Development of a Human Antibody Tolerant Mouse Model to Assess the Immunogenicity Risk Due to Aggregated Biotherapeutics

Patient-Centric Quality Standards

To ensure the quality, safety and efficacy of medicinal products, it is necessary to develop and execute appropriate manufacturing process and product control strategies. Traditionally, product control strategies have focused on testing known quality attributes with limits derived from levels administered in preclinical and clinical studies with an associated statistical analysis to account for variability. However, not all quality attributes have impact to the patient and those with the potential to impact safety and efficacy may not be significant when dosed at patient-centric levels. Therefore, achieving patient-centricity is understanding patient relevance, which is defined as the level of impact that a quality attribute could have on safety and efficacy within the potential exposure range. A patient-centric quality standard (PCQS) is therefore a set of patient relevant attributes and their associated acceptance ranges to which a drug product should conform within the expected patient exposure range. This manuscript describes historical perspectives details the way to create and leverage a PCQS in a variety of pharmaceutical product modalities.

A High Threshold of Biotherapeutic Aggregate Numbers is Needed to Induce an Immunogenic Response In Vitro, In Vivo, and in the Clinic

BACKGROUND AND PURPOSE

There is concern that subvisible aggregates in biotherapeutic drug products pose a risk to patient safety. We investigated the threshold of biotherapeutic aggregates needed to induce immunogenic responses.

METHODS AND RESULTS

Highly aggregated samples were tested in cell-based assays and induced cellular responses in a manner that depended on the number of particles. The threshold of immune activation varied by disease state (cancer, rheumatoid arthritis, allergy), concomitant therapies, and particle number. Compared to healthy donors, disease state patients showed an equal or lower response at the late phase (7 days), suggesting they may not have a higher risk of responding to aggregates. Xeno-het mice were used to assess the threshold of immune activation in vivo. Although highly aggregated samples (~ 1,600,000 particles/mL) induced a weak and transient immunogenic response in mice, a 100-fold dilution of this sample (~ 16,000 particles/mL) did not induce immunogenicity. To confirm this result, subvisible particles (up to ~ 18,000 particles/mL, containing aggregates and silicone oil droplets) produced under representative administration practices (created upon infusion of a drug product through an IV catheter) did not induce a response in cell-based assays or appear to increase the rate of adverse events or immunogenicity during phase 3 clinical trials.

CONCLUSION

The ability of biotherapeutic aggregates to elicit an immune response in vitro, in vivo, and in the clinic depends on high numbers of particles. This suggests that there is a high threshold for aggregates to induce an immunogenic response which is well beyond that seen in standard biotherapeutic drug products.

Does Aggregation of Therapeutic IgGs in PBS Offer a True Picture of What Happens in Models Derived from Human Body Fluids?

Therapeutic proteins such as monoclonal antibodies (mAb) are known to form aggregates due to various factors. Phosphate buffered saline (PBS), human serum, and human serum filtrate (HSF) are some of the models used to analyze mAb stability in physiologically relevant in-vitro conditions. In this study, aggregation of mAb in PBS and models derived from body fluids seeded with mAb samples subjected to various stresses were compared. Samples containing mAb subjected to pH, temperature, UV light, stirring, and interfacial agitation stress were seeded into different models for 2 case studies. In the first case study, %HMW (high molecular weight species) of mAb in PBS and HSF were compared using size exclusion chromatography. It was found that change in %HMW was higher in PBS compared to HSF. For example, PBS containing mAb that was subjected to UV light stress showed change in HMW by >10 % over 72 h, but the change was <5 % in HSF. In second case study, aggregates particles of FITC tagged mAb were monitored in PBS and serum using fluorescence microscope image processing. It was found that PBS and serum containing mAb subjected to stirring and interfacial agitation resulted in aggregates of >2 µm size, and average size and percentage number of particles having >10 µm size was higher in serum compared to PBS at all analysis time point. Overall, it was found that aggregation of mAb in PBS was different from that in human body fluids. Second case study also showed the importance of advanced strategies for further characterization of mAb in serum.

