Rituximab (monoclonal anti-CD20 antibody): mechanisms of action and resistance

Treatment of Refractory Pemphigus with the Anti-CD20 Monoclonal Antibody (Rituximab)

BACKGROUND

Pemphigus is a severe blistering disorder caused by autoantibodies to desmogleins 1 and 3. Because some patients with pemphigus never enter into remission, new immunosuppressants are warranted. Rituximab is a chimeric monoclonal antibody binding to the CD20 antigen on B cells, which proved to be effective in recalcitrant pemphigus.

OBJECTIVES

To evaluate the efficacy and safety of rituximab in refractory pemphigus and to investigate its effects on the autoantibody profile.

PATIENTS AND METHODS

Six patients with recalcitrant pemphigus were treated. Rituximab was administered intravenously at a dosage of 375 mg/m2 body surface once weekly for 4 weeks.

RESULTS

Three pemphigus foliaceus patients and 1 with mucocutaneous pemphigus vulgaris (PV) showed complete response over a follow-up period of up to 18 months. In one oral PV, control of the disease was achieved using pulse therapy with cyclophosphamide following rituximab withdrawal. In one PV with vegetating features, good improvement was obtained after 6 rituximab infusions. All patients tolerated the treatment well. Anti-desmoglein autoantibodies significantly decreased only in pemphigus foliaceus.

CONCLUSIONS

This study highlights that rituximab is a valuable drug for refractory pemphigus, although the response of mucous membranes and cutaneous folds may be delayed.

Recombinant chimeric antibody hCAb as a novel anti-human colorectal carcinoma agent

A new chimeric IgG1 antibody hCAb which could be specifically directed against a cell surface-associated glycoprotein of colorectal cancer cells was prepared by genetic engineering technology in our lab. In this study, we explored the potential therapeutic mechanisms and described the evaluation of hCAb directed against colorectal cancer. The standard 51Cr release assay showed that like many other clinically validated IgG1 monoclonal antibodies, hCAb primarily acts by antibody-dependent cell-mediated cytotoxicity (ADCC). The maximal cell lysis of ADCC induced by hCAb was over 50% in the presence of peripheral blood mononuclear cells (PBMCs). Moreover, in vivo studies showed potent antitumor effects in nude mice with SW480 and Hce-8693 tumor xenografts. The treatment with hCAb induced a dramatic reduction (over 70%) in tumor volume in comparison to untreated control group. Furthermore, during the period of treatment, the animals treated by hCAb did not show signs of wasting or other visible signs of toxicity. No obvious tissue damage in vital organs was detected. The chimeric antibody hCAb may be a promising candidate in the treatment of human colorectal cancer. This study can provide a reference for the potential application of hCAb in clinical trial.

Structural basis for recognition of CD20 by therapeutic antibody Rituximab

Rituximab is a widely used monoclonal antibody drug for treating certain lymphomas and autoimmune diseases. To understand the molecular mechanism of recognition of human CD20 by Rituximab, we determined the crystal structure of the Rituximab Fab in complex with a synthesized peptide comprising the CD20 epitope (residues 163-187) at 2.6-A resolution. The combining site of the Fab consists of four complementarity determining regions that form a large, deep pocket to accommodate the epitope peptide. The bound peptide assumes a unique cyclic conformation that is constrained by a disulfide bond and a rigid proline residue (Pro(172)). The (170)ANPS(173) motif of CD20 is deeply embedded into the pocket on the antibody surface and plays an essential role in the recognition and binding of Rituximab. The antigen-antibody interactions involve both hydrogen bonds and van der Waals contacts and display a high degree of structural and chemical complementarity. These results provide a molecular basis for the specific recognition of CD20 by Rituximab as well as valuable information for development of improved antibody drugs with better specificity and higher affinity.

Development of rituximab-resistant lymphoma clones with altered cell signaling and cross-resistance to chemotherapy

Immunotherapy with rituximab (chimeric anti-CD20 monoclonal antibody, Rituxan), alone or in conjunction with chemotherapy, has significantly improved the treatment outcome of lymphoma patients. Via an elusive mechanism, a subpopulation of patients becomes unresponsive and/or relapses. To recapitulate various aspects of acquired resistance, rituximab-resistant (RR) clones were established from lymphoma lines and compared with parental cells. Surface CD20 expression was diminished in the clones. The clones neither responded to rituximab-mediated growth reduction or complement-dependent cytotoxicity nor underwent apoptosis in response to cross-linked rituximab. Rituximab failed to chemosensitize the RR clones, which exhibited constitutive hyperactivation of the nuclear factor-kappaB and extracellular signal-regulated kinase 1/2 pathways, leading to overexpression of B-cell lymphoma protein 2 (Bcl-2), Bcl-2-related gene (long alternatively spliced variant of Bcl-x gene), and myeloid cell differentiation 1 and higher drug resistance. Unlike parental cells, rituximab neither inhibited the activity of these pathways nor diminished the expression of resistant factors. Pharmacologic inhibitors of the survival pathways or Bcl-2 family members reduced the activity of these pathways, diminished antiapoptotic protein expression, and chemosensitized the RR clones. These novel in vitro results denote that continuous long-term rituximab exposure culminates in RR clones that do not respond to rituximab-mediated effects, have altered cellular signaling dynamics, and exhibit different genetic and phenotypic properties compared with parental cells. The data also reveal that although RR clones exhibit higher resistance to rituximab and cytotoxic drugs, these clones can be chemosensitized following treatment with pharmacologic inhibitors (e.g., dehydroxymethylepoxyquinomicin, bortezomib, PD098059) that target survival/antiapoptotic pathways. The findings also identify intracellular targets for potential molecular therapeutic intervention to increase treatment efficacy. The significance and potential clinical relevance of the findings are discussed.

Rituximab (anti-CD20) zur Behandlung von bullösen Autoimmundermatosen

Treatment of autoimmune bullous diseases can often be challenging and primarily consists of conventional systemic corticosteroids and other immunosuppressant agents. Rituximab is a chimeric monoclonal antibody against human CD20 leading to a transitory B-cell depletion with a lowering of autoantibody levels. Applications for autoimmune diseases have emerged in recent years and case reports support the use of rituximab in different autoimmune blistering disorders. Of the patients treated, 90% showed significant clinical improvement. In about a third of these patients, a clinical remission requiring further immunosuppressive medication was achieved, and in about a quarter, complete long-term remission was induced. About one third of patients suffered from serious adverse events after rituximab treatment. The combination of rituximab and intravenous immune globulin or immunoadsorption appears to be advantageous in severe cases. Randomized controlled trials are necessary to better determine the efficacy and adverse effects of rituximab in the treatment of autoimmune blistering diseases.

Monoclonal Antibodies for B-Cell Lymphomas: Rituximab and Beyond

The year 2007 marks the 10th anniversary of approval by the U.S. Food and Drug Adminstration of the first monoclonal antibody for the treatment of cancer. Rituximab, an anti-CD20 chimeric monoclonal antibody, was approved for the treatment of patients with relapsed/refractory low-grade B-cell non-Hodgkin lymphomas. From an immunologic perspective, this therapeutic indication provided the long-elusive validation of immunotherapy as the fourth modality of treatment for patients with cancer. From a clinical perspective, it was hard to imagine then that this nonchemotherapeutic approach would dramatically impact the management of patients with almost every type of B-cell malignancy and that it would even find a place as a therapeutic option for patients with non-malignant disorders. Although thousands of patients have been treated worldwide with rituximab, there is still debate regarding its mechanism(s) of action. The demonstration that a number of patients do not benefit with this treatment and that no cures have been achieved with single-agent rituximab prompted several investigators to identify those barriers limiting the efficacy of this monoclonal antibody. Here, we summarize what we have learned in the past 10 years about rituximab efficacy and its mechanisms of action and resistance. We also discuss the new generation of monoclonal antibodies, the development of which has been spurred by the widespread success of anti-CD20 MAb therapy.

