Mice carrying a CD20 gene disruption

Sequential antigen loss and branching evolution in lymphoma after CD19- and CD20-targeted T-cell-redirecting therapy

ABSTRACT

CD19 chimeric antigen receptor (CAR) T cells and CD20 targeting T-cell-engaging bispecific antibodies (bispecs) have been approved in B-cell non-Hodgkin lymphoma lately, heralding a new clinical setting in which patients are treated with both approaches, sequentially. The aim of our study was to investigate the selective pressure of CD19- and CD20-directed therapy on the clonal architecture in lymphoma. Using a broad analytical pipeline on 28 longitudinally collected specimen from 7 patients, we identified truncating mutations in the gene encoding CD20 conferring antigen loss in 80% of patients relapsing from CD20 bispecs. Pronounced T-cell exhaustion was identified in cases with progressive disease and retained CD20 expression. We also confirmed CD19 loss after CAR T-cell therapy and reported the case of sequential CD19 and CD20 loss. We observed branching evolution with re-emergence of CD20+ subclones at later time points and spatial heterogeneity for CD20 expression in response to targeted therapy. Our results highlight immunotherapy as not only an evolutionary bottleneck selecting for antigen loss variants but also complex evolutionary pathways underlying disease progression from these novel therapies.

Advances in Current Drugs and Formulations for the Management of Atopic Dermatitis

Atopic dermatitis (AD) is a chronic, relapsing inflammatory skin disease with a complex pathophysiology. Treatment of AD remains challenging owing to the presence of a wide spectrum of clinical phenotypes and limited response to existing therapies. However, recent genetic, immunological, and pathophysiological insights into the disease mechanism resulted in the invention of novel therapeutic drug candidates. This review provides a comprehensive overview of current therapies and assesses various novel drug delivery strategies currently under clinical investigation. Further, this review majorly emphasizes on various topical treatments including emollient therapies, barrier repair agents, topical corticosteroids (TCS), phosphodiesterase 4 (PDE4) inhibitors, calcineurin inhibitors, and Janus kinase (JAK)-signal transducer and activator of transcription (STAT) pathway inhibitors. It also discusses biological and systemic therapies, upcoming treatments based on ongoing clinical trials. Additionally, this review scrutinized the use of pharmaceutical inactive ingredients in the approved topical dosage forms for AD treatment.

Targeting NF-κB Signaling in Cancer Stem Cells: A Narrative Review

Among the cell populations existing within a tumor, cancer stem cells are responsible for metastasis formation and chemotherapeutic resistance. In the present review, we focus on the transcription factor NF-κB, which is present in every cell type including cancer stem cells. NF-κB is involved in pro-tumor inflammation by its target gene interleukin 1 (IL1) and can be activated by a feed-forward loop in an IL1-dependent manner. Here, we summarize current strategies targeting NF-κB by chemicals and biologicals within an integrated cancer therapy. Specifically, we start with a tyrosine kinase inhibitor targeting epidermal growth factor (EGF)-receptor-mediated phosphorylation. Furthermore, we summarize current strategies of multiple myeloma treatment involving lenalidomide, bortezomib, and dexamethasone as potential NF-κB inhibitors. Finally, we discuss programmed death-ligand 1 (PD-L1) as an NF-κB target gene and its role in checkpoint therapy. We conclude, that NF-κB inhibition by specific inhibitors of IκB kinase was of no clinical use but inhibition of upstream and downstream targets with drugs or biologicals might be a fruitful way to treat cancer stem cells.

Role of Rituximab in the Treatment of Pemphigus Vulgaris: Patient Selection and Acceptability

Anti-CD20 monoclonal antibody rituximab is an approved adjuvant treatment, in combination with oral corticosteroids, for patients with pemphigus vulgaris, a severe and potentially life-threatening autoimmune blistering skin disorder. Updated approaches to the management of pemphigus vulgaris support rituximab as a first-line adjuvant treatment to induce remission early in the course of disease; however, its feasibility in the clinical setting is often reduced by a series of limitations, including high cost of this biological drug, physician and patient concern for the risk of adverse reactions, and uncertainty regarding the optimum dosing and schedule of administration. The standard approved rituximab dosages, which are derived from lymphoma protocols, have been recognized to exceed the effective dose required for inducing B cell depletion, since the B cell burden in pemphigus vulgaris is much lower than in lymphoproliferative disorders. To overcome these limitations, recent research has investigated alternative regimens of rituximab, using lower doses of the drug. Moreover, differences in patient and disease characteristics that are highlighted in the literature strongly suggest that therapy should be tailored individually on a case-by-case basis: personalized treatment schedules may be necessary to optimize response to treatment and tolerability in different subjects, with the possibility of repeated infusions for severe forms and in case of relapse. Finally, low-dose regimens of rituximab were suggested to be favorable during the COVID-19 pandemic by providing a lesser degree of immune cell depletion while retaining a sufficient response. In conclusion, the current literature suggests that lower-dose regimens of rituximab are not only tolerable and cost-effective but may also be associated with a positive response in pemphigus vulgaris, comparable to that achieved with higher doses especially in early disease. Further evidence from rigorous clinical trials will be required to optimize lower-dose regimens of RTX and establish their position within the treatment scenario of pemphigus vulgaris.