A humanized minipig model for the toxicological testing of therapeutic recombinant antibodies

The safety of most human recombinant proteins can be evaluated in transgenic mice tolerant to specific human proteins. However, owing to insufficient genetic diversity and to fundamental differences in immune mechanisms, small-animal models of human diseases are often unsuitable for immunogenicity testing and for predicting adverse outcomes in human patients. Most human therapeutic antibodies trigger xenogeneic responses in wild-type animals and thus rapid clearance of the drugs, which makes in vivo toxicological testing of human antibodies challenging. Here we report the generation of Göttingen minipigs carrying a mini-repertoire of human genes for the immunoglobulin heavy chains γ1 and γ4 and the immunoglobulin light chain κ. In line with observations in human patients, the genetically modified minipigs tolerated the clinically non-immunogenic IgG1κ-isotype monoclonal antibodies daratumumab and bevacizumab, and elicited antibodies against the checkpoint inhibitor atezolizumab and the engineered interleukin cergutuzumab amunaleukin. The humanized minipigs can facilitate the safety and efficacy testing of therapeutic antibodies.

Immunogenicity Risk Assessment of Spontaneously Occurring Therapeutic Monoclonal Antibody Aggregates

Aggregates of therapeutic proteins have been associated with increased immunogenicity in pre-clinical models as well as in human patients. Recent studies to understand aggregates and their immunogenicity risks use artificial stress methods to induce high levels of aggregation. These methods may be less biologically relevant in terms of their quantity than those that occur spontaneously during processing and storage. Here we describe the immunogenicity risk due to spontaneously occurring therapeutic antibody aggregates using peripheral blood mononuclear cells (PBMC) and a cell line with a reporter gene for immune activation: THP-1 BLUE NFκB. The spontaneously occurring therapeutic protein aggregates were obtained from process intermediates and final formulated drug substance from stability retains. Spontaneously occurring aggregates elicited innate immune responses for several donors in a PBMC assay with cytokine and chemokine production as a readout for immune activation. Meanwhile, no significant adaptive phase responses to spontaneously occurring aggregate samples were detected. While the THP-1 BLUE NFκB cell line and PBMC assays both responded to high stress induced aggregates, only the PBMC from a limited subset of donors responded to processing-induced aggregates. In this case study, levels of antibody aggregation occurring at process relevant levels are lower than those induced by stirring and may pose lower risk in vivo. Our methodologies can further inform additional immunogenicity risk assessments using a pre-clinical in vitro risk assessment approach utilizing human derived immune cells.

Enhanced immunogenic potential of cancer immunotherapy antibodies in human IgG1 transgenic mice

ABBREVIATIONS

ADA Anti-Drug Antibodies; BCR B Cell Receptor; BId Idiotype-specific B Cell; BiTE Bispecific T cell Engager; BMC Bone Marrow Chimeric Mice; BSA Bovine Serum Albumin; CDR Complementary Determining Region; CEA Carcinoembryonic Antigen; CIT Cancer Immunotherapy; CitAbs Cancer Immunotherapy Antibodies; DC Dendritic Cell; ELISA Enzyme-Linked Immunosorbent Assay; FcRn Neonatal Fc Receptor; FcyR Fc gamma Receptor; GM-CSF Granulocyte-Macrophage Colony Stimulating Factor; gMFI Geometric Mean Fluorescence Intensity; H Heavy Chain; IC Immune Complex; Id Idiotype; IgA Immunoglobulin alpha; IgG1 Immunoglobulin gamma 1; IL-2 Interleukin 2; IL-2R Interleukin 2 Receptor; IL2v Interleukin 2 Variant; IVIG1 Intravenous Immunoglobulin 1; KLH Keyhole Limpet Hemocyanin; L Light Chain; MAPPs MHC-associated Peptide Proteomics; MHC Major Histocompatibility Complex; PBMC Peripheral Blood Mononuclear Cells; PBS Phosphate Buffered Saline; SHM Somatic Hypermutation; scFv Single-chain Variable Fragment; TCR T cell Receptor; TFc Fc-specific T cell; TId Id-specific T cell; UV Ultraviolet; V Variable.

Assay format diversity in pre-clinical immunogenicity risk assessment: Toward a possible harmonization of antigenicity assays

A major impediment to successful use of therapeutic protein drugs is their ability to induce anti-drug antibodies (ADA) that can alter treatment efficacy and safety in a significant number of patients. To this aim, in silico, in vitro, and in vivo tools have been developed to assess sequence and other liabilities contributing to ADA development at different stages of the immune response. However, variability exists between similar assays developed by different investigators due to the complexity of assays, a degree of uncertainty about the underlying science, and their intended use. The impact of protocol variations on the outcome of the assays, i.e., on the immunogenicity risk assigned to a given drug candidate, cannot always be precisely assessed. Here, the Non-Clinical Immunogenicity Risk Assessment working group of the European Immunogenicity Platform (EIP) reviews currently used assays and protocols and discusses feasibility and next steps toward harmonization and standardization.

