Effects of subclass change on the structural stability of chimeric, humanized, and human antibodies under thermal stress

Single-domain antibodies and aptamers drive new opportunities for neurodegenerative disease research

Neurodegenerative diseases (NDs) in mammals, such as Alzheimer's disease (AD), Parkinson's disease (PD), and transmissible spongiform encephalopathies (TSEs), are characterized by the accumulation of misfolded proteins in the central nervous system (CNS). Despite the presence of these pathogenic proteins, the immune response in affected individuals remains notably muted. Traditional immunological strategies, particularly those reliant on monoclonal antibodies (mAbs), face challenges related to tissue penetration, blood-brain barrier (BBB) crossing, and maintaining protein stability. This has led to a burgeoning interest in alternative immunotherapeutic avenues. Notably, single-domain antibodies (or nanobodies) and aptamers have emerged as promising candidates, as their reduced size facilitates high affinity antigen binding and they exhibit superior biophysical stability compared to mAbs. Aptamers, synthetic molecules generated from DNA or RNA ligands, present both rapid production times and cost-effective solutions. Both nanobodies and aptamers exhibit inherent qualities suitable for ND research and therapeutic development. Cross-seeding events must be considered in both traditional and small-molecule-based immunodiagnostic and therapeutic approaches, as well as subsequent neurotoxic impacts and complications beyond protein aggregates. This review delineates the challenges traditional immunological methods pose in ND research and underscores the potential of nanobodies and aptamers in advancing next-generation ND diagnostics and therapeutics.

Light exacerbates local and global effects induced by pH unfolding of Ipilimumab

Monoclonal antibodies (mAbs) are an essential class of therapeutic proteins for the treatment of cancer, autoimmune and rare diseases. During their production, storage, and administration processes, these proteins encounter various stressors such as temperature fluctuations, vibrations, and light exposure, able to induce chemico-physical modifications to their structure. Viral inactivation is a key step in downstream processes, and it is achieved by titration of the mAb at low pH, followed by neutralization. The changes of the pH pose a significant risk of unfolding and subsequent aggregation to proteins, thereby affecting their manufacturing. This study aims to investigate whether a combined exposure to light during the viral inactivation process can further affect the structural integrity of Ipilimumab, a mAb primarily used in the treatment of metastatic melanoma. The biophysical and biochemical characterization of Ipilimumab revealed that pH variation is a considerable risk for its stability with irreversible unfolding at pH 2. The threshold for Ipilimumab denaturation lies between pH 2 and 3 and is correlated with the loss of the protein structural cooperativity, which is the most critical factor determining the protein refolding. Light has demonstrated to exacerbate some local and global effects making pH-induced exposed regions more vulnerable to structural and chemical changes. Therefore, specific precautions to real-life exposure to ambient light during the sterilization process of mAbs should be considered to avoid loss of the therapeutic activity and to increase the yield of production. Our findings underscore the critical role of pH optimization in preserving the structural integrity and therapeutic efficacy of mAbs. Moreover, a detailed conformational study on the structural modifications of Ipilimumab may improve the chemico-physical knowledge of this effective drug and suggest new production strategies for more stable products under some kind of stress conditions.

Extrapolating differential scanning calorimetry data for monoclonal antibodies to low temperatures

For irreversible denaturation transitions such as those exhibited by monoclonal antibodies, differential scanning calorimetry provides the denaturation temperature, Tm, the rate of denaturation at Tm, and the activation energy at Tm. These three quantities are essential but not sufficient for an accurate extrapolation of the rate of denaturation to temperatures of 25 °C and below. We have observed that the activation energy is not constant but temperature dependent due to the existence of an activation heat capacity, Cp,a. It is shown in this paper that a model that incorporates Cp,a is able to account for previous observations like, for example, that increasing the Tm does not always improve the stability at low temperatures; that some antibodies exhibit lower stabilities at 5 °C than at 25 °C; or that low temperature stabilities do not follow the rank order derived from Tm values. Most importantly, the activation heat capacity model is able to reproduce time dependent stabilities measured by size exclusion chromatography at low temperatures.

A case study of a bispecific antibody manufacturability assessment and optimization during discovery stage and its implications

The manufacturability assessment and optimization of bispecific antibodies (bsAbs) during the discovery stage are crucial for the success of the drug development process, impacting the speed and cost of advancing such therapeutics to the Investigational New Drug (IND) stage and ultimately to the market. The complexity of bsAbs creates challenges in employing effective evaluation methods to detect developability risks in early discovery stage, and poses difficulties in identifying the root causes and implementing subsequent engineering solutions. This study presents a case of engineering a bsAb that displayed a normal solution appearance during the discovery phase but underwent significant precipitation when subjected to agitation stress during 15 L Chemistry, Manufacturing, and Control (CMC) production Leveraging analytical tools, structural analysis, in silico prediction, and wet-lab validations, the key molecular origins responsible for the observed precipitation were identified and addressed. Sequence engineering to reduce protein surface hydrophobicity and enhance conformational stability proved effective in resolving agitation-induced aggregation. The refined bsAb sequences enabled successful mass production in CMC department. The findings of this case study contribute to the understanding of the fundamental mechanism of agitation-induced aggregation and offer a potential protein engineering procedure for addressing similar issues in bsAb. Furthermore, this case study emphasizes the significance of a close partnership between Discovery and CMC teams. Integrating CMC's rigorous evaluation methods with Discovery's engineering capability can facilitate a streamlined development process for bsAb molecules.

Systematic analysis of Fc mutations designed to reduce binding to Fc-gamma receptors

Elimination of the binding of immunoglobulin Fc to Fc gamma receptors is highly desirable for the avoidance of unwanted inflammatory responses to therapeutic antibodies and fusion proteins. Many different approaches have been used in the clinic, but they have not been systematically compared. We have now produced a matched set of anti-CD20 antibodies with different Fc subclasses and variants and compared their activity for binding to C1q, Fc-gamma receptors and in cell-based assays. Most of the variants still have significant levels of activity in one or more of these assays and many of them have impaired temperature stability compared with the corresponding wild-type antibody.

