Development of NanoLuc bridging immunoassay for detection of anti-drug antibodies

Drug-tolerant detection of anti-drug antibodies in an antigen-binding assay using europium chelate fluorescence

Accurate anti-drug antibody (ADA) measurements in patient sera requires dissociation of ADA-drug complexes combined with sensitive and specific ADA detection. Bridging type immunoassays are often used despite several disadvantages associated with this approach. A good drug-tolerant alternative is the acid-dissociation radioimmunoassay (ARIA), but this method is not easily implemented in most labs as specialized facilities are required for working with radioactive materials. We describe an innovative method for ADA detection that combines the advantages of antigen binding tests like the ARIA with the convenience of regular immunoassays. This acid-dissociation lanthanide-fluorescence immunoassay (ALFIA) involves dissociation of ADA-drug complexes, followed by binding to an europium-labeled drug derivative and subsequently an IgG pulldown on Sepharose beads. After europium elution, detection is achieved by measuring time-resolved fluorescence originating from europium chelate complexes. We measured anti-adalimumab ADA levels in sera of 94 rheumatoid arthritis patients using the ALFIA and showed this method to be highly drug tolerant, sensitive and specific for anti-adalimumab ADAs.

Lumit: A Homogeneous Bioluminescent Immunoassay for Detecting Diverse Analytes and Intracellular Protein Targets

Traditional immunoassays to detect secreted or intracellular proteins can be tedious, require multiple washing steps, and are not easily adaptable to a high-throughput screening (HTS) format. To overcome these limitations, we developed Lumit, a novel immunoassay approach that combines bioluminescent enzyme subunit complementation technology and immunodetection. This bioluminescent immunoassay does not require washes or liquid transfers and takes less than 2 h to complete in a homogeneous "Add and Read" format. In this chapter, we describe step-by-step protocols to create Lumit immunoassays for the detection of (1) secreted cytokines from cells, (2) phosphorylation levels of a specific signaling pathway node protein, and (3) a biochemical protein-protein interaction between a viral surface protein and its human receptor.

Development of a rapid, simple, and sensitive point-of-care technology platform utilizing ternary NanoLuc

Point-of-care tests are highly valuable in providing fast results for medical decisions for greater flexibility in patient care. Many diagnostic tests, such as ELISAs, that are commonly used within clinical laboratory settings require trained technicians, laborious workflows, and complex instrumentation hindering their translation into point-of-care applications. Herein, we demonstrate the use of a homogeneous, bioluminescent-based, split reporter platform that enables a simple, sensitive, and rapid method for analyte detection in clinical samples. We developed this point-of-care application using an optimized ternary, split-NanoLuc luciferase reporter system that consists of two small reporter peptides added as appendages to analyte-specific affinity reagents. A bright, stable bioluminescent signal is generated as the affinity reagents bind to the analyte, allowing for proximity-induced complementation between the two reporter peptides and the polypeptide protein, in addition to the furimazine substrate. Through lyophilization of the stabilized reporter system with the formulated substrate, we demonstrate a shelf-stable, all-in-one, add-and-read analyte-detection system for use in complex sample matrices at the point-of-care. We highlight the modularity of this platform using two distinct SARS-CoV-2 model systems: SARS-CoV-2 N-antigen detection for active infections and anti-SARS-CoV-2 antibodies for immunity status detection using chemically conjugated or genetically fused affinity reagents, respectively. This technology provides a simple and standardized method to develop rapid, robust, and sensitive analyte-detection assays with flexible assay formatting making this an ideal platform for research, clinical laboratory, as well as point-of-care applications utilizing a simple handheld luminometer.

Engineered Amber-Emitting Nano Luciferase and Its Use for Immunobioluminescence Imaging In Vivo

The NanoLuc luciferase (NLuc) and its furimazine (FRZ) substrate have revolutionized bioluminescence (BL) assays and imaging. However, the use of the NLuc-FRZ luciferase-luciferin pair for mammalian tissue imaging is hindered by the low tissue penetration of the emitting blue photons. Here, we present the development of an NLuc mutant, QLuc, which catalyzes the oxidation of a synthetic QTZ luciferin for bright and red-shifted emission peaking at ∼585 nm. Compared to other small single-domain NLuc mutants, this amber-light-emitting luciferase exhibited improved performance for imaging deep-tissue targets in live mice. Leveraging this novel bioluminescent reporter, we further pursued in vivo immunobioluminescence imaging (immunoBLI), which used a fusion protein of a single-chain variable antibody fragment (scFv) and QLuc for molecular imaging of tumor-associated antigens in a xenograft mouse model. As one of the most red-shifted NLuc variants, we expect QLuc to find broad applications in noninvasive mammalian imaging. Moreover, the immunoBLI method complements immunofluorescence imaging and immuno-positron emission tomography (immunoPET), serving as a convenient and nonradioactive molecular imaging tool for animal models in basic and preclinical research.

