Roy Jefferis

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.

Glycosylation as a strategy to improve antibody-based therapeutics

To date, more than 20 recombinant immunoglobulin G (IgG) antibody therapeutics are licensed for the treatment of various diseases. The mechanism of action of recombinant monoclonal antibodies (rMAbs) has been extensively investigated and several distinct pathways have been defined; selective activation of specific pathways may optimize clinical outcomes for different diseases, such as cancer and chronic inflammation. Human IgG is a glycoprotein with oligosaccharides attached at a single site. These are essential to the mode of action of rMAbs, and the antibody efficacy can vary depending on the particular oligosaccharide that is attached. Methods are now becoming available that allow the production of rMAbs bearing pre-selected oligosaccharides — glycoforms — to provide maximum efficacy for a given disease indication. This Review summarizes current knowledge of these methods and avenues for their exploitation in the clinic.

IgG-Fc-mediated effector functions : molecular definition of interaction sites for effector ligands and the role of glycosylation

Summary: The Fr region of human IgG expresses interaction sites for many effector ligands. In this review the topographical distributions often of these sites are discussed in relation to functional requirement. It is apparent that interaction sites localised to the inter‐CH2‐CH3 domain region of the Fc allow for functional divalency, whereas sites localised to the hinge proximal region of the CH2 domain are functionally monovalent, with expression of the latter sites being particularly dependent on glycosylation. All x‐ray crystal structures for Fc and Fc‐ligand complexes report that the protein structure of the hinge proximal region of the CH2 domain is “disordered”, suggesting “internal mobility”. We propose a model in which such “internal mobility” results in the generation of a dynamic equilibrium between multiple conformers, certain of which express interaction sites specific to individual ligands. The emerging understanding of the influence of oligosaccharide/protein interactions on protein conformation and biological function of IgG antibodies suggests a potential to generate novel glycoforms of antibody molecules having unique profiles of effector functions.

Antibody therapeutics: isotype and glycoform selection.

Recombinant monoclonal antibody (rMAb) therapy may be instituted to achieve one of two broad outcomes: i) killing of cells or organisms (e.g., cancer cells, bacteria); and ii) neutralisation of soluble molecules (e.g., cytokines in chronic disease or toxins in infection). The choice of rMAb isotype is a critical decision in the development of a therapeutic antibody as it will determine the biological activities triggered in vivo. It is not possible, however, to accurately predict the in vivo activity because multiple parameters impact on the functional outcome, for example, IgG subclass, IgG-Fc glycoform, epitope density, cellular Fc receptors polymorphisms and so on. The present understanding of the molecular interactions between IgG-Fc and effector ligands in vitro has allowed the generation of new antibody structures with altered/improved effector function profiles that may prove optimal for given disease indications. Thus, when maximal antibody-dependent cell-mediated cytotoxicity activity is indicated a non-fucosylated IgG1 format may be optimal; when minimal activity is indicated an aglycosylated IgG2 may be the form of choice.

Use of antibody-coated red cells for the sensitive detection of antigen and in rosette tests for cells bearing surface immunoglobulins

Conditions for an improved chromic chloride method for the attachment of antibody to red cells are described. The method, which is applicable to whole Ig fractions as well as affinity-purified antibodies, is reproducible and has a sensitivity for detection of antigen in the nanogram range. The coated cells may be used in a rosette assay for the detection of cell surface-bound antigens.

Human immunoglobulin allotypes Possible implications for immunogenicity

More than twenty recombinant monoclonal antibodies are approved as therapeutics. Almost all of these are based on the whole IgG isotype format, but vary in the origin of the variable regions between mouse (chimeric), humanized mouse and fully human sequences; all of those with whole IgG format employ human constant region sequences. Currently, the opposing merits of the four IgG subclasses are considered with respect to the in vivo biological activities considered to be appropriate to the disease indication being treated. Human heavy chain genes also exhibit extensive structural polymorphism(s) and, being closely linked, are inherited as a haplotype. Polymorphisms (allotypes) within the IgG isotype were originally discovered and described using serological reagents derived from humans; demonstrating that allotypic variants can be immunogenic and provoke antibody responses as a result of allo-immunisation. The serologically defined allotypes differ widely within and between population groups; therefore, a mAb of a given allotype will, inevitably, be delivered to a cohort of patients homozygous for the alternative allotype. This publication reviews the serologically defined human IgG allotypes and considers the potential for allotype differences to contribute to or potentiate immunogenicity.

Glycosylation of human IgG-Fc: influences on structure revealed by differential scanning micro-calorimetry.

