Antibody specificity controls in vivo effector mechanisms of anti-CD20 reagents

Complement C5 Inhibition Reduces T Cell-Mediated Allograft Vasculopathy Caused by Both Alloantibody and Ischemia Reperfusion Injury in Humanized Mice

Allograft vasculopathy (AV) is characterized by diffuse stenoses in the vasculature of solid organ transplants. Previously, we developed two humanized models showing that alloantibody and ischemia reperfusion injury (IRI) exacerbated T cell-mediated AV in human arterial xenografts in vivo. Herein we examined a causal role for terminal complement activation in both settings. IRI, in contrast to alloantibody, elicited widespread membrane attack complex (MAC) assembly throughout the vessel wall. Both alloantibody and IRI caused early (24 h) and robust endothelial cell (EC) activation localized to regions of intimal MAC deposition, indicated by increases in nuclear factor kappa B (NF-κB)-inducing kinase, an MAC-dependent activator of noncanonical NF-kB, VCAM-1 expression and Gr-1+ neutrophil infiltration. Endothelial cell activation by alloantibody was inhibited by antimouse C5 mAb, but not by anti-C5a mAb or by control mAb, implicating MAC as the primary target of anti-C5 mAb. Antimouse C5 mAb significantly reduced alloantibody- and IRI-enhanced T cell infiltration and AV-like changes, including neointimal hyperplasia as well as intraluminal thrombosis in a subset of IRI-treated arterial grafts. These results indicate that increased AV lesion formation in response to either alloantibody or IRI is dependent on complement C5 activation and, accordingly, inhibition of this pathway may attenuate AV.

Influence of R-CHOP Therapy on Immune System Restoration in Patients with B-Cell Lymphoma

OBJECTIVE

To assess the immunosuppressive effect of R-CHOP in patients with B-cell lymphoma at 2 years.

METHODS

Parameters of humoral and cell-mediated immunity were assessed in 89 patients with diffuse large B-cell lymphoma or follicular lymphoma before and after 6-8 cycles of R-CHOP-14 or R-CHOP-21 regimen.

RESULTS

Data on pre- and posttreatment serum IgG (sIgG) levels were available for all 89 patients, while the corresponding data on serum CD20+, CD3+, CD4+, and CD8+ lymphocyte counts were available in only 43. Median sIgG levels significantly decreased from 1,221 mg/dl (baseline) to 733 mg/dl (after chemotherapy) (p < 0.001). Although CD20+ and CD4+ cell counts decreased (p < 0.001), no significant effect of chemotherapy on CD3+ and CD8+ cell counts was observed. CD20+ cell counts were restored to baseline levels at the 12-month follow-up. sIgG levels and CD4+ cell counts were not completely restored at 24 months, indicating a sustained immunosuppressive effect of R-CHOP in these patients. The incidence of infections over the 2-year period was 16.3-23.6%.

CONCLUSION

The immunosuppressive effect of R-CHOP in newly diagnosed cases of B-cell lymphoma tends to persist for >2 years, although sIgG levels were restored more quickly than CD4+ cell counts.

Optimising B-cell depletion in autoimmune disease: is obinutuzumab the answer?

In Rheumatoid Arthritis (RA) and Systemic Lupus Erythematosus (SLE), B-cell depletion therapy using rituximab results in variable clinical responses between individuals, which likely relates to variable B-cell depletion in the presence of immune defects. Outcomes in clinical trials with other type I anti-CD20 mAbs, ocrelizumab and ofatumumab, are comparable to rituximab. A mechanistically different type II mAb, obinutuzumab (OBZ), with greater capacity for B-cell depletion, has recently entered clinical trials in SLE. Here we consider whether type II anti-CD20 mAbs will provide mechanistic advantages to overcome the disease-related immune defects in autoimmune diseases such as SLE.

Recipient C6 rs9200 genotype is associated with hepatocellular carcinoma recurrence after orthotopic liver transplantation in a Han Chinese population

Hepatocellular carcinoma (HCC) recurrence is one of the leading causes of death after orthotopic liver transplantation (OLT). The sixth complement component (C6) is a late-acting complement protein that participates in the assembly of the membrane attack complex, which has an indispensable role in innate and acquired immune responses, as well as cancer immune surveillance. However, studies assessing the association between C6 and HCC recurrence after OLT are scarce. This study aimed to evaluate the association of donor and recipient C6 single-nucleotide polymorphisms with the risk for HCC recurrence after OLT. A total of 71 adult patients who underwent primary LT for HCC were enrolled. HCC recurrence was observed in 26 (36.6%) patients. Ten single-nucleotide polymorphisms were genotyped and analyzed in both donor and recipient groups. Patients with the rs9200 heterozygous GA variant presented significantly higher HCC recurrence rates (54.17 vs 27.66%, P=0.028), and lower cumulative tumor-free survival and overall survival (P=0.006 and P=0.013, respectively) compared with those harboring the GG/AA genotype, in multivariate logistic regression and Cox regression analyses. The rs9200 heterozygous GA variant in C6 persisted as a statistically independent prognostic factor (P<0.05) for predicting HCC recurrence after OLT. In conclusion, recipient C6 rs9200 polymorphism is associated with HCC recurrence after OLT, and improves the predictive value of clinical models.

Obinutuzumab for the treatment of indolent lymphoma

Obinutuzumab is a humanized, type II anti-CD20 monoclonal antibody designed for strong induction of direct cell death and antibody-dependent cell-mediated cytotoxicity. The Phase III GADOLIN trial tested the clinical efficacy of obinutuzumab plus bendamustine followed by obinutuzumab monotherapy in rituximab-refractory indolent non-Hodgkin lymphoma versus treatment with bendamustine alone. It demonstrated significantly longer progression-free survival for the obinutuzumab-containing regimen in this difficult to treat patient group. Based on the results of this trial, US FDA approval was most recently granted for obinutuzumab in the treatment of follicular lymphoma that has relapsed after or was refractory to a rituximab-containing regimen. This article summarizes the available data on chemistry, pharmacokinetics, clinical efficacy and safety of obinutuzumab in the treatment of indolent non-Hodgkin lymphoma.

