Table of Contents

Volume 4, Issue 3

  May/June 2012

  Pages 291 - 418

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EDITORIAL

Open Access Article

Insights from Fc receptor biology: A route to improved antibody reagents

Jenny M. Woof
Pages 291 - 293
http://dx.doi.org/10.4161/mabs.20100
Abstract | Full Text | PDF

Fc receptors and their interaction with antibodies will be a major theme at the forthcoming FASEB Science Research Conference on Immunoreceptors to be held in Snowmass this July (details available at www.faseb.org/src/home.aspx, follow the tabs for Immunoreceptors). Since its inception in the mid 1980s, this meeting series has maintained a focus on Fc receptors, and this year’s meeting will be no exception.




REVIEW

Lepidopteran cells, an alternative for the production of recombinant antibodies?

Martine Cérutti and Josée Golay
Pages 294 - 309
http://dx.doi.org/10.4161/mabs.19942
Abstract | Full Text | PDF

Monoclonal antibodies are used with great success in many different therapeutic domains. In order to satisfy the growing demand and to lower the production cost of these molecules, many alternative systems have been explored. Among them, the baculovirus/insect cells system is a good candidate. This system is very safe, given that the baculoviruses have a highly restricted host range and they are not pathogenic to vertebrates or plants. But the major asset is the speed with which it is possible to obtain very stable recombinant viruses capable of producing fully active proteins whose glycosylation pattern can be modulated to make it similar to the human one. These features could ultimately make the difference by enabling the production of antibodies with very low costs. However, efforts are still needed, in particular to increase production rates and thus make this system commercially viable for the production of these therapeutic agents.




REPORTS

Development and validation of an antibody-dependent cell-mediated cytotoxicity-reporter gene assay

Bhavin S. Parekh, Elaine Berger, Sharon Sibley, Suntara Cahya, Liqun Xiao, Melinda Ann LaCerte, Peter Vaillancourt, Scott Wooden and Dennis Gately
Pages 310 - 318
http://dx.doi.org/10.4161/mabs.19873
Abstract | Full Text | PDF

Humanized monoclonal antibodies (mAbs) are the fastest growing class of biological therapeutics that are being developed for various medical indications, and more than 30 mAbs are already approved and in the market place. Antibody-dependent cell-mediated cytotoxicity (ADCC) is an important biological function attributed to the mechanism of action of several therapeutic antibodies, particularly oncology targeting mAbs. The ADCC assay is a complicated and highly variable assay. Thus, the use of an ADCC assay as a lot release test or a stability test for clinical trial batches of mAbs has been a substantial challenge to install in quality control laboratories. We describe here the development and validation of an alternate approach, an ADCC-reporter gene assay that is based on the key attributes of the PBMC-based ADCC assay. We tested the biological relevance of this assay using an anti-CD20 based model and demonstrated that this ADCC-reporter assay correlated well with standard ADCC assays when induced with the drugable human isotypes [IgG1, IgG2, IgG4, IgG4S > P (S228P) and IgG4PAA (S228P, F234A, L235A)] and with IgG1 isotype variants with varying amounts of fucosylation. This data demonstrates that the ADCC-reporter gene assay has performance characteristics (accuracy, precision and robustness) to be used not only as a potency assay for lot release and stability testing for antibody therapeutics, but also as a key assay for the characterization and process development of therapeutic molecules.

Open Access Article

Solubility evaluation of murine hybridoma antibodies

Stacey Spencer, Deidra Bethea, T. Shantha Raju, Jill Giles-Komar and Yiqing Feng
Pages 319 - 325
http://dx.doi.org/10.4161/mabs.19869
Abstract | Full Text | PDF

The successful development of antibody therapeutics depends on the molecules having properties that are suitable for manufacturing, as well as use by patients. Because high solubility is a desirable property for antibodies, screening for solubility has become an essential step during the early candidate selection process. In considering the screening process, we formed a hypothesis that hybridoma antibodies are filtered by nature to possess high solubility and tested this hypothesis using a large number of murine hybridoma-derived antibodies. Using the cross-interaction chromatography (CIC) method, we screened the solubility of 92 murine hybridoma-derived monoclonal antibodies and found that all of these molecules exhibited CIC profiles that are indicative of high solubility (>100mg/mL). Further investigations revealed that variable region N-linked glycosylation or isoelectric parameters are unlikely to contribute to the high solubility of these antibodies. These results support the general hypothesis that hybridoma monoclonal antibodies are highly soluble.

