Interference of anti-streptavidin antibodies: More common than we thought? In relation to six confirmed cases

Automated immunoassays are extensively used in routine laboratory diagnostics of endocrine disorders because of their advantages, such as high sensitivity, precision, and specificity. However, these methods are limited by the susceptibility of the immunochemical reaction to various interferences. They may present interferences related to the assay's design, for example, the endogenous presence of anti-streptavidin antibodies (ASA) in platforms that use the biotin-streptavidin interaction. To date, there have been few reports in the literature of interference from endogenous ASA. However, such antibodies would potentially lead to falsely decreased or increased results of hormones that can lead to incorrect diagnoses. We report six patients with unusual thyroid function tests, incongruent to their clinical findings. They present elevated concentrations of total T3 and T4 and TSH values within the reference range when measured at Cobas 8000® e801 module (Roche Diagnostics®). Neither patient had been taking biotin; however, all demonstrated the presence of ASA causing falsely high results on competitive assays and also falsely low results on sandwich assays. The hormone panel was also analyzed in the same samples using a different platform available in our laboratory: Cobas 6000® e601 module (Roche Diagnostics®). Nine samples were sent to an external laboratory to be measured with the chemiluminescent method: ADVIA Centaur® (Siemens® Healthcare Diagnostics). The interference seems to affect e801 module and competitive assays the most without affecting results obtained by this chemiluminescent method. This interference could potentially affect other assays performed on the same platform, such as ATPO and estradiol. Finally, laboratories should suspect the presence of interference when there is no correlation between the hormone profile and the patient's clinic. The biotin neutralization protocol demonstrated its effectiveness to eliminate ASA interference.

Hydrogel based protein biochip for parallel detection of biomarkers for diagnosis of a Systemic Inflammatory Response Syndrome (SIRS) in human serum

The Systemic Inflammatory Response Syndrome (SIRS), a sepsis related inflammatory state, is a self-defense mechanism against specific and nonspecific stimuli. The six most extensively studied inflammatory biomarkers for the clinical diagnosis of SIRS are interleukin 4 (hIL-4), interleukin 6 (hIL-6), interleukin 10 (hIL-10), tumor necrosis factor alpha (hTNF-α), interferon gamma (hIFN-γ) and procalcitonin (hPCT). These biomarkers are naturally present (but usually only at low concentration) in SIRS infected patients [1, 2] and thus the development of a highly sensitive detection method is of major clinical interest. However, the existing analytical techniques are lacking in required analytical sensitivity and parallel determination of these biomarkers. We developed a fast, easy and cost-efficient protein microarray biochip where the capture molecules are attached on hydrogel spots, enabling SIRS diagnosis by parallel detection of these six clinically relevant biomarkers with a sample volume of 25 μl. With our hydrogel based protein microarray biochip we achieved a limit of detection for hIL-4 of 75.2 pg/ml, for hIL-6 of 45.1 pg/ml, for hIL-10 of 71.5 pg/ml, for hTNF-α of 56.7 pg/ml, for IFN-γ of 46.4 pg/ml and for hPCT of 1.1 ng/ml in spiked human serum demonstrating sufficient sensitivity for clinical usage. Additionally, we demonstrated successful detection of two relevant SIRS biomarkers in clinical patient samples with a turnaround time of the complete analysis from sample-to-answer in less than 200 minutes.

Real-Time Profiling of Anti-(Epithelial Cell Adhesion Molecule)-Based Immune Capture from Molecules to Cells Using Multiparameter Surface Plasmon Resonance

Antibodies of epithelial cell-adhesion molecule (anti-EpCAM)-based interfaces have proven to be highly efficient at capturing circulating tumor cells (CTCs). To achieve the bonding of anti-EpCAM to the interface, biotin and streptavidin are used to modify the surface. These processes are critical to subsequent cell-capture efficiencies. However, quantitative research on the interactions between biotin, streptavidin, and biotinylated anti-EpCAM on the interface is lacking. In this work, the thermodynamics and kinetics of biomolecular interactions were determined by using surface plasmon resonance. The equilibrium binding affinities for biotinylated anti-EpCAM to streptavidin and streptavidin to biotin (illustrated by biotin-PEG400-thiol) were found to be 2.75 × 10⁶ and 8.82 × 10⁶ M^-1, respectively. Each streptavidin can bind up to 2.30 biotinylated anti-EpCAM under thermodynamic equilibrium. The findings provide useful information to optimize the modification of anti-EpCAM and improve the capture efficiency of CTCs.

[Anti-estreptavidin antibodies. Diagnostic confusion by biochemical interference]

We present the case of a patient who, during studies for fertility and subsequent pregnancy, showed an altered thyroid profile with elevated levels of free T4 and normal TSH. After ruling out a thyrotropic adenoma and in the absence of clinical symptoms of hyperthyroidism, the possibility of analytical interference in the immunoassays used to measure hormones was investigated. Interferences caused by heterophile antibodies, macro TSH, anti-thyroid antibodies, biotin, and to a lesser extent anti-streptavidin and anti-ruthenium antibodies have been described. The analysis of the patient was carried out in a self-analyzer whose platform uses the streptavidin-biotin system that is very susceptible to several interferents. A proposed algorithm includes a series of simple tests to perform and interpret that allow detecting or ruling out the presence of interferents. Accordingly, a comparison was made with a different analytical platform (which does not use the streptavidin-biotin system), serial dilutions, precipitation with polyethylene glycol 6000 and treatment with microparticles coated with streptavidin. Results obtained confirmed the presence of anti-streptavidin antibodies in the patient's serum. In the case of disagreements between clinical manifestations and laboratory results, the possibility of methodological interferences should be investigated in order to avoid the potential iatrogenic risk involved in an erroneous biochemical interpretation.

Apparent Hyperthyroidism Caused by Biotin-Like Interference from IgM Anti-Streptavidin Antibodies

BACKGROUND

Exclusion of analytical interference is important when there is discrepancy between clinical and laboratory findings. However, interferences on immunoassays are often mistaken as isolated laboratory artefacts. The mechanism of a rare cause of interference in two patients that caused erroneous thyroid function tests, and also affects many other biotin dependent immunoassays, was characterized and reported.

PATIENT FINDINGS

Patient 1 was a 77-year-old female with worsening fatigue while taking carbimazole over several years. Her thyroid function tests, however, were not suggestive of hypothyroidism. Patient 2 was a 25-year-old female also prescribed carbimazole for apparent primary hyperthyroidism. Despite an elevated free thyroxine, the lowest thyrotropin on record was 0.17 mIU/L. In both cases, thyroid function tests performed by an alternative method were markedly different. Further characterization of both patients' serum demonstrated analytical interference on many immunoassays using the biotin-streptavidin interaction. Sandwich assays (e.g., thyrotropin, follicle-stimulating hormone, troponin T, beta-human chorionic gonadotropin) were falsely low, while competitive assays (e.g., free thyroxine, free triiodothyronine, TSH binding inhibitory immunoglobulin) were falsely high. Pre-incubation of serum with streptavidin microparticles removed the analytical interference, initially suggesting the cause of interference was biotin. However, neither patient had been taking biotin. Instead, a ∼100 kDa immunoglobulin M (IgM) immunoglobulin with high affinity to streptavidin was isolated from each patient's serum. The findings confirm IgM anti-streptavidin antibodies as the cause of analytical interference.

SUMMARY

Two patients with apparent hyperthyroidism as a result of analytical interference caused by IgM anti-streptavidin antibodies are described.

CONCLUSION

Analytical interference identified on one immunoassay should raise the possibility of other affected results. Characterization of interference may help to identify other potentially affected immunoassays. In the case of anti-streptavidin antibodies, the pattern of interference mimics that due to biotin ingestion. However, the degree of interference varies between individual assays and between patients.

