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.

Development and evaluation of a sensitive enzyme-linked oligonucleotide-sorbent assay for detection of polymerase chain reaction-amplified hepatitis C virus of genotypes 1-6

A high-throughput polymerase chain reaction (PCR)-based enzyme-linked oligonucleotide-sorbent assay (ELOSA) was developed for use in the diagnostic testing of serum from patients who may be infected with different hepatitis C virus (HCV) genotypes. Twelve genotype-specific 5'-aminated DNA-coated probes were designed based on the variable 5'-untranslated region sequences of the HCV genotypes 1-6. Using 100 clinical serum samples, the performance of the PCR-ELOSA method was compared with Roche's COBAS Amplicor HCV Monitor V2.0 assay and the VERSANT HCV genotype assay (LiPA), and the overall agreement was 99% at the level of HCV genotypes with a detection range of 2.0 x 10(2) to 1.0 x 10(7)IU/ml for PCR-ELOSA. The PCR-ELOSA was more comprehensive as demonstrated by the fact that approximately 20% of the samples with different subtypes could be discriminated by this method but not by LiPA. In addition, the PCR-ELOSA system showed high accuracy (CV<or=6.36%) and even higher reproducibility (CV<or=5.55%). Thus, this novel PCR-ELOSA system provides a sensitive and versatile alternative to current HCV detection assays.

Sensitivity by combination: immuno-PCR and related technologies

The versatility of immunoassays for the detection of antigens can be combined with the signal amplification power of nucleic acid amplification techniques in a broad range of innovative detection strategies. This review summarizes the spectrum of both, DNA-modification techniques used for assay enhancement and the resulting key applications. In particular, it focuses on the highly sensitive immuno-PCR (IPCR) method. This technique is based on chimeric conjugates of specific antibodies and nucleic acid molecules, the latter of which are used as markers to be amplified by PCR or related techniques for signal generation and read-out. Various strategies for the combination of antigen detection and nucleic acid amplification are discussed with regard to their laboratory analytic performance, including novel approaches to the conjugation of antibodies with DNA, and alternative pathways for signal amplification and detection. A critical assessment of advantages and drawbacks of these methods for a number of applications in clinical diagnostics and research is conducted. The examples include the detection of viral and bacterial antigens, tumor markers, toxins, pathogens, cytokines and other targets in different biological sample materials.

New immuno-PCR assay for detection of low concentrations of shiga toxin 2 and its variants

Shiga toxin (Stx)-producing Escherichia coli (STEC) strains secrete toxins that are major virulence factors and diagnostic targets, but some STEC strains secrete Stx in amounts that cannot be detected using conventional cell cytotoxicity or immunological assays. Therefore, there is an urgent need for more-sensitive Stx detection methods. We describe the development of an assay that can detect low concentrations of Stx2 and its variants. An immuno-PCR Stx2 assay was developed based on an enzyme immunoassay (EIA) combining antibody capture and DNA amplification to increase the signal. The immuno-PCR assay detected 10 pg/ml of purified Stx2, compared to 1 ng/ml Stx2 detected by commercial EIA. Consequently, immuno-PCR detected Stx2 and its variants in STEC strains that produce the toxins at levels that are nondetectable by using the EIA, as well as the Stx2 in EIA-negative enriched stool cultures from patients. Our data demonstrate that the immuno-PCR developed here is a highly sensitive and specific method for the detection of trace amounts of Stx2 and Stx2 variants. It is therefore suitable for use by clinical microbiological laboratories to improve the toxin detection in clinical samples.

Detecting antigens by quantitative immuno-PCR

The quantitative immuno-PCR (qIPCR) technology combines the advantages of flexible and robust immunoassays with the exponential signal amplification power of PCR. The qIPCR allows one to detect antigens using specific antibodies labeled with double-stranded DNA. The label is used for signal generation by quantitative PCR. Because of the efficiency of nucleic acid amplification, qIPCR typically leads to a 10- to 1,000-fold increase in sensitivity compared to an analogous enzyme-amplified immunoassay. A standard protocol of a qIPCR assay to detect human interleukin 6 (IL-6) using a sandwich immunoassay combined with real-time PCR readout is described here. The protocol includes initial immobilization of the antigen, and coupling of this antigen with antibody-DNA conjugates is then carried out by (a) the stepwise assembly of biotinylated antibody, streptavidin and biotinylated DNA, (b) the use of a biotinylated antibody and an anti-biotin-DNA conjugate or (c) the employment of an anti-IL-6 antibody-DNA conjugate. Following the assembly of signal-generating immunocomplexes, real-time PCR is used to amplify and record the signal. Depending on the coupling strategy, the qIPCR assays require 4-7 h with only about 3 h hands-on-time. The use of qIPCR assays enables the detection of rare biomarkers in complex biological samples that are poorly accessible by conventional immunoassays. Therefore, qIPCR offers novel opportunities for the biomedical analysis of, for instance, neurodegenerative diseases and viral infections as well as new tools for the development of novel pharmaceuticals.

