Targeted anti-cancer therapy using rituximab, a chimaeric anti-CD20 antibody (IDEC-C2B8) in the treatment of non-Hodgkin's B-cell lymphoma

Acquired immunodeficiency syndrome-associated lymphomas are efficiently lysed through complement-dependent cytotoxicity and antibody-dependent cellular cytotoxicity by rituximab

Rituximab (Mabthera) and alemtuzumab (Campath(R), Mabcampath(R)) are non-conjugated IgG1 therapeutic monoclonal antibodies directed against the CD20 and CD52 surface antigens respectively. They are presently used in the therapy of indolent B-cell non-Hodgkin's lymphoma (B-NHL) and of B-cell chronic lymphocytic leukaemia, and are thought to act mainly through complement-dependent cytotoxicity (CDC) and antibody-dependent cellular cytotoxicity (ADCC). Here we have analysed the capacity of these two monoclonal antibodies to lyse cell lines of acquired immunodeficiency syndrome (AIDS)-related B-NHL through either complement activation or antibody-dependent cytotoxicity. Rituximab strongly activated both CDC and ADCC against CD20-positive AIDS-NHL cells lines, inducing up to 60-98% and 20% specific lysis respectively. In contrast, alemtuzumab was a poor activator of CDC, even in the AIDS-NHL cell lines expressing high amounts of CD52, leading to a lysis of only 1-30%, whereas it was at least as strong as rituximab in inducing ADCC of the same lines (up to 30% specific lysis). Altogether, these data offer a first in vitro rationale supporting the therapeutic use of rituximab for CD20-positive AIDS-NHL.

Rituximab-mediated sensitization of B-non-Hodgkin's lymphoma (NHL) to cytotoxicity induced by paclitaxel, gemcitabine, and vinorelbine

Non-Hodgkin's lymphoma (NHL) responds initially to chemotherapy, however, the disease often relapses and acquires a chemoresistant phenotype. Third line treatment options such as paclitaxel, gemcitabine, and vinorelbine have been tried in patients with refractory or relapsed NHL with antilymphoma activity. Currently, rituximab (anti-CD20) has been approved for treatment of indolent NHL, with significant activity in a wide spectrum of B-cell malignancies, though a percentage of patients do not respond to rituximab treatment. Previous findings from our laboratory have demonstrated that rituximab can sensitize drug-resistant NHL B-lymphoma in vitro to some chemotherapeutic drugs. Hence, in this study, we examined the effect of combination treatment of rituximab and the drugs paclitaxel, gemcitabine, and vinorelbine on various NHL cell lines. Our findings indicate that pretreatment of NHL tumor cells with rituximab sensitizes drug-resistant NHL tumor cells to drug-mediated cytotoxicity. These findings suggest the potential clinical application of combination treatments of rituximab and paclitaxel, gemcitabine or vinorelbine in the treatment of drug/rituximab refractory non-Hodgkin's lymphoma.

Monoclonal antibody therapy for B-cell lymphoma

Treatment strategies and outcomes for patients with non-Hodgkin's lymphoma (NHL) are undergoing rapid and important evolution. We have recently witnessed the advent of novel targeted therapies, such as gene therapies, active immunotherapies, antisense therapies, new small molecules and biologicals, and monoclonal antibodies (MoAbs). The first MoAb approved for the treatment of cancer, rituximab, was approved in 1997 and has been rapidly incorporated into treatment regimens for NHL. In a randomized trial in combination with CHOP chemotherapy (cyclophosphamide, hydroxydaunomycin, vincristine, and prednisone), rituximab showed superiority to CHOP for patients with diffuse large cell NHL (DLCL).The rituximab + CHOP combination has become the gold standard for frontline therapy for DLCL and has shown significant activity in the management of follicular NHL. In February 2002, the first radioimmunotherapeutic agent for the treatment of cancer, ibritumomab tiuxetan (Zevalin), was approved. Ibritumomab tiuxetan, an yttrium-labeled antibody used in conjunction with rituximab, has significant activity in follicular and transformed NHL. Use of rituximab has proved that antibodies are safe and active even as single agents. The results have helped dispel the negativity and biases resulting from many years of disappointing results in this important area of research. Results with rituximab have opened the doors to continued research and have provided the impetus necessary for renewed enthusiasm and optimism in continuing the search for curative regimens for patients with NHL.