False biochemical diagnosis of hyperthyroidism in streptavidin-biotin-based immunoassays: the problem of biotin intake and related interferences

Immunoassays are now commonly used for hormone measurement, in high throughput analytical platforms. Immunoassays are generally robust to interference. However, endogenous analytical error may occur in some patients; this may be encountered in biotin supplementation or in the presence of anti-streptavidin antibody, in immunoassays involving streptavidin-biotin interaction. In these cases, the interference may induce both false positive and false negative results, and simulate a seemingly coherent hormonal profile. It is to be feared that this type of errors will be more frequently observed. This review underlines the importance of keeping close interactions between biologists and clinicians to be able to correlate the hormonal assay results with the clinical picture.

Detection of Transgenes on DNA Fibers

Fluorescence in situ hybridization (FISH) was developed for detecting specific DNA sequences directly on mitotic or meiotic chromosomes. However, the resolution of FISH on chromosomes is limited by condensed structure of chromatin, and it is difficult to differentiate two target sites close to each other. To overcome this issue, the objects was changed to stretched DNA fibers, and this fiber FISH technique has now been used for revealing genome structure at molecular level. Hybridization and detection procedures of fiber FISH are common with FISH on chromosomes. Therefore, application of fiber FISH is not difficult for the researchers of some experience in ordinary FISH. DNA fibers can be released from nuclei fixed on glass slides using a detergent. The DNA fibers were shred in FISH procedure, and the resultant fragments became small bead-like shape. This makes FISH signals on DNA fibers a series of dots. The size of DNA in the dot is estimated to be approximately 1 kb, it corresponding to the resolution of fiber FISH. This makes it possible to analyze structures of transgenes on DNA fibers in detail.

Re-evaluation of biotin-streptavidin conjugation in Förster resonance energy transfer applications

Bioaffinity conjugation between streptavidin (SA) and biotin has been widely used to link donors and acceptors for investigating the distance-dependent Förster resonance energy transfer (FRET). When studying a commonly used FRET system of (QD-SA)-(biotin-DNA-dye) [donor: quantum dot (QD); acceptor: small organic fluorescent dye; and linker: deoxyribose nucleic acid (DNA) molecule via SA-biotin conjugation], however, a contradictory finding was recently reported in the literature. It was found that the FRET lost its dependence on the number of DNA base pairs when using a phosphate-buffered saline (PBS) solution. We found that the conflicted results were caused by the ionic strength of the adopted buffer solutions. Our results suggest that the dependent FRET on the number of DNA bases is favorable in a low-ionic-strength buffer, whereas in relatively high-ionic-strength buffers, the FRET loses the DNA length dependence. We propose that the independence is mainly caused by the conformational change of DNA molecules from a stretched to a coiled mode when the cations in the high-ionic-strength buffer neutralize the negatively charged backbone of DNA molecules, thereby bringing the acceptors close to the donors.

Bioconjugates of rhizavidin with single domain antibodies as bifunctional immunoreagents

Use of the avidin-biotin binding interaction for immunoassay applications is widespread. One advantageous immunoreagent is the recombinant fusion of an antibody fragment with a biotin binding protein. These genetic fusions alleviate the need to prepare chemical conjugates to achieve molecules that combine target recognition with signal transduction or to facilitate the directional immobilization of the binding element. In order for such a fusion protein to be useful, however, it must be able to be produced in good yield. Unfortunately, recombinant production of avidin or streptavidin as well as bioconjugates derived thereof has been problematic. An alternative biotin binding molecule called rhizavidin has been described, which forms a homodimer instead of a tetramer, but it has not been evaluated in genetic fusions with antibody binding domains. Single domain antibodies, the variable domain derived from camelid heavy chain only antibodies, offer binding domains with high affinity, and solubility that are well expressed in Escherichia coli. In this work, we prepared an anti-ricin single domain antibody - rhizavidin bioconjugate and evaluated it on the basis of its production in E. coli and on its activity in comparison to a streptavidin core bioconjugate and unfused single domain antibody. The single domain antibody-rhizavidin bioconjugate produced much better than its streptavidin core counterparts, yielding an average of 14 mg/L, a 20-fold improvement. When used in assays the rhizavidin conjugate provided the same desirable characteristics as the streptavidin core fusion as both capture and detection reagents. Since rhizavidin and single domain antibodies both display impressive thermal stabilities their fusion provides a route to achieve robust bifunctional immunoreagents.

A simplified method to attach antibodies on liposomes by biotin-streptavidin affinity for rapid and economical screening of targeted liposomes

The biotin-Streptavidin (STREP) technique for attachment of monoclonal antibodies (mAbs) (or other ligand types) on liposome surface offers high attachment yield, however it is time consuming and expensive due to the number of steps used and the consumption of large quantities of STREP. Herein, a simplified, fast and economic technique, by incubating pre-mixed biotin-mAb/STREP with biotin-liposomes, at a 3:1:1 biotin-mAb/STREP/biotin-LIP ratio (mol/mol/mol) was evaluated. The physichochemical properties, final mAb attachment yield and targeting potential of liposomes decorated with an anti-transferrin receptor mAb (TfR-mAb), prepared by the simple method (SM) and the conventional method (CM), were compared. The vesicle uptake by hCMEC/D3 cells (known to overexpress TfR) were considered as a measure of liposome targeting capability. Results show that both targeted liposome types (SM and CM) have small size (mean diameters around 150 nm), low poly-dispersity (approx. 0.20) and similar mAb attachment yield (between 64-88%). However, the uptake of the SM-liposomes is slightly lower compared to CM-LIP (24-30% decrease), suggesting that the modulated conformation of mAbs on the liposome surface (triplets attached to one single STREP molecule) results in decreased targeting capability. Nevertheless, the simpler and faster one-step preparation procedure which has very high lipid recovery (> 95%) compared to the CM (50-60%) and 15-30 times lower consumption of STREP, may be a good alternative for initial screening of various mAbs as ligands for targeted liposomal or other nanotechnologies, during pre-clinical development.

Europium-quantum dot nanobioconjugates as luminescent probes for time-gated biosensing

Nanobioconjugates have been synthesized using cadmium selenide quantum dots (QDs), europium complexes (EuCs), and biotin. In those conjugates, long-lived photoluminescence (PL) is provided by the europium complexes, which efficiently transfer energy via Förster resonance energy transfer (FRET) to the QDs in close spatial proximity. As a result, the conjugates have a PL emission spectrum characteristic for QDs combined with the long PL decay time characteristic for EuCs. The nanobioconjugates synthesis strategy and photophysical properties are described as well as their performance in a time-resolved streptavidin-biotin PL assay. In order to prepare the QD-EuC-biotin conjugates, first an amphiphilic polymer has been functionalized with the EuC and biotin. Then, the polymer has been brought onto the surface of the QDs (either QD655 or QD705) to provide functionality and to make the QDs water dispersible. Due to a short distance between EuC and QD, an efficient FRET can be observed. Additionally, the QD-EuC-biotin conjugates’ functionality has been demonstratedin a PL assay yielding good signal discrimination, both from autofluorescence and directly excited QDs. These newly designed QD-EuC-biotin conjugates expand the class of highly sensitive tools for bioanalytical optical detection methods for diagnostic and imaging applications.