Improving therapeutic activity of anti-CD20 antibody therapy through immunomodulation in lymphoid malignancies

Nearly two decades ago rituximab heralded a new era in management of B cell malignancies significantly increasing response rates and survival. However, despite clear therapeutic advantage, significant numbers of patients become refractory to anti-CD20 mAb therapy, suggesting urgent improvements are required. It is now well recognized that the suppressive tumor microenvironment plays an important role in the outcome of anti-CD20 mAb therapy and that manipulation of this environment may improve the efficacy and produce long-term tumor control. The past few years have seen a surge of interest in immunomodulatory agents capable of overwriting immune suppressive networks into favorable clinical outcome. Currently, a number of such combinations with anti-CD20 mAb is under evaluation and some have produced encouraging outcomes in rituximab refractory disease. In this review, we give an outline of anti-CD20 mAbs and explore the combinations with immunomodulatory agents that enhance antitumor immunity through targeting stimulatory or inhibitory pathways and have proven potential to synergize with anti-CD20 mAb therapy. These agents, primarily mAbs, target CTLA-4, PD-1/PD-L1, and CD40.

Obinutuzumab for relapsed or refractory indolent non-Hodgkin's lymphomas

The use of anti-CD20 monoclonal antibodies (mAbs), such as rituximab, in CD20-positive B-cell malignancies has dramatically improved the outcome of chronic lymphoid leukemia and non-Hodgkin's lymphomas (NHL). However, the occurrence of relapse and development of rituximab-refractory disease highlight the need to develop novel anti-CD20 mAbs, with improved mechanisms of action. Obinutuzumab is the first humanized type II glycoengineered anti-CD20 mAb. In vitro and in vivo data suggested several differences compared with rituximab, including a low level of complement-dependent cytotoxicity and an increased direct nonapoptotic cell death. Moreover, the glycoengineered Fc-linked nonfucosylated oligosaccharide enhanced the Fc-Fcγ receptor (FcγR) IIIa interaction, resulting in improved antibody-dependent cellular cytotoxicity and phagocytosis. Preclinical models suggested that these differences translate into superior survival in murine lymphoma models. Phase I/II trials in monotherapy in relapsed or refractory B-cell NHL demonstrated that obinutuzumab has an acceptable safety profile, infusion-related reactions being the most common adverse event. In rituximab-refractory indolent NHL, the recent randomized phase III GADOLIN study demonstrated an improved median progression-free survival for patients treated with obinutuzumab plus bendamustine rather than bendamustine alone. Further trials are ongoing to determine the role of obinutuzumab as a first-line agent in the treatment of follicular lymphoma.

CD20-Targeting Immunotherapy Promotes Cellular Senescence in B-Cell Lymphoma

The CD20-targeting monoclonal antibody rituximab is an established component of immunochemotherapeutic regimens against B-cell lymphomas, where its coadministration with conventional anticancer agents has significantly improved long-term outcome. However, the cellular mechanisms by which rituximab exerts its antilymphoma activity are only partially understood. We show here that rituximab induces typical features of cellular senescence, a long-term growth arrest of viable cells with distinct biologic properties, in established B-cell lymphoma cell lines as well as primary transformed B cells. In addition, rituximab-based immunotherapy sensitized lymphoma cells to senescence induction by the chemotherapeutic compound adriamycin (a.k.a. doxorubicin), and, to a lesser extent, by the antimicrotubule agent vincristine. Anti-CD20 treatment further enhanced secretion of senescence-associated cytokines, and augmented the DNA damage response signaling cascade triggered by adriamycin. As the underlying prosenescence mechanism, we found intracellular reactive oxygen species (ROS) levels to be elevated in response to rituximab, and, in turn, the ROS scavenger N-acetylcysteine to largely abrogate rituximab-mediated senescence. Our results, further supported by gene set enrichment analyses in a clinical data set of chronic lymphocytic leukemia patient samples exposed to a rituximab-containing treatment regimen, provide important mechanistic insights into the biologic complexity of anti-CD20-evoked tumor responses, and unveil cellular senescence as a hitherto unrecognized effector principle of the antibody component in lymphoma immunochemotherapy. Mol Cancer Ther; 15(5); 1074-81. ©2016 AACR.

Antibody Therapies in Cancer

Antibody-based immunotherapy has become a standard treatment for a variety of cancers. Many well-developed antibodies disrupt signaling of various growth factor receptors for the treatment of a number of cancers by targeting surface antigens expressed on tumor cells. In recent years, a new family of antibodies is currently emerging in the clinic, which target immune cells rather than cancer cells. These immune-targeted therapies strive to augment antitumor immune responses by antagonizing immunosuppressive pathways or providing exogenous immune-activating stimuli, which have achieved dramatic results in several cancers. The future of cancer therapies is likely to combine these approaches with other treatments, including conventional therapies, to generate more effective treatments.

The complement system in cancer: Ambivalence between tumour destruction and promotion

Constituting a part of the innate immune system, the complement system consists of over 50 proteins either acting as part of a 3-branch activation cascade, a well-differentiated regulatory system in fluid phase or on each tissue, or as receptors translating the activation signal to multiple cellular effector functions. Complement serves as first line of defence against infections from bacteria, viruses and parasites by orchestrating the immune response through opsonisation, recruitment of immune cells to the site of infection and direct cell lysis. Complement is generally recognised as a protective mechanism against the formation of tumours in humans, but is often limited by various resistance mechanisms interfering with its cytotoxic action, now considered as a great barrier of successful antibody-based immunotherapy. However, recent studies also indicate a pro-tumourigenic potential of complement in certain cancers and under certain conditions. In this review, we present recent findings on the possible dual role of complement in destroying cancer, especially if resistance mechanisms are blocked, but also under certain inflammatory conditions-promoting tumour development.

Rituximab in autoimmune thrombotic thrombocytopenic purpura: A success story

Despite a significant improvement of thrombotic thrombocytopenic purpura (TTP) prognosis since the use of plasma exchange, morbidity and mortality remained significant because of poor response to standard treatment or exacerbations and relapses. Rituximab, a chimeric monoclonal antibody directed against the B-lymphocyte CD20 antigen, has shown a particular interest in this indication. Recent studies also reported strong evidence for its efficiency in the prevention of relapses. This review addresses these recent progresses and still opened questions in this topic: should rituximab be proposed in all patients at the acute phase? Should all patients benefit from a preemptive treatment? Is the infectious risk acceptable in this context?

