CD32B, the human inhibitory Fc-γ receptor IIB, as a target for monoclonal antibody therapy of B-cell lymphoma

The Immunosuppressive Receptor CD32b Regulation of Macrophage Polarization and Its Implications in Tumor Progression

Macrophages, pivotal components of the immune system, orchestrate host defense mechanisms in humans and mammals. Their polarization into classically activated macrophages (CAMs or M1) and alternatively activated macrophages (AAMs or M2) dictates distinct functional roles in immunity and tissue homeostasis. While the negative regulatory role of CD32b within the FC gamma receptor (FCγR) family is recognized across various immune cell types, its influence on macrophage polarization remains elusive. This study aimed to elucidate the regulatory role of CD32b in macrophage polarization and discern the differential expression markers between the M1 and M2 phenotypes following CD32b siRNA transfection. The results revealed a decrease in the CD32b levels in lipopolysaccharide (LPS)-treated M1 and an increase in interleukin-4 (IL-4)-treated M2 macrophages, as observed in macrophage Raw264.7 cells. Furthermore, CD32b siRNA transfection significantly downregulated the M2 markers (IL-10, VEGF, Arg-1, and STAT6), while upregulating the M1 markers (IL-6, NF-κB, NOS2, and STAT1) in the Raw264.7 cells. Similar findings were recapitulated in macrophage-rich adherent cells isolated from mouse spleens. Additionally, the cytopathological analysis of pleural effusions and ascitic fluids from patients with cancer revealed a positive correlation between advanced tumor stages, metastasis, and elevated CD32b levels. In conclusion, this study highlights the regulatory influence of CD32b in suppressing M1 expression and promoting M2 polarization. Moreover, heightened M2 activation and CD32b levels appear to correlate with tumor progression. A targeted CD32b blockade may serve as a novel therapeutic strategy to inhibit M2 macrophage polarization and is promising for anti-tumor intervention.

T cell-redirecting therapies in hematological malignancies: Current developments and novel strategies for improved targeting

T cell-redirecting therapies (TCRTs), such as chimeric antigen receptor (CAR) or T cell receptor (TCR) T cells and T cell engagers, have emerged as a highly effective treatment modality, particularly in the B and plasma cell-malignancy setting. However, many patients fail to achieve deep and durable responses; while the lack of truly unique tumor antigens, and concurrent on-target/off-tumor toxicities, have hindered the development of TCRTs for many other cancers. In this review, we discuss the recent developments in TCRT targets for hematological malignancies, as well as novel targeting strategies that aim to address these, and other, challenges.

Novel and multiple targets for chimeric antigen receptor-based therapies in lymphoma

Chimeric antigen receptor (CAR) T-cell therapy targeting CD19 in B-cell non-Hodgkin lymphoma (NHL) validates the utility of CAR-based therapy for lymphomatous malignancies. Despite the success, treatment failure due to CD19 antigen loss, mutation, or down-regulation remains the main obstacle to cure. On-target, off-tumor effect of CD19-CAR T leads to side effects such as prolonged B-cell aplasia, limiting the application of therapy in indolent diseases such as chronic lymphocytic leukemia (CLL). Alternative CAR targets and multi-specific CAR are potential solutions to improving cellular therapy outcomes in B-NHL. For Hodgkin lymphoma and T-cell lymphoma, several cell surface antigens have been studied as CAR targets, some of which already showed promising results in clinical trials. Some antigens are expressed by different lymphomas and could be used for designing tumor-agnostic CAR. Here, we reviewed the antigens that have been studied for novel CAR-based therapies, as well as CARs designed to target two or more antigens in the treatment of lymphoma.

Remodeling the Tumor Myeloid Landscape to Enhance Antitumor Antibody Immunotherapies

Among the diverse tumor resident immune cell types, tumor-associated macrophages (TAMs) are often the most abundant, possess an anti-inflammatory phenotype, orchestrate tumor immune evasion and are frequently associated with poor prognosis. However, TAMs can also be harnessed to destroy antibody-opsonized tumor cells through the process of antibody-dependent cellular phagocytosis (ADCP). Clinically important tumor-targeting monoclonal antibodies (mAb) such as Rituximab, Herceptin and Cetuximab, function, at least in part, by inducing macrophages to eliminate tumor cells via ADCP. For IgG mAb, this is mediated by antibody-binding activating Fc gamma receptors (FcγR), with resultant phagocytic activity impacted by the level of co-engagement with the single inhibitory FcγRIIb. Approaches to enhance ADCP in the tumor microenvironment include the repolarization of TAMs to proinflammatory phenotypes or the direct augmentation of ADCP by targeting so-called 'phagocytosis checkpoints'. Here we review the most promising new strategies targeting the cell surface molecules present on TAMs, which include the inhibition of 'don't eat me signals' or targeting immunostimulatory pathways with agonistic mAb and small molecules to augment tumor-targeting mAb immunotherapies and overcome therapeutic resistance.

Fc-Engineered Antibodies with Enhanced Fc-Effector Function for the Treatment of B-Cell Malignancies

Monoclonal antibody (mAb) therapy has rapidly changed the field of cancer therapy. In 1997, the CD20-targeting mAb rituximab was the first mAb to be approved by the U.S. Food and Drug Administration (FDA) for treatment of cancer. Within two decades, dozens of mAbs entered the clinic for treatment of several hematological cancers and solid tumors, and numerous more are under clinical investigation. The success of mAbs as cancer therapeutics lies in their ability to induce various cytotoxic machineries against specific targets. These cytotoxic machineries include antibody-dependent cellular cytotoxicity (ADCC), antibody-dependent cellular phagocytosis (ADCP), and complement-dependent cytotoxicity (CDC), which are all mediated via the fragment crystallizable (Fc) domain of mAbs. In this review article, we will outline the novel approaches of engineering these Fc domains of mAbs to enhance their Fc-effector function and thereby their anti-tumor potency, with specific focus to summarize their (pre-) clinical status for the treatment of B-cell malignancies, including chronic lymphocytic leukemia (CLL), B-cell non-Hodgkin lymphoma (B-NHL), and multiple myeloma (MM).

Development of Anti-CD32b Antibodies with Enhanced Fc Function for the Treatment of B and Plasma Cell Malignancies

The sole inhibitory Fcγ receptor CD32b (FcγRIIb) is expressed throughout B and plasma cell development and on their malignant counterparts. CD32b expression on malignant B cells is known to provide a mechanism of resistance to rituximab that can be ameliorated with a CD32b-blocking antibody. CD32b, therefore, represents an attractive tumor antigen for targeting with a monoclonal antibody (mAb). To this end, two anti-CD32b mAbs, NVS32b1 and NVS32b2, were developed. Their complementarity-determining regions (CDR) bind the CD32b Fc binding domain with high specificity and affinity while the Fc region is afucosylated to enhance activation of FcγRIIIa on immune effector cells. The NVS32b mAbs selectively target CD32b⁺ malignant cells and healthy B cells but not myeloid cells. They mediate potent killing of opsonized CD32b⁺ cells via antibody-dependent cellular cytotoxicity and phagocytosis (ADCC and ADCP) as well as complement-dependent cytotoxicity (CDC). In addition, NVS32b CDRs block the CD32b Fc-binding domain, thereby minimizing CD32b-mediated resistance to therapeutic mAbs including rituximab, obinutuzumab, and daratumumab. NVS32b mAbs demonstrate robust antitumor activity against CD32b⁺ xenografts in vivo and immunomodulatory activity including recruitment of macrophages to the tumor and enhancement of dendritic cell maturation in response to immune complexes. Finally, the activity of NVS32b mAbs on CD32b⁺ primary malignant B and plasma cells was confirmed using samples from patients with B-cell chronic lymphocytic leukemia (CLL) and multiple myeloma. The findings indicate the promising potential of NVS32b mAbs as a single agent or in combination with other mAb therapeutics for patients with CD32b⁺ malignant cells.

