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Journal of Inherited Metabolic Disease published by John Wiley & Sons Ltd on behalf of SSIEM Pegunigalsidase alfa, a novel PEGylated, covalently crosslinked form of α-galactosidase A developed as enzyme replacement therapy (ERT) for Fabry disease (FD), was designed to increase plasma half-life and reduce immunogenicity, thereby enhancing efficacy compared with available products. Symptomatic adults with FD participated in this open-label, 3-month dose-ranging study, followed by a 9-month extension. Three cohorts were enrolled in a stepwise manner, each receiving increased doses of pegunigalsidase alfa: 0.2, 1.0, 2.0 mg/kg, via intravenous infusion every other week. Pharmacokinetic analysis occurred on Day 1 and Months 3, 6, and 12. Kidney biopsies at baseline and Month 6 assessed peritubular capillary globotriaosylceramide (Gb3) content. Renal function, cardiac parameters, and other clinical endpoints were assessed throughout. Treatment-emergent adverse events (AEs) and presence of immunoglobulin G (IgG) antidrug antibodies (ADAs) were assessed. Sixteen patients completed 1 year's treatment. Mean terminal plasma half-life (each cohort) ranged from 53 to 121 hours. All 11 male and 1 of 7 female patients presented with classic FD phenotype, in whom renal peritubular capillary Gb3 inclusions were reduced by 84%. Mean estimated glomerular filtration rate was 111 mL/min/1.73 m 2 at baseline, remaining stable throughout treatment. Three patients developed treatment-induced IgG ADAs; following 1 year's treatment, all became ADA-negative. Nearly all treatment-emergent AEs were mild or moderate. One patient withdrew from the study following a serious related AE. Pegunigalsidase alfa may represent an advance in ERT for FD, based on its unique pharmacokinetics and apparent low immunogenicity.

Plants are a promising alternative for the production of biotherapeutics. Manufacturing in-planta adds plant specific glycans. To understand immunogenic potential of these glycans, we developed a validated method to detect plant specific glycan antibodies in human serum. Using this assay, low prevalence of pre-existing anti-plant glycan antibodies was found in healthy humans (13.5%) and in glucocerebrosidase-deficient Gaucher disease (GD) patients (5%). A low incidence (9% in naïve patient and none in treatment experienced patients) of induced anti-plant glycan antibodies was observed in GD patients after up to 30 months replacement therapy treatment with taliglucerase alfa, a version of human glucocerebrosidase produced in plant cells. Detailed evaluation of clinical safety and efficacy endpoints indicated that anti-plant glycan antibodies did not affect the safety or efficacy of taliglucerase alfa in patients. This study shows the benefit of using large scale human trials to evaluate the immunogenicity risk of plant derived glycans, and indicates no apparent risk related to anti-plant glycan antibodies.

The administration of biological therapeutics may result in the development of anti-drug antibodies (ADAs) in treated subjects. In some cases, ADA responses may result in the loss of therapeutic efficacy due to the formation of neutralizing ADAs (NAbs). An important characteristic of anti-drug NAbs is their direct inhibitory effect on the pharmacological activity of the therapeutic. Neutralizing antibody responses are of particular concern for biologic products with an endogenous homolog whose activity can be potentially dampened or completely inhibited by the NAbs leading to an autoimmune-type deficiency syndrome. Therefore, it is important that ADAs are detected and characterized appropriately using sensitive and reliable methods. The design, development and optimization of cell-based assays used for detection of NAbs have been published previously by Gupta et al. 2007 [1]. This paper provides recommendations on best practices for the validation of cell-based NAb assay and suggested validation parameters based on the experience of the authors.

Biotherapeutics, including recombinant or plasma-derived human proteins and antibody-based molecules, have emerged as an important class of pharmaceuticals. Aggregation and immunogenicity are among the major bottlenecks during discovery and development of biotherapeutics. Computational tools that can predict aggregation prone regions as well as T- and B-cell immune epitopes from protein sequence and structure have become available recently. Here, we describe a potential coupling between aggregation and immunogenicity: T-cell and B-cell immune epitopes in therapeutic proteins may contain aggregation-prone regions. The details of biological mechanisms behind this observation remain to be understood. However, our observation opens up an exciting potential for rational design of de-immunized novel, as well as follow on biotherapeutics with reduced aggregation propensity.

An evaluation of potential antibody formation to biologic therapeutics during the course of nonclinical safety studies and its impact on the toxicity profile is expected under current regulatory guidance and is accepted standard practice. However, approaches for incorporating this information in the interpretation of nonclinical safety studies are not clearly established. Described here are the immunological basis of anti-drug antibody formation to biopharmaceuticals (immunogenicity) in laboratory animals, and approaches for generating and interpreting immunogenicity data from nonclinical safety studies of biotechnology-derived therapeutics to support their progression to clinical evaluation. We subscribe that immunogenicity testing strategies should be adapted to the specific needs of each therapeutic development program, and data generated from such analyses should be integrated with available clinical and anatomic pathology, pharmacokinetic, and pharmacodynamic data to properly interpret nonclinical studies.

