Glycosylation of Recombinant Antibody Therapeutics

Post-translational modifications in the context of therapeutic proteins

The majority of protein-based biopharmaceuticals approved or in clinical trials bear some form of post-translational modification (PTM), which can profoundly affect protein properties relevant to their therapeutic application. Whereas glycosylation represents the most common modification, additional PTMs, including carboxylation, hydroxylation, sulfation and amidation, are characteristic of some products. The relationship between structure and function is understood for many PTMs but remains incomplete for others, particularly in the case of complex PTMs, such as glycosylation. A better understanding of such structural-functional relationships will facilitate the development of second-generation products displaying a PTM profile engineered to optimize therapeutic usefulness.

Higher levels of sialylated Fc glycans in immunoglobulin G molecules can adversely impact functionality

Although it is now clear that certain Fc glycan structures on immunoglobulin G (IgG) antibodies (Abs) can have a dramatic influence on binding to selected Fcgamma receptors (FcgammaR) and on Fc-mediated immune functions, the effects of all known Fc glycan structures still have not been exhaustively studied. We report that in vitro analyses of pairs of monoclonal human IgG Abs that differ in the amount of sialic acid in their Fc glycans revealed that, for each of the three Ab pairs we examined, higher levels of sialylation were associated with reduced activity in Ab-dependent cellular cytotoxicity (ADCC) assays. This relationship between sialylation and ADCC activity was observed regardless of whether the differences in the extent of sialylation were derived by different Ab production processes, use of a lectin column to separate monoclonal Ab preparations into differentially sialylated fractions, or use of direct in vitro glycoengineering methods to convert a lesser sialylated Ab into a highly sialylated Ab. Subsequent investigations revealed that, depending on the individual Ab and how the differences in sialylation were derived, the lower ADCC potency of the more sialylated variants was apparently due to lower-affinity binding to FcgammaRIIIa on natural killer (NK) cells and/or, more interestingly, lower-affinity binding to cell-surface antigen. Our data provide the first example of an Fc glycan structure impacting antigen binding and suggest that avoiding Fc glycan sialylation can offer another means of optimizing ADCC activity of Abs.

Development of recombinant human polyclonal antibodies for the treatment of complex human diseases

Antibodies are a central factor in the immunity against invading pathogens, such as bacteria and viruses, as well as against malignantly transformed cells. Natural antibody responses are polyclonal, comprising antibodies against several epitopes, thus increasing the probability of eliminating the invading pathogen or malignant cell. The pharmacological advantage of polyclonality is exploited in the plasma-derived immunoglobulin products used at present to treat a number of infectious diseases. However, the use of plasma-derived products is limited by their cost, inconvenience of use and potential for transferring diseases from the donor to the patient. Symphogen has developed technologies to capture the advantages of antibody polyclonality while eliminating the potential safety risk associated with the sourcing of human material. Hence, the Symplex technology has been developed to identify diverse repertoires of target-specific, fully human antibodies. For the controlled manufacture of recombinant polyclonal antibody drugs, Symphogen has developed the Sympress technology. Combined, these two technologies allow the identification and industrial manufacturing of recombinant human polyclonal antibodies for medical use in humans. The authors believe that this new class of therapeutic antibodies will be advantageous in the treatment of complex human diseases, such as cancer and infection, as it allows the combination of several treatment modalities in one drug.

Comparison of biological activity among nonfucosylated therapeutic IgG1 antibodies with three different N-linked Fc oligosaccharides: the high-mannose, hybrid, and complex types