Simple, Rapid Chemical Labeling and Screening of Antibodies with Luminescent Peptides

Sensitive and selective detection assays are essential for the accurate measurement of analytes in both clinical and research laboratories. Immunoassays that rely on nonoverlapping antibodies directed against the same target analyte (e.g., sandwich enzyme-linked immunosorbent assays (ELISAs)) are commonly used molecular detection technologies. Use of split enzyme reporters has simplified the workflow for these traditionally complex assays. However, identifying functional antibody pairs for a given target analyte can be cumbersome, as it generally involves generating and screening panels of antibodies conjugated to reporters. Accordingly, we sought a faster and easier reporter conjugation strategy to streamline antibody screening. We describe here the development of such a method that is based on an optimized ternary NanoLuc luciferase. This bioluminescence complementation system is comprised of a reagent-based thermally stable polypeptide (LgTrip) and two small peptide tags (β9 and β10) with lysine-reactive handles for direct conjugation onto antibodies. These reagents enable fast, single-step, wash-free antibody labeling and sensitive functional screening. Simplicity, speed, and utility of the one-pot labeling technology are demonstrated in screening antibody pairs for the analyte interleukin-4. The screen resulted in the rapid development of a sensitive homogeneous immunoassay for this clinically relevant cytokine.

Bioluminescent Bridging Immunoassay for Anti-Drug Antibody (ADA) Detection

Any immune reaction to therapeutic antibodies will impact the drug efficacy and can have serious consequences for patient safety. Therefore, detection and reporting of anti-drug antibodies (ADA) during clinical trials is required by regulatory agencies during drug approval process. We have developed a bioluminescent bridging immunoassay for ADA detection, which uses an extremely bright NanoLuc enzyme as a reporter. The assay is sensitive with a wide dynamic range and meets the FDA drug tolerance guideline of detecting 100 ng/ml of ADA in the presence of 500-fold excess of free drug. We describe detailed protocols for development of ADA assays using therapeutic Trastuzumab as a model drug and an anti-Trastuzumab antibody as an example of immune response.

Regulation of PXR Function by Coactivator and Corepressor Proteins: Ligand Binding Is Just the Beginning

The pregnane X receptor (PXR, NR1I2) is a nuclear receptor which exerts its regulatory function by heterodimerization with the retinoid-X-receptor α (RXRα, NR2B1) and binding to the promoter and enhancer regions of diverse target genes. PXR is involved in the regulation of drug metabolism and excretion, metabolic and immunological functions and cancer pathogenesis. PXR activity is strongly regulated by the association with coactivator and corepressor proteins. Coactivator proteins exhibit histone acetyltransferase or histone methyltransferase activity or associate with proteins having one of these activities, thus promoting chromatin decondensation and activation of the gene expression. On the contrary, corepressor proteins promote histone deacetylation and therefore favor chromatin condensation and repression of the gene expression. Several studies pointed to clear cell- and ligand-specific differences in the activation of PXR. In this article, we will review the critical role of coactivator and corepressor proteins as molecular determinants of the specificity of PXR-mediated effects. As already known for other nuclear receptors, understanding the complex mechanism of PXR activation in each cell type and under particular physiological and pathophysiological conditions may lead to the development of selective modulators with therapeutic potential.

Development of a Human Estrogen Receptor Dimerization Assay for the Estrogenic Endocrine-Disrupting Chemicals Using Bioluminescence Resonance Energy Transfer

Endocrine-disrupting chemicals (EDCs) are found in food and various other substances, including pesticides and plastics. EDCs are easily absorbed into the body and have the ability to mimic or block hormone function. The radioligand binding assay based on the estrogen receptors binding affinity is widely used to detect estrogenic EDCs but is limited to radioactive substances and requires specific conditions. As an alternative, we developed a human cell-based dimerization assay for detecting EDC-mediated ER-alpha (ERα) dimerization using bioluminescence resonance energy transfer (BRET). The resultant novel BRET-based on the ERα dimerization assay was used to identify the binding affinity of 17β-estradiol (E2), 17α-estradiol, corticosterone, diethylhexyl phthalate, bisphenol A, and 4-nonylphenol with ERα by measuring the corresponding BRET signals. Consequently, the BRET signals from five chemicals except corticosterone showed a dose-dependent sigmoidal curve for ERα, and these chemicals were suggested as positive chemicals for ERα. In contrast, corticosterone, which induced a BRET signal comparable to that of the vehicle control, was suggested as a negative chemical for ERα. Therefore, these results were consistent with the results of the existing binding assay for ERα and suggested that a novel BRET system can provide information about EDCs-mediated dimerization to ERα.