Obinutuzumab (GA101) vs. rituximab significantly enhances cell death, antibody-dependent cytotoxicity and improves overall survival against CD20+ primary mediastinal B-cell lymphoma (PMBL) in a xenograft NOD-scid IL2Rgnull (NSG) mouse model: a potential targeted agent in the treatment of PMBL

Primary mediastinal large B-cell lymphoma (PMBL), a distinct mature B-cell lymphoma, expresses CD20 and has recently been successfully treated with the combination of a type I anti-CD20 monoclonal antibody, rituximab, with multiple combination chemotherapy regimens. Obinutuzumab is a glycoengineered type II anti-CD20 monoclonal antibody (mAb), recognizing a unique CD20 extracellular membrane epitope with enhanced antibody dependent cellular cytotoxicity (ADCC) vs rituximab. We hypothesize that obinutuzumab vs rituximab will significantly enhance in-vitro and in-vivo cytotoxicity against PMBL. PMBL cells were treated with equal dose of obinutuzumab and rituximab for 24 hours (1–100 μg/ml). ADCC were performed with ex-vivo expanded natural killer cells at 10:1 E: T ratio. Mice were xenografted with intravenous injections of luciferase expressing Karpas1106P cells and treated every 7 days for 8 weeks. Tumor burden was monitored by IVIS spectrum system. Compared with rituximab, obinutuzumab significantly inhibited PMBL cell proliferation (p = 0.01), promoted apoptosis (p = 0.05) and enhanced ADCC (p = 0.0002) against PMBL. Similarly, in PMBL xenografted NOD scid gamma mice, obinutuzumab significantly enhanced survival than rituximab when treated with equal doses (p = 0.05). Taken together our results suggest that obinutuzumab significantly enhanced natural killer cytotoxicity, reduced PMBL proliferation and prolonged the overall survival in humanized PMBL xenografted NOD scid gamma mice.

B cell modulation strategies in the improvement of transplantation outcomes

Successful transplantation outcome is the final goal in most end stage and nonfunctional organs; however, despite using different therapeutic strategies, antibody-mediated rejection is still a big obstacle. B cells have a key role in transplant rejection by several functions, such as antibody production, antigen presenting, contribution in T cell activation, forming the germinal center, and tertiary lymphoid organs. Therefore, B cells modulation seems to be very crucial in transplant outcome. A double-edged sword function is considered for B cells during transplantation; On the one hand, antibody production against the transplanted organ induces antibody-mediated rejection. On the other hand, IL10 production by regulatory B (Breg) cells induces graft tolerance. Nowadays, several monoclonal antibodies (mAb) are available for B cell modulation that are routinely used in transplant recipients, among which rituximab (anti-CD20 mAb) act in eliminating B cells. However, there are some other monoclonal antibodies, such as epratuzumab and Inotuzumab ozogamicin (IO), which exert anti-CD22 activity, resulting in disruption of B cell functions and induction of tolerance in autoimmune disease or B cell malignancies; that notwithstanding, these mAbs have not yet been tried in transplantation. In this review, we focus on different methods for modulating the activity of B cells as well as induction of Breg cells, aiming to prevent the allograft rejection.

Mouse Models of Rheumatoid Arthritis for Studies on Immunopathogenesis and Preclinical Testing of Fc Receptor-Targeting Biologics

<b><i>Background:</i></b> Rheumatoid arthritis (RA) is a chronic autoimmune disease that causes inflammation, swelling, and pain in the joints and involves systemic complications. Mouse models of RA have been extensively used to model the pathogenesis of RA and to develop effective therapies. Although many components of the immune system have been studied in these models, the role of crystallizable fragment (Fc) gamma receptors (FcγRs) in RA has been sorely neglected. The aim of this review was to introduce the different mouse models of RA and to describe the different drug development strategies that have been tested in these models to target FcγR function, with the focus being on drugs that have been made from the Fc of immunoglobulin G (IgG). <b><i>Summary:</i></b> Evidence suggests that FcγRs play a major role in immune complex-induced inflammation in autoimmune diseases, such as RA. However, there is limited knowledge on the importance of FcγRs in the human disease even though there has been extensive work in mouse models of RA. Numerous mouse models of RA are available, with each model depicting certain aspects of the disease. Induced models of RA have nonspecific immune activation with cartilage-directed autoimmunity, whereas spontaneous models of RA develop without immunization, which results in a more chronic form of arthritis. These models have been used to test FcγR-targeting monoclonal antibodies, intravenous immunoglobulin (IVIg), subcutaneously administered IVIg, and recombinant Fcs for their ability to interact with and modify FcγR function. Recombinant Fcs avidly bind FcγRs and exhibit enhanced therapeutic efficacy in mouse models of RA. <b><i>Key Message:</i></b> The therapeutic utility of targeting FcγRs with recombinant Fcs is great and should be explored in human clinical trials for autoimmune diseases, such as RA.

Reprogramming the Constant Region of Immunoglobulin G Subclasses for Enhanced Therapeutic Potency against Cancer

The constant region of immunoglobulin (Ig) G antibodies is responsible for their effector immune mechanism and prolongs serum half-life, while the fragment variable (Fv) region is responsible for cellular or tissue targeting. Therefore, antibody engineering for cancer therapeutics focuses on both functional efficacy of the constant region and tissue- or cell-specificity of the Fv region. In the functional aspect of therapeutic purposes, antibody engineers in both academia and industry have capitalized on the constant region of different IgG subclasses and engineered the constant region to enhance therapeutic efficacy against cancer, leading to a number of successes for cancer patients in clinical settings. In this article, we review IgG subclasses for cancer therapeutics, including (i) IgG1, (ii) IgG2, 3, and 4, (iii) recent findings on Fc receptor functions, and (iv) future directions of reprogramming the constant region of IgG to maximize the efficacy of antibody drug molecules in cancer patients.

There Is (Scientific) Strength in Numbers: A Comprehensive Quantitation of Fc Gamma Receptor Numbers on Human and Murine Peripheral Blood Leukocytes

Antibodies are essential mediators of immunological defense mechanisms, are clinically used as therapeutic agents, but are also functionally involved in various immune-mediated disorders. Whereas IgG antibodies accomplish some of their biological tasks autonomously, many functions depend on their binding to activating and inhibitory Fcγ receptors (FcγR). From a qualitative point of view expression patterns of FcγR on immunologically relevant cell types are well-characterized both for mice and humans. Surprisingly, however, there is only quite limited information available on actual quantities of FcγR expressed by the different leukocyte populations. In this study we provide a comprehensive data set assessing quantitatively how many individual human and mouse FcγRs are expressed on B cells, NK cells, eosinophils, neutrophils, basophils and both classical, and non-classical monocytes under steady state conditions. Moreover, among human donors we found two groups with different expression levels of the inhibitory FcγRIIb on monocytes which appears to correlate with haplotypes of the activating FcγRIIIa.

