Native-like aggregates of factor VIII are immunogenic in von Willebrand factor deficient and hemophilia a mice

Biophysical and biochemical nature of amorphous protein oligomers determines the strength of immune response and the generation of T-cell memory

Here, we used domain 3 of dengue virus serotype 3 envelope protein (D3ED3), a natively folded globular low-immunogenicity protein, to ask whether the biophysical nature of amorphous oligomers can affect immunogenicity. We prepared nearly identical 30 ~ 50 nm-sized amorphous oligomers in five distinct ways and looked at any correlation between their biophysical properties and immunogenicity. One oligomer type was produced using our SCP tag (solubility controlling peptide) made of 5 isoleucines (C5I). The others were prepared by miss-shuffling the SS bonds (Ms), heating (Ht), stirring (St) and freeze-thaw (FT). Dynamic light scattering showed that all five formulations contained oligomers of approximately identical sizes with hydrodynamic radii (Rh) between 30 and 55 nm. Circular dichroism (cd) indicated that the secondary structure content of oligomers formed by stirring and freeze-thaw was essentially identical to that of the native monomeric D3ED3. The secondary structure content of the Ms showed moderate changes, whereas the C5I and heat-induced (Ht) oligomers exhibited a significant change. The Ms contained D3ED3 with intermolecular SS bonds as assessed by nonreducing size exclusion chromatography (SEC). Immunization in JcL:ICR mice showed that both C5I and Ms significantly increased the anti-D3ED3 IgG titre. Ht, St and FT were only mildly immunogenic, similar to the monomeric D3ED3. Cell surface CD marker analysis by flow cytometry confirmed that immunization with Ms generated a strong central and effector T-cell memory. Our observations indeed suggest that controlled oligomerization can provide a new, adjuvant-free method for increasing a protein's immunogenicity, yielding a potentially powerful platform for protein-based (subunit) vaccines.

Immunogenicity of Therapeutic Biological Modalities - Lessons from Hemophilia A Therapies

The introduction and development of biologics such as therapeutic proteins, gene-, and cell-based therapy have revolutionized the scope of treatment for many diseases. However, a significant portion of the patients develop unwanted immune reactions against these novel biological modalities, referred to as immunogenicity, and no longer benefit from the treatments. In the current review, using Hemophilia A (HA) therapy as an example, we will discuss the immunogenicity issue of multiple biological modalities. Currently, the number of therapeutic modalities that are approved or recently explored to treat HA, a hereditary bleeding disorder, is increasing rapidly. These include, but are not limited to, recombinant factor VIII proteins, PEGylated FVIII, FVIII Fc fusion protein, bispecific monoclonal antibodies, gene replacement therapy, gene editing therapy, and cell-based therapy. They offer the patients a broader range of more advanced and effective treatment options, yet immunogenicity remains the most critical complication in the management of this disorder. Recent advances in strategies to manage and mitigate immunogenicity will also be reviewed.

Pharmaceutical Aspects and Clinical Evaluation of COVID-19 Vaccines

COVID-19, the disease caused by the novel severe acute respiratory syndrome-associated coronavirus 2 (SARS-CoV-2), was first detected in December 2019 and has since morphed into a global pandemic claiming over 2.4 million human lives and severely impacting global economy. The race for a safe and efficacious vaccine was thus initiated with government agencies as well as major pharmaceutical companies as frontrunners. An ideal vaccine would activate multiple arms of the adaptive immune system to generate cytotoxic T cell responses as well as neutralizing antibody responses, while avoiding pathological or deleterious immune responses that result in tissue damage or exacerbation of the disease. Developing an effective vaccine requires an inter-disciplinary effort involving virology, protein biology, biotechnology, immunology and pharmaceutical sciences. In this review, we provide a brief overview of the pathology and immune responses to SARS-CoV-2, which are fundamental to vaccine development. We then summarize the rationale for developing COVID-19 vaccines and provide novel insights into vaccine development from a pharmaceutical science perspective, such as selection of different antigens, adjuvants, delivery platforms and formulations. Finally, we review multiple clinical trial outcomes of novel vaccines in terms of safety and efficacy.

