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

Production technologies for monoclonal antibodies and their fragments

In recent years, monoclonal antibodies have emerged as an increasingly important class of human therapeutics. A variety of forms of antibodies, including fragments such as Fabs, Fab'2s and single-chain Fvs, are also being evaluated for a range of different purposes. A variety of expression systems and improvements within these systems have been developed to address these growing and diverse needs.

A glycoprotein from Spirometra erinaceieuropaei plerocercoids suppresses osteoclastogenesis and proinflammatory cytokine gene expression

Various parasites modify the immune-reactions of the host. We have previously shown that crude excretory/secretory (ES) products from plerocercoids of Spirometra erinaceieuropaei, the plerocercoids of which cause sparganosis in humans, suppress the expression of tumor necrosis factor (TNF)-alpha and IL-1beta in lipopolysaccharide (LPS)-stimulated macrophages. As osteoclasts are cells of the monocyte/macrophage lineage, we hypothesised that ES products might suppress receptor activator of nuclear factor kappaB ligand-induced osteoclastogenesis. Crude ES products from plerocercoids suppressed osteoclastogenesis, judged by tartrate-resistant acid phosphatase (TRAP)-positive multinuclear cell counting, and the mature osteoclast-specific gene expression (calcitonin receptor and TRAP). Second, we purified the inhibitory factor for osteoclastogenesis from the crude ES products. The factor was a trypsin-sensitive glycoprotein and had a relative molecular mass of 90 kDa. The glycoprotein, plerocercoid-immunosuppressive factor, from crude ES products could suppress the gene expression of TNF-alpha, IL-1beta and NO synthesis in LPS-stimulated RAW264.7 macrophages.

Dysregulation of TGF-beta1 receptor activation leads to abnormal lung development and emphysema-like phenotype in core fucose-deficient mice

The core fucosylation (alpha1,6-fucosylation) of glycoproteins is widely distributed in mammalian tissues, and is altered under pathological conditions. To investigate physiological functions of the core fucose, we generated alpha1,6-fucosyltransferase (Fut8)-null mice and found that disruption of Fut8 induces severe growth retardation and death during postnatal development. Histopathological analysis revealed that Fut8(-/-) mice showed emphysema-like changes in the lung, verified by a physiological compliance analysis. Biochemical studies indicated that lungs from Fut8(-/-) mice exhibit a marked overexpression of matrix metalloproteinases (MMPs), such as MMP-12 and MMP-13, highly associated with lung-destructive phenotypes, and a down-regulation of extracellular matrix (ECM) proteins such as elastin, as well as retarded alveolar epithelia cell differentiation. These changes should be consistent with a deficiency in TGF-beta1 signaling, a pleiotropic factor that controls ECM homeostasis by down-regulating MMP expression and inducing ECM protein components. In fact, Fut8(-/-) mice have a marked dysregulation of TGF-beta1 receptor activation and signaling, as assessed by TGF-beta1 binding assays and Smad2 phosphorylation analysis. We also show that these TGF-beta1 receptor defects found in Fut8(-/-) cells can be rescued by reintroducing Fut8 into Fut8(-/-) cells. Furthermore, exogenous TGF-beta1 potentially rescued emphysema-like phenotype and concomitantly reduced MMP expression in Fut8(-/-) lung. We propose that the lack of core fucosylation of TGF-beta1 receptors is crucial for a developmental and progressive/destructive emphysema, suggesting that perturbation of this function could underlie certain cases of human emphysema.

Fucose removal from complex-type oligosaccharide enhances the antibody-dependent cellular cytotoxicity of single-gene-encoded antibody comprising a single-chain antibody linked the antibody constant region

Fucose removal from complex-type oligosaccharide of human IgG1-type antibody results in a great enhancement of antibody-dependent cellular cytotoxicity (ADCC). The aim of this study was to clarify the effect of fucose removal on effector functions of a single-gene-encoded antibody with an scFv used as the binding domain. We generated both a fucose-negative anti-tumor associated glycoprotein (TAG)-72 scFv-Fc using alpha-1,6-fucosyltransferase knock-out CHO cells and a highly fucosylated scFv-Fc from parental CHO cells. Expression, assembly and antigen binding activity of the scFv-Fcs were not influenced by fucose removal. The scFv-Fc lacking fucose exhibited significantly more potent FcgammaRIIIa binding and ADCC compared to highly fucosylated scFv-Fc. These results prove that ADCC enhancement by fucose-removal is effective in not only whole IgG1, but also scFv-Fc, and thus increases the potential of Fc-fusion proteins as therapeutic candidates.

Selection, design, and engineering of therapeutic antibodies

mAbs account for an increasing portion of marketed human biological therapeutics. As a consequence, the importance of optimal selection, design, and engineering of these not only has expanded in the past 2 decades but also is now coming into play as a competitive factor. This review delineates the 4 basic areas for optimal therapeutic antibody selection and provides examples of the increasing number of considerations necessary for, and options available for, antibody design. Though some of the advances in antibody technology (eg, antibodies derived from phage-display libraries) have already made it to market, other more recent advances, such as engineering antibodies for enhanced effector functions, may not be far behind, especially given the increasing competition for therapeutic antibodies to the same target (eg, anti-CD20 and anti-TNF-alpha).