Deciphering the Interaction between Neonatal Fc Receptor and Antibodies Using a Homogeneous Bioluminescent Immunoassay

Long half-life of therapeutic Abs and Fc fusion proteins is crucial to their efficacy and is, in part, regulated by their interaction with neonatal Fc receptor (FcRn). However, the current methods (e.g., surface plasmon resonance and biolayer interferometry) for measurement of interaction between IgG and FcRn (IgG/FcRn) require either FcRn or IgG to be immobilized on the surface, which is known to introduce experimental artifacts and have led to conflicting data. To study IgG/FcRn interactions in solution, without a need for surface immobilization, we developed a novel (to our knowledge), solution-based homogeneous binding immunoassay based on NanoBiT luminescent protein complementation technology. We optimized the assay (NanoBiT FcRn assay) for human FcRn, mouse FcRn, rat FcRn, and cynomolgus FcRn and used them to determine the binding affinities of a panel of eight Abs. Assays could successfully capture the modulation in IgG/FcRn binding based on changes in Fc fragment of the Abs. We also looked at the individual contribution of Fc and F(ab)₂ on the IgG/FcRn interaction and found that Fc is the main driver for the interaction at pH 6. Our work highlights the importance of using orthogonal methods to validate affinity data generated using biosensor platforms. Moreover, the simple add-and-read format of the NanoBiT FcRn assay is amenable for high-throughput screening during early Ab discovery phase.

Preparation of Luciferase-fused Peptides for Immunoassay of Amyloid Beta

An immunoassay, such as the enzyme-linked immunosorbent assay (ELISA), is an analytical method that utilizes the interaction of antigens and antibodies. Enzyme-labeled antigens require both molecular recognition by the antibody and enzymatic activity as a reporter. We designed and constructed an immunodetection system for amyloid beta peptides (Aβ) using an enzyme-labeled antigen expressed from Escherichia coli. Aβ(1-16) fused with renilla luciferase was prepared as the enzyme-labeled antigen. In the presence of this luciferase-fused peptide, the luminescence of coelenterazine-h was observed. The influence of the fusion with Aβ on the luminescence reaction was insignificant. Surface plasmon resonance analysis indicated that the interaction between the luciferase-fused Aβ and anti-Aβ antibody was sufficiently strong. In the competitive ELISA assay for Aβ detection using the luciferase-fused Aβ, the luminescence intensity decreased as the Aβ concentration increased.

Toward a Point-of-Need Bioluminescence-Based Immunoassay Utilizing a Complete Shelf-Stable Reagent

Enzyme-linked immunosorbent assays (ELISAs) are used extensively for the detection and quantification of biomolecules in clinical diagnostics as well as in basic research. Although broadly used, the inherent complexities of ELISAs preclude their utility for straightforward point-of-need testing, where speed and simplicity are essential. With this in mind, we developed a bioluminescence-based immunoassay format that provides a sensitive and simple method for detecting biomolecules in clinical samples. We utilized a ternary, split-NanoLuc luciferase complementation reporter consisting of two small peptides (11mer, 13mer) and a 17 kDa polypeptide combined with a luminogenic substrate to create a complete, shelf-stable add-and-read assay detection reagent. Directed evolution was used to optimize reporter constituent sequences to impart chemical and thermal stability, as well as solubility, while formulation optimization was applied to stabilize an all-in-one reagent that can be reconstituted in aqueous buffers or sample matrices. The result of these efforts is a robust, first-generation bioluminescence-based homogenous immunoassay reporter platform where all assay components can be configured into a stable lyophilized cake, supporting homogeneous, rapid, and sensitive one-step biomolecule quantification in complex human samples. This technology represents a promising alternative immunoassay format with significant potential to bring critical diagnostic molecular detection testing closer to the point-of-need.