Boosting therapeutic potency of antibodies by taming Fc domain functions

Monoclonal antibodies (mAbs) are one of the most widely used drug platforms for infectious diseases or cancer therapeutics because they selectively target pathogens, infectious cells, cancerous cells, and even immune cells. In this way, they mediate the elimination of target molecules and cells with fewer side effects than other therapeutic modalities. In particular, cancer therapeutic mAbs can recognize cell-surface proteins on target cells and then kill the targeted cells by multiple mechanisms that are dependent upon a fragment crystallizable (Fc) domain interacting with effector Fc gamma receptors, including antibody-dependent cell-mediated cytotoxicity and antibody-dependent cell-mediated phagocytosis. Extensive engineering efforts have been made toward tuning Fc functions by either reinforcing (e.g. for targeted therapy) or disabling (e.g. for immune checkpoint blockade therapy) effector functions and prolonging the serum half-lives of antibodies, as necessary. In this report, we review Fc engineering efforts to improve therapeutic potency, and propose future antibody engineering directions that can fulfill unmet medical needs.

Fine-tuning the function of monoclonal antibodies (mAbs) holds promise for developing new therapeutic agents. Antibodies bind to pathogens or cancer cells, flagging them with Fc (fragment crystallizable) domain for destruction by the immune system. mAbs attached only to specific target cells enable lower side effect than other conventional drugs. Sang Taek Jung at Korea University and Tae Hyun Kang at Kookmin University, both in Seoul, reviewed recent developments in engineering therapeutic potency of mAbs. They report that mAbs can be engineered to activate effective immune cell types to treat a particular disease. Engineering can also increase mAbs’ persistence in the blood, enabling less frequent administration. Antibodies engineered to bind to two different antigens at once can also improve therapeutic efficacy. Applying these techniques could help developing new treatments against cancer, and infectious and autoimmune diseases.

Cyclophosphamide Enhances Cancer Antibody Immunotherapy in the Resistant Bone Marrow Niche by Modulating Macrophage FcγR Expression

Therapy-resistant microenvironments represent a major barrier toward effective elimination of disseminated cancer. Many hematologic and solid tumors are resistant to therapeutic antibodies in the bone marrow (BM), but not in the periphery (e.g., spleen). We previously showed that cyclophosphamide (CTX) sensitizes the BM niche to antibody therapeutics. Here, we show that (i) BM resistance was induced not only by the tumor but also by the intrinsic BM microenvironment; (ii) CTX treatment overcame both intrinsic and extrinsic resistance mechanisms by augmenting macrophage activation and phagocytosis, including significant upregulation of activating Fcγ receptors (FcγRIII and FcγRIV) and downregulation of the inhibitory receptor, FcγRIIB; and (iii) CTX synergized with cetuximab (anti-EGFR) and trastuzumab (anti-Her2) in eliminating metastatic breast cancer in the BM of humanized mice. These findings provide insights into the mechanisms by which CTX synergizes with antibody therapeutics in resistant niche-specific organs and its applicability in treating BM-resident tumors.

Influence of the bispecific antibody IgG subclass on T cell redirection

T cell redirection mediated by bispecific antibodies (BsAbs) is a promising cancer therapy. Dual antigen binding is necessary for potent T cell redirection and is influenced by the structural characteristics of a BsAb, which are dependent on its IgG subclass. In this study, model BsAbs targeting CD19xCD3 were generated in variants of IgG1, IgG2, and IgG4 carrying Fc mutations that reduce FcγR interaction, and two chimeric IgG subclasses termed IgG1:2 and IgG4:2, in which the IgG1- or IgG4-F(ab)2 are grafted on an IgG2 Fc. Molecules containing an IgG2 or IgG4-F(ab)2 domain were confirmed to be the most structurally compact molecules. All BsAbs were shown to bind both of their target proteins (and corresponding cells) equally well. However, CD19xCD3 IgG2 did not bind both antigens simultaneously as measured by the absence of cellular clustering of T cells with target cells. This translated to a reduced potency of IgG2 BsAbs in T-cell redirection assays. The activity of IgG2 BsAbs was fully restored in the chimeric subclasses IgG4:2 and IgG1:2. This confirmed the major contribution of the F(ab)2 region to the BsAb's functional activity and demonstrated that function of BsAbs can be modulated by engineering molecules combining different Fc and F(ab)2 domains. Abbreviations: ADCC: Antibody-dependent cellular cytotoxicity; AlphaScreenTM: Amplified Luminescent Proximity Homogeneous Assay Screening; ANOVA: Analysis of variance; BiTE: bispecific T-cell engager; BSA: bovine serum albumin; BsAb: bispecific antibody; cFAE: controlled Fab-arm exchange; CDC: complement-dependent cellular cytotoxicity; CIEX: cation-exchange; CIR: chimeric immune receptor; DPBS: Dulbecco's phosphate-buffered saline; EC50 value: effective concentration to reach half-maximum effect; EGFR: epidermal growth factor receptor; EI: expansion index (RAt=x/RAt=0); FACS: fluorescence-activated cell sorting; FVD: fixable viability dye; HI-HPLC: hydrophobic interaction HPLC; HI-FBS: heat-inactivated fetal bovine serum; HPLC: high-pressure liquid chromatography; IC50 value: effective concentration to reach half-maximum inhibition; IQ: Inhibition Quotient; IS: immunological synapse; MES: 2-(N-morpholino)ethanesulfonic acid; R-PE: recombinant phycoerythrin; RA: red area in μm2/well; RD: receptor density; RFP: red fluorescent protein; Rg: radius of gyration; RSV: respiratory syncytial virus; SAXS: small-angle x-ray scattering; scFv: single-chain variable fragment; SD: standard deviation; SPR: surface plasmon resonance; WT: wild-type.

Conceptual Approaches to Modulating Antibody Effector Functions and Circulation Half-Life

Antibodies and Fc-fusion antibody-like proteins have become successful biologics developed for cancer treatment, passive immunity against infection, addiction, and autoimmune diseases. In general these biopharmaceuticals can be used for blocking protein:protein interactions, crosslinking host receptors to induce signaling, recruiting effector cells to targets, and fixing complement. With the vast capability of antibodies to affect infectious and genetic diseases much effort has been placed on improving and tailoring antibodies for specific functions. While antibody:antigen engagement is critical for an efficacious antibody biologic, equally as important are the hinge and constant domains of the heavy chain. It is the hinge and constant domains of the antibody that engage host receptors or complement protein to mediate a myriad of effector functions and regulate antibody circulation. Molecular and structural studies have provided insight into how the hinge and constant domains from antibodies across different species, isotypes, subclasses, and alleles are recognized by host cell receptors and complement protein C1q. The molecular details of these interactions have led to manipulation of the sequences and glycosylation of hinge and constant domains to enhance or reduce antibody effector functions and circulating half-life. This review will describe the concepts being applied to optimize the hinge and crystallizable fragment of antibodies, and it will detail how these interactions can be tuned up or down to mediate a biological function that confers a desired disease outcome.