Sensitive immunoassay of a biomarker tumor necrosis factor-alpha based on poly(guanine)-functionalized silica nanoparticle label

A novel electrochemical immunosensor for the detection of tumor necrosis factor-alpha (TNF-alpha) based on poly(guanine)-functionalized silica nanoparticles (NPs) label is presented. The detection of mouse TNF-alpha via immunological reaction is based on a dual signal amplification: (1) a large amount of guanine residues introduced on the electrode surface through sandwich immunoreaction and poly(guanine)-functionalized silica NP label; (2) Ru(bpy)3(2+)-induced catalytic oxidation of guanine, which results in great enhancement of anodic current. The synthesized silica NP conjugates were characterized with atomic force microscopy, X-ray photoelectron spectroscopy, and electrochemistry. These experiments confirmed that poly(guanine) and avidin were immobilized on the surface of silica NPs. The performance of the electrochemical immunosensor was evaluated and some experiment parameters (e.g., concentration of Ru(bpy)3(2+), incubation time of TNF-alpha, etc.) were optimized. The detection limit for TNF-alpha is found to be 5.0 x 10(-11) g mL(-1) (2.0 pM), which corresponds to 60 amol of TNF-alpha in 30 microL of sample. This immunosensor based on the poly(guanine)-functionalized silica NP label offers great promise for rapid, simple, cost-effective analysis of biological samples.

Detection of norovirus capsid proteins in faecal and food samples by a real time immuno-PCR method

AIMS

To develop a sensitive real time immuno-polymerase chain reaction (rtI-PCR) method for detecting norovirus (NV) capsid protein in food samples.

METHODS AND RESULTS

The viral antigens were captured by two polyclonal antisera against recombinant Norwalk viral-like particles (rNVLPs). Biotin-conjugated antibodies, avidin and biotin-conjugated DNA reporter were used to convert the protein signals into DNA signals. The reporter DNA was then amplified by addition of primers and PCR. A real time PCR method was used in order to perform a quantitative post-PCR analysis. One hundred rNVLPs (10 fg) and a NV sample containing 660 rNVLPs equivalent particle units (66 fg) could be detected by this method.

CONCLUSION

The PCR inhibitors present in the food samples had minimal effect on antigen capture and were removed by multiple wash steps during the rtI-PCR procedure. The sensitivity of rtI-PCR was >1000-fold higher than the standard enzyme-linked immunosorbent assay and approximately 10 times higher than reverse transcription PCR in detection of NV capsid protein in stool and food samples.

SIGNIFICANCE AND IMPACT OF THE STUDY

This is the first report of a rtI-PCR method to detect NV in contaminated food samples without concentration or purification of the virus.

TNF alpha production to TLR2 ligands in active IBD patients

Strong evidence suggests that microbial components are involved in the etiopathology of inflammatory bowel diseases (IBD). Since pathogen-associated molecular patterns are recognized by TLRs, dysregulation of TLR-mediated microbial recognition could be taking place in IBD patients. An in vitro assay with different TLR agonists was used to reproduce the immunostimulation via TLR ligands. Elevated TNFalpha production was found in response to LTA and Zymosan in 48% of active Crohn's disease and ulcerative colitis patients when compared to inactive patients or controls. The expression of CD14 did not differ in active patients, whereas TLR2 was significantly upregulated on monocytes from 71% of those patients with high production of TNFalpha. The marked increase of TNFalpha response to TLR2 ligands correlated with a higher TLR2 expression in a group of IBD patients, suggesting that an abnormal mechanism may provide an excess of inflammatory mediators during the active phase of IBDs.

Immuno-PCR: high sensitivity detection of proteins by nucleic acid amplification

Nucleic acid amplification techniques are used for signal generation in antibody-based immunoassays, thereby dramatically enhancing the sensitivity of conventional immunoassays. Methodological aspects, as well as applications of this novel approach, are summarized in this review, with an emphasis on immuno-polymerase chain reaction (IPCR). IPCR is based on chimeric conjugates of specific antibodies and nucleic acid molecules, the latter of which are used as markers to be amplified by PCR for signal generation. The enormous efficiency of nucleic acid amplification typically leads to a 100-10,000-fold increase in sensitivity, as compared with the analogous enzyme-amplified immunoassay. The evolution of IPCR included the development of efficient reagents, the design of assay formats and the maintenance of functionality, even within complex biological matrices. Eventually, IPCR crossed the border from being a research method to a routine laboratory technique, enabling a broad range of applications in immunological research and clinical diagnostics.