Internalization of rituximab and the efficiency of B Cell depletion in rheumatoid arthritis and systemic lupus erythematosus

Objective

Rituximab, a type I anti‐CD20 monoclonal antibody (mAb), induces incomplete B cell depletion in some patients with rheumatoid arthritis (RA) and systemic lupus erythematosus (SLE), thus contributing to a poor clinical response. The mechanisms of this resistance remain elusive. The purpose of this study was to determine whether type II mAb are more efficient than type I mAb at depleting B cells from RA and SLE patients, whether internalization influences the efficiency of depletion, and whether Fcγ receptor type IIb (FcγRIIb) and the B cell receptor regulate this internalization process.

Methods

We used an in vitro whole blood B cell–depletion assay to assess the efficiency of depletion, flow cytometry to study cell surface protein expression, and surface fluorescence–quenching assays to assess rituximab internalization, in samples from patients with RA and patients with SLE. Paired t‐test or Mann‐Whitney U test was used to compare groups, and Spearman's rank correlation test was used to assess correlation.

Results

We found that type II mAb internalized significantly less rituximab than type I mAb and depleted B cells from patients with RA and SLE at least 2‐fold more efficiently than type I mAb. Internalization of rituximab was highly variable between patients, was regulated by FcγRIIb, and inversely correlated with cytotoxicity in whole blood B cell–depletion assays. The lowest levels of internalization were seen in IgD– B cells, including postswitched (IgD–CD27+) memory cells. Internalization of type I anti‐CD20 mAb was also partially inhibited by anti‐IgM stimulation.

Conclusion

Variability in internalization of rituximab was observed and was correlated with impaired B cell depletion. Therefore, slower‐internalizing type II mAb should be considered as alternative B cell–depleting agents for the treatment of RA and SLE.

Mechanisms of action of therapeutic antibodies for cancer

The therapeutic utility of antibodies and their derivatives is achieved by various means. The FDA has approved several targeted antibodies that disrupt signaling of various growth factor receptors for the treatment of a number of cancers. Rituximab, and other anti-CD20 monoclonal antibodies are active in B cell malignancies. As more experience has been gained with anti-CD20 monoclonal antibodies, the multifactorial nature of their anti-tumor mechanisms has emerged. Other targeted antibodies function to dampen inhibitory checkpoints. These checkpoint inhibitors have recently achieved dramatic results in several cancers, including melanoma. These and related antibodies continue to be investigated in the clinical and pre-clinical settings. Novel antibody structures that target two or more antigens have also made their way into clinical use. Tumor targeted antibodies can also be conjugated to chemo- or radiotherapeutic agents, or catalytic toxins, as a means to deliver toxic payloads to cancer cells. Here we provide a review of these mechanisms and a discussion of their relevance to current and future clinical applications.

Emerging immunotherapy and strategies directly targeting B cells for the treatment of diffuse large B-cell lymphoma

During the last decade, significant prolonged survival in diffusive large B-cell lymphoma (DLBCL) has been observed. The efficacy of initial treatment improved mostly due to addition of a chimeric anti-CD20 monoclonal antibody (rituximab) to standard chemotherapeutic regimens. Moreover, accurate understanding of DLBCL pathogenesis and remarkable progress in gene expression profiling have led to the development of a variety of tumor-specific regimens. Novel agents target directly the pathways involved in signal transduction, lead to apoptosis and cancer cells differentiation. In this article, we mainly focus on new treatment options, such as monoclonal antibodies, tyrosine kinase inhibitors and immunomodulatory drugs, currently investigated in aggressive B-cell lymphoma with particular attention to DLBCL type.

Obinutuzumab for the treatment of patients with previously untreated chronic lymphocytic leukemia: overview and perspective

Chronic lymphocytic leukemia (CLL) is the most common lymphoproliferative disorder in the Western world and predominantly affects older people. Until recently, most studies in CLL focused on younger patients in whom intensive therapy with the addition of rituximab to fludarabine and cyclophosphamide was shown to improve survival. Obinutuzumab is a novel type II anti-CD20 monoclonal antibody (mAb) that recently demonstrated an overall survival advantage when combined with chemotherapy in previously untreated older patients with CLL and comorbidities. Obinutuzumab was superior to rituximab in this same study in terms of response rates and progression-free survival. Several preclinical and early phase clinical studies also support the efficacy of obinutuzumab. The most frequent adverse event noted with obinutuzumab is infusion-related reactions, which occur more frequently than with rituximab and are typically restricted to the first cycle of therapy. Based on these results, obinutuzumab should be considered the gold standard mAb for combination with chemotherapy in previously untreated patients with CLL and comorbidities. The marked efficacy of obinutuzumab with a weak chemotherapy backbone implies significant potency of this mAb, making it the ideal partner for combination studies with other agents in CLL.

Randomized Phase II Trial Comparing Obinutuzumab (GA101) With Rituximab in Patients With Relapsed CD20+ Indolent B-Cell Non-Hodgkin Lymphoma: Final Analysis of the GAUSS Study

PURPOSE

Obinutuzumab (GA101), a novel glycoengineered type II anti-CD20 monoclonal antibody, demonstrated responses in single-arm studies of patients with relapsed/refractory non-Hodgkin lymphoma. This is the first prospective, randomized study comparing safety and efficacy of obinutuzumab with rituximab in relapsed indolent lymphoma. The primary end point of this study was the overall response rate (ORR) in patients with follicular lymphoma after induction and safety in patients with indolent lymphoma.

PATIENTS AND METHODS

A total of 175 patients with relapsed CD20(+) indolent lymphoma requiring therapy and with previous response to a rituximab-containing regimen were randomly assigned (1:1) to four once-per-week infusions of either obinutuzumab (1,000 mg) or rituximab (375 mg/m(2)). Patients without evidence of disease progression after induction therapy received obinutuzumab or rituximab maintenance therapy every 2 months for up to 2 years.

RESULTS

Among patients with follicular lymphoma (n = 149), ORR seemed higher for obinutuzumab than rituximab (44.6% v 33.3%; P = .08). This observation was also demonstrated by a blinded independent review panel that measured a higher ORR for obinutuzumab (44.6% v 26.7%; P = .01). However, this difference did not translate into an improvement in progression-free survival. No new safety signals were observed for obinutuzumab, and the incidence of adverse events was balanced between arms, with the exception of infusion-related reactions and cough, which were higher in the obinutuzumab arm.