Important roles of CD32 in promoting suppression of IL-4 induced immune responses by a novel anti-IL-4Rα therapeutic antibody

Asthma is characterized by airway hyperresponsiveness and inflammation, as well as underlying structural changes to the airways. Interleukin-4 (IL-4) is a key T-helper type 2 (Th2) cytokine that plays important roles in the pathogenesis of atopic and eosinophilic asthma. We developed a novel humanized anti-IL-4Rα antibody that can potently inhibit IL-4/IL-13-mediated TF-1 cell proliferation. Using monocytes isolated from human peripheral blood mononuclear cells (PBMCs), we revealed a critical role of CD32 in modulating the immune responses of monocytes in response to blockade of IL-4Rα signaling pathway. We, therefore, devised a new strategy to increase the efficacy of the anti-IL-4Rα monoclonal antibody for the treatment of asthma and other atopic diseases by co-engaging CD32 and IL-4Rα on monocytic cells by choosing IgG classes or Fc mutations with higher affinities for CD32. The antibody with selectively enhanced affinity for CD32A displayed superior suppression of IL-4-induced monocytes’ activities, including the down-regulation of CD23 expression. Intriguingly, further analysis demonstrated that both CD32A and CD32B contributed to the enhancement of antibody-mediated suppression of CD23 expression from monocytes in response to blockade of IL-4Rα signaling. Furthermore, inhibition of IgE secretion from human PBMC by the antibody variants further suggests that the complex allergic inflammation mediated by IL-4/IL-4Rα signaling might result from a global network where multiple cell types that express multiple FcγRs are all involved, of which CD32, especially CD32A, is a key mediator. In this respect, our study provides new insights into designing therapeutic antibodies for targeting Th2 cytokine-mediated allergic pathogenesis.

Targeting the Antibody Checkpoints to Enhance Cancer Immunotherapy-Focus on FcγRIIB

Immunotherapy with therapeutic antibodies has increased survival for patients with hematologic and solid cancers. Still, a significant fraction of patients fails to respond to therapy or acquire resistance. Understanding and overcoming mechanisms of resistance to antibody drugs, and in particular those common to antibody drugs as a class, is therefore highly warranted and holds promise to improve response rates, duration of response and potentially overall survival. Activating and inhibitory Fc gamma receptors (FcγR) are known to coordinately regulate therapeutic activity of tumor direct-targeting antibodies. Similar, but also divergent, roles for FcγRs in controlling efficacy of immune modulatory antibodies e.g., checkpoint inhibitors have been indicated from mouse studies, and were recently implicated in contributing to efficacy in the human clinical setting. Here we discuss evidence and mechanisms by which Fc gamma receptors–the “antibody checkpoints”–regulate antibody-induced antitumor immunity. We further discuss how targeted blockade of the sole known inhibitory antibody checkpoint FcγRIIB may help overcome resistance and boost activity of clinically validated and emerging antibodies in cancer immunotherapy.

Frontline Treatment for Older Patients with Mantle Cell Lymphoma

The natural history of mantle cell lymphoma (MCL) undergoing chemotherapy is a cyclical pattern of remission followed by recurrence of disease due to acquired chemotherapy resistance. The median age of the occurrence of MCL is 65 years, so half of the newly diagnosed MCL patients are considered "elderly." The tolerance to long-term chemotherapy in elderly patients is decreased; hence, the response to frontline therapy used is of paramount importance. We hope that our review may guide clinicians in treating such populations in a more personalized and evidence-based manner.In the older patients with risk variables, frontline treatment is determined according to different body status of fit, unfit or compromised, and frail. In the fit patients, the pursuit of remission and prolongation of survival might currently justify the use of more intense and toxic therapies. For unfit or compromised older patients, disease control needs to be prioritized, maintaining a balance between the benefits and toxicities of the treatment. For frail patients, tolerance of treatment and minimizing myelotoxicity should be the primary focus. "Chemotherapy-free" regimens are likely to be considered as the first-line strategy for this population. On the other hand, in the older MCL population without risk variables, observation or "watch and wait" can prevent overtreatment. Furthermore, more clinical trials and research studies on novel agents and targeted therapies need to be translated into the general population to provide optimal treatment and to guide personalized treatment. IMPLICATIONS FOR PRACTICE: This review emphasizes the importance of frontline therapies for older MCL patients. MCL patients commonly experience a cyclical pattern of remission followed by recurrence of disease due to acquired chemotherapy resistance. As a special population, elderly patients have various comorbidities and decreased organ function, which may reduce the chances of undergoing treatment for recurrent disease. Thus, this older population of patients with MCL should be treated separately and exceptionally. So far, systematic reviews with regard to frontline treatment for older patients with MCL have not been encountered, but the hope is that this review may guide clinicians in treating such populations in a more personalized and evidence-based manner.

Evaluating Anti-CD32b F(ab) Conformation Using Molecular Dynamics and Small-Angle X-Ray Scattering

Complementary strategies of small-angle x-ray scattering (SAXS) and crystallographic analysis are often used to determine atomistic three-dimensional models of macromolecules and their variability in solution. This combination of techniques is particularly valuable when applied to macromolecular complexes to detect changes within the individual binding partners. Here, we determine the x-ray crystallographic structure of a F(ab) fragment in complex with CD32b, the only inhibitory Fc-γ receptor in humans, and compare the structure of the F(ab) from the crystal complex to SAXS data for the F(ab) alone in solution. We investigate changes in F(ab) structure by predicting theoretical scattering profiles for atomistic structures extracted from molecular dynamics (MD) simulations of the F(ab) and assessing the agreement of these structures to our experimental SAXS data. Through principal component analysis, we are able to extract principal motions observed during the MD trajectory and evaluate the influence of these motions on the agreement of structures to the F(ab) SAXS data. Changes in the F(ab) elbow angle were found to be important to reach agreement with the experimental data; however, further discrepancies were apparent between our F(ab) structure from the crystal complex and SAXS data. By analyzing multiple MD structures observed in similar regions of the principal component analysis, we were able to pinpoint these discrepancies to a specific loop region in the F(ab) heavy chain. This method, therefore, not only allows determination of global changes but also allows identification of localized motions important for determining the agreement between atomistic structures and SAXS data. In this particular case, the findings allowed us to discount the hypothesis that structural changes were induced upon complex formation, a significant find informing the drug development process. The methodology described here is generally applicable to deconvolute global and local changes of macromolecular structures and is well suited to other systems.

Identification of a five B cell-associated gene prognostic and predictive signature for advanced glioma patients harboring immunosuppressive subtype preference

High grade gliomas contribute to most brain tumor mortality. A few studies reported that the immune system affected glioma development, and immune biomarkers helped understand the disease and formulate effective immunotherapy for patients. Currently, no B lymphocyte-based prognostic signature was reported in gliomas. By applying 78 B cell lineage-specific genes, we conducted a whole-genome gene expression analysis in 782 high grade gliomas derived from three independent datasets by Cox regression analysis and risk score method for signature identification, and then used Gene Ontology, Gene Set Enrichment Analysis, and other statistical methods for functional annotations of the signature-defined differences. We developed a five B cell-associated gene signature for prognosis of high grade glioma patients, which is independent of clinicopathological and genetic features. The signature identified high risk patients suitable for chemoradiotherapy, whereas low risk patients should rule out chemotherapy with radiotherapy only. We found that tumors of TCGA Mesenchymal subtype and wild type IDH1 were preferentially stratified to the high risk group, which bore strong immunosuppressive microenvironment, while tumors of TCGA Proneural subtype and mutated IDH1 were significantly accumulated to the low risk group, which exhibited less immunosuppressive state. The five B cell-associated gene signature predicts poor survival of high risk patients bearing strong immunosuppression and helps select optimal therapeutic regimens for glioma patients.

