V region carbohydrate and antibody expression

Evaluation of Phage Display Biopanning Strategies for the Selection of Anti-Cell Surface Receptor Antibodies

Monoclonal antibodies (mAbs) are one of the most successful and versatile protein-based pharmaceutical products used to treat multiple pathological conditions. The remarkable specificity of mAbs and their affinity for biological targets has led to the implementation of mAbs in the therapeutic regime of oncogenic, chronic inflammatory, cardiovascular, and infectious diseases. Thus, the discovery of novel mAbs with defined functional activities is of crucial importance to expand our ability to address current and future clinical challenges. In vitro, antigen-driven affinity selection employing phage display biopanning is a commonly used technique to isolate mAbs. The success of biopanning is dependent on the quality and the presentation format of the antigen, which is critical when isolating mAbs against membrane protein targets. Here, we provide a comprehensive investigation of two established panning strategies, surface-tethering of a recombinant extracellular domain and cell-based biopanning, to examine the impact of antigen presentation on selection outcomes with regards to the isolation of positive mAbs with functional potential against a proof-of-concept type I cell surface receptor. Based on the higher sequence diversity of the resulting antibody repertoire, presentation of a type I membrane protein in soluble form was more advantageous over presentation in cell-based format. Our results will contribute to inform and guide future antibody discovery campaigns against cell surface proteins.

Micro-Heterogeneity of Antibody Molecules

Therapeutic monoclonal antibodies (mAbs) are mostly of the IgG class and constitute highly efficacious biopharmaceuticals for a wide range of clinical indications. Full-length IgG mAbs are large proteins that are subject to multiple posttranslational modifications (PTMs) during biosynthesis, purification, or storage, resulting in micro-heterogeneity. The production of recombinant mAbs in nonhuman cell lines may result in loss of structural fidelity and the generation of variants having altered stability, biological activities, and/or immunogenic potential. Additionally, even fully human therapeutic mAbs are of unique specificity, by design, and, consequently, of unique structure; therefore, structural elements may be recognized as non-self by individuals within an outbred human population to provoke an anti-therapeutic/anti-drug antibody (ATA/ADA) response. Consequently, regulatory authorities require that the structure of a potential mAb drug product is comprehensively characterized employing state-of-the-art orthogonal analytical technologies; the PTM profile may define a set of critical quality attributes (CQAs) for the drug product that must be maintained, employing quality by design parameters, throughout the lifetime of the drug. Glycosylation of IgG-Fc, at Asn297 on each heavy chain, is an established CQA since its presence and fine structure can have a profound impact on efficacy and safety. The glycoform profile of serum-derived IgG is highly heterogeneous while mAbs produced in mammalian cells in vitro is less heterogeneous and can be "orchestrated" depending on the cell line employed and the culture conditions adopted. Thus, the gross structure and PTM profile of a given mAb, established for the drug substance gaining regulatory approval, have to be maintained for the lifespan of the drug. This review outlines our current understanding of common PTMs detected in mAbs and endogenous IgG and the relationship between a variant's structural attribute and its impact on clinical performance.

Importance and Monitoring of Therapeutic Immunoglobulin G Glycosylation

The complex diantennary-type oligosaccharides at Asn297 residues of the IgG heavy chains have a profound impact on the safety and efficacy of therapeutic IgG monoclonal antibodies (mAbs). Fc glycosylation of a mAb is an established critical quality attribute (CQA), and its oligosaccharide profile is required to be thoroughly characterized by state-of-the-art analytical methods. The Fc oligosaccharides are highly heterogeneous, and the differentially glycosylated species (glycoforms) of IgG express unique biological activities. Glycoengineering is a promising approach for the production of selected mAb glycoforms with improved effector functions, and non- and low-fucosylated mAbs exhibiting enhanced antibody-dependent cellular cytotoxicity activity have been approved or are under clinical evaluation for treatment of cancers, autoimmune/chronic inflammatory diseases, and infection. Recently, the chemoenzymatic glycoengineering method that allows for the transfer of structurally defined oligosaccharides to Asn-linked GlcNAc residues with glycosynthase has been developed for remodeling of IgG-Fc oligosaccharides with high efficiency and flexibility. Additionally, various glycoengineering methods have been developed that utilize the Fc oligosaccharides of IgG as reaction handles to conjugate cytotoxic agents by "click chemistry", providing new routes to the design of antibody-drug conjugates (ADCs) with tightly controlled drug-antibody ratios (DARs) and homogeneity. This review focuses on current understanding of the biological relevance of individual IgG glycoforms and advances in the development of next-generation antibody therapeutics with improved efficacy and safety through glycoengineering.