The regulation and function of CD20: an "enigma" of B-cell biology and targeted therapy

The introduction of anti-CD20 monoclonal antibodies such as rituximab, ofatumumab, or obinutuzumab improved the therapy of B-cell malignancies even though the precise physiological role and regulation of CD20 remains unclear. Furthermore, CD20 expression is highly variable between different B-cell malignancies, patients with the same malignancy, and even between intraclonal subpopulations in an individual patient. Several epigenetic (EZH2, HDAC1/2, HDAC1/4, HDAC6, complex Sin3A-HDAC1) and transcription factors (USF, OCT1/2, PU.1, PiP, ELK1, ETS1, SP1, NFκB, FOXO1, CREM, SMAD2/3) regulating CD20 expression (encoded by MS4A1) have been characterized. CD20 is induced in the context of microenvironmental interactions by CXCR4/SDF1 (CXCL12) chemokine signaling and the molecular function of CD20 has been linked to the signaling propensity of B-cell receptor (BCR). CD20 has also been shown to interact with multiple other surface proteins on B cells (such as CD40, MHCII, CD53, CD81, CD82, and CBP). Current efforts to combine anti-CD20 monoclonal antibodies with BCR signaling inhibitors targeting BTK or PI3K (ibrutinib, acalabrutinib, idelalisib, duvelisib) or BH3-mimetics (venetoclax) lead to the necessity to better understand both the mechanisms of regulation and the biological functions of CD20. This is underscored by the observation that CD20 is decreased in response to the "BCR inhibitor" ibrutinib which largely prevents its successful combination with rituximab. Several small molecules (such as histone deacetylase inhibitors, DNA methyl-transferase inhibitors, aurora kinase A/B inhibitors, farnesyltransferase inhibitors, FOXO1 inhibitors, and bryostatin-1) are being tested to upregulate cell-surface CD20 levels and increase the efficacy of anti-CD20 monoclonal antibodies. Herein, we review the current understanding of CD20 function, and the mechanisms of its regulation in normal and malignant B cells, highlighting the therapeutic implications.

Calcium Channel Blockers Impair the Antitumor Activity of Anti-CD20 Monoclonal Antibodies by Blocking EGR-1 Induction

Direct cell death induction, in addition to immune-effector cell-mediated mechanisms, is one of the key mechanisms of action of anti-CD20 antibodies, and yet the signaling pathways implicated remain poorly investigated. Here we show that the transcription factor EGR-1 is rapidly induced by anti-CD20 antibodies and is a key mediator for CD20-induced cell death. EGR-1 induction results from an increased calcium influx induced by anti-CD20 antibodies. We show that both rituximab and obinutuzumab induce calcium influx, albeit through different mechanisms, and this influx is crucial for cell death induction. Inhibition of the calcium flux with calcium channel blockers (CCB) abolished EGR-1 induction and impaired the efficacy of anti-CD20 antibodies in preclinical in vitro and in vivo models. Finally, we investigated the impact of CCBs in patients treated with anti-CD20 antibodies included in the clinical trials GOYA and REMARC, and found that patients simultaneously receiving CCBs and anti-CD20 therapy have a shorter progression-free survival and overall survival. These results reveal EGR-1 as a key mediator of the direct cytotoxic activity of anti-CD20 antibodies and provide a rationale to evaluate EGR-1 expression as a new biomarker to predict response to anti-CD20 treatment. In addition, our findings show that calcium influx is required for anti-CD20-mediated tumor cell death and suggest that simultaneous administration of calcium channel blocking agents could be deleterious in patients receiving anti-CD20-based immunotherapy.

CD20 is dispensable for B-cell receptor signaling but is required for proper actin polymerization, adhesion and migration of malignant B cells

Surface protein CD20 serves as the critical target of immunotherapy in various B-cell malignancies for decades, however its biological function and regulation remain largely elusive. Better understanding of CD20 function may help to design improved rational therapies to prevent development of resistance. Using CRISPR/Cas9 technique, we have abrogated CD20 expression in five different malignant B-cell lines. We show that CD20 deletion has no effect upon B-cell receptor signaling or calcium flux. Also B-cell survival and proliferation is unaffected in the absence of CD20. On the contrary, we found a strong defect in actin cytoskeleton polymerization and, consequently, defective cell adhesion and migration in response to homeostatic chemokines SDF1α, CCL19 and CCL21. Mechanistically, we could identify a reduction in chemokine-triggered PYK2 activation, a calcium-activated signaling protein involved in activation of MAP kinases and cytoskeleton regulation. These cellular defects in consequence result in a severely disturbed homing of B cells in vivo.