Time-resolved FRET -based approach for antibody detection - a new serodiagnostic concept

Förster resonance energy transfer (FRET) is a phenomenon widely utilized in biomedical research of macromolecular interactions. In FRET energy is transferred between two fluorophores, the donor and the acceptor. Herein we describe a novel approach utilizing time-resolved FRET (TR-FRET) for the detection of antibodies not only in a solution-phase homogenous assay but also in single- and two-step solid-phase assays. Our method is based on the principle that the Y-shaped immunoglobulin G molecule is able to simultaneously bind two identical antigen molecules. Hence, if a specific IgG is mixed with donor- and acceptor-labeled antigens, the binding of antigens can be measured by TR-FRET. Using donor- and acceptor-labeled streptavidins (SAs) in conjunction with a polyclonal and a monoclonal anti-SA antibody we demonstrate that this approach is fully functional. In addition we characterize the immune complexes responsible for the TR-FRET signal using density gradient ultracentrifugation and solid-phase immunoassays. The homogenous TR-FRET assay described provides a rapid and robust tool for antibody detection, with a wide potential in medical diagnostics.

Antibody discovery ex vivo accelerated by the LacO/LacI regulatory network

Monoclonal antibodies (mAbs) can be potent and highly specific therapeutics, diagnostics and research reagents. Nonetheless, mAb discovery using current in vivo or in vitro approaches can be costly and time-consuming, with no guarantee of success. We have established a platform for rapid discovery and optimization of mAbs ex vivo. This DTLacO platform derives from a chicken B cell line that has been engineered to enable rapid selection and seamless maturation of high affinity mAbs. We have validated the DTLacO platform by generation of high affinity and specific mAbs to five cell surface targets, the receptor tyrosine kinases VEGFR2 and TIE2, the glycoprotein TROP2, the small TNF receptor family member FN14, and the G protein-coupled receptor FZD10. mAb discovery is rapid and humanization is straightforward, establishing the utility of the DTLacO platform for identification of mAbs for therapeutic and other applications.

Antibody adsorption and orientation on hydrophobic surfaces

The orientation of a monoclonal, anti-streptavidin human IgG1 antibody on a model hydrophobic, CH(3)-terminated surface (1-dodecanethiol self-assembled monolayer on gold) was studied by monitoring the mechanical coupling between the adsorbed layer and the surface as well as the binding of molecular probes to the antibodies. In this study, the streptavidin antigen was used as a probe for the Fab portions of the antibody, while bacteria-derived Protein G' was used as a probe for the Fc region. Bovine serum albumin (BSA) acted as a blocking protein. Monolayer coverage occurred around 468 ng/cm(2). Below 100 ng/cm(2), antibodies were found to adsorb flat-on, tightly coupled to the surface and unable to capture their antigen, whereas the Fc region was able to bind Protein G'. At half-monolayer coverage, there was a transition in the mechanism of adsorption to allow for vertically oriented antibodies, as evidenced by the binding of both Protein G' and streptavidin as well as looser mechanical coupling with the surface. Monolayer coverage was characterized by a reduced level in probe binding per antibody and an even less rigid coupling to the surface.

Pancreatic islets engineered with SA-FasL protein establish robust localized tolerance by inducing regulatory T cells in mice

Allogeneic islet transplantation is an important therapeutic approach for the treatment of type 1 diabetes. Clinical application of this approach, however, is severely curtailed by allograft rejection primarily initiated by pathogenic effector T cells regardless of chronic use of immunosuppression. Given the role of Fas-mediated signaling in regulating effector T cell responses, we tested if pancreatic islets can be engineered ex vivo to display on their surface an apoptotic form of Fas ligand protein chimeric with streptavidin (SA-FasL) and whether such engineered islets induce tolerance in allogeneic hosts. Islets were modified with biotin following efficient engineering with SA-FasL protein that persisted on the surface of islets for >1 wk in vitro. SA-FasL-engineered islet grafts established euglycemia in chemically diabetic syngeneic mice indefinitely, demonstrating functionality and lack of acute toxicity. Most importantly, the transplantation of SA-FasL-engineered BALB/c islet grafts in conjunction with a short course of rapamycin treatment resulted in robust localized tolerance in 100% of C57BL/6 recipients. Tolerance was initiated and maintained by CD4(+)CD25(+)Foxp3(+) regulatory T (Treg) cells, as their depletion early during tolerance induction or late after established tolerance resulted in prompt graft rejection. Furthermore, Treg cells sorted from graft-draining lymph nodes, but not spleen, of long-term graft recipients prevented the rejection of unmodified allogeneic islets in an adoptive transfer model, further confirming the Treg role in established tolerance. Engineering islets ex vivo in a rapid and efficient manner to display on their surface immunomodulatory proteins represents a novel, safe, and clinically applicable approach with important implications for the treatment of type 1 diabetes.

The therapeutic potential of SA-sCD40L in the orthotopic model of superficial bladder cancer

BACKGROUND

Intravesical administration is an important treatment against superficial bladder cancer and CD40L is essential for the protective anti-tumor immunity. In situ gene therapy with CD40L was demonstrated to successfully inhibit tumor cell growth in the orthotopic mouse model of bladder cancer. In the present study, we prepared streptavidin (SA)-tagged sCD40L and developed a novel immunotherapy for superficial bladder cancer based on the strong interaction between streptavidin and biotin.

MATERIAL AND METHODS

The SA-sCD40L fusion protein was expressed in E. coli and purified on the Ni-NTA column. After refolding with dialysis, the bi-function of the fusion protein was determined by flow cytometric analysis for streptaidin-mediated surface modification of MB49 bladder cancer cells and a mouse B cell CD40L-dependent proliferation assay. The mouse orthotopic model of MB49 superficial bladder cancer was used to evaluate the efficacy of SA-sCD40L immunotherapy.

RESULTS

The SA-sCD40L fusion protein exhibited both full biotin-binding property and CD40L bioactivity. After intravesical instillation, the SA-sCD40L bi-functional fusion protein was durably immobilized on the biotinylated mucosal surface of bladder wall for up to four days. The SA-sCD40L treatment significantly prolonged the survival of MB49 tumor-bearing mice and cured 50% of mice with MB49 superficial bladder cancer without significant adverse effects. In addition, more tumor-infiltrating CD4(+)or CD8(+) T cells were observed in SA-sCD40L-treated group.

CONCLUSION

Intravesical immobilization of SA-sCD40L elicited a strong and long-lasting immunity against the MB49 bladder cancer.

[Preparation and application of a novel HCV diagnostic antigen fused to streptavidin]

OBJECTIVE

To prepare streptavidin-tagged hepatitis C virus (HCV) fusion protein and explore its application for the detection of antibody against HCV infection.

METHODS

A recombinant plasmid pET-11d-C44P-SA was constructed, which coding a novel HCV diagnostic antigens (C44P) and streptavidin (SA) fusion protein, and the fusion protein was generated with BL21 (DE3) E Coli and identified by Western Blot analysis. Then the fusion protein was purified through the Ni-NTA affinity chromatography and over 90% purity has been achieved. Anti-HCV ELISAs were developed when the fusion protein was used in the biotin-pre-coated microplate or ordinary microplate, and then the sensitivity and specificity of the ELISA were evaluated with confirmed human sera panels.

RESULTS

The fusion protein was expressed in high yields and purified successfully, the ELISA detection of anti-HCV with human sera panel indicated that its sensitivity and specificity is higher when SA-tagged HCV antigen (C44P-SA) coated in biotin-pre-coated microplate, compared to C44P or C44P-SA coated in ordinary microplate.

CONCLUSION

The sensitivity and specificity of anti-HCV ELISA can be improved when a novel HCV diagnostic antigen fused to SA combined with the biotin- pre-coated microplate. This study laid a foundation for improving the performance of HCV diagnostics.