New revelations from an old receptor: Immunoregulatory functions of the inhibitory Fc gamma receptor, FcγRIIB (CD32B)

The Fc gamma receptor IIB (FcγRIIB/CD32B) was generated million years ago during evolution. It is the sole inhibitory receptor for IgG, and has long been associated with the regulation of humoral immunity and innate immune homeostasis. However, new and surprising functions of FcγRIIB are emerging. In particular, FcγRIIB has been shown to perform unexpected activatory roles in both immune-signaling and monoclonal antibody (mAb) immunotherapy. Furthermore, although ITIM signaling is an integral part of FcγRIIB regulatory activity, it is now clear that inhibition/activation of immune responses can occur independently of the ITIM. In light of these new findings, we present an overview of the established and noncanonical functions of FcγRIIB and discuss how this knowledge might be exploited therapeutically.

FcγRII-binding Centyrins mediate agonism and antibody-dependent cellular phagocytosis when fused to an anti-OX40 antibody

Immunostimulatory antibodies against the tumor necrosis factor receptors (TNFR) are emerging as promising cancer immunotherapies. The agonism activity of such antibodies depends on crosslinking to Fc gamma RIIB receptor (FcγRIIB) to enable the antibody multimerization that drives TNFR activation. Previously, Fc engineering was used to enhance the binding of such antibodies to Fcγ receptors. Here, we report the identification of Centyrins as alternative scaffold proteins with binding affinities to homologous FcγRIIB and FcγRIIA, but not to other types of Fcγ receptors. One Centyrin, S29, was engineered at distinct positions of an anti-OX40 SF2 antibody to generate bispecific and tetravalent molecules named as mAbtyrins. Regardless of the position of S29 on the SF2 antibody, SF2-S29 mAbtyrins could bind FcγRIIB and FcγRIIA specifically while maintaining binding to OX40 receptors. In a NFκB reporter assay, attachment of S29 Centyrin molecules at the C-termini, but not the N-termini, resulted in SF2 antibodies with increased agonism owing to FcγRIIB crosslinking. The mAbtyrins also showed agonism in T-cell activation assays with immobilized FcγRIIB and FcγRIIA, but this activity was confined to mAbtyrins with S29 specifically at the C-termini of antibody heavy chains. Furthermore, regardless of the position of the molecule, S29 Centyrin could equip an otherwise Fc-silent antibody with antibody-dependent cellular phagocytosis activity without affecting the antibody's intrinsic antibody-dependent cell-meditated cytotoxicity and complement-dependent cytotoxicity. In summary, the appropriate adoption FcγRII-binding Centyrins as functional modules represents a novel strategy to engineer therapeutic antibodies with improved functionalities.

A novel bispecific DARPin targeting FcγRIIB and FcεRI-bound IgE inhibits allergic responses

BACKGROUND

Binding of allergen-specific IgE to its high-affinity receptor FcεRI on basophils and mast cells is a central event in the development of allergies. Exposure of these cells to allergens induces the release of soluble mediators causing allergic symptoms. The inhibitory low-affinity IgG Fc-receptor FcγRIIB is co-expressed on allergic effector cells and has been implicated in negative regulation of immediate hypersensitivity responses. In order to harvest the inhibitory function of this receptor, we aimed to select specific binders against FcγRIIB and to generate a bispecific molecule simultaneously targeting FcγRIIB and FcεRI-bound IgE on the surface of allergic effector cells.

METHODS

We selected FcγRIIB-specific binding molecules from a library of designed ankyrin repeat proteins using ribosome display technology. The bispecific binding modality was generated by molecular cloning and recombinant protein expression. We determined binding characteristics on molecular and cellular levels using SPR, ELISA, and flow cytometry. The inhibitory potential of the newly described molecules was assessed in different cellular degranulation assays ex vivo and in a mouse model of passive systemic anaphylaxis.

RESULTS

We demonstrate that the selected DARPin^® proteins recognize FcγRIIB with high affinity. Furthermore, the bispecific binding protein successfully interferes with allergen-induced cell degranulation and efficiently inhibits systemic anaphylaxis in vivo. Mechanistically, we report that FcγRIIB-mediated inhibition of effector cell activation requires direct ligation to an activating FcεRI receptor.

CONCLUSION

The described bispecific DARPin protein has the ability to co-ligate FcγRIIB with FcεRI-bound IgE on allergic effector cells and represents an efficient dual-modality to interfere with allergic hypersensitivity reactions.

FcγRIIb expression in early stage chronic lymphocytic leukemia

In normal B-cells, B-cell antigen receptor (BCR) signaling can be negatively regulated by the low-affinity receptor FcγRIIb (CD32b). To better understand the role of FcγRIIb in chronic lymphocytic leukemia (CLL), we correlated its expression on 155 samples from newly-diagnosed Binet A patients with clinical characteristics and outcome. FcγRIIb expression was similar in normal B-cells and leukemic cells, this being heterogenous among patients and within CLL clones. FcγRIIb expression did not correlate with well known prognostic markers [disease stage, serum beta-2 microglobulin (B2M), IGHV mutational status, expression of ZAP-70 and CD38, and cytogenetics] except for a weak concordance with CD49d. Moreover, patients with low FcγRIIb expression (69/155, 44.5%) required therapy earlier than those with high FcγRIIb expression (86/155, 55.5%) (median 151.4 months vs. not reached; p=.071). These results encourage further investigation on the role of FcγRIIb in CLL biology and prognostic significance in larger series of patients.

Harnessing co-stimulatory TNF receptors for cancer immunotherapy: Current approaches and future opportunities

Co-stimulatory tumor necrosis factor receptors (TNFRs) can sculpt the responsiveness of T cells recognizing tumor-associated antigens. For this reason, agonist antibodies targeting CD137, CD357, CD134 and CD27 have received considerable attention for their therapeutic utility in enhancing anti-tumor immune responses, particularly in combination with other immuno-modulatory antibodies targeting co-inhibitory pathways in T cells. The design of therapeutic antibodies that optimally engage and activate co-stimulatory TNFRs presents an important challenge of how to promote effective anti-tumor immunity while avoiding serious immune-related adverse events. Here we review our current understanding of the expression, signaling and structural features of CD137, CD357, CD134 and CD27, and how this may inform the design of pharmacologically active immuno-modulatory antibodies targeting these receptors. This includes the integration of our emerging knowledge of the role of Fcγ receptors (FcγRs) in facilitating antibody-mediated receptor clustering and forward signaling, as well as promoting immune effector cell-mediated activities. Finally, we bring our current preclinical and clinical knowledge of co-stimulatory TNFR antibodies into the context of opportunities for next generation molecules with improved pharmacologic properties.