Immune response with long-term memory triggered by amorphous aggregates of misfolded anti-EGFR VHH-7D12 is directed against the native VHH-7D12 as well as the framework of the analogous VHH-9G8

We previously demonstrated that amorphous aggregates of misfolded V_HH-7D12 antibodies (V_HH-Mis), a potential anti-EGFR drug, can generate a robust serum IgG response. Here we investigate the immunogenic nature, especially the specificity of the immune response induced by V_HH-Mis. To this end, we used two natively folded and 77% identical anti-EGFR V_HHs (V_HH-7D12 and V_HH-9G8) that possess a common framework but distinct complementarity determining regions (CDRs). In 60% of mice immunized with V_HH-Mis, the anti-V_HH-7D12 IgG titer was stronger than the anti-V_HH-9G8 titer (Group-1). In the remaining mice (40%; Group-2), the anti-V_HH-7D12 and anti-V_HH-9G8 titer were almost identical. We rationalized these results by hypothesizing that mice in Group-1 produced IgG mostly against the V_HH-7D12's CDRs, whereas in Group-2 mice, they targeted the V_HH's framework. The IgG specificity against V_HH-7D12 and V_HH-9G8 was essentially unchanged over 17 weeks in both groups. Further, in all mice (Group-1&2) re-immunized with native V_HH-7D12, the IgG titer against V_HH-7D12 increased sharply but not against V_HH-9G8. On the other hand, none of the three Group-1 mice re-immunized with native V_HH-9G8 showed immunogenicity against V_HH-7D12 nor V_HH-9G8. Whereas, in Group-2 mice (three/three) re-immunized with V_HH-9G8, the IgG titers against both V_HHs increased but slowly. Flow-cytometric studies showed that V_HH-Mis immunized mice generated a higher number of effector and central memory T-cells. Overall, these observations indicate that amorphous aggregates made of a misfolded V_HH can induce serum IgG against its natively folded self and analogous V_HHs having a similar framework but distinct CDRs. Furthermore, a robust long-term immune response with memory was established against its natively folded self but with a nil-to-moderate immune response against natively folded V_HH analogs.

Subvisible Particles in Solutions of Remicade in Intravenous Saline Activate Immune System Pathways in In Vitro Human Cell Systems

Among patients that receive Remicade® therapy, more than 20% have adverse infusion related reactions and approximately 50% have immunogenic responses.^1-3 Upon characterization of initial Remicade®-IV solution we observed a high concentration of subvisible particles that could inadvertently be delivered to patients. This solution was processed through the IV infusion system, mimicking the typical clinical administration setup - either with or without an in-line filter connected to the IV line. The samples generated thereafter were tested using various in vitro assays for activation of the innate immune system via cytokine release in whole blood and in peripheral blood mononuclear cell (PBMC) cultures, and activation of the Toll like receptors (TLRs). Activation of the adaptive immune system was evaluated by monitoring upregulation of surface receptors on dendritic cells (DCs) and CD4+ T cell proliferation in response to IV solution of Remicade®. Our results indicate that subvisible particles in Remicade®-saline solution have a significant role in activation of the immune system but there are extrinsic factors potentially contributed by the in-line filters or other process parameters that also contribute to immune system activation.

Characterization of protein unable to bind von Willebrand factor in recombinant factor VIII products

BACKGROUND

Therapeutic products with coagulation factor VIII (FVIII) have a wide range of specific activities, implying presence of protein with altered structure. Previous studies showed that recombinant FVIII products (rFVIII) contain a fraction (FVIIIFT ) unable to bind von Willebrand factor (VWF) and reported to lack activity. Because of loss of function(s), FVIIIFT can be defined as a product-related impurity, whose properties and levels in rFVIII products should be investigated.

OBJECTIVE

To isolate and characterize the FVIIIFT fraction in rFVIII products.

METHODS

Protein fractions unable (FVIIIFT ) and able (FVIIIEL ) to bind VWF were isolated from rFVIII products using immobilized VWF affinity chromatography (IVAC) and characterized by gel electrophoresis, immunoblotting, FVIII activity test, surface plasmon resonance, mass spectrometry, and for plasma clearance in mice.

