Spectroscopic studies on IgG aggregate formation

Spectroscopic properties of various blood antigens/antibodies

Since the traditional method generates biological waste, there is a significant demand for an easy, quick technique of blood type identification without contamination. In fact, individuals can be divided into four main blood groups whose antigens are available in red blood cell (RBC) membranes and the antibodies in the plasma. Here, UV-vis and photoluminescence (PL) spectroscopic methods are systematically used to find the spectra of blood typing antigens (A, B and AB) and antibodies i.e. A-Anti, B-Anti, AB-Anti and D reagent. The PL spectra of RBCs in different blood groups as well as the corresponding antibodies are successfully resolved for the purpose of blood typing. The unique photophysical characteristics of these biomolecules including signal intensity and peak emission wavelength in PL spectra are lucidly anticipated to accurately discriminate ABO groups. PL spectra of RBC in positive blood typing indicate larger signal and shorter emission peak wavelength corresponding to negative ones. Furthermore, the monoclonal antibody PL emissions emphasize that Anti-A benefits higher intensity and shorter peak wavelength (blue shift) than B-Anti. In the following, lucid blue shifts are obtained in terms of antibody concentrations accompanying the elevation of fluorescence signal, most likely due to the aggregation induced emission (AIE) phenomenon, quite the opposite of the aggregation-caused quenching (ACQ) that is widely observed from conventional chromophore. Those are envisaged as unique properties of each antibody to utilize in the spectral blood typing.

Monitoring antibody aggregation in early drug development using Raman spectroscopy and perturbation-correlation moving windows

In this study, we demonstrate the sensitivity of two-dimensional perturbation-correlation moving windows (PCMW) to characterize conformational transitions in antibodies. An understanding of how physiochemical properties affect protein stability and instigate aggregation is essential for the engineering of antibodies. In order to establish the potential of PCMW as a technique for early identification of aggregation mechanisms during antibody development, five antibodies with varying propensity to aggregate were compared. Raman spectra were acquired, using a 532 nm excitation wavelength as the protein samples were heated from 56 to 78 °C and analyzed with PCMW. Initial principal component analysis confirmed a trend between the observed spectral variations and increasing temperature for all five samples. Analysis using PCMW revealed that when spectral variations were directly related to temperature, distinct differences in conformational changes could be determined between samples related to protein stability, providing a greater understanding of the aggregation mechanisms of problematic antibody variants.

Temperature denaturation and aggregation of a multi-domain protein (IgG1) investigated with an array of complementary biophysical methods

Proteins are used as drugs against different pathologies because of their potential specificity of action with fewer side effects. However, their production and successful storage imposes a greater challenge compared to small molecule drugs. Though the determination of protein thermal stability is commonly used to find the optimum storage conditions for biopharmaceuticals, a multi-technique approach should be applied more often when investigating complex systems to understand the structure of the species that contribute to the different transitions, thereby gaining insight about the processes of both unfolding and aggregation. This knowledge is crucial for identifying those conformational changes which are likely to lead to aggregation/degradation allowing a more rational approach to biopharmaceutical production and formulation. This is particularly important in the case of multi-domain proteins, such as IgGs, which can undergo multiple transitions due to independent unfolding of the domains. In this work, we have followed the thermal denaturation of a monoclonal antibody by using different biophysical techniques with complementary strengths, providing an example of how the information gathered suggests a way to intervene to stabilise the wanted conformation (monomeric protein). Indeed, in this particular case, an optimisation of storage conditions based on only thermal stability studies would have led to the stabilisation of an undesired product, a population of low molecular weight oligomers.

Forced degradation of therapeutic proteins

The scope of this paper is to review approaches used for forced degradation (synonym, stress testing) of therapeutic proteins. Forced degradation studies play a central role in the development of therapeutic proteins, for example, for candidate selection, molecule characterization, formulation development, assay development, and comparability studies. Typical stress methods are addressed within this review, such as exposure to elevated temperatures, freeze-thawing, mechanical stress, oxidation, light, as well as various materials and devices used in the clinics during final administration. Stability testing is briefly described as far as relevant to the discussion of forced degradation studies. Whereas stability-testing requirements are defined in regulatory guidelines, standard procedures for forced degradation of therapeutic proteins are largely unavailable, except for photostability. Possible selection criteria to identify appropriate stress conditions and recommendations for setting up forced degradation studies for the different phases of development of therapeutic proteins are presented.