CONCLUSION

Obinutuzumab demonstrated a higher ORR without appreciable differences in safety compared with rituximab. However, the clinical benefit of obinutuzumab in this setting remains unclear and should be evaluated within phase III trials.

CD38 Monoclonal Antibody Therapies for Multiple Myeloma

The goal of this review is to provide historical, recent preclinical, and current clinical summaries of efforts to understand the CD38 molecule and to develop monoclonal antibodies that target it. We focus particularly on efforts involving multiple myeloma, a malignancy of terminally differentiated B cells that remains incurable despite many advances. An era of anti-CD38 monoclonal antibody therapy for myeloma is approaching, one that, we hope, will enable patients to live longer and better lives.

Antibody modulation: Limiting the efficacy of therapeutic antibodies

Monoclonal antibodies (mAb) have revolutionised the way in which we treat disease. From cancer to autoimmunity, antibody therapy has been responsible for some of the most impressive clinical responses observed in the last 2 decades. A key component of this success has been their generally low levels of toxicity, and unique mechanisms of action. These two facets have allowed them to (a) be integrated rapidly into clinical practice in combination with conventional radio- and chemo-therapies and (b) to avoid the resistance mechanisms typically observed with classical small molecule drugs, such as upregulation of drug efflux transporters, dysregulation of apoptosis and mutations in key target enzymes/pathways. Although success with mAb therapies has been impressive, they are also subject to their own resistance mechanisms. In this perspective we discuss the various ways in which mAb therapeutics can be inhibited, concentrating mainly on the ways in which they can be removed from the target cell surface-a process called modulation. This can be achieved either in a cis-fashion on a single cell or in trans, precipitated by engagement with a second phagocytic cell. The evidence for each of these processes will be discussed, in addition to possible therapeutic strategies that might be employed to inhibit or reverse them.

Obinutuzumab in hematologic malignancies: lessons learned to date

The routine use of anti-CD20 monoclonal antibodies (mAbs) has improved patient outcomes in CD20-positive non-Hodgkin's lymphoma (NHL) and chronic lymphocytic leukemia (CLL). Despite the clinical success achieved with rituximab, relapses are still common with further improvements in anti-CD20 mAb efficacy required. Many novel anti-CD20 antibodies are in development, but obinutuzumab is currently the only type II glycoengineered anti-CD20 mAb in clinical testing. Obinutuzumab has increased antibody-dependent cell-mediated cytotoxicity, reduced complement-dependent cytotoxicity and enhanced direct non-apoptotic cell death. In preclinical models, obinutuzumab induced superior tumor remission compared with rituximab at the equivalent dose levels, and was active in rituximab-refractory tumors. Obinutuzumab exhibits encouraging efficacy as monotherapy in NHL, and combined with chemotherapy in relapsed/refractory NHL and treatment-naïve symptomatic CLL. In a recent randomized, phase III trial in patients with untreated comorbid CLL, overall response rate was significantly greater (78% vs. 65%, P<0.0001) and median progression-free survival was significantly prolonged (26.7 vs. 15.2months, P<0.0001) for obinutuzumab plus chlorambucil vs. rituximab plus chlorambucil. Obinutuzumab is a type II anti-CD20 antibody that utilizes distinct mechanisms of action relative to type I antibodies like rituximab and has led to significant clinical improvement over rituximab in a phase III trial in CLL. Further trials are ongoing to determine whether such improvements in outcome will be seen in CD20-positive B-cell malignancies.

A Two-Step Pretargeted Nanotherapy for CD20 Crosslinking May Achieve Superior Anti-Lymphoma Efficacy to Rituximab

The use of rituximab, an anti-CD20 mAb, in combination with chemotherapy is the current standard for the treatment of B-cell lymphomas. However, because of a significant number of treatment failures, there is a demand for new, improved therapeutics. Here, we designed a nanomedicine that crosslinks CD20 and directly induces apoptosis of B-cells without the need for toxins or immune effector functions. The therapeutic system comprises a pretargeting component (anti-CD20 Fab' conjugated with an oligonucleotide1) and a crosslinking component (N-(2-hydroxypropyl)methacrylamide (HPMA) copolymer grafted with multiple complementary oligonucleotide2). Consecutive treatment with the two components resulted in CD20 clustering on the cell surface and effectively killed malignant B-cells in vivo. To enhance therapeutic efficacy, a two-step pretargeting approach was employed. We showed that the time lag between the two doses can be optimized based on pharmacokinetics and biodistribution of the Fab'-oligonucleotide1 conjugate. In a mouse model of human non-Hodgkin lymphoma (NHL), increasing the time lag from 1 h to 5 h resulted in dramatically improved tumor growth inhibition and animal survival. When the 5 h interval was used, the nanotherapy was more efficacious than rituximab and led to complete eradication of lymphoma cells with no signs of metastasis or disease recurrence. We further evaluated the nanomedicine using patient mantle cell lymphoma cells; the treatment demonstrated more potent apoptosis-inducing activity than rituximab hyper-crosslinked with secondary antibodies. In summary, our approach may constitute a novel treatment for NHL and other B-cell malignancies with significant advantages over conventional chemo-immunotherapy.

A new frontier in haematology - combining pharmacokinetic with pharmacodynamic factors to improve choice and dose of drug

The issue of tailored dosing adjusted according to a range of patient-specific factors other than bodyweight or body surface area is of large and increasing clinical and financial concern. Even if it is known that dosing alterations are likely to be required for parameters such as body composition, gender and pharmacogenetics, the amount of dosing change is unknown. Thus, pharmacokinetically guided dosing is making a resurgence, particularly in areas of medicine where there are cost constraints or safety issues, such as in haematology medications. However, the evidence to support the behaviour is minimal, particularly when long-term outcomes are considered. In haematology, there are particular issues around efficacy, toxicity and overall cost. Newer targeted agents, such as the monoclonal antibody rituximab and the tyrosine kinase inhibitor imatinib, whilst clearly being highly effective, are dosed on a milligram per square metre (rituximab) or fixed dose basis (imatinib), regardless of body composition, tumour aspects or comorbidity. This review questions this practice and raises important clinical issues; specifically, the clinical potential for combined pharmacokinetically and pharmacodynamically guided dosing of new targeted agents in haematological malignancies. This pharmacokinetically and pharmacodynamically guided dosing is an emerging area of clinical pharmacology, driven predominantly by toxicity, efficacy and cost issues, but also because reasonable outcomes are being noted with more appropriately dosed older medications adjusted for patient-specific factors. Clinical trials to investigate the optimization of rituximab dose scheduling are required.