RESULTS AND CONCLUSIONS

A robust IVAC methodology was developed and applied for analysis of 10 rFVIII products marketed in the United States. FVIIIFT was found at various contents (0.4%-21.5%) in all products. Compared with FVIIIEL , FVIIIFT had similar patterns of polypeptide bands by gel electrophoresis, but lower functional activity. In several representative products, FVIIIFT was found to have reduced sulfation at Tyr1680, important for VWF binding, decreased interaction with a low-density lipoprotein receptor-related protein 1 fragment, and faster plasma clearance in mice. These findings provide basic characterization of FVIIIFT and demonstrate a potential for IVAC to control this impurity in rFVIII products to improve their efficacy in therapy of hemophilia A.

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.

Immune Responses to Plasma-Derived Versus Recombinant FVIII Products

The most severe side effect of hemophilia treatment is the inhibitor development occurring in 30% of patients, during the earliest stages of treatment with factor (F)VIII concentrates. These catastrophic immune responses rapidly inactivate the infused FVIII, rendering the treatment ineffective. This complication is associated with a substantial morbidity and mortality. The risk factors involved in the onset of the inhibitors are both genetic and environmental. The source of FVIII products, i.e. plasma-derived or recombinant FVIII products, is considered one of the most relevant factors for inhibitor development. Numerous studies in the literature report conflicting data on the different immunogenicity of the products. The SIPPET randomized trial showed an increased in the inhibitor rate in patients using recombinant FVIII products than those receiving plasma-derived products in the first exposure days. The SIPPET randomized trial showed an increase in the inhibitor rate in patients using recombinant FVIII products compared to those treated with plasma-derived products in the first days of exposure. The potential increase in the immunogenicity of recombinant products can be attributed to several factors such as: the different post-translational modification in different cell lines, the presence of protein aggregates, and the role played by the chaperon protein of FVIII, the von Willebrand factor, which modulates the uptake of FVIII by antigen presenting cells (APCs). Furthermore, the presence of non-neutralizing antibodies against FVIII has shown to be in increased inhibitor development as demonstrated in a sub-analysis of the SIPPET study. In addition, the presence of the specific subclasses of the immunoglobulins may also be an important biomarker to indicate whether the inhibitor will evolve into a persistent neutralizing antibody or a transient one that would disappear without any specific treatment. Recently, the availability of novel non-replacement therapies as well as emicizumab, administered by weekly subcutaneous infusion, have significantly changed the quality of life of patients with inhibitors showing a considerable reduction of the annual bleeding rate and in most patients the absence of bleeding. Although, these novel drugs improve patients' quality of life, they do not abolish the need to infuse FVIII during acute bleeding or surgery. Therefore, the issue of immunogenicity against FVIII still remains an important side effect of hemophilia treatment.

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.

Immunogenicity of Bioproducts: Cellular Models to Evaluate the Impact of Therapeutic Antibody Aggregates

Patients treated with bioproducts (BPs) frequently develop anti-drug antibodies (ADAs) with potential neutralizing capacities leading to loss of clinical response or potential hypersensitivity reactions. Many factors can influence BP immunogenicity and could be related to the patient, the treatment, as well as to the product itself. Among these latter factors, it is now well accepted that BP aggregation is associated with an increased potential for immunogenicity, as aggregates seem to be correlated with ADA development. Moreover, the presence of high-affinity ADAs suggests a CD4 T-cell dependent adaptive immune response and therefore a pivotal role for antigen-presenting cells (APCs), such as dendritic cells (DCs). In this review, we address the in vitro methods developed to evaluate how monoclonal antibodies could trigger the immunization process by focusing on the role of aggregated antibodies in the establishment of this response. In particular, we will present the different cell-based assays that have been used to assess the potential of antibodies and their aggregates to modulate cellular mechanisms leading to activation and the biological parameters (cellular activation markers, proliferation and secreted molecules) that can be measured to evaluate the different cell activation stages and their consequences in the propagation of the immune response. Indeed, the use of such strategies could help evaluate the risk of BP immunogenicity and their role in mitigating this risk.