Glucocorticoids and rituximab in vitro: synergistic direct antiproliferative and apoptotic effects

Rituximab, a chimeric human immunoglobulin G1(IgG1) anti-CD20 monoclonal antibody has been shown to mediate cytotoxicity in malignant B cells via several mechanisms in vitro. These include direct antiproliferative and apoptotic effects, complement-dependent cytotoxicity (CDC), and antibody-dependent cell-mediated cytotoxicity (ADCC). Glucocorticoids (GCs) are often administered in conjunction with rituximab in chemotherapeutic regimens or as premedication to reduce infusion-related symptoms. The effects of GCs on CDC and ADCC, and the direct apoptotic and antiproliferative effects of rituximab are unknown. Therefore, we evaluated these mechanisms in 9 B-cell non-Hodgkin lymphoma (B-NHL) cell lines using rituximab and GCs. Rituximab and dexamethasone induced synergistic growth inhibition in 6 B-NHL cell lines. Dexamethasone and rituximab induced significant G1 arrest in 9 of 9 cell lines. The combination of rituximab and dexamethasone resulted in supra-additive increases in phosphatidylserine exposure and hypodiploid DNA content in 5 and 3 B-NHL cell lines, respectively. CDC and ADCC were neither impaired nor enhanced when dexamethasone and rituximab were administered concurrently. However, preincubation of both effector and tumor cells with dexamethasone reduced specific lysis in ADCC assays in 4 B-NHL cell lines. Preincubation of tumor cell lines with dexamethasone significantly increased cell sensitivity to CDC in 3 B-NHL cell lines. We conclude that the addition of dexamethasone to rituximab results in supra-additive cytotoxicity with respect to its direct antiproliferative and apoptotic effects, induces a cell-dependent increased sensitivity to rituximab-induced CDC, and has minimal negative impact on ADCC when used simultaneously with rituximab.

Lack of fucose on human IgG1 N-linked oligosaccharide improves binding to human Fcgamma RIII and antibody-dependent cellular toxicity

Lec13 cells, a variant Chinese hamster ovary cell line, were used to produce human IgG1 that were deficient in fucose attached to the Asn(297)-linked carbohydrate but were otherwise similar to that found in IgG1 produced in normal Chinese hamster ovary cell lines and from human serum. Lack of fucose on the IgG1 had no effect on binding to human FcgammaRI, C1q, or the neonatal Fc receptor. Although no change in affinity was found for the His(131) polymorphic form of human FcgammaRIIA, a slight improvement in binding was evident for FcgammaRIIB and the Arg(131) FcgammaRIIA polymorphic form. In contrast, binding of the fucose-deficient IgG1 to human FcgammaRIIIA was improved up to 50-fold. Antibody-dependent cellular cytotoxicity assays using purified peripheral blood monocytes or natural killer cells from several donors showed enhanced cytotoxicity, especially evident at lower antibody concentrations. When combined with an IgG1 Fc protein variant that exhibited enhanced antibody-dependent cellular cytotoxicity, the lack of fucose was synergistic.

Rituximab: Ongoing and future clinical development

Monoclonal antibodies have been used as therapeutic agents for many years. In 1997, rituximab (Rituxan; Genentech, Inc, South San Francisco, CA, and IDEC Pharmaceuticals, San Diego, CA) became the first monoclonal antibody to be approved by the US Food and Drug Administration for a cancer indication. The use of rituximab in the treatment of low-grade or follicular, relapsed, or refractory CD20-positive B-cell non-Hodgkin's lymphoma was approved in November 1997 for United States marketing under the trade name Rituxan. In June 1998, rituximab was approved for all European Union countries under the trade name MabThera as therapy for patients with stage III/IV, follicular, chemoresistant, or relapsed (≥ 2 relapses) non-Hodgkin's lymphoma. To date, rituximab has been approved in 56 countries. Over 125,000 patients have been treated with this antibody in the United States alone. Rituximab served to heighten interest in the therapeutic applications of monoclonal antibodies. Literally dozens of antibodies are currently under investigation for a variety of malignant and non-neoplastic indications. The US Food and Drug Administration approved a new (revised) package insert in early 2001. These revisions have been communicated to physicians via a "Dear Doctor Letter" and will appear in the 2002 edition of the Physicians' Desk Reference. A significant amount of clinical research has been performed over the past 9 years, which has served to further our understanding of the potential clinical applications for this novel therapeutic agent. Ongoing and future clinical trials are reviewed in this article. However, much remains to be accomplished in key areas such as combinations with chemotherapy, biologics (including other antibodies), and radiotherapy/radioimmunotherapy; its role within multimodality regimens; and other malignant (beyond low-grade non-Hodgkin's lymphoma) and nonmalignant applications. Semin Oncol 29 (suppl 2):105-112. Copyright © 2002 by W.B. Saunders Company.