Non-fucosylated therapeutic antibodies as next-generation therapeutic antibodies

Most of the existing therapeutic antibodies that have been licensed and developed as medical agents are of the human IgG1 isotype, the molecular weight of which is approximately 150 kDa. Human IgG1 is a glycoprotein bearing two N-linked biantennary complex-type oligosaccharides bound to the antibody constant region (Fc), in which the majority of the oligosaccharides are core fucosylated, and it exercises the effector functions of antibody-dependent cellular cytotoxicity (ADCC) and complement-dependent cytotoxicity through the interaction of the Fc with either leukocyte receptors (FcgammaRs) or complement. Recently, therapeutic antibodies have been shown to improve overall survival as well as time to disease progression in a variety of human malignancies, such as breast, colon and haematological cancers, and genetic analysis of FcgammaR polymorphisms of cancer patients has demonstrated that ADCC is a major antineoplasm mechanism responsible for clinical efficacy. However, the ADCC of existing licensed therapeutic antibodies has been found to be strongly inhibited by serum due to nonnpecific IgG competing for binding of the therapeutics to FcgammaRIIIa on natural killer cells, which leads to the requirement of a significant amount of drug and very high costs associated with such therapies. Moreover, enhanced ADCC of non-fucosylated forms of therapeutic antibodies through improved FcgammaRIIIa binding is shown to be inhibited by the fucosylated counterparts. In fact, non-fucosylated therapeutic antibodies, not including the fucosylated forms, exhibit the strongest and most saturable in vitro and ex vivo ADCC among such antibody variants with improved FcgammaRIIIa binding as those bearing naturally occurring oligosaccharide heterogeneities and artificial amino acid mutations, even in the presence of plasma IgG. Robust stable production of completely non-fucosylated therapeutic antibodies in a fixed quality has been achieved by the generation of a unique host cell line, in which the endogenous alpha-1,6-fucosyltransferase (FUT8) gene is knocked out. Thus, the application of non-fucosylated antibodies is expected to be a promising approach as next-generation therapeutic antibodies with improved efficacy, even when administrated at low doses in humans in vivo. Clinical trials using non-fucosylated antibody therapeutics are underway at present.

Fatal adenoviral hepatitis after rituximab therapy

Rituximab is an anti-CD20 monoclonal antibody used in the treatment of B-cell proliferative disorders. Although it is very effective in many cases, a number of case reports in the literature have described fatal viral reactivations associated with rituximab therapy. We report what is to our knowledge the first case of fatal adenoviral hepatitis in a patient with Waldenstrom macroglobulinemia treated with rituximab. This case is a new example of an emerging pattern of association between rituximab therapy and fatal viral reactivations, and it urges increased vigilance when using rituximab-based treatment regimens.

Fcgamma receptor-dependent effector mechanisms regulate CD19 and CD20 antibody immunotherapies for B lymphocyte malignancies and autoimmunity

Immunotherapy using Rituximab, an unconjugated CD20 monoclonal antibody, has proven effective for treating non-Hodgkin's lymphoma and autoimmune disease. CD19 antibody immunotherapy is also effective in mouse models of lymphoma and autoimmunity. In both cases, mouse models have demonstrated that effector cell networks effectively deplete the vast majority of circulating and tissue B lymphocytes through Fcgamma receptor-dependent pathways. In mice, B cell depletion is predominantly, if not exclusively, mediated by monocytes. CD20 mAbs rapidly deplete circulating and tissue B cells in an antibody isotype-restricted manner with a hierarchy of antibody effectiveness: IgG2a/c > IgG1 > IgG2b >> IgG3. Depending on antibody isotype, mouse B cell depletion is regulated by FcgammaRI-, FcgammaRII-, FcgammaRIII-, and FcgammaRIV-dependent pathways. The potency of IgG2a/c mAbs for B cell depletion in vivo results from FcgammaRIV interactions, with likely contributions from high-affinity FcgammaRI. IgG1 mAbs induce B cell depletion through preferential, if not exclusive, interactions with low-affinity FcgammaRIII, while IgG2b mAbs interact preferentially with intermediate-affinity FcgammaRIV. By contrast, inhibitory FcgammaRIIB-deficiency significantly increases CD20 mAb-induced B cell depletion at low mAb doses by enhancing monocyte function. Thus, isotype-specific mAb interactions with distinct FcgammaRs contribute significantly to the effectiveness of CD20 mAbs in vivo. These results provide a molecular basis for earlier observations that human FcgammaRII and FcgammaRIII polymorphisms correlate with the in vivo effectiveness of CD20 antibody therapy. That the innate monocyte network depletes B cells through FcgammaR-dependent pathways during immunotherapy has important clinical implications for CD19, CD20, and other antibody-based therapies for the treatment of diverse B cell malignancies and autoimmune disease.

The CD20/alphaCD20 'suicide' system: novel vectors with improved safety and expression profiles and efficient elimination of CD20-transgenic T cells

Adoptive transfer of T lymphocytes is an attractive strategy for many experimental treatment strategies for cancer. Unfortunately, manipulated T cells could be responsible for serious adverse events. Retroviral CD20-transduced T cells may be able to control these unwanted effects. CD20-positive cells are sensitive to rituximab (RTX), a monoclonal antibody specific for CD20. This permits their selective elimination in vivo in case of adverse events. To this end, a system is required that permits efficient and safe transduction of donor T cells and effective elimination of CD20-positive T cells. We constructed different CD20-encoding retroviral vectors and investigated the impact of inclusion of the woodchuck post-transcriptional regulatory element (WPRE) and the chicken hypersensitivity site 4 insulator elements on the levels, homogeneity and stability of CD20 expression. Importantly, inclusion of either WPRE or insulator elements in the retroviral vector resulted in a dramatic improvement in the stability of CD20 expression. The insulator element also led to a much more homogeneous level of CD20 expression. We also show the efficient elimination of the CD20-transgenic T cells via RTX by different effector mechanisms. In conclusion, we have constructed CD20-encoding retroviral vectors with improved efficiency and safety profiles, which can be used as a suicide strategy.

Enhanced Fc-dependent cellular cytotoxicity of Fc fusion proteins derived from TNF receptor II and LFA-3 by fucose removal from Asn-linked oligosaccharides

Fucose removal from complex-type oligosaccharide of human IgGs results in a major enhancement of Fc-dependent cellular cytotoxicity. The aim of this study was to determine the effect of fucose removal on the effector function of another class of clinically important molecules that can effect cellular cytotoxicity, Fc fusion proteins. The receptors chosen for study were TNF receptor II and LFA-3, both of which have therapeutic significance. The fucosylated versions of these fusion proteins were produced in unmodified CHO cells, whereas the nonfucosylated counterparts were produced in CHO cells with alpha-1,6-fucosyltransferase, an enzyme required for fucosylation, knocked-out. Whilst binding activity of TNFRII-Fc and LFA-3-Fc were unchanged by fucose-removal, nonfucosylated Fc fusion proteins exhibited significantly higher Fc receptor gammaIIIa-binding and increased Fc-mediated cytotoxicity on target cells compared to fucosylated counterparts. Notably, in case of TNFRII-Fc, only the nonfucosylated protein exhibited potent Fc dependent cytotoxicity to transmembrane TNF-alpha expressing cells. These results prove that enhancement of Fc dependent cellular cytotoxicity by fucose-removal is effective in not only whole IgG but also Fc fusion proteins, and thus widens the potential of Fc-fusion proteins as therapeutic candidates.

Phase I Study of Bryostatin 1 and Fludarabine in Patients with Chronic Lymphocytic Leukemia and Indolent (Non-Hodgkin's) Lymphoma

PURPOSE

Preclinical studies suggested that bryostatin 1 might potentiate the therapeutic effects of fludarabine in the treatment of hematologic malignancies. We undertook a phase I study to identify appropriate schedules and doses of bryostatin 1 and fludarabine to be used in phase II studies.