Complement in therapy and disease: Regulating the complement system with antibody-based therapeutics

Complement is recognized as a key player in a wide range of normal as well as disease-related immune, developmental and homeostatic processes. Knowledge of complement components, structures, interactions, and cross-talk with other biological systems continues to grow and this leads to novel treatments for cancer, infectious, autoimmune- or age-related diseases as well as for preventing transplantation rejection. Antibodies are superbly suited to be developed into therapeutics with appropriate complement stimulatory or inhibitory activity. Here we review the design, development and future of antibody-based drugs that enhance or dampen the complement system.

Clinical role of obinutuzumab in the treatment of naive patients with chronic lymphocytic leukemia

The introduction of targeted therapy against CD20⁺ with the monoclonal antibody rituximab has dramatically improved the survival of B-cell non-Hodgkin lymphoma including chronic lymphocytic leukemia (CLL)/small lymphocytic lymphoma. Unfortunately, CLL remains incurable with chemoimmunotherapy, with many patients having refractory or relapsing disease after rituximab-containing therapy. Obinutuzumab (GA101) is a novel humanized Type II anti-CD20 monoclonal antibody that has been investigated and compared to rituximab. Here, we provide an overview of obinutuzumab, including its mechanisms of action, preclinical data, and Phase I to III clinical studies. Preclinical data illustrate obinutuzumab’s higher potency compared to rituximab through antibody-dependent cellular cytotoxicity and direct cell death. Recently, the CLL11 study presented a significant benefit from obinutuzumab chemoimmunotherapy and supports its use for treatment-naive unfit CLL patients. Herein, we review that obinutuzumab is both a safe and effective alternative to rituximab.

Emerging drugs for diffuse large B-cell lymphoma

Diffuse large B-cell lymphoma (DLBCL) is the most frequent non-Hodgkin lymphoma in western countries. Despite the addition of rituximab to chemotherapy, the prognosis is still poor and almost one-third of patients fail or relapse after first-line treatment. Gene expression profiling has identified three main signatures related to subgroups with different biological characteristics and responses to treatment. Novel agents targeting the oncogenic drivers of these subsets are currently under investigation with the aim of providing a tailored approach and avoiding unnecessary toxicity. Herein, we review the emerging therapies for DLBCL with a focus on preclinical and early clinical trials as well as future directions.

Activatory and inhibitory Fcγ receptors augment rituximab-mediated internalization of CD20 independent of signaling via the cytoplasmic domain

Type I anti-CD20 mAb such as rituximab and ofatumumab engage with the inhibitory FcγR, FcγRIIb on the surface of B cells, resulting in immunoreceptor tyrosine-based inhibitory motif (ITIM) phosphorylation. Internalization of the CD20·mAb·FcγRIIb complex follows, the rate of which correlates with FcγRIIb expression. In contrast, although type II anti-CD20 mAb such as tositumomab and obinutuzumab also interact with and activate FcγRIIb, this interaction fails to augment the rate of CD20·mAb internalization, raising the question of whether ITIM phosphorylation plays any role in this process. We have assessed the molecular requirements for the internalization process and demonstrate that in contrast to internalization of IgG immune complexes, FcγRIIb-augmented internalization of rituximab-ligated CD20 occurs independently of the FcγRIIb ITIM, indicating that signaling downstream of FcγRIIb is not required. In transfected cells, activatory FcγRI, FcγRIIa, and FcγRIIIa augmented internalization of rituximab-ligated CD20 in a similar manner. However, FcγRIIa mediated a slower rate of internalization than cells expressing equivalent levels of the highly homologous FcγRIIb. The difference was maintained in cells expressing FcγRIIa and FcγRIIb lacking cytoplasmic domains and in which the transmembrane domains had been exchanged. This difference may be due to increased degradation of FcγRIIa, which traffics to lysosomes independently of rituximab. We conclude that the cytoplasmic domain of FcγR is not required for promoting internalization of rituximab-ligated CD20. Instead, we propose that FcγR provides a structural role in augmenting endocytosis that differs from that employed during the endocytosis of immune complexes.

Regulation of complement and modulation of its activity in monoclonal antibody therapy of cancer

The complement system is a powerful tool of the innate immune system to eradicate pathogens. Both in vitro and in vivo evidence indicates that therapeutic anti-tumor monoclonal antibodies (mAbs) can activate the complement system by the classical pathway. However, the contribution of complement to the efficacy of mAbs is still debated, mainly due to the lack of convincing data in patients. A beneficial role for complement during mAb therapy is supported by the fact that cancer cells often upregulate complement-regulatory proteins (CRPs). Polymorphisms in various CRPs were previously associated with complement-mediated disorders.

In this review the role of complement in anti-tumor mAb therapy will be discussed with special emphasis on strategies aiming at modifying complement activity. In the future, clinical efficacy of mAbs with enhanced effector functions together with comprehensive analysis of polymorphisms in CRPs in mAb-treated patients will further clarify the role of complement in mAb therapy.

New antibody approaches to lymphoma therapy

The CD20-directed monoclonal antibody rituximab established a new era in lymphoma therapy. Since then other epitopes on the lymphoma surface have been identified as potential targets for monoclonal antibodies (mAb). While most mAbs eliminate lymphoma cells mainly by antibody-dependent cellular cytotoxicity, complement-dependent cytotoxicity or direct cell death, others counter mechanisms utilized by malignant cells to evade immune surveillance. Expression of PD-L1 on malignant or stromal cells in the tumor environment for example leads to T-cell anergy. Targeting either PD-1 or PD-L1 via mAbs can indirectly eliminate cancer cells by unblocking the host intrinsic immune response. Yet another mechanism of targeted therapy with mAbs are bi-specific T-cell engagers (BiTE) such as blinatumomab, which directly engages the host immune cells. These examples highlight the broad spectrum of available therapies targeting the lymphoma surface with mAbs utilizing both passive and active immune pathways. Many of these agents have already demonstrated significant activity in clinical trials. In this review we will focus on novel CD20-directed antibodies as well as mAbs directed against newer targets like CD19, CD22, CD40, CD52 and CCR4. In addition we will review mAbs unblocking immune checkpoints and the BiTE blinatumomab. Given the success of mAbs and the expansion in active and passive immunotherapies, these agents will play an increasing role in the treatment of lymphomas.