Therapeutic activity of humanized anti-CD20 monoclonal antibody and polymorphism in IgG Fc receptor FcgammaRIIIa gene

Given that the FcgammaRIIIa receptor 158V allotype displays a higher affinity for human immunoglobulin G1 and increased antibody-dependent cellular cytotoxicity, the aim of this study was to determine the influence of that FCGR3A polymorphism on the therapeutic response to rituximab, an anti-CD20 humanized immunoglobulin G1 increasingly used in the treatment of non-Hodgkin lymphomas. The FCGR3A-158V/F genotype was determined in 49 patients having received rituximab for a previously untreated follicular non-Hodgkin lymphoma. The clinical response and the disappearance of the BCL2-JH gene rearrangement in both peripheral blood and bone marrow were evaluated at 2 months (M2) and at 1 year (M12). The study population consisted of 20% FCGR3A-158V homozygous patients, 35% FCGR3A-158F homozygous patients, and 45% heterozygous patients (FCGR3A-158F carriers). The objective response rates at M2 and M12 were 100% and 90%, respectively, in FCGR3A-158V homozygous patients compared with 67% (P =.03) and 51% (P =.03), respectively, in FCGR3A-158F carriers. A disappearance of the BCL2-JH gene rearrangement in both peripheral blood and marrow was observed at M12 in 5 of 6 of homozygous FCGR3A-158V patients compared with 5 of 17 of FCGR3A-158F carriers (P =.03). The homozygous FCGR3A-158V genotype was confirmed to be the single parameter associated with clinical and molecular responses by multivariate analysis. This study showed an association between the FCGR3A genotype and clinical and molecular responses to rituximab. This finding will certainly give rise to new pharmacogenetic approaches to the management of patients with non-Hodgkin lymphomas.

Cutaneous large B-cell lymphoma of the leg masquerading as a chronic venous ulcer

We report on a 74-year-old female patient with a primary cutaneous CD20+, diffuse large cell B-cell lymphoma of the lower leg resembling a chronic non-healing leg ulcer. There was no evidence of systemic involvement on computed tomography (CT) scans of the chest, abdomen and pelvis; a slightly enlarged lymph node in the right groin showed dermatopathic lymphadenopathy on histology and immunohistochemistry. Involvement of the bone marrow and peripheral blood was ruled out by punch biopsy and fluorescent activated cell sorter (FACS) analysis of the blood, respectively. Therapeutic anti-CD20 monoclonal antibody rituximab was given at 375 mg m(-2) i.v. once weekly for 7 weeks, without adverse effects, resulting in a minor improvement in the centre of the ulcerated tumour. Unfortunately, the response was not maintained, and after 7 weeks of treatment the patient started to develop new tumour lesions at the border of the ulcer. Local radiotherapy was started and combined photon and electron beam irradiation induced complete remission of the B-cell lymphoma.

CD20 levels determine the in vitro susceptibility to rituximab and complement of B-cell chronic lymphocytic leukemia: further regulation by CD55 and CD59

