Antibody therapeutics:

Optimized nonclinical safety assessment strategies supporting clinical development of therapeutic monoclonal antibodies targeting inflammatory diseases

An increasing number of immunomodulatory monoclonal antibodies (mAbs) and IgG Fc fusion proteins are either approved or in early-to-late stage clinical trials for the treatment of chronic inflammatory conditions, autoimmune diseases and organ transplant rejection. The exquisite specificity of mAbs, in combination with their multi-functional properties, high potency, long half-life (permitting intermittent dosing and prolonged pharamcological effects), and general lack of off-target toxicity makes them ideal therapeutics. Dosing with mAbs for these severe and debilitating but often non life-threatening diseases is usually prolonged, for several months or years, and not only affects adults, including sensitive populations such as woman of child-bearing potential (WoCBP) and the elderly, but also children. Immunosuppression is usually a therapeutic goal of these mAbs and when administered to patients whose treatment program often involves other immunosuppressive therapies, there is an inherent risk for frank immunosuppression and reduced host defence which when prolonged increases the risk of infection and cancer. In addition when mAbs interact with the immune system they can induce other adverse immune-mediated drug reactions such as infusion reactions, cytokine release syndrome, anaphylaxis, immune-complex-mediated pathology and autoimmunity. An overview of the nonclinical safety assessment and risk mitigation strategies utilized to characterize these immunomodulatory mAbs and Fc fusion proteins to support first-in human (FIH) studies and futher clinical development in inflammatory disease indications is provided. Specific emphasis is placed on the design of studies to qualify animal species for toxicology studies, early studies to investigate safety and define PK/PD relationships, FIH-enabling and chronic toxicology studies, immunotoxicity, developmental, reproductive and juvenile toxicity studies and studies to determine the potential for immunosuppression and reduced host defence against infection and cancer. Nonclinical strategies to facilitate clinical and market entry in the most efficient timeframe are presented.

Small-angle x-ray scattering screening complements conventional biophysical analysis: comparative structural and biophysical analysis of monoclonal antibodies IgG1, IgG2, and IgG4

A crucial step in the development of therapeutic monoclonal antibodies is the selection of robust pharmaceutical candidates and screening of efficacious protein formulations to increase the resistance toward physicochemical degradation and aggregation during processing and storage. Here, we introduce small-angle X-ray scattering (SAXS) to characterize antibody solution behavior, which strongly complements conventional biophysical analysis. First, we apply a variety of conventional biophysical techniques for the evaluation of structural, conformational, and colloidal stability and report a systematic comparison between designed humanized IgG1, IgG2, and IgG4 with identical variable regions. Then, the high information content of SAXS data enables sensitive detection of structural differences between three IgG subclasses at neutral pH and rapid formation of dimers of IgG2 and IgG4 at low pH. We reveal subclass-specific variation in intermolecular repulsion already at low and medium protein concentrations, which explains the observed improved stability of IgG1 with respect to aggregation. We show how excipients dramatically influence such repulsive effects, hence demonstrating the potential application of extensive SAXS screening in antibody selection, eventual engineering, and formulation development.

Site-specific photoconjugation of antibodies using chemically synthesized IgG-binding domains

Site-specific labeling of antibodies can be performed using the immunoglobulin-binding Z domain, derived from staphylococcal protein A (SpA), which has a well-characterized binding site in the Fc region of antibodies. By introducing a photoactivable probe in the Z domain, a covalent bond can be formed between the Z domain and the antibody by irradiation with UV light. The aim of this study was to improve the conjugation yield for labeling of different subclasses of IgG having different sequence composition, using a photoactivated Z domain variant. Four different variants of the Z domain (Z5BPA, Z5BBA, Z32BPA, and Z32BBA) were synthesized to investigate the influence of the position of the photoactivable probe and the presence of a flexible linker between the probe and the protein. For two of the variants, the photoreactive benzophenone group was introduced as part of an amino acid side chain by incorporation of the unnatural amino acid benzoylphenylalanine (BPA) during peptide synthesis. For the other two variants, the photoreactive benzophenone group was attached via a flexible linker by coupling of benzoylbenzoic acid (BBA) to the ε-amino group of a selectively deprotected lysine residue. Photoconjugation experiments using human IgG1, mouse IgG1, and mouse IgG2A demonstrated efficient conjugation for all antibodies. It was shown that differences in linker length had a large impact on the conjugation efficiency for labeling of mouse IgG1, whereas the positioning of the photoactivable probe in the sequence of the protein had a larger effect for mouse IgG2A. Conjugation to human IgG1 was only to a minor extent affected by position or linker length. For each subclass of antibody, the best variant tested using a standard conjugation protocol resulted in conjugation efficiencies of 41-66%, which corresponds to on average approximately one Z domain attached to each antibody. As a combination of the two best performing variants, Z5BBA and Z32BPA, a Z domain variant with two photoactivable probes (Z5BBA32BPA) was also synthesized with the aim of targeting a wider panel of antibody subclasses and species. This new reagent could efficiently couple to all antibody subclasses that were targeted by the single benzophenone-labeled Z domain variants, with conjugation efficiencies of 26-41%.

Antibody Engineering

Advanced molecular biology techniques developed during the past few decades have allowed the industry to exploit and commercialize the natural defense mechanisms that antibodies provide. This review discusses the latest advances in antibody-engineering technologies to enhance clinical efficacy and outcomes. For the constant regions, the choice of the antibody class and isotype has to be made carefully to suit the therapeutic applications. Engineering of the Fc region, either by direct targeted mutagenesis or by modifying the nature of its N -glycan, has played an important role in recent years in increasing half-life or controlling effector functions. The variable regions of the antibody are responsible for binding affinity and exquisite specificity to the target molecule, which together with the Fc determine the drug's efficacy and influence the drug dose required to obtain the desired effectiveness. A key requirement during antibody development is therefore to affinity mature the variable regions when necessary, so that they bind the therapeutic target with sufficiently high affinity to guarantee effective occupancy over prolonged periods. If the antibody was obtained from a non-human source, such as rodents, a humanization process has to be applied to minimize immunogenicity while maintaining the desired binding affinity and selectivity. Finally, we discuss the next next-generation antibodies, such as antibody-drug conjugates, bispecific antibodies, and immunocytokines, which are being developed to meet future challenges.

Antibody-based therapy in colorectal cancer

Treatment in patients with nonresectable and resectable colorectal cancer at the advanced stage is challenging, therefore intensive strategies such as chemotherapy, signaling inhibitors and monoclonal antibodies (mAbs) to control the disease are required. mAbs are particularly promising tools owing to their target specificities and strong antitumor activities through multiple mechanisms, as shown by rituximab in B-cell non-Hodgkin's lymphoma and trastuzumab in breast cancer. Three mAbs (cetuximab, bevacizumab and panitumumab) have been approved for the treatment of colorectal cancer in the USA and many other mAbs are being tested in clinical trials. The potential of antibody therapy is associated with several mechanisms including interference of vital signaling pathways targeted by the antibody and immune cytotoxicity selectively directed against tumor cells by tumor-bound antibody through the Fc portion of the antibody, such as antibody-dependent cellular cytotoxicity and complement-dependent cytotoxicity. Moreover, recent experimental findings have shown that immune complexes formed by therapeutic mAbs with tumor-released antigens could augment the induction of tumor-specific cytotoxic CD8(+) T cells through activation of APCs. In addition, antibodies targeting immune checkpoints on hematopoietic cells have recently opened a new avenue for the treatment of cancer. In this review, we focus on mAb treatment in colorectal cancer and its immunological aspects.