Sedimentation Velocity Analytical Ultracentrifugation of Oxidized Recombinant Full-Length Factor VIII

Anti-drug antibodies to coagulation factor VIII (fVIII), often termed inhibitors, present the greatest economical and treatment related obstacle in the management of hemophilia A. Although several genetic and environmental risk factors associated with inhibitor development have been identified, the precise mechanisms responsible for the immune response to exogenous fVIII therapies remain undefined. Clinical trials suggest there is an increased immunogenic potential of recombinant fVIII compared to plasma-derived products. Additional biochemical and immunological studies have demonstrated that changes in recombinant fVIII production and formulation can alter fVIII structure and immunogenicity. Recently, one study demonstrated increased immunogenicity of the recombinant fVIII product Helixate in hemophilia A mice following oxidation with hypochlorite (ClO⁻). It is widely reported that protein aggregates within drug products can induce adverse immune reactions in patients. Several studies have therefore investigated the prevalence of molecular aggregates in commercial recombinant products with and without use-relevant stress and agitation. To investigate the potential link between oxidation-induced immunogenicity and molecular aggregation, we analyzed the recombinant fVIII product, Helixate, via sedimentation velocity analytical ultracentrifugation following oxidation with ClO⁻. At 80 μM ClO⁻, a concentration that reduced the specific-activity by 67%, no detectable increase in large molecular aggregates (s > 12 S) was observed when compared to non-oxidized fVIII. This lack of aggregates was demonstrated both in commercial excipient as well as a HEPES buffered saline formulation. These data suggest that oxidation induced immunogenicity is independent of aggregate-mediated immune response. Therefore, our data support multiple, independent mechanisms underlying fVIII immunogenicity.

Immunogenicity of Protein Pharmaceuticals

Protein therapeutics have drastically changed the landscape of treatment for many diseases by providing a regimen that is highly specific and lacks many off-target toxicities. The clinical utility of many therapeutic proteins has been undermined by the potential development of unwanted immune responses against the protein, limiting their efficacy and negatively impacting its safety profile. This review attempts to provide an overview of immunogenicity of therapeutic proteins, including immune mechanisms and factors influencing immunogenicity, impact of immunogenicity, preclinical screening methods, and strategies to mitigate immunogenicity.

How Full-Length FVIII Benefits from Its Heterogeneity - Insights into the Role of the B-Domain

Purpose

To explore how the natural heterogeneity of human coagulation factor VIII (FVIII) and the processing of its B-domain specifically modulate protein aggregation.

Methods

Recombinant FVIII (rFVIII) molecular species containing 70% or 20% B-domain, and B-domain-deleted rFVIII (BDD-rFVIII), were separated from full-length recombinant FVIII (FL-rFVIII). Purified human plasma-derived FVIII (pdFVIII) was used as a comparator. Heterogeneity and aggregation of the various rFVIII molecular species, FL-rFVIII and pdFVIII were analysed by SDS-PAGE, dynamic light scattering, high-performance size-exclusion chromatography and flow cytometry-based particle analysis.

Results

FL-rFVIII and pdFVIII were heterogeneous in nature and demonstrated similar resistance to aggregation under physical stress. Differences were observed between these and among rFVIII molecular species. FVIII molecular species exhibited diverging aggregation pathways dependent on B-domain content. The propensity to form aggregates increased with decreasing proportions of B-domain, whereas the opposite was observed for oligomer formation. Development of cross-β sheet-containing aggregates in BDD-rFVIII induced effective homologous seeding and faster aggregation. Naturally heterogeneous FL-rFVIII and pdFVIII displayed the lowest propensity to aggregate in all experiments.

Conclusions

These results demonstrate that pdFVIII and FL-rFVIII have similar levels of molecular heterogeneity, and suggest that heterogeneity and the B-domain are involved in stabilising FVIII by modulating its aggregation pathway.

Electronic supplementary material

The online version of this article (10.1007/s11095-019-2599-2) contains supplementary material, which is available to authorized users.

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.

