Anti-therapeutic Antibodies Research Articles

Immunogenicity of protein therapeutics: The key causes, consequences and challenges

The immunogenicity of protein therapeutics has so far proven to be difficult to predict in patients, with many biologics inducing undesirable immune responses directed towards the therapeutic resulting in reduced efficacy, anaphylaxis and occasionally life threatening autoimmunity. The most common effect of administrating an immunogenic protein therapeutic is the development of a high affinity anti-therapeutic antibody response. Furthermore, it is clear from clinical studies that protein therapeutics derived from endogenous human proteins are capable of stimulating undesirable immune responses in patients, and as a consequence, the prediction and reduction of immunogenicity has been the focus of intense research. This review will outline the principle causes of the immunogenicity in protein therapeutics, and describe the development of pre-clinical models that can be used to aid in the prediction of the immunogenic potential of novel protein therapeutics prior to administration in man.

A novel homogeneous Biotin–digoxigenin based assay for the detection of human anti-therapeutic antibodies in autoimmune serum

Electrochemiluminescence (ECL) assays have been widely used for the detection of anti-therapeutic antibodies (ATAs) against biotherapeutics. With the discontinuation of BioVeris® (BV) ECL platform, an alternative technology was needed to replace BV assays to ensure continuous support of multi-year clinical studies. After evaluation of several immunoassay platforms, a novel homogeneous Biotin–digoxigenin (DIG) based bridging ELISA format was selected to develop an anti-rhuMAbX antibody screening assay to test serum samples from rheumatoid arthritis (RA) patients. With a homogeneous overnight sample incubation, the Biotin–DIG ELISA achieved comparable relative sensitivity and free drug tolerance to the previous BV ATA assay for rhuMAbX. To abrogate potential auto-antibody interference in RA sera, various assay conditions were thoroughly evaluated and a horseradish peroxidase (HRP)-conjugated chicken anti-DIG antibody was selected as the detection conjugate. Other potential interferences from serum Biotin, naturally occurring anti-avidin antibodies, and concomitant medications such as digoxin and hydrocortisone, which have similar structures to digoxigenin, were also investigated. Under optimized final assay conditions, the Biotin–DIG assay showed a relative sensitivity of approximately 11ng/mL using a polyclonal anti-complementarity determining region (CDR) enriched positive control; the assay could detect 500ng/mL of the positive control in the presence of approximately 27μg/mL of rhuMAbX in RA serum. In addition, a confirmatory step was optimized for the assay based upon pre-incubating serum samples with an excess of free drug. Overall, the Biotin–DIG assay met the performance requirements for an ATA screening assay and had comparable sensitivity and drug tolerance to the BV assay; therefore this assay was a suitable replacement for the BV assay used for previous clinical studies of rhuMAbX. The Biotin–DIG based assay format can be broadly used as an effective screening platform for the detection of anti-therapeutic antibodies.

Impact of Matrix-Associated Soluble Factors on The Specificity of The Immunogenicity Assessment

Specificity and sensitivity are essential in assays for immunogenicity assessment of biotherapeutics. Nonspecific interactions from excess therapeutic or anti-therapeutic antibody, soluble ligands (e.g., target receptor), or serum proteins associated with autoimmune conditions (e.g., rheumatoid factor) in samples can impact the detection of a true anti-therapeutic response. Electrochemiluminescence-based bridging assay formats could eliminate the interference due to rheumatoid factor with no pretreatment with Melon Gel™ or aggregated IgG. The interference due to soluble factors was not platform specific for the four therapeutics evaluated in this study. Melon Gel pretreatment and avidin high-bind (Meso Scale Discovery) plates can effectively reduce interference due to rheumatoid factor in ELISA- and electrochemiluminescence-based assays, respectively. Excess levels of therapeutic and anti-therapeutic antibodies in bridging assays can impact assay specificity.