The anti-erbB3 antibody MM-121/SAR256212 in combination with trastuzumab exerts potent antitumor activity against trastuzumab-resistant breast cancer cells

Background

Elevated expression of erbB3 receptor has been reported to induce resistance to therapeutic agents, including trastuzumab in erbB2-overexpressing breast cancer. Our recent studies indicate that erbB3 interacts with both erbB2 and IGF-1 receptor to form a heterotrimeric complex in trastuzumab-resistant breast cancer cells. Herein, we investigate the antitumor activity of MM-121/SAR256212, a fully human anti-erbB3 antibody (Ab), against two erbB2-overexpressing breast cancer cell lines resistant to trastuzumab.

Methods

MTS-based proliferation assays were used to determine cell viability upon treatment of trastuzumab and/or MM-121/SAR256212. Cell cycle progression was examined by flow cytometric analysis. Western blot analyses were performed to determine the expression and activation of proteins. Tumor xenografts were established by inoculation of the trastuzumab-resistant BT474-HR20 cells into nude mice. The tumor-bearing mice were treated with trastuzumab and/or MM-121/SAR256212 via i.p injection to determine the Abs’ antitumor activity. Immunohistochemical analyses were carried out to study the Abs’ inhibitory effects on tumor cell proliferation and induction of apoptosis in vivo.

Results

MM-121 significantly enhanced trastuzumab-induced growth inhibition in two sensitive and two resistant breast cancer cell lines. MM-121 in combination with trastuzumab resulted in a dramatic reduction of phosphorylated erbB3 (P-erbB3) and Akt (P-Akt) in the in vitro studies. MM-121 combined with trastuzumab did not induce apoptosis in the trastuzumab-resistant cell lines under our cell culture condition, rather induced cell cycle G1 arrest mainly associated with the upregulation of p27^kip1. Interestingly, in the tumor xenograft model established from the trastuzumab-resistant cells, MM-121 in combination with trastuzumab as compared to either agent alone dramatically inhibited tumor growth correlated with a significant reduction of Ki67 staining and increase of cleaved caspase-3 in the tumor tissues.

Conclusions

The combination of MM-121 and trastuzumab not only inhibits erbB2-overexpressing breast cancer cell proliferation, but also promotes the otherwise trastuzumab-resistant cells undergoing apoptosis in an in vivo xenografts model. Thus, MM-121 exhibits potent antitumor activity when combined with trastuzumab under the studied conditions. Our data suggest that further studies regarding the suitability of MM-121 for treatment of breast cancer patients whose tumors overexpress erbB2 and become resistant to trastuzumab may be warranted.

Effects of subclass change on the structural stability of chimeric, humanized, and human antibodies under thermal stress

To address how changes in the subclass of antibody molecules affect their thermodynamic stability, we prepared three types of four monoclonal antibody molecules (chimeric, humanized, and human) and analyzed their structural stability under thermal stress by using size-exclusion chromatography, differential scanning calorimetry (DSC), circular dichroism (CD), and differential scanning fluoroscopy (DSF) with SYPRO Orange as a dye probe. All four molecules showed the same trend in change of structural stability; the order of the total amount of aggregates was IgG1 < IgG2 < IgG4. We thus successfully cross-validated the effects of subclass change on the structural stability of antibodies under thermal stress by using four methods. The T(h) values obtained with DSF were well correlated with the onset temperatures obtained with DSC and CD, suggesting that structural perturbation of the CH2 region could be monitored by using DSF. Our results suggested that variable domains dominated changes in structural stability and that the physicochemical properties of the constant regions of IgG were not altered, regardless of the variable regions fused.

Generation and comparative characterization of glycosylated and aglycosylated human IgG1 antibodies

Monoclonal antibodies (mAbs) are the fastest growing class of biopharmaceuticals reflecting their diverse applications in research and the clinic. The correct glycosylation of mAbs is required to elicit effector functions such as complement-dependent and antibody-dependent cell-mediated cytotoxicity, although these may be undesirable for the treatment of certain chronic diseases. To gain insight into the properties of glycan-deficient mAbs, we generated and characterized six different aglycosylated human IgG1 mAbs (carrying the N297A mutation) and compared them to their glycosylated counterparts. We found no differences in solubility or heterogeneity, and all mAbs the remained stable in stress tests at 4 and 37 °C. Surface plasmon resonance spectroscopy showed no differences in binding affinity, and the in vivo terminal serum half-life and plasma clearance were similar in rats. However, differential scanning calorimetry revealed that the aglycosylated mAbs contained a less stable C(H)2 domain and they were also significantly more susceptible to pH-induced aggregation. We conclude that aglycosylated mAbs are functionally equivalent to their glycosylated counterparts and could be particularly suitable for certain therapeutic applications, such as the treatment of chronic diseases.

An anti-TNFR1 scFv-HSA fusion protein as selective antagonist of TNF action

IZI-06.1 is a humanized anti-TNFR1 single-chain fragment variable (scFv) that selectively inhibits binding of tumor necrosis factor (TNF) and lymphotoxin alpha to tumor necrosis factor receptor 1 (TNFR1) but not TNFR2. Recently, IZI-06.1 was converted into a fully human IgG1 antibody (ATROSAB) for the treatment of inflammatory diseases. Here, we compare the bivalent ATROSAB with a monovalent scFv-human serum albumin (HSA) fusion protein lacking any antibody-associated effector functions and possessing approximately only half the molecular mass of an IgG, which should facilitate accumulation in inflamed tissues. Furthermore, the half-life of the scFv should be strongly extended while maintaining monovalent binding, avoiding a possible signal transduction by receptor cross-linking in the absence of TNF. The scFv-HSA fusion protein was produced by stably transfected Chinese hamster ovary cells and purified by affinity chromatography. The fusion protein bound specifically to TNFR1 in enzyme-linked immunosorbent assay and TNFR1-transfected mouse embryonic fibroblasts. Affinity determined by quartz crystal microbalance was reduced compared with ATROSAB, which resulted also in a reduced inhibitory activity. Compared with the scFv fragment, the half-life of the fusion protein was significantly increased, although not reaching the long half-life of ATROSAB. In summary, the scFv-HSA may provide an alternative to the full-length IgG1 with the ability to selectively inhibit TNFR1 and exploiting the pharmacokinetic properties of albumin.

Engineered protease-resistant antibodies with selectable cell-killing functions

Molecularly engineered antibodies with fit-for-purpose properties will differentiate next generation antibody therapeutics from traditional IgG1 scaffolds. One requirement for engineering the most appropriate properties for a particular therapeutic area is an understanding of the intricacies of the target microenvironment in which the antibody is expected to function. Our group and others have demonstrated that proteases secreted by invasive tumors and pathological microorganisms are capable of cleaving human IgG1, the most commonly adopted isotype among monoclonal antibody therapeutics. Specific cleavage in the lower hinge of IgG1 results in a loss of Fc-mediated cell-killing functions without a concomitant loss of antigen binding capability or circulating antibody half-life. Proteolytic cleavage in the hinge region by tumor-associated or microbial proteases is postulated as a means of evading host immune responses, and antibodies engineered with potent cell-killing functions that are also resistant to hinge proteolysis are of interest. Mutation of the lower hinge region of an IgG1 resulted in protease resistance but also resulted in a profound loss of Fc-mediated cell-killing functions. In the present study, we demonstrate that specific mutations of the CH2 domain in conjunction with lower hinge mutations can restore and sometimes enhance cell-killing functions while still retaining protease resistance. By identifying mutations that can restore either complement- or Fcγ receptor-mediated functions on a protease-resistant scaffold, we were able to generate a novel protease-resistant platform with selective cell-killing functionality.