N-linked glycosylation modulates the immunogenicity of recombinant human factor VIII in hemophilia A mice

Immune responses to factor VIII remain the greatest complication in the treatment of severe hemophilia A. Recent epidemiological evidence has highlighted that recombinant factor VIII produced in baby hamster kidney cells is more immunogenic than factor VIII produced in Chinese hamster ovary cells. Glycosylation differences have been hypothesized to influence the immunogenicity of these synthetic concentrates. In two hemophilia A mouse models, baby hamster kidney cell-derived factor VIII elicited a stronger immune response compared to Chinese hamster ovary cell-derived factor VIII. Furthermore, factor VIII produced in baby hamster kidney cells exhibited accelerated clearance from circulation independent of von Willebrand factor. Lectin and mass spectrometry analysis of total N-linked glycans revealed differences in high-mannose glycans, sialylation, and the occupancy of glycan sites. Factor VIII desialylation did not influence binding to murine splenocytes or dendritic cells, nor surface co-stimulatory molecule expression. We did, however, observe increased levels of immunoglobulin M specific to baby hamster kidney-derived factor VIII in naïve hemophilia A mice. De-N-glycosylation enhanced immunoglobulin M binding, suggesting that N-glycan occupancy masks epitopes. Elevated levels of immunoglobulin M and immunoglobulin G specific to baby hamster kidney-derived factor VIII were also observed in healthy individuals, and de-N-glycosylation increased immunoglobulin G binding. Collectively, our data suggest that factor VIII produced in baby hamster kidney cells is more immunogenic than that produced in Chinese hamster ovary cells, and that incomplete occupancy of N-linked glycosylation sites leads to the formation of immunoglobulin M- and immunoglobulin G-factor VIII immune complexes that contribute to the enhanced clearance and immunogenicity in these mouse models of hemophilia A.

Comparative analysis of marketed factor VIII products: recombinant products are not alike vis-a-vis soluble protein aggregates and subvisible particles

Essentials Aggregation is a critical quality attribute of protein therapeutics influencing immunogenicity. Aggregates and subvisible particles in 9 recombinant factor VIII (rFVIII) products were analyzed. Major differences in aggregate and particle concentrations were detected after reconstitution. rFVIII product quality determined aggregation propensity under use-relevant stress.

SUMMARY

Background Recombinant protein technologies have facilitated the development of novel factor VIII (FVIII) therapeutics with improved production efficiency, potency and half-live, and a low risk of viral transmission. The increasing number of recombinant FVIII (rFVIII) products and information on their efficacy, safety and cost allow patients and healthcare professionals to adjust treatment to individual needs. Nonetheless, 20-32% of previously untreated patients with severe hemophilia A develop inhibitory antibodies to rFVIII following treatment. The root cause of the immunogenicity of rFVIII products is not well understood. Data for human interferon and human insulin products suggest that critical quality parameters such as soluble protein aggregates (SPAs) and subvisible particles (SVPs) influence the immunogenicity of protein therapeutics. Therefore, we analyzed SPA and SVP concentrations in commercially available rFVIII products and determined how these parameters change upon exposure of rFVIII products to relevant stress conditions. Objectives Compare critical quality parameters such as SPA and SVP concentrations in rFVIII products under intended use and use-relevant stress conditions. Methods Nine rFVIII products (≥ 3 lots each) were analyzed by high-performance liquid chromatography-size exclusion chromatography (HPLC-SEC) and flow cytometry-based particle analysis. Results/conclusions SPAs and SVPs were present at different concentrations in all freshly reconstituted rFVIII products: SPA concentrations ranged from 0.2% to 11.6%; SVPs were 0.7 × 106 to 114.0 × 106 / 1000 IU. Under use-relevant stress conditions (agitation and shear stress) the products formed additional SPAs and SVPs to different degrees. The collected data indicate that product quality determines its propensity to form SVPs and SPAs, and highlights differences between marketed rFVIII products.

Challenges and Opportunities for the Subcutaneous Delivery of Therapeutic Proteins

Biotherapeutics is a rapidly growing drug class, and over 200 biotherapeutics have already obtained approval, with about 50 of these being approved in 2015 and 2016 alone. Several hundred protein therapeutic products are still in the pipeline, including interesting new approaches to treatment. Owing to patients' convenience of at home administration and reduced number of hospital visits as well as the reduction in treatment costs, subcutaneous (SC) administration of biologics is of increasing interest. Although several avenues for treatment using biotherapeutics are being explored, there is still a sufficient gap in knowledge regarding the interplay of formulation conditions, immunogenicity, and pharmacokinetics (PK) of the absorption of these compounds when they are given SC. This review seeks to highlight the major concerns and important factors governing this route of administration and suggest a holistic approach for effective SC delivery.