Systematic analysis of Fc mutations designed to enhance binding to Fc-gamma receptors

A critical attribute of therapeutic antibodies is their ability to engage with humoral or cellular effector mechanisms, and this depends on the ability of the Fc region to bind to complement (C1q) or Fc receptors. Investigators have sought to optimize these effects by engineering the Fc region to bind to a greater or lesser extent to individual receptors. Different approaches have been used in the clinic, but they have not been systematically compared. We have now produced a matched set of anti-CD20 antibodies representing a range of variants and compared their activity in cell-based assays for complement-dependent cytotoxicity, antibody-dependent cell-mediated cytotoxicity, and antibody-dependent phagocytosis using a range of individual Fc receptors. We have also compared the thermal stability of the variants by differential scanning fluorimetry (DSF). The results reveal a spectrum of activities which may be appropriate for different applications.

Role of Domain-Domain Interactions on the Self-Association and Physical Stability of Monoclonal Antibodies: Effect of pH and Salt

Monoclonal antibodies (mAbs) make up a major class of biotherapeutics with a wide range of clinical applications. Their physical stability can be affected by various environmental factors. For instance, an acidic pH can be encountered during different stages of the mAb manufacturing process, including purification and storage. Therefore, understanding the behavior of flexible mAb molecules in acidic solution environments will benefit the development of stable mAb products. This study used small-angle X-ray scattering (SAXS) and complementary biophysical characterization techniques to investigate the conformational flexibility and protein-protein interactions (PPI) of a model mAb molecule under near-neutral and acidic conditions. The study also characterized the interactions between Fab and Fc fragments under the same buffer conditions to identify domain-domain interactions. The results suggest that solution pH significantly influences mAb flexibility and thus could help mAbs remain physically stable by maximizing local electrostatic repulsions when mAbs become crowded in solution. Under acidic buffer conditions, both Fab and Fc contribute to the repulsive PPI observed among the full mAb at a low ionic strength. However, as ionic strength increases, hydrophobic interactions lead to the self-association of Fc fragments and, subsequently, could affect the aggregation state of the mAb.

Profiling the Biophysical Developability Properties of Common IgG1 Fc Effector Silencing Variants

Therapeutic antibodies represent the most significant modality in biologics, with around 150 approved drugs on the market. In addition to specific target binding mediated by the variable fragments (Fvs) of the heavy and light chains, antibodies possess effector functions through binding of the constant region (Fc) to Fcγ receptors (FcγR), which allow immune cells to attack and kill target cells using a variety of mechanisms. However, for some applications, including T-cell-engaging bispecifics, this effector function is typically undesired. Mutations within the lower hinge and the second constant domain (CH2) of IgG1 that comprise the FcγR binding interface reduce or eliminate effector function ("Fc silencing") while retaining binding to the neonatal Fc receptor (FcRn), important for normal antibody pharmacokinetics (PKs). Comprehensive profiling of biophysical developability properties would benefit the choice of constant region variants for development. Here, we produce a large panel of representative mutations previously described in the literature and in many cases in clinical or approved molecules, generate select combinations thereof, and characterize their binding and biophysical properties. We find that some commonly used CH2 mutations, including D265A and P331S, are effective in reducing binding to FcγR but significantly reduce stability, promoting aggregation, particularly under acidic conditions commonly employed in manufacturing. We highlight mutation sets that are particularly effective for eliminating Fc effector function with the retention of WT-like stability, including L234A, L235A, and S267K (LALA-S267K), L234A, L235E, and S267K (LALE-S267K), L234A, L235A, and P329A (LALA-P329A), and L234A, L235E, and P329G (LALE-P329G).

Strategies for overcoming protein and peptide instability in biodegradable drug delivery systems

The global pharmaceutical market has recently shifted its focus from small molecule drugs to peptide, protein, and nucleic acid drugs, which now comprise a majority of the top-selling pharmaceutical products on the market. Although these biologics often offer improved drug specificity, new mechanisms of action, and/or enhanced efficacy, they also present new challenges, including an increased potential for degradation and a need for frequent administration via more invasive administration routes, which can limit patient access, patient adherence, and ultimately the clinical impact of these drugs. Controlled-release systems have the potential to mitigate these challenges by offering superior control over in vivo drug levels, localizing these drugs to tissues of interest (e.g., tumors), and reducing administration frequency. Unfortunately, adapting controlled-release devices to release biologics has proven difficult due to the poor stability of biologics. In this review, we summarize the current state of controlled-release peptides and proteins, discuss existing techniques used to stabilize these drugs through encapsulation, storage, and in vivo release, and provide perspective on the most promising opportunities for the clinical translation of controlled-release peptides and proteins.

Treatment alternatives for multidrug-resistant fungal pathogens

Several fungal pathogens are becoming resistant to conventional fungal infection treatments, and some fungal pathogens have become multidrug resistant. Alternative treatments include fungal vaccines, natural or synthetic monoclonal antibody (mAb) injections, or potentially natural or synthetic mAbs produced in vivo by packaged mRNA. Specifically synthesized proteins can mask distinctive pathogenic fungal surface proteins and target pathogenic fungal proteins to stop fungal infections. Treatments could use direct injections or injections of packaged mRNA with instructions for patient synthesis of either the natural or synthetic mAbs. These alternative treatments offer potentially significant advantages compared with existing treatments for fungal pathogens. Teaser: New fungal pathogen treatment approaches can use natural or synthetic monoclonal antibodies to activate immune cells and treat specific fungal infections that are now multidrug resistant to conventional antifungal drugs.

Constant domain polymorphisms influence monoclonal antibody stability and dynamics

The constant regions of clinical monoclonal antibodies are derived from a select number of allotypes found in IgG subclasses. Despite a long-term acknowledgment that this diversity may impact both antibody function and developability, there is a lack of data on the stability of variants carrying these mutations. Here, we generated a panel of IgG1, IgG2, and IgG3 antibodies with 32 unique constant region alleles and performed a systematic comparison of stability using red edge excitation shift (REES). This technique exploits the fluorescent properties of tryptophan residues to measure antibody structural dynamics which predict flexibility and the propensity to unfold. Our REES measurements revealed broad stability differences between subclasses with IgG3 possessing the poorest overall stability. Further interrogation of differences between variants within each subclass enabled the high-resolution profiling of individual allotype stabilities. Crucially, these observed differences were not found to be linked to N297-linked glycan heterogeneity. Our work demonstrates diverse stabilities (and dynamics) for a range of naturally occurring constant domain alleles and the utility of REES as a method for rapid and sensitive antibody stability profiling, requiring only laboratory spectrophotometry equipment.