Glycosylation-dependent antitumor therapeutic monoclonal antibodies

The therapeutic market for monoclonal antibodies (MAbs) has grown exponentially since 2000. It is expected that the world-wide market for MAbs could reach $125 billion in 2020. For cancer treatment alone, more than 30 MAbs have been approved by the US Food and Drug Administration since 1997. Unlike structure-defined small molecule-based anti-cancer drugs, the expensive MAb is a mixture of heterogeneously glycosylated proteins. All MAbs typically have a single N-glycosylation site on each of the Fc region. The clinical efficacy of the MAbs depends on the N-glycan structures. Loss of N-glycosylation on the MAbs leads to the loss of the ability to activate complement, to bind to Fc receptors, and to induce antibody-dependent cellular cytotoxicity (ADCC). Moreover, antigen-antibody complexes produced from N-glycan-deficient MAbs are failed to be eliminated rapidly from the blood circulation. Even in certain cases, the N-glycan heterogeneity does not significantly influence pharmacokinetics or half-life of MAbs, reduced terminal galactosylation decreases complement-dependent cytotoxicity, the absence of core fucosylation enhances ADCC due to the increased affinities for the FcγRIIIа receptor, and high sialylation levels reduce ADCC activity and impact inflammatory responses. Furthermore, only mammalian cell lines that make human-like N-glycan structures can be used for MAbs production since certain mammalian cell lines can produce non-human glycan epitopes such as galactose-α-1,3-galactose and N-glycolylneuraminic acid (NGNA), which can trigger unwanted immune response. Therefore, mastering the knowledge of N-glycan structures and glycobiology is the key to produce and provide patients with reliable MAbs with consistent glycosylation profile and expected clinical efficacy.

Glycosylation engineering of therapeutic IgG antibodies: challenges for the safety, functionality and efficacy

Glycosylation of the Fc region of IgG has a profound impact on the safety and clinical efficacy of therapeutic antibodies. While the biantennary complex-type oligosaccharide attached to Asn297 of the Fc is essential for antibody effector functions, fucose and outer-arm sugars attached to the core heptasaccharide that generate structural heterogeneity (glycoforms) exhibit unique biological activities. Hence, efficient and quantitative glycan analysis techniques have been increasingly important for the development and quality control of therapeutic antibodies, and glycan profiles of the Fc are recognized as critical quality attributes. In the past decade our understanding of the influence of glycosylation on the structure/function of IgG-Fc has grown rapidly through X-ray crystallographic and nuclear magnetic resonance studies, which provides possibilities for the design of novel antibody therapeutics. Furthermore, the chemoenzymatic glycoengineering approach using endoglycosidase-based glycosynthases may facilitate the development of homogeneous IgG glycoforms with desirable functionality as next-generation therapeutic antibodies. Thus, the Fc glycans are fertile ground for the improvement of the safety, functionality, and efficacy of therapeutic IgG antibodies in the era of precision medicine.