Laboratory-scale protein striping system for patterning biomolecules onto paper-based immunochromatographic test strips

A method for patterning narrow lines of biomolecules onto nitrocellulose membranes using laboratory syringe pumps is described. One syringe pump is used to drive the biomolecule solution through a needle, while another modified syringe pump acts as a one-dimensional translation stage, moving the needle across the membrane much like a pen. This method consumes very small volumes of reagents, and is a viable option for laboratory-scale fabrication and prototyping of point-of-care rapid diagnostic test strips.

Electronic anabolic steroid recognition with carbon nanotube field-effect transistors

A proof of concept of the electronic detection of two anabolic steroids, stanozolol (Stz) and methylboldenone (MB), was carried out using two specific antibodies and arrays of carbon nanotube field-effect transistors (CNTFETs). Antibodies specific for Stz and MB were prepared and immobilized on the carbon nanotubes (CNTs) using two different approaches: direct noncovalent bonding of antibodies to the devices and bonding the antibodies covalently to a polymer previously attached to the CNTFETs. The results indicated that CNTFETs bonded to specific antibodies covalently or noncovalently are able to detect the presence of steroids. Statistically significant changes in the threshold voltage and drain current were registered in the transistors, allowing the steroids to be recognized. On the other hand, it was determined that the specific antibodies do not detect other steroids other than Stz and MB, such as nandrolone (ND) because, in this case, statistically significant changes in the transistors were not detected. The polymer prevents the aggregation of antibodies on the electrodes and decreases the transistor hysteresis. Nevertheless, it is not able to avoid the nonspecific adsorption of streptavidin, meaning that nonspecific adsorption on CNTs remains a problem and that this methodology is only useful for purified samples. Regarding the detection mechanism, in addition to charge transfer, Schottky barrier, SB, modification, and scattering potential reported by other authors, an electron/hole trapping mechanism leading to hysteresis modification has been determined. The presence of polymer seems to hinder the modulation of the electrode-CNT contact.

Monoclonal antibody interactions with micro- and nanoparticles: adsorption, aggregation, and accelerated stress studies

Therapeutic proteins are exposed to various wetted surfaces that could shed subvisible particles. In this work we measured the adsorption of a monoclonal antibody (mAb) to various microparticles, characterized the adsorbed mAb secondary structure, and determined the reversibility of adsorption. We also developed and used a front-face fluorescence quenching method to determine that the mAb tertiary structure was near-native when adsorbed to glass, cellulose, and silica. Initial adsorption to each of the materials tested was rapid. During incubation studies, exposure to the air-water interface was a significant cause of aggregation but acted independently of the effects of microparticles. Incubations with glass, cellulose, stainless steel, or Fe(2)O(3) microparticles gave very different results. Cellulose preferentially adsorbed aggregates from solution. Glass and Fe(2)O(3) adsorbed the mAb but did not cause aggregation. Adsorption to stainless steel microparticles was irreversible, and caused appearance of soluble aggregates upon incubation. The secondary structure of mAb adsorbed to glass and cellulose was near-native. We suggest that the protocol described in this work could be a useful preformulation stress screening tool to determine the sensitivity of a therapeutic protein to exposure to common surfaces encountered during processing and storage.

Enhanced Antigen-Specific Antibody and Cytokine Responses When Targeting Antigen to Human FcGAMMA Receptor Type I Using an Anti-Human FcGAMMA Receptor Type I-Streptavidin Fusion Protein in an Adjuvant-Free System

There is a continuing need for alternatives to current human adjuvants. Recombinant protein vaccines, which target antigen to human Fc gamma receptor type I (hFcgammaRI) on hFcgammaRI-expressing antigen presenting cells, provide one potential alternative. Using a recombinant anti-hFcgammaRI-antigen fusion protein and adjuvant independent mouse model, we demonstrate enhanced antigen-specific antibody responses to low doses of antigen, when targeting antigen to hFcgammaRI in vivo. Enhanced antibody production to hFcyRI-targeted antigen is evident in both primary and secondary immune responses, as compared to that of non-targeted antigen. Furthermore, antibody isotype and cytokine responses following immunization with hFcgammaRI-targeted antigen, suggest enhancement of both Th1 and Th2 responses.

Immunoassay on a power-free microchip with laminar flow-assisted dendritic amplification

We demonstrate a rapid (<30 min) and ultrasensitive (sub-picomolar) immunoassay on a microchip which needs no external power sources for fluid transport. We previously reported a rapid immunoassay of human C-reactive protein (CRP) on the power-free microchip with moderate sensitivity, i.e., a limit of detection (LOD) in sub-nanomolar range, due to the lack of signal amplification. In the current work, we have improved the LOD by 3 orders of magnitude by employing dendritic amplification (DA) methods. Specifically, a sandwich immunocomplex with a biotinylated secondary antibody was constructed on the inner surface of the microchannel as described in the previous report. Onto the immunocomplex, solutions of FITC-labeled streptavidin (F-SA) and biotinylated anti-streptavidin (B-anti-SA) were supplied to grow a dendritic structure. First, we alternately supplied the two solutions for layer-by-layer growth up to three layers. As a result, we obtained an LOD of 0.21 pM with a CRP sample volume of 1.0 microL and assay time of approximately 30 min under an ordinary fluorescence microscope. Second, to reduce the number of incubation steps, we have devised a new DA method: laminar flow-assisted dendritic amplification (LFDA). In this method, F-SA and B-anti-SA were simultaneously and continuously supplied from two laminar streams formed by a Y-shaped microchannel. The immunoassay with the LFDA for 10 min (total assay time of approximately 23 min) with a CRP sample volume of 0.5 microL yielded an LOD of 0.15 pM, which is equivalent to 75 zmol. The combination of the power-free microchip and the LFDA will provide a new opportunity for ultrasensitive point-of-care testing.

A novel multimeric form of FasL modulates the ability of diabetogenic T cells to mediate type 1 diabetes in an adoptive transfer model

Activation induced cell death (AICD) via Fas/FasL is the primary homeostatic molecular mechanism employed by the immune system to control activated T-cell responses and promote tolerance to self-antigens. We herein investigated the ability of a novel multimeric form of FasL chimeric with streptavidin (SA-FasL) having potent apoptotic activity to induce apoptosis in diabetogenic T cells and modulate insulin-dependent type 1 diabetes (IDDM) in an adoptive transfer model. Diabetogenic splenocytes from NOD/Lt females were co-cultured in vitro with SA-FasL, SA control protein, or alone without protein, and adoptively transferred into NOD/Lt-Rag1(null) recipients for diabetes development. All animals receiving control (Alone: n=16 or SA: n=17) cells developed diabetes on average by 6 weeks, whereas animals receiving SA-FasL-treated (n=25) cells exhibited significantly delayed progression (p<.001) and decreased incidence (70%). This effect was associated with an increase in CD4(+)CD25(+) T cells and correlated with FoxP3 expression in pancreatic lymph nodes. Extracorporeal treatment of peripheral blood lymphocytes using SA-FasL during disease onset represents a novel approach that may alter the ability of pathogenic T cells to mediate diabetes and have therapeutic utility in clinical management of IDDM.

Modified tobacco mosaic virus particles as scaffolds for display of protein antigens for vaccine applications

Display of peptides or proteins in an ordered, repetitive array, such as on the surface of a virus-like particle, is known to induce an enhanced immune response relative to vaccination with the "free" protein antigen. The coat protein of Tobacco mosaic virus (TMV) can accommodate short peptide insertions into the primary sequence, but the display of larger protein moieties as genetic fusions to the capsid protein has not been possible. We employed a randomized library approach to introduce a reactive lysine at the externally located amino terminus of the coat protein, which facilitated biotinylation of the capsid. To characterize display of heterologous proteins on the virion surface, we bound a model antigen (green fluorescent protein (GFP)-streptavidin (SA), expressed and purified from plants) to the biotinylated TMV particles, creating a GFP-SA decorated virus particle. A GFP-SA tetramer loading of 26% was obtained, corresponding to approximately 2200 GFP moieties displayed per intact virion. We evaluated the immunogenicity of GFP decorated virions in both mice and guinea pigs and found augmented humoral IgG titers in both species, relative to unbound GFP-SA tetramer. Next, we fused an N-terminal fragment of the Canine oral papillomavirus L2 protein to streptavidin. With TMV display, the L2 protein fragment was significantly more immunogenic than uncoupled antigen when tested in mice. By demonstrating the presentation of whole proteins, this study expands the utility of TMV as a vaccine scaffold beyond that which is possible by genetic manipulation.