EXPERIMENTAL DESIGN

Patients with chronic lymphocytic leukemia (CLL) or indolent lymphoma received fludarabine daily for 5 days and a single dose of bryostatin 1 via a 24-hour continuous infusion either before or after the fludarabine course. Doses were escalated in successive patients until recommended phase II doses for each sequence were identified on the basis of dose-limiting toxic events.

RESULTS

Bryostatin 1 can be administered safely and tolerably with full dose fludarabine (25 mg/m(2)/d x 5). The recommended bryostatin 1 phase II dose is 50 microg/m(2) for both sequences, bryostatin 1 --> fludarabine and fludarabine --> bryostatin 1. The combination is active against both CLL and indolent lymphomas with responses seen in patients who had been previously treated with fludarabine. Correlative studies do not support the hypothesis that bryostatin 1 potentiates fludarabine activity through down-regulation of protein kinase C in target cells.

CONCLUSIONS

Bryostatin 1 can be administered with full dose fludarabine, and the combination is moderately active in patients with persistent disease following prior treatment. In view of the activity of monoclonal antibodies such as the anti-CD20 monoclonal antibody rituximab in the treatment of CLL and indolent lymphomas, the concept of combining bryostatin 1 and fludarabine with rituximab warrants future consideration.

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

Human CD32B (FcγRIIB), the low-affinity inhibitory receptor for IgG, is the predominant Fc receptor (FcR) present on B cells. Immunohistochemical and expression studies have identified CD32B expression in a variety of B-cell malignancies, suggesting that CD32B is a potential immunotherapeutic target for B-cell malignancies. A high-affinity monoclonal antibody (mAb 2B6), from a novel panel of anti–human CD32B–specific mAbs, was chimerized (ch2B6) and humanized (hu2B6-3.5). Both ch2B6 and hu2B6-3.5 were capable of directing cytotoxicity by peripheral blood mononuclear cells and monocyte-derived macrophages against B-lymphoma lines in vitro. In a human B-cell lymphoma mouse xenograft model, administration of ch2B6 or hu2B6-3.5 reduced tumor growth rate and improved tumor-free survival. Both the in vitro and in vivo activities of 2B6 required an intact Fc, suggesting an FcR-mediated mechanism of action. These data support the hypothesis that CD32B is a viable target for mAb treatment of B-cell lymphoproliferative disorders.

Update on the treatment of lupus nephritis

Lupus nephritis (LN) is a major cause of morbidity and mortality in patients with systemic lupus erythematosus. Although the use of aggressive immunosuppression has improved both patient and renal survival over the past several decades, the optimal treatment of LN remains challenging. Improved outcomes have come at the expense of significant adverse effects owing to therapy. Moreover with long-term survival, the chronic adverse effects of effective therapies including risk of malignancy, atherosclerosis, infertility, and bone disease all become more important. Finally, some patients fail to achieve remission with standard cytotoxic therapy and others relapse when therapy is reduced. For these reasons, recent clinical trials have attempted to define alternate treatment protocols that appear to be efficacious in achieving and maintaining remission, but with less toxicity than standard regimens. This paper discusses established and newer treatment options for patients with proliferative and membranous LN, with an emphasis on the results of these recent clinical trials. We also review the experimental and human data regarding some of the novel targeted forms of therapy that are under investigation and in different phases of clinical trials.

Intralesional and intravenous treatment of cutaneous B-cell lymphomas with the monoclonal anti-CD20 antibody rituximab: report and follow-up of eight cases

BACKGROUND

Rituximab (MabThera); Roche, Basel, Switzerland; an anti-CD20 chimeric monoclonal antibody) has been shown to have significant activity in nodal B-cell lymphomas, with few associated adverse effects. Its efficacy and safety were first demonstrated in the treatment of systemic B-cell lymphomas. Intravenous and subsequently intralesional administration of rituximab have also been reported to be effective and well tolerated in cutaneous B-cell lymphoma (CBCL). The comparative efficacy of intravenous vs. intralesional rituximab in CBCL is not known.

OBJECTIVES

To evaluate the objective response rate, relapse rate, time to progression, and tolerance in patients with CBCL treated with intravenous or intralesional rituximab.

METHODS

Eight patients with multiple primary CBCL (four follicle centre lymphoma and four marginal zone lymphoma) were treated with intralesional rituximab (six patients; 10-30 mg per lesion, three times weekly for one or two cycles at a 4-week interval) or intravenous rituximab (two patients; 375 mg m(-2) once weekly for four consecutive weeks).

RESULTS

Complete clinical remission was obtained in all cases. The two patients treated intravenously did not relapse during a follow-up period of 18-24 months. Four of six patients treated intralesionally presented a relapse of new lesions at another site within a mean of 6 months after treatment. The injected lesions did not, however, recur. New lesions also responded to another cycle of intralesional rituximab. Tolerance to treatment was very good in both treatment groups.

CONCLUSIONS

Rituximab therapy of CBCL appears to have a potential advantage in cases where lesions are localized in sites that are difficult to treat with radiotherapy or surgery and in which secondary scarring or alopecia is likely. Intralesional injections of rituximab allow the use of considerably smaller doses compared with intravenous treatment, with similar response rates and tolerance. However, within a 12-month follow-up period, relapse of CBCL with new lesions at distinct sites was frequently observed after intralesional treatment.

Rituximab but not Other anti-CD20 Antibodies Reverses Multidrug Resistance in 2 B lymphoma Cell Lines, Blocks the Activity of P-glycoprotein (P-gp), and Induces P-gp to Translocate out of Lipid Rafts

The objective of this study was to investigate the ability of the anti-CD20 antibody, Rituximab (RTX), to inhibit the activity of P-glycoprotein (P-gp), and reverse multidrug resistance (MDR) in 2 P-gp/CD20 lymphoma cell lines. We determined whether RTX would chemosensitize the 2 P-gp cell lines in vitro, and inhibit the ability of the cells to efflux Rhodamine 123. One cell line was infected with an MDR1 vector and the other was generated by drug selection. We also determined whether RTX induced P-gp to translocate out of lipid rafts. RTX chemosensitized 2 different MDR cell lines, inhibited the activity of P-gp in both, and induced P-gp to translocate out of lipid rafts in the 1 cell line that was studied in greater detail. In contrast, 3 other anti-CD20 antibodies did not chemosensitize, inhibit the activity of P-gp, or induce it to translocate out of rafts, despite the fact that 1 antibody recognized the same epitope on CD20. Our results suggest that RTX can chemosensitize 2 CD20/P-gp cell lines in vitro by inhibiting the activity of the P-gp pump. The inhibition of P-gp activity correlated with the ability of RTX to induce P-gp to translocate out of lipid rafts. Although the mechanisms by which RTX effects P-gp translocation and activity are not yet known, they are not associated with acid-sphingomyelinase activation in raft microdomains, as described for the antiproliferative activity of RTX.

Rituximab (anti-CD20) adjunctive therapy for opsoclonus-myoclonus syndrome

PURPOSE

To determine if rituximab, an anti-CD20 monoclonal antibody, reduces cerebrospinal fluid (CSF) B-cell expansion in opsoclonus-myoclonus syndrome (OMS) and results in clinical improvement.

METHODS

Sixteen children with OMS and increased % CD20 B-cells in CSF received 4 rituximab infusions (375 mg/m IV) as add-on therapy to corticotropin (ACTH), intravenous immunoglobulins, or both, and were reevaluated 6 months later. Outcome measures were clinical (motor function, behavior, sleep) and immunologic (CSF and blood immunophenotype and Ig levels). Controls were 16 age-matched and sex-matched children, who did not have OMS.

RESULTS

After rituximab, 81% of OMS had a lower motor severity score, and 44% improved one severity category. Mean total score decreased by 44% (P = 0.0005). Rituximab reduced rage score, nighttime awakenings, and the number of children with opsoclonus, action myoclonus, drooling, gait ataxia, and rage. Despite a 51% reduction in ACTH dose, 9 of 11 children on ACTH did not relapse. The percentage of CSF CD19 (and CD20) B-cells was lowered in all children (undetectable in 6), with a 90% reduction in the group mean (P = 0.00003). CSF B-cells were no longer expanded compared with controls. In blood, CD19 B-cells decreased (-90%, P = 0.0003), as did the CSF:blood CD19 B-cell ratio (P = 0.00003). Serum IgM fell by 69% (below reference range), with no statistically significant change in IgG or IgA.

