pg) was determined. Activation of PMNs and monocytes in response to stimulation with Aa and Pg was assessed by means of change in mCD14 expression. Periodontitis is associated with an enrichment of the FcgammaRIII(+) monocytes (P = 0.015) with concomitant low mCD14 (P = 0.001). Unadjusted data showed that the subjects culture-positive for Aa (Aa(+)) had significantly lower expression of monocytic FcgammaRI (P = 0.005) and FcgammaRIIa (P = 0.015) than Pg(+) subjects. The FcgammaRI was still lower on monocytes from Aa(+) subjects after adjusting for the background factors (P = 0.037). PMNs from Aa(+) subjects responded in a hyper-reactive manner, in particular when stimulated with Aa (P = 0.011). Lower FcgammaRs expression by monocytes is related to a higher susceptibility of a subject to become infected with Aa. The higher proportion of FcgammaRIII(+) monocytes may be involved in the chronicity of this condition. Hyper-reactive PMNs in Aa(+) subjects may contribute to accelerated breakdown of tooth-supportive tissues.

A phase-I trial of the epidermal growth factor receptor directed bispecific antibody MDX-447 without and with recombinant human granulocyte-colony stimulating factor in patients with advanced solid tumors

INTRODUCTION

MDX-447 is a bispecific antibody directed against the epidermal growth factor receptor (EGFR) and the high affinity Fc receptor (FcgammaRI). Preclinical data suggest that co-administration of granulocyte-colony stimulating factor (G-CSF) may enhance the tumor cytotoxicity of bispecific antibodies.

METHODS

In group 1, patients received MDX-447 intravenously (i.v.) weekly. Dose levels of MDX-447 evaluated in group 1 were 1, 3.5, 7, 10, 15, 20, 30, and 40 mg/m(2). In group 2, patients received MDX-447 IV weekly with G-CSF (3 mcg/kg/day) subcutaneously (days -3 to +2, 5-9, 12-16, etc.). Dose levels of MDX-447 evaluated in group 2 were 1, 3.5, 7, 10, and 15 mg/m(2).

RESULTS

Sixty-four patients with advanced solid tumors were treated. Forty-one patients received MDX-447 alone (group 1); 23 patients received MDX-447 + G-CSF (group 2). Hypotension was the predominant dose-limiting toxicity (DLT) in both treatment groups, with seven patients experiencing >or= grade 3 events. MDX-447 half-life (T(1/2)) ranged from 1.9 to 8.4 h, with no obvious differences between the two treatment groups. MDX-447 binding to neutrophils and peak levels of circulating tumor necrosis factor alpha (TNFalpha) and interleukin-6 (IL-6) were higher in group 2. The MTD for MDX-447 alone was 30 mg/m(2). When G-CSF was given with MDX-447, treatment was not well tolerated and group 2 was closed early because of safety concerns, with the last patient being treated at the 7 mg/m(2) dose level. There were no objective complete or partial responses in either group.

CONCLUSION

MDX-447 alone was generally well tolerated, but did not achieve objective tumor responses. The MTD for MDX-447 alone was 30 mg/m(2) weekly. Co-administration of G-CSF with MDX-447 precluded meaningful dose escalation.

Rheumatoid peripheral blood phagocytes are primed for activation but have impaired Fc-mediated generation of reactive oxygen species

Significant levels of circulating immune complexes (ICs) containing rheumatoid factors and immunoglobulin G in peripheral blood are a characteristic feature of rheumatoid arthritis (RA). ICs interact through Fcγ receptors (FcγR) to activate phagocytes in numerous inflammatory processes. The high concentration of neutrophils in synovial fluid during active phases of the disease, together with their destructive capacity, pose important questions as to their role in the pathogenesis of RA. Functional defects in RA or control peripheral blood neutrophil FcγRs were examined with a specific FcγR-mediated reactive oxygen species (ROS) assay. Heterologous cross-linking of FcγRIIa and FcγRIIIb on neutrophils resulted in a significantly decreased production of ROS by RA cells compared with controls matched for age and sex. However, expression and homologous ligation of receptors did not differ between these groups. These data suggest that neutrophil priming does occur before emigration into the joint and that blood neutrophils from patients with RA have a functional impairment in cooperative FcγR-mediated ROS generation. This may account for the increased susceptibility to bacterial infection that arises in patients with severe disease.