Development and optimization of a cell-based neutralizing antibody assay using a sample pre-treatment step to eliminate serum interference

We developed a neutralizing antibody assay (NAb assay), based upon the complement-dependent cytotoxicity (CDC) activity of a monoclonal human IgG(1) therapeutic (IgT), to characterize anti-therapeutic antibodies (ATA) in autoimmune patient serum. Neutralizing antibodies (NAb) were measured by a decrease in the extent of CDC mediated by 50 ng/mL IgT, on a lymphoblastoid cell line. A sample pre-treatment procedure, utilizing a Protein A/G resin to purify total immunoglobulins, was optimized for use in the NAb assay to eliminate the non-specific assay interferents observed in individual serum samples from rheumatoid arthritis patients. In some individuals, the addition of naïve serum to the assay completely inhibited CDC activity. After sample pre-treatment, the variability of the CDC response induced by IgT in individual serum samples from a drug-naïve RA population, tested over three days, was only 3%, irrespective of complement immune complexes or rheumatoid factor levels. The pre-treatment procedure was performed on samples and matrix controls as part of each assay. The NAb assay was able to recover and detect polyclonal ATA from human serum at a concentration of 0.25 microg/mL with pre-treatment. Dose-dependent neutralization of IgT was observed, however, a simple positive/negative reporting scheme was adopted. The NAb assay was found to have the desired properties of specificity, robustness, precision and recovery for validation to support the characterization of ATA in clinical samples.

Prediction of Immunogenicity of Therapeutic Proteins

Most protein therapeutics have the potential to induce undesirable immune responses in patients. Many patients develop anti-therapeutic antibodies, which can affect the safety and efficacy of the therapeutic protein, particularly if the response is neutralizing. There are a variety of factors that influence the immunogenicity of protein therapeutics and, in particular, the presence of B- and T-cell epitopes is considered to be of importance. In silico tools to identify the location of both B- and T-cell epitopes and to assess the potential for immunogenicity have been developed, and such tools provide an alternative to more complex in vitro or in vivo immunogenicity assays. This article reviews computational epitope prediction methods and also the use of manually curated databases containing experimentally derived epitope data. However, due to the complexities of the molecular interactions involved in epitope recognition by the immune system, the heterogeneity of key proteins in human populations and the adaptive nature of the immune response, in silico methods have not yet achieved a level of accuracy that enables them to be used as stand-alone tools for predicting clinical immunogenicity. Computational methods, particularly with regard to T-cell epitopes, only consider a limited number of events in the process of epitope formation and therefore routinely over-predict the number of epitopes within a molecule. Epitope databases such as the Immune Epitope Database (IEDB) and the proprietary T Cell Epitope Database (TCED) have reached a size and level of organization that increases their utility; however, they are not exhaustive. These methods have greatest utility as an adjunct to in vitro assays where they can be used either to reduce the amount and complexity of the in vitro screening, or they can be used as tools to analyze the sequence of the identified epitope in order to locate amino acids critical for its properties.

A novel gamma-fitting statistical method for anti-drug antibody assays to establish assay cut points for data with non-normal distribution

In recent years there has been growing recognition of the impact of anti-drug or anti-therapeutic antibodies (ADAs, ATAs) on the pharmacokinetic and pharmacodynamic behavior of the drug, which ultimately affects drug exposure and activity. These anti-drug antibodies can also impact safety of the therapeutic by inducing a range of reactions from hypersensitivity to neutralization of the activity of an endogenous protein. Assessments of immunogenicity, therefore, are critically dependent on the bioanalytical method used to test samples, in which a positive versus negative reactivity is determined by a statistically derived cut point based on the distribution of drug naïve samples. For non-normally distributed data, a novel gamma-fitting method for obtaining assay cut points is presented. Non-normal immunogenicity data distributions, which tend to be unimodal and positively skewed, can often be modeled by 3-parameter gamma fits. Under a gamma regime, gamma based cut points were found to be more accurate (closer to their targeted false positive rates) compared to normal or log-normal methods and more precise (smaller standard errors of cut point estimators) compared with the nonparametric percentile method. Under a gamma regime, normal theory based methods for estimating cut points targeting a 5% false positive rate were found in computer simulation experiments to have, on average, false positive rates ranging from 6.2 to 8.3% (or positive biases between + 1.2 and + 3.3%) with bias decreasing with the magnitude of the gamma shape parameter. The log-normal fits tended, on average, to underestimate false positive rates with negative biases as large a − 2.3% with absolute bias decreasing with the shape parameter. These results were consistent with the well known fact that gamma distributions become less skewed and closer to a normal distribution as their shape parameters increase. Inflated false positive rates, especially in a screening assay, shifts the emphasis to confirm test results in a subsequent test (confirmatory assay). On the other hand, deflated false positive rates in the case of screening immunogenicity assays will not meet the minimum 5% false positive target as proposed in the immunogenicity assay guidance white papers.