Modeling study of long-term stability of the monoclonal antibody infliximab and biosimilars using liquid-chromatography-tandem mass spectrometry and size-exclusion chromatography-multi-angle light scattering

Monoclonal antibodies (mAbs) represent a dynamic class of biopharmaceutical products, as evidenced by an increasing number of market authorizations for mAb innovator and biosimilar products. Stability studies are commonly performed during product development, for instance, to exclude unstable molecules, optimize the formulation or determine the storage limit. Such studies are time-consuming, especially for mAbs, because of their structural complexity which requires multiple analytical techniques to achieve a detailed characterization. We report the implementation of a novel methodology based on the accelerated stability assessment program (ASAP) in order to model the long-term stability of mAbs in relation to different structural aspects. Stability studies of innovator infliximab and two different biosimilars were performed using forced degradation conditions alongside in-use administration conditions in order to investigate their similarity regarding stability. Thus, characterization of post-translational modifications was achieved using liquid-chromatography-tandem mass spectrometry (LC-MS/MS) analysis, and the formation of aggregates and free chain fragments was characterized using size-exclusion chromatography-multi-angle light scattering (SEC-MALS-UV/RI) analysis. Consequently, ASAP models were investigated with regard to free chain fragmentation of mAbs concomitantly with N57 deamidation, located in the hypervariable region. Comparison of ASAP models and the long-term stability data from samples stored in intravenous bags demonstrated a relevant correlation, indicating the stability of the mAbs. The developed methodology highlighted the particularities of ASAP modeling for mAbs and demonstrated the possibility to independently consider the different types of degradation pathways in order to provide accurate and appropriate prediction of the long-term stability of this type of biomolecule.

Impact of IgG subclass on monoclonal antibody developability

IgG-based monoclonal antibody therapeutics, which are mainly IgG1, IgG2, and IgG4 subclasses or related variants, have dominated the biotherapeutics field for decades. Multiple laboratories have reported that the IgG subclasses possess different molecular characteristics that can affect their developability. For example, IgG1, the most popular IgG subclass for therapeutics, is known to have a characteristic degradation pathway related to its hinge fragility. However, there remains a paucity of studies that systematically evaluate the IgG subclasses on manufacturability and long-term stability. We thus conducted a systematic study of 12 mAbs derived from three sets of unrelated variable regions, each cloned into IgG1, an IgG1 variant with diminished effector functions, IgG2, and a stabilized IgG4 variant with further reduced FcγR interaction, to evaluate the impact of IgG subclass on manufacturability and high concentration stability in a common formulation buffer matrix. Our evaluation included Chinese hamster ovary cell productivity, host cell protein removal efficiency, N-linked glycan structure at the conserved N297 Fc position, solution appearance at high concentration, and aggregate growth, fragmentation, charge variant profile change, and post-translational modification upon thermal stress conditions or long-term storage at refrigerated temperature. Our results elucidated molecular attributes that are common to all IgG subclasses, as well as those that are unique to certain Fc domains, providing new insight into the effects of IgG subclass on antibody manufacturability and stability. These learnings can be used to enable a balanced decision on IgG subclass selection for therapeutic antibodies and aid in acceleration of their product development process.

Penpulimab for Relapsed or Refractory Classical Hodgkin Lymphoma: A Multicenter, Single-Arm, Pivotal Phase I/II Trial (AK105-201)

Background

Nearly all anti-PD-1 antibodies are of the IgG4 isotype, and thus possess residual FcR effector functions. Such anti-PD-1 antibodies are also associated with immune tolerance and escape due to instability of the CH3 domain and Fc-Fc interaction. In this trial, we examined the efficacy and safety of penpulimab, a novel IgG1 anti-PD-1 antibody that does not bind to the Fc receptor, in patients with refractory or relapsed classical Hodgkin lymphoma (R/R cHL).

Methods

Adult patients (≥18 years of age) with R/R cHL received 200 mg penpulimab once biweekly until disease progression or unacceptable toxicities for a maximum of 24 months. The primary endpoint was objective response rate (ORR) based on the Independent Radiology Review Committee per Lugano 2014 criteria. Secondary endpoints included progression-free survival (PFS), overall survival (OS), treatment-related adverse events (TRAEs) and immune-related adverse events (irAEs).

Results

A total of 94 patients were enrolled. The median follow-up was 15.8 months. The ORR was 89.4% (95% CI 80.8%, 95.0%) in the full analysis set (85 patients). Forty (47.1%) patients achieved complete remission, 36 (42.4%) patients achieved partial remission. The 12-month PFS rate was 72.1% (95% CI 60.5%, 80.8%) and the 18-month OS rate was 100%. Totally 97.9% (92/94) of patients experienced at least one TRAE. The rate of grade 3 and above TRAEs was 26.6% (25/94). In addition, 51 (54.3%) patients experienced an irAE, and 4 (4.3%) patients developed grade 3 or above irAEs. No irAE-related death occurred.

Conclusions

Penpulimab was effective and safe in patients with R/R cHL.

Integrated continuous biomanufacturing on pilot scale for acid-sensitive monoclonal antibodies

In this study, we demonstrated the first, to our knowledge, integrated continuous bioprocess (ICB) designed for the production of acid-sensitive monoclonal antibodies, prone to aggregate at low pH, on pilot scale. A high cell density perfusion culture, stably maintained at 100 x 10⁶ cells/mL, was integrated with the downstream process, consisting of a capture step with the recently developed Protein A ligand, Z_Ca ; a solvent/detergent-based virus inactivation; and two ion exchange chromatography steps. The use of a mild pH in the downstream process makes this ICB suitable for the purification of acid-sensitive monoclonal antibodies. Integration and automation of the downstream process were achieved using the Orbit software, and the same equipment and control system were used in initial small-scale trials and the pilot-scale downstream process. High recovery yields of around 90% and a productivity close to 1 g purified antibody/L/day were achieved, with a stable glycosylation pattern and efficient removal of impurities, such as host cell proteins and DNA. Finally, negligible levels of antibody aggregates were detected owing to the mild conditions used throughout the process. The present work paves the way for future industrial-scale integrated continuous biomanufacturing of all types of antibodies, regardless of acid stability. This article is protected by copyright. All rights reserved.