Fc Engineering Approaches to Enhance the Agonism and Effector Functions of an Anti-OX40 Antibody

Agonistic antibodies directed against immunostimulatory receptors belonging to the tumor necrosis factor receptor (TNFR) superfamily are emerging as promising cancer immunotherapies. Several Fc engineering approaches discovered recently can augment the anti-tumor activities of TNFR antibodies by enhancing their agonistic activities and/or effector functions. In this study, we compared these approaches for their effects on an anti-OX40 antibody. Both S267E/L328F and V12 mutations facilitated enhanced binding to FcγRIIB and thus increased FcγRIIB cross-linking mediated agonist activity. However, both mutations abrogated the binding to FcγRIIIA and thereby decreasing the antibody-dependent cellular cytotoxicity activities. In contrast, the E345R mutation, which can promote antibody multimerization upon receptor binding, facilitated anti-OX40 antibody to have increased agonism by promoting the clustering of OX40 receptors without the dependence on FcγRIIB cross-linking. Nonetheless, cross-linking to FcγRIIB can lead to a further boost of the agonism of the anti-OX40 antibody with IgG1 Fc but not with the silent IgG2σ Fc. The antibody-dependent cellular cytotoxicity and complement-dependent cytotoxicity activities of the anti-OX40 antibody with the E345R mutation were affected by the choice of IgG subtypes. However, there was little change in the antibody-dependent cellular phagocytosis activity. In summary, different Fc engineering approaches can guide the design of engineered antibodies to OX40 and other TNFR with improved anti-tumor activity.

Impairment on the lateral mobility induced by structural changes underlies the functional deficiency of the lupus-associated polymorphism FcγRIIB-T232

Xu et al. show that the lupus-associated polymorphism FcγRIIB-T232 has structural changes of the TM domain that reduces lateral mobility and inhibitory functions.

FcγRIIB functions to suppress the activation of immune cells. A single-nucleotide polymorphism in the transmembrane (TM) domain of FcγRIIB, FcγRIIB-T232, is associated with lupus. In this study, we investigated the pathogenic mechanism of FcγRIIB-T232 at both functional and structural levels. Our results showed that FcγRIIB-T232 exhibited significantly reduced lateral mobility compared with FcγRIIB-I232 and was significantly less enriched into the microclusters of immune complexes (ICs) after stimulation. However, if sufficient responding time is given for FcγRIIB-T232 to diffuse and interact with the ICs, FcγRIIB-T232 can restore its inhibitory function. Moreover, substituting the FcγRIIB-T232 TM domain with that of a fast floating CD86 molecule restored both the rapid mobility and the inhibitory function, which further corroborated the importance of fast mobility for FcγRIIB to function. Mechanistically, the crippled lateral mobility of FcγRIIB-T232 can be explained by the structural changes of the TM domain. Both atomistic simulations and nuclear magnetic resonance measurement indicated that the TM helix of FcγRIIB-T232 exhibited a more inclined orientation than that of FcγRIIB-I232, thus resulting in a longer region embedded in the membrane. Therefore, we conclude that the single-residue polymorphism T232 enforces the inclination of the TM domain and thereby reduces the lateral mobility and inhibitory functions of FcγRIIB.

Fc-gamma receptors: Attractive targets for autoimmune drug discovery searching for intelligent therapeutic designs

Autoantibody immune complexes (ICs) mediate pathogenesis in multiple autoimmune diseases via direct interference with target function, complement fixation, and interaction with Fc-gamma receptors (FcγRs). Through high avidity interactions, ICs are able to crosslink low affinity FcγRs expressed on a wide variety of effector cells, leading to secretion of pro-inflammatory mediators and inducing cytotoxicity, ultimately resulting in tissue injury. Given their relevance in numerous autoimmune diseases, FcγRs have been considered as attractive therapeutic targets for the last three decades. However, a limited number of investigational drug candidates have been developed targeting FcγRs and only a few approved therapeutics have been associated with impacting FcγRs. This review provides a historical overview of the different therapeutic approaches used to target FcγRs for the treatment of autoimmune and inflammatory diseases.

Regulation of Monoclonal Antibody Immunotherapy by FcγRIIB

Monoclonal antibodies (mAb) are revolutionising the treatment of many different diseases. Given their differing mode of action compared to most conventional chemotherapeutics and small molecule inhibitors, they possess the potential to be independent of common modes of treatment resistance and can typically be combined readily with existing treatments without dose-limiting toxicity. However, treatments with mAb rarely result in cure and so a full understanding of how these reagents work and can be optimised is key for their subsequent improvement. Here we review how an understanding of the biology of the inhibitory Fc receptor, FcγRIIB (CD32B), is leading to the development of improved mAb treatments.

FcγR requirements leading to successful immunotherapy

Monoclonal antibody (mAb) immunotherapy is currently experiencing an unprecedented amount of success, delivering blockbuster sales for the pharmaceutical industry. Having experienced several false dawns and overcoming technical issues which limited progress, we are now entering a golden period where mAbs are becoming a mainstay of treatment regimes for diseases ranging from cancer to autoimmunity. In this review, we discuss how these mAbs are most likely working and focus in particular on the key receptors that they interact with to precipitate their therapeutic effects. Although their targets may vary, their engagement with Fcγ receptors (FcγRs) on numerous immune effector cells is almost universal, and here we review their roles in delivering successful immunotherapy.

Antagonistic human FcγRIIB (CD32B) antibodies have anti-tumor activity and overcome resistance to antibody therapy in vivo

Therapeutic antibodies have transformed cancer therapy, unlocking mechanisms of action by engaging the immune system. Unfortunately, cures rarely occur and patients display intrinsic or acquired resistance. Here, we demonstrate the therapeutic potential of targeting human (h) FcγRIIB (CD32B), a receptor implicated in immune cell desensitization and tumor cell resistance. FcγRIIB-blocking antibodies prevented internalization of the CD20-specific antibody rituximab, thereby maximizing cell surface accessibility and immune effector cell mediated antitumor activity. In hFcγRIIB-transgenic (Tg) mice, FcγRIIB-blocking antibodies effectively deleted target cells in combination with rituximab, and other therapeutic antibodies, from resistance-prone stromal compartments. Similar efficacy was seen in primary human tumor xenografts, including with cells from patients with relapsed/refractory disease. These data support the further development of hFcγRIIB antibodies for clinical assessment.

Targeting the Fc receptor in autoimmune disease

INTRODUCTION

The Fc receptors (FcRs) and their interactions with immunoglobulin and innate immune opsonins, such as C-reactive protein, are key players in humoral and cellular immune responses. As the effector mechanism for some therapeutic monoclonal antibodies, and often a contributor to the pathogenesis and progression of autoimmunity, FcRs are promising targets for treating autoimmune diseases.

AREAS COVERED

This review discusses the nature of different FcRs and the various mechanisms of their involvement in initiating and modulating immunocyte functions and their biological consequences. It describes a range of current strategies in targeting FcRs and manipulating their interaction with specific ligands, while presenting the pros and cons of these approaches. This review also discusses potential new strategies including regulation of FcR expression and receptor crosstalk.

EXPERT OPINION

FcRs are appealing targets in the treatment of inflammatory autoimmune diseases. However, there are still knowledge limitations and technical challenges, the most important being a better understanding of the individual roles of each of the FcRs and enhancement of the specificity in targeting particular cell types and specific FcRs.