Quantitative evaluation of fucose reducing effects in a humanized antibody on Fcγ receptor binding and antibody-dependent cell-mediated cytotoxicity activities

Shan Chung, Valerie Quarmby, Xiaoying Gao, Yong Ying, Linda Lin, Chae Reed, Chris Fong, Wendy Lau, Zhihua J. Qiu, Amy Shen, Martin Vanderlaan and An Song
Pages 326 - 340
http://dx.doi.org/10.4161/mabs.19941
Abstract | Full Text | PDF

The presence or absence of core fucose in the Fc region N-linked glycans of antibodies affects their binding affinity toward FcγRIIIa as well as their antibody-dependent cell-mediated cytotoxicity (ADCC) activity. However, the quantitative nature of this structure-function relationship remains unclear. In this study, the in vitro biological activity of an afucosylated anti-CD20 antibody was fully characterized. Further, the effect of fucose reduction on Fc effector functions was quantitatively evaluated using the afucosylated antibody, its “regular” fucosylated counterpart and a series of mixtures containing varying proportions of “regular” and afucosylated materials. Compared with the “regular” fucosylated antibody, the afucosylated antibody demonstrated similar binding interactions with the target antigen (CD20), C1q and FcγRIa, moderate increases in binding to FcγRIIa and IIb, and substantially increased binding to FcγRIIIa. The afucosylated antibodies also showed comparable complement-dependent cytotoxicity activity but markedly increased ADCC activity. Based on EC₅₀ values derived from dose-response curves, our results indicate that the amount of afucosylated glycan in antibody samples correlate with both FcγRIIIa binding activity and ADCC activity in a linear fashion. Furthermore, the extent of ADCC enhancement due to fucose depletion was not affected by the FcγRIIIa genotype of the effector cells.

Femtomolar Fab binding affinities to a protein target by alternative CDR residue co-optimization strategies without phage or cell surface display

Christian Votsmeier, Hanna Plittersdorf, Oliver Hesse, Andreas Scheidig, Michael Strerath, Uwe Gritzan, Klaus Pellengahr, Peter Scholz, Andrea Eicker, David Myszka, Wayne M. Coco and Ulrich Haupts
Pages 341 - 348
http://dx.doi.org/10.4161/mabs.19981
Abstract | Full Text | PDF

In therapeutic or diagnostic antibody discovery, affinity maturation is frequently required to optimize binding properties. In some cases, achieving very high affinity is challenging using the display-based optimization technologies. Here we present an approach that begins with the creation and clonal, quantitative analysis of soluble Fab libraries with complete diversification in adjacent residue pairs encompassing every complementarity-determining region position. This was followed by alternative recombination approaches and high throughput screening to co-optimize large sets of the found improving mutations. We applied this approach to the affinity maturation of the anti-tumor necrosis factor antibody adalimumab and achieved ~500-fold affinity improvement, resulting in femtomolar binding. To our knowledge, this is the first report of the in vitro engineering of a femtomolar affinity antibody against a protein target without display screening. We compare our findings to a previous report that employed extensive mutagenesis and recombination libraries with yeast display screening. The present approach is widely applicable to the most challenging of affinity maturation efforts.