Update on obinutuzumab in the treatment of B-cell malignancies

INTRODUCTION

The anti-CD20 mAb rituximab has revolutionized the treatment of B-cell malignancies, improving outcome for patients. Despite these improvements, the majority of patients still relapse and become refractory to rituximab. Further efforts to improve anti-CD20 mAb efficacy have recently focused on obinutuzumab /GA101, a novel anti-CD20 mAb glycoengineered to display enhanced Fc-mediated effector mechanisms and induce direct cell death.

AREAS COVERED

We provide an overview of the current insights into the mechanisms of action of obinutuzumab focusing on how structural modifications and differences to rituximab led to designation of obinutuzumab as a type II antibody. We summarize data from preclinical studies and recent clinical trials including the Phase III trial in chronic lymphocytic leukemia (CLL), which led to FDA approval in November 2013.

EXPERT OPINION

Clinical data are now emerging confirming the promise of the initial preclinical data that demonstrated superior efficacy of obinutuzumab over rituximab at similar dosing. The emerging randomized Phase III data from older comorbid patients with previously untreated CLL demonstrated significant improvements in molecular remission rates and median progression-free survival of obinutuzumab plus chlorambucil versus rituximab plus chlorambucil. This emerging data provide reasons to be optimistic that outcomes for patients with B-cell malignancies can be further improved with obinutuzumab.

Translational medicine in action: anti-CD20 therapy in lymphoma

The introduction of rituximab for B cell lymphoma in the late 1990s inaugurated a new era of cancer therapy showcasing mAbs. mAbs are in principle an amalgamation of two characteristics of a perfect anticancer drug. First, rituximab is a therapy targeted to the tumor cell, but it carries fewer side effects than does chemotherapy. Second, with its ability to directly engage the host immune system, it could potentially elicit longer lasting anticancer immunity, although this remains to be proven. This review highlights the fundamental scientific discoveries that allowed the development of clinically successful anti-CD20 mAbs. Since the approval of rituximab, a considerable amount of work has been undertaken by different groups trying to understand the workings and limitations of anti-CD20s. All of these efforts will be critical in designing new mAbs to CD20 and other targets and, ultimately, of anticancer mAbs that will improve on, or even replace, chemotherapy.

Obinutuzumab for B-cell malignancies

INTRODUCTION

We analyse data for the use of obinutuzumab in the treatment of CD20(+) lymphoproliferative disorders with a focus on chronic lymphocytic leukaemia (CLL). Targeted therapy against CD20 with the mAb rituximab led to significant improvements in survival for patients with B-cell non-Hodgkin lymphoma (NHL) and is the current mainstay of treatment for CD20(+) malignancies. Despite this, many patients relapse or become refractory after rituximab-containing therapies, so efforts have been made to develop better anti-CD20 mAbs. Obinutuzumab recently demonstrated superiority over rituximab in the only published Phase III study comparing the two antibodies.

AREAS COVERED

Obinutuzumab is a humanised, anti-CD20 mAb being compared to rituximab in several Phase III studies. An overview of obinutuzumab, its mechanisms of action and results of Phase I-III studies are presented.

EXPERT OPINION

The demonstration of superiority of obinutuzumab over rituximab in the CLL11 Phase III study is potentially practice-changing. Obinutuzumab has also proven safe and efficacious in CD20(+) NHL in Phase I/II studies and results of Phase III studies in NHL are eagerly awaited. The potential implications of improved outcomes for CLL and NHL with the introduction of this more potent anti-CD20 antibody are tremendous given the impressive results obtained after the introduction of rituximab over a decade ago.

Enhancement of Rituximab-induced cell death by the physical association of CD20 with CD40 molecules on the cell surface

CD20 is an attractive therapeutic target given the success of its monoclonal antibody, Rituximab, in the treatment of B-cell malignancies and B-cell-mediated autoimmune diseases. Treatment with Rituximab causes a rapid depletion of B cells and a decrease in disease symptoms. Despite the clinical efficiency of Rituximab, its mechanism of action is not completely understood. In this study, we aimed at further investigating the Rituximab-induced cell death and the factors affecting such responses. Our results indicate that Rituximab-induced cell death depends on the nature of the cells and levels of CD20 expression on the cell surface. Coexpression of CD20 with CD40, a member of the TNF receptor family that is known to be physically associated with CD20 on the cell surface, enhances the apoptotic response induced by Rituximab. Inhibiting the formation of CD40 disulfide-bound-homodimers, a process required for some CD40 signaling, further enhances Rituximab-induced cell death. Cell death induced by anti-CD40 mAb is also upregulated by the presence of CD20, suggesting a bidirectional influence of the CD20/CD40 association. Moreover, treating cells with both anti-CD20 and anti-CD40 antibodies improves the cell death response induced by a single-agent treatment. These results highlight the role of the CD20/CD40 association in triggering B-cell depletion and may pave the way for an alternative more efficient therapeutic strategy in treating B-cell-mediated disorders.

Anti-CD20 monoclonal antibodies and associated viral hepatitis in hematological diseases

Over the past decade, the administration of anti-CD20 monoclonal antibodies such as rituximab has demonstrated various degrees of effectiveness and has improved patients’ outcomes during the treatment of autoimmune hematological disorders and hematological malignancies. However, the depletion of B-cells, the distribution of T-cell populations, and the reconstruction of host immunity resulting from the use of anti-CD20 monoclonal antibodies potentially lead to severe viral infections, such as hepatitis B virus (HBV), hepatitis C virus (HCV), parvovirus B19, and herpes viruses, in patients who are undergoing immune therapy or immunochemotherapy. Of these infections, HBV- and HCV-related hepatitis are a great concern in endemic areas because of the high morbidity and mortality rates in untreated patients. As a result, prophylaxis against HBV infection is becoming a standard of care in these areas. Parvovirus B19, a widespread pathogen that causes red blood cell aplasia in immunocompromised hosts, also causes hepatitis in healthy individuals. Recently, its association with hepatitis was recognized in a patient treated with rituximab. In addition, adenovirus, varicella-zoster virus, hepatitis E virus, and rituximab itself have been linked to the occurrence of hepatitis during or after rituximab treatments. The epidemiologies and pathogeneses of these etiologies remain unknown. Because of the increasing use of anti-CD20 monoclonal antibodies for the treatment of hematological malignancies or autoimmune hematological disorders, it is imperative that physicians understand and balance the risks of hepatotropic virus-associated hepatitis against the benefits of using anti-CD20 monoclonal antibodies.