Impact of IgG subclass on molecular properties of monoclonal antibodies

Immunoglobulin G-based monoclonal antibodies (mAbs) have become a dominant class of biotherapeutics in recent decades. Approved antibodies are mainly of the subclasses IgG1, IgG2, and IgG4, as well as their derivatives. Over the decades, the selection of IgG subclass has frequently been based on the needs of Fc gamma receptor engagement and effector functions for the desired mechanism of action, while the effect on drug product developability has been less thoroughly characterized. One of the major reasons is the lack of systematic understanding of the impact of IgG subclass on the molecular properties. Several efforts have been made recently to compare molecular property differences among these IgG subclasses, but the conclusions from these studies are sometimes obscured by the interference from variable regions. To further establish mechanistic understandings, we conducted a systematic study by grafting three independent variable regions onto human IgG1, an IgG1 variant, IgG2, and an IgG4 variant constant domains and evaluating the impact of subclass and variable regions on their molecular properties. Structural and computational analysis revealed specific molecular features that potentially account for the differential behavior of the IgG subclasses observed experimentally. Our data indicate that IgG subclass plays a significant role on molecular properties, either through direct effects or via the interplay with the variable region, the IgG1 mAbs tend to have higher solubility than either IgG2 or IgG4 mAbs in a common pH 6 buffer matrix, and solution behavior relies heavily on the charge status of the antibody at the desirable pH.

Reversibility and irreversibility in the temperature denaturation of monoclonal antibodies

There have been numerous studies of the temperature denaturation of monoclonal antibodies (mAbs) using differential scanning calorimetry (DSC). In general, mAbs are characterized by complex temperature denaturation transitions in which the various domains (CH2, CH3, Fab) give rise to different peaks in the heat capacity function. The complexity and overall irreversibility of the temperature denaturation transition is well known and has limited the number of publications with an in-depth analysis of the data. Here we report that the temperature denaturation of the CH2 domain is reversible and only becomes irreversible after denaturation of the Fab domain, which is intrinsically irreversible. For these studies we have used the HIV neutralizing monoclonal antibody 17b. To account for the experimental heat capacity function, a mixed denaturation model that combines multiple reversible and irreversible transitions has been developed. This model accounts well for the DSC data and for the pH dependence of the heat capacity function of 17b and other monoclonal antibodies for which data is available in the literature. It is expected that a more detailed analysis of the stability of monoclonal antibodies will contribute to the development of better approaches to understand and optimize the structural viability of these therapeutic macromolecules.

Coming together at the hinges: Therapeutic prospects of IgG3

The human IgG3 subclass is conspicuously absent among the formats for approved monoclonal antibody therapies and Fc fusion protein biologics. Concern about the potential for rapid degradation, reduced plasma half-life, and increased immunogenicity due to marked variation in allotypes has apparently outweighed the potential advantages of IgG3, which include high affinity for activating Fcγ receptors, effective complement fixation, and a long hinge that appears better suited for low abundance targets. This review aims to highlight distinguishing features of IgG3 and to explore its functional role in the immune response. We present studies of natural immunity and recombinant antibody therapies that elucidate key contributions of IgG3 and discuss historical roadblocks that no longer remain clearly relevant. Collectively, this body of evidence motivates thoughtful reconsideration of the clinical advancement of this distinctive antibody subclass for treatment of human diseases. Abbreviations: ADCC - Antibody-Dependent Cell-mediated CytotoxicityADE - Antibody-dependent enhancementAID - Activation-Induced Cytidine DeaminaseCH - Constant HeavyCHF - Complement factor HCSR - Class Switch RecombinationEM - Electron MicroscopyFab - Fragment, antigen bindingFc - Fragment, crystallizableFcRn - Neonatal Fc ReceptorFcγR - Fc gamma ReceptorHIV - Human Immunodeficiency VirusIg - ImmunoglobulinIgH - Immunoglobulin Heavy chain geneNHP - Non-Human Primate.

Highly selective Protein A resin allows for mild sodium chloride-mediated elution of antibodies

The manufacturability of therapeutic monoclonal antibodies is limited by the harsh conditions that antibodies are subjected to during the purification procedure, which in turn restricts the development of novel acid-sensitive antibodies. The gold standard for antibody purification, Protein A affinity chromatography, offers the selective capture of antibodies with great yields, but also poses a threat to the quality of the antibodies. Antibodies and Fc-fusion proteins risk forming aggregates as a consequence of the acidic elution from the Protein A ligands, compromising the potency and safety of the drug. Here, we present a novel, mild purification strategy based on a calcium-dependent ligand derived from Protein A, called Z_Ca. Antibodies captured on a high-capacity tetrameric Z_Ca resin in the presence of calcium can be eluted by removing the calcium ions through the addition of a chelator, and we describe the strive to find a sustainable alternative to the previously applied chelator EDTA. The naturally occurring chelator citrate is shown to seamlessly replace EDTA. Further buffer optimization reveals that the elution can be considerably improved by increasing the conductivity through the addition of 300 mM sodium chloride, leading to a very concentrated eluate. Remarkably, merely sodium chloride at a concentration of 50 mM is proven to be sufficient for calcium-dependent antibody release in a cost-efficient manner. Antibodies of subclasses IgG2 and IgG4 are eluted with sodium chloride at neutral pH and IgG1 at pH 6, due to varying affinities for the tetrameric Z_Ca, ranging between 90-780 nM. The mild elution of an IgG4 antibody eliminated the formation of aggregates, which constituted as much as 34% of all eluted antibody from MabSelect SuRe at pH 3. This novel purification strategy thus combines the valuable qualities of a Protein A resin, by providing high selectivity and a recovery of 88-99%, with an exceptionally mild elution step similar to ion-exchange chromatography, rendering considerably more functional antibody.

Generation of human scFv-IgG1Fc antibodies for detection of lymphatic filarial recombinant antigens, BmR1 and BmSXP

Lymphatic filariasis is a neglected parasitic disease that affects millions in tropical and subtropical countries and is caused by Wuchereria and Brugia species. Specific and sensitive detection methods are essential in mapping infected areas where rapid tests are needed to cover underdeveloped and remote regions, which facilitates eliminating the disease as a public health problem. A few commercialized rapid tests based on antigen or antibody detection are available, but the former only detects infection by Wuchereria species and cross-reacts with nonlymphatic filaria, whereas antibody detection might provide positive results of previous infection. Here, we report the production of three different recombinant immunoglobulin gamma (IgG)1 antibodies based on scFvs previously generated via human antibody phage display technology, that is, anti-BmR1 clone 4, anti-BmXSP clone 5B, and anti-BmXSP clone 2H2. The scFv sequences were cloned into a pCMV-IgG1 vector, then transfected into a HEK293F cell line. The generated antibodies were found to be able to bind to their respective targets even at relatively low concentration. Conjugation of Fc to scFv induces binder stability and provides multiple labeling sites for probes and signaling molecules that can be used in rapid tests.