Enzymatically-generated fluorescent detection in micro-channels with internal magnetic mixing for the development of parallel microfluidic ELISA

The Enzyme-Linked Immuno-Sorbent Assay, or ELISA, is commonly utilized to quantify small concentrations of specific proteins for a large variety of purposes, ranging from medical diagnosis to environmental analysis and food safety. However, this technique requires large volumes of costly reagents and long incubation periods. The use of microfluidics permits one to specifically address these drawbacks by decreasing both the volume and the distance of diffusion inside the micro-channels. Existing microfluidic systems are limited by the necessary control of extremely low flow rates to provide sufficient time for the molecules to interact with each other by diffusion only. In this paper, we describe a new microfluidic design for the realization of parallel ELISA in stop-flow conditions. Magnetic beads were used both as a solid phase to support the formation of the reactive immune complex and to achieve a magnetic mixing inside the channels. In order to test the detection procedure, the formation of the immune complex was performed off-chip before the reactive beads were injected into the reaction chamber. Anti-streptavidin antibodies were quantified with low picomolar sensitivity (0.1-6.7 pM), a linear range of 2 orders of magnitude and good reproducibility. This work represents the first step toward a new platform for simple, highly effective and parallel microfluidic ELISA.

Comparison of a tetravalent single-chain antibody-streptavidin fusion protein and an antibody-streptavidin chemical conjugate for pretargeted anti-CD20 radioimmunotherapy of B-cell lymphomas

The efficacy of radioimmunotherapy (RIT) for patients with relapsed non-Hodgkin lymphoma (NHL) is limited by nonspecific delivery of radiation to normal tissues due to the long circulating half-life of radiolabeled anti-CD20 antibodies (Abs). Pretargeted RIT using a covalent conjugate of the 1F5 anti-CD20 Ab with streptavidin (SA) has been shown to augment the efficacy of RIT and decrease toxicity compared with a directly labeled 1F5 Ab. We have engineered a tetravalent singlechain 1F5 (scFv)4SA fusion protein and compared it to the 1F5-SA conjugate. Athymic mice bearing Ramos lymphoma xenografts received either the conjugate or fusion protein, followed 20 hours later by a biotin-N-acetyl-galactosamine clearing agent, followed 4 hours later by 111In-DOTA-biotin. After 24 hours, 11.4% +/- 2.1% of the injected dose of radionuclide was present per gram of tumor (% ID/g) using 1F5 (scFv)4SA compared with 10.8% +/- 2.5% ID/g with 1F5 Ab-SA. Superior tumor-to-normal organ ratios of radioactivity were consistently seen using the fusion protein compared with the chemical conjugate (eg, tumor-to-blood ratio > 65:1 after 48 hours with the fusion protein, but < 7:1 with the conjugate). More than 90% of lymphomabearing mice could be cured with minimal toxicity using either reagent followed by 1200 muCi (44.4 MBq) 90Y-DOTA-biotin.

Generation of a multimeric form of CD40L with potent immunostimulatory activity using streptavidin as a chaperon

Effective aggregation of cell surface immune receptors with their ligands is critical in promoting humoral and cellular immune responses. Simulation of these interactions using soluble multimeric ligands having potent adjuvant effects may prove an effective alternative to agonistic antibodies as immunotherapeutics. Multimeric ligands may effectively engage their receptors, leading to aggregation and effective signal transduction. We exploited the structural characteristics of streptavidin (SA) for the generation of multimeric chimeric proteins. Streptavidin forms stable tetramers and oligomers under physiological conditions, and, as such, chimeric molecules with SA are expected to possess similar features. Two chimeric molecules consisting of the extracellular domains of human and mouse CD40L and a modified form of core streptavidin were generated. These proteins form stable oligomers that could only be dissociated into monomers by heating at 100 degrees C, but not 60 degrees C, under denaturing conditions. The chimeric proteins vigorously stimulated B cells, monocytes, and dendritic cells for the production of cytokines and chemokines and upregulation of immunostimulatory molecules. The use of SA as a chaperon presents a novel approach to generate multimeric immunological molecules with potent activities and their use as potential therapeutics for the treatment of cancer and other immune-based disorders.

Immuno-capture of Cryptosporidium parvum using micro-well array

A glass slide and micro-well array chip on which anti-Cryptosporidium parvum antibody was immobilized were used for the rapid capture and detection of C. parvum. Biotinylated anti-C. parvum antibodies were spotted onto the streptavidin-coated glass slides. C. parvum oocysts were captured specifically on the spot when more than 73 ng of anti-C. parvum antibody was applied onto the glass slide. However, C. parvum oocysts captured on the glass slide were detached by repeating washing steps. To improve the capture efficiency of oocysts, capture was performed in a micro-well format consisting of 1024 wells/2.5 mm2 (32 x 32 wells) fabricated as a chip by photolithography. Instead of a flat surface on a glass slide, each well was 30 microm in diameter and 10 microm in depth. Streptavidin was also immobilized onto the micro-well array. The biotinylated anti-C. parvum antibodies were immobilized efficiently onto the chip using a buffer containing 20% methanol. Using this technique C. parvum oocysts were stably captured onto the chip after repeated washing procedures. These data show that the newly designed micro-well array technique described here is useful for antibody-mediated C. parvum capture.

Rapid generation of specific antibodies by enhanced homologous recombination

In the chicken immune system, gene conversion, a type of homologous recombination, primarily contributes to diversification of the immunoglobulin gene. Here, we report on the rapid generation of specific monoclonal antibodies using the chicken DT40 B-cell line undergoing gene conversion. We discovered that the gene conversion frequency at the immunoglobulin locus is increased by treating DT40 cells with a histone deacetylase inhibitor, trichostatin A (TSA), thereby generating diversity at the immunoglobulin locus in the majority of treated cells. This indicates that TSA treatment accelerates the autonomous diversification of surface IgMs on DT40 cells. We took advantage of this effect to select DT40 cells producing specific antibodies with antigen-conjugated magnetic beads. This autonomously diversifying library (ADLib) selection system enables the quick establishment (approximately 1 week from a diversifying library) of various clones producing monoclonal IgMs with enough specificity and affinity for immunological assays, and is applicable to various biotechnologies including rational protein design.

Sensitivity of ex situ and in situ spectral surface plasmon resonance sensors in the analysis of protein arrays

We have investigated the sensitivity of ex situ (analysis under air condition) and in situ (analysis under liquid condition) spectral SPR sensors, which were self-constructed with fiber optic spectrometers. The sensitivity of SPR sensors was analyzed in the wavelength range of 550-780 nm by the interactions of streptavidin and biotinylated IgG, and the sensitivity was dependent on the wavelength of measurements. The sensitivity of an ex situ SPR sensor operated at the long wavelength range from 712 nm was approximately 2.6 times higher than that at the short wavelength range from 571 nm. In addition, the sensitivity of an ex situ spectral SPR sensor was about twice as high as that of an in situ spectral SPR sensor for the same resonance wavelength range. This was interpreted in that the difference in sensitivity between two SPR sensors was significantly caused by the evanescent field intensity at the metal/dielectric interface. Thus, it was suggested that ex situ spectral SPR sensors operated at the long wavelength range are sensitive biosensors for the high-throughput analysis of protein interactions on protein arrays.