How the discovery of rituximab impacted the treatment of B-cell non-Hodgkin's lymphomas

Non-Hodgkin's lymphoma (NHL) is the sixth-most common cancer in the UK, accounting for around 13,700 new cases every year. Until the late 1990s, treatment relied on intensive chemotherapy, such as CHOP (cyclophosphamide-doxorubicin HCl-vincristine [Oncovin]-prednisone). The use of standard CHOP therapy and its variations had resulted in poor five-year survival rates (as low as 26%), particularly in patients with aggressive NHL. Rituximab (Rituxan) was the first chimeric (mouse/human) monoclonal antibody approved for the treatment of NHL. It was approved by the US Food and Drug Administration in 1997 for indolent forms of NHL. It subsequently received EU approval in June 1998, and was licensed under the trade name Mabthera (Roche, Basel, Switzerland). It then went on to be approved for the first-line treatment of aggressive forms of NHL, such as diffuse large B-cell lymphoma (to be used in combination with CHOP or other anthracycline-based chemotherapy) in 2006. It is directed against the CD20 protein, an antigen found on the surface of B-cell lymphomas. With minimal toxicity, activity as a single-agent (for indolent forms of NHL) and safety when combined with chemotherapy (for aggressive forms), it represents great progress in this field. Here, we analyze how this antibody therapeutic was developed from basic molecular and cellular considerations through to preclinical and clinical evaluations and how it came to be a first-line treatment for NHL, and we discuss the impacts the advent of rituximab had on treatment outcomes for patients with DLBCL compared with the pre-rituximab era.

Host response genes associated with nodular gastritis in Helicobacter pylori infection

BACKGROUND

Chronic Helicobacter pylori infection in children induces lymphoid hyperplasia called nodular gastritis (NG) at the antral gastric mucosa. The aim of this study was to evaluate genes in gastric biopsy on microarray analysis, to identify molecules associated with NG on comparison with NG-negative pediatric corpus tissue and with H. pylori-infected adult tissue with atrophic gastritis (AG).

METHODS

Eight pediatric and six adult H. pylori-infected patients, as well as six pediatric and six adult uninfected patients were evaluated. All infected adults had AG. NG was observed in the antrum of all eight pediatric patients and in the corpus of three patients. Adult and uninfected patients were free of NG; that is, only pediatric H. pylori-infected patients had NG. Total RNA was purified from gastric biopsy, and microarray analysis was performed to compare gene expression between groups. The three infected children with NG in both the antrum and corpus were excluded from analysis of corpus samples.

RESULTS

The number of genes significantly up- or downregulated (fold change >3, P < 0.01) compared with uninfected controls varied widely: 72 in pediatric antrum, 45 in pediatric corpus, 103 in adult antrum and 71 in adult corpus. Nineteen genes had significantly altered expression in the antrum of NG tissue compared with NG-negative pediatric corpus tissue and adult AG tissue. The CD20 B-cell specific differentiation antigen had the most pronounced increase. Previously described regulators of NG development were not predominantly upregulated in the NG mucosa.

CONCLUSIONS

CD20 overexpression may play an important role in lymphoid follicle enlargement and NG.

Cancer stem cell surface markers on normal stem cells

The cancer stem cell (CSC) hypothesis has captured the attention of many scientists. It is believed that elimination of CSCs could possibly eradicate the whole cancer. CSC surface markers provide molecular targeted therapies for various cancers, using therapeutic antibodies specific for the CSC surface markers. Various CSC surface markers have been identified and published. Interestingly, most of the markers used to identify CSCs are derived from surface markers present on human embryonic stem cells (hESCs) or adult stem cells. In this review, we classify the currently known 40 CSC surface markers into 3 different categories, in terms of their expression in hESCs, adult stem cells, and normal tissue cells. Approximately 73% of current CSC surface markers appear to be present on embryonic or adult stem cells, and they are rarely expressed on normal tissue cells. The remaining CSC surface markers are considerably expressed even in normal tissue cells, and some of them have been extensively validated as CSC surface markers by various research groups. We discuss the significance of the categorized CSC surface markers, and provide insight into why surface markers on hESCs are an attractive source to find novel surface markers on CSCs.

Rituximab: modes of action, remaining dispute and future perspective

Less than two decades ago, immunotherapy joined chemotherapy and radiotherapy as an effective approach for the treatment of cancer. The anti-CD20 monoclonal antibody, rituximab, is now used to treat almost all types of non-Hodgkin's B-cell lymphomas, and it could be useful in the treatment of other diseases with B-cell involvement. Upon binding, rituximab induces death of the target cells. It seems to act not only by activating immune system defense mechanisms such as complement-dependent and antibody-dependent cellular cytotoxicity, but also by inducing direct cell death. In this paper, we review current knowledge on rituximab mechanisms of action, with particular attention to its direct effects, and also highlight potential future avenues of research.

The MS4A family: counting past 1, 2 and 3

The MS4A (membrane-spanning 4-domain family, subfamily A) family of proteins contains some well-known members including MS4A1 (CD20), MS4A2 (FcɛRIβ) and MS4A3 (HTm4). These three MS4A family members are expressed on the cell surface of specific leukocyte subsets and have been well characterized as having key roles in regulating cell activation, growth and development. However, beyond MS4A1-3 there are a large number of related molecules (18 to date in humans) where our understanding of their biological roles is at a relatively nascent stage. This review examines the larger MS4A family focusing on their structure, expression, regulation and characterized and/or emerging biological roles. Our own work on one family member MS4A8B, and its possible role in epithelial cell regulation, is also highlighted.

