Huub Schellekens

Structure-immunogenicity relationships of therapeutic proteins

As more recombinant human proteins become available on the market, the incidence of immunogenicity problems is rising. The antibodies formed against a therapeutic protein can result in serious clinical effects, such as loss of efficacy and neutralization of the endogenous protein with essential biological functions. Here we review the literature on the relations between the immunogenicity of the therapeutic proteins and their structural properties. The mechanisms by which protein therapeutics can induce antibodies as well as the models used to study immunogenicity are discussed. Examples of how the chemical structure (including amino acid sequence, glycosylation, and pegylation) can influence the incidence and level of antibody formation are given. Moreover, it is shown that physical degradation (especially aggregation) of the proteins as well as chemical decomposition (e.g., oxidation) may enhance the immune response. To what extent the presence of degradation products in protein formulations influences their immunogenicity still needs further investigation. Immunization of transgenic animals, tolerant for the human protein, with well-defined, artificially prepared degradation products of therapeutic proteins may shed more light on the structure-immunogenicity relationships of recombinant human proteins.

Immunogenicity of Therapeutic Proteins: Clinical Implications and Future Prospects

BACKGROUND Therapeutic proteins have revolutionized the treatment of many diseases. In the near future, many more therapeutic proteins are likely to become available for an increasingly wide range of indications. OBJECTIVES This article reviews the incidence, causes, and consequences of formation of antibodies to therapeutic proteins and suggests ways to address issues surrounding immunogenicity. METHODS Searches of MEDLINE and EMBASE databases were performed, covering the period 1990 to May 2002. Search terms included immunogenicity, antibodies, and the names of specific therapeutic proteins and classes of therapeutic proteins. Bibliographies of retrieved articles were not searched. RESULTS All exogenous proteins, including therapeutic ones, have the potential to cause antibody formation. The reported incidence of antibody formation with therapeutic proteins varies widely between proteins and between studies (depending on the assay techniques used). The clinical consequences of antibody formation vary with the type of antibody present; for example, neutralizing antibodies are more likely to cause loss of efficacy than nonneutralizing antibodies. The immunogenicity of therapeutic proteins can be influenced by many factors, including the genetic background of the patient, the type of disease, the type of protein (human or nonhuman), the presence of conjugates or fragments, the route of administration, dose frequency, and duration of treatment. Manufacturing, handling, and storage can introduce contaminants, or alter the 3-dimensional structure of the protein via oxidation or aggregate formation. Various means have been suggested by which therapeutic proteins might be modified to reduce their immunogenicity, including PEGylation, site-specific mutagenesis, exon shuffling, and humanization of monoclonal antibodies. In the future, it may even be possible to predict the immunogenicity of new therapeutic proteins more accurately, using specifically designed animal models, including nonhuman primates and transgenic mice. CONCLUSIONS Scientists and clinicians are becoming increasingly aware of the importance of assessing the immunogenicity of new molecules as they are introduced, and of existing molecules whenever they are modified or their manufacturing process is changed. Immune responses to therapeutic proteins are usually only of clinical significance if they are associated with the development of treatment resistance. Although various means to reduce the immunogenicity of therapeutic proteins have been suggested, monitoring for antibodies during clinical trials and postmarketing surveillance remains an important issue for all therapeutic proteins.

Bioequivalence and the immunogenicity of biopharmaceuticals.

The expiry of the first patents for recombinant-DNA-derived biopharmaceuticals will open the possibility of marketing generics, if they can be shown to be essentially similar to the innovator product. However, as shown by the problem of immunogenicity, the properties of biopharmaceuticals are dependent on many factors, including downstream processing and formulation. Products from different sources cannot be assumed to be bioequivalent, even if identical genes are expressed in the same host cells and similar production methods are used. Some of the influencing factors are still unknown, which makes it impossible to completely predict biological behaviour, such as immunogenicity, which can sometimes lead to serious side effects.