Open Access Article

Targeting malignant B cells with an immunotoxin against ROR1

Sivasubramanian Baskar, Adrian Wiestner, Wyndham H. Wilson, Ira Pastan and Christoph Rader
Pages 349 - 361
http://dx.doi.org/10.4161/mabs.19870
Abstract | Full Text | PDF

The selective cell surface expression of receptor tyrosine kinase-like orphan receptor 1 (ROR1) in chronic lymphocytic leukemia (CLL) and mantle cell lymphoma (MCL) has made ROR1 a novel and promising target for therapeutic monoclonal antibodies (mAbs). Four mouse mAbs generated by hybridoma technology exhibited specific binding to human ROR1. Epitope mapping studies showed that two mAbs (2A2 and 2D11) recognized N-terminal epitopes in the extracellular region of ROR1 and the other two (1A1 and 1A7) recognized C-terminal epitopes. A ROR1- immunotoxin (BT-1) consisting of truncated Pseudomonas exotoxin A (PE38) and the V_H and V_L fragments of 2A2-IgG was made recombinantly. Both 2A2-IgG and BT-1 showed dose-dependent and selective binding to primary CLL and MCL cells and MCL cell lines. Kinetic analyses revealed 0.12-nM (2A2-IgG) to 65-nM (BT-1) avidity/affinity to hROR1, depicting bivalent and monovalent interactions, respectively. After binding to cell surface ROR1, 2A2-IgG and BT-1 were partially internalized by primary CLL cells and MCL cell lines, and BT-1 induced profound apoptosis of ROR1-expressing MCL cell lines in vitro (EC₅₀ = 16 pM–16 nM), but did not affect ROR1-negative cell lines. Our data suggest that ROR1-immunotoxins such as BT-1 could serve as targeted therapeutic agents for ROR1-expressing B cell malignancies and other cancers.

Impact of linker and conjugation chemistry on antigen binding, Fc receptor binding and thermal stability of model antibody-drug conjugates

Mauro Acchione, Hyewon Kwon, Claudia M. Jochheim and William M. Atkins
Pages 362 - 372
http://dx.doi.org/10.4161/mabs.19449
Abstract | Full Text | PDF

Antibody-drug conjugates (ADCs) with biotin as a model cargo tethered to IgG1 mAbs via different linkers and conjugation methods were prepared and tested for thermostability and ability to bind target antigen and Fc receptor. Most conjugates demonstrated decreased thermostability relative to unconjugated antibody, based on DSC, with carbohydrate and amine coupled ADCs showing the least effect compared with thiol coupled conjugates. A strong correlation between biotin-load and loss of stability is observed with thiol conjugation to one IgG scaffold, but the stability of a second IgG scaffold is relatively insensitive to biotin load. The same correlation for amine coupling was less significant. Binding of antibody to antigen and Fc receptor was investigated using surface plasmon resonance. None of the conjugates exhibited altered antigen affinity. Fc receptor FcγIIb (CD32b) interactions were investigated using captured antibody conjugate. Protein G and Protein A, known inhibitors of Fc receptor (FcR) binding to IgG, were also used to extend the analysis of the impact of conjugation on Fc receptor binding. H10_NPEG4 was the only conjugate to show significant negative impact to FcR binding, which is likely due to higher biotin-load compared with the other ADCs. The ADC aHIS_NLC and aHIS_TPEG8 demonstrated some loss in affinity for FcR, but to much lower extent. The general insensitivity of target binding and effector function of the IgG1 platform to conjugation highlight their utility. The observed changes in thermostability require consideration for the choice of conjugation chemistry, depending on the system being pursued and particular application of the conjugate.

Fluorescent IgG fusion proteins made in E. coli

Yael Luria, Dina Raichlin and Itai Benhar
Pages 373 - 384
http://dx.doi.org/10.4161/mabs.19581
Abstract | Full Text | PDF

Antibodies are among the most powerful tools in biological and biomedical research and are presently the fastest growing category of new bio-pharmaceutics. The most common format of antibody applied for therapeutic, diagnostic and analytical purposes is the IgG format. For medical applications, recombinant IgGs are made in cultured mammalian cells in a process that is too expensive to be considered for producing antibodies for diagnostic and analytical purposes. Therefore, for such purposes, mouse monoclonal antibodies or polyclonal sera from immunized animals are used. While looking for an easier and more rapid way to prepare full-length IgGs for therapeutic purposes, we recently developed and reported an expression and purification protocol for full-length IgGs, and IgG-based fusion proteins in E. coli, called “Inclonals.” By applying the Inclonals technology, we could generate full-length IgGs that are genetically fused to toxins. The aim of the study described herein was to evaluate the possibility of applying the “Inclonals” technology for preparing IgG-fluorophore fusion proteins. We found that IgG fused to the green fluorescent proteins enhanced GFP (EGFP) while maintaining functionality in binding, lost most of its fluorescence during the refolding process. In contrast, we found that green fluorescent Superfolder GFP (SFGFP)-fused IgG and red fluorescent mCherry-fused IgG were functional in antigen binding and maintained fluorescence intensity. In addition, we found that we can link several SFGFPs in tandem to each IgG, with fluorescence intensity increasing accordingly. Fluorescent IgGs made in E. coli may become attractive alternatives to monoclonal or polyclonal fluorescent antibodies derived from animals.