Allelic-dependent expression of an activating Fc receptor on B cells enhances humoral immune responses

B cells are pivotal regulators of acquired immune responses, and recent work in both experimental murine models and humans has demonstrated that subtle changes in the regulation of B cell function can substantially alter immunological responses. The balance of negative and positive signals in maintaining an appropriate B cell activation threshold is critical in B lymphocyte immune tolerance and autoreactivity. FcγRIIb (CD32B), the only recognized Fcγ receptor on B cells, provides immunoglobulin G (IgG)-mediated negative modulation through a tyrosine-based inhibition motif, which down-regulates B cell receptor-initiated signaling. These properties make FcγRIIb a promising target for antibody-based therapy. We report the discovery of allele-dependent expression of the activating FcγRIIc on B cells. Identical to FcγRIIb in the extracellular domain, FcγRIIc has a tyrosine-based activation motif in its cytoplasmic domain. In both human B cells and B cells from mice transgenic for human FcγRIIc, FcγRIIc expression counterbalances the negative feedback of FcγRIIb and enhances humoral responses to immunization in mice and to BioThrax vaccination in a human anthrax vaccine trial. Moreover, the FCGR2C-ORF allele is associated with the risk of development of autoimmunity in humans. FcγRIIc expression on B cells challenges the prevailing paradigm of unidirectional negative feedback by IgG immune complexes via the inhibitory FcγRIIb, is a previously unrecognized determinant in human antibody/autoantibody responses, and opens the opportunity for more precise personalized use of B cell-targeted antibody-based therapy.

CD19 and CD32b differentially regulate human B cell responsiveness

B cell activation is regulated by a variety of signals. CD19 positively regulates B cell activation, augmenting signals delivered through the BCR complex. In contrast, CD32b contains an ITIM and negatively regulates BCR signaling. Importantly, there are drugs currently in clinical trials and preclinical development that cross-link CD32b to molecules within the BCR complex. We wanted to address how single engagement versus cotargeting these molecules affects human B cell function. When B cells from healthy individuals were activated by signals that mimic a T cell response (IL-21 costimulation), ligation of CD32b, but not CD19, inhibited B cell expansion and plasma cell (PC) differentiation. In contrast, when B cells were activated through TLR, anti-CD19, but not anti-CD32b, blunted the response. However, when both CD19 and CD32b were coengaged by a bispecific anti-CD19×CD32b Ab, both types of stimuli were potently inhibited. Cross-linking CD19 with CD32b also inhibited Ab-independent functions of B cells, such as HLA upregulation, cytokine production, and the ability of B cells to prime CD4(+) T cells. Finally, although cross-linking CD19 and CD32b inhibited PC differentiation of primary B cells, it did not alter Ig production from pre-established PCs. These data elucidate the mechanism by which a complex set of signals determines the fate of B cell responsiveness. Although signals through CD19 influence TLR-driven activation, CD32b impacts the magnitude of the response following IL-21 costimulation. Therefore, simultaneous targeting of multiple surface molecules may be a necessary approach to comprehensively modulate B cell activation in vivo.

Inhibitory FcγRIIb (CD32b) becomes activated by therapeutic mAb in both cis and trans and drives internalization according to antibody specificity

A major feature that distinguishes type I from type II anti-CD20 monoclonal antibodies (mAbs) and reduces their therapeutic efficacy is the tendency to internalize from the cell surface. We have shown previously that the extent of internalization correlates with the capacity of type I mAb to simultaneously engage both CD20 and the inhibitory Fcγ receptor, FcγRIIb, in a bipolar configuration. Here, we investigated whether mAbs directed at other B-cell surface receptors also engaged FcγRIIb and whether this interaction promoted internalization. Most mAbs engaged and activated FcγRIIb, with the strength of activation related to the level of mAb bound to the cell surface. However, engagement did not affect internalization of most mAb-ligated receptors, either in cell lines or primary chronic lymphocytic leukemia cells with the exception of CD19 and CD38. Furthermore, at high cell concentrations/density both cis and trans interactions between cell-surface bound mAb and FcγRIIb were evident, but trans interactions did not inhibit type I anti-CD20 mAb-mediated internalization. These data identify that FcγRIIb is engaged by many mAbs in both cis and trans configurations, triggering its activation, but that internalization via FcγRIIb occurs for only a select subset. These findings have implications when designing new antibody-based therapeutics.

B-cell regulation and its application to transplantation

There has been increasing interest in the role played by B cells and their associated antibody in the immune response to an allograft, driven by the need to undertake antibody-incompatible transplantation and evidence suggesting that B cells play a role in acute T-cell-mediated rejection and in acute and chronic antibody-mediated rejection. This review focuses on the molecular events, both activating and inhibitory, which control B-cell activation, and considers how this information might inform therapeutic strategies. Potential targets include the BAFF (B-cell-activating factor belonging to the tumour necrosis factor family) and CD40-CD40L pathways and inhibitory molecules, such as CD22 and FcγRIIB. B cells can also play an immunomodulatory role via interleukin (IL)10 production and may contribute to transplant tolerance. The expansion of allograft-specific IL10-producing B cells may be an additional therapeutic goal. Thus, the treatment paradigm required in transplantation has shifted from that of simple B-cell depletion, to that of a more subtle, differential manipulation of different B-cell subsets.

Effective phagocytosis of low Her2 tumor cell lines with engineered, aglycosylated IgG displaying high FcγRIIa affinity and selectivity

Glycans anchored to residue N297 of the antibody IgG Fc domain are critical in mediating binding toward FcγRs to direct both adaptive and innate immune responses. However, using a full length bacterial IgG display system, we have isolated aglycosylated Fc domains with mutations that confer up to a 160-fold increase in the affinity toward the low affinity FcγRIIa-R131 allele as well as high selectivity against binding to the remarkably homologous human inhibitory receptor, FcγRIIb. The mutant Fc domain (AglycoT-Fc1004) contained a total of 5 amino acid substitutions that conferred an activating to inhibitory ratio of 25 (A/I ratio; FcyRIIa-R131:FcγRIIb). Incorporation of this engineered Fc into trastuzumab, an anti-Her2 antibody, resulted in a 75% increase in tumor cell phagocytosis by macrophages compared to that of the parental glycosylated trastuzumab with both medium and low Her2-expressing cancer cells. A mathematical model has been developed to help explain how receptor affinity and the A/I ratio relate to improved antibody dependent cell-mediated phagocytosis. Our model provides guidelines for the future engineering of Fc domains with enhanced effector function.

Development of a human monoclonal antibody for potential therapy of CD27-expressing lymphoma and leukemia

PURPOSE

The TNF receptor superfamily member CD27 is best known for its important role in T-cell immunity but is also recognized as a cell-surface marker on a number of B- and T-cell malignancies. In this article, we describe a novel human monoclonal antibody (mAb) specific for CD27 with properties that suggest a potential utility against malignancies that express CD27.

EXPERIMENTAL DESIGN

The fully human mAb 1F5 was generated using human Ig transgenic mice and characterized by analytical and functional assays in vitro. Severe combined immunodeficient (SCID) mice inoculated with human CD27-expressing lymphoma cells were administered 1F5 to investigate direct antitumor effects. A pilot study of 1F5 was conducted in non-human primates to assess toxicity.

RESULTS

1F5 binds with high affinity and specificity to human and macaque CD27 and competes with ligand binding. 1F5 activates T cells only in combination with T-cell receptor stimulation and does not induce proliferation of primary CD27-expressing tumor cells. 1F5 significantly enhanced the survival of SCID mice bearing Raji or Daudi tumors, which may be mediated through direct effector mechanisms such as antibody-dependent cellular cytotoxicity. Importantly, administration of up to 10 mg/kg of 1F5 to cynomolgus monkeys was well tolerated without evidence of significant toxicity or depletion of circulating lymphocytes.