CONCLUSIONS

Rituximab seems efficacious and safe as adjunctive therapy for OMS. Selective targeting of CSF B lymphocytes represents a novel and valuable paradigm shift in the therapy for centrally mediated paraneoplastic disorders.

Rituximab: A monoclonal antibody to CD20 used in the treatment of pemphigus vulgaris

BACKGROUND

Rituximab is an anti-CD20 chimeric antibody that selectively targets B lymphocytes. Recently, it has been reported to be beneficial in treating pemphigus vulgaris.

OBJECTIVE

Our aim was to review the English-language literature on the treatment of pemphigus vulgaris (PV) with rituximab and to determine its efficacy and influence on clinical outcome(s).

MATERIAL AND METHODS

A retrospective review of the literature on the use of rituximab in the treatment of PV was conducted. Seventeen patients in 10 reports were described and their data were reviewed.

RESULTS

The majority of patients received one course of rituximab along with conventional immunosuppressive therapy as concomitant therapy; 88% of the patients demonstrated improvement. More than half of the patients were followed up for more than 6 months after rituximab treatment; they appeared to be clinically disease free, but were still receiving conventional immunosuppressive therapy. Side effects in most patients were transient and infusion related. Serious infections occurred in 4 patients. One patient died.

LIMITATIONS

The sample size of this study is small; there is no uniformity of data collection or measurement of key and critical indices, and follow-up was limited.

CONCLUSION

Rituximab may be a promising agent in treatment of PV.

Minimal residual disease in hairy cell leukemia patients assessed by clone-specific polymerase chain reaction

Cladribine induces long-term complete remission in hairy cell leukemia (HCL) patients but does not clear minimal residual disease (MRD) according to high-sensitivity PCR assays. To quantify MRD in patients after anti-CD22 recombinant immunotoxin BL22 and other agents, we used a relative quantitative PCR (RQ-PCR) assay using a primer and probe, both patient specific for the immunoglobulin heavy chain rearrangement. Using this method, we were able to detect one Bonna 12 HCL cell in either 10(6) Jurkat cells or in 10(6) normal mononuclear cells. We studied 84 samples from 10 patients, taken before or after treatment with BL22 and other agents. Patient-specific RQ-PCR was much more sensitive than flow cytometry, which in turn was (as recently reported) more sensitive than PCR using consensus primers. RQ-PCR was positive in 62 of 62 (100%) flow-positive samples in 10 patients and in 20 of 22 (91%) flow-negative samples in six patients. The relative level of MRD as quantified by RQ-PCR correlated with disease status and remission. Thus, patient-specific RQ-PCR is the most sensitive test for MRD in HCL patients and could be used to determine maximal response in patients obtaining multiple cycles of nonmyelotoxic biological treatment for this disease.

Antibody and immunomodulatory agents in treatment of indolent non-Hodgkin's lymphoma

Immunomodulatory agents, including cytokines, monoclonal antibodies, and CpG oligonucleotides, have properties that suggest they have the ability to augment rituximab in the treatment of non-Hodgkin's lymphoma. Although several clinical trials have promising results, no randomized trials of reasonable size have been performed to date, limiting the ability to discern whether combinations of immunomodulatory agents with rituximab impact clinical outcome. Until such trials are mature, we do not recommend using these agents in combination outside of the research setting.

IMC-EB10, an anti-FLT3 monoclonal antibody, prolongs survival and reduces nonobese diabetic/severe combined immunodeficient engraftment of some acute lymphoblastic leukemia cell lines and primary leukemic samples

The class III receptor tyrosine kinase FLT3 is expressed on the blasts of >90% of patients with B-lineage acute lymphoblastic leukemias (ALL). In addition, it is expressed at extremely high levels in ALL patients with mixed lineage leukemia rearrangements or hyperdiploidy and is sometimes mutated in these same patients. In this report, we investigate the effects of treating ALL cell lines and primary samples with human anti-FLT3 monoclonal antibodies (mAb) capable of preventing binding of FLT3 ligand. In vitro studies, examining the ability of two anti-FLT3 mAbs (IMC-EB10 and IMC-NC7) to affect FLT3 activation and downstream signaling in ALL cell lines and primary blasts, yielded variable results. FLT3 phosphorylation was consistently inhibited by IMC-NC7 treatment, but in some cell lines, IMC-EB10 actually stimulated FLT3 activation, possibly as a result of antibody-mediated receptor dimerization. Through antibody-dependent, cell-mediated cytotoxicity, such an antibody could still prove efficacious against leukemia cells in vivo. In fact, IMC-EB10 treatment significantly prolonged survival and/or reduced engraftment of several ALL cell lines and primary ALL samples in nonobese diabetic/severe combined immunodeficient (NOD/SCID) mice. This occurred even when IMC-EB10 treatment resulted in FLT3 activation in vitro. Moreover, fluorescence-activated cell sorting and PCR analysis of IMC-EB10-treated NOD/SCID mice surviving 150 days post-leukemic cell injection revealed that FLT3 immunotherapy reduced leukemic engraftment below the level of detection in these assays (<0.001%). Furthermore, in vivo IMC-EB10 treatment did not select for resistant cells, because cells surviving IMC-EB10 treatment remain sensitive to IMC-EB10 cytotoxicity upon retransplantation. In vivo studies involving either partial depletion or activation of natural killer (NK) cells show that most of the cytotoxic effect of IMC-EB10 is mediated through NK cells. Therefore, such an antibody, either naked or conjugated to radioactive isotopes or cytotoxic agents, may prove useful in the therapy of infant ALL as well as childhood and adult ALL patients whose blasts typically express FLT3.

A high throughput electrochemiluminescent cell-binding assay for therapeutic anti-CD20 antibody selection

A cell-based ELISA using suspension WIL2 cells in 96-well format was previously developed for measuring relative binding affinities of humanized anti-CD20 variants. We further developed a new cell-binding assay that uses high binding capacity carbon electrode plates for rapid attachment of suspension WIL2 cells and electrochemiluminescence for detection. Compared to the cell-based ELISA, which requires centrifugation for the manual wash steps, significant improvement in assay throughput was achieved by using a microplate washer. The assay can be performed on both 96- and 384-well plates with a standard curve range of 2.74-2000 ng/ml, which is wider than the range of 15.6-1000 ng/ml for the cell-based ELISA. Using CD20 expressing CHO cell clones, surface expression of >or=33,000 CD20 molecules was sufficient to obtain a dose-response curve in 384-well format. Relative affinities of 15 humanized variants correlated well (r(2)=0.94) between electrochemiluminescent cell-binding assay and cell-based ELISA. A competitive assay format, using mouse anti-CD20 antibody as the tracer, with a dose-response range of 27.4-20,000 ng/ml was also developed. The new cell-binding assay method can be used to efficiently support humanization process for selection of anti-CD20 antibody drug candidates and to characterize antibody binding to other cell surface proteins.

Posttransplant Lymphoproliferative Disorders in Liver Transplanted Patients: A Report of Four Cases

BACKGROUND

Posttransplant lymphoproliferative disorders (PTLDs) are an uncommon but important cause of morbidity and mortality in solid organ transplant recipients. They are often the result of Epstein-Barr virus (EBV)-induced proliferation of B-lymphocytes in the setting of immunosuppression.

PATIENTS AND METHODS

We retrospectively analyzed four cases of PTLD after liver transplantation. In all patients immunosuppression was reduced and anti-CD20 monoclonal antibody (rituximab) was administered. In two of four patients, EBV viral load was positive in the peripheral blood, and gancyclovir was therefore also prescribed. Chemotherapy (CHOP) was used as a rescue in the event of treatment failure.