Immunogenicity Challenges Associated with Subcutaneous Delivery of Therapeutic Proteins

The subcutaneous route of administration has provided convenient and non-inferior delivery of therapeutic proteins compared to intravenous infusion, but there is potential for enhanced immunogenicity toward subcutaneously administered proteins in a subset of patients. Unwanted anti-drug antibody response toward proteins or monoclonal antibodies upon repeated administration is shown to impact the pharmacokinetics and efficacy of multiple biologics. Unique immunogenicity challenges of the subcutaneous route have been realized through various preclinical and clinical examples, although subcutaneous delivery has often demonstrated comparable immunogenicity to intravenous administration. Beyond route of administration as a treatment-related factor of immunogenicity, certain product-related risk factors are particularly relevant to subcutaneously administered proteins. This review attempts to provide an overview of the mechanism of immune response toward proteins administered subcutaneously (subcutaneous proteins) and comments on product-related risk factors related to protein structure and stability, dosage form, and aggregation. A two-wave mechanism of antigen presentation in the immune response toward subcutaneous proteins is described, and interaction with dynamic antigen-presenting cells possessing high antigen processing efficiency and migratory activity may drive immunogenicity. Mitigation strategies for immunogenicity are discussed, including those in general use clinically and those currently in development. Mechanistic insights along with consideration of risk factors involved inspire theoretical strategies to provide antigen-specific, long-lasting effects for maintaining the safety and efficacy of therapeutic proteins.

The Impact of Product and Process Related Critical Quality Attributes on Immunogenicity and Adverse Immunological Effects of Biotherapeutics

The pharmaceutical industry has experienced great successes with protein therapeutics in the last two decades and with novel modalities, including cell therapies and gene therapies, more recently. Biotherapeutics are complex in structure and present challenges for discovery, development, regulatory, and life cycle management. Biotherapeutics can interact with the immune system that may lead to undesired immunological responses, including immunogenicity, hypersensitivity reactions (HSR), injection site reactions (ISR), and others. Many product and process related critical quality attributes (CQAs) have the potential to trigger or augment such immunological responses to the product. Tremendous efforts, both clinically and preclinically, have been invested to understand the impact of product and process related CQAs on adverse immunological effects. The information and knowledge are critical for the implementation of Quality by Design (QbD), which requires risk assessment and establishment of specifications and control strategies for CQAs. A quality target product profile (QTPP) that identifies the key CQAs through process development can help assign severity scores based on safety, immunogenicity, pharmacokinetics (PK) and pharmacodynamics (PD) of the molecule. Gaps and future directions related to biotherapeutics and emerging novel modalities are presented.

Strategies for Setting Patient-Centric Commercial Specifications for Biotherapeutic Products

Commercial specifications for a new biotherapeutic product are a critical component of the product's overall control strategy that ensures safety and efficacy. This paper describes strategies for setting commercial specifications as proposed by a consortium of industry development scientists. The specifications for some attributes are guided by compendia and regulatory guidance. For other product quality attributes (PQAs), product knowledge and the understanding of attribute criticality built throughout product development should drive specification setting. The foundation of PQA knowledge is an understanding of potential patient impact through an assessment of potency, PK, immunogenicity and safety. In addition to PQA knowledge, the ability of the manufacturing process to consistently meet specifications, typically assessed through statistical analyses, is an important consideration in the specification-setting process. Setting acceptance criteria that are unnecessarily narrow can impact the ability to supply product or prohibit consideration of future convenient dosage forms. Patient-centric specifications enable appropriate control over higher risk PQAs to ensure product quality for the patient, and flexibility for lower risk PQAs for a sustainable supply chain. This paper captures common strategic approaches for setting specifications for standard biotherapeutic products such as monoclonal antibodies and includes considerations for ensuring specifications are patient centric.