Rituximab in the treatment of peripheral neuropathy associated with monoclonal gammopathy

Peripheral neuropathy associated with immunoglobulin (Ig)M gammopathy and anti-myelin-associated glycoprotein antibodies is frequently treatment-resistant and different treatment regimens carry substantial toxicity and side effects. More recently, the chimeric anti-CD20 monoclonal antibody rituximab has shown benefits in the treatment of peripheral neuropathy associated with IgM gammopathy with a favorable side-effect profile. There are no published reports of its use in the treatment of neuropathy associated with IgG and IgA gammopathies. Rituximab is usually given at 375 mg/m(2) intravenously with four weekly doses that may be repeated after 6-12 months. Large controlled studies are still pending but rituximab is an exciting and promising treatment offering another option in the treatment of peripheral neuropathy associated with IgM monoclonal gammopathy.

Reduced T-dependent humoral immunity in CD20-deficient mice

CD20 is a tetraspanning membrane protein expressed on B lymphocytes. CD20 deficiency in both mice and humans has recently been shown to have deleterious effects on Ab responses to T-independent Ags; however, no effect on T-dependent immunity has been reported. In this study, we used a Cd20⁻/⁻ mouse line to evaluate Ab responses to adeno-associated virus and SRBCs. The neutralizing Ab response to adeno-associated virus was significantly reduced by CD20 deficiency; both primary (IgM) and secondary (IgG1 and IgG2b) responses to SRBC were also reduced in Cd20⁻/⁻ mice, and this was associated with a reduction in the number of germinal center B cells. A successful humoral response requires the integration of intracellular signaling networks that critically rely on calcium mobilization. In this article, we confirm that BCR-mediated calcium mobilization is reduced in Cd20⁻/⁻ murine B cells after BCR stimulation in vitro, and further show that the reduction is due to an effect on calcium influx rather than calcium release from intracellular stores. Calcium-dependent upregulation of CD69 was impaired in CD20-deficient B cells, as was upregulation of CD86. Altogether, this study demonstrates a role for CD20 in B cell activation and T-dependent humoral immunity.

Anti-CD20 monoclonal antibodies: beyond B-cells

Anti-CD20 monoclonal antibodies (MoAbs), employed in treating CD20⁺ lymphomas and autoimmune diseases, appear to have broader functions than just eradicating malignant B-cells and decreasing autoantibody production. Rituximab-induced T-cell inactivation, reported both in-vitro and in-vivo, may contribute to the increased risk of T-cell-dependent infections, observed in patients receiving this therapy. T-cell polarization into a suppressive phenotype, often observed in patients receiving rituximab for autoimmune disorders, was reported to be associated with prolonged remissions. Elimination of B-cells serving as antigen-presenting cells, thereby causing impaired T-cell activation, could play a significant role in induction of these changes. Direct binding of rituximab to a CD20dim T-cell population, inducing its depletion, may contribute to the decreased T-cell activation following rituximab therapy. Further investigation of the complex network through which rituximab and new anti-CD20 MoAbs act, would advance the employment of these agents in different clinical settings.

Anti-CD20 monoclonal antibodies in chronic lymphocytic leukemia

INTRODUCTION

The last decade has witnesd immense progress in the treatment of chronic lymphocytic leukemia (CLL). Chemoimmunotherapy (CIT) combining rituximab and fludarabine with cyclophosphamide (FCR) in the frontline setting has clearly been shown to improve outcomes in patients with CLL. Building on the success achieved with rituximab, other anti-CD20 monoclonal antibodies (mAbs) are being investigated. Novel bioengineering techniques have helped in the development of anti-CD20 mAbs. One antibody, ofatumumab, was recently approved for the treatment of refractory CLL. A type II anti-CD20 mAb, GA-101 (obinutuzumab), is currently in clinical trials. This short review focuses on ongoing clinical trials of anti-CD20 mAbs in CLL.

AREAS COVERED

Literature search was performed using PubMed ( www.clinicaltrials.gov (till August 2012)), and recent American Society of Clinical Oncology (ASCO), American Society of Hematology (ASH), European Hematology association (EHA), International workshop on CLL (iwCLL) abstracts, using the primary search terms 'anti-CD20 monoclonal antibody' with/without CLL. Articles were chosen on the basis of relevance of anti-CD20 mAbs to CLL therapy.

EXPERT OPINION

Rituximab, the prototype anti-CD20 mAb, forms the core of CIT in CLL. The success of rituximab and ofatumumab has led investigators to evaluate other anti-CD20 mAbs in the treatment of CLL.

Generation of induced pluripotent stem cells from mouse cancer cells

Reprogramming of cancer cells into induced pluripotent stem cells (iPSCs) opens up the possibility of converting malignant cells into any cell type, including those best suited to be developed as cancer vaccines. Mouse models are needed to evaluate and optimize the therapeutic efficacy of such novel cancer vaccines. However, only human cancer cell lines have been reported as being reprogrammed into iPSCs. Here, we report a proof-of-principle study which shows that mouse cancer cells can be reprogrammed into iPSCs that are capable of subsequent differentiation. Four canonical reprogramming transcription factors, Oct3/4, Sox2, Klf4, and c-Myc, were introduced by plasmid transfection into mouse Lewis lung carcinoma D122 harboring Nanog-GFP reporter. Green fluorescent cells were found clustered into embryonic stem cell (ESC)-like colonies expressing ESC markers, Oct4 and SSEA-1. Bisulfite genomic sequencing analyses of these cells revealed hypomethylation of the Nanog promoter. The expression of a host of pluripotency genes by these reprogrammed cells at levels similar to those of ESCs was confirmed by quantitative real-time PCR. Functional pluripotency of the reprogrammed cells was demonstrated by their ability to form embryoid bodies and differentiate into neuronal progenitors on retinoic acid treatment. This study indicates the feasibility of developing iPSC-based experimental cancer vaccines for immunotherapy in mouse models.