Complement-dependent cytotoxicity is thought to be an important mechanism of action of the anti-CD20 monoclonal antibody rituximab. This study investigates the sensitivity of freshly isolated cells obtained from 33 patients with B-cell chronic lymphocytic leukemia (B-CLL), 5 patients with prolymphocytic leukemia (PLL), and 6 patients with mantle cell lymphoma (MCL) to be lysed by rituximab and complement in vitro. The results showed that in B-CLL and PLL, the levels of CD20, measured by standard immunofluorescence or using calibrated beads, correlated linearly with the lytic response (coefficient greater than or equal to 0.9; P <.0001). Furthermore, the correlation remained highly significant when the 6 patients with MCL were included in the analysis (coefficient 0.91; P <.0001), which suggests that CD20 levels primarily determine lysis regardless of diagnostic group. The role of the complement inhibitors CD46, CD55, and CD59 was also investigated. All B-CLL and PLL cells expressed these molecules, but at different levels. CD46 was relatively weak on all samples (mean fluorescence intensity less than 100), whereas CD55 and CD59 showed variability of expression (mean fluorescence intensity 20-1200 and 20-250, respectively). Although CD55 and CD59 levels did not permit prediction of complement susceptibility, the functional block of these inhibitors demonstrated that they play an important role in regulating complement-dependent cytotoxicity. Thus, lysis of poorly responding B-CLL samples was increased 5- to 6-fold after blocking both CD55 and CD59, whereas that of high responders was essentially complete in the presence of a single blocking antibody. These data demonstrate that CD20, CD55, and CD59 are important factors determining the in vitro response to rituximab and complement and indicate potential strategies to improve the clinical response to this biologic therapy.

CD20 antibody (C2B8)-induced apoptosis of lymphoma cells promotes phagocytosis by dendritic cells and cross-priming of CD8+ cytotoxic T cells

C2B8 (Rituximab, MabThera) is a chimeric mouse/human monoclonal antibody (mAb) directed against the human B cell-restricted cell surface antigen CD20 which is used as an alternative medication in the treatment of B cell non-Hodgkin lymphomas (NHL). Treatment of CD20+ B cells with C2B8 triggers different cell damaging effects including complement-dependent lysis of tumor cells, antibody-dependent cellular cytotoxicity and induction of apoptosis. Dendritic cells (DC) have recently been shown to ingest cell debris and to present associated antigens even on MHC class I molecules, a mechanism called cross-presentation. In this study, we investigated whether C2B8 treatment of lymphoma promotes the induction of CD8+ T cell responses against lymphoma cell-associated antigens via, cross-presentation. We used Daudi lymphoma cells as a model system in our studies and could demonstrate, that C2B8-treated Daudi cells undergo apoptosis, are phagocytosed by DC and induce in DC typical features of maturation; among them, the induction of CD83 expression as well as the up-regulation of prominent accessory molecules (CD40, CD86) and MHC molecules. Importantly, upon co-culture of such lymphoma cell-pulsed DC with autologous T cells, we could induce efficient cytotoxic T cell (CTL) responses against Daudi cell-associated antigens. These findings suggest that antibody treatment of tumor cells can, in addition to its direct cell damaging effects, under certain conditions, contribute to an induction of potentially protective cytotoxic T cell responses.

Expression of complement inhibitors CD46, CD55, and CD59 on tumor cells does not predict clinical outcome after rituximab treatment in follicular non-Hodgkin lymphoma

Rituximab is a chimeric monoclonal antibody that targets B-cell-specific antigen CD20 and an effective treatment for B-cell non-Hodgkin lymphoma. Although it is readily used in clinical practice, the exact mechanism of its antitumor effect is unclear. One potential mechanism involves complement-mediated cytotoxicity. It has been shown that rituximab induces complement-mediated cytotoxicity in follicular lymphoma cells in vitro, and complement inhibitors CD55 and CD59 may regulate this process. To determine whether complement inhibitors play a role in regulating the antitumor effect of rituximab, the expression of complement inhibitors CD46, CD55, and CD59 was analyzed in pretreatment tumor cells from 29 rituximab-treated follicular lymphoma patients. Among them, 8 patients achieved complete responses, 11 patients achieved partial responses, and 10 patients showed no or minimal responses to rituximab treatment. Expression of surface CD20, CD46, CD55, and CD59 was determined by 2-color flow cytometry. Although the CD59 level was slightly lower in the complete response group, there was no statistically significant difference in the expression of individual complement inhibitor CD46 (mean channel fluorescence [MCF]: NR, 26.4; PR, 21.9; CR, 29.9), CD55 (MCF: NR, 16.4; PR, 14.9; CR, 23.2), or CD59 (MCF: NR, 41.6; PR, 40.6; CR, 30.6), the combination of any 2 inhibitors, or all 3 on tumor cells from 3 response groups. In addition, there was no difference in the rituximab-induced complement-mediated cytotoxicity in an in vitro assay using tumor cells from 3 response groups. Thus, CD46, CD55, and CD59 expression on pretreatment tumor cells, or their susceptibility to in vitro complement-mediated killing, does not predict clinical outcome after rituximab treatment.