The structure of asparagine-linked oligosaccharides attached to the antibody constant region (Fc) of human immunoglobulin G1 (IgG1) has been shown to affect the pharmacokinetics and antibody effector functions of antibody-dependent cellular cytotoxicity (ADCC) and complement-dependent cytotoxicity (CDC). However, it is still unclear how differences in the N-linked oligosaccharide structures impact the biological activities of antibodies, especially those lacking core fucose. Here, we succeeded in generating core fucose-lacking human IgG1 antibodies with three different N-linked Fc oligosaccharides, namely, a high-mannose, hybrid, and complex type, using the same producing clone, and compared their activities. Cultivation of an alpha-1,6-fucosyltransferase (FUT8) knockout Chinese hamster ovary cell line in the presence or absence of a glycosidase inhibitor (either swainsonine or kifunensine) yielded antibody production of each of the three types without contamination by the others. Two of three types of nonnaturally occurring atypical oligosaccharide IgG1, except the complex type, reduced the affinity for both human lymphocyte receptor IIIa (FcgammaRIIIa) and the C1q component of the complement, resulting in reduction of ADCC and CDC. The bulky structure of the nonreducing end of N-linked Fc oligosaccharides is considered to contribute the CDC change, whereas the structural change in the reducing end, i.e. the removal of core fucose, causes ADCC enhancement through improved FcgammaRIIIa binding. In the pharmacokinetic profile, although no significant difference of human neonatal Fc receptor (FcRn)-binding affinity was observed among the three types, the complex type showed longer serum half-lives than the other types irrespective of core fucosylation in mice, which also suggests the contribution of the nonreducing end structure. The present study provides basic information on the effects of core fucose-lacking N-linked Fc oligosaccharides on antibody biological activities.

A KDEL-tagged monoclonal antibody is efficiently retained in the endoplasmic reticulum in leaves, but is both partially secreted and sorted to protein storage vacuoles in seeds

Transgenic plants are attractive biological systems for the large-scale production of pharmaceutical proteins. In particular, seeds offer special advantages, such as ease of handling and long-term stable storage. Nevertheless, most of the studies of the expression of antibodies in plants have been performed in leaves. We report the expression of a secreted (sec-Ab) or KDEL-tagged (Ab-KDEL) mutant of the 14D9 monoclonal antibody in transgenic tobacco leaves and seeds. Although the KDEL sequence has little effect on the accumulation of the antibody in leaves, it leads to a higher antibody yield in seeds. sec-Ab(Leaf) purified from leaf contains complex N-glycans, including Lewis(a) epitopes, as typically found in extracellular glycoproteins. In contrast, Ab-KDEL(Leaf) bears only high-mannose-type oligosaccharides (mostly Man 7 and 8) consistent with an efficient endoplasmic reticulum (ER) retention/cis-Golgi retrieval of the antibody. sec-Ab and Ab-KDEL gamma chains purified from seeds are cleaved by proteases and contain complex N-glycans indicating maturation in the late Golgi compartments. Consistent with glycosylation of the protein, Ab-KDEL(Seed) was partially secreted and sorted to protein storage vacuoles (PSVs) in seeds and not found in the ER. This dual targeting may be due to KDEL-mediated targeting to the PSV and to a partial saturation of the vacuolar sorting machinery. Taken together, our results reveal important differences in the ER retention and vacuolar sorting machinery between leaves and seeds. In addition, we demonstrate that a plant-made antibody with triantennary high-mannose-type N-glycans has similar Fab functionality to its counterpart with biantennary complex N-glycans, but the former antibody interacts with protein A in a stronger manner and is more immunogenic than the latter. Such differences could be related to a variable immunoglobulin G (IgG)-Fc folding that would depend on the size of the N-glycan.

Formulation and delivery issues for monoclonal antibody therapeutics

Antibodies can have exquisite specificity of target recognition and thus generate highly selective outcomes following their systemic administration. While antibodies can have high specificity, the doses required to treat patients, particularly for a chronic condition, are typically large. Fortunately, advances in production and purification capacities have allowed for the exceptionally large amounts of highly purified monoclonal antibodies to be produced. Additionally, genetic engineering of antibodies has provided a stable of antibody-like proteins that can be easier to prepare. Together, these advances have made antibody-based therapies one of the most commonly pursued pharmaceuticals in biotechnology pipelines. With this success, however, has come a series of technical challenges in the formulation of antibody-based materials to maintain sufficient stability in a variety of configurations and sometimes at particularly high concentrations. This review focuses on issues related to identifying and verifying stable antibody-based formulations.

Engineering of therapeutic antibodies to minimize immunogenicity and optimize function

One of the first difficulties in developing monoclonal antibody therapeutics was the recognition that human anti-mouse antibody (HAMA) response limited the administration of murine antibodies. Creative science has lead to a number of ways to counter the immunogenicity of non-human antibodies, primarily through chimeric, humanized, de-immunized, and most recently, human-sequence therapeutic antibodies. Once therapeutic antibodies of low or no immunogenicity were available, the creativity then turned to engineering both the antigen-binding domains (e.g., affinity maturation, stability) and altering the effector functions (e.g. antibody-dependent cellular cytotoxicity, complement-dependent cellular cytotoxicity, and clearance rate).