The importance of human FcgammaRI in mediating protection to malaria

The success of passive immunization suggests that antibody-based therapies will be effective at controlling malaria. We describe the development of fully human antibodies specific for Plasmodium falciparum by antibody repertoire cloning from phage display libraries generated from immune Gambian adults. Although these novel reagents bind with strong affinity to malaria parasites, it remains unclear if in vitro assays are predictive of functional immunity in humans, due to the lack of suitable animal models permissive for P. falciparum. A potentially useful solution described herein allows the antimalarial efficacy of human antibodies to be determined using rodent malaria parasites transgenic for P. falciparum antigens in mice also transgenic for human Fc-receptors. These human IgG1s cured animals of an otherwise lethal malaria infection, and protection was crucially dependent on human FcγRI. This important finding documents the capacity of FcγRI to mediate potent antimalaria immunity and supports the development of FcγRI-directed therapy for human malaria.

Malaria rivals HIV and tuberculosis as the world's most deadly infection killing a child every 30 seconds. Antibodies and their receptors (Fc-receptors) have been shown to be vital for the development of protective immunity, and as such they act as correlates of protection in studies aimed at defining the best antigens to incorporate into current vaccines. Understanding antibody types and Fc-receptors that optimally induce immunity is therefore vital to developing the best vaccines. Surrogate markers of antibody efficacy currently rely on in vitro assays that are laborious and difficult to reproduce. It remains unclear if such in vitro assays are predictive of functional immunity in humans due to the lack of suitable animal models permissive for Plasmodium falciparum. Here, we create a transgenic in vivo mouse model that has significant advantage over the use of new world primates, the only other model for human malaria. We demonstrate that this model defines an Fc-dependent mechanism of parasite destruction that cannot be assessed in current in vitro assays. The model provides both a test for therapeutic antibody efficacy prior to clinical trials in humans and an important tool in malaria vaccine development.

The involvement of Fc gamma receptor gene polymorphisms in Kawasaki disease

Kawasaki disease is an acute febrile syndrome in infancy, characterized by vasculitis of medium-sized arteries. Without treatment the disease can lead to coronary artery lesions (CAL) in approximately 25% of the children. Therapy consists of intravenous immunoglobulins (IVIG), leading to a decrease of complications to 5-16%. Little is known about the working mechanisms of IVIG. In this study we evaluated the involvement of Fcgamma receptors (FcgammaRs) in Kawasaki disease by the determination of the frequency of known single nucleotide polymorphisms (SNPs) in the genes coding for the FcgammaRs and compared this with frequencies in a cohort of healthy controls. There was no difference in the distribution of the functionally relevant genotypes for FcgammaRIIa-131H/R, FcgammaRIIb-232I/T, FcgammaRIIIa-158 V/F and FcgammaRIIIb-NA1/NA2 between the patient group and the healthy controls. Furthermore, there were no polymorphisms linked to the disease severity as indicated by the absence or development of CAL during the disease. Altered transcription or expression of FcgammaR on specific cell types of the immune system may still play a role in susceptibility and treatment success, but at a level different from the functional SNPs in FcgammaR genes tested in this study.

Role of apoptotic signaling pathways in regulation of inflammatory responses to ricin in primary murine macrophages

Because of its lethal effects, ease of preparation, and ability to be delivered by aerosolization, ricin has been developed as a lethal weapon by various terrorist groups. When introduced into the pulmonary system of rodents, ricin causes pathological changes in the lung that are known to occur in acute respiratory distress syndrome (ARDS). Early response cytokines such as TNF-alpha and IL-1 are known to play a critical role in the pathogenesis of ARDS. Ricin induces the release of these pro-inflammatory cytokines and the transcriptional activation of the genes that encode them in vitro and in vivo. Macrophages, considered to act as upstream regulators of inflammatory cascades, may play a central role in the pathogenesis and the development of ricin-induced ARDS because of their ability to make and secrete pro-inflammatory cytokines. Exposure of primary macrophages to ricin in vitro led to activation of stress-activated protein kinases, increased expression of pro-inflammatory mRNA transcripts, subsequent increase in the synthesis and secretion of TNF-alpha, and apoptotic cell death. Interestingly, macrophages required the engagement of the apoptotic cascade for the maximal synthesis and release of some pro-inflammatory mediators. This work identifies a cross talk between the apoptotic and inflammatory signaling pathways induced by ricin in primary macrophages.