An engineered Fc variant of an IgG eliminates all immune effector functions via structural perturbations

The Fc variant of IgG2, designated as IgG2σ, was engineered with V234A/G237A /P238S/H268A/V309L/A330S/P331S substitutions to eliminate affinity for Fcγ receptors and C1q complement protein and consequently, immune effector functions. IgG2σ was compared to other previously well-characterized Fc 'muted' variants, including aglycosylated IgG1, IgG2m4 (H268Q/V309L/A330S/P331S, changes to IgG4), and IgG4 ProAlaAla (S228P/L234A/L235A) in its capacity to bind FcγRs and activate various immune-stimulatory responses. In contrast to the previously characterized muted Fc variants, which retain selective FcγR binding and effector functions, IgG2σ shows no detectable binding to the Fcγ receptors in affinity and avidity measurements, nor any detectable antibody-dependent cytotoxicity, phagocytosis, complement activity, or Fc-mediated cytokine release. Moreover, IgG2σ shows minimal immunogenic potential by T-cell epitope analysis. The circulating half-life of IgG2σ in monkeys is extended relative to IgG1 and IgG2, in spite of similar in vitro binding to recombinant FcRn. The three-dimensional structure of the Fc, needed for assessing the basis for the absence of effector function, was compared with that of IgG2 revealing a number of conformational differences near the hinge region of the CH2 domain that result from the amino acid substitutions. Modeling reveals that at least one of the key interactions with FcγRs is disrupted by a conformational change that reorients P329 to a position that prevents it from interacting with conserved W90 and W113 residues of the FcγRs. Inspection of the structure also indicated significant changes to the conformations of D270 and P329 in the CH2 domain that could negatively impact C1q binding. Thus, structural perturbations of the Fc provide a rationale for the loss of function. In toto, these properties of IgG2σ suggest that it is a superior alternative to previously described IgG variants of minimal effector function, for future therapeutic applications of non-immunostimulatory mAb and Fc-fusion platforms.

Pharmacokinetics, pharmacodynamics and physiologically-based pharmacokinetic modelling of monoclonal antibodies

Development of monoclonal antibodies (mAbs) and their functional derivatives represents a growing segment of the development pipeline in the pharmaceutical industry. More than 25 mAbs and derivatives have been approved for a variety of therapeutic applications. In addition, around 500 mAbs and derivatives are currently in different stages of development. mAbs are considered to be large molecule therapeutics (in general, they are 2-3 orders of magnitude larger than small chemical molecule therapeutics), but they are not just big chemicals. These compounds demonstrate much more complex pharmacokinetic and pharmacodynamic behaviour than small molecules. Because of their large size and relatively poor membrane permeability and instability in the conditions of the gastrointestinal tract, parenteral administration is the most usual route of administration. The rate and extent of mAb distribution is very slow and depends on extravasation in tissue, distribution within the particular tissue, and degradation. Elimination primarily happens via catabolism to peptides and amino acids. Although not definitive, work has been published to define the human tissues mainly involved in the elimination of mAbs, and it seems that many cells throughout the body are involved. mAbs can be targeted against many soluble or membrane-bound targets, thus these compounds may act by a variety of mechanisms to achieve their pharmacological effect. mAbs targeting soluble antigen generally exhibit linear elimination, whereas those targeting membrane-bound antigen often exhibit non-linear elimination, mainly due to target-mediated drug disposition (TMDD). The high-affinity interaction of mAbs and their derivatives with the pharmacological target can often result in non-linear pharmacokinetics. Because of species differences (particularly due to differences in target affinity and abundance) in the pharmacokinetics and pharmacodynamics of mAbs, pharmacokinetic/pharmacodynamic modelling of mAbs has been used routinely to expedite the development of mAbs and their derivatives and has been utilized to help in the selection of appropriate dose regimens. Although modelling approaches have helped to explain variability in both pharmacokinetic and pharmacodynamic properties of these drugs, there is a clear need for more complex models to improve understanding of pharmacokinetic processes and pharmacodynamic interactions of mAbs with the immune system. There are different approaches applied to physiologically based pharmacokinetic (PBPK) modelling of mAbs and important differences between the models developed. Some key additional features that need to be accounted for in PBPK models of mAbs are neonatal Fc receptor (FcRn; an important salvage mechanism for antibodies) binding, TMDD and lymph flow. Several models have been described incorporating some or all of these features and the use of PBPK models are expected to expand over the next few years.

Different glycosylation pattern of human IgG1 and IgG3 antibodies isolated from transiently as well as permanently transfected cell lines

The effector functions of IgG depend on the presence of carbohydrates attached to asparagine 297 in the Fc-portion. In this report, glycosylation profiles of recombinant wild-type and mutant IgG1 and IgG3 antibodies produced from three cell lines were analysed using LC-ESI-Orbitrap. Clear differences were detected between IgG1 and IgG3 glycoforms, where IgG1 generally contained fucosylated glycoforms, whilst IgG3 mainly were non-fucosylated. When using NS-0 and J558L cells for permanent transfection, IgG1 wt glycoforms differed between the two cell lines, whilst IgG3 wt glycoforms did not. Transiently transfected HEK 293E cells were used to produce IgG1 and IgG3 wt and mutants, affecting complement activation. Cell supernatants were harvested at early and late time points and analysed separately. IgGs harvested late showed simpler and less developed glycosylation structure compared to those harvested early. The IgG harvested early was slightly more effective in complement activation than those harvested late, whilst the antibody-dependent cell-mediated cytotoxicity was unaltered. Generally, the glycosylation pattern of the mutants tested, including a hinge truncate mutant of IgG3, did not differ significantly from the wild-type IgGs. The striking difference in glycosylation pattern of IgG1 compared to IgG3 therefore appears not to be due to the long hinge region of IgG3 (62 amino acids) relative to the IgG1 hinge region (15 amino acids). Furthermore, mutation variants at or near the C1q binding site showed similar glycosylation structure and difference in their complement activation activity observed earlier is thus most likely due to differences in protein structure only.