Safety-Related Regulatory Actions for Biologicals Approved in the United States and the European Union

CONTEXT Biologicals are a relatively new class of medicines that carry specific risks (eg, immunogenicity). However, limited information is available on the nature and timing of safety problems with their use that were identified after approval. OBJECTIVE To determine the nature, frequency, and timing of safety-related regulatory actions for biologicals following approval in the United States and/or the European Union. DESIGN AND SETTING Follow-up of a group of biologicals approved in the United States and/or European Union between January 1995 and June 2007. Vaccines, allergenic products, and products for further manufacture and transfusion purposes were excluded. MAIN OUTCOME MEASURES Nature, frequency, and timing of safety-related regulatory actions defined as (1) dear healthcare professional letters (United States) and direct healthcare professional communications (European Union), (2) black box warnings (United States), and (3) safety-related marketing withdrawals (United States and European Union) issued between January 1995 and June 2008. RESULTS A total of 174 biologicals were approved (136 in the United States and 105 in the European Union, of which 67 were approved in both regions). Eighty-two safety-related regulatory actions (46 dear healthcare professional letters, 17 direct healthcare professional communications, 19 black box warnings, and no withdrawals) were issued for 41 of the 174 different biologicals (23.6%). The probability of a first safety-related regulatory action, derived from Kaplan-Meier analyses, was 14% (95% confidence interval [CI], 9%-19%) 3 years after approval and 29% (95% CI, 20%-37%) 10 years after approval. Biologicals first in class to obtain approval had a higher risk for a first safety-related regulatory action compared with later approved products in that class (12.0/1000 vs 2.9/1000 months, respectively; hazard ratio, 3.7 [95% CI, 1.5-9.5]). Warnings mostly concerned the classes general disorders and administration site conditions, infections and infestations, immune system disorders and neoplasms benign, malignant, and unspecified. CONCLUSIONS The nature of safety problems identified after approval for biologicals is often related to the immunomodulatory effect (infections). Because the biologicals first to be approved in a class were more likely to be subjected to regulatory action, close monitoring is recommended.

Cloning and expression of the chromosomal immune interferon gene of the rat.

The chromosomal immune interferon gene of the rat (IFN‐gamma) was identified by screening a recombinant rat lambda phage library with a human IFN‐gamma cDNA probe. In contrast to the genes of other rat IFNs, this rat IFN‐gamma chromosomal gene contains introns and its structural organization closely resembles that of the human and murine IFN‐gamma genes. The rat IFN‐gamma gene encodes a signal sequence of 19 amino acids followed by the mature IFN‐gamma protein of 137 amino acids. The gene was expressed under control of the simian virus 40 (SV40) early promoter in Chinese hamster ovary (CHO) cells deficient in dihydrofolate reductase (DHFR) after co‐transformation with a plasmid containing the mouse DHFR gene. Initial transformants with a DHFR+ phenotype produced IFN‐gamma titres ranging from 20 to 1600 units/ml. After stepwise increases in the concentration of methotrexate (MTX) in the growth medium of transformed CHO cells, MTX‐resistant clones producing 80 000‐100 000 units per ml were isolated. Protein analysis of supernatants of these MTX‐resistant cells by polyacrylamide gel electrophoresis revealed a product with an apparent mol. wt. of 18 000 daltons which was not detectable in the growth medium of DHFR+ transformants that did not produce IFN. The product was identified as rat IFN‐gamma and constituted approximately 5% of the proteins excreted from these cells.

The purification and characterization of rat gamma interferon by use of two monoclonal antibodies

Two mouse monoclonal antibodies, designated DB-1 and DB-2, were isolated and used for the purification and characterization of recombinant rat interferon gamma (rRIF-gamma) derived from Chinese hamster ovary (CHO) cells. The two antibodies belong to different classes (DB-1 is an IgG1 and DB-2 an IgA) and display similar epitope specificities as shown in competition binding experiments. Both antibodies, raised against rRIF-gamma, exhibited high affinity for rat and mouse gamma interferon and efficiently neutralized the antiviral activity of both animal interferon species. Affinity chromatography analysis showed that a column with immobilized DB-1 was capable of complete binding of rat and mouse gamma interferon, both natural and recombinant DNA-derived. As visualized by SDS-polyacrylamide gel electrophoresis and Western blot analysis, the purified rRIF-gamma preparation consisted of at least seven molecular forms with Mr values ranging between 14 000 and 25 000, with a relative abundance of a 18 000 Mr protein. Gel permeation chromatography of crude rRIF-gamma gave coincident peaks of rRIF-gamma proteins (all different forms) and interferon activity corresponding to a Mr value of 45 000. The results suggest that the molecular heterogeneity was due to differential glycosylation and was not the consequence of a proteolytic degradation process.