Glycosylation of the Fc region of IgG (IgG-Fc) is essential for the full expression of Fc effector functions. The profound differences in functional activity observed between glycosylated and aglycosylated IgG have not previously been paralleled by the demonstration of large-scale structural changes. In the present study differential scanning microcalorimetry (DSMC) was used to investigate IgG-Fc glycoprotein stability and to determine the thermodynamic parameters for thermal unfolding, which will include a contribution from the intra-molecular oligosaccharide-protein interactions. The thermogram obtained for glycosylated IgG1-Fc yielded two clearly defined transitions whilst the glycosylated IgG4-Fc exhibited a single transition. The methodology was also able to reveal measurable differences in the stability of IgG4-Fc glycoforms differing by the presence or absence of terminal galactose residues; deglycosylated IgG4-Fc exhibited two transitions with evidence for destabilisation of the C(H)2 domain.

Quantitation of the oligosaccharides of human serum IgG from patients with rheumatoid arthritis: a critical evaluation of different methods

Several different chromatographic methods and a lectin-based assay have been compared for the quantitation of oligosaccharides released from immunoglobulin G (IgG). The analysis of a series of IgG samples purified from the serum of rheumatoid arthritis patients was carried out by these methods to evaluate the percentage of the glycoforms having 0, 1 or 2 galactose residues (G0, G1 and G2) in order to (a) identify the method that can be most widely used for quantitation, (b) accurately define the range of G0 values found in patients with rheumatoid arthritis, and (c) make available a series of characterised standards for distribution to clinical chemistry laboratories. The chromatographic methods involved: release of oligosaccharides by glycoamidase A after protease digestion followed by HPLC analysis of aminopyridine derivatives on reverse phase and normal phase columns; hydrazinolysis treatment with exoglycosidases (G0 mix) and Biogel P4 chromatography of 2-aminobenzamide (2-AB) derivatives; hydrazinolysis and weak anion exchange or normal phase HPLC of 2-AB derivatives; release of oligosaccharides by PNGase F and either Biogel P4 chromatography of 2-AB derivatives or HPAEC-PAD analysis of native oligosaccharides. The G0 values given by these methods compared favourably with each other and a dot blot assay of denatured IgG interaction with Ricinus communis agglutinin and Bandeiraea simplicifolialectin II. The HPLC and HPAEC methods give additional information that may be important in less routine assays.

IgG1 heavy chain-coding gene polymorphism (G1m allotypes) and development of antibodies-to-infliximab

Objective The chimeric anti-tumor necrosis factor-&agr; antibody infliximab is known to induce antibodies-to-infliximab (ATI) in some treated patients. Immunogenicity in murine variable domains is expected; however, constant domains of its human heavy &ggr;1 chain may also be implicated as it expresses G1m1 and G1m17 allotypes. This allelic form may be immunogenic in patients that are homozygous for the G1m3 allotype commonly expressed in Caucasoid populations. Methods As G1m allotypic divergence may explain the presence of ATI or may influence their concentration, a genotyping method was developed and validated to determine antithetical (i.e. mutually exclusive) G1m3 and G1m17 allotypes (amino acid 120 of CH1 according to the international ImMunoGeneTics information system unique numbering) at the IGHG1 gene level (CH1 359g/a nucleotide polymorphism). Two hundred forty-five blood donors and 118 previously described patients suffering from Crohns disease, treated with infliximab, and having developed ATI in 73 of them, were genotyped. Results The IGHG1 CH1 359g/a polymorphism does not depart from the Hardy–Weinberg equilibrium in the control population, and allele frequencies were similar in controls and patients. No association was found between the patient G1m allotypes and the presence of ATI or their concentration. It remains possible that anti-Gm1 antibodies are not well detected by the enzyme-linked immunosorbent assays used for ATI detection and/or that the G1m allotypes are minor antigens on IgG1. Conclusion The IGHG1 polymorphism does not seem to play a major role in the induction of ATI. Further analyses will be required to determine whether it is also the case for humanized or fully human antibodies bearing the same G1m allotypes.

Human Antibodies Elicited by a Pneumococcal Vaccine Express Idiotypic Determinants Indicative of Vh3 Gene Segment Usage

Human immunodeficiency virus (HIV)-infected persons manifest decreased antibody responses to pneumococcal polysaccharide vaccines. Since human antibody responses to polysaccharides are often restricted, the molecular structure of antibodies elicited by a 23-valent pneumococcal vaccine was analyzed. Anti-idiotypic reagents were used to detect V(H)1, V(H)3, and V(H)4 gene usage by antibodies to pneumococcal capsular polysaccharides in HIV-uninfected and HIV-infected subjects by ELISA. HIV-uninfected persons generated beta-mercaptoethanol-sensitive and -resistant antibodies to pneumococcal capsular polysaccharides expressing V(H)3 determinants recognized by the D12, 16.84, and B6 monoclonal antibodies; antibodies expressing V(H)1 determinants were not detected, and V(H)4 determinants were expressed by beta-mercaptoethanol-sensitive antibodies only; and HIV-infected subjects had significantly lower capsular polysaccharide-specific and V(H)3-positive antibody responses. These findings confirm decreased antibody responses to pneumococcal vaccination in HIV-infected persons and suggest that their poor responses may result from HIV-associated depletion of restricted B cell subsets.