The N14 anti-afamin antibody Fab: a rare VL1 CDR glycosylation, crystallographic re-sequencing, molecular plasticity and conservative versus enthusiastic modelling

The monoclonal antibody N14 is used as a detection antibody in ELISA kits for the human glycoprotein afamin, a member of the albumin family, which has recently gained interest in the capture and stabilization of Wnt signalling proteins, and for its role in metabolic syndrome and papillary thyroid carcinoma. As a rare occurrence, the N14 Fab is N-glycosylated at Asn26L at the onset of the VL1 antigen-binding loop, with the α-1-6 core fucosylated complex glycan facing out of the L1 complementarity-determining region. The crystal structures of two non-apparent (pseudo) isomorphous crystals of the N14 Fab were analyzed, which differ significantly in the elbow angles, thereby cautioning against the overinterpretation of domain movements upon antigen binding. In addition, the map quality at 1.9 Å resolution was sufficient to crystallographically re-sequence the variable VL and VH domains and to detect discrepancies in the hybridoma-derived sequence. Finally, a conservatively refined parsimonious model is presented and its statistics are compared with those from a less conservatively built model that has been modelled more enthusiastically. Improvements to the PDB validation reports affecting ligands, clashscore and buried surface calculations are suggested.

Fractionation of Fab glycosylated immunoglobulin G with concanavalin A chromatography unveils new structural properties of the molecule

Concanavalin A (ConA) chromatography has been extensively used to separate asymmetric Immunoglobulin G (IgG), which possesses oligosaccharide attached to one of the two F(ab')2 arms, from symmetric IgG with no glycan attached to Fab fragments. In this study, applying affinity chromatography, silver stain, Western blot and lectin stain techniques, N- linked oligosaccharide attached to Fab fragment was demonstrated to be exposed on the surface of the protein and be accessible by ConA. In contrast, N- linked oligosaccharide attached to asparagine (Asn) 297 of IgG Fc was located in the inside of the natural protein and was inaccessible by ConA. In addition to asymmetric IgG, there are also detectable level of IgG with both F(ab')2 arms glycosylated that has not been reported previously. The discoveries of new basic molecular structure of IgG would have implications in understanding the function and properties of this important immune molecule with clinical applications.

Functional Characterization of AAV-Expressed Recombinant Anti-VEGF Single-Chain Variable Fragments In Vitro

PURPOSE

Most retinal neovascular disorders are caused by upregulation of vascular endothelial growth factor (VEGF) expression. These disorders are treated with repeated injections of anti-VEGF molecules, which may have severe side effects. The expression of anti-VEGF molecules by the retina itself in a controlled manner following adeno-associated viral (AAV) gene transfer could be a replacement of this therapy.

METHODS

The open reading frames (orf) of the light and the heavy chain of ranibizumab were cloned into an expression plasmid separated by an internal ribosomal entry site (IRES). The construct was mutated to generate ranibizumab single-chain variable fragments (scFv). Expression was verified by western blotting and the concentrations were measured with a custom-made ranibizumab ELISA. Biological activity, VEGF-binding properties, and the doxycycline-dependent induction of anti-VEGF expression were tested. An AAV2/5 vector was generated containing the optimal variant Ra02.

RESULTS

Ra01-Ra05 molecules were detected in the cell culture medium. While the VEGF-binding affinity was significantly lower for Ra01 and Ra02 compared to Lucentis(®), the inhibition of cell migration was comparable and the maximum inhibition of Ra01 and Ra02 was reached at lower doses. The expression of Ra01 and Ra02 was shown to be regulable with the TetOn-system(®) as plasmid (Ra01, Ra02) and AAV vector construct (Ra02).

CONCLUSION

Ra01 and Ra02 can be produced in eukaryotic cells after AAV-mediated gene transfer in a regulable manner in vitro and display comparable biological activity as Lucentis. These results are the basis for in vivo studies in human VEGF-overexpressing mice, a model for human neovascular disorders.