Systemic lupus erythematosus: multiple immunological phenotypes in a complex genetic disease

Systemic lupus erythematosus (SLE) is a complex polygenic autoimmune disease characterized by the presence of anti-nuclear autoantibodies (ANAs) that are often detectable years prior to the onset of clinical disease. The disease is associated with a chronic activation of the immune system, with the most severe forms progressing to inflammatory damage that can impact multiple organ systems in afflicted individuals. Current therapeutic strategies poorly control disease manifestations and are generally immunosuppressive. Recent studies in human patient populations and animal models have associated elements of the innate immune system and abnormalities in the immature B lymphocyte receptor repertoires with disease initiation. A variety of cytokines, most notably type I interferons, play important roles in disease pathogenesis and effector mechanisms. The genetic basis for disease susceptibility is complex, and analyses in humans and mice have identified multiple susceptibility loci, several of which are located in genomic regions that are syntenic between humans and mice. The complexities of the genetic interactions that mediate lupus have been investigated in murine model systems by characterizing the progressive development of disease in strains expressing various combinations of susceptibility alleles. These analyses indicate that genetic epistasis dramatically impact disease development and support the feasibility of identifying molecular pathways that can suppress disease progression without completely impairing normal immune function.

Fc gamma receptors and cancer

FcgammaRs are a family of heterogeneous molecules that play opposite roles in immune response and control the effector functions of IgG antibodies. In many cancers, IgG antibodies are produced that recognize cancer cells, form immune complexes and therefore, activate FcgammaR. The therapeutic efficacy of monoclonal IgG antibodies against hematopoietic and epithelial tumors also argue for an important role of IgG antibodies in anti-tumor defenses. Since the 1980s, a series of lines of evidence in experimental models and in humans strongly suggest that FcgammaR are involved in the therapeutic activity of monoclonal IgG antibodies by activating the cytotoxic activity of FcgammaR-positive cells such as NK cells, monocytes, macrophages and neutrophils and by increasing antigen presentation by dendritic cells. Since many cell types co-express activating and inhibitory FcgammaR, the FcgammaR-dependent effector functions of IgG anti-tumor antibodies are counterbalanced by the inhibitory FcgammaRIIB. In addition, some tumor cells express FcgammaR either constitutively, such as B cell lymphomas or ectopically, such as 40% of human metastatic melanoma. The tumor FcgammaR isoform is preferentially FcgammaRIIB, which is functional at least in human metastatic melanoma. This review summarizes these data and discusses how FcgammaRIIB expression may influence the anti-tumor immune reaction and how beneficial or deleterious this expression could be for the efficiency of therapeutics based on monoclonal anti-tumor antibodies.

Compensation of endogenous IgG mediated inhibition of antibody-dependent cellular cytotoxicity by glyco-engineering of therapeutic antibodies

A major limitation to the application of therapeutic IgG antibodies (Abs) is their reduced in vivo efficacy compared to their high efficacy as measured in vitro. Recently, Preithner et al. showed that the high amount of endogenous serum IgG impairs the antibody-dependent cellular cytotoxicity effector function (ADCC) of therapeutic Abs in vivo by competing for binding to Fcgamma-RIII on the effector cells. Modification of the glycosylation moieties attached to the Fc part of the Ab, e.g. de-fucosylation, has been shown to increase ADCC activity. We here show that the ADCC activity of a fucose-deficient, moss-produced therapeutic IgG is not impaired by normal human serum. The increased ADCC activity of the fucose-deficient Ab variant even in the presence of high endogenous IgG indicates that glyco-engineering of Abs may translate into improved clinical efficacy. Noteworthy, moss production of glyco-modified Abs should be applicable to a broad variety of therapeutic Abs currently in use indicative for the potential of this technology platform.

Targeting antigens to dendritic cells in vivo

Dendritic cells (DCs) play a key role in antigen-specific immune regulation. DCs take up and process antigens and present these as peptides through MHC molecules to T cells. Recent pre-clinical and clinical studies have exploited DCs as a means to improve vaccine efficiency. In these studies, monocyte-derived autologous DCs are loaded ex vivo with antigens and re-administered to the patient. These tailor-made vaccines are costly and labor intensive, and therefore less suitable for large-scale immunization programs. As a next step in the development of DC vaccines, it is proposed to load DCs with antigens in vivo. Drug delivery systems harboring antigens have been targeted to DCs via specific surface receptors preferentially expressed by DCs, resulting in priming of humoral and cellular immune responses. The present review focuses on the various antigen delivery systems that are currently in use and the DC surface receptors they target.