RESULTS

Even if no severe adverse events were observed during the treatment period, our treatment approach to PTLD was not effective, and only one patient out of four is still alive.

CONCLUSIONS

Well-designed clinical trials are necessary to evaluate the role of this combined approach in the treatment of PTLD in liver transplant recipients.

Nonfucosylated Therapeutic IgG1 Antibody Can Evade the Inhibitory Effect of Serum Immunoglobulin G on Antibody-Dependent Cellular Cytotoxicity through its High Binding to FcγRIIIa

PURPOSE

Recent studies have revealed that fucosylated therapeutic IgG1s need high concentrations to compensate for FcgammaRIIIa-competitive inhibition of antibody-dependent cellular cytotoxicity (ADCC) by endogenous human plasma IgG. Here, we investigated whether ADCC of nonfucosylated therapeutic IgG1 is also influenced by plasma IgG in the same way as fucosylated IgG1s.

EXPERIMENTAL DESIGN

Ex vivo ADCC upon CD20+ human B cells was induced by incubation of human whole blood with nonfucosylated and/or fucosylated anti-CD20 IgG1s rituximab, and quantified by measuring the remaining CD19+ human B cells using flow cytometry.

RESULTS

Nonfucosylated anti-CD20 showed markedly higher (over 100-fold based on EC50) ex vivo B-cell depletion activity than its fucosylated counterpart in the presence of plasma IgG. The efficacy of fucosylated anti-CD20 was greatly diminished in plasma, resulting in the need for a high concentration (over 1.0 microg/mL) to achieve saturated efficacy. In contrast, nonfucosylated anti-CD20 reached saturated ADCC at lower concentrations (0.01-0.1 microg/mL) with much higher efficacy than fucosylated anti-CD20 in all nine donors through improved FcgammaRIIIa binding. Noteworthy, the high efficacy of nonfucosylated anti-CD20 was inhibited by addition of fucosylated anti-CD20. Thus, the efficacy of a 1:9 mixture (10 microg/mL) of nonfucosylated and fucosylated anti-CD20s was inferior to that of a 1,000-fold dilution (0.01 microg/mL) of nonfucosylated anti-CD20 alone.

CONCLUSIONS

Our data showed that nonfucosylated IgG1, not including fucosylated counterparts, can evade the inhibitory effect of plasma IgG on ADCC through its high FcgammaRIIIa binding. Hence, nonfucosylated IgG1 exhibits strong therapeutic potential through dramatically enhanced ADCC at low doses in humans in vivo.

Oral chlorambucil for extranodal, marginal zone, B-cell lymphoma of mucosa-associated lymphoid tissue of the orbit

PURPOSE

To report the outcome of oral chlorambucil as a single treatment in patients with orbital mucosa-associated lymphoid tissue (MALT) lymphoma.

DESIGN

Retrospective nonrandomized clinical study.

PARTICIPANTS

Thirty-three patients with isolated orbital MALT lymphoma.

METHODS

Medical records of all patients with histology-verified orbital MALT lymphoma treated with oral chlorambucil at the Royal Melbourne Hospital were reviewed.

MAIN OUTCOME MEASURES

Complete clinical response, partial response, local relapse, systemic extension (distant relapse), and survival.

RESULTS

Thirty-three patients (19 female; mean age, 69 years) participated in the study. Patients received an average of 4 courses of oral chlorambucil with a mean total dose of 600 mg. The lacrimal gland was the most frequent site of occurrence (24%), followed by the conjunctiva, eyelid, and superior orbit. Orbital mass, swelling, and diplopia were common presenting signs. Complete response was noted in 26 patients (79%). In 2 of the patients with complete clinical response, mild residual thickening was noted on follow-up orbital imaging studies. Four patients (12%) showed disease recurrence or relapse. Mean follow-up time was 32 (+/-20) months (range, 8 months-6 years; median, 26 months). None of the patients developed granulocytopenia secondary to chemotherapy, and none suffered significant nausea or vomiting. One patient with malignant transformation died 12 months after diagnosis and initial treatment.

CONCLUSIONS

Systemic chemotherapy with chlorambucil is a reasonable option in patients with orbital MALT lymphoma. It is associated with minimal to no side effects. Additionally, it may be well tolerated by elderly patients and also may treat subclinical disease elsewhere.

Monoclonal antibody as therapy for malignant lymphomas

Rituximab was the first monoclonal antibody to have been registered for the treatment of B-cell lymphomas. Randomized studies have demonstrated its activity in follicular lymphoma, mantle-cell lymphoma, and diffuse large B-cell lymphoma in untreated or relapsing patients. Because of its high activity and low toxicity ratio, rituximab has transformed the outcome of patients with B-cell lymphoma. A combination of rituximab plus chemotherapy, R-CHOP, has the highest efficacy ever described with any chemotherapy in diffuse large B-cell lymphoma and follicular lymphoma. The role of radio-labelled antibodies is still to be defined.

MT110: A novel bispecific single-chain antibody construct with high efficacy in eradicating established tumors

We have developed a novel single-chain Ep-CAM-/CD3-bispecific single-chain antibody construct designated MT110. MT110 redirected unstimulated human peripheral T cells to induce the specific lysis of every Ep-CAM-expressing tumor cell line tested. MT110 induced a costimulation independent polyclonal activation of CD4- and CD8-positive T cells as seen by de novo expression of CD69 and CD25, and secretion of interferon gamma, tumor necrosis factor alpha, and interleukins 2, 4 and 10. CD8-positive T cells made the major contribution to redirected tumor cell lysis by MT110. With a delay, CD4-positive cells could also contribute presumably as consequence of a dramatic upregulation of granzyme B expression. MT110 was highly efficacious in a NOD/SCID mouse model with subcutaneously growing SW480 human colon cancer cells. Five daily doses of 1 microg MT110 on days 0-4 completely prevented tumor outgrowth in all mice treated. The bispecific antibody construct also led to a durable eradication of established tumors in all mice treated with 1 microg doses of MT110 on days 8-12 after tumor inoculation. Finally, MT110 could eradicate patient-derived metastatic ovarian cancer tissue growing under the skin of NOD/SCID mice. MT110 appears as an attractive bispecific antibody candidate for treatment of human Ep-CAM-overexpressing carcinomas.

The Shaving Reaction: Rituximab/CD20 Complexes Are Removed from Mantle Cell Lymphoma and Chronic Lymphocytic Leukemia Cells by THP-1 Monocytes

Clinical investigations have revealed that infusion of immunotherapeutic mAbs directed to normal or tumor cells can lead to loss of targeted epitopes, a phenomenon called antigenic modulation. Recently, we reported that rituximab treatment of chronic lymphocytic leukemia patients induced substantial loss of CD20 on B cells found in the circulation after rituximab infusion, when rituximab plasma concentrations were high. Such antigenic modulation can severely compromise therapeutic efficacy, and we postulated that B cells had been stripped (shaved) of the rituximab/CD20 complex by monocytes or macrophages in a reaction mediated by FcgammaR. We developed an in vitro model to replicate this in vivo shaving process, based on reacting rituximab-opsonized CD20(+) cells with acceptor THP-1 monocytes. After 45 min at 37 degrees C, rituximab and CD20 are removed from opsonized cells, and both are demonstrable on acceptor THP-1 cells. The reaction occurs equally well in the presence and absence of normal human serum, and monocytes isolated from peripheral blood also promote shaving of CD20 from rituximab-opsonized cells. Tests with inhibitors and use of F(ab')(2) of rituximab indicate transfer of rituximab/CD20 complexes to THP-1 cells is mediated by FcgammaR. Antigenic modulation described in previous reports may have been mediated by such shaving, and our findings may have profound implications for the use of mAbs in the immunotherapy of cancer.