Galactosylation variations in marketed therapeutic antibodies

T. Shantha Raju and Robert E. Jordan
Pages 385 - 391
http://dx.doi.org/10.4161/mabs.19868
Abstract | Full Text | PDF

There are currently ~25 recombinant full-length IgGs (rIgGs) in the market that have been approved by regulatory agencies as biotherapeutics to treat various human diseases. Most of these are based on IgG1k framework and are either chimeric, humanized or human antibodies manufactured using either Chinese hamster ovary (CHO) cells or mouse myeloma cells as the expression system. Because CHO and mouse myeloma cells are mammalian cells, rIgGs produced in these cell lines are typically N-glycosylated at the conserved asparagine (Asn) residues in the CH2 domain of the Fc, which is also the case with serum IgGs. The Fc glycans present in these rIgGs are for the most part complex biantennary oligosaccharides with heterogeneity associated with the presence or the absence of several different terminal sugars. The major Fc glycans of rIgGs contain 0 or 1 or 2 (G0, G1 and G2, respectively) terminal galactose residues as non-reducing termini and their relative proportions may vary depending on the cell culture conditions in which they were expressed. Since glycosylation is strongly associated with antibody effector functions and terminal galactosylation may affect some of those functions, a panel of commercially available therapeutic rIgGs expressed in CHO cells and mouse myeloma cells were examined for their galactosylation patterns. The results suggest that the rIgGs expressed in CHO cells are generally less galactosylated compared to the rIgGs expressed in mouse myeloma cells. Accordingly, rIgGs produced in CHO cells tend to contain higher levels of G0 glycans compared with rIgGs produced in mouse myeloma cell lines. Despite the apparent wide variability in galactose content, adverse events or safety issues have not been associated with specific galactosylation patterns of therapeutic antibodies. Nevertheless, galactosylation may have an effect on the mechanisms of action of some therapeutic antibodies (e.g., effector pathways) and hence further studies to assess effects on product efficacy may be warranted for such antibodies. For antibodies that do not require effector functions for biological activity, however, setting a narrow specification range for galactose content may be unnecessary.




BRIEF REPORT

Monoclonal antibodies: Longitudinal prescribing information analysis of hypersensitivity reactions

Konstantin Kleyman and Debra S. Weintraub
Pages 392 - 397
http://dx.doi.org/10.4161/mabs.19895
Abstract | Full Text | PDF

Monoclonal antibodies (mAbs) are known to cause hypersensitivity reactions (HSRs). The reactions pose a significant challenge to investigators, regulators, and health providers. Because HSRs cannot be predicted through the pharmacological basis of a therapy, clinical data are often relied upon to detect the reactions. Unfortunately, clinical studies are often unable to adequately characterize HSRs especially in therapies for orphan diseases. HSRs can go undetected until post-marketing safety surveillance when a large number of patients have been exposed to the therapy. The presented data demonstrates how hypersensitivity reaction warnings have changed over time in the prescribing information (PI), i.e., the drug package insert, through August 1, 2011 for 28 US-marketed mAbs. Tracking all PI revisions for each mAb over time revealed that hypersensitivity warning statements were expanded to include more severe manifestations. Over the course of a mAb therapy’s life cycle, the hypersensitivity warning is twice more likely to be upgraded than downgraded in priority. Approximately 85% of hypersensitivity-associated fatality warnings were added in PI revisions as a result of post-marketing experience. Over 60% (20/33) of revisions to hypersensitivity warnings occurred within 3–4 y of product approval. While HSRs are generally recognized and described in the initial PI of mAbs, fatal HSRs are most commonly observed in post-marketing surveillance. Results of this study suggest that initial product labeling information may not describe rare but clinically significant occurrences of severe or fatal HSRs, but subsequent label revisions include rare events observed during post-marketed product use.