Evaluation of a non-Arrhenius model for therapeutic monoclonal antibody aggregation

Understanding antibody aggregation is of great significance for the pharmaceutical industry. We studied the aggregation of five different therapeutic monoclonal antibodies (mAbs) with size-exclusion chromatography-high-performance liquid chromatography (SEC-HPLC), fluorescence spectroscopy, electron microscopy, and light scattering methods at various temperatures with the aim of gaining insight into the aggregation process and developing models of it. In particular, we find that the kinetics can be described by a second-order model and are non-Arrhenius. Thus, we develop a non-Arrhenius model to connect accelerated aggregation experiments at high temperature to long-term storage experiments at low temperature. We evaluate our model by predicting mAb aggregation and comparing it with long-term behavior. Our results suggest that the number of monomers and mAb conformations within aggregates vary with the size and age of the aggregates, and that only certain sizes of aggregates are populated in the solution. We also propose a kinetic model based on conformational changes of proteins and monomer peak loss kinetics from SEC-HPLC. This model could be employed for a detail analysis of mAb aggregation kinetics.

High concentration formulation feasibility of human immunoglubulin G for subcutaneous administration

The delivery of monoclonal antibodies (mAbs) as subcutaneous (sc) injections hinges on the high dose requirement of these usually low potency molecules. This necessitates their formulation as high concentration solutions or suspensions, which presents a formidable formulation challenge due to the concentration-driven protein aggregation and high solution viscosity generated at these conditions. The objective of this study was to evaluate the feasibility of spray-drying in preparing stable, high concentration formulations of mAbs. A model polyclonal antibody, human immunoglobulin G (IgG) was formulated as dry powder using Nektar's glass stabilization technology. Formulation in sugar glasses stabilized IgG during spray-drying and maintained the protein's secondary structure. Further, in contrast to the bulk material, the glass-stabilized powders successfully reconstituted at 200 mg/mL IgG without loss of the protein monomer. Spectroscopic analysis confirmed that upon high concentration reconstitution, spray-dried glass-stabilized IgG retained both its secondary and tertiary structure. Further, the spray-dried powder reconstituted within a few minutes yielding clear, low viscosity solutions that syringed easily through narrow (28 G) needles. The results of this study suggest that formulation in spray-dried, glass-stabilized powders may enable the development of products suitable for sc administration of mAbs and other low potency protein therapeutics.

Immune Complexes Bind Preferentially to FcγRIIA (CD32) on Apoptotic Neutrophils, Leading to Augmented Phagocytosis by Macrophages and Release of Proinflammatory Cytokines

Many human inflammatory diseases are associated with tissue deposition of immune complexes and influx of neutrophils. We show that immune complexes bind preferentially to apoptotic neutrophils via FcgammaRIIA (CD32) and that increased binding is associated with clustering of immune complexes on the plasma membrane of the apoptotic cell. Phagocytosis of immune complex-opsonized apoptotic neutrophils by human macrophages was substantially enhanced (4.4-fold increase compared with control apoptotic neutrophils) and stimulated macrophages to release the proinflammatory cytokines TNF-alpha and IL-6. Immune complexes may perturb the normal pathways for clearance of apoptotic neutrophils by augmenting their clearance at the price of proinflammatory cytokine release. This represents a novel mechanism by which immune complexes may modulate the resolution of inflammation.

The thermal stability of immunoglobulin: unfolding and aggregation of a multi-domain protein

The denaturation of immunoglobulin G was studied by different calorimetric methods and circular dichroism spectroscopy. The thermogram of the immunoglobulin showed two main transitions that are a superimposition of distinct denaturation steps. It was shown that the two transitions have different sensitivities to changes in temperature and pH. The two peaks represent the F(ab) and F(c) fragments of the IgG molecule. The F(ab) fragment is most sensitive to heat treatment, whereas the F(c) fragment is most sensitive to decreasing pH. The transitions were independent, and the unfolding was immediately followed by an irreversible aggregation step. Below the unfolding temperature, the unfolding is the rate-determining step in the overall denaturation process. At higher temperatures where a relatively high concentration of (partially) unfolded IgG molecules is present, the rate of aggregation is so fast that IgG molecules become locked in aggregates before they are completely denatured. Furthermore, the structure of the aggregates formed depends on the denaturation method. The circular dichroism spectrum of the IgG is also strongly affected by both heat treatment and low pH treatment. It was shown that a strong correlation exists between the denaturation transitions as observed by calorimetry and the changes in secondary structure derived from circular dichroism. After both heat- and low-pH-induced denaturation, a significant fraction of the secondary structure remains.