Synergism between fludarabine and rituximab revealed in a follicular lymphoma cell line resistant to the cytotoxic activity of either drug alone

We have shown previously that the anti-CD20 chimaeric monoclonal antibody rituximab exerts its effects on neoplastic B-lymphoma cell lines in part via complement-dependent cytotoxicity. In addition, membrane expression levels of complement inhibitory proteins CD55 and CD59 play a role in determining susceptibility to lysis. We have identified one t(14;18)-positive human B-cell non Hodgkin's lymphoma cell line (Karpas 422) that is resistant to rituximab and complement and used it for subsequent studies on the possible interaction between this novel therapeutic agent and established antineoplastic drugs. We have exposed Karpas to several chemotherapeutic agents (doxorubicin, idarubicin, cisplatin, taxol) for different time periods and subsequently exposed the cells to rituximab and human complement. The combination of these drugs with rituximab induced an additive cytotoxic effect. In contrast, exposure to fludarabine (1 microg/ml for 48-72 h) showed a synergistic effect, with cell lysis increasing from 10% to 20% using fludarabine or rituximab and complement alone to about 70% with both cytotoxic agents. Analysis of the mechanism for this synergistic effect showed that fludarabine downmodulates the membrane expression of CD55 (from 96% to 55% positive cells) without significantly altering CD20 levels. Northern analysis demonstrated that fludarabine induced a general downmodulation of steady state mRNA levels with no change in transcription rate detected in run-off assays. The study of the effect of fludarabine and rituximab in six freshly isolated B-cell chronic lymphocytic leukaemia (B-CLL) samples showed that, in most cases, fludarabine has an additive cytotoxic activity with rituximab and complement. This report gives a rational support for clinical studies with combinations of drugs, including monoclonal antibodies and fludarabine.

High resolution mapping of the binding site on human IgG1 for Fc gamma RI, Fc gamma RII, Fc gamma RIII, and FcRn and design of IgG1 variants with improved binding to the Fc gamma R

Immunoglobulin G (IgG) Fc receptors play a critical role in linking IgG antibody-mediated immune responses with cellular effector functions. A high resolution map of the binding site on human IgG1 for human Fc gamma RI, Fc gamma RIIA, Fc gamma RIIB, Fc gamma RIIIA, and FcRn receptors has been determined. A common set of IgG1 residues is involved in binding to all Fc gamma R; Fc gamma RII and Fc gamma RIII also utilize residues outside this common set. In addition to residues which, when altered, abrogated binding to one or more of the receptors, several residues were found that improved binding only to specific receptors or simultaneously improved binding to one type of receptor and reduced binding to another type. Select IgG1 variants with improved binding to Fc gamma RIIIA exhibited up to 100% enhancement in antibody-dependent cell cytotoxicity using human effector cells; these variants included changes at residues not found at the binding interface in the IgG/Fc gamma RIIIA co-crystal structure (Sondermann, P., Huber, R., Oosthuizen, V., and Jacob, U. (2000) Nature 406, 267-273). These engineered antibodies may have important implications for improving antibody therapeutic efficacy.

Engineered antibodies with increased activity to recruit complement

This manuscript describes two sites in a human IgG1 that, when mutated individually or in combination, result in a dramatic increase in C1q binding and complement-dependent cytotoxicity activity. These two residues, K326 and E333, are located at the extreme ends of the C1q binding epicenter in the C(H)2 domain of a human IgG. A mutation to tryptophan at K326 debilitates Ab-dependent cell-mediated cytotoxicity activity. In addition, substitutions of the residues E333 with serine and of K326 with tryptophan in a human IgG2 confer biological activity in the complement-dependent cytotoxicity assay in which the wild-type IgG2 is inactive. This study reveals that the residues K326 and E333 play a significant role in the control of the biological activity of an IgG molecule and can rescue the activity of an inactive IgG isotype.