Resistance--the true face of biological defiance

Biological therapeutics are widely used in chronic inflammatory and malignant disease. The underlying mechanisms of treatment failure for these drugs are poorly understood. Resistance to these biological agents and the further subdivision into intrinsic and acquired resistance are not clearly defined. In this review, we explore the current understanding of the mechanisms of action of several biological agents as well as the complex biological processes that underlie resistance. A better understanding of why biologicals fail might help to improve their single or combinational use and will ultimately help to alleviate disease burden more efficiently.

Rituximab resistance

Rituximab has become a ubiquitous component of treatment regimens for follicular non-Hodgkin lymphoma. Despite widespread clinical use, the mechanisms by which tumor cells resist rituximab-mediated destruction remain unclear. Rituximab relies in part on immune effector mechanisms for its antitumor effect, and thus resistance may be mediated not only by intrinsic tumor-cell alterations but also by the host immunological environment. In this article, we explore the mechanisms of action of rituximab, the incidence of rituximab resistance, and potential mechanisms of resistance. Finally, we discuss novel approaches to modulate the antibody, the tumor cell, and the host immunologic environment to overcome rituximab resistance. Further research into the mechanisms of rituximab resistance will be essential to improving the efficacy of anti-CD20 therapy in NHL, and may also pay dividends in the optimization of monoclonal antibody therapy across a wide range of diseases.

Diversity in antibody-based approaches to non-Hodgkin lymphoma

Non-Hodgkin lymphoma (NHL) remains one of the most common cancers in the US, with survival dependent on the type and stage of disease. B-cell lymphomas account for approximately 85% of all cases of NHL, and are commonly treated with chemotherapy, or monoclonal antibodies (mAbs) that target CD20 antigens on the surface of malignant tumors. The use of mAbs, either as single agents or in combination with chemotherapy, has made a huge impact on NHL survival rates. Rituximab remains the most commonly used and established mAb, and is used in a wide range of NHLs, but does not produce an effective therapeutic response in all patients. Novel therapeutics with enhanced binding affinity or alternative antigen targets are currently in development and in some cases have demonstrated improved efficacy over currently available treatments. Radioimmunotherapy has been included in transplant conditioning regimens to improve long-term disease control while limiting toxicity. These regimens have been safe, effective, and feasible, and are therefore promising for patients who cannot tolerate high-dose chemotherapy and/or total body irradiation.

CD20 as a target for therapeutic type I and II monoclonal antibodies

The last decade has seen the monoclonal antibody (mAb), rituximab, transform clinical management of many non-Hodgkin lymphomas and more recently provide new opportunities for controlling autoimmune conditions, such as rheumatoid arthritis. Although not yet fully determined, the explanation for this success appears to lie with the inherent properties of its target, CD20, which allow rituximab to recruit potent cytotoxic effectors with unusual efficiency. In this review we detail the properties of CD20 that make it such an effective therapeutic target and describe how different mAbs change the membrane distribution and internalization of CD20 and have distinct modes of cytotoxic activity.

CD20 deficiency in humans results in impaired T cell-independent antibody responses

CD20 was the first B cell differentiation antigen identified, and CD20-specific mAbs are commonly used for the treatment of B cell malignancies and autoantibody-mediated autoimmune diseases. Despite this the role of CD20 in human B cell physiology has remained elusive. We describe here a juvenile patient with CD20 deficiency due to a homozygous mutation in a splice junction of the CD20 gene (also known as MS4A1) that results in "cryptic" splicing and nonfunctional mRNA species. Analysis of this patient has led us to conclude that CD20 has a central role in the generation of T cell-independent (TI) antibody responses. Key evidence to support this conclusion was provided by the observation that although antigen-independent B cells developed normally in the absence of CD20 expression, antibody formation, particularly after vaccination with TI antigens, was strongly impaired in the patient. Consistent with this, TI antipolysaccharide B cell responses were severely impeded in CD20-deficient mice. Our study therefore identifies what we believe to be a novel type of humoral immunodeficiency caused by CD20 deficiency and characterized by normal development of antigen-independent B cells, along with a reduced capacity to mount proper antibody responses.