The immunogenicity of an anti-EGFR single domain antibody (VHH) is enhanced by misfolded amorphous aggregation but not by heat-induced aggregation

Amorphous aggregates of therapeutic proteins can provoke an unwanted immune response (anti-drug antibodies; ADAs), but counter-examples have led to some controversy. Amorphous aggregates can possess unique biophysical and biochemical attributes depending on both the way they are generated and the protein's biophysical/biochemical properties. Here, we examine the immunogenicity of an anti-EGFR single domain antibody (V_HH) in four types of amorphous aggregates: two heat-aggregated V_HH incubated at 65 °C (V_HH-65) and 95 °C (V_HH-95), a misfolded V_HH isolated from the insoluble fraction of the E. coli lysate (V_HH-Ins), and a low solubility misfolded V_HH produced by miss-shuffling the SS bonds of the native V_HH (V_HH-Mis). Biophysical and biochemical measurements indicated that V_HH was indeed natively folded, monomeric, and β-sheeted; that V_HH-65 was partially unfolded and formed aggregates with a Z-average (Zave) of 771 nm; whereas V_HH-95 was unfolded and formed aggregates of 1722 nm; and that both V_HH-Ins and V_HH-Mis were misfolded with non-native intermolecular SS bonds and formed aggregates with a Zave of 1846 nm and 1951 nm, respectively. The IgG level generated in Jcl:ICR mice determined by ELISA showed that the native V_HH was barely immunogenic, V_HH-95 was not immunogenic, while V_HH-65 was mildly immunogenic. By contrast, the misfolded aggregates, V_HH-Ins and V_HH-Mis, having a Zave and an aggregation propensity similar to that of V_HH-95, were highly immunogenic. These findings indicate the critical role of the biochemical and biophysical attributes of the amorphous aggregates in generating an immune response against a protein, rather than just their sizes.

The Impact of the Metal Interface on the Stability and Quality of a Therapeutic Fusion Protein

Subvisible particle formation, which occurs after the sterile filtration step of the fill/finish process, is a challenge that may occur during the development of biotherapeutics with complex molecular structures. Here, we show that a stainless steel pump head from a rotary piston pump produces more protein aggregates, past the limit of the acceptable quality range for subvisible particle counts, in comparison to a ceramic pump head. The quartz crystal microbalance was used to quantify the primary layer, proteins irreversibly adsorbed at the solid-liquid interface, and the secondary diffuse gel-like layer interacting on top of the primary layer. The results showed that the mass of protein irreversibly adsorbed onto stainless steel sensors is greater than on an aluminum oxide surface (ceramic pump mimic). This suggests that the amount of adsorbed protein plays a role in surface-induced protein aggregation at the solid-liquid interface.

Silicone Oil Particles in Prefilled Syringes With Human Monoclonal Antibody, Representative of Real-World Drug Products, Did Not Increase Immunogenicity in In Vivo and In Vitro Model Systems

Silicone oil is a lubricant for prefilled syringes (PFS), a common primary container for biotherapeutics. Silicone oil particles (SiOP) shed from PFS are a concern for patients due to their potential for increased immunogenicity and therefore also of regulatory concern. To address the safety concern in a context of manufacturing and distribution of drug product (DP), SiOP was increased (up to ∼25,000 particles/mL) in PFS filled with mAb1, a fully human antibody drug, by simulated handling of DP mimicked by drop shock. These samples are characterized in a companion report (Jiao N et al. J Pharm Sci. 2020). The risk of immunogenicity was then assessed using in vitro and in vivo immune model systems. The impact of a common DP excipient, polysorbate 80, on both the formation and biological consequences of SiOP was also tested. SiOP was found associated with (1) minimal cytokine secretion from human peripheral blood mononuclear cells, (2) no response in cell lines that report NF-κB/AP-1 signaling, and (3) no antidrug antibodies or significant cytokine production in transgenic Xeno-het mice, whether or not mAb1 or polysorbate 80 was present. These results suggest that SiOP in mAb1, representative of real-world DP in PFS, poses no increased risk of immunogenicity.

Nonclinical immunogenicity risk assessment of therapeutic proteins

Therapeutic protein drugs have significantly improved the management of many severe and chronic diseases. However, their development and optimal clinical application are complicated by the induction of unwanted immune responses. Therapeutic protein-induced antidrug antibodies can alter drug pharmacokinetics and pharmacodynamics leading to impaired efficacy and occasionally serious safety issues. There has been a growing interest over the past decade in developing methods to assess the risk of unwanted immunogenicity during preclinical drug development, with the aim to mitigate the risk during the molecular design phase, clinical development and when products reach the market. Here, we discuss approaches to therapeutic protein immunogenicity risk assessment, with attention to assays and in vivo models used to mitigate this risk.