The role of complement in tumor growth

Complement is a central part of the immune system that has developed as a first defense against non-self cells. Neoplastic transformation is accompanied by an increased capacity of the malignant cells to activate complement. In fact, clinical data demonstrate complement activation in cancer patients. On the basis of the use of protective mechanisms by malignant cells, complement activation has traditionally been considered part of the body's immunosurveillance against cancer. Inhibitory mechanisms of complement activation allow cancer cells to escape from complement-mediated elimination and hamper the clinical efficacy of monoclonal antibody-based cancer immunotherapies. To overcome this limitation, many strategies have been developed with the goal of improving complement-mediated effector mechanisms. However, significant work in recent years has identified new and surprising roles for complement activation within the tumor microenvironment. Recent reports suggest that complement elements can promote tumor growth in the context of chronic inflammation. This chapter reviews the data describing the role of complement activation in cancer immunity, which offers insights that may aid the development of more effective therapeutic approaches to control cancer.

Reformatting of scFv antibodies into the scFv-Fc format and their downstream purification

The scFv-Fc format allows for rapid characterization of candidate scFvs isolated from phage display libraries before conversion into a full-length IgG. This format offers several advantages over the phage display-derived scFv, including bivalent binding, longer half-life, and Fc-mediated effector functions. Here, a detailed method is presented, which describes the cloning, expression, and purification of an scFv-Fc fragment, starting from scFv fragments obtained from a phage display library. This method facilitates the rapid screening of candidate antibodies, prior to a more time-consuming conversion into a full IgG format. Alternatively, the scFv-Fc format may be used in the clinic for therapeutic applications.

Glycoengineered CD20 antibody obinutuzumab activates neutrophils and mediates phagocytosis through CD16B more efficiently than rituximab

Phagocytosis of CLL targets by neutrophils is a novel mechanism of action of the glycoengineered anti-CD20 antibody obinutuzumab. This mechanism takes place in physiological conditions and requires CD16B and CD32A.

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

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

Emerging cell and cytokine targets in rheumatoid arthritis

Despite major progress in the treatment of rheumatoid arthritis (RA), strong unmet medical need remains, as only a minor proportion of patients reach sustained clinical remission. New approaches are therefore necessary, and include manipulation of regulatory T cells, which might be able to restore the disturbed immune system and could even lead to a cure if this restored regulation were to prove sustainable. Logistical and conceptual problems, however, beset this attractive therapeutic approach, including difficulties with ex vivo expansion of cells, specificity of targeting and the optimal time point of administration. Therefore, alternative avenues are being investigated, such as targeting B-cell effector functions and newly identified proinflammatory cytokines. On the basis of success with B-cell depleting therapy using anti-CD20 agents, further treatment modalities are now exploring direct or indirect interference in B-cell-mediated immunity with the use of agents directed against other B-cell surface molecules. Novel approaches target intracellular B-cell signalling and regulatory B cells. New cytokine-directed therapies target important proinflammatory mediators such as GM-CSF, new members of the IL-1 family, IL-6 and its receptor, IL-17, IL-20, IL-21, IL-23 as well as synovium-specific targets. This article reviews these emerging cell and cytokine targets with special focus on biologic agents, some of which might reach the clinic soon whereas others will require considerable time in development. Nevertheless, these exciting new approaches will considerably enhance our repertoire in the battle against this potentially devastating disease.

Preclinical activity of the type II CD20 antibody GA101 (obinutuzumab) compared with rituximab and ofatumumab in vitro and in xenograft models

We report the first preclinical in vitro and in vivo comparison of GA101 (obinutuzumab), a novel glycoengineered type II CD20 monoclonal antibody, with rituximab and ofatumumab, the two currently approved type I CD20 antibodies. The three antibodies were compared in assays measuring direct cell death (AnnexinV/PI staining and time-lapse microscopy), complement-dependent cytotoxicity (CDC), antibody-dependent cell-mediated cytotoxicity (ADCC), antibody-dependent cell-mediated phagocytosis (ADCP), and internalization. The models used for the comparison of their activity in vivo were SU-DHL4 and RL xenografts. GA101 was found to be superior to rituximab and ofatumumab in the induction of direct cell death (independent of mechanical manipulation required for cell aggregate disruption formed by antibody treatment), whereas it was 10 to 1,000 times less potent in mediating CDC. GA101 showed superior activity to rituximab and ofatumumab in ADCC and whole-blood B-cell depletion assays, and was comparable with these two in ADCP. GA101 also showed slower internalization rate upon binding to CD20 than rituximab and ofatumumab. In vivo, GA101 induced a strong antitumor effect, including complete tumor remission in the SU-DHL4 model and overall superior efficacy compared with both rituximab and ofatumumab. When rituximab-pretreated animals were used, second-line treatment with GA101 was still able to control tumor progression, whereas tumors escaped rituximab treatment. Taken together, the preclinical data show that the glyoengineered type II CD20 antibody GA101 is differentiated from the two approved type I CD20 antibodies rituximab and ofatumumab by its overall preclinical activity, further supporting its clinical investigation.

Obinutuzumab (GA101) in patients with relapsed/refractory indolent non-Hodgkin lymphoma: results from the phase II GAUGUIN study

PURPOSE

The phase II part of the phase I/II GAUGUIN study evaluated the efficacy and safety of two different doses of obinutuzumab (GA101), a type II, glycoengineered, humanized anti-CD20 monoclonal antibody, in patients with relapsed/refractory indolent non-Hodgkin lymphoma.

PATIENTS AND METHODS

Patients were randomly assigned to receive eight cycles of obinutuzumab (GA101) as a flat dose of 400 mg on days 1 and 8 of cycle 1 and also on day 1 of cycles 2 to 8 (400/400 mg) or 1,600 mg on days 1 and 8 of cycle 1 and 800 mg on day 1 of cycles 2 to 8 (1,600/800 mg).