Molecular mechanisms of resistance to Rituximab and pharmacologic strategies for its circumvention

The introduction of Rituximab has greatly improved therapeutic options for patients with B-cell non-Hodgkin lymphoma (B-NHL). However, a substantial fraction of patients with aggressive B-NHL fails first-line therapy, and most patients with relapsing indolent B-NHL eventually acquire Rituximab resistance. Molecular understanding of the underlying mechanisms facilitates the development of pharmacologic strategies to overcome resistance. Rituximab exerts its activity on CD20-expressing B-cells by indirect and direct effector mechanisms. Indirect mechanisms are complement-dependent cytotoxicity (CDC), and antibody-dependent cell-mediated cytotoxicity (ADCC). Direct activities, such as growth inhibition, induction of apoptosis and chemosensitisation, have been reported, but are less defined. Moreover, the relative contribution of CDC, ADCC and direct mechanisms to the activity of Rituximab in vivo is unclear. Down-regulation of CD20 and expression of complement inhibitors have been described as escape mechanisms in B-NHL. Recent reports suggest that deregulated phosphoinositide-3-kinase (PI3K)/Akt, mitogen-activated kinases (MAPK) and nuclear-factor kappaB (NF-kappaB), as well as up-regulation of anti-apoptotic proteins may determine the efficacy of Rituximab to kill B-NHL cells in vitro and in vivo. The latter signalling pathways are attractive targets for pharmacologic modulation of resistance to Rituximab. With the advent of new inhibitors and antibodies, rationally designed clinical trials addressing Rituximab resistance are feasible.

Ten years of rituximab in NHL

BACKGROUND

Rituximab, a chimeric mouse/human monoclonal antibody targeting the pan-B-cell antigenic marker CD20, was the first monoclonal antibody licensed for use in the treatment of cancer.

OBJECTIVE

This review focuses on the impact of rituximab in the treatment of patients with B-cell non-Hodgkin lymphoma (NHL).

METHODS

Three key areas related to the use of rituximab in B-cell NHL are discussed: mechanism of action, clinical efficacy in both indolent and aggressive disease, and safety of its use as both monotherapy and in combination with chemotherapy.

RESULTS/CONCLUSIONS

Rituximab has demonstrated significant clinical efficacy in the treatment of NHL, particularly in combination with chemotherapy, and its use has revolutionized the treatment of both indolent and aggressive B-cell NHL over the past decade. Furthermore, consistent toxicity data have been obtained with a safe and tolerable profile in most patients.

New insights into the mechanisms of action of radioimmunotherapy in lymphoma

The exquisite sensitivity of haematological malignancies to targeted radiation alongside the impressive results achieved by the pioneers in this field suggests that radioimmunotherapy is likely to be a productive area for future clinical research. Recent experimental work has demonstrated that the combination of targeted radiation and antibody effector mechanisms are critical to long-term clearance of tumour. This review provides the background of clinical and biological insights into the mechanisms of action of radioimmunotherapy.

B-cell depletion using an anti-CD20 antibody augments antitumor immune responses and immunotherapy in nonhematopoetic murine tumor models

The role played by B cells in cancer biology is complex and somewhat controversial. Previous studies using genetically engineered mice suggest that B cells may be immunosuppressive and inhibit tumor rejection. However, the effects of B-cell depletion employing an antibody in mice bearing solid tumors has not been tested owing to difficulties in making an effective antimouse CD20 antibody (similar to rituximab). Injection of a newly developed antimouse CD20 antibody was effective in depleting circulating B cells from blood and lymph nodes, although depletion was less complete in the spleen. B-cell depletion slowed the growth of new solid tumors (not expressing CD20) and retarded the growth of established tumors but did not induce tumor regression. However, when the antibody was combined with an active immunotherapy approach using an adenovirus vaccine expressing the human papilloma virus-E7 gene (Ad.E7) in mice bearing TC1 tumors (murine lung cancer cells expressing human papilloma virus-E7), we noted enhanced antitumor effects and increased numbers of tetramer+/CD8+ T cells within the spleens and activated CD8+ T cells within tumors. B-cell depletion using an anti-CD20 antibody was thus effective in retarding tumor growth in multiple solid tumor models and augmenting immunotherapy in a tumor vaccine model. These studies raise the possibility that B-cell depletion may be a useful adjunct in human immunotherapy trials.

NK cell-mediated lysis is essential to kill Epstein-Barr virus transformed lymphoblastoid B cells when using rituximab

Rituximab is a humanized chimeric monoclonal antibody, targeted against the pan B cell marker CD20. It is frequently used to treat a variety of B cell lymphomas and immunosuppression associated lymphoproliferations such as posttransplant lymphoproliferative disorder (PTLD). The response rate of rituximab treatment is 65%, but the exact in vivo mechanism of action is not yet fully understood, although antibody-dependent cell-mediated cytotoxicity (ADCC), complement-dependent cytotoxicity (CDC), and direct induction of apoptosis have been suggested as effector mechanism. Rituximab may affect different types of lymphomas through different mechanisms. As lymphoblastoid cell lines (LCLs) are well-established in vitro models of PTLD, we investigated the effect of rituximab on these cells using a custom built automated laser confocal fluorescent microscope. We found that rituximab alone was not effective at inducing cell death of EBV-transformed B cells. The antibody was effective in the complement-mediated CDC. Rituximab could induce NK cell-mediated ADCC but it was more effective in the presence of untreated fresh human plasma compared to heat-inactivated human plasma. Our data suggest that complement-enhanced NK-mediated ADCC is required for effective rituximab mediated killing of EBV-transformed B cells. Determining and monitoring of serum complement levels and in vitro killing efficacy of NK cells of PTLD patients might help to predict resistant cases to rituximab therapy. On the other hand our results suggest a possibility that rituximab should be combined only with cytotoxic drugs that spare NK function when treating PTLD patients.