The appropriate evaluation of the immunogenicity of biopharmaceuticals is of major importance for their successful development and licensure. Antibodies elicited by these products in many cases cause no detectable clinical effects in humans. However, antibodies to some therapeutic proteins have been shown to cause a variety of clinical consequences ranging from relatively mild to serious adverse events. In addition, antibodies can affect drug efficacy. In non-clinical studies, anti-drug antibodies (ADA) can complicate interpretation of the toxicity, pharmacokinetic (PK) and pharmacodynamic (PD) data. Therefore, it is important to develop testing strategies that provide valid assessments of antibody responses in both non-clinical and clinical studies. This document provides recommendations for antibody testing strategies stemming from the experience of contributing authors. The recommendations are intended to foster a more unified approach to antibody testing across the biopharmaceutical industry. The strategies proposed are also expected to contribute to better understanding of antibody responses and to further advance immunogenicity evaluation.

Throughout the life cycle of biopharmaceutical products, bioanalytical support is provided using ligand binding assays to measure the drug product for pharmacokinetic, pharmacodynamic, and immunogenicity studies. The specificity and selectivity of these ligand binding assays are highly dependent on the ligand binding reagents. Thus the selection, characterization, and management processes for ligand binding reagents are crucial to successful assay development and application. This report describes process considerations for selection and characterization of ligand binding reagents that are integral parts of the different phases of assay development. Changes in expression, purification, modification, and storage of the ligand binding reagents may have a profound effect on the ligand binding assay performance. Thus long-term management of the critical ligand binding assay reagents is addressed including suggested characterization criteria that allow ligand binding reagents to be used in as consistent a manner as possible. Examples of challenges related to the selection, modification, and characterization of ligand binding reagents are included.

The administration of biological therapeutics can evoke some level of immune response to the drug product in the receiving subjects. An immune response comprised of neutralizing antibodies can lead to loss of efficacy or potentially more serious clinical sequelae. Therefore, it is important to monitor the immunogenicity of biological therapeutics throughout the drug product development cycle. Immunoassays are typically used to screen for the presence and development of anti-drug product antibodies. However, in-vitro cell-based assays prove extremely useful for the characterization of immunoassay-positive samples to determine if the detected antibodies have neutralizing properties. This document provides scientific recommendations based on the experience of the authors for the development of cell-based assays for the detection of neutralizing antibodies in non-clinical and clinical studies.

Summary Reliable risk assessment for biotherapeutics requires accurate evaluation of risk factors associated with immunogenicity. Immunogenicity risk assessment tools were developed and applied to investigate the immunogenicity of a fully human therapeutic monoclonal antibody, ATR-107 [anti-interleukin (IL)-21 receptor] that elicited anti-drug antibodies (ADA) in 76% of healthy subjects in a Phase 1 study. Because the ATR-107 target is expressed on dendritic cells (DCs), the immunogenicity risk related to engagement with DC and antigen presentation pathways was studied. Despite the presence of IL-21R on DCs, ATR-107 did not bind to the DCs more extensively than the control therapeutic antibody (PF-1) that had elicited low clinical ADA incidence. However, ATR-107, but not the control therapeutic antibody, was translocated to the DC late endosomes, co-localized with intracellular antigen-D related (HLA-DR) molecules and presented a dominant T cell epitope overlapping the complementarity determining region 2 (CDR2) of the light chain. ATR-107 induced increased DC activation exemplified by up-regulation of DC surface expression of CD86, CD274 (PD-L1) and CD40, increased expansion of activated DC populations expressing CD86hi, CD40hi, CD83hi, programmed death ligand 1 (PD-L1)hi, HLA-DRhi or CCR7hi, as well as elevated secretion of tumour necrosis factor (TNF)-α by DCs. DCs exposed to ATR-107 stimulated an autologous T cell proliferative response in human donor cells, in concert with the detection of immunoglobulin (Ig)G-type anti-ATR-107 antibody response in clinical samples. Collectively, the enhanced engagement of antigen presentation machinery by ATR-107 was suggested. The approaches and findings described in this study may be relevant to identifying lower immunogenicity risk targets and therapeutic molecules.

Therapeutic protein products (TPPs) are of considerable value in the treatment of a variety of diseases, including cancer, hemophilia, and autoimmune diseases. The success of TPP mainly results from prolonged half-life, increased target specificity and decreased intrinsic toxicity compared with small molecule drugs. However, unwanted immune responses against TPP, such as generation of anti-drug antibody, can impact both drug efficacy and patient safety, which has led to requirements for increased monitoring in regulatory studies and clinical practice, termination of drug development, or even withdrawal of marketed products. We present an overview of current knowledge on immunogenicity of TPP and its impact on efficacy and safety. We also discuss methods for measurement and prediction of immunogenicity and review both product-related and patient-related risk factors that affect its development, and efforts that may be taken to mitigate it. Lastly, we discuss gaps in knowledge and technology and what is needed to fill these.