RESULTS

Forty patients were enrolled, including 34 with follicular lymphoma; 38 of 40 patients had previously received rituximab and 22 of 40 were rituximab refractory. The overall response rate at the end of treatment was 55% (95% CI, 32% to 76%) in the 1,600/800-mg group (9% complete responders) and 17% (95% CI, 4% to 41%) in the 400/400-mg group (no complete responders). Five of 10 rituximab-refractory patients had an end-of-treatment response in the 1,600/800-mg group versus one of 12 in the 400/400-mg group. Median progression-free survival was 11.9 months in the 1,600/800-mg group (range, 1.8 to 33.9+ months) and 6.0 months in the 400/400-mg group (range, 1.0 to 33.9+ months). The most common adverse events were infusion-related reactions (IRRs) seen in 73% of patients, but only two patients had grade 3 to 4 IRRs (both in the 1,600/800-mg group). No IRRs were considered serious, and no patients withdrew for IRRs.

CONCLUSION

The 1,600/800-mg dose schedule of obinutuzumab (GA101) has encouraging activity with an acceptable safety profile in relapsed/refractory indolent non-Hodgkin lymphoma.

Obinutuzumab (GA101) monotherapy in relapsed/refractory diffuse large b-cell lymphoma or mantle-cell lymphoma: results from the phase II GAUGUIN study

PURPOSE

Obinutuzumab (GA101), a type II, glycoengineered, humanized anti-CD20 monoclonal antibody, was superior to rituximab in human diffuse large B-cell lymphoma (DLBCL) and mantle-cell lymphoma (MCL) xenograft models. In phase I of our study, obinutuzumab (GA101) exhibited encouraging activity but no clear dose-response relationship, and few patients had aggressive histologies. The efficacy and safety of two doses of obinutuzumab (GA101) were explored in our randomized phase II trial in patients with heavily pretreated DBLCL and MCL.

PATIENTS AND METHODS

Patients were randomly assigned to receive eight cycles of obinutuzumab (GA101) either as a flat dose of 400 mg for all infusions (days 1 and 8 of cycle 1; day 1 of cycles 2 to 8) or 1,600 mg on days 1 and 8 of cycle 1 and 800 mg on day 1 of cycles 2 to 8.

RESULTS

Forty patients were enrolled: 21 patients in the 400/400-mg treatment arm (DLBCL, n = 10; MCL, n = 11) and 19 patients in the 1,600/800-mg arm (DLBCL, n = 15; MCL, n = 4). End-of-treatment response was 28% (32% and 24% in the 1,600/800-mg and 400/400-mg study arms, respectively). Best overall response rates were 37% in the 1,600/800-mg arm and 24% in the 400/400-mg study arm (DLBCL, eight [32%] of 25 patients; MCL, four [27%] of 15 patients). Five (20%) of 25 rituximab-refractory patients exhibited treatment response, including four of 12 in the 1,600/800-mg group. The most common adverse events were infusion-related reactions (IRRs), which were manageable. Three patients had grade 3/4 IRRs. Grade 3/4 neutropenia was seen in only one patient.

CONCLUSION

Obinutuzumab (GA101) 1,600/800 mg achieves early steady-state concentration and clinical activity with an acceptable safety profile in relapsed/refractory DLBCL and MCL, supporting further exploration.

Function-first antibody discovery: Embracing the unpredictable biology of antibodies

Therapeutic antibodies may mediate antineoplastic effects by altering the biological functions of their target, by directly stimulating the demise of cancer cells or by activating antibody-dependent immune effector mechanisms. We have recently provided in vivo proof-of-concept for a "function-first" target and drug discovery platform in which antibodies against a multitude of tumor-associated antigens are screened for biological effects in a target-unbiased manner.

Rituximab biosimilars

INTRODUCTION

Rituximab is a monoclonal antibody targeting CD20, used to treat B cell malignancies and B cell-mediated autoimmune diseases. Rituximab has the largest market of any monoclonal antibody therapeutic. Its patent will expire within the next few years and several manufacturers have already produced or are developing rituximab biosimilars that aim to match the innovator rituximab as closely as possible.

AREAS COVERED

In this review, we discuss key factors that determine the efficacy of rituximab therapy, potential technical challenges in the manufacture and evaluation of biosimilars, regulatory considerations regarding the review and approval of biosimilars, and the current status of biosimilar rituximab development by various manufacturers. Due to the nature of the topic, literature searches included conference abstracts, regulatory and industry websites as well as peer reviewed literature.

EXPERT OPINION

Cost is a key limitation of current biologics usage and there is a political impetus to the licensing of biosimilars. Concerns regarding potential dissimilarities of biosimilars are legitimate, but surmountable with techniques for in vitro, in vivo and clinical testing and more clearly defined regulatory requirements. These should provide reassurance to prescribers. However, the cost of manufacturing and licensing a biosimilar remains high and the reduction in cost may be more limited than for a non-biologic small molecule drug and its generic version. This cost reduction will be critical to the impact and use of rituximab biosimilars.

Construction and characterization of recombinant human C9 or C7 linked to single chain Fv directed to CD25

Complement-dependent cytotoxicity (CDC) is a potent promoter of tumor clearance during monoclonal antibody therapy. Complement activation on antibody-bearing tumor cells results in formation of the membrane attack complex (MAC), which activates cell death. The complement activation cascade that bridges between antibody binding and MAC formation is regulated by complement inhibitors that are over-expressed on tumor cells. In order to bypass those complement regulators, we have designed an immunoconjugate composed of a humanized single chain Fv of an anti-Tac (CD25) monoclonal antibody fused at its C terminus either to complement protein C9 (scFv-C9) or to complement C7 (scFv-C7) and tagged with six histidines at the C terminal end. Recombinant scFv-C9 and scFv-C7 were expressed in 293T cells and purified. Both are shown to efficiently bind to CD25-positive tumor cells. In addition, scFv-C9, but not scFv-C7, increases MAC deposition on the cells and enhances complement-mediated cell death of target CD25-positive cells. Thus, scFv-C9 fusion protein is potentially a novel reagent for application in cancer immunotherapy.