CONCLUSIONS

Collectively, the data suggest that the human mAb 1F5, which has recently entered clinical development under the name CDX-1127, may provide direct antitumor activity against CD27-expressing lymphoma or leukemia, independent of its potential to enhance immunity through its agonistic properties.

Fc receptor-targeted therapies for the treatment of inflammation, cancer and beyond

The direct or indirect targeting of antibody Fc receptors (FcRs) presents unique opportunities and interesting challenges for the treatment of inflammatory diseases, cancer and infection. Biological responses induced via the Fc portions of antibodies are powerful, complex and unusual, and comprise both activating and inhibitory effects. These properties can be exploited in the engineering of therapeutic monoclonal antibodies to improve their activity in vivo. FcRs have also emerged as key participants in the pathogenesis of several important autoimmune diseases, including systemic lupus erythematosus and rheumatoid arthritis. Therapeutic approaches based on antagonizing FcR function with small molecules or biological drugs such as monoclonal antibodies and recombinant soluble FcR ectodomains have gained momentum. This Review addresses various strategies to manipulate FcR function to overcome immune complex-mediated inflammatory diseases, and considers approaches to improve antibody-based anticancer therapies.

Rituximab inhibits Kv1.3 channels in human B lymphoma cells via activation of FcγRIIB receptors

Kv1.3 channels play an important role in modulating lymphocyte proliferation and apoptosis. We hypothesized that Kv1.3 channels in B lymphocytes might be regulated by rituximab, an antibody to CD20, a drug for treatments of B-cell lymphomas and autoimmune diseases. Using both whole-cell and cell-attached patch-clamp techniques, we found that rituximab inhibited Kv1.3 channels in Daudi human B lymphoma cells by promoting the channel inactivation at a concentration which was much greater than that required for activation of CD20. The effect of rituximab on Kv1.3 channels was abolished after selective blockade of FcγRIIB receptors with anti-FcγRIIB antibody. Western blot experiments showed that Daudi B cells expressed both Kv1.3 channel and the low affinity Fc receptor, FcγRIIB, which could be activated by the Fc region of rituximab. In contrast, normal lymphocytes expressed less Kv1.3 channels with faster inactivation. Confocal microscopy and flow cytometry data showed that rituximab induced apoptosis of Daudi B cells and that the effect was attenuated by blockade of FcγRIIB receptors and partially mimicked by inhibition of Kv1.3 channels. These results suggest that in addition to previously described complement-dependent cytotoxicity, rituximab also induces apoptosis of malignant B lymphocyte by stimulating FcγRIIB receptors and inhibiting Kv1.3 channels.

Antibodies against CD20 or B-cell receptor induce similar transcription patterns in human lymphoma cell lines

Background

CD20 is a cell surface protein exclusively expressed on B cells. It is a clinically validated target for Non-Hodgkin's lymphomas (NHL) and autoimmune diseases. The B cell receptor (BCR) plays an important role for development and proliferation of pre-B and B cells. Physical interaction of CD20 with BCR and components of the BCR signaling cascade has been reported but the consequences are not fully understood.

Methodology

In this study we employed antibodies against CD20 and against the BCR to trigger the respective signaling. These antibodies induced very similar expression patterns of up- and down-regulated genes in NHL cell lines indicating that CD20 may play a role in BCR signaling and vice versa. Two of the genes that were rapidly and transiently induced by both stimuli are CCL3 and CCL4. 4 hours after stimulation the concentration of these chemokines in culture medium reaches a maximum. Spleen tyrosine kinase Syk is a cytoplasmic tyrosine kinase and a key component of BCR signaling. Both siRNA mediated silencing of Syk and inhibition by selective small molecule inhibitors impaired CCL3/CCL4 protein induction after treatment with either anti-CD20 or anti-BCR antibodies.

Conclusion

Our results suggest that treatment with anti-CD20 antibodies triggers at least partially a BCR activation-like response in NHL cell lines.

Non-classical binding of a polyreactive α-type anti-idiotypic antibody to B cells

Detailed information on the immunological relevance of α-type anti-idiotypic antibodies is lacking after more than 30 years since Jerne postulated his Idiotypic Network Theory. The B7Y33 mutant is a mouse-human chimeric version of the B7 MAb, a polyreactive α-type anti-idiotypic antibody, generated against an anti-GM2 ganglioside IgM Ab1 antibody. It retained the unusual self-binding activity and multispecificity of the parental murine antibody, being able to recognize several anti-ganglioside IgM antibodies as well as non-immunoglobulin antigens. Previous work with the murine B7 MAb suggested that this antibody might have immunoregulatory properties, and therefore we investigated the possible interaction of B7Y33 with immune cells. We found that B7Y33 binds to human and murine B lymphocytes. Inhibition assays using flow cytometry indicated that this antibody is capable of binding the Fc γ receptor II (FcγRII). The recognition of FcγRII-expressing K562, Raji and Daudi human cell lines, together with the capability of inhibiting the binding of an anti-human FcγRII antibody to these cells, suggest that B7Y33 interacts with both the FcγRIIa and FcγRIIb isoforms. We evaluated the contribution to the binding of different surface-exposed residues at the top of the heavy chain variable region (VH) CDR loops through the construction of mutants with substitutions in the three conventional VH CDRs (HCDRs) and the "HCDR4", located in the framework 3 (HFR3). In addition, we assessed the involvement of the Fc region by performing key mutations in the CH2 domain. Furthermore, chimeric hybrid molecules were obtained by combining the B7Y33 heavy chain with unrelated light chains. Our results indicate that the multispecificity and self-binding properties of B7Y33 are not linked to its recognition of B lineage cells, and that this phenomenon occurs in a non-classical way with the participation of both the variable and constant regions of the antibody. Two possible models for this interaction are proposed, with B7Y33 binding to two FcγRIIb molecules through the Fc and Fv regions, or simultaneously to FcγRIIb and another unknown antigen on B cells. The FcγRIIb has recently received great attention as an attractive target for therapies directed to B lymphocytes. The recognition of peripheral B lymphocytes from B cell chronic lymphocytic leukemia (B-CLL) patients by B7Y33 suggests its potential application for the treatment of B cell malignancies.

Metastatic melanomas express inhibitory low affinity fc gamma receptor and escape humoral immunity

Our research, inspired by the pioneering works of Isaac Witz in the 1980s, established that 40% of human metastatic melanomas express ectopically inhibitory Fc gamma receptors (FcγRIIB), while they are detected on less than 5% of primary cutaneous melanoma and not on melanocytes. We demonstrated that these tumoral FcγRIIB act as decoy receptors that bind the Fc portion of antimelanoma IgG, which may prevent Fc recognition by the effector cells of the immune system and allow the metastatic melanoma to escape the humoral/natural immune response. The FcγRIIB is able to inhibit the ADCC (antibody dependent cell cytotoxicity) in vitro. Interestingly, the percentage of melanoma expressing the FcγRIIB is high (70%) in organs like the liver, which is rich in patrolling NK (natural killer) cells that exercise their antitumoral activity by ADCC. We found that this tumoral FcγRIIB is fully functional and that its inhibitory potential can be triggered depending on the specificity of the anti-tumor antibody with which it interacts. Together these observations elucidate how metastatic melanomas interact with and potentially evade humoral immunity and provide direction for the improvement of anti-melanoma monoclonal antibody therapy.