Targeting Bcl-2 family proteins modulates the sensitivity of B-cell lymphoma to rituximab-induced apoptosis

The chimeric monoclonal antibody rituximab is the standard of care for patients with B-cell non-Hodgkin lymphoma (B-NHL). Rituximab mediates complement-dependent cytotoxicity and antibody-dependent cellular cytotoxicity of CD20-positive human B cells. In addition, rituximab sensitizes B-NHL cells to cytotoxic chemotherapy and has direct apoptotic and antiproliferative effects. Whereas expression of the CD20 antigen is a natural prerequisite for rituximab sensitivity, cell-autonomous factors determining the response of B-NHL to rituximab are less defined. To this end, we have studied rituximab-induced apoptosis in human B-NHL models. We find that rituximab directly triggers apoptosis via the mitochondrial pathway of caspase activation. Expression of antiapoptotic Bcl-xL confers resistance against rituximab-induced apoptosis in vitro and rituximab treatment of xenografted B-NHL in vivo. B-NHL cells insensitive to rituximab-induced apoptosis exhibit increased endogenous expression of multiple antiapoptotic Bcl-2 family proteins, or activation of phosphatidylinositol-3-kinase signaling resulting in up-regulation of Mcl-1. The former resistance pattern is overcome by treatment with the BH3-mimetic ABT-737, the latter by combining rituximab with pharmacologic phosphatidylinositol-3-kinase inhibitors. In conclusion, sensitivity of B-NHL cells to rituximab-induced apoptosis is determined at the level of mitochondria. Pharmacologic modulation of Bcl-2 family proteins or their upstream regulators is a promising strategy to overcome rituximab resistance.

Bi20 (fBTA05), a novel trifunctional bispecific antibody (anti-CD20 x anti-CD3), mediates efficient killing of B-cell lymphoma cells even with very low CD20 expression levels

Trifunctional bispecific antibodies can efficiently mediate tumor cell killing by redirecting T cells and immune accessory cells to the tumor cell. Here, we describe the new trifunctional antibody, Bi20 (FBTA05, anti-CD20 x anti-CD3), that connects B cells and T cells via its variable regions and recruits FcgammaRI(+) accessory immune cells via its Fc region. Bi20 mediated efficient and specific lysis of B-cell lines and of B cells with low CD20 expression levels that were derived from CLL patients. Remarkably, T-cell activation and tumor cell killing occurred in an entirely autologous setting without additional effector cells in 5 of 8 samples. In comparison, rituximab, a chimeric monoclonal CD20 antibody, demonstrated a significantly lower B-cell eradication rate. Additionally, Bi20, but not rituximab, upregulated the activation markers CD25 and CD69 on both CD4(+) and CD8(+) T cells in the presence of accessory immune cells. CD14(+) accessory cells and the monocyte cell line THP-1 were activated via binding of the Fc region of Bi20, given that T cells were simultaneously engaged by the antibody. Bi20 induced a strong Th1 cytokine pattern characterized by high IFN-gamma and very low IL-4 secretion. In conclusion, Bi20 may offer new immunotherapeutic options for the treatment of B-cell lymphomas.

Suppression of proteoglycan-induced arthritis by anti-CD20 B Cell depletion therapy is mediated by reduction in autoantibodies and CD4+ T cell reactivity

B cells have been implicated in the pathogenesis of rheumatoid arthritis (RA) since the discovery of RA as an autoimmune disease. There is renewed interest in B cells in RA based on the clinical efficacy of B cell depletion therapy in RA patients. Although, reduced titers of rheumatoid factor and anti-cyclic citrullinated peptide Abs are recorded, the mechanisms that convey clinical improvement are incompletely understood. In the proteoglycan-induced arthritis (PGIA) mouse model of RA, we reported that Ag-specific B cells have two important functions in the development of arthritis. PG-specific B cells are required as autoantibody-producing cells as well as Ag-specific APCs. Herein we report on the effects of anti-CD20 mAb B cell depletion therapy in PGIA. Mice were sensitized to PG and treated with anti-CD20 Ab at a time when PG-specific autoantibodies and T cell activation were evident but before acute arthritis. In mice treated with anti-CD20 mAb, development of arthritis was significantly reduced in comparison to control mAb-treated mice. B cell depletion reduced the PG-specific autoantibody response. Furthermore, there was a significant reduction in the PG-specific CD4(+) T cell recall response as well as significantly fewer PG-specific CD4(+) T cells producing IFN-gamma and IL-17, but not IL-4. The reduction in PG-specific T cells was confirmed by the inability of CD4(+) T cells from B cell-depleted mice to adoptively transfer disease into SCID mice. Overall, B cell depletion during PGIA significantly reduced disease and inhibited both autoreactive B cell and T cell function.

CD20 homo-oligomers physically associate with the B cell antigen receptor. Dissociation upon receptor engagement and recruitment of phosphoproteins and calmodulin-binding proteins

B cell antigen receptor (BCR) signaling initiates sustained cellular calcium influx necessary for the development, differentiation, and activation of B lymphocytes. CD20 is a B cell-restricted tetraspanning protein organized in the plasma membrane as multimeric molecular complexes involved in BCR-activated calcium entry. Using coprecipitation of native CD20 with tagged or truncated forms of the molecule, we provide here direct evidence of CD20 homo-oligomerization into tetramers. Additionally, the function of CD20 was explored by examining its association with surface-labeled and intracellular proteins before and after BCR signaling. Two major surface-labeled proteins that coprecipitated with CD20 were identified as the heavy and light chains of cell surface IgM, the antigen-binding components of the BCR. After activation, BCR-CD20 complexes dissociated, and phosphoproteins and calmodulin-binding proteins were transiently recruited to CD20. These data provide new evidence of the involvement of CD20 in signaling downstream of the BCR and, together with the previously described involvement of CD20 in calcium influx, the first evidence of physical coupling of the BCR to a calcium entry pathway.