Developability assessment for monoclonal antibody drug candidates: a case study

Various screening approaches are used by industry to evaluate development risks associated with discovery candidates. This process has become more complicated with biological therapeutics, a class dominated by monoclonal antibodies (mAb), and, increasingly, their derivative constructs. Effective early assessment for drug-like properties (DLP) can save time and costs by allowing a more complete consideration of issues that could impact the desired end result of a stable drug product. Here we report a case study of four IgG1 mAbs, with sequence variations in the variable domain region, screened as a set of possible drug candidates. Our comprehensive, tiered approach used a battery of analytical tools to assess molecular characteristics, conformational stability, colloidal stability, and short-term storage stability. While most DLP for the four candidates were developmentally acceptable and comparable, mAb-2 was associated with adverse colloidal properties. Further investigation of mAb-2 in an expanded pH range revealed a propensity for phase separation, indicating a need for the additional product development effort. Our results support that comprehensive DLP assessments in an expanded pH range are beneficial in identifying development options for promising molecules that show challenging stability trends. This adaptable approach may be especially useful in the development of increasingly complex antibody constructs.

Antibody stability: A key to performance - Analysis, influences and improvement

An antibody's stability greatly influences its performance (i.e. its specificity and affinity). Thus, stability is a major issue for researchers and manufacturers, especially with the increasing use of antibodies in therapeutics, diagnostics and rapid analytical platforms. Here we review antibody stability under five headings: (i) measurement techniques; (ii) stability issues in expression and production (expression, proteolysis, aggregation); (iii) effects of antibody format and engineering on stability and (iv) formulation, drying and storage conditions. We consider more than 100 sources, including patents, and conclude with (v) recommendations to promote antibody stability.

R409K mutation prevents acid-induced aggregation of human IgG4

Human immunoglobulin G isotype 4 (IgG4) antibodies are suitable for use in either the antagonist or agonist format because their low effector functions prevent target cytotoxicity or unwanted cytokine secretion. However, while manufacturing therapeutic antibodies, they are exposed to low pH during purification, and IgG4 is more susceptible to low-pH-induced aggregation than IgG1. Therefore, we investigated the underlying mechanisms of IgG4 aggregation at low pH and engineered an IgG4 with enhanced stability. By swapping the constant regions of IgG1 and IgG4, we determined that the constant heavy chain (CH3) domain is critical for aggregate formation, but a core-hinge-stabilizing S228P mutation in IgG4 is insufficient for preventing aggregation. To identify the aggregation-prone amino acid, we substituted the CH3 domain of IgG4 with that of IgG1, changing IgG4 Arg409 to a Lys, thereby preventing the aggregation of the IgG4 variant as effectively as in IgG1. A stabilizing effect was also recorded with other variable-region variants. Analysis of thermal stability using differential scanning calorimetry revealed that the R409K substitution increased the Tm value of CH3, suggesting that the R409K mutation contributed to the structural strengthening of the CH3-CH3 interaction. The R409K mutation did not influence the binding to antigens/human Fcγ receptors; whereas, the concurrent S228P and R409K mutations in IgG4 suppressed Fab-arm exchange drastically and as effectively as in IgG1, in both in vitro and in vivo in mice models. Our findings suggest that the IgG4 R409K variant represents a potential therapeutic IgG for use in low-effector-activity format that exhibits increased stability.

Thermal and Chemical Unfolding of a Monoclonal IgG1 Antibody: Application of the Multistate Zimm-Bragg Theory

The thermal unfolding of a recombinant monoclonal antibody IgG1 (mAb) was measured with differential scanning calorimetry (DSC). The DSC thermograms reveal a pretransition at 72°C with an unfolding enthalpy of ΔH_cal ∼200-300 kcal/mol and a main transition at 85°C with an enthalpy of ∼900-1000 kcal/mol. In contrast to small single-domain proteins, mAb unfolding is a complex reaction that is analyzed with the multistate Zimm-Bragg theory. For the investigated mAb, unfolding is characterized by a cooperativity parameter σ ∼6 × 10^-5 and a Gibbs free energy of unfolding of g_nu ∼100 cal/mol per amino acid. The enthalpy of unfolding provides the number of amino acid residues ν participating in the unfolding reaction. On average, ν∼220 ± 50 amino acids are involved in the pretransition and ν∼850 ± 30 in the main transition, accounting for ∼90% of all amino acids. Thermal unfolding was further studied in the presence of guanidineHCl. The chemical denaturant reduces the unfolding enthalpy ΔH_cal and lowers the midpoint temperature T_m. Both parameters depend linearly on the concentration of denaturant. The guanidineHCl concentrations needed to unfold mAb at 25°C are predicted to be 2-3 M for the pretransition and 5-7 M for the main transition, varying with pH. GuanidineHCl binds to mAb with an exothermic binding enthalpy, which partially compensates the endothermic mAb unfolding enthalpy. The number of guanidineHCl molecules bound upon unfolding is deduced from the DSC thermograms. The bound guanidineHCl-to-unfolded amino acid ratio is 0.79 for the pretransition and 0.55 for the main transition. The pretransition binds more denaturant molecules and is more sensitive to unfolding than the main transition. The current study shows the strength of the Zimm-Bragg theory for the quantitative description of unfolding events of large, therapeutic proteins, such as a monoclonal antibody.

Engineering a human IgG2 antibody stable at low pH

IgG2 subclass antibodies have unique properties that include low effector function and a rigid hinge region. Although some IgG2 subclasses have been clinically tested and approved for therapeutic use, they have a higher propensity than IgG1 for aggregation, which can curtail or abolish their biological activity and enhance their immunogenicity. In this regard, acid-induced aggregation of monoclonal antibodies during purification and virus inactivation must be prevented. In the present study, we replaced the constant domain of IgG2 with that of IgG1, using anti-2,4-dinitrophenol (DNP) IgG2 as a model antibody, and investigated whether that would confer greater stability. While the anti-DNP IgG2 antibody showed significant aggregation at low pH, this was reduced for the IgG2 antibody containing the IgG1 CH2 domain. Substituting three amino acids within the CH2 domain-namely, F300Y, V309L, and T339A (IgG2_YLA)-reduced aggregation at low pH and increased CH2 transition temperature, as determined by differential scanning calorimetric analysis. IgG2_YLA exhibited similar antigen-binding capacity to IgG2, low affinity for FcγRIIIa, and low binding ability to C1q. The same YLA substitution also reduced the aggregation of panitumumab, another IgG2 antibody, at low pH. Our engineered human IgG2 antibody showed reduced aggregation during bioprocessing and provides a basis for designing improved IgG2 antibodies for therapeutic applications.