Immuno-quantitative polymerase chain reaction for detection and quantitation of prion protein

Immuno-polymerase chain reaction (PCR) is an extremely sensitive detection method, combining the specificity of antibody detection and the sensitivity of PCR. We have developed an immuno-quantitative PCR (iqPCR), exploiting real-time PCR technology, in order to improve this immuno-detection method and make it quantitative. To illustrate the advantages of iqPCR, we have compared it with a conventional enzyme linked immuno sorbent assay (ELISA) technique in experiments aimed at detecting the cellular and the resistant form of prion protein in bovine brain extract. The iqPCR technique proved to be more sensitive than ELISA, so it could be a technique of choice for the diagnosis of infected animals both at an ante mortem and post-mortem stage.

A highly sensitive immuno-polymerase chain reaction assay for Clostridium botulinum neurotoxin type A

Our goal was to develop a sensitive method for detecting Clostridium botulinum neurotoxin type A (BoNT/A). We were able to detect BoNT/A in the femtogram (10(-15)g) range using an indirect immuno-polymerase chain reaction (immuno-PCR) assay and an indirect sandwich immuno-PCR assay. For the indirect immuno-PCR assay, enzyme-linked immunosorbent assay (ELISA) plates were coated with BoNT/A that was recognized by anti-BoNT/A monoclonal antibody. For the indirect sandwich immuno-PCR assay, the monoclonal antibody was immobilized on ELISA plates for detecting BoNT/A that was recognized by its polyclonal antibodies. Reporter DNA was prepared by PCR amplification using biotinylated 5'-primers, and it was coupled with biotinylated antibodies through streptavidin. In order to increase sensitivity and reduce background noise, the amounts of reporter DNA (ranging from 50 fg to 50 ng) and streptavidin (ranging from 0.125 ng to 8 ng) were optimized. Using the optimized concentration of reporter DNA and streptavidin, both indirect and indirect sandwich immuno-PCR assays detected BoNT/A as low as 50 fg. These results are a 10(5)-fold improvement over conventional indirect ELISA and indirect sandwich ELISA methods. The assays we developed are currently the most sensitive methods for detecting BoNT/A.

A highly sensitive immuno-PCR assay for detecting Group A Streptococcus

A highly sensitive hybrid assay, based on immuno polymerase chain reaction (immuno-PCR) and enzyme-linked immunosorbent assay (ELISA) techniques, was developed for the detection of pathogenic Group A Streptococcus (Strep A). Cells were disrupted by sonication and then coated onto the walls of Maxisorp microtiter plates. Next, biotinylated anti-Group A monoclonal antibody (mAb) was bound to the antigen and then linked, via a streptavidin (STV) bridge, to biotinylated reporter DNA. After extensive washing, the denatured reporter DNA was transferred to PCR tubes, amplified, electrophoresed, and used as the signal for detection of bacteria. The minimum detection limit of this assay is the equivalent of approximately one one-thousandth of a Streptococcus pyogenes cell, even in the presence of 100,000 Escherichia coli cells. The combination of multiple antigens per cell and PCR amplification provides the extreme sensitivity in this immuno-PCR assay. No cross-reaction was found with other Streptococcus species. We also directly linked the anti-Group A monoclonal antibody to DNA using succinimidyl 4-[N-maleimidomethyl]-cyclohexane-1-carboxylate (SMCC). The sensitivity using directly linked antibody-reporter DNA was approximately 10 cells. Because this assay could be adapted for detection of many different bacteria in a variety of sample types, we tested the potential for interference from substances that could be present in clinical, food, and environmental samples. Sonicated meat or human plasma did not inhibit detection; however, extracts of concentrated soil samples were somewhat inhibitory. This highly specific, sensitive, and robust assay could be applied to clinical detection of Group A Streptococcus and serves as a model for other immuno-PCR assays.

A quantitative immuno-PCR assay for the detection of mumps-specific IgG

Sensitive assays are required for seroprevalence studies of measles, mumps and rubella (MMR)-vaccinated populations where many may have low levels of antibodies. This protocol describes a quantitative immuno-PCR assay to detect mumps-specific IgG antibodies. The purpose of the protocol is to determine the immune status of individuals to mumps. Mumps-specific IgG from a dilution of patients serum is bound by recombinant mumps nucleoprotein coated on the surface of microtitre plate wells. Bound antibody is detected by PCR using a conjugate of anti-human IgG covalently coupled to an oligonucleotide. The oligonucleotide is detected by the addition of target DNA, designed to hybridise to the oligonucleotide and serve as a template for real-time PCR using the LightCycler. The quantity of target DNA detected by the PCR depends upon the level of specific antibody in the test sample.