Evaluation of a 3D Human Artificial Lymph Node as Test Model for the Assessment of Immunogenicity of Protein Aggregates

The immunogenicity of protein aggregates has been investigated in numerous studies. Nevertheless, it is still unknown which kind of protein aggregates enhance immunogenicity the most. The ability of the currently used in vitro and in vivo systems regarding their predictability of immunogenicity in humans is often questionable, and results are partially contradictive. In this study, we used a 2D in vitro assay and a complex 3D human artificial lymph node model to predict the immunogenicity of protein aggregates of bevacizumab and adalimumab. The monoclonal antibodies were exposed to different stress conditions such as light, heat, and mechanical stress to trigger the formation of protein aggregates and particles, and samples were analyzed thoroughly. Cells and culture supernatants were harvested and analyzed for dendritic cell marker and cytokines. Our study in the artificial lymph node model revealed that bevacizumab after exposure to heat triggered a TH1- and proinflammatory immune response, whereas no trend of immune responses was seen for adalimumab after exposure to different stress conditions. The human artificial lymph node model represents a new test model for testing the immunogenicity of protein aggregates combining the relevance of a 3D human system with the rather easy handling of an in vitro setup.

Test models for the evaluation of immunogenicity of protein aggregates

Protein aggregates have been discussed for a long time as a potential risk factor for immunogenicity in patients. Meanwhile, many research groups have investigated the immunogenicity of differently produced aggregates using in vitro or in vivo models. Despite all knowledge gained in these studies still little is known about the mechanisms of immunogenicity and the kind of protein aggregates bearing the greatest risk for immunogenicity. The choice of a suitable test model regarding the predictability of immunogenicity of protein aggregates in humans plays a major role and influences results and conclusions substantially. In this review we will provide an overview of the test models recently used for the evaluation of immunogenicity of protein aggregates; we will discuss advantages and drawbacks regarding their usability and predictive power for immunogenicity in humans.

Protein Adsorption and Layer Formation at the Stainless Steel-Solution Interface Mediates Shear-Induced Particle Formation for an IgG1 Monoclonal Antibody

Passage of specific protein solutions through certain pumps, tubing, and/or filling nozzles can result in the production of unwanted subvisible protein particles (SVPs). In this work, surface-mediated SVP formation was investigated. Specifically, the effects of different solid interface materials, interfacial shear rates, and protein concentrations on SVP formation were measured for the National Institute of Standards and Technology monoclonal antibody (NISTmAb), a reference IgG1 monoclonal antibody (mAb). A stainless steel rotary piston pump was used to identify formulation and process parameters that affect aggregation, and a flow cell (alumina or stainless steel interface) was used to further investigate the effect of different interface materials and/or interfacial shear rates. SVP particles produced were monitored using flow microscopy or flow cytometry. Neutron reflectometry and a quartz crystal microbalance with dissipation monitoring were used to characterize adsorption and properties of NISTmAb at the stainless steel interface. Pump/shear cell experiments showed that the NISTmAb concentration and interface material had a significant effect on SVP formation, while the effects of interfacial shear rate and passage number were less important. At the higher NISTmAb concentrations, the adsorbed protein became structurally altered at the stainless steel interface. The primary adsorbed layer remained largely undisturbed during flow, suggesting that SVP formation at high NISTmAb concentration was caused by the disruption of patches and/or secondary interactions.

Chemical and Biophysical Characteristics of Monoclonal Antibody Solutions Containing Aggregates Formed during Metal Catalyzed Oxidation

PURPOSE

To physicochemically characterize and compare monoclonal antibody (mAb) solutions containing aggregates generated via metal catalyzed oxidation (MCO).

METHODS

Two monoclonal IgG2s (mAb1 and mAb2) and one monoclonal IgG1 (rituximab) were exposed to MCO with the copper/ascorbic acid oxidative system, by using several different methods. The products obtained were characterized by complementary techniques for aggregate and particle analysis (from oligomers to micron sized species), and mass spectrometry methods to determine the residual copper content and chemical modifications of the proteins.

RESULTS

The particle size distribution and the morphology of the protein aggregates generated were similar for all mAbs, independent of the MCO method used. There were differences in both residual copper content and in chemical modification of specific residues, which appear to be dependent on both the protein sequence and the protocol used. All products showed a significant increase in the levels of oxidized His, Trp, and Met residues, with differences in extent of modification and specific amino acid residues modified.

CONCLUSION

The extent of total oxidation and the amino acid residues with the greatest oxidation rate depend on a combination of the MCO method used and the protein sequence.