Structural changes of IgG induced by heat treatment and by adsorption onto a hydrophobic Teflon surface studied by circular dichroism spectroscopy

Thermal denaturation of mouse monoclonal immunoglobulin G (isotype 1), as well as structural rearrangements resulting from adsorption on a hydrophobic Teflon surface, are studied by circular dichroism spectroscopy. Both heat-induced and adsorption-induced denaturation do not lead to complete unfolding into an extended polypeptide chain, but leave a significant part of the IgG molecule in a globular or corpuscular form. Heating dissolved IgG causes a decrease of the fractions of beta-sheet and beta-turn conformations, whereas those of random coil and, to a lesser extent, alpha-helix increase. Adsorption enhances the formation of alpha-helices and random coils, but the beta-sheet content is strongly reduced. Heating adsorbed IgG results in a gradual break-down of the alpha-helix and beta-turn contents, and a concomitant formation of beta-sheet structures. Thus, the structural changes in IgG caused by heating and by adsorption, respectively, are very different. However, after heating, the structure of adsorbed IgG approaches the structure of thermally denatured IgG in solution.

Binding of soluble natural ligands to a soluble human T-cell receptor fragment produced in Escherichia coli

An Escherichia coli expression system has been developed to produce milligram quantities of the variable domains of a human T-cell receptor from a cytotoxic T cell that recognizes the HLA-A2-influenza matrix peptide complex as a single polypeptide chain. The recombinant protein was purified by metal-chelate chromatography and then refolded in a redox buffer system. The refolded protein was shown to directly bind both Staphylococcus aureus enterotoxin B and the major histocompatibility complex protein-peptide complex using a BIAcore biosensor. Thus this preparation of a single-chain, variable-domain, T-cell receptor fragment can bind both of its natural ligands and some of it is therefore a functional fragment of the receptor molecule.

Interaction of aglycosyl immunoglobulins with the IgG Fc transport receptor from neonatal rat gut: comparison of deglycosylation by tunicamycin treatment and genetic engineering

The role of carbohydrate in the structure and function of immuno-globulin Fc regions has been studied using the interaction of a monoclonal mouse IgG2b anti-NIP antibody with the IgG Fc transport receptor from neonatal rat gut. An aglycosyl variant of this immunoglobulin, in which site-directed mutagenesis had been used to eliminate the carbohydrate attachment site in the CH2 domain by changing Asn297 to Ala, was compared in this system to aglycosyl immunoglobulin prepared from immunoglobulin-secreting cells treated with tunicamycin to inhibit N-linked glycosylation. Loss of carbohydrate from the heavy chain was confirmed for both methods by Western blotting of the separated chains with Concanavalin A, and no significant differences in circular dichroism spectra were found between glycosylated and non-glycosylated mutants. Removal of carbohydrate by site-directed mutagenesis had no effect on binding of the immunoglobulin to the Fc transport receptor (FcTR) in vitro or transport from the gut to blood in vivo. Short-term clearance from circulation and degradation by gut contents in vitro were similarly unaffected. Mutation of Glu235 to Leu, an alteration that allows binding to human monocyte Fc gamma RI, did not alter the interaction with FcTR. However, treatment of wild-type or aglycosyl mutant cells with tunicamycin resulted in immunoglobulin which was less stable, cleared more rapidly and was transported slightly less efficiently. These findings indicate that the binding site for the FcTR may be unique among Fc-binding ligands, and that tunicamycin treatment may cause alterations in the immunoglobulin molecule in addition to loss of N-linked carbohydrate.

Isolation and characterization of IgG2a-reactive autoantibodies from influenza virus-infected BALB/c mice

Repeated influenza virus infection induces the production of dominantly IgG2a-type virus-specific antibodies as well as the appearance of IgG2a-reactive autoantibodies in BALB/c mice characterized by low spontaneous rheumatoid factor-type autoantibody production. IgG2a-reactive autoantibody-producing hybridomas could be isolated from the spleen of influenza virus-infected BALB/c mice. The mAb produced by these clones represent not only IgM but also IgG and IgA isotypes and show strong isotype or isoallotype specificity. The common functional property of these autoantibodies is their preferential- and high-affinity binding to complexed, solid-phase-bound or heat-aggregated IgG2a when compared to native soluble or cell-bound IgG2a. The mechanism of induction and the possible biological function of these autoantibodies are discussed in the light of their fine specificity and functional properties.