Membrane ion-exchange chromatography for process-scale antibody purification

The large-scale production of recombinant monoclonal antibodies demands economical purification processes with high throughputs. The potential for ion-exchange membrane adsorbers to replace traditional ion-exchange columns was evaluated. Breakthrough capacities of commercially available cation-exchange membranes were determined as a function of flow-rate and layer number. Due to economic and process restrictions, cation-exchange membranes may not currently be advantageous for process-scale antibody purification in a bind and elute mode. However, anion-exchange membranes in a flow-through mode may provide a reasonable alternative to columns for the removal of low levels of impurities such as DNA, host cell protein, and virus.

Biologic response of B lymphoma cells to anti-CD20 monoclonal antibody rituximab in vitro: CD55 and CD59 regulate complement-mediated cell lysis

The chimeric anti-CD20 MAb rituximab has recently become a treatment of choice for low-grade or follicular non-Hodgkin's lymphomas (FL) with a response rate of about 50%. In this report, we have investigated the mechanism of action of rituximab on 4 FL and 1 Burkitt's lymphoma (BL) cell lines, 3 fresh FL samples and normal B cells in vitro. Rituximab efficiently blocks the proliferation of normal B cells, but not that of the lymphoma lines. We did not detect significant apoptosis of the cell lines in response to rituximab alone. All cell lines were targets of antibody-dependent cellular cytotoxicity (ADCC). On the other hand, human complement-mediated lysis was highly variable between cell lines, ranging from 100% lysis to complete resistance. Investigation of the role of the complement inhibitors CD35, CD46, CD55, and CD59 showed that CD55, and to a lesser extent CD59, are important regulators of complement-mediated cytotoxicity (CDC) in FL cell lines as well as in fresh cases of FL: Blocking CD55 and/or CD59 function with specific antibodies significantly increased CDC in FL cells. We conclude that CDC and ADCC are major mechanisms of action of rituximab on B-cell lymphomas and that a heterogeneous susceptibility of different lymphoma cells to complement may be at least in part responsible for the heterogeneity of the response of different patients to rituximab in vivo. Furthermore, we suggest that the relative levels of CD55 and CD59 may become useful markers to predict the clinical response.

Biologic response of B lymphoma cells to anti-CD20 monoclonal antibody rituximab in vitro: CD55 and CD59 regulate complement-mediated cell lysis

The chimeric anti-CD20 MAb rituximab has recently become a treatment of choice for low-grade or follicular non-Hodgkin's lymphomas (FL) with a response rate of about 50%. In this report, we have investigated the mechanism of action of rituximab on 4 FL and 1 Burkitt's lymphoma (BL) cell lines, 3 fresh FL samples and normal B cells in vitro. Rituximab efficiently blocks the proliferation of normal B cells, but not that of the lymphoma lines. We did not detect significant apoptosis of the cell lines in response to rituximab alone. All cell lines were targets of antibody-dependent cellular cytotoxicity (ADCC). On the other hand, human complement-mediated lysis was highly variable between cell lines, ranging from 100% lysis to complete resistance. Investigation of the role of the complement inhibitors CD35, CD46, CD55, and CD59 showed that CD55, and to a lesser extent CD59, are important regulators of complement-mediated cytotoxicity (CDC) in FL cell lines as well as in fresh cases of FL: Blocking CD55 and/or CD59 function with specific antibodies significantly increased CDC in FL cells. We conclude that CDC and ADCC are major mechanisms of action of rituximab on B-cell lymphomas and that a heterogeneous susceptibility of different lymphoma cells to complement may be at least in part responsible for the heterogeneity of the response of different patients to rituximab in vivo. Furthermore, we suggest that the relative levels of CD55 and CD59 may become useful markers to predict the clinical response.

Tumor lysis syndrome occurring after the administration of rituximab in lymphoproliferative disorders: high-grade non-Hodgkin's lymphoma and chronic lymphocytic leukemia

Rituximab, an anti-CD20 antibody, has been recently approved for the treatment of low-grade or follicular non-Hodgkin's lymphoma (NHL). Because of its relatively benign side effect profile, it has been considered a nontoxic alternative to chemotherapy. Recently, however, tumor lysis syndrome (TLS) resulting from rituximab has been reported in a patient with chronic lymphocytic leukemia (CLL). We herein present two cases of rituximab-induced TLS. The first case occurred in a patient with high-grade NHL, while the second case occurred in a patient with CLL. We also present a summary of the literature regarding TLS induced by immunotherapies.