CD64-Directed Immunotoxin Inhibits Arthritis in a Novel CD64 Transgenic Rat Model

Macrophages are known to play a key role during inflammation in rheumatoid arthritis (RA). Inflammatory macrophages have increased expression of CD64, the high-affinity receptor for IgG. Targeting this receptor through a CD64-directed immunotoxin, composed of an Ab against CD64 and Ricin A, results in effective killing of inflammatory macrophages. In this study, we show elevated levels of CD64 on synovial macrophages in both synovial lining and synovial fluid in RA patients. The CD64-directed immunotoxin efficiently eliminates activated synovial macrophages in vitro, while leaving quiescent, low CD64-expressing macrophages unaffected. To examine whether killing of CD64 macrophages results in therapeutic effects in vivo, we established an adjuvant arthritis (AA) model in newly generated human CD64 (hCD64) transgenic rats. We demonstrate that hCD64 regulation in this transgenic rat model is similar as in humans. After AA induction, treatment with CD64-directed immunotoxin results in significant inhibition of disease activity. There is a direct correlation between immunotoxin treatment and decreased macrophage numbers, followed by diminished inflammation and bone erosion in paws of these hCD64 transgenic rats. These data support synovial macrophages to play a crucial role in joint inflammation in AA in rats and in human RA. Selective elimination of inflammatory macrophages through a CD64-directed immunotoxin may provide a novel approach for treatment of RA.

Efficient inhibition of HIV-1 replication in human immature monocyte-derived dendritic cells by purified anti-HIV-1 IgG without induction of maturation

During mucosal HIV transmission, immature dendritic cells (DCs) present in the mucosa are among the first cellular targets of the virus. Previous studies have analyzed the inhibition of HIV-1 transfer from human mature DCs to T lymphocytes by neutralizing IgG, but so far no in vitro data regarding the capacity of antibodies to inhibit HIV-1 infection of immature DCs have been reported. Here, we found an increased HIV-inhibitory activity of monoclonal IgG and purified polyclonal IgG when immature monocyte-derived dendritic cells (iMDDCs) were used as target cells instead of autologous blood lymphocytes. We showed that FcgammaRII is involved in the mechanism for inhibiting HIV-1 infection of iMDDCs by IgG, whereas no induction of maturation was detected at concentrations of IgG that result in a 90% reduction of HIV replication. After induction of FcgammaRI expression on iMDDCs by IFN-gamma, an augmentation of the HIV-inhibitory activity of IgG, related to the expression of FcgammaRI, was observed. Taken together, our results demonstrate the participation of FcgammaRs in HIV-1 inhibition by IgG when iMDDCs are the targets. We propose that IgG is able to efficiently inhibit HIV-1 replication in iMDDCs and should be one of the components to be induced by vaccination.

Cancer immunotherapy

Cancer is the second leading cause of death in the industrialized world. Most cancer patients are treated by a combination of surgery, radiation and/or chemotherapy. Whereas the primary tumor can, in most cases, be efficiently treated by a combination of these standard therapies, preventing the metastatic spread of the disease through disseminated tumor cells is often not effective. The eradication of disseminated tumor cells present in the blood circulation and micro-metastases in distant organs therefore represents another promising approach in cancer immunotherapy. Main strategies of cancer immunotherapy aim at exploiting the therapeutic potential of tumor-specific antibodies and cellular immune effector mechanisms. Whereas passive antibody therapy relies on the repeated application of large quantities of tumor antigen-specific antibodies, active immunotherapy aims at the generation of a tumor-specific immune response combining both humoral and cytotoxic T cell effector mechanisms by the host's immune system following vaccination. In the first part of this review, concurrent developments in active and passive cancer immunotherapy are discussed. In the second part, the various approaches for the production of optimized monoclonal antibodies used for anti-cancer vaccination are summarized.