Blockade of bulky lymphoma-associated CD55 expression by RNA interference overcomes resistance to complement-dependent cytotoxicity with rituximab

Recently, anti-CD20 (rituximab) and anti-Her2/neu (trastuzumab) antibodies have been developed and applied to the treatment of malignant lymphoma and breast cancer, respectively. However, bulky lymphoma is known to be resistant to rituximab therapy, and this needs to be overcome. Fresh lymphoma cells were collected from 30 patients with non-Hodgkin's lymphoma, the expression of CD20 and CD55 was examined by flow cytometry, and complement-dependent cytotoxicity (CDC) assays were carried out. Susceptibility to CDC with rituximab was decreased in a tumor size-dependent manner (r=-0.895, P<0.0001), but not in a CD20-dependent manner (r=-0.076, P=0.6807) using clinical samples. One complement-inhibitory protein, CD55, contributed to bulky lymphoma-related resistance to CDC with rituximab. A decrease in susceptibility to CDC with rituximab was statistically dependent on CD55 expression (r=-0.927, P<0.0001) and the relationship between tumor size and CD55 expression showed a significant positive correlation (r=0.921, P<0.0001) using clinical samples. To overcome the resistance to rituximab by high expression of CD55 in bulky lymphoma masses, small interfering RNA (siRNA) was designed from the DNA sequence corresponding to nucleic acids 1-380 of the CD55 cDNA. Introduction of this siRNA decreased CD55 expression in the breast cancer cell line SK-BR3 and in CD20-positive cells of patients with recurrent lymphoma; resistance to CDC was also inhibited. This observation gives us a novel strategy to suppress bulky disease-related resistance to monoclonal antibody treatment.

Pure red cell aplasia in B-cell lymphoproliferative disorder treated with rituximab: Report of two cases and review of the literature

Pure red cell aplasia (PRCA) is an unusual cause of anemia in patients with chronic lymphoproliferative disorders. Here, we present two cases of PRCA, one associated with chronic lymphocytic leukemia (CLL) and the other with splenic marginal zone lymphoma, in which the PRCA responded dramatically to treatment with rituximab. We then review the literature on PRCA in lymphoma and response to rituximab. PRCA associated with CLL or lymphoma may be another indication for rituximab therapy.

Development of Antibodies and Chimeric Molecules for Cancer Immunotherapy

Monoclonal antibodies are among the most rapidly expanding class of therapeutics for cancer treatment. Monoclonal antibodies targeting non-Hodgkin's lymphoma (NHL), Her-2/neu highly expressing metastatic breast cancer, colorectal cancer, acute myelogenous leukemia, and B-cell chronic lymphocytic leukemia (CLL) have received FDA approval. Promising new targets for antibody therapy include cellular growth factor receptors, mediators of tumor-driven neo-angiogenesis, as well as host negative immunoregulatory checkpoints that impede an effective immune response to neoplasia. Antibody efficacy has been increased by genetic engineering to humanize the antibodies and to increase their effector functions including antibody dependent cellular cytotoxicity. Furthermore, antibodies have been armed with cytokines, chemotherapeutic agents, toxins, and radionuclides to augment their efficacy as tumor cytotoxic agents. As a consequence of these advances, 30 years after their first development, monoclonal antibodies have become an important standard approach for the therapy of neoplasia with 19 therapeutic monoclonal antibodies now approved by the FDA including 8 for the treatment of cancer.

Engineered antibodies act as targeted therapies in cancer treatment

Over the last two decades cancer cure rates have not gone up as expected, and the effectiveness of chemotherapy has reached a plateau. This has prompted a search for targeted therapies with higher efficacy and lesser toxicities. Monoclonal antibodies against cancer cells offer targeted therapies with little or no toxicities against normal tissues. In this review we will discuss the concepts behind the development of monoclonal antibodies in cancer and their present status in the clinic. Specifically, we will discuss the clinical use of Rituximab (RituxanO), Trastuzumab (HerceptinO) and Bevacizumab (AvastinO) in various cancers and the key clinical trials that have led to their incorporation in cancer therapeutics.

Immunotherapy using unconjugated CD19 monoclonal antibodies in animal models for B lymphocyte malignancies and autoimmune disease

Immunotherapy with unconjugated CD20 monoclonal antibodies has proven effective for treating non-Hodgkin's lymphoma and autoimmune disease. CD20 immunotherapy depletes mature B cells but does not effectively deplete pre-B or immature B cells, some B cell subpopulations, antibody-producing cells, or their malignant counterparts. Because CD19 is expressed earlier during B cell development, a therapeutic strategy for the treatment of early lymphoblastic leukemias/lymphomas was developed by using CD19-specific monoclonal antibodies in a transgenic mouse expressing human CD19. Pre-B cells and their malignant counterparts were depleted as well as antibody- and autoantibody-producing cells. These results demonstrate clinical utility for the treatment of diverse B cell malignancies, autoimmune disease, and humoral transplant rejection.

Direct Antilymphoma Effects on Human Lymphoma Cells of Monotherapy and Combination Therapy with CD20 and HLA-DR Antibodies and 90Y-Labeled HLA-DR Antibodies

PURPOSE

Monoclonal antibodies (mAb) in combination and mAbs combined with a radionuclide (radioimmunotherapy) have both been more effective in patients than mAb monotherapy.

EXPERIMENTAL DESIGN

Using assays of cell growth and viability, the dose response and temporal characteristics of CD20 (rituximab) and HLA-DR (Lym-1) mAbs, singly and in combination, and of 90Y-conjugated Lym-1 mAb have been characterized in five human lymphoma cell lines (B35M, Raji, SU-DHL-4, SU-DHL-6, and Ramos) spanning Burkitt's to diffuse large cell lymphoma. Although Ramos had a lower HLA-DR density, these cell lines were otherwise selected because of high cell surface CD20 and HLA-DR abundance. Assays of cell growth and death were done using microscopy and trypan blue dye.

RESULTS

Lym-1 and rituximab, used singly, showed direct antilymphoma effects; those of Lym-1 were often more potent than those of rituximab. Combinations of these mAbs were more effective, sometimes synergistic, than either mAb singly, even in more resistant SU-DHL-4 cells. Conjugation of 90Y to Lym-1 also augmented potency in all cell lines and overcame resistance to both Lym-1 and rituximab in Ramos cells.

CONCLUSIONS

Lym-1 exhibited substantially greater direct antilymphoma effects than rituximab in lymphoma cells in culture. Combination of Lym-1 with rituximab or 90Y increased potency and overcame treatment resistance in lymphoma cells. Greater use of combination therapies of this type to increase potency and range of effectiveness seems likely to improve patient outcome.

Engineering of monoclonal antibodies and antibody-based fusion proteins: successes and challenges

Monoclonal antibodies (mAbs) and antibody-based fusion molecules have now come of age as therapeutics. Eighteen mAbs and two fusion molecules are on the market. mAbs directed against new targets are progressing at a rapid rate with the help of proteomics and genomics approaches. Many technical efforts have been made to generate a second-generation mAb with decreased immunogenicity and with optimised effector functions. The development of molecular engineering techniques applied to antibody molecules has also made it possible to design fusion molecules exhibiting different modules with bifunctional activities. Different approaches developed over the last two decades to generate and optimise therapeutic antibodies and antibody-based fusion molecules are described, with a particular focus on antibodies and fusion proteins used in oncology and inflammatory diseases. Some current technical challenges and trends are also discussed.

IgG subclass-independent improvement of antibody-dependent cellular cytotoxicity by fucose removal from Asn297-linked oligosaccharides

Fucose depletion from oligosaccharides of human IgG1-type antibodies results in a great enhancement of antibody-dependent cellular cytotoxicity (ADCC). The aim of this study was to clarify the effect of fucose removal on effector functions of all human IgG subclasses. A panel of anti-CD20 chimeric antibodies having a matched set of human heavy chain subclasses with different fucose contents in their oligosaccharides was constructed using wild-type and fucosyltransferase-knockout Chinese hamster ovary cells as host cells. As found previously for IgG1, fucose-negative variant of IgG2, IgG3, and IgG4 exhibited enhanced ADCC and FcgammaRIIIa binding compared with their highly fucosylated counterparts. In contrast, fucose removal did not affect complement-dependent cytotoxicity (CDC) of any IgGs. Consequently, fucose removal from IgG2 and IgG4 resulted in a unique effector function profile; they had potent ADCC and no CDC. In conclusion fucose depletion can provide a panel of IgGs with enhanced ADCC without an impact on other inherent properties specific for each IgG subclass, such as CDC.