Considerations for the Design of Antibody-Based Therapeutics

Antibody-based proteins have become an important class of biologic therapeutics, due in large part to the stability, specificity, and adaptability of the antibody framework. Indeed, antibodies not only have the inherent ability to bind both antigens and endogenous immune receptors but also have proven extremely amenable to protein engineering. Thus, several derivatives of the monoclonal antibody format, including bispecific antibodies, antibody-drug conjugates, and antibody fragments, have demonstrated efficacy for treating human disease, particularly in the fields of immunology and oncology. Reviewed here are considerations for the design of antibody-based therapeutics, including immunological context, therapeutic mechanisms, and engineering strategies. First, characteristics of antibodies are introduced, with emphasis on structural domains, functionally important receptors, isotypic and allotypic differences, and modifications such as glycosylation. Then, aspects of therapeutic antibody design are discussed, including identification of antigen-specific variable regions, choice of expression system, use of multispecific formats, and design of antibody derivatives based on fragmentation, oligomerization, or conjugation to other functional moieties. Finally, strategies to enhance antibody function through protein engineering are reviewed while highlighting the impact of fundamental biophysical properties on protein developability.

Antigen-binding affinity and thermostability of chimeric mouse-chicken IgY and mouse-human IgG antibodies with identical variable domains

Constant (C)-region switching of heavy (H) and/or light (L) chains in antibodies (Abs) can affect their affinity and specificity, as demonstrated using mouse, human, and chimeric mouse-human (MH) Abs. However, the consequences of C-region switching between evolutionarily distinct mammalian and avian Abs remain unknown. To explore C-region switching in mouse-chicken (MC) Abs, we investigated antigen-binding parameters and thermal stability of chimeric MC-6C407 and MC-3D8 IgY Abs compared with parental mouse IgGs and chimeric MH Abs (MH-6C407 IgG and MH-3D8 IgG) bearing identical corresponding variable (V) regions. The two MC-IgYs exhibited differences in antigen-binding parameters and thermal stability from their parental mouse Abs. However, changes were similar to or less than those between chimeric MH Abs and their parental mouse Abs. The results demonstrate that mammalian and avian Abs share compatible V-C region interfaces, which may be conducive for the design and utilization of mammalian-avian chimeric Abs.

Assessing localized conformational stability of antibody-drug conjugate by protein conformation assay

Antibody-drug conjugates (ADCs) are a class of attractive therapeutic agents to fight cancer with conjugation of potent chemical agents on target-selective antibodies. The conceptually elegant approach has encountered mounting practical challenges in combining the mAb and potent drug while maintaining the conformational and physiochemical stability of the bioconjugates. The attachment of hydrophobic drug-linker with antibody could potentially alter the antibody conformational scaffold, locally or globally. Here we propose to use a protein conformation assay (PCA) to measure the higher-order structure of antibodies upon drug-linker conjugation. The PCA analysis provides insights into the formation of partially unfolded ADCs, which may correlate with protein stability and aggregation propensity. To further elucidate the cause of the unfolding events, in-depth peptide mapping combined with the PCA conformational footprints were performed on a commercial ADC trastuzumab emtansine in this study. The locally altered conformational hot-spots observed in PCA matched with conjugation sites with high occupancy rate identified in peptide mapping. In summary, by combining PCA and in-depth peptide mapping, a snapshot of ADC structural conformation and stability profile could be obtained and provide a swift and convenient measurement of the 'fitness' of ADC to facilitate payload selection, conjugation process development and early predictive developability assessment.

Protein aggregation and mitigation strategy in low pH viral inactivation for monoclonal antibody purification

Significant amounts of soluble product aggregates were observed during low-pH viral inactivation (VI) scale-up for an IgG4 monoclonal antibody (mAb IgG4-N1), while small-scale experiments in the same condition showed negligible aggregation. Poor mixing and product exposure to low pH were identified as the root cause. To gain a mechanistic understanding of the problem, protein aggregation properties were studied by varying critical parameters including pH, hold time and protein concentration. Comprehensive biophysical characterization of product monomers and aggregates was performed using fluorescence-size-exclusion chromatography, differential scanning fluorimetry, fluorescence spectroscopy, and dynamic light scattering. Results showed IgG4-N1 partially unfolds at about pH 3.3 where the product molecules still exist largely as monomers owing to strong inter-molecular repulsions and favorable colloidal stability. In the subsequent neutralization step, however, the conformationally changed monomers are prone to aggregation due to weaker inter-molecular repulsions following the pH transition from 3.3 to 5.5. Surface charge calculations using homology modeling suggested that intra-molecular repulsions, especially between CH2 domains, may contribute to the IgG4-N1 unfolding at ≤ pH 3.3. Computational fluid dynamics (CFD) modeling was employed to simulate the conditions of pH titration to reduce the risk of aggregate formation. The low-pH zones during acid addition were characterized using CFD modeling and correlated to the condition causing severe product aggregation. The CFD tool integrated with the mAb solution properties was used to optimize the VI operating parameters for successful scale-up demonstration. Our research revealed the governing aggregation mechanism for IgG4-N1 under acidic conditions by linking its molecular properties and various process-related parameters to macroscopic aggregation phenomena. This study also provides useful insights into the cause and mitigation of low-pH-induced IgG4 aggregation in downstream VI operation.

Effect of allotypic variation of human IgG1 on the thermal stability of disulfide-linked knobs-into-holes mutants of the Fc for stable bispecific antibody design

Background

Disulfide-linked knobs-into-holes (dKiH) mutation is a well-validated antibody engineering technique to force heterodimer formation of different Fcs for efficient production of bispecific antibodies. An artificial disulfide bond is created between mutated cysteine residues in CH3 domain of human IgG1 Fc whose positions are 354 of the “knob” and 349 of the “hole” heavy chains. The disulfide bond is located adjacent to the exposed loop with allotypic variations at positions 356 and 358. Effects of the variation on the biophysical property of the Fc protein with dKiH mutations have not been reported.

Methods

We produced dKiH Fc proteins of high purity by affinity-tag fusion to the hole chain and IdeS treatment, which enabled removal of mispaired side products. Thermal stability was analyzed in a differential scanning calorimetry instrument.

Results

We firstly analyzed the effect of the difference in allotypes of the Fcs on the thermal stability of the heterodimeric Fc. We observed different melting profiles of the two allotypes (G1m1 and nG1m1) showing slightly higher melting temperature of G1m1 than nG1m1. Additionally, we showed different characteristics among heterodimers with different combinations of the allotypes in knob and hole chains.