Fluorescence-microscopy-based image analysis for analyte-dependent particle doublet detection in a single-step immunoagglutination assay

A novel fluorescence-microscopy-based image analysis method for classification of singlet and doublet latex particles is demonstrated and applied to a particle-based immunoagglutination assay for quantification of biomolecules in microliter-volume bulk samples. The image analysis method, verified by flow cytometric agglutination analysis, is based on a pattern recognition algorithm employing Gaussian-base-function fitting which allows robust identification and counting of singlets, doublets, and higher agglomerates of fluorescent microparticles. The immunoagglutination assay is experimentally modeled by a biotin-streptavidin interaction, with the goal of both theoretically and experimentally investigating the performance of a general immunoagglutination-based assay. For this purpose a theoretical model of the initial agglutination kinetics, based on particle diffusion combined with a steric factor determined by the level of specific and nonspecific agglutination, was developed. The theoretical model combined with the experimental data can be used to optimize an agglutination-based assay with regard to sensitivity and dynamic range and to estimate the affinity, receptor surface density, molecular and binding site sizes, and level of nonspecific binding that is present in the assay. The experimental results are in good agreement with the theoretical model, indicating the usefulness of the model for immunoagglutination assay optimization.

Use of biotinylated 17β-estradiol in enzyme-immunoassay development: Spacer length and chemical structure of the bridge are the main determinants in simultaneous streptavidin–antibody binding

17beta-estradiol (E2) concentrations are in the low pg/ml range in plasma. To develop a sensitive enzyme immunoassay (EIA) for E2-determination a highly specific antibody raised against a 6-carboxymethyl (CMO)-E2-bovine serum albumine conjugate was used. Based on 6-CMO-E2 and 6-amino-E2, four biotinylated tracers with two different spacer lengths between E2 and biotin were synthesized using biotinylation reagents in one step reactions. All amino-based tracers were unsuitable for assay development because the antibody binding was too weak compared to the analyte E2. For 6-CMO-based tracers the simultaneous binding of the tracer to the antibody and streptavidin seems to be the determining step in the procedure depending on incubation temperature and spacer lengths. While a short spacer of 9 carbon atoms was susceptible to room temperature, a longer spacer of 16 carbon atoms showed nearly the same results for incubation at 4 degrees C or at room temperature. The absolute detection limit of this system was 0.63 pg/well. For sample clean-up, porcine plasma was solvent-extracted and depending on the initial plasma volume further purified by solvent partition. Determination of reproducibility resulted in intraassay coefficients of variation of 13% and 5.3% for samples with E2-levels of 15 pg/ml and 236 pg/ml, respectively. Measurement of E2-spiked blood plasma revealed recoveries of 83% up to 100% for E2 concentrations between 50 pg/ml and 1000 pg/ml. Only for the lowest concentration (20 pg/ml) a recovery of 58% was observed. Correlation of the EIA with an established radio immunoassay resulted in r=0.991 using the same antibody.

Ligand-installed PEGylated bionanosphere

The synthesis of poly(ethylene glycol)-b-poly(2-N,N-dimethylaminoethylmethacrylate) processing an acetal group at the PEG chain end (acetal-PEGPAMA) is reported. The obtained acetal-PEGPAMA block copolymer was found to reduce tetrachloroauric acid at room temperature to produce gold nanoparticles. The size of these nanoparticles was controllable in the range of 6 to 13 nm by changing the initial Au3+: polymer ratio. In addition to the reduction of tetrachloroauric acid, acetal-PEGPAMA bonds on the surface of the obtained gold nanoparticles to improve their dispersion stability in an aqueous medium even at a salt concentration as high as two. Biotinyl-PEGPAMA-anchored gold nanoparticles undergo specific aggregation in the presence of streptavidin thereby revealing their promising utility as colloidal sensing systems for use in biological systems. Biotin-PEGPAMA can also be utilised for the preparation of a functionally PEGylated quantum dot (QD). When CdCl2 and Na2S were mixed in aqueous media in the presence of the biotin-PEGPAMA, a CdS QD with an approximately 5 nm size was prepared. The polyamine segment was anchored onto the surface of the formed CdS nanoparticle, whereas the PEG segment was tethered onto the surface to form a hydrophilic palisade, thus improving the dispersion stability in aqueous media even under a high salt concentration condition. An effective fluorescent resonance energy transfer (FRET) was observed by the specific interaction of the biotin-PEGPAMA stabilised CdS QD with TexasRed-labelled streptavidin with the physiological ionic strength of 0.15 M. The extent of the energy transfer was in proportion to the concentration of the TexasRed-streptavidin. This FRET system using the PEGylated CdS QD coupled with fluorescent-labelled protein can be utilised as a highly sensitive bioanalytical system.

Construction and diversification of yeast cell surface displayed libraries by yeast mating: application to the affinity maturation of Fab antibody fragments

Yeast display is a powerful technology for the affinity maturation of human antibody fragments. However, the technology thus far has been limited by the size of antibody libraries that can be generated, as using current transformation protocols libraries of only between 10(6) and 10(7) are typically possible. We have recently shown that Fab antibodies can be displayed on the cell surface of Saccharomyces cerevisiae [van den Beucken, T., Pieters, H., Steukers, M., van der Vaart, M., Ladner, R.C., Hoogenboom, H.R., Hufton, S.E., 2003. Affinity maturation of Fab antibody fragments by fluorescent-activated cell sorting of yeast-displayed libraries. FEBS Lett. 546, 288-294]. This discovery and the knowledge that Fab antibodies are heterodimeric suggest that independent repertoires of heavy chain (HC) and light chain (LC) can be constructed in haploid yeast strains of opposite mating type. These separate repertoires can then be combined by highly efficient yeast mating. Using this approach, we have rapidly generated a naive human Fab yeast display library of over 10(9) clones. In addition, utilizing error-prone polymerase chain reaction, we have diversified Fab sequences and generated combinatorial and hierarchical chain shuffled libraries with complexities of up to 5 x 10(9) clones. These libraries have been selected for higher affinity using a repeating process of mating-driven chain shuffling and flow cytometric sorting.

A magnetoelastic bioaffinity-based sensor for avidin

A magnetoelastic bioaffinity sensor coupled with biocatalytic precipitation is described for avidin detection. The non-specific adsorption characteristics of streptavidin on different functionalized sensor surfaces are examined. It is found that a biotinylated poly(ethylene glycol) (PEG) interface can effectively block non-specific adsorption of proteins. Coupled with the PEG immobilized sensor surface, alkaline phosphatase (AP) labeled streptavidin is used to track specific binding on the sensor. This mass-change-based signal is amplified by the accumulation on the sensor of insoluble products of 5-bromo-4-chloro-3-indolyl phosphate catalyzed by AP. The resulting mass loading on the sensor surface in turn shifts the resonance frequency of the magnetoelastic sensors, with an avidin detection limit of approximately 200 ng/ml.

Microsurface plasmon resonance biosensing based on gold-nanoparticle film

We use a gold-nanoparticle coated film to achieve highly spatially resolved biosensing that is based on localized surface-plasmon resonance. Unlike the planar gold film employed for conventional surface-plasmon resonance sensing, the gold-nanoparticle film relies exclusively on shifting of the peak extinction wavelength for detection of biointeraction and does not depend critically on the angle of incidence. These characteristics permit integration of surface-plasmon resonance with large-numerical-aperture optics to achieve biosensing with high sensitivity and spatial resolution as high as 25 microm.