The Carbohydrate at FcγRIIIa Asn-162

FcgammaRIIIa plays a prominent role in the elimination of tumor cells by antibody-based cancer therapies. Non-fucosylated bisected IgGs bind this receptor with increased affinity and trigger FcgammaRIII-mediated effector functions more efficiently than native, fucosylated antibodies. In this study the contribution of the carbohydrates of both binding partners to the strength of the complex was analyzed. Glycoengineering of the antibody increased affinity for two polymorphic forms of soluble human FcgammaRIIIa (by up to 50-fold) but did not affect binding to the inhibitory FcgammaRIIb receptor. While the absence of carbohydrate at FcgammaRIIIa's Asn-162 increased affinity for native IgG, presumably due to the removal of steric hindrance caused by the bulky sugars, it unexpectedly reduced affinity for glycoengineered (GE) antibodies by over one order of magnitude, bringing the affinity down to the same level as for native IgG. We conclude that the high affinity between GE antibodies and FcgammaRIII is mediated by productive interactions formed between the receptor carbohydrate attached at Asn-162 and regions of the Fc that are only accessible when it is nonfucosylated. As FcgammaRIIIa and FcgammaRIIIb are the only human Fcgamma receptors glycosylated at this position, the proposed interactions explain the observed selective affinity increase of GE antibodies for only these receptors. Furthermore, we predict from our structural model that only one of the two Fc-fucose residues needs to be absent for increased binding affinity toward FcgammaRIII. This information can be exploited for the design of new antibodies with altered Fc receptor binding affinity and enhanced therapeutic potential.

Improved effector functions of a therapeutic monoclonal Lewis Y-specific antibody by glycoform engineering

The aim of the present study was to produce glycosylation variants of the therapeutic Lewis Y-specific humanized IgG1 antibody IGN311 to enhance cell-killing effector function. This was achieved via genetic engineering of the glycosylation machinery of the antibody-producing host. Antibody genes were transiently cotransfected with acetyl-glycosaminyltransferase-III genes into human embryonic kidney-EBV nuclear antigen cells. A control wild-type antibody, IGN311wt, was expressed in the same host using identical expression vectors, but without cotransfection of genes for acetyl-glycosaminyltransferase-III expression. Both expression products were purified to homogeneity and characterized. The glyco-engineered expression product (IGN312-Glyco-I) showed a remarkably homogenous N-linked glycosylation pattern consisting of one major hybrid-type, non-fucosylated and agalactosylated form carrying a bisecting GlcNAc-group. Wild-type expression product (IGN311wt) on the other hand was glycosylated by a multitude of different core-fucosylated complex-type structures of variable degrees of galactosylation. Target affinity of the glyco-engineered antibody as well as heavy and light chain assembly were not affected by acetyl-glycosaminyltransferase-III expression. In vitro experiments showed a approximately 10-fold increase of antibody-dependent cellular cytotoxicity of the glyco-engineered antibody using different Lewis Y-positive target cancer cell lines (SK-BR-3, SK-BR-5, OVCAR-3, and Kato-III). Complement-mediated cytotoxicity of IGN312-Glyco-I was 0.4-fold reduced using SK-BR-5 as target cell line. The reduction of complement activation could be prevented and even converted into a slight increase of activity by using a different molecular-biological approach directing the glycosylation towards increased levels of complex N-linked oligosaccharides of bisected, non-fucosylated type, as a result of cotransfection of mannosidase II together with acetyl-glycosaminyltransferase-III.

Human macrophages simultaneously express membrane-C1q and Fc-receptors for IgG

Membrane C1q (mC1q) of macrophages (MPhi) is a precursor of the IgG-binding serum protein C1q. Thus, mC1q potentially provides one of several Fcgamma binding sites of mature MPhi and we analyzed whether simultaneous expression occurs of established receptors for IgG, FcgammaRI, II, and III, and mC1q during in vitro differentiation of MPhi. Using flow cytometry, immunoprecipitation combined with Western blotting and Northern blot analysis mC1q was hardly detected in freshly isolated blood monocytes, but increasingly in developing monocyte-derived MPhi. Laser scanning fluorescence microscopy confirmed the membrane localization of mC1q. Two-color-staining flow cytometry experiments indicated that mC1q and all three types of FcgammaRs are simultaneously expressed on mature monocyte-derived MPhi. A high correlation was found for the expression of mC1q and FcgammaRs, in particular FcgammaRII, but not mC1q and CD14, another marker of monocytes/MPhi.