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

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

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

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

Characterization by liquid chromatography combined with mass spectrometry of monoclonal anti-IGF-1 receptor antibodies produced in CHO and NS0 cells

7H2HM is a new humanized recombinant monoclonal antibody (MAb) directed against insulin-like growth factor-1 receptor and produced in CHO cells. Homogeneity of intact antibody, reduced light and heavy chains, Fab and Fc fragments were investigated by analytical methods based on mass (SDS-PAGE, SEC), charge (IEF, C-IEX) and hydrophobicity differences (RP-HPLC, HIC) and compared side-by-side with A2CHM, produced in NS0 cells. Primary structures and disulfide bridge pairing were analyzed by microsequencing (Edman degradation), mass spectrometry (MALDI-TOF, ES-TOF) and peptide mapping after enzymatic digestion (Trypsin, endoprotease Lys-C, papain). The light chains demonstrated the expected sequences. The heavy chains yielded post-translational modifications previously reported for other recombinant humanized or human IgG1 such as N-terminal pyroglutamic acid, C-terminal lysine clipping and N-glycosylation for asparagine 297. More surprisingly, two-thirds of the 7H2HM heavy chains were shown to contain an additional 24-amino-acid sequence, corresponding to the translation of an intron located between the variable and the constant domains. Taken together these data suggest that 7H2HM is a mixture of three families of antibodies corresponding (i) to the expected structure (17%; 14,9297 Da; 1330 amino acids), (ii) a variant with a translated intron in one heavy chains (33%; 15,2878 Da; 1354 amino acids) and (iii) a variant with translated introns in two heavy chains (50%; 15,4459 Da; 1378 amino acids), respectively. RP-HPLC is not a commonly used chromatographic method to assess purity of monoclonal antibodies but unlike to SEC and SDS-PAGE, was able to show and to quantify the family of structures present in 7H2HM, which were also identified by peptide mapping, mass spectrometry and microsequencing.

Flow cytometric assay for determination of FcgammaRIIIA-158 V/F polymorphism

A single nucleotide polymorphism (SNP) of the FCGR3A gene results in two allotypes of Fcgamma receptor IIIA (FcgammaRIIIA) with valine (V) or phenylalanine (F) at amino acid 158. Since the FcgammaRIIIA-158 V/F polymorphism is associated with the efficacy of monoclonal antibody (mAb) treatment and a risk factor for autoimmune disease, widely applicable methods to assess the SNP are needed. We developed a novel flow cytometric test for this polymorphism using a mAb that recognized only the FcgammaRIIIA-158 V allele (MEM-154) together with a mAb that detected both FcgammaRIIIA-158 alleles (3G8). The expression of both FcgammaRIIIA epitopes on natural killer (NK) cells from 37 healthy donors were measured and compared to the FCGR3A genotype determined by a 5' nuclease assay. FcgammaRIIIA expression levels in individuals with identical FCGR3A genotypes varied considerably, resulting in overlapping immunofluorescences by both 3G8 and MEM-154 between FcgammaRIIIA-158 V/F allotypes. However, the ratio between fluorescences measured using those mAbs in a single individual predicted the FCGR3A genotype with 100% sensitivity and specificity. The novel flow cytometric assay for the FcgammaRIIIA-158 V/F polymorphism that is based on the MEM-154/3G8 fluorescence ratio requires commercially available reagents and a three-color flow cytometer only.

Production of human monoclonal antibody in eggs of chimeric chickens

The tubular gland of the chicken oviduct is an attractive system for protein expression as large quantities of proteins are deposited in the egg, the production of eggs is easily scalable and good manufacturing practices for therapeutics from eggs have been established. Here we examined the ability of upstream and downstream DNA sequences of ovalbumin, a protein produced exclusively in very high quantities in chicken egg white, to drive tissue-specific expression of human mAb in chicken eggs. To accommodate these large regulatory regions, we established and transfected lines of chicken embryonic stem (cES) cells and formed chimeras that express mAb from cES cell-derived tubular gland cells. Eggs from high-grade chimeras contained up to 3 mg of mAb that possesses enhanced antibody-dependent cellular cytotoxicity (ADCC), nonantigenic glycosylation, acceptable half-life, excellent antigen recognition and good rates of internalization.

Design of humanized antibodies: from anti-Tac to Zenapax

Since the introduction of hybridoma technology, monoclonal antibodies have become one of the most important tools in the biosciences, finding diverse applications including their use in the therapy of human disease. Initial attempts to use monoclonal antibodies as therapeutics were hampered, however, by the potent immunogenicity of mouse (and other rodent) antibodies in humans. Humanization technology has made it possible to remove the immunogenicity associated with the use of rodent antibodies, or at least to reduce it to an acceptable level for clinical use in humans, thus facilitating the application of monoclonal antibodies to the treatment of human disease. To date, nine humanized monoclonal antibodies have been approved for use as human therapeutics in the United States. In this paper, we describe procedures for antibody humanization with an emphasis on strategies for designing humanized antibodies with the aid of computer-guided modeling of antibody variable domains, using as an example the humanized anti-CD25 monoclonal antibody, Zenapax.

Engineered vascular-targeting antibody-interferon-gamma fusion protein for cancer therapy

A number of cytokines are either approved drugs or are in advanced clinical trials, yet these biopharmaceuticals do not typically localize efficiently in solid tumors and manifest their therapeutic potential at the expense of severe side effects. The targeted delivery of cytokines to solid tumors is a promising avenue for increasing the therapeutic index of these biopharmaceuticals. We engineered a fusion protein between scFv(L19), a human antibody fragment specific to the EDB domain of fibronectin, and a cysteine-free mutant of murine interferon-gamma. The resulting fusion protein was capable of targeting new blood vessels in solid tumors, and the targeting efficiency was strikingly increased in tumor-bearing knockout mice lacking the interferon-gamma receptor. ScFv(L19)-interferon-gamma displayed a strong antitumor effect in both subcutaneous and metastatic murine F9 teratocarcinomas, but was not efficacious as single agent when used to treat C51 and CT26 tumors. The potency of this fusion protein could be substantially enhanced by combination with doxorubicin and other immunocytokines. These findings are of clinical relevance, as the EDB domain is a marker of angiogenesis, with identical sequence in mouse and man, which is abundantly expressed in a variety of aggressive solid tumors but is undetectable in most normal tissues.