Three-dimensional structure of the human myeloma IgG2

Human immunoglobulin G, subclass 2 (hIgG2), plays an important role in immunity to bacterial pathogens and in numerous pathological conditions. However, there is a lack of information regarding the three-dimensional (3D) structure of the hIgG2 molecule. We used electron microscopy (EM), differential scanning microcalorimetry (DSC) and fluorescence for structural analysis of the hIgG2. DSC and fluorescence indicated two types of interaction between C_H1 domain of Fab (antigen-binding fragment/subunit) and C_H2 domain of Fc (complement fixation fragment/subunit) simultaneously present in the sample: close interaction, which increases the thermostability of both, C_H1 and C_H2 domains, and weak (or no) interaction, which is typical for most IgGs but not hIgG2. Thermodynamics could not determine if both types of interactions are present within a single molecule. To address this question, EM was used. We employed a single-particle reconstruction and negative staining approach to reveal the three-dimensional structure of the hIgG2. A three-dimensional model of hIgG2 was created at 1.78 nm resolution. The hIgG2 is asymmetrical: one Fab subunit is in close proximity to the upper portion of the Fc subunit (C_H2 domain) and the other Fab is distant from Fc. The plane of Fab subunits is nearly perpendicular to Fc. EM structure of the hIgG2 is in good agreement with thermodynamic data: a Fab distant from Fc should exhibit a lower melting temperature while a Fab interacting with Fc should exhibit a higher melting temperature. Both types of Fab subunits exist within one molecule resembling an A/B hIgG2 isoform introduced earlier on physicochemical level by Dillon et al. (2008). In such an arrangement, the access to the upper portion of Fc subunit is partially blocked by a Fab subunit. That might explain for instance why hIgG2 mildly activates complement and binds poorly to Fc receptors. Understanding of the three-dimensional structure of the hIgG2 should lead to better design of antibody-based therapeutics.

Complementary MS methods assist conformational characterization of antibodies with altered S-S bonding networks

As therapeutic monoclonal antibodies (mAbs) become a major focus in biotechnology and a source of the next-generation drugs, new analytical methods or combination methods are needed for monitoring changes in higher order structure and effects of post-translational modifications. The complexity of these molecules and their vulnerability to structural change provide a serious challenge. We describe here the use of complementary mass spectrometry methods that not only characterize mutant mAbs but also may provide a general framework for characterizing higher order structure of other protein therapeutics and biosimilars. To frame the challenge, we selected members of the IgG2 subclass that have distinct disulfide isomeric structures as a model to evaluate an overall approach that uses ion mobility, top-down MS sequencing, and protein footprinting in the form of fast photochemical oxidation of proteins (FPOP). These three methods are rapid, sensitive, respond to subtle changes in conformation of Cys → Ser mutants of an IgG2, each representing a single disulfide isoform, and may be used in series to probe higher order structure. The outcome suggests that this approach of using various methods in combination can assist the development and quality control of protein therapeutics.

Autoantibodies targeting tumor-associated antigens in metastatic cancer: Sialylated IgGs as candidate anti-inflammatory antibodies

In addition to the well-established effector functions of IgGs, including direct cytotoxicity and antibody-dependent cellular cytotoxicity, some populations of IgGs may exert anti-inflammatory effects. Here, we describe a population of antibodies that form in the natural course of metastatic cancer and contain glycans that terminate with sialic acid. We demonstrate that both the titer of these antibodies and their level of sialylation are relatively stable throughout the progression of metastatic melanoma. The sialylation pattern of these antibodies somehow correlates with their specificity for tumor-associated antigens, as IgGs targeting several antigens associated with infectious agents are relatively poor of sialic acid. We also show that some antibodies targeting the melanoma-associated antigen NY-ESO-1 bind to the human C-type lectin CD209 (DC-SIGN). We propose that these antibodies are candidate anti-inflammatory antibodies. The presence of anti-inflammatory antibodies in cancer patients may explain, at least in part, why tumors persist and spread in the host despite strong tumor-specific humoral responses. The elucidation of the cellular and molecular pathways involved in the induction of anti-inflammatory antibodies specific for tumor-associated antigens and their function may yield important insights into how tumors evade immune detection and progress.

Monovalent IgG4 molecules: immunoglobulin Fc mutations that result in a monomeric structure

Antibodies have become the fastest growing class of biological therapeutics, in part due to their exquisite specificity and ability to modulate protein-protein interactions with a high biological potency. The relatively large size and bivalency of antibodies, however, limits their use as therapeutics in certain circumstances. Antibody fragments, such as single-chain variable fragments and antigen binding-fragments, have emerged as viable alternatives, but without further modifications these monovalent formats have reduced terminal serum half-lives because of their small size and lack of an Fc domain, which is required for FcRn-mediated recycling. Using rational engineering of the IgG4 Fc domain to disrupt key interactions at the CH3-CH3 interface, we identified a number of point mutations that abolish Fc dimerization and created half-antibodies, a novel monovalent antibody format that retains a monomeric Fc domain. Introduction of these mutations into an IgG1 framework also led to the creation of half-antibodies. These half-antibodies were shown to be soluble, thermodynamically stable and monomeric, characteristics that are favorable for use as therapeutic proteins. Despite significantly reduced FcRn binding in vitro, which suggests that avidity gains in a dimeric Fc are critical to optimal FcRn binding, this format demonstrated an increased terminal serum half-life compared with that expected for most alternative antibody fragments.

Impact of immune complex size and glycosylation on IgG binding to human FcγRs

IgG molecules are widely used as therapeutic agents either in the form of intact Abs or as Fc fusion proteins. Although efficient binding of the IgG Fc fragment to cellular FcγRs may be essential to achieve a high cytolytic activity, it may be advantageous for other applications to limit or abolish this interaction. Genetic or biochemical approaches have been used to generate these non-FcγR-binding IgG variants. By using soluble versions of FcγRs and monomeric versions of these altered IgG molecules, it was demonstrated that these IgG variants no longer bind to FcγRs. Importantly, however, these assays do not reflect the physiologic interaction of IgG with low-affinity cellular FcγRs occurring in the form of multimeric immune complexes. In this study, we investigated how the size of an immune complex can affect the interaction of normal and various versions of potentially non-FcγR-binding IgG variants with cellular FcγRs. We show that neither the D265A mutation nor EndoS treatment resulting in IgG molecules with only one N-acetylglucosamine and a fucose residue was fully able to abolish the interaction of all IgG subclasses with cellular FcγRs, suggesting that IgG subclass-specific strategies are essential to fully interfere with human FcγR binding.

Chemical and structural analysis of an antibody folding intermediate trapped during glycan biosynthesis

Human IgG Fc glycosylation modulates immunological effector functions such as antibody-dependent cellular cytotoxicity and phagocytosis. Engineering of Fc glycans therefore enables fine-tuning of the therapeutic properties of monoclonal antibodies. The N-linked glycans of Fc are typically complex-type, forming a network of noncovalent interactions along the protein surface of the Cγ2 domain. Here, we manipulate the mammalian glycan-processing pathway to trap IgG1 Fc at sequential stages of maturation, from oligomannose- to hybrid- to complex-type glycans, and show that the Fc is structurally stabilized following the transition of glycans from their hybrid- to complex-type state. X-ray crystallographic analysis of this hybrid-type intermediate reveals that N-linked glycans undergo conformational changes upon maturation, including a flip within the trimannosyl core. Our crystal structure of this intermediate reveals a molecular basis for antibody biogenesis and provides a template for the structure-guided engineering of the protein-glycan interface of therapeutic antibodies.

Determination of antibody glycosylation by mass spectrometry

Immunoglobulin (Ig) G is formed by two antigen-binding moieties termed Fabs and a conserved Fc -portion, which interacts with components of the immune systems. Within the Fc, N-linked carbohydrates are attached to each conserved asparagine residue at position 297 within the CH2 domain. These oligosaccharide moieties introduce a higher degree of heterogeneity within the molecule, by influencing stability of the antibody and its mediated effector functions, such as antibody-dependent cellular cytotoxicity and complement-dependent cytotoxicity (CDC). The carbohydrate moieties can vary strongly depending on the production host and can be manipulated by different fermentation conditions, thereby influencing the function of the antibody. Therefore it is necessary to carefully monitor changes in the carbohydrate composition during cell line development and production processes. This chapter describes two different mass spectrometry based methods used for analyses of the carbohydrate moieties attached to the Fc-part of human IgG1. In the first approach, the glycans are released from the antibody by endoglycosidase (Peptide N Glycosidase F) digestion and monitored by matrix-assisted laser desorption ionization-time-of-flight mass spectrometry (MS), whereas in the second method the carbohydrate structures, still attached to an enzymatically produced Fc-fragment, are analyzed by electrospray ionization mass spectrometry.