Comparison of the Fc glycosylation of fetal and maternal immunoglobulin G

Human immunoglobulin G (IgG) molecules are composed of two Fab portions and one Fc portion. The glycans attached to the Fc portions of IgG are known to modulate its biological activity as they influence interaction with both complement and various cellular Fc receptors. IgG glycosylation changes significantly with pregnancy, showing a vast increase in galactosylation and sialylation and a concomitant decrease in the incidence of bisecting GlcNAc. Maternal IgGs are actively transported to the fetus by the neonatal Fc receptor (FcRn) expressed in syncytiotrophoblasts in the placenta, providing the fetus and newborn with immunological protection. Two earlier reports described significant differences in total glycosylation between fetal and maternal IgG, suggesting a possible glycosylation-selective transport via the placenta. These results might suggest an alternative maternal transport pathway, since FcRn binding to IgG does not depend on Fc-glycosylation. These early studies were performed by releasing N-glycans from total IgG. Here, we chose for an alternative approach analyzing IgG Fc glycosylation at the glycopeptide level in an Fc-specific manner, providing glycosylation profiles for IgG1 and IgG4 as well as combined Fc glycosylation profiles of IgG2 and 3. The analysis of ten pairs of fetal and maternal IgG samples revealed largely comparable Fc glycosylation for all the analyzed subclasses. Average levels of galactosylation, sialylation, bisecting GlcNAc and fucosylation were very similar for the fetal and maternal IgGs. Our data suggest that the placental IgG transport is not Fc glycosylation selective.

Generation of diploid Pichia pastoris strains by mating and their application for recombinant protein production

Background

Yeast mating provides an efficient means for strain and library construction. However, biotechnological applications of mating in the methylotrophic yeast Pichia pastoris have been hampered because of concerns about strain stability of P. pastoris diploids. The aim of the study reported here is to investigate heterologous protein expression in diploid P. pastoris strains and to evaluate diploid strain stability using high cell density fermentation processes.

Results

By using a monoclonal antibody as a target protein, we demonstrate that recombinant protein production in both wild-type and glycoengineered P. pastoris diploids is stable and efficient during a nutrient rich shake flask cultivation. When diploid strains were cultivated under bioreactor conditions, sporulation was observed. Nevertheless, both wild-type and glycoengineered P. pastoris diploids showed robust productivity and secreted recombinant antibody of high quality. Specifically, the yeast culture maintained a diploid state for 240 h post-induction phase while protein titer and N-linked glycosylation profiles were comparable to that of a haploid strain expressing the same antibody. As an application of mating, we also constructed an antibody display library and used mating to generate novel full-length antibody sequences.

Conclusions

To the best of our knowledge, this study reports for the first time a comprehensive characterization of recombinant protein expression and fermentation using diploid P. pastoris strains. Data presented here support the use of mating for various applications including strain consolidation, variable-region glycosylation antibody display library, and process optimization.

Enhanced bovine herpesvirus type 1 neutralization by multimerized single-chain variable antibody fragments regardless of differential glycosylation

Single-chain variable antibody fragments (scFvs) with a 2-amino-acid linker capable of multimerization as di-, tri-, or tetrabodies that neutralize bovine herpesvirus type 1 (BoHV-1) in vitro were constructed and expressed in Pichia pastoris. In contrast to the monomeric form, multimeric scFvs had a higher virus neutralization potency, as evidenced by a 2-fold increase in their ability to neutralize BoHV-1 due to avidity effects. Mass spectrum (quadrupole time of flight [Q-TOF]) analyses of multimeric scFv demonstrated extensive heterogeneity due to differential cleavage, variable glycosylation (1 to 9 mannose residues), and the incorporation of minor unidentified adducts. Regardless of the differential glycosylation patterns, the scFvs recognized non-gB or -gE target viral epitopes in the BoHV-1 envelope fraction in a Western blot and also neutralized BoHV-1 in infected Madin-Darby kidney (MDBK) cells in vitro. Indirect evidence for the noncovalent multimerization of scFv was the presence of a major peak of multimerized scFv without a His tag (due to differential cleavage) in the Q-TOF profile, unlike monomeric scFv, which copurified with normally His-tagged scFv and recognized the target antigen. Overall, differentially glycosylated recombinant scFvs against BoHV-1 with a short linker (2 amino acids) are capable of assembly into functional multimers that confer high avidity, resulting in increased virus neutralization in vitro compared to that of monovalent scFv with a long (18-amino-acid) flexible linker. Overall, recombinant multimerized scFv5-2L potentially provides a high-potency therapeutic and immunodiagnostic reagent against BoHV-1, which is suitable for passive immunization and topical application.