Effective lysis of lymphoma cells with a stabilised bispecific single-chain Fv antibody against CD19 and FcgammaRIII (CD16)

A recombinant bispecific single-chain fragment variable antibody (bsscFv), directed against the B-cell antigen CD19 and the low affinity Fc-receptor FcgammaRIII (CD16), was designed for use in the treatment of patients with leukaemias and lymphomas. The Fc-portions of whole antibodies were deliberately eliminated in this construct to avoid undesired effector functions. A stabilised bsscFv, ds[CD19 x CD16], was generated, in which disulphide bonds bridging the respective variable light (VL) and variable heavy (VH) chains were introduced into both component single-chain (sc)Fvs. After production in 293T cells and chromatographic purification, ds[CD19 x CD16] specifically and simultaneously bound both antigens. The serum stability of ds[CD19 x CD16] was increased more than threefold when compared with the unstabilised counterpart, while other biological properties were not affected by these mutations. In antibody-dependent cellular cytotoxicity experiments, ds[CD19 x CD16] mediated specific lysis of both CD19-positive malignant human B-lymphoid cell lines and primary tumour cells from patients with B-cell chronic lymphocytic leukaemia or B-cell acute lymphoblastic leukaemia. Natural killer cells, mononuclear cells (MNCs) from healthy donors and, in some instances, MNCs isolated from patients after allogeneic stem cell transplantation, were used as effectors. Thus, ds[CD19 x CD16] holds promise for the treatment of CD19(+) B-lineage malignancies.

Repeated immunization induces the increase in fucose content on antigen-specific IgG N-linked oligosaccharides

OBJECTIVE

In order to investigate whether repeated immunization induces changes in IgG glycosylation, we analyzed the composition of oligosaccharides on antigen-specific IgGs obtained from mice that received different amounts of immunization boosts.

METHODS

Three groups of mice were immunized with ovalbumin (OVA) and boosted once, twice, or three times, respectively, with an interval of 1 week. The patterns of oligosaccharides present in anti-OVA specific IgGs were analyzed using lectin-enzyme-linked immunosorbent assay (ELISA) and lectin-blot.

RESULTS

The repeated injection of OVA induced both the production of specific IgGs and an increase of fucose content in N-linked oligosaccharides of the IgGs. The lowest IgG fucosylation was observed in mice boosted once, whereas the highest fucosylation rate was observed in mice boosted three times. ELISA assay demonstrated that there was a positive relationship between the fucose content and amount of immunization boosts.

CONCLUSIONS

IgG fucosylation increases during repeated immunization with ovalbumin. The alteration of IgG fucosylation may have important biological significance.

Core fucosylation of N-linked glycans in leukocyte adhesion deficiency/congenital disorder of glycosylation IIc fibroblasts

Leukocyte adhesion deficiency/congenital disorder of glycosylation IIc (LAD II/CDG IIc) is a genetic disease characterized by a decreased expression of fucose in glycoconjugates, resulting in leukocyte adhesion deficiency and severe morphological and neurological abnormalities. The biochemical defect is a reduced transport of guanosine diphosphate-L-fucose (GDP-L-fucose) from cytosol into the Golgi compartment, which reduces its availability as substrate for fucosyltransferases. The aim of this study was to determine the effects of a limited supply of GDP-L-fucose inside the Golgi on core fucosylation (alpha1,6-fucose linked to core N-acetylglucosamine [GlcNAc]) of N-linked glycans in LAD II fibroblasts. The results showed that, although [3H]fucose incorporation was generally reduced in LAD II cells, core fucosylation was affected to a greater extent compared with other types of fucosylation of N-linked oligosaccharides. In particular, core fucosylation was found to be nearly absent in biantennary negatively charged oligosaccharides, whereas other types of structures, in particular triantennary neutral species, were less affected by the reduction. Expression and activity of alpha1,6-fucosyltransferase (FUT8) in control and LAD II fibroblasts were comparable, thus excluding the possibility of a decreased activity of the transferase. The data obtained confirm that the concentration of GDP-L-fucose inside the Golgi can differentially affect the various types of fucosylation in vivo and also indicate that core fucosylation is not dependent only on the availability of GDP-L-fucose, but it is significantly influenced by the type of oligosaccharide structure. The relevant reduction in core fucosylation observed in some species of oligosaccharides could also provide clues for the identification of glycans involved in the severe developmental abnormalities observed in LAD II.

Engineering Chinese hamster ovary cells to maximize effector function of produced antibodies using FUT8 siRNA

We explored the possibility of converting established antibody-producing cells to cells producing high antibody-dependent cellular cytotoxicity (ADCC) antibodies. The conversion was made by constitutive expression of small interfering RNA (siRNA) against alpha1,6 fucosyltransferase (FUT8). We found two effective siRNAs, which reduce FUT8 mRNA expression to 20% when introduced into Chinese hamster ovary (CHO)/DG44 cells. Selection for Lens culinaris agglutinin (LCA)-resistant clones after introduction of the FUT8 siRNA expression plasmids yields clones producing highly defucosylated (approximately 60%) antibody with over 100-fold higher ADCC compared to antibody produced by the parental cells (approximately 10% defucosylated). Moreover, the selected clones remain stable, producing defucosylated antibody even in serum-free fed-batch culture. Our results demonstrate that constitutive FUT8 siRNA expression can control the oligosaccharide structure of recombinant antibody produced by CHO cells to yield antibodies with dramatically enhanced ADCC.