Conclusion

Allotypic variations affected melting profiles of dKiH Fc proteins possibly with larger contribution of variations adjacent to the disulfide linkage.

Science and art of protein formulation development

Protein pharmaceuticals have become a significant class of marketed drug products and are expected to grow steadily over the next decade. Development of a commercial protein product is, however, a rather complex process. A critical step in this process is formulation development, enabling the final product configuration. A number of challenges still exist in the formulation development process. This review is intended to discuss these challenges, to illustrate the basic formulation development processes, and to compare the options and strategies in practical formulation development.

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.

A stable engineered human IgG3 antibody with decreased aggregation during antibody expression and low pH stress

Human IgG comprises four subclasses with different biological functions. The IgG3 subclass has a unique character, exhibiting high effector function and Fab arm flexibility. However, it is not used as a therapeutic drug owing to an enhanced susceptibility to proteolysis. Antibody aggregation control is also important for therapeutic antibody development. To date, there have been few reports of IgG3 aggregation during protein expression and the low pH conditions needed for purification and virus inactivation. This study explored the potential of IgG3 antibody for therapeutics using anti‐CD20 IgG3 as a model to investigate aggregate formation. Initially, anti‐CD20 IgG3 antibody showed substantial aggregate formation during expression and low pH treatment. To circumvent this phenomenon, we systematically exchanged IgG3 constant domains with those of IgG1, a stable IgG. IgG3 antibody with the IgG1 CH3 domain exhibited reduced aggregate formation during expression. Differential scanning calorimetric analysis of individual amino acid substitutions revealed that two amino acid mutations in the CH3 domain, N392K and M397V, reduced aggregation and increased CH3 transition temperature. The engineered human IgG3 antibody was further improved by additional mutations of R435H to obtain IgG3KVH to achieve protein A binding and showed similar antigen binding as wild‐type IgG3. IgG3KVH also exhibited high binding activity for FcγRIIIa and C1q. In summary, we have successfully established an engineered human IgG3 antibody with reduced aggregation during bioprocessing, which will contribute to the better design of therapeutic antibodies with high effector function and Fab arm flexibility.

Selecting and engineering monoclonal antibodies with drug-like specificity

Despite the recent explosion in the use of monoclonal antibodies (mAbs) as drugs, it remains a significant challenge to generate antibodies with a combination of physicochemical properties that are optimal for therapeutic applications. We argue that one of the most important and underappreciated drug-like antibody properties is high specificity - defined here as low levels of antibody non-specific and self-interactions - which is linked to low off-target binding and slow antibody clearance in vivo and high solubility and low viscosity in vitro. Here, we review the latest advances in characterizing antibody specificity and elucidating its molecular determinants as well as using these findings to improve the selection and engineering of antibodies with extremely high, drug-like specificity.

Probing Conformational Diversity of Fc Domains in Aggregation-Prone Monoclonal Antibodies

PURPOSE

Fc domains are an integral component of monoclonal antibodies (mAbs) and Fc-based fusion proteins. Engineering mutations in the Fc domain is a common approach to achieve desired effector function and clinical efficacy of therapeutic mAbs. It remains debatable, however, whether molecular engineering either by changing glycosylation patterns or by amino acid mutation in Fc domain could impact the higher order structure of Fc domain potentially leading to increased aggregation propensities in mAbs.

METHODS

Here, we use NMR fingerprinting analysis of Fc domains, generated from selected Pfizer mAbs with similar glycosylation patterns, to address this question. Specifically, we use high resolution 2D [¹³C-¹H] NMR spectra of Fc fragments, which fingerprints methyl sidechain bearing residues, to probe the correlation of higher order structure with the storage stability of mAbs. Thermal calorimetric studies were also performed to assess the stability of mAb fragments.

RESULTS

Unlike NMR fingerprinting, thermal melting temperature as obtained from calorimetric studies for the intact mAbs and fragments (Fc and Fab), did not reveal any correlation with the aggregation propensities of mAbs. Despite >97% sequence homology, NMR data suggests that higher order structure of Fc domains could be dynamic and may result in unique conformation(s) in solution.

CONCLUSION

The overall glycosylation pattern of these mAbs being similar, these conformation(s) could be linked to the inherent plasticity of the Fc domain, and may act as early transients to the overall aggregation of mAbs.

Pre-adsorption of antibodies enables targeting of nanocarriers despite a biomolecular corona

To promote drug delivery to exact sites and cell types, the surface of nanocarriers is functionalized with targeting antibodies or ligands, typically coupled by covalent chemistry. Once the nanocarrier is exposed to biological fluid such as plasma, however, its surface is inevitably covered with various biomolecules forming the protein corona, which masks the targeting ability of the nanoparticle. Here, we show that we can use a pre-adsorption process to attach targeting antibodies to the surface of the nanocarrier. Pre-adsorbed antibodies remain functional and are not completely exchanged or covered by the biomolecular corona, whereas coupled antibodies are more affected by this shielding. We conclude that pre-adsorption is potentially a versatile, efficient and rapid method of attaching targeting moieties to the surface of nanocarriers.

Signature of Antibody Domain Exchange by Native Mass Spectrometry and Collision-Induced Unfolding

The development of domain-exchanged antibodies offers a route to high-affinity targeting to clustered multivalent epitopes, such as those associated with viral infections and many cancers. One strategy to generate these antibodies is to introduce mutations into target antibodies to drive domain exchange using the only known naturally occurring domain-exchanged anti-HIV (anti-human immunodeficiency virus) IgG1 antibody, 2G12 , as a template. Here, we show that domain exchange can be sensitively monitored by ion-mobility mass spectrometry and gas-phase collision-induced unfolding. Using native 2G12 and a mutated form that disrupts domain exchange such that it has a canonical IgG1 architecture ( 2G12 I19R ), we show that the two forms can be readily distinguished by their unfolding profiles. Importantly, the same signature of domain exchange is observed for both intact antibody and isolated Fab fragments. The development of a mass spectrometric method to detect antibody domain exchange will enable rapid screening and selection of candidate antibodies engineered to exhibit this and other unusual quaternary antibody architectures.

Synthetic glycopolymers as modulators of protein aggregation: influences of chemical composition, topology and concentration

Synthetic glycopolymers with a variable macromolecular architecture and carbohydrate moieties are utilised to modulate stress-induced aggregation of monoclonal antibodies.