Recommendations for clinical use of data on neutralising antibodies to interferon-beta therapy in multiple sclerosis

The identification of factors that can affect the efficacy of immunomodulatory drugs in relapsing-remitting multiple sclerosis (MS) is important. For the available interferon-beta products, neutralising antibodies (NAb) have been shown to affect treatment efficacy. In June, 2009, a panel of experts in MS and NAbs to interferon-beta therapy convened in Amsterdam, Netherlands, under the auspices of the Neutralizing Antibodies on Interferon beta in Multiple Sclerosis consortium, a European-based project of the 6th Framework Programme of the European Commission, to review and discuss data on NAbs and their practical consequences for the treatment of patients with MS on interferon beta. The panel believed that information about NAbs and other markers of biological activity of interferons (ie, myxovirus resistance protein A [MxA]) can be integrated with clinical and imaging indicators to guide individual treatment decisions. In cases of sustained high-titre NAb positivity and/or lack of MxA bioactivity, a switch to a non-interferon-beta therapy should be considered. In patients who are doing poorly clinically, therapy should be switched irrespective of NAb or MxA bioactivity.

The Immunogenicity of Polyethylene Glycol: Facts and Fiction

ABSTRACTAn increasing number of pegylated therapeutic proteins and drug targeting compounds are being introduced in the clinic. Pegylation is intended to increase circulation time and to reduce an immunogenic response. Recently however a number of publications have appeared claiming that the polyethylene glycol (PEG) moiety of these products in itself may be immunogenic and that the induced anti-PEG antibodies are linked to enhanced blood clearance and reduced efficacy of the products. A critical review of the literature shows that most, if not all assays for anti-PEG antibodies are flawed and lack specificity. Also the biological effects induced by anti-PEG antibodies lack the characteristics of a bona fide antibody reaction. Standardization of the anti-PEG assays and the development of reference sera are urgently needed.

Biosimilar therapeutics—what do we need to consider?

Patents for the first generation of approved biopharmaceuticals have either expired or are about to expire. Thus the market is opening for generic versions, referred to as ‘biosimilars’ (European Union) or ‘follow-on protein products’ (United States). Healthcare professionals need to understand the critical issues surrounding the use of biosimilars to make informed treatment decisions. The complex high-molecular-weight three-dimensional structures of biopharmaceuticals, their heterogeneity and dependence on production in living cells makes them different from classical chemical drugs. Current analytical methods cannot characterize these complex molecules sufficiently to confirm structural equivalence with reference molecules. Verification of the similarity of biosimilars to innovator biopharmaceuticals remains a key challenge. Furthermore, a critical safety issue, the immunogenicity of biopharmaceuticals, has been highlighted in recent years, confirming a need for comprehensive immunogenicity testing prior to approval and extended post-marketing surveillance. Biosimilars present a new set of challenges for regulatory authorities when compared with conventional generics. While the demonstration of a pharmacokinetic similarity is sufficient for conventional, small-molecule generic agents, a number of issues will make the approval of biosimilars more complicated. Documents recently published by the European Medicines Agency (EMEA) outlining requirements for the market approval of biosimilars provide much-needed guidance. The EMEA has approved a number of biosimilar products in a scientifically rigorous and balanced process. Outstanding issues include the interchangeability of biosimilars and innovator products, the possible need for unique naming to differentiate the various biopharmaceutical products, and more comprehensive labelling for biosimilars to include relevant clinical data.

Immunological mechanism underlying the immune response to recombinant human protein therapeutics

Recombinant human (rhu) protein therapeutics are powerful tools to treat several severe diseases such as multiple sclerosis and diabetes mellitus, among others. A major drawback of these proteins is the production of anti-drug antibodies (ADAs). In some cases, these ADAs have neutralizing capacity and can interfere with the efficacy and safety of the drug. Little is known about the immunological mechanisms underlying the unwanted immune response against human homolog protein therapeutics. This article aims to provide current insights into recent immunological developments and to link this with regard to production of ADAs. A particular focus is given to aggregates being present in a rhu protein formulation and their impact on the immune system, subsequently leading to breakage of tolerance and formation of ADAs. Aggregation is one of the key factors in immunogenicity and by reducing aggregation one can reduce immunogenicity and make drugs safer and more efficient.