SHORT COMMUNICATION

Immunopotentiating properties of a multispecific α-anti-idiotype antibody

Tays Hernández, Cristina Mateo de Acosta and Rolando Pérez
Pages 398 - 402
http://dx.doi.org/10.4161/mabs.19872
Abstract | Full Text | PDF

Multispecificity is not a well-understood property of some antibodies. Different functions have been attributed to multispecific natural antibodies, commonly associated with the neutralization and clearance of antigens. Much less is known about the role of antibodies like these, based on their idiotypic connectivity. B7Y33 is a chimeric IgG1 version of a polyreactive α anti-idiotype antibody that is able to interact with different immunoglobulin and non-immunoglobulin antigens. Here we report the capacity of this antibody to enhance the immunogenicity of several autologous IgMs in adjuvant-free conditions. Our results suggest that the formation of immune complexes seems to be necessary, but not sufficient, to this activity. The potential involvement of the interaction of B7Y33 with the FcγRIIb is discussed.




PERSPECTIVE

The birth pangs of monoclonal antibody therapeutics: The failure and legacy of Centoxin

Lara Marks
Pages 403 - 412
http://dx.doi.org/10.4161/mabs.19909
Abstract | Full Text | PDF

This paper examines the development and termination of nebacumab (Centoxin®), a human IgM monoclonal antibody (mAb) drug frequently cited as one of the notable failures of the early biopharmaceutical industry. The non-approval of Centoxin in the United States in 1992 generated major concerns at the time about the future viability of any mAb therapeutics. For Centocor, the biotechnology company that developed Centoxin, the drug posed formidable challenges in terms of safety, clinical efficacy, patient selection, the overall economic costs of health care, as well as financial backing. Indeed, Centocor's development of the drug brought it to the brink of bankruptcy. This article shows how many of the experiences learned with Centoxin paved the way for the current successes in therapeutic mAb development.




EDITOR'S CORNER

Open Access Article

Marketed therapeutic antibodies compendium

Janice M. Reichert
Pages 413 - 415
http://dx.doi.org/10.4161/mabs.19931
Abstract | Full Text | PDF

Therapeutic monoclonal antibodies (mAbs) are currently being approved for marketing in Europe and the United States, as well as other countries, on a regular basis. As more mAbs become available to physicians and patients, keeping track of the number, types, production cell lines, antigenic targets, and dates and locations of approvals has become challenging. Data are presented here for 34 mAbs that were approved in either Europe or the United States (US) as of March 2012, and nimotuzumab, which is marketed outside Europe and the US. Of the 34 mAbs, 28 (abciximab, rituximab, basiliximab, palivizumab, infliximab, trastuzumab, alemtuzumab, adalimumab, tositumomab-I131, cetuximab, ibrituximab tiuxetan, omalizumab, bevacizumab, natalizumab, ranibizumab, panitumumab, eculizumab, certolizumab pegol, golimumab, canakinumab, catumaxomab, ustekinumab, tocilizumab, ofatumumab, denosumab, belimumab, ipilimumab, brentuximab) are currently marketed in Europe or the US. Data for six therapeutic mAbs (muromonab-CD3, nebacumab, edrecolomab, daclizumab, gemtuzumab ozogamicin, efalizumab) that were approved but have been withdrawn or discontinued from marketing in Europe or the US are also included.

Open Access Article

2012 upcoming meetings

Janice M. Reichert
Pages 416 - 418
http://dx.doi.org/10.4161/mabs.19976
Abstract | Full Text | PDF

The Summer 2012 conference season provides ample opportunities to attend meetings that feature topics relevant to antibody research and development (R&D). Meetings such as these serve critical informational and educational functions and are key networking opportunities. Locations are spread throughout the world, reflecting the global nature of antibody R&D.