Technology comparisons for anti-therapeutic antibody and neutralizing antibody assays in the context of an anti-TNF pharmacokinetic study

A single-dose cynomolgus monkey pharmacokinetic study was performed comparing two monoclonal anti-TNF antibodies (mAbs), GNExTNFvF and Humira®. Normal pharmacokinetic profiles were observed over the first week of the study, followed by a rapid drop in serum mAb levels after day 8. In order to determine whether an anti-therapeutic antibody (ATA) response led to the abnormal clearance of antibody in this study, ATA assays were developed using two electrochemiluminescent technologies, BioVeris and Meso Scale Discovery (MSD). Characterization of the assays demonstrated that the two platforms gave similar sensitivities and tolerance to the presence of therapeutic antibody. Analysis of the cynomolgus monkey serum samples revealed that all animals developed significant ATA titers with log titer values of 2–4, with the BioVeris and MSD technologies giving very similar results. Immunodepletion studies confirmed the CDR-specificity of the ATA response for the GNExTNFvF-dosed cynos, although the Humira-dosed cynos showed both CDR-specific and human IgG1 framework-specific ATAs. To further characterize the ATA response, neutralizing antibody (NAb) assays were developed using two different approaches, flow cytometry and MSD. Flow cytometry and MSD cell-binding assays used Jurkat cells transfected with noncleavable TNF (huTNF NC). Neutralizing activity was assessed by the ability of ATA-positive serum samples to block the binding of biotinylated anti-TNF to huTNF NC Jurkat cells, showing that all but one animal developed neutralizing antibodies. Although both technologies displayed similar trends, the MSD approach showed greater differentiation between samples and could detect a broader range of neutralizing activities.

Reducing the Immunogenicity of Protein Therapeutics

Protein therapeutics, such as antibodies, enzymes and toxins, are very promising reagents for the treatment of human disease. However, many therapeutic proteins are known to elicit immune responses when administered to humans. Certain antibodies work by neutralization; others reduce drug efficacy. It is clear that helper T cells are an important factor in the development of class-switched and affinity-maturated anti-therapeutic protein antibodies. Elimination of the T cell epitope seems reasonable, but it is probably impossible to remove all T cell epitopes from protein drugs because T cell epitopes are closely related to the major histocompatibility complex (MHC) molecules, which are known to be highly polymorphic. Accordingly, a possible practical approach for reducing immunogenicity involves the removal of B cell epitopes. In this case, reducing the affinity between the antigen and the B cell receptor may reduce B cell activation, even though the T cell will still be activated. Also a B cell epitope is not restricted by MHC class II molecules. This review seeks to address the identification and the characterization of B cell epitopes, and reports on the development of strategies for reducing immune response with modified B cell epitopes.

A non-radioactive method for detecting neutralizing antibodies against therapeutic proteins in serum

The presence of neutralizing antibodies against protein therapeutics continues to cause concern in the biomedical field. These antibodies not only reduce the efficacy of the protein therapeutics, but may also block the normal function of their endogenous counterparts, which can result in serious health risks to the patient. To date, a limited number of in vitro cell-based bioassays for detecting neutralizing antibodies against therapeutic proteins have been developed. However, many of the existing assays involve the use of radioactive materials. We have established a novel and non-radioactive bioassay system for detecting neutralizing antibodies in patient serum samples. Our assay measures the cell metabolic activities that are closely associated with cell proliferation and apoptosis. The biologic effect of the therapeutic protein and the capability of the antibodies to neutralize the therapeutics are reflected by changes of the cellular metabolic activities triggered by the administration of the therapeutics or presence of the anti-therapeutic protein antibodies. Compared with existing assays, this new assay is equally or more sensitive, and completely eliminates the use of radioactive materials.

Detection of neutralizing anti-therapeutic protein antibodies in serum or plasma samples containing high levels of the therapeutic protein

Neutralizing antibodies against therapeutic proteins can be potentially harmful if the antibody blocks not only the therapeutic activities of the therapeutic protein but also the normal functions of the endogenous counterpart. Detection of the neutralizing anti-therapeutic protein antibodies generally relies on bioassays measuring changes in the biologic activity of the therapeutic protein triggered by the presence of the antibody. Most of the bioassays, particularly the cell-based in vitro assays, fail to detect neutralizing anti-therapeutic protein antibodies when the remaining therapeutic protein level in the assay samples is high. The remaining therapeutic protein, either a free molecule or an immune complex with anti-therapeutic protein antibodies, can inhibit the neutralizing activity of the antibody and prevent detection. We describe the development of a procedure that uses acid dissociation and affinity adsorption to remove therapeutic protein from assay samples. With this procedure, we can detect the presence of neutralizing anti-therapeutic protein antibodies from samples containing high levels of therapeutic protein.