Cutting Edge: C3d Functions as a Molecular Adjuvant in the Absence of CD21/35 Expression

Complement component C3 covalently attaches to Ags following activation, where the C3d cleavage fragment can function as a molecular adjuvant to augment humoral immune responses. C3d is proposed to exert its adjuvant-like activities by targeting Ags to the C3d receptor (CD21/35) expressed by B cells and follicular dendritic cells. To directly assess the importance of CD21/35 in mediating the immunostimulatory effects of C3d, CD21/35-deficient (CD21/35(-/-)) mice were immunized with streptavidin (SA), SA-C3dg tetramers, recombinant HIV gp120 (gp120), or gp120 fused with linear multimers of C3d. Remarkably, SA- and gp120-specific Ab responses were significantly augmented in CD21/35(-/-) mice when these Ags were complexed with C3d in comparison to Ag alone. In fact, primary and secondary Ab responses and Ab-forming cell responses of CD21/35(-/-) mice approached those of wild-type mice immunized with SA-C3dg and gp120-C3d. Thus, C3d can function as a molecular adjuvant in the absence of CD21/35 expression.

Development and application of a pig IL-8 ELISA detection system

Interleukin 8 (IL-8) is a chemotactic and activating chemokine, especially for neutrophils, which plays an important role in inflammatory process. A pig IL-8 specific enzyme-linked immunosorbent assay (ELISA) was developed to measure IL-8 concentrations in cell culture supernatants and biological fluids. A streptavidin-biotin amplified sandwich method uses mouse capture mAb IZ8.03 and detection biotinylated mouse mAb IZ8.04 against recombinant pig IL-8. The assay specifically and reproducibly recognizes both recombinant and natural pig IL-8. A working range of the assay is 16-1000 pg/mL and takes a mere 3.5 h of incubation time. This pig IL-8 ELISA is a suitable alternative way of measurement of IL-8 concentrations to time consuming and laborious IL-8 bioassays.

Mortalin imaging in normal and cancer cells with quantum dot immuno-conjugates

Quantum dots are the nanoparticles that are recently emerging as an alternative to organic fluorescence probes in cell biology and biomedicine, and have several predictive advantages. These include their i) broad absorption spectra allowing visualization with single light source, ii) exceptional photo-stability allowing long term studies and iii) narrow and symmetrical emission spectrum that is controlled by their size and material composition. These unique properties allow simultaneous excitation of different size of quantum dots with a single excitation light source, their simultaneous resolution and visualization as different colors. At present there are only a few studies that have tested quantum dots in cellular imaging. We describe here the use of quantum dots in mortalin imaging of normal and cancer cells. Mortalin staining pattern with quantum dots in both normal and cancer cells mimicked those obtained with organic florescence probes and were considerably stable.

A novel approach to cancer immunotherapy: tumor cells decorated with CD80 generate effective antitumor immunity

Malignant cells often elude the immune system by lacking costimulatory signals required for the generation of effective antitumor immunity. Immunization with tumor cells genetically modified to express costimulatory molecules is a highly promising approach to cancer immunotherapy. However, genetic modification of tumor cells is not only labor/time intensive but is also less efficient and bears safety concerns. To override these complications, we have recently developed a novel technology that allows for efficient and durable display of exogenous proteins on the surface of a cell within 2 h. This technology involves modification of the cell membrane with a biotin derivative and decoration of biotinylated cells with proteins chimeric with core streptavidin. A chimeric molecule composed of the extracellular domains of the human CD80 costimulatory molecule and core streptavidin (CD80-SA) was efficiently displayed on the cell surface, where it persisted with a t(1/2) of >10 days in vivo. Tumors from patients with advanced stage gynecologic cancers decorated with CD80-SA elicited potent ex vivo tumor-specific proliferative and cytotoxic responses in autologous lymphocytes. Immunization with tumor cells decorated with CD80-SA completely prevented tumor growth in an aggressive model of mouse lymphoma. This technology may serve as a fast, efficient, and safe alternative to gene transfer approaches for engineering tumor cells for use in immunotherapy and research.

Pretarget radiotherapy with an anti-CD25 antibody-streptavidin fusion protein was effective in therapy of leukemia/lymphoma xenografts

Although radioimmunotherapy with radiolabeled intact monoclonal antibodies has demonstrated efficacy in the treatment of lymphoma, it provides low tumor-to-normal-tissue radionuclide target ratios and unwanted prolonged radiation exposure to the bone marrow. To overcome these obstacles, the administration of the radionuclide was separated from that of the antibody by using an anti-IL-2 receptor alpha antibody single chain Fv-streptavidin fusion protein, followed by radiolabeled biotin to treat lymphoma or leukemia xenografted mice. This Pretarget approach provided extremely rapid and effective tumor targeting, permitting the use of short-lived alpha-emitting radionuclides. With the beta-emitter (90)Y, all of the 10 lymphoma-xenografted mice were cured. With the alpha-emitter (213)Bi, significant efficacy was obtained in treating leukemic mice, and, furthermore, when combined with immunotherapy, 7 of 10 leukemic mice were cured. Thus, Pretarget radioimmunotherapy is very promising and could represent the next generation in the treatment of lymphoma and leukemia.

A two-component modular approach for enhancing T-cell activation utilizing a unique anti-FcgammaRI-streptavidin construct and microspheres coated with biotinylated-antigen

The professional antigen presenting cell (APC) plays an essential role in the initiation and propagation of the acquired immune response. Thus, much work has been done in designing strategies that target vaccine antigen (Ag) to APC. Utilizing recombinant DNA technology, we have created a unique two-component system that delivers biotinylated Ag to the Fc gamma receptor type I (FcgammaRI) on APC. Our studies demonstrate that we can successfully engineer FcgammaRI-specific targeting element proteins that simultaneously bind both biotin and recognize FcgammaRI. Additionally, we are able to engineer biotinylated Ag, which form functional elements when adsorbed onto latex microspheres. Furthermore, the targeting and functional element components bind to each other and successfully form two-component immunogens. T-cell activation in response to targeted Ag-laden microspheres is 10- to 100-fold greater than the response to the non-targeted Ag-laden microspheres. This enhancement is 100- to 1000-fold greater than the responses generated to soluble Ag. Thus, our results suggest that specific targeting of Ag-laden microspheres to FcgammaRI may significantly enhance the adjuvant properties of microparticulate delivery systems. Further development of this system may help to elucidate the mechanisms involved in generating enhanced responses to APC-targeted vaccines and significantly advance vaccine technology.

Generation of a human IgG3-streptavidin fusion protein. Implications for the inhibition and elimination of auto-reactive B cells

Antibodies against self-molecules play a significant role in the development and progression of Systemic Lupus Erythematosus, as well as a number of other autoimmune disorders. Immunosuppressive drugs have been used to control this process. However, they are normally not specific to the offending cell, and can actually suppress beneficial immune responses to pathogens. In this paper a genetically engineered targeting molecule is described, which has the capacity to target antigen-specific B cells for inhibition or elimination. The targeting molecule is a fusion of streptavidin subunit to the constant region of human IgG3 (IgG3-Av). It is demonstrated by ELISA and flow cytometry that IgG3-Av binds biotinylated antigen as well as human Fc gamma receptors present on myeloid cells. It is also shown by confocal microscopy and flow cytometry, that IgG3-Av can mediate Fc receptor-dependent phagocytosis of latex microspheres adsorbed with biotinylated antigen. Furthermore, the IgG3-Av construct can modulate Ca++ flux, characteristic of B cell inhibition as well as ADCC of B cells in an antigen-specific manner. In summary, these studies describe an approach, which has the potential to be used as a treatment to inhibit or remove antigen-specific (auto-reactive) B cells.