Enhanced efficacy of gemcitabine in combination with anti-CD20 monoclonal antibody against CD20+ non-Hodgkin's lymphoma cell lines in vitro and in scid mice

Background

Despite exciting new targeted therapeutics against non-Hodgkin's lymphoma (NHL), chemotherapy remains a cornerstone of therapy. While purine nucleoside analogs have significant activity in low grade NHL, the pyrimidine nucleoside analog gemcitabine has been less extensively studied, but has important activity. Use of the anti-CD20 monoclonal antibody rituximab in combination with chemotherapy for B-NHL is becoming prevalent in clinical practice, but has not been extensively studied in pre-clinical models.

Methods

We have tested the activity of gemcitabine ± rituximab in vitro and in scid/human NHL xenograft models. We used two t(14;18)+, CD20+ follicular B cell NHL cell lines, DoHH2 a transformed NHL line and WSU-FSCCL isolated from pleural fluid of a patient with indolent NHL.

Results

Gemcitabine is cytotoxic to DoHH2 and WSU-FSCCL cells in vitro, and the IC₅₀ is 2–3 fold lower in the presence of rituximab. Apoptosis is also enhanced in the presence of rituximab. Clearance of NHL cells from ascites in scid mice is prolonged by the combination, as compared with either agent alone. Most importantly, survival of scid mice bearing human NHL cells is significantly prolonged by the combination of gemcitabine + rituximab.

Conclusion

Based on our pre-clinical data showing prolonged survival of mice bearing human lymphoma cell line xenografts after treatment with gemcitabine + anti-CD20 antibody, this combination, expected to have non-overlapping toxicity profiles, should be explored in clinical trials.

Inactivation of Myc in murine two-hit B lymphomas causes dormancy with elevated levels of interleukin 10 receptor and CD20: implications for adjuvant therapies

Overexpression of c-Myc and inactivation of p53 are hallmarks of human Burkitt's lymphomas. We had previously showed that transduction of murine p53-null bone marrow cells with a Myc-encoding retrovirus is sufficient for B lymphomagenesis. To address the role of Myc in tumor sustenance, we generated lymphomas induced by the Myc-estrogen receptor fusion protein (MycER). Engrafted hosts were continuously treated with the ER ligand 4-hydroxytamoxifen (4-OHT) to allow tumor formation. Subsequent inactivation of MycER via 4-OHT deprivation resulted in tumor stasis but only partial regression. At the cellular level, dormant neoplastic lymphocytes withdrew from mitosis and underwent further B-cell differentiation. Concomitantly, they up-regulated genes involved in lymphocyte proliferation and survival, most notably interleukin 10 receptor alpha (IL10Ralpha) and CD20, the target for antibody therapy with Rituxan. We found that overexpression of IL10Ralpha affords significant proliferative advantages and in 4-OHT-deprived animals correlates with eventual tumor relapse. Both dormant and relapsing tumors maintain IL10Ralpha expression suggesting that they might be sensitive to emerging drugs targeting the IL-10 pathway. Up-regulation of CD20 following Myc inactivation was also observed in immortalized human lymphocytes. Importantly, in this system, Myc(OFF)CD20(HIGH) cells were more prone to Rituxan-induced apoptosis than Myc(ON)CD20(MED). Thus, targeting Myc, while moderately effective on its own, shapes the phenotype of dormant neoplastic cells and sensitizes them to adjuvant molecular therapies.

Rituximab-Induced Inhibition of YY1 and Bcl-xLExpression in Ramos Non-Hodgkin’s Lymphoma Cell Line via Inhibition of NF-κB Activity: Role of YY1 and Bcl-xLin Fas Resistance and Chemoresistance, Respectively

Rituximab treatment of B non-Hodgkin's lymphoma (NHL) cell lines inhibits the constitutive NF-kappaB activity and results in the sensitization of tumor cells to both chemotherapy and Fas-induced apoptosis. Cells expressing dominant active IkappaB or treated with NF-kappaB-specific inhibitors were sensitive to both drugs and Fas agonist mAb (CH-11)-induced apoptosis. Down-regulation of Bcl-xL expression via inhibition of NF-kappaB activity correlated with chemosensitivity. The direct role of Bcl-xL in chemoresistance was demonstrated by the use of Bcl-xL-overexpressing Ramos cells, Ramos hemagglutinin (HA)-Bcl-x, which were not sensitized by rituximab to drug-induced apoptosis. However, inhibition of Bcl-xL in Ramos HA-Bcl-x resulted in sensitization to drug-induced apoptosis. The role of Bcl-xL expression in the regulation of Fas resistance was not apparent; Ramos HA-Bcl-x cells were as sensitive as the wild type to CH-11-induced apoptosis. Several lines of evidence support the direct role of the transcription repressor yin-yang 1 (YY1) in the regulation of resistance to CH-11-induced apoptosis. Inhibition of YY1 activity by either rituximab or the NO donor DETANONOate or after transfection with YY1 small interfering RNA resulted in up-regulation of Fas expression and sensitization to CH-11-induced apoptosis. These findings suggest two mechanisms underlying the chemosensitization and immunosensitization of B-NHL cells by rituximab via inhibition of NF-kappaB. The regulation of chemoresistance by NF-kappaB is mediated via Bcl-xL expression, whereas the regulation of Fas resistance by NF-kappaB is mediated via YY1 expression and activity. The potential clinical significance of these findings is discussed.

Anti-CD20 monoclonal antibody (rituximab) in the treatment of pemphigus

BACKGROUND

Pemphigus is a severe autoimmune blistering disorder caused by autoantibodies to desmoglein 1 and 3. The disease course is typically severe, thus requiring multiple immunosuppressive agents. The treatment is still challenging and in some patients with recalcitrant disease, therapies fail and therapeutic options are limited.

OBJECTIVES

To investigate whether depletion of B lymphocytes that are thought to produce disease-causing autoantibodies shows a long-term benefit in pemphigus.

METHODS

Five patients diagnosed as having pemphigus vulgaris and pemphigus foliaceus were treated with the monoclonal antibody rituximab. Rituximab was administered intravenously at a dosage of 375 mg m(-2) once weekly for 4 weeks.

RESULTS

The treatment was well tolerated and all patients showed a good response over a follow-up period of up to 3 years, allowing immunosuppressive treatment to be reduced or terminated. B-cell depletion persisted for 6-12 months, and in one patient for almost 3 years.

CONCLUSIONS

This study highlights the prolonged effect and disease control after one single course of rituximab and further extends the spectrum of treatments of bullous autoimmune disorders.

Rituximab therapy of lymphoma is enhanced by orally administered (1-->3),(1-->4)-D-beta-glucan

By activating complement, antitumor monoclonal antibodies coat tumor cells with iC3b. beta-glucans, naturally occurring glucose polymers, bind to the lectin domain of the leukocyte receptor CR3, prime it for binding to iC3b, and trigger cytotoxicity of iC3b-coated tumor cells. We studied the combination of the complement-activating antibody rituximab with barley-derived (1-->3),(1-->4)-beta-D-glucan (BG) against CD-20 positive lymphoma xenografts in SCID mice. Growth of established subcutaneous non-Hodgkin's lymphoma (NHL) (Daudi and EBV-derived B-NHL) or Hodgkin's disease (Hs445 and RPMI6666) was significantly suppressed in mice treated with a combination of intravenous rituximab and oral BG, when compared to mice treated with rituximab or BG alone. Survival of mice with disseminated lymphoma was significantly increased in the combination group as compared to other treatment groups. No clinical toxicity was observed. The therapeutic efficacy and lack of toxicity of this combination supports further investigation into its clinical utility.