Heat denaturation of the antibody, a multi-domain protein

The antibody is one of the most well-studied multi-domain proteins because of its abundance and physiological importance. In this article, we describe the effect of the complex, multi-domain structure of the antibody on its denaturation by heat. Natural antibodies are composed of 6 to 70 immunoglobulin fold domains, and are irreversibly denatured at high temperatures. Although the separated single immunoglobulin fold domain can be refolded after heat denaturation, denaturation of pairs of such domains is irreversible. Each antibody subclass exhibits a distinct heat tolerance, and IgE is especially known to be heat-labile. IgE starts unfolding at a lower temperature compared to other antibodies, because of the low stability of its CH3 domain. Each immunoglobulin domain starts unfolding at different temperatures. For instance, the CH3 domain of IgG unfolds at a higher temperature than its CH2 domain. Thus, the antibody has a mixture of folded and unfolded structures at a certain temperature. Co-existence of these folded and unfolded domains in a single polypeptide chain may increase the tendency to aggregate which causes the inactivation of the antibody.

Engineering an IgG Scaffold Lacking Effector Function with Optimized Developability

IgG isotypes can differentially bind to Fcγ receptors and complement, making the selection of which isotype to pursue for development of a particular therapeutic antibody important in determining the safety and efficacy of the drug. IgG2 and IgG4 isotypes have significantly lower binding affinity to Fcγ receptors. Recent evidence suggests that the IgG2 isotype is not completely devoid of effector function, whereas the IgG4 isotype can undergo in vivo Fab arm exchange leading to bispecific antibody and off-target effects. Here an attempt was made to engineer an IgG1-based scaffold lacking effector function but with stability equivalent to that of the parent IgG1. Care was taken to ensure that both stability and lack of effector function was achieved with a minimum number of mutations. Among the Asn²⁹⁷ mutants that result in lack of glycosylation and thus loss of effector function, we demonstrate that the N297G variant has better stability and developability compared with the N297Q or N297A variants. To further improve the stability of N297G, we introduced a novel engineered disulfide bond at a solvent inaccessible location in the CH2 domain. The resulting scaffold has stability greater than or equivalent to that of the parental IgG1 scaffold. Extensive biophysical analyses and pharmacokinetic (PK) studies in mouse, rat, and monkey further confirmed the developability of this unique scaffold, and suggest that it could be used for all Fc containing therapeutics (e.g. antibodies, bispecific antibodies, and Fc fusions) requiring lack of effector function or elimination of binding to Fcγ receptors.

Stabilizing the CH2 Domain of an Antibody by Engineering in an Enhanced Aromatic Sequon

Monoclonal antibodies (mAbs) exhibiting highly selective binding to a protein target constitute a large and growing proportion of the therapeutics market. Aggregation of mAbs results in the loss of their therapeutic efficacy and can result in deleterious immune responses. The CH2 domain comprising part of the Fc portion of Immunoglobulin G (IgG) is typically the least stable domain in IgG-type antibodies and therefore influences their aggregation propensity. We stabilized the CH2 domain by engineering an enhanced aromatic sequon (EAS) into the N-glycosylated C'E loop and observed a 4.8 °C increase in the melting temperature of the purified IgG1 Fc fragment. This EAS-stabilized CH2 domain also conferred enhanced stability against thermal and low pH induced aggregation in the context of a full-length monoclonal IgG1 antibody. The crystal structure of the EAS-stabilized (Q295F/Y296A) IgG1 Fc fragment confirms the design principle, i.e., the importance of the GlcNAc1•F295 interaction, and surprisingly reveals that the core fucose attached to GlcNAc1 also engages in an interaction with F295. Inhibition of core fucosylation confirms the contribution of the fucose-Phe interaction to the stabilization. The Q295F/Y296A mutations also modulate the binding affinity of the full-length antibody to Fc receptors by decreasing the binding to low affinity Fc gamma receptors (FcγRIIa, FcγRIIIa, and FcγRIIIb), while maintaining wild-type binding affinity to FcRn and FcγRI. Our results demonstrate that engineering an EAS into the N-glycosylated reverse turn on the C'E loop leads to stabilizing N-glycan-protein interactions in antibodies and that this modification modulates antibody-Fc receptor binding.

Acid-induced aggregation propensity of nivolumab is dependent on the Fc

Nivolumab, an anti-programmed death (PD)1 IgG4 antibody, has shown notable success as a cancer treatment. Here, we report that nivolumab was susceptible to aggregation during manufacturing, particularly in routine purification steps. Our experimental results showed that exposure to low pH caused aggregation of nivolumab, and the Fc was primarily responsible for an acid-induced unfolding phenomenon. To compare the intrinsic propensity of acid-induced aggregation for other IgGs subclasses, tocilizumab (IgG1), panitumumab (IgG2) and atezolizumab (aglyco-IgG1) were also investigated. The accurate pH threshold of acid-induced aggregation for individual IgG Fc subclasses was identified and ranked as: IgG1 < aglyco-IgG1 < IgG2 < IgG4. This result was cross-validated by thermostability and conformation analysis. We also assessed the effect of several protein stabilizers on nivolumab, and found mannitol ameliorated the acid-induced aggregation of the molecule. Our results provide valuable insight into downstream manufacturing process development, especially for immune checkpoint modulating molecules with a human IgG4 backbone.

Investigating Therapeutic Protein Structure with Diethylpyrocarbonate Labeling and Mass Spectrometry

Protein therapeutics are rapidly transforming the pharmaceutical industry. Unlike for small molecule therapeutics, current technologies are challenged to provide the rapid, high-resolution analyses of protein higher order structures needed to ensure drug efficacy and safety. Consequently, significant attention has turned to developing new methods that can quickly, accurately, and reproducibly characterize the three-dimensional structure of protein therapeutics. In this work, we describe a method that uses diethylpyrocarbonate (DEPC) labeling and mass spectrometry to detect three-dimensional structural changes in therapeutic proteins that have been exposed to degrading conditions. Using β2-microglobulin, immunoglobulin G1, and human growth hormone as model systems, we demonstrate that DEPC labeling can identify both specific protein regions that mediate aggregation and those regions that undergo more subtle structural changes upon mishandling of these proteins. Importantly, DEPC labeling is able to provide information for up to 30% of the surface residues in a given protein, thereby providing excellent structural resolution. Given the simplicity of the DEPC labeling chemistry and the relatively straightforward mass spectral analysis of DEPC-labeled proteins, we expect this method should be amenable to a wide range of protein therapeutics and their different formulations.