Influence of variable domain glycosylation on anti-neutrophil cytoplasmic autoantibodies and anti-glomerular basement membrane autoantibodies

Background

The pathophysiological significance of variable region glycosylation of autoantibodies is still unclear. In the current study, the influence of the variable region N-linked oligosaccharides on the reactivity of three autoantibody specificities was investigated with Sambucus nigra agglutinin (SNA), which mainly binds to oligosaccharides with terminal α2, 6-linked sialic acid on the variable region of IgG.

Methods

Twenty-seven patients with serum positive anti-neutrophil cytoplasmic autoantibodies (ANCA) against myeploperoxidase (MPO) or proteinase 3 (PR3), or autoantibodies against glomerular basement membrane (GBM) were included. Total IgG was isolated and separated into non-SNA-binding and SNA-binding fractions with SNA affinity chromatography. Antigen-specific IgG was purified by immunoaffinity chromatography.

Results

At the same concentration of IgG, the antigen binding level of non-SNA-binding IgG was significantly lower than that of SNA-binding IgG for MPO-ANCA (absorbance value at 405 nm, 0.572 ± 0.590 vs. 0.962 ± 0.670, P < 0.001) and for PR3-ANCA (0.362 ± 0.530 vs. 0.560 ± 0.531, P = 0.003). The antigen binding level of non-SNA-binding IgG was significantly higher than that of SNA-binding IgG for anti-GBM antibodies (1.301 ± 0.594 vs. 1.172 ± 0.583, P = 0.044). The level of variable region glycosylation of total IgG was significantly lower than that of affinity-purified MPO-ANCA (1.021 ± 0.201 vs. 1.434 ± 0.134, P = 0.004). The level of variable region glycosylation of total IgG was significantly higher than that of affinity-purified anti-GBM antibodies (1.034 ± 0.340 vs. 0.734 ± 0.333, P = 0.007). The SNA-binding fraction of MPO-ANCA-containing IgG and PR3-ANCA-containing IgG induced higher levels of neutrophil oxygen radical production than the corresponding non-SNA-binding fractions (P < 0.001 and P = 0.043, respectively). The level of variable region glycosylation of affinity-purified MPO-ANCA was higher in active AAV than the same patients in remission (P = 0.001).

Conclusion

Characteristics of variable region glycosylation of ANCA and anti-GBM antibodies were different from that of total IgG, which might influence the antigen-binding ability of these antibodies. Variable region glycosylation of ANCA might influence the effect of ANCA-induced neutrophils respiratory burst.

Glycosylation of surface Ig creates a functional bridge between human follicular lymphoma and microenvironmental lectins

Surface Ig (sIg) of follicular lymphoma (FL) is vital for tumor cell survival. We found previously that the Ig in FL is unusual, because the variable region genes carry sequence motifs for N-glycan addition. These are introduced by somatic mutation and are tumor specific. Unexpectedly, added glycans terminate at high mannose, suggesting a potentially important interaction of FL cells with mannose-binding lectins of the innate immune system. We have now identified mannosylated IgM at the surface of primary lymphoma cells. Recombinant lectin domains of the mannose receptor (MR) or DC-SIGN bind mannosylated Igs in vitro and bind to FL cells, signaling sIgM-associated increases in intracellular Ca(2+). Lectins also bind to normal B cells but fail to signal. In contrast, anti-Ig signaled similarly in both FL and normal B cells. Mannosylation patterns were mimicked by FL Ig-derived single-chain Fvs (scFv), providing probes for potential receptors. Mannosylated scFv bound specifically to the lectin domains of the MR and DC-SIGN and blocked signaling. Mannosylated scFv also bound to DC-SIGN on the surface of dendritic cells. This unique lymphoma-specific interaction of sIg with lectins of innate immunity reveals a potential route for microenvironmental support of tumor cells, mediated via the key B-cell receptor.