B-cell inhibitors as therapy for rheumatoid arthritis: an update

A revolution in the treatment of rheumatoid arthritis has occurred in recent years. This holds particularly true for B-cell-directed therapies for rheumatoid arthritis. The approval of rituximab for the treatment of rheumatoid arthritis has not only expanded the armamentarium of therapies for rheumatologists, but it has also led the way to better understanding of the biologic sequelae of these treatments as well as the potential to better understand the etiology of autoimmune diseases. This review updates the latest B-cell therapies in rheumatoid arthritis.

Depletion of B cells in murine lupus: efficacy and resistance

In mice, genetic deletion of B cells strongly suppresses systemic autoimmunity, providing a rationale for depleting B cells to treat autoimmunity. In fact, B cell depletion with rituximab is approved for rheumatoid arthritis patients, and clinical trials are underway for systemic lupus erythematosus. Yet, basic questions concerning mechanism, pathologic effect, and extent of B cell depletion cannot be easily studied in humans. To better understand how B cell depletion affects autoimmunity, we have generated a transgenic mouse expressing human CD20 on B cells in an autoimmune-prone MRL/MpJ-Fas(lpr) (MRL/lpr) background. Using high doses of a murine anti-human CD20 mAb, we were able to achieve significant depletion of B cells, which in turn markedly ameliorated clinical and histologic disease as well as antinuclear Ab and serum autoantibody levels. However, we also found that B cells were quite refractory to depletion in autoimmune-prone strains compared with non-autoimmune-prone strains. This was true with multiple anti-CD20 Abs, including a new anti-mouse CD20 Ab, and in several different autoimmune-prone strains. Thus, whereas successful B cell depletion is a promising therapy for lupus, at least some patients might be resistant to the therapy as a byproduct of the autoimmune condition itself.

Phase I to III Trials of Anti–B Cell Therapy in Non–Hodgkin's Lymphoma

Led by the anti-CD20 antibody rituximab, therapeutic monoclonal antibodies have dramatically altered the treatment of patients with non-Hodgkin's lymphoma. As the understanding of the biology of this novel therapy improves, so does the potential for further progress. There are currently four monoclonal antibodies approved by the Food and Drug Administration for the treatment of B-cell malignancies and dozens more are in various stages of development. The indications for the currently available antibodies, both labeled and unlabeled, are being expanded to include first-line treatment, maintenance strategies, and combinations with chemotherapy. Newer agents are being engineered to target novel antigens, and to interact more specifically with the host immune system. These promising therapeutics face a significant challenge in evaluation and integration in the post-rituximab world.

Radioimmunotherapy as a Therapeutic Option for Non-Hodgkin’s Lymphoma

Radioimmunotherapy (RIT) represents a relatively new antibody-based radiopharmaceutical treatment for patients with various kinds of tumors. Although the field has a long history of preclinical and clinical investigations using many different agents, to date, only 2 of these immunologically targeted radiopharmaceuticals have been cleared for commercial sale. Both of these agents ((90)Y-ibritumomab tiuxetan or "Zevalin" [Biogen-Idec, Boston, MA] and (131)I-tositumomab or "Bexxar" [GlaxoSmithKline Research, Triangle Park, NC]) are directed against the CD20 surface antigen found on normal mature B cells and greater than 95% of B-cell non-Hodgkin lymphoma (NHL). Both compounds produce similar impressive clinical outcomes (approximately 20%-40% complete response rates and 60%-80% overall response rates for patients with indolent B-cell NHL). Current protocol-based investigations of anti-CD20 RIT relate to new clinical uses and new CD20(+) targets.

Rituximab: applications in dermatology

Rituximab is a chimeric anti-CD20 monoclonal antibody which has been used extensively for B-lymphocytic malignancies. In addition, applications for autoimmune diseases have emerged in recent years. Case reports support the use of rituximab in certain dermatologic conditions, including paraneoplastic pemphigus, pemphigus vulgaris, graft versus host disease, and cutaneous B-cell malignancies. Clinical trials are lacking and would be an appropriate next step.

Cancer therapeutic antibodies come of age: targeting minimal residual disease

Ten years after the first clinical application of Rituximab, an anti-CD20 recombinant monoclonal antibody, immunotherapy has become common practice in oncology wards. Thanks to the great diversity of the immune system and the powerful methodology of genetic engineering, the pharmacologic potential of antibody-based therapy is far from exhaustion. The recent application of Trastuzumab, an antibody to a receptor tyrosine kinase, in adjuvant breast cancer therapy marks the beginning of a new phase in cancer treatment. Here we discuss molecular mechanisms of antibody-based therapy, the emerging ability to target minimal disease and the therapeutic potential of combining antibodies with other modalities.