Current and future issues in the manufacturing and development of monoclonal antibodies

Despite a slow beginning, monoclonal antibodies have had many successes over the past decade. It is important that these successes continue, bringing more products for more indications to market. Although manufacturing is not the most common cause of product failure, product quality issues can delay antibody development. Manufacturing has depended on the triad of process validation, process control and product testing. Applying product knowledge proactively to manufacturing (quality by design) may allow greater flexibility and maintain or improve product quality. An integrated approach to biological characterization is an important aspect of product knowledge. Greater product knowledge also facilitates development in other disciplines. Independent of manufacturing strategy, there are a number of regulatory hurdles in initial and ongoing antibody development. These are described to help prevent unnecessary delays.

Optimization of a reversed-phase high-performance liquid chromatography/mass spectrometry method for characterizing recombinant antibody heterogeneity and stability

An enhanced analytical RP-HPLC/MS method was developed for monitoring the stability and production of intact and fragmented monoclonal antibodies (MAbs). The use of high column temperatures (70-80 degrees C), organic solvents with high eluotropic strength coefficients (isopropyl and n-propyl alcohols), and Zorbax StableBond columns, were critical for good recovery and resolution of immunoglobulin G1 (IgG1) and IgG2 monoclonal antibodies. Using this method, cleavage products of a degraded IgG1 antibody were clearly separated and identified by in-line electrospray ionization time-of-flight (ESI-TOF) mass spectrometry generating exact masses and unique terminal ladder sequences. The glycosylation profile, including mapping of the terminal galactose and fucose heterogeneity of the N-linked sugars, was determined by mass spectrometry of intact MAbs. In addition, we discovered that several IgG2 MAbs exhibited greater structural heterogeneity compared to IgG1s. Mass spectral characterization data and reduction data suggested that the heterogeneity is disulfide related. This reversed-phase LC/MS method represents a key advancement in monitoring intact MAb production and stability.

Electron Capture Dissociation Mass Spectrometry in Characterization of Peptides and Proteins

Electron capture dissociation (ECD) represents one of the most recent and significant advancements in tandem mass spectrometry (MS/MS) for the identification and characterization of polypeptides. In comparison with the conventional fragmentation techniques, such as collisionally activated dissociation (CAD), ECD provides more extensive sequence fragments, while allowing the labile modifications to remain intact during backbone fragmentation--an important attribute for characterizing post-translational modifications. Herein, we present a brief overview of the ECD technique as well as selected applications in characterization of peptides and proteins. Case studies including characterization and localization of amino acid glycosylation, methionine oxidation, acylation, and "top-down" protein mass spectrometry using ECD will be presented. A recent technique, coined as electron transfer dissociation (ETD), will be also discussed briefly.

Monoclonal anti-D antibodies to prevent alloimmunization: lessons from clinical trials

In the past 20 years, numerous monoclonal anti-D antibodies have been developed in order to replace the human plasma derived anti-D immunoglobulins, using different in vitro functional assays as screening methods. Some of these monoclonal antibodies have been evaluated in exploratory in vivo clinical trials, notably for their ability to mediate the clearance of D-positive red cells. A review of these reported trials is presented and the results are analyzed in the light of the newly published hypothesis conferring an important role to some Fc-FcgammaR interactions and to the glycosylation-dependent potency of the monoclonal anti-D antibodies.

Differential glycosylation of polyclonal IgG, IgG-Fc and IgG-Fab isolated from the sera of patients with ANCA-associated systemic vasculitis