Inhibition of tumor growth by plant-derived mAb

The tumor-associated antigen EpCAM (GA733-2) is a highly expressed target on adenocarcinoma cells, as defined by murine mAb CO17-1A. We recently developed a transgenic plant system for the safe and inexpensive production of large quantities of mAb CO17-1A as a future source of clinical-grade protein. Although the glycosylation pattern of plant-derived mAb (mAb(P)) CO17-1A differs considerably from that of the mammalian-derived mAb (mAb(M)), we show here that the biological activity of both mAbs is quite similar. mAb(P) heavy and light chains assembled to bind the recombinant antigen GA733-2E and specifically bound to human SW948 colorectal carcinoma cells expressing the antigen GA733-2 to the same extent as mAb(M). mAb(P) was as effective as mAb(M) CO17-1A in inhibiting tumor growth of xenotransplanted SW948 cells in nude mice. These results suggest the promise of transgenic plants as a useful alternative way to produce full-size mAb for cancer immunotherapy.

Tailor-made antibody therapeutics

Therapeutic antibodies represent one of the fastest growing areas of the pharmaceutical industry. There are currently 18 monoclonal antibodies in the market that have been approved by the FDA and over 150 in clinical developments. Driven by innovation and technological developments, scientists have gone beyond the traditional antibody molecules. Antibodies have been engineered in a variety of ways to meet the challenges posed by different biological settings. Described in this review is an abridged account of the different ways antibodies have been tailored to make them efficient drug molecules.

Glyco-engineering of moss lacking plant-specific sugar residues

The commercial production of complex pharmaceutical proteins from human origin in plants is currently limited through differences in protein N-glycosylation pattern between plants and humans. On the one hand, plant-specific alpha(1,3)-fucose and beta(1,2)-xylose residues were shown to bear strong immunogenic potential. On the other hand, terminal beta(1,4)-galactose, a sugar common on N-glycans of pharmaceutically relevant proteins, e.g., antibodies, is missing in plant N-glycan structures. For safe and flexible production of pharmaceutical proteins, the humanisation of plant protein N-glycosylation is essential. Here, we present an approach that combines avoidance of plant-specific and introduction of human glycan structures. Transgenic strains of the moss Physcomitrella patens were created in which the alpha(1,3)-fucosyltransferase and beta(1,2)-xylosyltransferase genes were knocked out by targeted insertion of the human beta(1,4)-galactosyltransferase coding sequence in both of the plant genes (knockin). The transgenics lacked alpha(1,3)-fucose and beta(1,2)-xylose residues, whereas beta(1,4)-galactose residues appeared on protein N-glycans. Despite these significant biochemical changes, the plants did not differ from wild type with regard to overall morphology under standard cultivation conditions. Furthermore, the glyco-engineered plants secreted a transiently expressed recombinant human protein, the vascular endothelial growth factor, in the same concentration as unmodified moss, indicating that the performed changes in glycosylation did not impair the secretory pathway of the moss. The combined knockout/knockin approach presented here, leads to a new generation of engineered moss and towards the safe and flexible production of correctly processed pharmaceutical proteins with humanised N-glycosylation profiles.

Animal cell cultures: recent achievements and perspectives in the production of biopharmaceuticals

There has been a rapid increase in the number and demand for approved biopharmaceuticals produced from animal cell culture processes over the last few years. In part, this has been due to the efficacy of several humanized monoclonal antibodies that are required at large doses for therapeutic use. There have also been several identifiable advances in animal cell technology that has enabled efficient biomanufacture of these products. Gene vector systems allow high specific protein expression and some minimize the undesirable process of gene silencing that may occur in prolonged culture. Characterization of cellular metabolism and physiology has enabled the design of fed-batch and perfusion bioreactor processes that has allowed a significant improvement in product yield, some of which are now approaching 5 g/L. Many of these processes are now being designed in serum-free and animal-component-free media to ensure that products are not contaminated with the adventitious agents found in bovine serum. There are several areas that can be identified that could lead to further improvement in cell culture systems. This includes the down-regulation of apoptosis to enable prolonged cell survival under potentially adverse conditions. The characterization of the critical parameters of glycosylation should enable process control to reduce the heterogeneity of glycoforms so that production processes are consistent. Further improvement may also be made by the identification of glycoforms with enhanced biological activity to enhance clinical efficacy. The ability to produce the ever-increasing number of biopharmaceuticals by animal cell culture is dependent on sufficient bioreactor capacity in the industry. A recent shortfall in available worldwide culture capacity has encouraged commercial activity in contract manufacturing operations. However, some analysts indicate that this still may not be enough and that future manufacturing demand may exceed production capacity as the number of approved biotherapeutics increases.

Enhanced Natural Killer Cell Binding and Activation by Low-Fucose IgG1 Antibody Results in Potent Antibody-Dependent Cellular Cytotoxicity Induction at Lower Antigen Density

PURPOSE

Recent studies have revealed that fucose removal from the oligosaccharides of human IgG1 antibodies results in a significant enhancement of antibody-dependent cellular cytotoxicity (ADCC) via improved IgG1 binding to FcgammaRIIIa. In this report, we investigated the relationship between enhanced ADCC and antigen density on target cells using IgG1 antibodies with reduced fucose.

EXPERIMENTAL DESIGN

Using EL4 cell-derived transfectants with differential expression levels of exogenous human CC chemokine receptor 4 or human CD20 as target cells, ADCC of fucose variants of chimeric IgG1 antibodies specific for these antigens were measured. We further investigated IgG1 binding to natural killer (NK) cells and NK cell activation during ADCC induction to elucidate the mechanism by which low-fucose IgG1 induces ADCC upon target cells with low antigen expression.