Glycosylation of Recombinant Antibody Therapeutics

The adaptive immune system has the capacity to produce antibodies with a virtually infinite repertoire of specificities. Recombinant antibodies specific for human targets are established in the clinic as therapeutics and represent a major new class of drug. Therapeutic efficacy depends on the formation of complexes with target molecules and subsequent activation of downstream biologic effector mechanisms that result in elimination of the target. The activation of effector mechanisms is dependent on structural characteristics of the antibody molecule that result from posttranslational modifications, in particular, glycosylation. The production of therapeutic antibody with a consistent human glycoform profile has been and remains a considerable challenge to the biopharmaceutical industry. Recent research has shown that individual glycoforms of antibody may provide optimal efficacy for selected outcomes. Thus a further challenge will be the production of a second generation of antibody therapeutics customized for their clinical indication.

Effect of constant and variable domain glycosylation on pharmacokinetics of therapeutic antibodies in mice

Previous studies on the effect of glycosylation on the elimination rate of antibodies have produced conflicting results. Here, we performed pharmacokinetic studies in mice with two preparations of a monoclonal IgG1 antibody enriched for complex type or high mannose type oligosaccharides at the Fc glycosylation site. No significant difference in the serum half-life was found between the two antibody glycoforms, nor was any difference observed in the serum half-lives of different complex type glycoforms. To evaluate the influence of glycosylation within the variable domain, a second monoclonal antibody, glycosylated in both the Fc and Fv domains, was separated into fractions containing different amounts of Fv-associated sialic acid and administered to mice. Again, no significant difference was found in the clearance rates of variants carrying different amounts of Fv-associated sialic acid or lacking Fv-glycosylation. These results suggest that glycosylation has little or no impact on the pharmacokinetic behavior of these two monoclonal antibodies in mice.

Remarkable selective glycosylation of the immunoglobulin variable region in follicular lymphoma

Follicular lymphoma (FL) generally expresses immunoglobulin (Ig) with somatically mutated variable (V) region genes. Surprisingly, these almost always carry introduced motifs available for N-glycosylation (Asn-X-Ser/Thr). Introduced motifs are uncommon on normal B cells, but are on other germinal center (GC)-associated B-cell malignancies suggesting a site-specific role. They are not evident in mutated chronic lymphocytic leukemia (CLL) or myeloma. Recently, we found that the glycosylation sites are unusual in containing oligomannose glycans, which are apparently displayed on tumor cell surface IgM. This suggests a potential interaction with a mannose receptor in the GC. However, natural N-glycosylation sites exist in germline (GL) V region genes, particularly the V4-34 gene expressed by normal B cells and by some malignancies, including CLL, potentially undermining the selective importance for FL. To compare oligosaccharide addition at the introduced and natural sites, we expressed V region genes as single chain Fv (scFv) and analyzed the added glycans. In contrast to introduced sites, which were oligomannosylated, the natural GL motif in the V4-34 sequence had no added sugars. The remarkable selective glycosylation within the heavy chain V region gene of FL apparently permits only limited processing to oligomannose at somatically mutated motifs, creating a feature exploitable by GC lymphomas.

Contrasting glycosylation profiles between Fab and Fc of a human IgG protein studied by electrospray ionization mass spectrometry