Expanded bed protein A affinity chromatography of a recombinant humanized monoclonal antibody: process development, operation, and comparison with a packed bed method

We show that expanded bed protein A affinity chromatography using Streamline rProtein A media is an efficient method for purifying a recombinant humanized monoclonal antibody from unclarified Chinese hamster ovary cell culture fluid and that it provides purification performance comparable to using a packed bed. We determined that the dynamic capacity of the expanded bed media is related to flow rate (measured in column volumes per hour) by a power function, which allows a high capacity at a low flow rate. At 250 cm h-1 with a 25 cm bed height (10 column volumes h-1), the dynamic capacity is 30 g l-1. The yield and purity (measured by the amount of host cell proteins, DNA, SDS-PAGE, and turbidity) of the antibody purified by expanded bed is comparable to the yield and purity obtained on a standard packed bed method using Prosep A media.

Real-time control of antibody loading during protein A affinity chromatography using an on-line assay

We show that an on-line chromatographic assay can reliably control antibody loading in real-time during protein A affinity chromatography purification of a recombinant antibody from clarified Chinese hamster ovary cell culture fluid. The on-line assay directly sampled preparative column effluent and provided real-time measurement of antibody breakthrough during loading. The on-line assay used protein A immobilized on perfusion chromatography media, equilibrated with phosphate-buffered saline at pH 7.2 and eluted with phosphate-buffered saline at pH 2.2. The assay reliably ended loading at 1% breakthrough with minimal yield loss. Reproducible yield and purity were obtained over 23 consecutive cycles. Yield remained constant while breakthrough capacity and the antibody concentration in the load changed.

Feasibility of antibody production in plants for human therapeutic use

From the description above, the diversity of antibodies as a class of potential therapeutic agents is weighed against the constraints of developing any therapeutic molecule. Although much of this limit is specific to the antibody design, plant-based production systems have a potential to impact commercialization by making larger volume products manageable, with lower up-front capital requirements. Due to their novel glycosylation pattern (Faye et al. 1989), plants at present may not create antibodies with all the functions of mammalian-glycosylated antibodies (Wright and Morrison 1994). This is not a limit for all current products. Success is dependent on fusing the efficient agriculture infrastructure with the narrow tolerances required for a drug production system. Further validation of plants as a production system will come as more therapeutics from plants follow the corn-produced material through human clinical trials.

Characterization of scFv-Ig Constructs Generated from the Anti-CD20 mAb 1F5 Using Linker Peptides of Varying Lengths

The heavy (VH) and light (VL) chain variable regions of the murine anti-human CD20 mAb 1F5 were cloned, and four single-chain Ab (scFv) molecules were constructed using linker peptides of variable lengths to join the VH and VL domains. Three constructs were engineered using linker peptides of 15, 10, and 5 aa residues consisting of (GGGGS)3, (GGGGS)2, and (GGGGS)1 sequences, respectively, whereas the fourth was prepared by joining the VH and VL domains directly. Each construct was fused to a derivative of human IgG1 (hinge plus CH2 plus CH3) to facilitate purification using staphylococcal protein A. The aggregation and CD20 binding properties of these four 1F5 scFv-Ig derivatives produced were investigated. Both size-exclusion HPLC column analysis and Western blots of proteins subjected to nonreducing SDS-PAGE suggested that all four 1F5 scFv-Ig were monomeric with m.w. of ∼55 kDa. The CD20 binding properties of the four 1F5 scFv-Ig were studied by ELISA and flow cytometry. The 1F5 scFv-Ig with the 5-aa linker (GS1) demonstrated significantly superior binding to CD20-expressing target cells, compared with the other scFv-Ig constructs. Scatchard analysis of the radiolabeled monovalent GS1 scFv-Ig revealed a binding avidity of 1.35 × 108 M−1 compared with an avidity of 7.56 × 108 M−1 for the native bivalent 1F5 Ab. These findings suggest that the GS1 scFv-Ig with a short linker peptide of ∼5 aa is the best of the engineered constructs for future studies.