RESULTS

Low-fucose IgG1s showed potent ADCC at low antigen densities at which their corresponding high-fucose counterparts could not induce measurable ADCC. The quantitative analysis revealed that fucose depletion could reduce the antigen amount on target cells required for constant degrees of ADCC induction by 10-fold for CC chemokine receptor 4 and 3-fold for CD20. IgG1 binding to NK cells was increased by ligating IgG1 with clustered antigen, especially for low-fucose IgG1. Up-regulation of an activation marker, CD69, on NK cells, particularly the CD56(dim) subset, in the presence of both the antibody and target cells was much greater for the low-fucose antibodies.

CONCLUSIONS

Our data showed that fucose removal from IgG1 could reduce the antigen amount required for ADCC induction via efficient recruitment and activation of NK cells.

Characterizing biological products and assessing comparability following manufacturing changes

Changes in production methods of a biological product may necessitate an assessment of comparability to ensure that these manufacturing changes have not affected the safety, identity, purity, or efficacy of the product. Depending on the nature of the protein or the change, this assessment consists of a hierarchy of sequential tests in analytical testing, preclinical animal studies and clinical studies. Differences in analytical test results between pre- and post-change products may require functional testing to establish the biological or clinical significance of the observed difference. An underlying principle of comparability is that under certain conditions, protein products may be considered comparable on the basis of analytical testing results alone. However, the ability to compare biological materials is solely dependent on the tests used, since no single analytical method is able to compare every aspect of protein structure or function. The advantages and disadvantages of any given method depends on the protein property being characterized.

The humanization of N-glycosylation pathways in yeast

Yeast and other fungal protein-expression hosts have been extensively used to produce industrial enzymes, and are often the expression system of choice when manufacturing costs are of primary concern. However, for the production of therapeutic glycoproteins intended for use in humans, yeast have been less useful owing to their inability to modify proteins with human glycosylation structures. Yeast N-glycosylation is of the high-mannose type, which confers a short half-life in vivo and thereby compromises the efficacy of most therapeutic glycoproteins. Several approaches to humanizing yeast N-glycosylation pathways have been attempted over the past decade with limited success. Recently however, advances in the glycoengineering of yeast and the expression of therapeutic glycoproteins with humanized N-glycosylation structures have shown significant promise - this review summarizes the most important developments in the field.

Effects of Drug Loading on the Antitumor Activity of a Monoclonal Antibody Drug Conjugate

PURPOSE

An antibody-drug conjugate consisting of monomethyl auristatin E (MMAE) conjugated to the anti-CD30 monoclonal antibody (mAb) cAC10, with eight drug moieties per mAb, was previously shown to have potent cytotoxic activity against CD30(+) malignant cells. To determine the effect of drug loading on antibody-drug conjugate therapeutic potential, we assessed cAC10 antibody-drug conjugates containing different drug-mAb ratios in vitro and in vivo.

EXPERIMENTAL DESIGN

Coupling MMAE to the cysteines that comprise the interchain disulfides of cAC10 created an antibody-drug conjugate population, which was purified using hydrophobic interaction chromatography to yield antibody-drug conjugates with two, four, and eight drugs per antibody (E2, E4, and E8, respectively). Antibody-drug conjugate potency was tested in vitro against CD30(+) lines followed by in vivo xenograft models. The maximum-tolerated dose and pharmacokinetic profiles of the antibody-drug conjugates were investigated in mice.

RESULTS

Although antibody-drug conjugate potency in vitro was directly dependent on drug loading (IC(50) values E8<E4<E2), the in vivo antitumor activity of E4 was comparable with E8 at equal mAb doses, although the E4 contained half the amount of MMAE per mAb. E2 was also an active antitumor agent but required higher doses. The maximum-tolerated dose of E2 in mice was at least double that of E4, which in turn was twice that of E8. MMAE loading affected plasma clearance, as E8 cleared 3-fold faster than E4 and 5-fold faster than E2.

CONCLUSIONS

By decreasing drug loading per antibody, the therapeutic index was increased demonstrating that drug loading is a key design parameter for antibody-drug conjugates.

Enhancement of the antibody-dependent cellular cytotoxicity of low-fucose IgG1 Is independent of FcgammaRIIIa functional polymorphism

PURPOSE

The most common polymorphic variant of Fcgamma receptor type IIIa (FcgammaRIIIa), FcgammaRIIIa-158F, has been associated with inferior clinical responses to anti-CD20 chimeric IgG1 rituximab compared with FcgammaRIIIa-158V. As we previously found that removal of fucose residues from the oligosaccharides of human IgG1 results in enhanced antibody-dependent cellular cytotoxicity, we compared the effects of the FcgammaRIIIa gene (FCGR3A) polymorphism on normal and low-fucose versions of rituximab on antibody-dependent cellular cytotoxicity.

EXPERIMENTAL DESIGN

The polymorphism at position 158 of FcgammaRIIIa was determined for the peripheral blood mononuclear cells (PBMCs) of 20 healthy donors. The PBMCs were then used as effector cells to compare the antibody-dependent cellular cytotoxicity of rituximab and a low-fucose version, KM3065. The contributions of the different cell types within the PBMC to antibody-dependent cellular cytotoxicity were examined.

RESULTS

We found KM3065-mediated antibody-dependent cellular cytotoxicity was increased 10 to 100-fold compared with rituximab for each of the 20 donors. In contrast to rituximab, KM3065 antibody-dependent cellular cytotoxicity enhancement was similar for both FCGR3A alleles and thus independent of genotype. In addition, antibody-dependent cellular cytotoxicity of both KM3065 and rituximab requires natural killer cells but not monocytes nor polymorphonuclear cells. The antibody-dependent cellular cytotoxicity (ADCC) of each of the 20 donors correlated with the natural killer cell numbers present in the PBMCs. Importantly, using KM3065, the ADCC mediated by effector cells bearing the lower affinity variant FcgammaRIIIa-158F was significantly increased compared with rituximab-mediated ADCC using effector cells bearing the higher affinity FcgammaRIIIa-158V receptors.