Development of a quantitative immuno-PCR assay and its use to detect mumps-specific IgG in serum

Determination of the immune status of individuals to vaccine-preventable diseases requires an assay that can detect antibodies that may be present at very low levels, especially when natural or vaccine exposure may have been many years previously. Immuno-PCR (iPCR) has recently been described as an ultrasensitive method for the detection of antigens and we have adapted the method for the quantification of antibodies to mumps virus. The procedure used was similar to an indirect ELISA except that the detecting antibody (anti-human IgG) was chemically conjugated to a short capture oligonucleotide rather than an enzyme. The capture oligonucleotide was then detected by the addition of target DNA, which was designed to hybridise to the capture oligonucleotide and function as a template for real-time PCR. The quantity of target DNA detected by the PCR depended upon the level of specific antibody in the test sample. We found that the sensitivity (and specificity) of the iPCR assay did not exceed that of the conventional ELISA. The sensitivity was limited by nonspecific binding of human IgG to the solid phase. Further development of reagents and assay formats is necessary to fully exploit the potential of quantitative iPCR, so that potential improvements in the sensitivity of anti-mumps IgG detection can be realised.

Tumor Necrosis Factor-α in Serum of Patients with Inflammatory Bowel Disease as Measured by a Highly Sensitive Immuno-PCR

Background: The significance of serum concentrations of tumor necrosis factor-α (TNF-α) in the pathogenesis of inflammatory bowel disease (IBD) is uncertain. We measured TNF-α in serum from IBD patients by immuno-PCR to analyze the relationship between TNF-α and pathophysiologic state in IBD.

Methods: Serum samples were collected from 54 healthy blood donors, 29 patients with ulcerative colitis (UC; 46 samples), and 7 patients with Crohn disease (CD; 8 samples). DNA label was generated by PCR amplification using biotinylated primer and was bound with streptavidin to biotinylated third antibody. TNF-α sandwiched by antibodies was detected by PCR amplification of the DNA label.

Results: TNF-α could be measured in all samples. The median serum concentration in IBD patients overall was ∼390-fold higher than in healthy donors (median increase, 380-fold for UC, 640-fold for CD). The median serum TNF-α concentration was 1.7-fold higher in the active stage of UC than in the inactive stage (P &lt;0.05), and this difference could be detected in individual patients.

Conclusions: Sensitive measurement of serum TNF-α could provide an important pathophysiologic marker for the presence and activity of IBD.

Detection of Clostridium botulinum neurotoxin type A using immuno-PCR

AIMS

An immuno-polymerase chain reaction (immuno-PCR) has been developed for the sensitive detection of antigens, which greatly extends the detection limits of immunoassays. In the current study, the method was applied to the detection of Clostridium botulinum neurotoxin type A (BTx-A).

METHODS AND RESULTS

Anti-BTx-A antibody-DNA conjugates were synthesized using a heterobifunctional cross-linker reagent to covalently link the reporter DNA and the antibodies. The antibody-DNA conjugates with antigens were amplified by PCR, and dose-dependent relationships for each analyte were demonstrated. Detection limits of immuno-PCR for BTx-A (3.33 x 10(-17) mol) exceeded the conventional enzyme-linked immunosorbent assay (3.33 x 10(-14) mol) by a 1000-fold enhancement in detection sensitivity.

CONCLUSION

Detection of BTx-A antigens by immuno-PCR demonstrated 100% sensitivity and 100% specificity in 100-fold magnitude below the detection limit of ELISA.

SIGNIFICANCE AND IMPACT OF THE STUDY

It is concluded that the immuno-PCR method could be used to detect a very low level of BTx-A for clinical diagnosis.

A highly sensitive immuno-polymerase chain reaction assay for human angiotensinogen using the identical first and second polyclonal antibodies

We describe an immuno-polymerase chain reaction (immuno-PCR) assay for the detection of human angiotensinogen using identical first and second polyclonal antibodies. The reporter DNA was initially generated by PCR amplification using a biotinylated primer, and was bound with streptavidin to biotinylated second antibody. Human recombinant angiotensinogen sandwiched by antibodies was detected by amplifying the reporter DNA using PCR. To reduce the effect of nonspecific amplification, the optimal concentrations of streptavidin and DNA label were determined to be 0.1 mg/l and 0.5 ng/l, respectively. The detection limit of the immuno-PCR assay was 0.1 ng/l, an approximately 2.5x10(5)-fold improvement compared with a conventional enzyme-linked immunosorbent assay. These results indicate that a highly sensitive immuno-PCR for human angiotensinogen can be developed even with identical first and second polyclonal antibodies.

The new era of automated immunoassay

Use of immunoassays and other ligand-binding assays in clinical diagnosis has increased dramatically during the last several years. Despite impressive technical advances, "mass production" of these assays in a routine laboratory still presents many difficulties. This review of ligand-binding assay technology highlights some recent developments, emphasizing challenges and possible solutions for cost-effective patient care.