Crosstalk between human IgG isotypes and murine effector cells

Development of human therapeutic Abs has led to reduced immunogenicity and optimal interactions with the human immune system in patients. Humanization had as a consequence that efficacy studies performed in mouse models, which represent a crucial step in preclinical development, are more difficult to interpret because of gaps in our knowledge of the activation of murine effector cells by human IgG (hIgG) remain. We therefore developed full sets of human and mouse isotype variants of human Abs targeting epidermal growth factor receptor and CD20 to explore the crosstalk with mouse FcγRs (mFcγRs) and murine effector cells. Analysis of mFcγR binding demonstrated that hIgG1 and hIgG3 bound to all four mFcγRs, with hIgG3 having the highest affinity. hIgG1 nevertheless was more potent than hIgG3 in inducing Ab-dependent cellular cytotoxicity (ADCC) and Ab-dependent cellular phagocytosis with mouse NK cells, mouse polymorphonuclear leukocytes, and mouse macrophages. hIgG4 bound to all mFcγRs except mFcγRIV and showed comparable interactions with murine effector cells to hIgG3. hIgG4 is thus active in the murine immune system, in contrast with its inert phenotype in the human system. hIgG2 bound to mFcγRIIb and mFcγRIII, and induced potent ADCC with mouse NK cells and mouse polymorphonuclear leukocytes. hIgG2 induced weak ADCC and, remarkably, was unable to induce Ab-dependent cellular phagocytosis with mouse macrophages. Finally, the isotypes were studied in s.c. and i.v. tumor xenograft models, which confirmed hIgG1 to be the most potent human isotype in mouse models. These data enhance our understanding of the crosstalk between hIgGs and murine effector cells, permitting a better interpretation of human Ab efficacy studies in mouse models.

Immunogenicity to biologics: mechanisms, prediction and reduction

Currently, there is a significant rise in the development and clinical use of a unique class of pharmaceuticals termed as Biopharmaceuticals or Biologics, in the management of a range of disease conditions with, remarkable therapeutic benefits. However, there is an equally growing concern regarding development of adverse effects like immunogenicity in the form of anti-drug antibodies (ADA) production and hypersensitivity. Immunogenicity to biologics represents a significant hurdle in the continuing therapy of patients in a number of disease settings. Efforts focussed on the identification of factors that contribute towards the onset of immunogenic response to biologics have led to reductions in the incidence of immunogenicity. An in-depth understanding of the cellular and molecular mechanism underpinning immunogenic responses will likely improve the safety profile of biologics. This review addresses the mechanistic basis of ADA generation to biologics, with emphasis on the role of antigen processing and presentation in this process. The article also addresses the potential contribution of complement system in augmenting or modulating this response. Identifying specific factors that influences processing and presentation of biologic-derived antigens in different genotype and disease background may offer additional options for intervention in the immunogenic process and consequently, the management of immunogenicity to biologics.

Antibody-drug conjugates: using monoclonal antibodies for delivery of cytotoxic payloads to cancer cells

One approach to improving activity of anticancer drugs is to conjugate them to antibodies that recognize tumor-associated, cell-surface antigens. The antibody-drug conjugate concept evolved following major advances, first, in the development of humanized and fully human antibodies; second, in the discoveries of highly cytotoxic compounds ('drugs) linkable to antibodies; and finally, in the optimization of linkers that couple the drug to the antibody and provide sufficient stability of the antibody-drug conjugate in the circulation, optimal activation of the drug in the tumor, and the ability of the activated drug to overcome multidrug resistance. In this article, we will review the considerations for selecting a target antigen, the design of the conjugate, and the pre-clinical and clinical experiences with the current generation of antibody-drug conjugates.

Fc-fusion proteins: new developments and future perspectives

Since the first description in 1989 of CD4-Fc-fusion antagonists that inhibit human immune deficiency virus entry into T cells, Fc-fusion proteins have been intensely investigated for their effectiveness to curb a range of pathologies, with several notable recent successes coming to market. These promising outcomes have stimulated the development of novel approaches to improve their efficacy and safety, while also broadening their clinical remit to other uses such as vaccines and intravenous immunoglobulin therapy. This increased attention has also led to non-clinical applications of Fc-fusions, such as affinity reagents in microarray devices. Here we discuss recent results and more generally applicable strategies to improve Fc-fusion proteins for each application, with particular attention to the newer, less charted areas.

Current and Potential Uses of Immunocytokines as Cancer Immunotherapy

Immunocytokines (ICs) are a class of molecules created by linking tumor-reactive monoclonal antibodies to cytokines that are able to activate immune cells. Tumor selective localization is provided by the ability of the mAb component to bind to molecules found on the tumor cell surface or molecules found selectively in the tumor microenvronment. In this way the cytokine component of the immunocytokine is selectively localized to sites of tumor and can activate immune cells with appropriate receptors for the cytokine. Immunocytokines have been made and tested by us, and others, using a variety of tumor-reactive mAbs linked to distinct cytokines. To date, the majority of clinical progress has been made with ICs that have linked human interleukin-2 (IL2) to a select number of tumor reactive mAbs that had already been in prior clinical testing as non-modified mAbs (Figure 1). Here we briefly review the background for the creation of ICs, summarize current clinical progress, emphasize mechanisms of action for ICs that are distinct from those of their constituent components, and present some directions for future development and testing.

Detection and quantitation of afucosylated N-linked oligosaccharides in recombinant monoclonal antibodies using enzymatic digestion and LC-MS

The presence of N-linked oligosaccharides in the CH2 domain has a significant impact on the structure, stability, and biological functions of recombinant monoclonal antibodies. The impact is also highly dependent on the specific oligosaccharide structures. The absence of core-fucose has been demonstrated to result in increased binding affinity to Fcγ receptors and, thus, enhanced antibody-dependent cellular cytotoxicity (ADCC). Therefore, a method that can specifically determine the level of oligosaccharides without the core-fucose (afucosylation) is highly desired. In the current study, recombinant monoclonal antibodies and tryptic peptides from the antibodies were digested using endoglycosidases F2 and H, which cleaves the glycosidic bond between the two primary GlcNAc residues. As a result, various oligosaccharides of either complex type or high mannose type that are commonly observed for recombinant monoclonal antibodies are converted to either GlcNAc residue only or GlcNAc with the core-fucose. The level of GlcNAc represents the sum of all afucosylated oligosaccharides, whereas the level of GlcNAc with the core-fucose represents the sum of all fucosylated oligosaccharides. LC-MS analysis of the enzymatically digested antibodies after reduction provided a quick estimate of the levels of afucosylation. An accurate determination of the level of afucosylation was obtained by LC-MS analysis of glycopeptides after trypsin digestion.