CONCLUSIONS

The use of low-fucose antibodies might improve the therapeutic effects of anti-CD20 therapy for all patients independent of FcgammaRIIIa phenotype beyond that currently seen with even the most responsive patients.

Characterization of humanized antibodies secreted by Aspergillus niger

Two different humanized immunoglobulin G1(kappa) antibodies and an Fab' fragment were produced by Aspergillus niger. The antibodies were secreted into the culture supernatant. Both light and heavy chains were initially synthesized as fusion proteins with native glucoamylase. After antibody assembly, cleavage by A. niger KexB protease allowed the release of free antibody. Purification by hydrophobic charge induction chromatography proved effective at removing any antibody to which glucoamylase remained attached. Glycosylation at N297 in the Fc region of the heavy chain was observed, but this site was unoccupied on approximately 50% of the heavy chains. The glycan was of the high-mannose type, with some galactose present, and the size ranged from Hex(6)GlcNAc(2) to Hex(15)GlcNAc(2). An aglycosyl mutant form of antibody was also produced. No significant difference between the glycosylated antibody produced by Aspergillus and that produced by mammalian cell cultures was observed in tests for affinity, avidity, pharmacokinetics, or antibody-dependent cellular cytotoxicity function.

Rituximab-dependent cytotoxicity by natural killer cells: influence of FCGR3A polymorphism on the concentration-effect relationship

The FCGR3A gene dimorphism generates two allotypes: FcgammaRIIIa-158V and FcgammaRIIIa-158F. The genotype homozygous for FcgammaRIIIa-158V (VV) is associated with higher clinical response to rituximab, a chimeric anti-CD20 IgG1 used in the treatment of B lymphoproliferative malignancies. Our objective was to determine whether this genetic association relates to rituximab-dependent cytotoxicity mediated by FcgammaRIIIa/CD16a+ cells. The number of CD16+ circulating monocytes, T cells, and natural killer (NK) cells in 54 donors was first shown to be unrelated to FCGR3A polymorphism. We then demonstrated that FcgammaRIIIa-158V displays higher affinity for rituximab than FcgammaRIIIa-158F by comparing rituximab concentrations inhibiting the binding of 3G8 mAb (anti-CD16) with VV NK cells and NK cells homozygous for FcgammaRIIIa-158F (FF). VV and FF NK cells killed Daudi cells similarly after FcgammaRIIIa engagement by saturating concentrations of rituximab or 3G8. However, the rituximab concentration resulting in 50% lysis (EC(50)) observed with NK cells from VV donors was 4.2 times lower than that observed with NK cells from FF donors (on average 0.00096 and 0.00402 microg/ml, respectively, P = 0.0043). Finally, the functional difference between VV and FF NK cells was restricted to rituximab concentrations weakly sensitizing CD20. This study supports the conclusion that FCGR3A genotype is associated with response to rituximab because it affects the relationship between rituximab concentration and NK cell-mediated lysis of CD20+ cells. Rituximab administration could therefore be adjusted according to FCGR3A genotype.

Monomeric IgG in Intravenous Ig Preparations Is a Functional Antagonist of FcγRII and FcγRIIIb

Intravenous Ig preparations (IVIg), originally developed as a substitution therapy for patients with low plasma IgG, are nowadays frequently used in the treatment of various immune diseases. However, the mechanism of action of IVIg in these diseases remains elusive and is often referred to as "immunomodulatory." We hypothesized that monomeric IgG may act as a low-affinity FcgammaR antagonist and sought experimental evidence for this hypothesis. Human neutrophils as well FcgammaRIIa-transfected IIA1.6 cells were used as FcgammaR-positive cells and aggregated IgG (aIgG) or stable dimeric IgG as FcgammaR-specific agonists for these cells. We found that monomeric IgG purified from IVIg at concentrations similar to that of IgG in plasma, diminished the binding of stable dimeric IgG to FcgammaRIIa transfectants, reduced aIgG-induced influx of Ca(2+) ions into the cytosol of neutrophils, and attenuated the aIgG-induced release of elastase. Notably, monomeric IgG by itself did not elicit these responses, nor did it affect these processes in response to fMLP. Absorption of IgG from normal plasma revealed that plasma IgG exerted similar effects as monomeric IgG in IVIg. In addition, adding monomeric IgG to blood of healthy volunteers showed a dose-dependent decrease of aIgG-induced elastase release. Finally, we observed decreased aIgG-induced polymorphonuclear neutrophil responses in two hypogammaglobulinemic patients upon treatment with IVIg. We conclude that monomeric IgG at physiological levels acts as a low-affinity FcgammaR antagonist. Moreover, FcgammaR antagonism constitutes an immunomodulatory effect of IVIg.