Induction of Apoptosis Using Inhibitors of Lysophosphatidic Acid Acyltransferase- and Anti-CD20 Monoclonal Antibodies for Treatment of Human Non-Hodgkin's Lymphomas

PURPOSE

Lysophosphatidic acid acyltransferase-beta (LPAAT-beta) is a transmembrane enzyme critical for the biosynthesis of phosphoglycerides whose product, phosphatidic acid, plays a key role in raf and AKT/mTor-mediated signal transduction.

EXPERIMENTAL DESIGN

LPAAT-beta may be a novel target for anticancer therapy, and, thus, we examined the effects of a series of inhibitors of LPAAT-beta on multiple human non-Hodgkin's lymphoma cell lines in vitro and in vivo.

RESULTS

We showed that five LPAAT-beta inhibitors at doses of 500 nmol/L routinely inhibited growth in a panel of human lymphoma cell lines in vitro by >90%, as measured by [3H]thymidine incorporation. Apoptotic effects of the LPAAT-beta inhibitors were evaluated either alone or in combination with the anti-CD20 antibody, Rituximab. The LPAAT-beta inhibitors induced caspase-mediated apoptosis at 50 to 100 nmol/L in up to 90% of non-Hodgkin's lymphoma cells. The combination of Rituximab and an LPAAT-beta inhibitor resulted in a 2-fold increase in apoptosis compared with either agent alone. To assess the combination of Rituximab and a LPAAT-beta inhibitor in vivo, groups of athymic mice bearing s.c. human Ramos lymphoma xenografts were treated with the LPAAT-beta inhibitor CT-32228 i.p. (75 mg/kg) daily for 5 d/wk x 4 weeks (total 20 doses), Rituximab i.p. (10 mg/kg) weekly x 4 weeks (4 doses total), or CT-32228 plus Rituximab combined. Treatment with either CT-32228 or Rituximab alone showed an approximate 50% xenograft growth delay; however, complete responses were only observed when the two agents were delivered together.

CONCLUSIONS

These data suggest that Rituximab, combined with a LPAAT-beta inhibitor, may provide enhanced therapeutic effects through apoptotic mechanisms.

The peritoneal cavity provides a protective niche for B1 and conventional B lymphocytes during anti-CD20 immunotherapy in mice

Although anti-CD20 immunotherapy effectively treats human lymphoma and autoimmune disease, the in vivo effect of immunotherapy on tissue B cells and their subsets is generally unknown. To address this, anti-mouse CD20 mAbs were used in a mouse model in which the extent and kinetics of tissue B cell depletion could be assessed in vivo. CD20 mAb treatment depleted most mature B cells within 2 days, with 95-98% of B cells in the bone marrow, blood, spleen, lymph nodes, and gut-associated lymphoid tissues depleted by day 7, including marginal zone and follicular B cells. The few spleen B cells remaining after CD20 mAb treatment included pre-B, immature, transitional, and some B1 B cells that expressed CD20 at low levels. By contrast, peritoneal cavity B cells expressed normal CD20 densities and were coated with CD20 mAb, but only 30-43% of B1 cells and 43-78% of B2 cells were depleted by day 7. Spleen B cells adoptively transferred into the peritoneal cavity were similarly resistant to mAb-induced depletion, while transferred B cells that had migrated to the spleen were depleted. However, peritoneal B1 and B2 cells were effectively depleted in mAb-treated wild-type and C3-deficient mice by thioglycolate-induced monocyte migration into this otherwise privileged niche. Inflammation-elicited effector cells did not promote peritoneal cavity B cell depletion in FcR-deficient mice treated with CD20 mAb. Thus, the majority of CD20(+) cells and B cell subsets within lymphoid tissues and the peritoneum could be depleted efficiently in vivo through Fc-dependent, but C-independent pathways during anti-CD20 immunotherapy.

Evolving role of rituximab in the treatment of patients with non-Hodgkin's lymphoma

Rituximab is the first monoclonal antibody to have been registered for the treatment of B-cell lymphomas. Randomized studies have demonstrated its activity in follicular lymphoma, mantle cell lymphoma, and diffuse large B-cell lymphoma in untreated or relapsing patients. Rituximab has transformed the outcome of these patients because of its high activity and low toxicity. A combination of rituximab plus cyclophosphamide, doxorubicin, vincristine, and prednisone, has the highest efficacy ever described with any chemotherapy in diffuse large B-cell lymphoma and follicular lymphoma.

Gastrointestinal complications in renal transplant recipients

Gastrointestinal complications are frequent in renal transplant recipients and can include oral lesions, esophagitis, peptic ulcer, diarrhea, colon disorders and malignancy. Oral lesions may be caused by drugs such as cyclosporine and sirolimus, by virus or fungal infections. Leukoplakia may develop in patients with Epstein-Barr virus (EBV) infection. The commonest esophageal disorder is represented by fungal esophagitis usually caused by candida. A number of patients may suffer from nausea, vomiting and gastric discomfort. These disorders are more frequent in patients treated with mycophenolate mofetil (MMF). Peptic ulcer is more rare than in the past. Patients with a history of peptic ulcer are particularly prone to this complication. Other gastroduodenal disorders are caused by cytomegalovirus (CMV) and herpes simplex infection. Diarrhea is a frequent disorder which may be caused by pathogen microorganisms or by immunosuppressive agents. The differential diagnosis may be difficult. Colon disorders mainly consist of hemorrhage, usually sustained by CMV infection, or perforation which may be caused by diverticulitis or intestinal ischemia. Colon cancer, anal carcinoma, and EBV-associated lymphoproliferative disorders are particularly frequent in transplant recipients. A particular gastric lymphoma called mucosa-associated lymphoid tissue (MALT) lymphoma may develop in renal transplant patients. It usually responds to the eradication of Helicobacter pylori.

T cells armed with anti-CD3 x anti-CD20 bispecific antibody enhance killing of CD20+ malignant B cells and bypass complement-mediated rituximab resistance in vitro

OBJECTIVE

Resistance to rituximab, a chimeric monoclonal antibody that binds to CD20, is a major limitation for the successful treatment of patients with non-Hodgkin lymphoma and other CD20+ B-cell malignancies. To circumvent rituximab resistance in these patient populations, we have constructed a bispecific antibody (BiAb), anti-CD3 x anti-CD20 (CD20Bi), that combines rituximab targeting with non-major histocompatibility complex (non-MHC)-restricted cytotoxicity mediated by activated T cells (ATC).

MATERIALS AND METHODS

Activated T cells were obtained from anti-CD3 activated peripheral blood mononuclear cells (PBMC) of normal donors or the leukapheresis products of patients by culturing in the presence of interleukin-2 for 6-14 days. After ATC expansion, the cells were armed with CD20Bi. Killing activity was evaluated by 51Cr-release assay.

RESULTS

Arming ATC with as little as 5 ng CD20Bi/10(6) cells significantly increased cytotoxicity above unarmed ATC. CD20Bi-armed ATC (50 ng/10(6) cells) efficiently lysed CD20+ cell lines at E:T of 6.25-50, but not the nonhematologic, CD20- SK-BR-3 cell line. High levels of cytotoxicity mediated by CD20Bi-armed ATC (p < 0.05) could not be blocked by an 8000-fold excess of soluble rituximab. CD20Bi-armed ATC in the presence of complement killed ARH-77 cells, a rituximab-complement pathway-resistant multiple myeloma, significantly (p < 0.05) better than rituximab or unarmed ATC, suggesting that CD20Bi-armed ATC may be clinically effective for treatment of rituximab-resistant CD20+ hematologic malignancies.

CONCLUSIONS

Our findings demonstrate that CD20Bi-armed ATC enhance cytotoxicity against CD20+ B-cell lines and circumvent complement-mediated rituximab resistance, providing a strong rationale for this immune-based strategy for the treatment of rituximab-refractory CD20+ B-cell malignancies.