A conserved structural feature of human IgG molecules is the presence of an oligosaccharide moiety within the Fc region at Asn297. In addition, 15-20% of normal polyclonal IgG molecules bear N-linked oligosaccharides in the variable (V) regions of the light (L) and/or heavy (H) chains. Electrospray ionization mass spectrometry (ESI-MS) has been applied to the glycan analysis of two IgG1 myeloma proteins (Wid and Cri) after mild reduction and acidification. Heterogeneous ion peaks were observed for both the H and L chains of Wid in contrast to Cri whose L chain peak was homogeneous. Site-specific deglycosylation of the H and L chains of IgG Wid was achieved under native conditions with peptide-N-glycosidase F and endoglycosidase F2, respectively. The Fc glycoforms differed between the two proteins in that Cri-Fc bears diantennary complex-type glycans that are fully core-fucosylated and partially sialylated while Wid-Fc glycans are non-fucosylated, partially galactosylated and non-sialylated. In contrast to the Fc glycans, the L chain glycans of Wid were shown to be fucosylated, fully galactosylated and sialylated, indicating that the glycosylation machinery of the Wid-producing myeloma cells is intact. Thus, combination of the two endoglycosidases can provide a simple means of glycan analysis of both Fab and Fc by ESI-MS, which may contribute to the development of therapeutic IgG with customized glycan profiles.

The impact of glycosylation on the biological function and structure of human immunoglobulins

Immunoglobulins are the major secretory products of the adaptive immune system. Each is characterized by a distinctive set of glycoforms that reflects the wide variation in the number, type, and location of their oligosaccharides. In a given physiological state, glycoform populations are reproducible; therefore, disease-associated alterations provide diagnostic biomarkers (e.g., for rheumatoid arthritis) and contribute to disease pathogenesis. The oligosaccharides provide important recognition epitopes that engage with lectins, endowing the immunoglobulins with an expanded functional repertoire. The sugars play specific structural roles, maintaining and modulating effector functions that are physiologically relevant and can be manipulated to optimize the properties of therapeutic antibodies. New molecular models of all the immunoglobulins are included to provide a basis for informed and critical discussion. The models were constructed by combining glycan sequencing data with oligosaccharide linkage and dynamics information from the Glycobiology Institute experimental database and protein structural data from "The Protein Data Bank."

Human Follicular Lymphoma Cells Contain Oligomannose Glycans in the Antigen-binding Site of the B-cell Receptor

Expression of surface immunoglobulin appears critical for the growth and survival of B-cell lymphomas. In follicular lymphoma, we found previously that the Ig variable (V) regions in the B-cell receptor express a strikingly high incidence of N-glycosylation sequons, NX(S/T). These potential glycosylation sites are introduced by somatic mutation and are lymphoma-specific, pointing to their involvement in tumor pathogenesis. Analysis of the V region sugars from lymphoma-derived IgG/IgM reveals that they are mostly oligomannose and, remarkably, are located in the antigen-binding site, possibly precluding conventional antigen binding. The Fc region contains complex glycans, confirming that the normal glycan processing pathway is intact. Binding studies indicate that the oligomannose glycans occupying the V regions are accessible to mannose-binding lectin. These findings suggest a potential contribution to lymphoma pathogenesis involving antigen-independent interaction of surface immunoglobulin of the B-cell receptor with mannose-binding molecules of innate immunity in the germinal center.

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).

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.

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.

A point mutation in the Ch3 domain of human IgG3 inhibits antibody secretion without affecting antigen specificity

Immunoglobulins (Ig) require correct folding and assembly of both heavy (H) and light (L) chains to form a functional H2L2 dimer that is secreted from plasma cells. This process is dependent upon the endoplasmic reticulum (ER) chaperone BiP, which targets improperly, folded or assembled Ig molecules for degradation. While investigating the mechanism of low IgG3 secretion, we identified a missense mutation L368P in the Ch3 region of the human gamma3 H-chain that was associated with impaired secretion of intact and functional Ig. The non-secreted H-chains displayed slower electrophoretic migration than secreted H-chains, consistent with them being glycosylated in the ER but not fully processed in the golgi apparatus and secretory pathway. Reversion of the mutated codon to wild type restored secretion of the IgG3, which displayed the same fine specificity for antigen as non-secreted IgG3. However, the non-secreted IgG3 was not opsonic in an in vitro phagocytosis assay. The results indicate that correct IgG3 Ch3 domain folding is essential for secretion and effective function but does not affect specificity for antigen.