Defucosylated Chimeric Anti-CC Chemokine Receptor 4 IgG1 with Enhanced Antibody-Dependent Cellular Cytotoxicity Shows Potent Therapeutic Activity to T-Cell Leukemia and Lymphoma

Human IgG1 antibodies with low fucose contents in their asparagine-linked oligosaccharides have been shown recently to exhibit potent antibody-dependent cellular cytotoxicity (ADCC) in vitro. To additionally investigate the efficacy of the human IgG1 with enhanced ADCC, we generated the defucosylated chimeric anti-CC chemokine receptor 4 (CCR4) IgG1 antibody KM2760. KM2760 exhibited much higher ADCC using human peripheral blood mononuclear cells (PBMCs) as effector cells compared with the highly fucosylated, but otherwise identical IgG1, KM3060. In addition, KM2760 also exhibited potent ADCC in the presence of lower concentrations of human PBMCs than KM3060. Because CCR4 is a selective marker of T-cell leukemia/lymphoma, the effectiveness of KM2760 for T-cell malignancy was evaluated in several mouse models. First, to compare the antitumor activity of KM2760 and KM3060, we constructed a human PBMC-engrafted mouse model to determine ADCC efficacy with human effector cells. In this model, KM2760 showed significantly higher antitumor efficacy than KM3060, indicating that KM2760 retains its high potency in vivo. Second, KM2760 suppressed tumor growth in both syngeneic and xenograft mouse models in which human PBMCs were not engrafted. Although murine effector cells exhibited marginal ADCC mediated by KM2760 and KM3060, KM2760 unexpectedly showed higher efficacy than KM3060 in a syngeneic mouse model, suggesting that KM2760 functions in murine effector system in vivo via an unknown mechanism that differs from that in human. These results indicate that defucosylated antibodies with enhanced ADCC as well as potent antitumor activity in vivo are promising candidates for the novel antibody-based therapy.

Fucose Depletion from Human IgG1 Oligosaccharide Enhances Binding Enthalpy and Association Rate Between IgG1 and FcγRIIIa

Depletion of fucose from human IgG1 oligosaccharide improves its affinity for Fcgamma receptor IIIa (FcgammaRIIIa). This is the first case where a glycoform modification is shown to improve glycoprotein affinity for the receptors without carbohydrate-binding capacity, suggesting a novel glyco-engineering strategy to improve ligand-receptor binding. To address the mechanisms of affinity improvement by the fucose depletion, we used isothermal titration calorimetry (ITC) and biosensor analysis with surface plasmon resonance. ITC demonstrated that IgG1-FcgammaRIIIa binding was driven by favorable binding enthalpy (DeltaH) but opposed by unfavorable binding entropy change (DeltaS). Fucose depletion from IgG1 enhanced the favorable DeltaH, leading to the increase in the binding constant of IgG1 for the receptor by a factor of 20-30. The increase in the affinity was mainly attributed to an enhanced association rate. A triple amino acid substitution in IgG1, S298A/E333A/K334A, is also known to improve IgG1 affinity for FcgammaRIIIa. ITC demonstrated that the amino acid substitution attenuated the unfavorable DeltaS resulting in a three- to fourfold increase in the binding constant. The affinity enhancement by the amino acid substitution was due to a reduced dissociation rate. These results indicate that the mechanism of affinity improvement by the fucose depletion is quite distinct from that by the amino acid substitution. Defucosylated IgG1 exhibited higher antibody-dependent cellular cytotoxicity (ADCC) than S298A/E333A/K334A-IgG1, showing a correlation between IgG1 affinity for FcgammaRIIIa and ADCC. We also examined the effect of FcgammaRIIIa polymorphism (Val158/Phe158) on IgG1-FcgammaRIIIa binding. The Phe to Val substitution increased FcgammaRIIIa affinity for IgG1 in an enthalpy-driven manner with the reduced dissociation rate. These results together highlight the distinctive functional improvement of affinity by IgG1 defucosylation and suggest that engineering of non-interfacial monosaccharides can improve glycoprotein affinity for receptors via an enthalpy-driven and association rate-assisted mechanism.

Chimeric CD19 antibody mediates cytotoxic activity against leukemic blasts with effector cells from pediatric patients who received T-cell-depleted allografts

Relapse is a major problem after transplantation in children with acute B-lineage leukemias, and new therapies are needed to increase graft-versus-leukemia (GvL) effects without inducing graft-versus-host disease (GvHD). Here, we studied the ability of effector cells recovered from patients after transplantation with positive-selected stem cells from alternative donors to induce antibody-dependent cellular cytotoxicity (ADCC). For this purpose, a chimeric CD19 antibody, CD19-4G7chim, was generated. This antibody efficiently mediated ADCC against primary acute lymphoblastic leukemia (ALL) blasts by using purified natural killer (NK) cells from healthy donors or mononuclear cells from patients as effector cells. Increased lysis was obtained after stimulation of effector cells with interleukin-2 (IL-2). ADCC was not prevented by inhibitory effects mediated by HLA class I. We propose that treatment with chimeric CD19 antibodies leading to ADCC by donor-derived NK cells may become a therapeutic option for the post-transplantation treatment of minimal residual B-lineage ALLs.

Human antibody–Fc receptor interactions illuminated by crystal structures

Immunoglobulins couple the recognition of invading pathogens with the triggering of potent effector mechanisms for pathogen elimination. Different immunoglobulin classes trigger different effector mechanisms through interaction of immunoglobulin Fc regions with specific Fc receptors (FcRs) on immune cells. Here, we review the structural information that is emerging on three human immunoglobulin classes and their FcRs. New insights are provided, including an understanding of the antibody conformational adjustments that are required to bring effector cell and target cell membranes sufficiently close for efficient killing and signal transduction to occur. The results might also open up new possibilities for the design of therapeutic antibodies.