Protein Nanoparticles Promote Microparticle Formation in Intravenous Immunoglobulin Solutions During Freeze-Thawing and Agitation Stresses

In this study, we investigated the potential roles of nanoparticles (<100 nm) and submicron (100-1000 nm) particles in the formation of microparticles (>1000 nm) in protein formulations under some pharmaceutically relevant stress conditions. Exposure of intravenous immunoglobulin solutions to the interface-associated stresses of freeze-thawing or agitation resulted in relatively large increases in microparticle concentrations, which depended directly on the levels of pre-existing nano- and submicron particles. Thus, agglomeration of nanoparticles and submicron particles appears to play a role in microparticle formation under these stresses. In contrast, increases in microparticle concentrations during quiescent incubation at elevated temperatures were independent of the initial nano- and submicron particle concentrations in solution.

Biological considerations of plasma-derived and recombinant factor VIII immunogenicity

In hemophilia A, the most severe complication of factor VIII (FVIII) replacement therapy involves the formation of FVIII neutralizing antibodies, also known as inhibitors, in 25% to 30% of patients. This adverse event is associated with a significant increase in morbidity and economic burden, thus highlighting the need to identify methods to limit FVIII immunogenicity. Inhibitor development is regulated by a complex balance of genetic factors, such as FVIII genotype, and environmental variables, such as coexistent inflammation. One of the hypothesized risk factors of inhibitor development is the source of the FVIII concentrate, which could be either recombinant or plasma derived. Differential immunogenicity of these concentrates has been documented in several recent epidemiologic studies, thus generating significant debate within the hemophilia treatment community. To date, these discussions have been unable to reach a consensus regarding how these outcomes might be integrated into enhancing clinical care. Moreover, the biological mechanistic explanations for the observed differences are poorly understood. In this article, we complement the existing epidemiologic investigations with an overview of the range of possible biochemical and immunologic mechanisms that may contribute to the different immune outcomes observed with plasma-derived and recombinant FVIII products.

Microparticles and Nanoparticles Delivered in Intravenous Saline and in an Intravenous Solution of a Therapeutic Antibody Product

Intravenous (IV) infusion is used for administration of a large proportion of biologic therapeutics, including most monoclonal antibody products. In this study, we determined the subvisible particle levels in IV solutions and after the solutions were processed with an IV administration setup that mimicked the typical clinical method of administration. IV saline in bags manufactured by both Hospira and Baxter contained 1600-8000 microparticles/mL and 4-73 × 10⁶ nanoparticles/mL in solution. When IV immunoglobulin was diluted into the IV saline, 3700-23,000 microparticles/mL and 18-240 × 10⁶ nanoparticles/mL were detected. During processing of the solution through the IV system, in-line filters removed most microparticles. However, there were still 1-21 × 10⁶ nanoparticles/mL in IV saline and 7-83 × 10⁶ nanoparticles/mL in IV immunoglobulin diluted in saline. Finally, in samples processed through in-line filters, we found relatively large microparticles (20-60 μm) that were composed of protein or polycarbonate. These particles resulted from shedding of polycarbonate and sloughing off of protein films downstream from the filter membrane. Overall, the results document that even with in-line filters in place, high levels of subvisible particles are delivered to patients and there is a need for improved, more effective filters and IV solutions with lower particle levels.

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.