Production, characterization, and pharmacokinetic properties of antibodies with N-linked mannose-5 glycans

The effector functions of therapeutic antibodies are strongly affected by the specific glycans added to the Fc domain during post-translational processing. Antibodies bearing high levels of N-linked mannose-5 glycan (Man5) have been reported to exhibit enhanced antibody-dependent cell-mediated cytotoxicity (ADCC) compared with antibodies with fucosylated complex or hybrid glycans. To better understand the relationship between antibodies with high levels of Man5 and their biological activity in vivo, we developed an approach to generate substantially homogeneous antibodies bearing the Man5 glycoform. A mannosidase inhibitor, kifunensine, was first incorporated in the cell culture process to generate antibodies with a distribution of high mannose glycoforms. Antibodies were then purified and treated with a mannosidase for trimming to Man5 in vitro. This 2-step approach can consistently generate antibodies with > 99% Man5 glycan. Antibodies bearing varying levels of Man5 were studied to compare ADCC and Fcγ receptor binding, and they showed enhanced ADCC activity and increased binding affinity to the FcγRIIIA. In addition, the clearance rate of antibodies bearing Man8/9 and Man5 glycans was determined in a pharmacokinetics study in mice. When compared with historical data, the antibodies bearing the high mannose glycoform exhibited faster clearance rate compared with antibodies bearing the fucosylated complex glycoform, while the pharmacokinetic properties of antibodies with Man8/9 and Man5 glycoforms appeared similar. In addition, we identified the presence of a mannosidase in mouse serum that converted most Man8/9 to Man6 after 24 h.

Selective deactivation of serum IgG: a general strategy for the enhancement of monoclonal antibody receptor interactions

Serum IgG is a potent inhibitor of monoclonal antibody (mAb) binding to the cell-surface Fcγ receptors (FcγRs), which mediate cytotoxic and phagocytic effector functions. Here, we show that this competition can be eliminated, selectively, by the introduction to serum of (i) an enzyme that displaces Fc from FcγRs and (ii) a modification present in the therapeutic mAb that renders it resistant to that enzyme. Specifically, we show that (i) EndoS (endoglycosidase S) cleaves only complex-type glycans of the type found on IgG but (ii) is inactive against an engineered IgG Fc with oligomannose-type glycans. EndoS thus reduces FcγR binding of serum IgG, but not that of engineered mAb. Introduction of both the engineered mAb and endoglycosidase in serum leads to a dramatic increase in FcγR binding compared to the introduction of mAb in serum alone. Antibody receptor refocusing is a general technique for boosting the effector signal of therapeutic antibodies.

Avidity confers FcγR binding and immune effector function to aglycosylated immunoglobulin G1

Immunoglobulin G (IgG) antibodies are an integral part of the adaptive immune response that provide a direct link between humoral and cellular components of the immune system. Insights into relationships between the structure and function of human IgGs have prompted molecular engineering efforts to enhance or eliminate specific properties, such as Fc-mediated immune effector functions. Human IgGs have an N-glycosylation site at Asn297, located in the second heavy chain constant region (CH2). The composition of the Fc glycan can have substantial impacts on Fc gamma receptor(FcγR) binding. The removal of the glycan through enzymatic deglycosylation or mutagenesis of the N-linked glycosylation site has been reported to "silence" FcγR-binding and effector functions, particularly with assays that measure monomeric binding. However, interactions between IgGs and FcγRs are not limited to monomeric interactions but can be influenced by avidity, which takes into account the sum of multimeric interactions between antigen-engaged IgGs and FcγRs. We show here that under in vitro conditions, which allowed avidity binding, aglycosylated IgGs can bind to one of the FcγRs, FcγRI, and mediate effector functions. These studies highlight how the valency of a molecular interaction (monomeric binding versus avidity binding) can influence antibody/FcγR interactions such that avidity effects can translate very low intrinsic affinities into significant functional outcomes.

Monoclonal antibodies and toxins--a perspective on function and isotype

Antibody therapy remains the only effective treatment for toxin-mediated diseases. The development of hybridoma technology has allowed the isolation of monoclonal antibodies (mAbs) with high specificity and defined properties, and numerous mAbs have been purified and characterized for their protective efficacy against different toxins. This review summarizes the mAb studies for 6 toxins—Shiga toxin, pertussis toxin, anthrax toxin, ricin toxin, botulinum toxin, and Staphylococcal enterotoxin B (SEB)—and analyzes the prevalence of mAb functions and their isotypes. Here we show that most toxin-binding mAbs resulted from immunization are non-protective and that mAbs with potential therapeutic use are preferably characterized. Various common practices and caveats of protection studies are discussed, with the goal of providing insights for the design of future research on antibody-toxin interactions.

Increasing the clinical efficacy of NK and antibody-mediated cancer immunotherapy: potential predictors of successful clinical outcome based on observations in high-risk neuroblastoma

Disease recurrence is frequent in high-risk neuroblastoma (NBL) patients even after multi-modality aggressive treatment [a combination of chemotherapy, surgical resection, local radiation therapy, autologous stem cell transplantation, and cis-retinoic acid (CRA)]. Recent clinical studies have explored the use of monoclonal antibodies (mAbs) that bind to disialoganglioside (GD₂), highly expressed in NBL, as a means to enable immune effector cells to destroy NBL cells via antibody-dependent cell-mediated cytotoxicity (ADCC). Preclinical data indicate that ADCC can be more effective when appropriate effector cells are activated by cytokines. Clinical studies have pursued this by administering anti-GD₂ mAb in combination with ADCC-enhancing cytokines (IL2 and GM-CSF), a regimen that has demonstrated improved cancer-free survival. More recently, early clinical studies have used a fusion protein that consists of the anti-GD₂ mAb directly linked to IL2, and anti-tumor responses were seen in the Phase II setting. Analyses of genes that code for receptors that influence ADCC activity and natural killer (NK) cell function [Fc receptor (FcR), killer immunoglublin-like receptor (KIR), and KIR-ligand (KIR-L)] suggest patients with anti-tumor activity are more likely to have certain genotype profiles. Further analyses will need to be conducted to determine whether these genotypes can be used as predictive markers for favorable therapeutic outcome. In this review, we discuss factors that affect response to mAb-based tumor therapies such as hu14.18-IL2. Many of our observations have been made in the context of NBL; however, we will also include some observations made with mAbs targeting other tumor types that are consistent with results in NBL. Therefore, we hypothesize that the NBL observations discussed here may also be relevant to mAb therapy for other cancers, in which ADCC is known to play a role.

The role of sialic acid as a modulator of the anti-inflammatory activity of IgG

Immunoglobulin G (IgG) molecules can have two completely opposing activities. They can be very potent pro-inflammatory mediators on the one hand, directing the effector functions of the innate immune system towards infected cells, tumor cells or healthy tissues in the case of autoimmune diseases. On the other hand, a mixture of IgG molecules purified from the blood of ten thousands of healthy donors is used as an anti-inflammatory treatment for many autoimmune diseases since several decades. It has become evident only recently that certain residues in the sugar moiety attached to the IgG constant fragment can dramatically alter the pro- and anti-inflammatory activities of IgG. This review will focus on sialic acid residues as a modulator of the anti-inflammatory activity and provide an overview of situations where serum IgG glycosylation and sialylation is altered and which molecular and cellular pathways may be involved in this immunomodulatory pathway.