Establishment ofFUT8 knockout Chinese hamster ovary cells: An ideal host cell line for producing completely defucosylated antibodies with enhanced antibody-dependent cellular cytotoxicity

To generate industrially applicable new host cell lines for antibody production with optimizing antibody-dependent cellular cytotoxicity (ADCC) we disrupted both FUT8 alleles in a Chinese hamster ovary (CHO)/DG44 cell line by sequential homologous recombination. FUT8 encodes an alpha-1,6-fucosyltransferase that catalyzes the transfer of fucose from GDP-fucose to N-acetylglucosamine (GlcNAc) in an alpha-1,6 linkage. FUT8(-/-) cell lines have morphology and growth kinetics similar to those of the parent, and produce completely defucosylated recombinant antibodies. FUT8(-/-)-produced chimeric anti-CD20 IgG1 shows the same level of antigen-binding activity and complement-dependent cytotoxicity (CDC) as the FUT8(+/+)-produced, comparable antibody, Rituxan. In contrast, FUT8(-/-)-produced anti-CD20 IgG1 strongly binds to human Fcgamma-receptor IIIa (FcgammaRIIIa) and dramatically enhances ADCC to approximately 100-fold that of Rituxan. Our results demonstrate that FUT8(-/-) cells are ideal host cell lines to stably produce completely defucosylated high-ADCC antibodies with fixed quality and efficacy for therapeutic use.

Glycosylation of FcgammaRIII in N163 as mechanism of regulating receptor affinity

Human FcgammaRIII (CD16) is a low-affinity receptor for immunoglobulin G (IgG). There are two different isoforms of this protein: CD16a (transmembranous, expressed on natural killer cells and on macrophages) and CD16b (glycosylphosphatidylinositol-linked, expressed on neutrophilic granulocytes in two allelic forms NA1 and NA2). Both forms of the protein have a variable glycosylation pattern. The NA1 allele of CD16B has four asparagine (N)-linked glycosylation sites. One of them (N163) is localized in the ligand-binding site of domain II. This site is shared by the NA2 allele and CD16A. To examine the functional role of the glycosylation we mutated the four glycosylation sites of the NA1 allele (N39, N75, N163, N170) into glutamine (Q). HEK293 cells were stably transfected with the single mutants and wild-type CD16 as control. We determined binding of human IgG to transfected cells using immunofluorescence studies with anti-human IgG antibody. Monomeric IgG bound to N163Q transfectants with higher affinity than to other transfectants, showing that glycosylation in N163 influences the affinity of CD16 to its ligand. In addition, preincubation of WT-CD16-transfected cells with Tunicamycin (an inhibitor of N-glycosylation) resulted in an increased binding of monomeric IgG whereas N163Q-CD16-transfected cells remained unaffected. Therefore, glycosylation in N163 is a mechanism of regulating affinity of FcgammaRIII to its ligand IgG.

Designing proteins for therapeutic applications

Protein design is becoming an increasingly useful tool for optimizing protein drugs and creating novel biotherapeutics. Recent progress includes the engineering of monoclonal antibodies, cytokines, enzymes and viral fusion inhibitors.

Antibody engineering for therapeutics

With the acceptance of antibodies as therapeutics, a diversity of engineered antibody forms have been created to improve their efficacy, including enhancing the effector functions of full-length antibodies, delivering toxins to kill cells or cytokines in order to stimulate the immune system, and bispecific antibodies to target multiple receptors. After years of in vitro investigation, many of these are now moving into clinical trials and are showing promise. A potential new type of effector function for antibodies, that is, the generation of reactive oxygen species that may effect inflammation or bacterial killing, has been elucidated. In addition, the field has expanded beyond a concentration on immunoglobulin G to include immunoglobulin A antibodies as potential therapeutics.

Rational design and engineering of therapeutic proteins

An increasing number of engineered protein therapeutics are currently being developed, tested in clinical trials and marketed for use. Many of these proteins arose out of hit-and-miss efforts to discover specific mutations, fusion partners or chemical modifications that confer desired properties. Through these efforts, several useful strategies have emerged for rational optimization of therapeutic candidates. The controlled manipulation of the physical, chemical and biological properties of proteins enabled by structure-based simulation is now being used to refine established rational engineering approaches and to advance new strategies. These methods provide clear, hypothesis-driven routes to solve problems that plague many proteins and to create novel mechanisms of action. We anticipate that rational protein engineering will shape the field of protein therapeutics dramatically by improving existing products and enabling the development of novel therapeutic agents.

The absence of fucose but not the presence of galactose or bisecting N-acetylglucosamine of human IgG1 complex-type oligosaccharides shows the critical role of enhancing antibody-dependent cellular cytotoxicity

An anti-human interleukin 5 receptor (hIL-5R) humanized immunoglobulin G1 (IgG1) and an anti-CD20 chimeric IgG1 produced by rat hybridoma YB2/0 cell lines showed more than 50-fold higher antibody-dependent cellular cytotoxicity (ADCC) using purified human peripheral blood mononuclear cells as effector than those produced by Chinese hamster ovary (CHO) cell lines. Monosaccharide composition and oligosaccharide profiling analysis showed that low fucose (Fuc) content of complex-type oligosaccharides was characteristic in YB2/0-produced IgG1s compared with high Fuc content of CHO-produced IgG1s. YB2/0-produced anti-hIL-5R IgG1 was subjected to Lens culinaris aggulutin affinity column and fractionated based on the contents of Fuc. The lower Fuc IgG1 had higher ADCC than the IgG1 before separation. In contrast, the content of bisecting GlcNAc of the IgG1 affected ADCC much less than that of Fuc. In addition, the correlation between Gal and ADCC was not observed. When the combined effect of Fuc and bisecting GlcNAc was examined in anti-CD20 IgG1, only a severalfold increase of ADCC was observed by the addition of GlcNAc to highly fucosylated IgG1. Quantitative PCR analysis indicated that YB2/0 cells had lower expression level of FUT8 mRNA, which codes alpha1,6-fucosyltransferase, than CHO cells. Overexpression of FUT8 mRNA in YB2/0 cells led to an increase of fucosylated oligosaccharides and decrease of ADCC of the IgG1. These results indicate that the lack of fucosylation of IgG1 has the most critical role in enhancement of ADCC, although several reports have suggested the importance of Gal or bisecting GlcNAc and provide important information to produce the effective therapeutic antibody.