The Role of Aggregates of Therapeutic Protein Products in Immunogenicity: An Evaluation by Mathematical Modeling

Therapeutic protein products (TPP) have been widely used to treat a variety of human diseases, including cancer, hemophilia, and autoimmune diseases. However, TPP can induce unwanted immune responses that can impact both drug efficacy and patient safety. The presence of aggregates is of particular concern as they have been implicated in inducing both T cell-independent and T cell-dependent immune responses. We used mathematical modeling to evaluate several mechanisms through which aggregates of TPP could contribute to the development of immunogenicity. Modeling interactions between aggregates and B cell receptors demonstrated that aggregates are unlikely to induce T cell-independent immune responses by cross-linking B cell receptors because the amount of signal transducing complex that can form under physiologically relevant conditions is limited. We systematically evaluate the role of aggregates in inducing T cell-dependent immune responses using a recently developed multiscale mechanistic mathematical model. Our analysis indicates that aggregates could contribute to T cell-dependent immune response by inducing high affinity epitopes which may not be present in the nonaggregated TPP and/or by enhancing danger signals to break tolerance. In summary, our computational analysis is suggestive of novel insights into the mechanisms underlying aggregate-induced immunogenicity, which could be used to develop mitigation strategies.

The Effect of Small Oligomeric Protein Aggregates on the Immunogenicity of Intravenous and Subcutaneous Administered Antibodies

The role of aggregates in the immunogenicity of biologics is a major concern. A recent US FDA guidance on the issue suggests that a gap in knowledge exists regarding the type and size of aggregates involved in the immunogenicity of biologics. Furthermore, the guidance suggests that current techniques cannot capture the crucial stages of protein aggregation. Using a protein unfolding model developed earlier, we generated and classified aggregates of two therapeutic antibodies based on size and conformation. The immunogenic potential of these aggregates were then tested in a murine model. Our findings show that small native-like oligomeric aggregates (<100 nm) are more immunogenic toward the native protein than monomer and large non-native aggregates in the micron-size range, irrespective of route of administration [intravenous (i.v.) vs. subcutaneous (s.c.)]. Those smaller oligomeric aggregates represented 5%-20% of the total protein concentration in the test formulations. Furthermore, in vitro data suggest that TNF-α production by bone marrow-derived dendritic cells could serve as a predictive marker for increased immunogenic risk of aggregates after s.c. administration. The use of orthogonal techniques such as fluorescence anisotropy and quasielastic light scattering may be useful to detect these oligomeric aggregates.

Soy phosphatidylinositol containing nanoparticle prolongs hemostatic activity of B-domain deleted factor VIII in hemophilia A mice

Factor VIII (FVIII) replacement therapy in hemophilia A (HA) is complicated by a short half-life and high incidence of inhibitory antibody response against the protein. Phosphatidylinositol (PI) containing lipidic nanoparticles have previously been shown to reduce the immunogenicity and prolong the half-life of full length FVIII. It has not been established whether this prolongation in half-life improves hemostatic efficacy and whether this approach could be extended to the B-domain deleted form of FVIII (BDD FVIII). In the current study, we evaluated the pharmacokinetics (PK), hemostatic efficacy, and immunogenicity of BDD FVIII associated with PI nanoparticles (PI-BDD FVIII) in HA mice. Comparative human PK was predicted using an "informed scaling" approach. PI-BDD FVIII showed an approximate 1.5-fold increase in terminal half-life compared with free BDD FVIII following i.v. bolus doses of 40 IU/kg. PI-BDD FVIII-treated animals retained hemostatic efficacy longer than the free FVIII-treated group in a tail vein transection model of hemostasis. PI association reduced the development of inhibitory and binding antibodies against BDD FVIII after a series of i.v. injections. The combined improvements in circulating half-life and hemostatic efficacy could significantly prolong the time above clinically established therapeutic thresholds of prophylactic FVIII replacement therapy in humans.

Effects of replacement of factor VIII amino acids Asp519 and Glu665 with Val on plasma survival and efficacy in vivo

Proteolytic cleavage of factor VIII (FVIII) to activated FVIIIa is required for participation in the coagulation cascade. The A2 domain is no longer covalently bound in the resulting activated heterotrimer and is highly unstable. Aspartic acid (D) 519 and glutamic acid (E) 665 at the A1-A2 and A2-A3 domain interfaces were identified as acidic residues in local hydrophobic pockets. Replacement with hydrophobic valine (V; D519V/E665V) improved the stability and activity of the mutant FVIII over the wild-type (WT) protein in several in vitro assays. In the current study, we examined the impact of mutations on secondary and tertiary structure as well as in vivo stability, pharmacokinetics (PK), efficacy, and immunogenicity in a murine model of Hemophilia A (HA). Biophysical characterization was performed with far-UV circular dichroism (CD) and fluorescence emission studies. PK and efficacy of FVIII was studied following i.v. bolus doses of 4, 10 and 40 IU/kg with chromogenic and tail clip assays. Immunogenicity was measured with the Bethesda assay and ELISA after a series of i.v. injections. Native secondary and tertiary structure was unaltered between variants. PK profiles were similar at higher doses, but at 4 IU/kg plasma survival of D519V/E665V was improved. Hemostasis at low concentrations was improved for the mutant. Immune response was similar between variants. Overall, these results demonstrate that stabilizing mutations in the A2 domain of FVIII can improve HA therapy in vivo.