Ex-vivo clonally expanded B lymphocytes infiltrating colorectal carcinoma are of mature immunophenotype and produce functional IgG

Background

Tumor infiltrating B cells (TiBc) have not yet been investigated in detail. This may at least in part be due to technical difficulties. Here we describe a straightforward and reproducible method to isolate and culture TiBc from primary colorectal carcinomas (CRC).

Methods/Results

TiBc cultures were generated by Epstein-Barr virus (EBV) immortalization. With this method, monoclonal TiBc cultures were obtained for 14/19 CRCs. As assessed by flow cytometry and ELISA, TiBc showed an activated immunophenotype (CD23⁺, CD80⁺) and produced immunoglobulin (Ig; IgG secretion in 55% of the cultures). In functional in vitro analysis, most of the IgGs specifically bound to allogeneic CRC target cells. These data suggest that TiBc are antigen-experienced and thus may exhibit functionality in situ. Additionally, mini-cultures generated from 12 further CRCs revealed TiBc outgrowth exclusively in the presence of EBV.

Conclusion

In summary, this simple method provides a cellular tool and our data set the stage for analysing the bivalent role of TiBc; being antigen-presenting cells on the one hand and tumor-specific antibody producers on the other. Additionally, the generation of long-term TiBc cultures and their monoclonal Ig may serve to identify novel tumor-specific antigens.

Mammalian stable expression of biotherapeutics

Many therapeutically relevant proteins, like IgG antibodies, are highly complex, multimeric glycoproteins that are difficult to express in microbial systems and thus usually produced in mammalian host cells. During the past two decades, stable mammalian expression technologies have made huge progress resulting in highly increased speed of cell line development and yield of manufacturing processes. Here, we give an overview of technologies that are applied at different stages of state-of-the-art cell line development processes for biomanufacturing.

Leveraging SBDD in protein therapeutic development: antibody engineering

Antibodies make up the largest, growing segment of protein therapeutics in the pharmaceutical and biotechnology industries. The development or engineering of therapeutic antibodies is based to a large extent on our knowledge of antibody structure and requires sophisticated methods that continue to evolve. In this chapter, after a review of what is known about the structure and functional properties of antibodies, the current, state-of-the-art antibody engineering methods are described. These methods include antibody humanization, antigen-affinity optimization, Fc engineering for modulated effector function and extended half-life, and engineering for improved stability and biophysical properties. X-ray crystallographic structures of antibody fragments and their complexes can play a critical role in guiding and, in some cases, accelerating these processes. These approaches represent guidelines for developing antibody therapeutics with the desired affinity, effector function, and biophysical properties.

Analysis of glycoforms on the glycosylation site and the glycans in monoclonal antibody biopharmaceuticals

Therapeutic monoclonal antibodies (mAbs), immunoglobulins, have been efficiently used in the treatment of many diseases, such as cancer, inflammatory and cardiovascular diseases, and organ transplantation. mAbs are glycoprotein molecules undergoing posttranslational modifications. Glycosylation is one of the posttranslational modifications. Different glycoforms that are important for maintaining the potency of mAb drugs show various biological activities. Therefore, the profile of the glycans and glycosylation sites should be determined to produce safe, good quality, consistent mAb drugs for human use. For this reason, simple, robust, accurate, and reproducible analytical methods need to be developed. In this article, chromatographic methods for the analysis of the glycoforms on the glycosylation site and the glycans in mAb biopharmaceuticals have been evaluated.

Competition for FcRn-mediated transport gives rise to short half-life of human IgG3 and offers therapeutic potential

Human IgG3 displays the strongest effector functions of all IgG subclasses but has a short half-life for unresolved reasons. Here we show that IgG3 binds to IgG-salvage receptor (FcRn), but that FcRn-mediated transport and rescue of IgG3 is inhibited in the presence of IgG1 due to intracellular competition between IgG1 and IgG3. We reveal that this occurs because of a single amino acid difference at position 435, where IgG3 has an arginine instead of the histidine found in all other IgG subclasses. While the presence of R435 in IgG increases binding to FcRn at neutral pH, it decreases binding at acidic pH, affecting the rescue efficiency-but only in the presence of H435-IgG. Importantly, we show that in humans the half-life of the H435-containing IgG3 allotype is comparable to IgG1. H435-IgG3 also gave enhanced protection against a pneumococcal challenge in mice, demonstrating H435-IgG3 to be a candidate for monoclonal antibody therapies.

Determining the phagocytic activity of clinical antibody samples

Antibody-driven phagocytosis is induced via the engagement of Fc receptors on professional phagocytes, and can contribute to both clearance as well as pathology of disease. While the properties of the variable domains of antibodies have long been considered critical to in vivo function, the ability of antibodies to recruit innate immune cells via their Fc domains has become increasingly appreciated as a major factor in their efficacy, both in the setting of recombinant monoclonal antibody therapy, as well as in the course of natural infection or vaccination(1-3). Importantly, despite its nomenclature as a constant domain, the antibody Fc domain does not have constant function, and is strongly modulated by IgG subclass (IgG1-4) and glycosylation at Asparagine 297(4-6). Thus, this method to study functional differences of antigen-specific antibodies in clinical samples will facilitate correlation of the phagocytic potential of antibodies to disease state, susceptibility to infection, progression, or clinical outcome. Furthermore, this effector function is particularly important in light of the documented ability of antibodies to enhance infection by providing pathogens access into host cells via Fc receptor-driven phagocytosis(7). Additionally, there is some evidence that phagocytic uptake of immune complexes can impact the Th1/Th2 polarization of the immune response(8). Here, we describe an assay designed to detect differences in antibody-induced phagocytosis, which may be caused by differential IgG subclass, glycan structure at Asn297, as well as the ability to form immune complexes of antigen-specific antibodies in a high-throughput fashion. To this end, 1 μm fluorescent beads are coated with antigen, then incubated with clinical antibody samples, generating fluorescent antigen specific immune complexes. These antibody-opsonized beads are then incubated with a monocytic cell line expressing multiple FcγRs, including both inhibitory and activating. Assay output can include phagocytic activity, cytokine secretion, and patterns of FcγRs usage, and are determined in a standardized manner, making this a highly useful system for parsing differences in this antibody-dependent effector function in both infection and vaccine-mediated protection(9).

The in vitro resistance of IgG2 to proteolytic attack concurs with a comparative paucity of autoantibodies against peptide analogs of the IgG2 hinge

The mammalian antibody repertoire comprises immunoglobulin (Ig) molecules of multiple isotypes and subclasses with varying functional properties. Among the four subclasses of the human IgG isotype, we found that IgG2 exhibits a particular resistance to human and bacterial proteases that readily cleave the IgG1 hinge region in vitro. Autoantibodies (IgGs) that recognize points of proteolytic cleavage in the IgG1 hinge are widespread in the healthy human population, suggesting that IgG1 fragmentation and the generation of cryptic antigens for host immune surveillance commonly occur in vivo. We previously reported that autoantibodies to cleaved IgG1s can restore Fc-mediated effector functions that are lost following proteolytic cleavage of the hinge. In contrast, it was not possible to demonstrate an analogous cohort of autoantibodies to IgG2 hinge epitope analogs, and there appeared to be no functional component in human serum with the ability to reconstitute Fc effector functions to a cell-bound IgG2 fragment. Thus, the results indicate that among the IgG subclasses, human IgG2 is uniquely resistant to a number of known pathological proteases and that autoimmune recognition to potential cleavage points in the IgG2 hinge appears to be absent in human circulation.