Biosimilarity under stress: A forced degradation study of Remicade® and Remsima™

Remsima™ (infliximab) is the first biosimilar monoclonal antibody (mAb) approved by the European Medical Agency and the US Food and Drug Administration. Remsima™ is highly similar to its reference product, Remicade®, with identical formulation components. The 2 products, however, are not identical; Remsima™ has higher levels of soluble aggregates, C-terminal lysine truncation, and fucosylated glycans. To understand if these attribute differences could be amplified during forced degradation, solutions and lyophilized powders of the 2 products were subjected to stress at elevated temperature (40-60°C) and humidity (dry-97% relative humidity). Stress-induced aggregation and degradation profiles were similar for the 2 products and resulted in loss of infliximab binding to tumor necrosis factor and FcγRIIIa. Appearances of protein aggregates and hydrolysis products were time- and humidity-dependent, with similar degradation rates observed for the reference and biosimilar products. Protein powder incubations at 40°C/97% relative humidity resulted in partial mAb unfolding and increased asparagine deamidation. Minor differences in heat capacity, fluorescence, levels of subvisible particulates, deamidation and protein fragments were observed in the 2 stressed products, but these differences were not statistically significant. The protein solution instability at 60°C, although quite significant, was also similar for both products. Despite the small initial analytical differences, Remicade® and Remsima™ displayed similar degradation mechanisms and kinetics. Thus, our results show that the 2 products are highly similar and infliximab's primary sequence largely defines their protein instabilities compared with the limited influence of small initial purity and glycosylation differences in the 2 products.

Immunogenicity of protein aggregates of a monoclonal antibody generated by forced shaking stress with siliconized and nonsiliconized syringes in BALB/c mice

OBJECTIVE

In this study, we aimed to investigate the immunogenicity of protein aggregates of monoclonal antibodies (mAbs), generated by forced shaking stress with siliconized and nonsiliconized syringes in a mouse model.

METHODS

Samples were filled in siliconized and nonsiliconized syringes with shaking and headspace air. Characterization studies were performed using high-performance size-exclusion chromatography, nanoparticle tracking analysis, flow cytometry, micro-flow imaging and resonant mass measurement. The samples (10 or 100 μg) were subcutaneously injected into BALB/c mice for 21 days, and the anti-drug antibody (ADA) concentrations were monitored.

KEY FINDINGS

In samples shaken with siliconized syringes [SO (+)], large amounts of submicron and subvisible protein aggregates were formed by interactions with silicone oil droplets. The characteristics of protein aggregates differed between the mAb solution and shaken samples, which strongly indicates that silicone oil accelerates protein aggregation. When administered at low doses, the ADA concentration in all samples increased with repeated injections, and SO (+) induced the highest immunogenicity. However, when administered at high doses, ADA concentration decreased following prolonged repeated administration for tolerance.

CONCLUSIONS

These results indicated that mAb protein aggregation induced immunogenicity in mice, and SO (+) induced higher immunogenicity than samples shaken with nonsiliconized syringe.

Perspectives on Subcutaneous Route of Administration as an Immunogenicity Risk Factor for Therapeutic Proteins

An increasing number of therapeutic proteins are being developed for delivery through the subcutaneous (SC) route of administration. Relative to intravenous (IV) administration, the SC route offers more convenience to patients, flexibility in dosing, and potential to reduce health care costs. There is a perception that SC administration can pose a higher immunogenicity risk than IV administration for a given protein. To evaluate whether there is a difference in therapeutic protein immunogenicity associated with administration routes, a more detailed understanding of the interactions with the immune system by each route is needed. Few approved therapeutic proteins have available clinical immunogenicity data sets in the public domain that represent both IV and SC administration routes. This has prevented a direct comparison of the 2 routes of administration across a large sample size. Of the 6 marketed products where SC and IV route-related incidences of anti-drug antibody (ADA) were available, 4 were associated with higher immunogenicity incidence with SC. In other cases, there was no apparent difference between the SC and IV routes. Overall, the ADA incidence was low (<15%) with no impact on safety or efficacy. The challenges associated with identifying specific risk factors unique to SC administration are discussed.