Post-translational modifications (PTMs) of proteins produced in vivo may be tissue, developmentally and/or disease specific. PTMs impact on the stability and function of proteins and offer a challenge to the commercial production of protein biotherapeutics. We have previously reported a marked deficit in galactosylation of oligosaccharides released from polyclonal IgG isolated from sera of patients with the anti-neutrophil cytoplasmic antibodies (ANCA) associated vasculitides; Wegener's granulomatosis (WG) and microscopic polyangiitis (MPA). Whilst normal polyclonal IgG molecules are glycosylated within the IgG-Fc region, approximately 20% of molecules also bear oligosaccharides attached to the variable regions of the light or heavy chain IgG-Fab. It is of interest, therefore to compare profiles of oligosaccharides released from the IgG-Fc and IgG-Fab of normal IgG with that isolated from the sera of patients with WG or MPA. This study shows that whilst the oligosaccharides released from ANCA IgG-Fc are hypogalactosylated those released from IgG-Fab are galactosylated and sialylated. These results show that hypogalactosylation of IgG-Fc is not due to a defect in the glycosylation or processing machinery. It rather suggests a subtle change in IgG-Fc conformation that influences the addition of galactose. Remarkably, this influence is exerted on all plasma cells. Interestingly, a licensed monoclonal antibody therapeutic, produced in Sp2/0 cells, is also shown to be hypogalactosylated in its IgG-Fc but fully galactosylated in its IgG-Fab.

In vitro galactosylation of human IgG at 1 kg scale using recombinant galactosyltransferase

The Fc effector functions of immunoglobulin G (IgG) antibodies are in part determined by structural features of carbohydrates linked to each of the paired gamma heavy chains in the antibody constant domain (C(H)2). One glycoform that has been shown to be advantageous is G2, where both arms of complex bi-antennary N-glycans terminate in galactose. In vitro treatment with glycosyltransferases can remodel heterogeneous IgG glycoforms, enabling preparation of IgG molecules with homogeneous glycan chains. Here we describe optimization of conditions for use of a soluble recombinant galactosyltransferase in vitro to remodel glycans of human serum IgG, and we demonstrate a scaled-up reaction in which >98% of neutral glycans attached to 1 kg IgG are converted to the G2 glycoform. Removal of glycosylation reagents from the product is achieved in one step by affinity chromatography on immobilized Protein A.

Impact of variable domain glycosylation on antibody clearance: An LC/MS characterization

Variable (Fv) domain N-glycosylation sites are found in approximately 20% of human immunoglobulin Gs (IgGs) in addition to the conserved N-glycosylation sites in the C(H)2 domains. The carbohydrate structures of the Fv glycans and their impact on in vivo half-life are not well characterized. Oligosaccharide structures in a humanized anti-Abeta IgG1 monoclonal antibody (Mab) with an N-glycosylation site in the complementary determining region (CDR2) of the heavy chain variable region were elucidated by LC/MS analysis following sequential exoglycosidase treatments of the endoproteinase Lys-C digest. Results showed that the major N-linked oligosaccharide structures in the Fv region have three characteristics (core-fucosylated biantennary oligosaccharides with one or two N-glycolylneuraminic acid [NeuGc] residues, zero or one alpha-linked Gal residue, and zero or one beta-linked GalNAc residue), whereas N-linked oligosaccharides in the Fc region contained typical Fc glycans (core-fucosylated, biantennary oligosaccharides with zero to two Gal residues). To elucidate the contribution of Fv glycans to the half-life of the antibody, a method that allows capture of the Mab and determination of its glycan structures at various time points after administration to mice was developed. Anti-Abeta antibody in mouse serum was immunocaptured by immobilized goat anti-human immunoglobulin Fc(gamma) antibody resin, and the captured material was treated with papain to generate Fab and Fc for LC/MS analysis. Different glycans in the Fc region showed the same clearance rate as demonstrated previously. In contrast to many other non-antibody glycosylated therapeutics, there is no strong correlation between oligosaccharide structures in the Fv region and their clearance rates in vivo. Our data indicated that biantennary oligosaccharides lacking galactosylation had slightly faster clearance rates than other structures in the Fv domain.

Biopharmaceutical production in plants: problems, solutions and opportunities

There are major structural differences between plant and mammalian N-linked glycans, with those from plants being immunogenic in most laboratory mammals and eliciting glycan-specific IgE and IgG antibodies in humans, when delivered parenterally. However, because humans are constantly exposed to plant glycoproteins in the diet, glycosylated plant-made pharmaceuticals (PMPs) should be acceptable for topical and oral administration. To exploit fully the potential that plants offer for the production of therapeutic proteins for parenteral administration, it might be necessary to inhibit plant-specific post-translational modifications to obtain "humanized" non-immunogenic N-glycans on PMPs. The benefits that could accrue are lower manufacturing costs, relative to mammalian cell culture, and a reduced risk of transmission of mammalian pathogens.