Determinants of autoantibody induction by conjugated papillomavirus virus-like particles

Immunization of mice with self-Ag arrayed on the surface of papillomavirus-like particles induces long-lasting high-titer IgG production by autoreactive B cells. In contrast, immunization with disorganized self-Ag linked to foreign Th epitopes induces weak autoantibody responses that are predominantly of the IgM isotype. In this study, we evaluated the structural correlates of autoantibody induction to determine the basis of these disparate observations, using a system in which mice were vaccinated with a fusion protein containing self (TNF-alpha) and foreign (streptavidin) components, conjugated to biotinylated virus-like particles (VLPs). Similar titers of autoantibodies to TNF-alpha were elicited using conjugated polyomavirus VLPs and papillomavirus VLPs, indicating that acute activation of dendritic cells by the Ag is not required. Strong autoantibody responses were also induced by conjugated papillomavirus capsid pentamers, indicating that a higher order particulate structure is also not required. However, a reduction of self-Ag density on VLP surfaces dramatically reduced the efficiency of IgG autoantibody induction. In contrast, the negative effects of reductions in foreign Ag density were limited and could be overcome by dosage and adjuvant. These data suggest that the immune system has evolved to differentially recognize closely spaced repetitive Ags and that the signals generated upon interactions with high-density self-Ags can overwhelm the normal mechanisms for B cell tolerance.

Generation and iterative affinity maturation of antibodies in vitro using hypermutating B-cell lines

We show that iterative antigen-mediated selection of B-cell lines that constitutively hypermutate their immunoglobulin V genes during culture can be exploited to generate antibodies in vitro. From Ramos, a hypermutating human B-cell line expressing IgM of unknown specificity, we derived descendants that exhibit stepwise improved binding to streptavidin. Binding is initially conferred by mutations in complementarity-determining regions (CDRs), but maturation is due to strategic framework mutations. A more powerful system is provided by a hypermutating chicken B-lymphoma line, owing to its rapid proliferation, high rate of mutation accumulation, and genetic tractability. Starting from a single cell, we selected parallel lineages of derivatives, making mutated antibodies of increasing affinity to independent test antigens. Selection is initiated at an exceedingly low affinity threshold, but antibodies can be delivered with nanomolar affinities. The strategy could prove useful for in vitro generation of antigen-specific monoclonal antibodies and may be extendable to the maturation of other protein-ligand interactions.

Preclinical evaluation of a humanized NR-LU-10 antibody-streptavidin fusion protein for pretargeted cancer therapy

A humanized single chain Fv antibody fragment specific to the EGP40 antigen was genetically engineered as a streptavidin fusion (scFvSA) for use in pretargeted radioimmunotherapy. The scFvSA construct was expressed as a soluble, tetrameric species in the Escherichia coli periplasm at 110-140 mg/liter. The fusion protein was purified from crude lysates by iminobiotin affinity chromatography with an overall yield of 50-60%. Characterization of the purified protein by SDS-PAGE, light scattering, and size exclusion chromatography demonstrated that the fusion protein was tetrameric with a molecular weight of approximately 172,000. Competitive immunoreactivity assays showed a two-fold greater binding to the antigen than the comparable whole antibody. The purified protein had a biotin disassociation rate identical to recombinant streptavidin and bound an average of three of four possible biotins per molecule. The radiolabeled fusion protein showed a faster blood clearance rate in normal mice than the corresponding whole antibody-streptavidin chemical conjugate. Tumor-specific targeting of a subsequently administered radionuclidechelate/biotin molecule was demonstrated in nude mice bearing SW1222 human colon carcinoma xenografts. A single dose of 800 microCi of 90Y-DOTA-biotin produced cures in mice with established subcutaneous human small cell lung or colon cancer xenografts.

Reduced antibody response to streptavidin through site-directed mutagenesis

Streptavidin provides an effective receptor for biotinylated tumoricidal molecules, including radionuclides, when conjugated to an antitumor antibody and administered systemically. Ideally, one would like to administer this bacterial protein to patients repeatedly, so as to maximize the antitumor effect without eliciting an immune response. Therefore, we attempted to reduce the antigenicity of streptavidin by mutating surface residues capable of forming high energy ionic or hydrophobic interactions. A crystallographic image of streptavidin was examined to identify residues with solvent-exposed side chains and residues critical to streptavidin's structure or function, and to define loops. Mutations were incorporated cumulatively into the protein sequence. Mutants were screened for tetramer formation, biotin dissociation, and reduced immunoreactivity with pooled patient sera. Patient antisera recognized one minor continuous epitope with binding locus at residue E101 and one major discontinuous epitope involving amino acid residues E51 and Y83. Mutation of residues E51, Y83, R53, and E116 reduced reactivity with patient sera to <10% that of streptavidin, but these mutations were no less antigenic in rabbits. Mutant 37, with 10 amino acid substitutions, was only 20% as antigenic as streptavidin. Rabbits immunized with either streptavidin or mutant 37 failed to recognize the alternative antigen. Biotin dissociated from mutant 37 four to five times faster than from streptavidin. Residues were identified with previously undescribed impact on biotin binding and protein folding. Thus, substitution of charged, aromatic, or large hydrophobic residues on the surface of streptavidin with smaller neutral residues reduced the molecule's ability to elicit an immune response in rabbits.

Expression, purification and applications of staphylococcal protein A fused to cellulose-binding domain

Because staphylococcal Protein A (ProtA) binds specifically to IgG, it has been used for many immunological manipulations, most notably antibody purification and diagnostics. Immobilization is required for most of these applications. Here we describe a genetic-engineering approach to immobilizing ProtA on cellulose, by fusing it to cellulose-binding domain (CBD) derived from the cellulose-binding Protein A of Clostridium cellulovorans. The bifunctional fusion protein was expressed in Escherichia coli, recovered on a cellulose column and purified by elution at alkaline pH. ProtA-CBD was used to purify IgG from rabbit serum and its ability to bind IgG from different sources was determined. The bifunctional chimaeric protein can bind up to 23.4 mg/ml human IgG at a ratio of 1 mol of ProtA-CBD/2 mol of human IgG, and can purify up to 11.6 mg/ml rabbit IgG from a serum. The ability to bind functionally active CBD-affinity reagents to cellulosic microtitre plates was demonstrated. Our results indicate that a combination of CBD-affinity reagents and cellulosic microtitre plates is an attractive diagnostics matrix for the following reasons: (i) cellulose exhibits very low non-specific binding; and (ii) CBD-fusion proteins bind directly to cellulose at high density. A unique signal-amplification method was developed based on the ability of ProtA-CBD to link stained cellulose particles to primary antibody in a Western blot.

High copy display of large proteins on phage for functional selections

We have isolated mutations in the major coat protein P8 of M13 phage that greatly increase the surface display of monomeric or oligomeric proteins. The monomeric protein, human growth hormone (hGH), was fused to the N terminus of P8; libraries of P8 variants were constructed and variants that increased hGH display were selected by binding to the extracellular domain of the hGH receptor. The hGH-P8 fusion protein was found to be extremely tolerant of mutations, and a number of P8 variants were found that increased display to levels that improved detection of the hGH-P8 fusion by almost 100-fold. The increased display likely results from better accommodation of the hGH-P8 fusion protein in the phage coat. Using this high copy display format, it was possible for the first time to detect variants of hGH with very weak affinities for the hGHbp (K(d)>1 microM). The display of a tetrameric protein, streptavidin (approximately 50 kDa), was also increased, suggesting the approach may be general to many proteins. The initial product of a natural or invented selection from a naive library is often a weakly functioning protein. These improvements in high copy display should facilitate the broader goal for selection of proteins with novel functions.