Extensive Chemical Modifications in the Primary Protein Structure of IgG1 Subvisible Particles Are Necessary for Breaking Immune Tolerance

A current concern with the use of therapeutic proteins is the likely presence of aggregates and submicrometer, subvisible, and visible particles. It has been proposed that aggregates and particles may lead to unwanted increases in the immune response with a possible impact on safety or efficacy. The aim of this study was thus to evaluate the ability of subvisible particles of a therapeutic antibody to break immune tolerance in an IgG1 transgenic mouse model and to understand the particle attributes that might play a role in this process. We investigated the immunogenic properties of subvisible particles (unfractionated, mixed populations, and well-defined particle size fractions) using a transgenic mouse model expressing a mini-repertoire of human IgG1 (hIgG1 tg). Immunization with proteinaceous subvisible particles generated by artificial stress conditions demonstrated that only subvisible particles bearing very extensive chemical modifications within the primary amino acid structure could break immune tolerance in the hIgG1 transgenic mouse model. Protein particles exhibiting low levels of chemical modification were not immunogenic in this model.

Comparative study of idursulfase beta and idursulfase in vitro and in vivo

Hunter syndrome is an X-linked lysosomal storage disease caused by a deficiency in the enzyme iduronate-2-sulfatase (IDS), leading to the accumulation of glycosaminoglycans (GAGs). Two recombinant enzymes, idursulfase and idursulfase beta are currently available for enzyme replacement therapy for Hunter syndrome. These two enzymes exhibited some differences in various clinical parameters in a recent clinical trial. Regarding the similarities and differences of these enzymes, previous research has characterized their biochemical and physicochemical properties. We compared the in vitro and in vivo efficacy of the two enzymes on patient fibroblasts and mouse model. Two enzymes were taken up into the cell and degraded GAGs accumulated in fibroblasts. In vivo studies of two enzymes revealed similar organ distribution and decreased urinary GAGs excretion. Especially, idursulfase beta exhibited enhanced in vitro efficacy for the lower concentration of treatment, in vivo efficacy in the degradation of tissue GAGs and improvement of bones, and revealed lower anti-drug antibody formation. A biochemical analysis showed that both enzymes show largely a similar glycosylation pattern, but the several peaks were different and quantity of aggregates of idursulfase beta was lower.

Use of In Vitro Assays to Assess Immunogenicity Risk of Antibody-Based Biotherapeutics

An In Vitro Comparative Immunogenicity Assessment (IVCIA) assay was evaluated as a tool for predicting the potential relative immunogenicity of biotherapeutic attributes. Peripheral blood mononuclear cells from up to 50 healthy naïve human donors were monitored up to 8 days for T-cell proliferation, the number of IL-2 or IFN-γ secreting cells, and the concentration of a panel of secreted cytokines. The response in the assay to 10 monoclonal antibodies was found to be in agreement with the clinical immunogenicity, suggesting that the assay might be applied to immunogenicity risk assessment of antibody biotherapeutic attributes. However, the response in the assay is a measure of T-cell functional activity and the alignment with clinical immunogenicity depends on several other factors. The assay was sensitive to sequence variants and could differentiate single point mutations of the same biotherapeutic. Nine mAbs that were highly aggregated by stirring induced a higher response in the assay than the original mAbs before stirring stress, in a manner that did not match the relative T-cell response of the original mAbs. In contrast, mAbs that were glycated by different sugars (galactose, glucose, and mannose) showed little to no increase in response in the assay above the response to the original mAbs before glycation treatment. The assay was also used successfully to assess similarity between multiple lots of the same mAb, both from the same manufacturer and from different manufacturers (biosimilars). A strategy for using the IVCIA assay for immunogenicity risk assessment during the entire lifespan development of biopharmaceuticals is proposed.

Mouse Models for Assessing Protein Immunogenicity: Lessons and Challenges

The success of clinical and commercial therapeutic proteins is rapidly increasing, but their potential immunogenicity is an ongoing concern. Most of the studies that have been conducted over the past few years to examine the importance of various product-related attributes (in particular several types of aggregates and particles) and treatment regimen (such as dose, dosing schedule, and route of administration) in the development of unwanted immune responses have utilized one of a variety of mouse models. In this review, we discuss the utility and drawbacks of different mouse models that have been used for this purpose. Moreover, we summarize the lessons these models have taught us and some of the challenges they present. Finally, we provide recommendations for future research utilizing mouse models to improve our understanding of critical factors that may contribute to protein immunogenicity.