Rates and impact of human antibody glycation in vivo

Glycation of immunoglobulin G (IgG) can result from incubation with a reducing sugar in vitro or during circulation in vivo. Upon injection of a recombinantly produced human therapeutic IgG into humans, changes in the glycation levels could be observed as a function of circulation time. Mass changes on the individual IgG polypeptide chains as the results of glycation were determined using reversed-phase liquid chromatography/mass spectrometry. Changes to the light and heavy chains were low but easily detectable at 0.00092 and 0.0021 glucose (Glc) additions per chain per day, respectively. Levels of glycation found on the Fc portion of IgG isolated from healthy subjects, using a similar analytical approach, were on average 0.045 Glc molecules per fragment. In vivo glycation rates could be approximated in vitro by modeling the physiological glycation reaction with a simplified incubation containing physiological Glc concentrations, pH and temperature but with a high concentration of a single purified IgG. To test the impact of glycation on IgG function, highly glycated IgG1 and IgG2 were prepared containing on average 42-49 Glc molecules per IgG. Binding to FcγIIIa receptors, neonatal Fc receptor or protein A was similar or identical to the non-glycated IgG controls. Although the modifications were well distributed throughout the protein sequence, and at high enough levels to affect the elution position by size-exclusion chromatography, no changes in the tested Fc functions were observed.

Antibodies in infectious diseases: polyclonals, monoclonals and niche biotechnology

Antibody preparations have a long history of providing protection from infectious diseases. Although antibodies remain the only natural host-derived defense mechanism capable of completely preventing infection, as products, they compete against inexpensive therapeutics such as antibiotics, small molecule inhibitors and active vaccines. The continued discovery in the monoclonal antibody (mAb) field of leads with broadened cross neutralization of viruses and demonstrable synergy of antibody with antibiotics for bacterial diseases, clearly show that innovation remains. The commercial success of mAbs in chronic disease has not been paralleled in infectious diseases for several reasons. Infectious disease immunotherapeutics are limited in scope as endemic diseases necessitate active vaccine development. Also, the complexity of these small markets draws the interest of niche companies rather than big pharmaceutical corporations. Lastly, the cost of goods for mAb therapeutics is inherently high for infectious agents due to the need for antibody cocktails, which better mimic polyclonal immunoglobulin preparations and prevent antigenic escape. In cases where vaccine or convalescent populations are available, current polyclonal hyperimmune immunoglobulin preparations (pIgG), with modern and highly efficient purification technology and standardized assays for potency, can make economic sense. Recent innovations to broaden the potency of mAb therapies, while reducing cost of production, are discussed herein. On the basis of centuries of effective use of Ab treatments, and with growing immunocompromised populations, the question is not whether antibodies have a bright future for infectious agents, but rather what formats are cost effective and generate safe and efficacious treatments to satisfy regulatory approval.

Clinical relevance and IgG subclass determination of non-HLA antibodies identified using endothelial cell precursors isolated from donor blood

BACKGROUND

ABO and human leukocyte antigen (HLA) alloantibodies provide major immunologic barriers to successful transplantation; however, there is increasing recognition for the role of anti-endothelial cell antibodies (AECAs) in allograft rejection. We investigated the relationship between AECAs identified using donor-derived endothelial cell precursors (ECPs) and kidney allograft rejection and function.

METHODS

Sixty live donor kidney recipients were tested pretransplant for AECAs and HLA-antibodies using flow cytometric crossmatch tests and solid-phase bead immunoassays. Renal allograft function was assessed by serum creatinine (SCr) values collected at early (mean, 50 days) and late (mean, 815 days) time points posttransplant and by incidence and type of rejection. Immunoglobulin G (IgG) subtype determination of both AECAs and HLA antibodies bound to ECPs was performed using flow cytometry.

RESULTS

Fourteen patients (23%) tested positive for donor-reactive IgG AECAs and had statistically higher SCr values and incidences of cellular rejection early posttransplant compared with 46 patients who tested negative (P=0.014 and P<0.05). SCr values were not statistically different late posttransplant. IgG subclass determination showed AECAs to be enriched for IgG2 and IgG4, subclasses that do not activate complement effectively. Detection of donor-reactive immunoglobulin M (IgM) AECAs did not correlate with increased SCr or incidence of rejection.

CONCLUSION

Crossmatch tests performed using donor-derived ECPs allow for the identification of alloantibodies that are associated with cellular rejection and are distinct from alloantibodies detected using lymphocytes.

A variant human IgG1-Fc mediates improved ADCC

Ribosome display was applied to the Fc region of human immunoglobulin G (IgG1) to select for improved binding to human FcγRIIIa, the receptor expressed on human natural killer cells that mediates antibody-dependent cellular cytotoxicity (ADCC). A library of human Fcγ1 variants was generated using error-prone polymerase chain reaction, and subjected to multiple rounds of ribosome display selection against progressively decreasing concentrations of soluble human FcγRIIIa, to enrich for improved binders. Radioimmunoassay and alphascreen analyses of the aglycosylated IgG-Fc output revealed variants with improved binding to FcγRIIIa relative to wild-type IgG-Fc. Subsequent expression in human (HEK-EBNA) cells generated glycosylated IgGs with modified activity in ADCC assays. One particular variant, 125_B01 triggered enhanced ADCC (EC(50) up to four-fold reduced with increased maximal lysis) relative to wild-type antibody, having more equal levels of ADCC for each allotype (V158/F158) of FcγRIIIa. Deconvolution of individual replacements within the variant showed that improved function arose from the Phe243Leu replacement within the CH2 domain, rather than the CH3 domain replacements Thr393Ala or His433Pro. Surprisingly, the oligosaccharide profiles of 125_B01 indicated more oligosaccharide chains lacking fucose, or with bisecting N-acetylglucosamine relative to wild-type IgG1, which correlates with improved function and the replacement Phe243Leu that is a carbohydrate contact residue within the C(H)2 domain.

Cell lines expressing mutant FX proteins to generate proteins with reduced rate of fucosylation: WO2010/141478

BACKGROUND

The application (WO 2010/141478) is in the field of glycobiology and deals with the synthesis of recombinant proteins with a reduced rate of fucosylation.

OBJECTIVE

It aims at generating mammalian cell lines that express mutant forms of GDP-4-keto-deoxy-mannose-3,5,-epimerase-4-reductase (FX) and cells that conditionally fucosylate proteins.

METHODS

Mutant forms of FX were synthesized, and mammalian cell lines genetically engineered to express mutant FX proteins and the protein of interest. Cell lines that conditionally fucosylate proteins were generated from a mutant FX form that has reduced ability to fucosylate glycoproteins at 37°C and not at 34°C.

RESULTS

Cells genetically engineered to express mutant forms of FX protein show reduced ability to fucosylate proteins, particularly antibodies, with rates as low as 5 - 0.5% fucosylation, compared to cells expressing wild-type FX.

CONCLUSION

Cells genetically engineered to express the mutant forms of FX protein provide a means to synthesize and express proteins with a reduced rate of fucosylation. The paradigm may be used to synthesize antibodies that mediate antibody-dependent cell-mediated cytotoxicity more efficiently. The application uses mammalian cell lines, genetically engineered to express mutant FX proteins, to synthesize and produce proteins with a reduced rate of fucosylation. The application claims the conditional control of protein fucosylation by FX mutant proteins.