Background. Bone morphogenetic proteins (BMPs) are potent inducers of bone formation. Functional and immunohistochemical studies have identified BMPs in a subset of osteosarcomas. In the present study, the authors extend the analysis of BMP expression to other bone and soft tissue sarcomas. Methods. Monoclonal antibody AbH3b2/17 against human BMP-2 and BMP-4 was used in avidin-biotin-immunoperoxidase assays with frozen sections of bone tumors (71 specimens), soft tissue sarcomas (69 specimens), and normal tissues. Results. Among bone tumors, BMP was detected in osteosarcomas (17 of 29 samples), malignant fibrous histiocytomas (MFHs) (6 of 6), and the spindle cell sarcomatous components of spindle cell (dedifferentiated) chondrosarcomas (4 of 4), but not in conventional chondrosarcomas (0 of 10) or Ewing's sarcomas (0 of 14). Histologic subtypes of osteosarcoma differed for BMP expression, with 8 of 9 fibrohistiocytic, 9 of 13 osteoblastic, and 0 of 5 chondroblastic lesions showing immunostaining. In all BMP-positive bone tumors, immunostaining was localized in the cytoplasm of primitive mesenchymal cells, with little or no staining in tumor matrix and more mature osteoblastic/chondrocytic cells. Among soft tissue sarcomas, MFHs (11 of 12), liposarcomas (5 of 11), leiomyosarcomas (3 of 9), and malignant schwannomas (3 of 8) showed cytoplasmic BMP immunostaining. Synovial sarcomas (0 of 9), rhabdomyosarcomas (0 of 8), and fibrosarcomas (0 of 7) were BMP-negative. All normal humantissues tested, including the tissues of a 16-week-old fetus, lacked BMP immunoreactivity. Conclusions. Bone morphogenetic protein is expressed in a subset of osteosarcomas, a high proportion of MFHs of bone and soft tissue, and in spindle cell chondrosarcomas. In these tumors, BMP is localized predominantly to the cytoplasm of malignant cells with primitive mesenchymal features; no or little BMP is detected in the more differentiated elements of bone and soft tissue sarcomas, Different histologic types of bone and soft tissue sarcomas may mimic discrete stages of mesenchymal differentiation as defined by BMP expression and histologic criteria.

Background. Bone morphogenetic proteins (BMP) induce ectopic bone formation in vivo and may play a role in normal bone development. In addition, bone morphogenetic activity, as measured in a bone-forming assay in immunodeficient, athymic nu/nu mice, is present in a proportion of osteosarcomas; this activity, which may be mediated by BMP, is correlated with a poor prognosis. Methods. The development of a monoclonal antibody against recombinant human BMP-2, AbH3b2/17, has allowed immunohistochemical localization of BMP in tumor tissues. Cryostat sections of osteosarcomas (21 tumor samples), chondrosarcomas (5 samples), and Ewing's sarcomas of bone (5 samples) were examined with AbH3b2/17 using the avidin-biotin-immunoperoxidase method. Results. The authors found AbH3b2/17 immunoreactivity in 12 of the 21 osteosarcoma samples (57% sensitivity) obtained from 20 patients. For one patient, samples of the primary lesion and a subsequent metastasis were tested, and only the latter showed AbH3b2/17 immunore-activity. The chondrosarcomas and Ewing's sarcomas examined showed no immunoreactivity. In antigen-positive osteosarcomas, AbH3b2/17 immunostaining was localized predominantly in the cytoplasm of tumor cells. Moreover, the proportion of AbH3b2/17-reactive cells varied among osteosarcomas with disparate histologic features. Conclusions. The authors identified a rapid and widely applicable method for detecting BMP expression in intact tissues, which may complement and enhance the bone-forming assay in nu/nu mice as a prognostic procedure in osteosarcomas.

SummaryThe pharmacokinetics of intravenously administered recombinant human factor IX (rhFIX) were studied in Sprague-Dawley rats and Beagle dogs. Rats received rhFIX (50 IU/kg once daily) for 28 days, and the plasma half-life was 5 h. Anti-Human Factor IX serum antibody levels were found in only 1 of 12 rats. The pharmacokinetic profiles of rhFIX or Mononine™, a purified human plasma-derived factor IX, after single 100 IU/kg IV doses in dogs, were similar. Peak plasma concentrations of rhFIX and Mononine™ were 4–5 μg/ml. The mean plasma half-lives were 13.2 ± 1.6 h for rhFIX and 13.3 ± 1.6 h for Mononine™. Dogs also received rhFIX (40 IU/kg IV, daily) for 28 days or Mononine™ (40 IU/kg IV daily) for 14 days. Anti-human Factor IX serum antibody levels were determined for each compound. Pharmacokinetic half-lives decreased in these treated dogs which developed antihuman Factor IX antibodies. The antibody responses in 28 day rhFIX (40 IU/kg) dogs were similar to 14 day Mononine™ (40 IU/kg) dogs.