Physical Characterization and Innate Immunogenicity of Aggregated Intravenous Immunoglobulin (IGIV) in an In Vitro Cell-Based Model

PURPOSE

To investigate in vitro the innate immune response to accelerated stress-induced aggregates of intravenous immunoglobulin (IGIV) using a well-defined human cell-line model, and to correlate the innate response to physical properties of the aggregates.

METHODS

IGIV aggregates were prepared by applying various accelerated stress methods, and particle size, count and structure were characterized. Immune cell activation as tracked by inflammatory cytokines released in response to aggregates was evaluated in vitro using peripheral blood mononuclear cells (PBMC), primary monocytes and immortalized human monocyte-like cell lines.

RESULTS

IGIV aggregates produced by mechanical stress induced higher cytokine release by PBMC and primary monocytes than aggregates formed by other stresses. Results with the monocytic cell line THP-1 paralleled trends in PBMC and primary monocytes. Effects were dose-dependent, enhanced by complement opsonization, and partially inhibited by blocking toll-like receptors (TLR2 and TLR4) and to a lesser extent by blocking Fc gamma receptors (FcγRs).

CONCLUSIONS

Stress-induced IGIV aggregates stimulate a dose-dependent cytokine response in human monocytes and THP-1 cells, mediated in part by TLRs, FcγRs and complement opsonization. THP-1 cells resemble primary monocytes in many respects with regard to tracking the innate response to IgG aggregates. Accordingly, the measurement of inflammatory cytokines released by THP-1 cells provides a readily accessible assay system to screen for the potential innate immunogenicity of IgG aggregates. The results also highlight the role of aggregate structure in interacting with the different receptors mediating innate immunity.

An optimized approach to the rapid assessment and detection of sequence variants in recombinant protein products

The development of sensitive techniques to detect sequence variants (SVs), which naturally arise due to DNA mutations and errors in transcription/translation (amino acid misincorporations), has resulted in increased attention to their potential presence in protein-based biologic drugs in recent years. Often, these SVs may be below 0.1%, adding challenges for consistent and accurate detection. Furthermore, the presence of false-positive (FP) signals, a hallmark of SV analysis, requires time-consuming analyst inspection of the data to sort true from erroneous signal. Consequently, gaps in information about the prevalence, type, and impact of SVs in marketed and in-development products are significant. Here, we report the results of a simple, straightforward, and sensitive approach to sequence variant analysis. This strategy employs mixing of two samples of an antibody or protein with the same amino acid sequence in a dilution series followed by subsequent sequence variant analysis. Using automated peptide map analysis software, a quantitative assessment of the levels of SVs in each sample can be made based on the signal derived from the mass spectrometric data. We used this strategy to rapidly detect differences in sequence variants in a monoclonal antibody after a change in process scale, and in a comparison of three mAbs as part of a biosimilar program. This approach is powerful, as true signals can be readily distinguished from FP signal, even at a level well below 0.1%, by using a simple linear regression analysis across the data set with none to minimal inspection of the MS/MS data. Additionally, the data produced from these studies can also be used to make a quantitative assessment of relative levels of product quality attributes. The information provided here extends the published knowledge about SVs and provides context for the discussion around the potential impact of these SVs on product heterogeneity and immunogenicity.

Physical characterization and in vitro biological impact of highly aggregated antibodies separated into size-enriched populations by fluorescence-activated cell sorting

An IgG2 monoclonal antibody (mAb) solution was subjected to stirring, generating high concentrations of nanometer and subvisible particles, which were then successfully size-enriched into different size bins by low-speed centrifugation or a combination of gravitational sedimentation and fluorescence-activated cell sorting (FACS). The size-fractionated mAb particles were assessed for their ability to elicit the release of cytokines from a population of donor-derived human peripheral blood mononuclear cells (PBMC) at two phases of the immune response. Fractions enriched in nanometer-sized particles showed a lower response than those enriched in micron-sized particles in this assay. Particles of 5-10 μm in size displayed elevated cytokine release profiles compared with other size ranges. Stir-stressed mAb particles had amorphous morphology, contained protein with partially altered secondary structure, elevated surface hydrophobicity (compared with controls), and trace levels of elemental fluorine. FACS size-enriched the mAb particle samples, yet did not notably alter the overall morphology or composition of particles as measured by microflow imaging, transmission electron microscopy, and scanning electron microscopy-energy dispersive X-ray spectroscopy. The utility and limitations of FACS for size separation of mAb particles and potential of in vitro PBMC studies to rank-order the immunogenic potential of various types of mAb particles are discussed.