Immunogenicity of subcutaneously administered therapeutic proteins--a mechanistic perspective

The administration of therapeutic proteins via the subcutaneous route (sc) is desired for compliance and convenience, but could be challenging due to perceived immunogenic potential or unwanted immune responses. There are clinical and preclinical data supporting as well as refuting the generalized notion that sc is more immunogenic. We provide a mechanistic perspective of immunogenicity of therapeutic proteins administered via the sc route and discuss strategies and opportunities for novel therapeutic approaches to mitigate immunogenicity.

High-dose monoclonal antibodies via the subcutaneous route: challenges and technical solutions, an industry perspective

This review summarizes the various challenges in product development involved in subcutaneous administration of high-dose monoclonal antibodies and attempts to provide an industry perspective of some of the available technologies and potential avenues to overcome these challenges.

Clotting factor concentrate switching and inhibitor development in hemophilia A

The development of alloantibodies or inhibitors is the most serious complication a patient with severe hemophilia can experience from treatment with clotting factor concentrates. Although common in previously untreated patients, inhibitor development is rare in multiply exposed, well-tolerized patients. There has been a nonevidence-based reluctance to change concentrate because of a perceived greater inhibitor risk after the switch, even though most patients are now likely to be using a concentrate on which they did not begin. Inhibitors in previously treated patients are observed in approximately 2 per 1000 patient/years, which makes it difficult to study and compare rates among different products. Because the baseline inhibitor risk in previously treated patients may vary over time, it is important to compare the risk in patients switching to a new product with that in a parallel control group of nonswitching patients or within a case-controlled study. The study designs imposed by regulators are suboptimal in detecting immunogenicity signals. The issue of immunogenicity of new products is likely to gain more relevance in the near future, with a call for effective postmarketing surveillance studies for all of the new engineered factor VIII concentrates with prolonged half-lives that are likely to enter clinical practice.

Relationship between potential aggregation-prone regions and HLA-DR-binding T-cell immune epitopes: implications for rational design of novel and follow-on therapeutic antibodies

Aggregation and unwanted immunogenicity are hurdles to avoid in successful commercial development of antibody-based therapeutics. In this article, the relationship between aggregation-prone regions (APRs), capable of forming cross-β motifs/amyloid fibrils, and major histocompatibility complex class II-restricted human leukocyte antigen (HLA)-DR-binding T-cell immune epitopes (TcIEs) is analyzed using amino acid sequences of 25 therapeutic antibodies, 55 TcIEs recognized by T-regulatory cells (tregitopes), 1000 randomly generated 15-residue-long peptides, 2257 human self-TcIEs (autoantigens), and 11 peptides in HLA-peptide cocrystal structures. Sequence analyses from these diverse sources consistently show a high level of correlation between APRs and TcIEs: approximately one-third of TcIEs contain APRs, but the majority of APRs occur within TcIE regions (TcIERs). Tregitopes also contain APRs. Most APR-containing TcIERs can bind multiple HLA-DR alleles, suggesting that aggregation-driven adverse immune responses could impact a broad segment of patient population. This article has identified common molecular sequence-structure loci that potentially contribute toward both manufacturability and safety profiles of the therapeutic antibodies, thereby laying a foundation for simultaneous optimization of these attributes in novel and follow-on candidates. Incidence of APRs within TcIERs is not special to biotherapeutics, self-TcIEs from human proteins, involved in various diseases, also contain predicted APRs and experimentally proven amyloid-fibril-forming peptide sequence portions.