Intracellular Ionic Strength Sensing Using NanoLuc

Intracellular ionic strength regulates myriad cellular processes that are fundamental to cellular survival and proliferation, including protein activity, aggregation, phase separation, and cell volume. It could be altered by changes in the activity of cellular signaling pathways, such as those that impact the activity of membrane-localized ion channels or by alterations in the microenvironmental osmolarity. Therefore, there is a demand for the development of sensitive tools for real-time monitoring of intracellular ionic strength. Here, we developed a bioluminescence-based intracellular ionic strength sensing strategy using the Nano Luciferase (NanoLuc) protein that has gained tremendous utility due to its high, long-lived bioluminescence output and thermal stability. Biochemical experiments using a recombinantly purified protein showed that NanoLuc bioluminescence is dependent on the ionic strength of the reaction buffer for a wide range of ionic strength conditions. Importantly, the decrease in the NanoLuc activity observed at higher ionic strengths could be reversed by decreasing the ionic strength of the reaction, thus making it suitable for sensing intracellular ionic strength alterations. Finally, we used an mNeonGreen–NanoLuc fusion protein to successfully monitor ionic strength alterations in a ratiometric manner through independent fluorescence and bioluminescence measurements in cell lysates and live cells. We envisage that the biosensing strategy developed here for detecting alterations in intracellular ionic strength will be applicable in a wide range of experiments, including high throughput cellular signaling, ion channel functional genomics, and drug discovery.

NanoLuc luciferase as a suitable fusion partner of recombinant antibody fragments for developing sensitive luminescent immunoassays

Enzyme-linked immunosorbent assays (ELISAs) are essential for monitoring various biomarkers. Competitive and noncompetitive (sandwich) assay formats are used to determine hapten and macromolecule levels, respectively. Both formats require more sensitive detection of reporter enzymes for greater assay sensitivities. We previously reported the utility of wild-type Gaussia luciferase (wtGLuc) as a fusion partner with antibody single-chain Fv fragments (scFvs) for developing sensitive luminescent ELISAs. Here, we evaluated utility of NanoLuc luciferase (NLuc), a recently developed luciferase, as fusion partner with scFvs from the view of comparison with wtGLuc and a mutant of alkaline phosphatase (ALP'). Thyroxine (T₄) and T₄-labeled albumin were chosen as model haptenic and macromolecular antigens, respectively. An in-house-prepared anti-T₄ scFv was fused with NLuc, wtGLuc, or ALP'. The scFv-NLuc fusion protein showed 47-fold and 29-fold lower limit of detection [LOD; 59 zmol (per assay)] than the wtGLuc- and ALP'-fusions, respectively. In a competitive T₄ ELISA, the NLuc-fusion showed 9.3- and 6.3-fold lower LOD, (0.67 pg) than the wtGLuc- and ALP'-fusions, respectively, with a higher specificity in clinical applications. A typical colorimetric ELISA using a peroxidase-labeled second antibody showed 70-fold higher LOD than NLuc-based ELISA. Another advantage of the NLuc-fusion was shown in the sandwich assays; the LOD of T₄-labeled albumin (5.0 fmol) was >6-fold lower than that of the other luminescent ELISAs. In an additional sandwich assay developed to count bacteriophage particles, NLuc enabled more sensitive determination than wtGLuc, whereas ALP' showed nearly equivalent performance. Its slowest alteration rate for light intensity after starting the enzyme reaction should enable robust batch-by-batch assay operations. Thus, we concluded that scFv-NLuc fusions serve as suitable probes in various types of immunoassays and may facilitate higher sensitivities with practical specificities.

Novel NanoLuc substrates enable bright two-population bioluminescence imaging in animals

Sensitive detection of two biological events in vivo has long been a goal in bioluminescence imaging. Antares, a fusion of the luciferase NanoLuc to the orange fluorescent protein CyOFP, has emerged as a bright bioluminescent reporter with orthogonal substrate specificity to firefly luciferase (FLuc) and its derivatives such as AkaLuc. However, the brightness of Antares in mice is limited by the poor solubility and bioavailability of the NanoLuc substrate furimazine. Here, we report a new substrate, hydrofurimazine, whose enhanced aqueous solubility allows delivery of higher doses to mice. In the liver, Antares with hydrofurimazine exhibited similar brightness to AkaLuc with its substrate AkaLumine. Further chemical exploration generated a second substrate, fluorofurimazine, with even higher brightness in vivo. We used Antares with fluorofurimazine to track tumor size and AkaLuc with AkaLumine to visualize CAR-T cells within the same mice, demonstrating the ability to perform two-population imaging with these two luciferase systems.

Regulatory and strategic considerations for addressing immunogenicity and related responses in biopharmaceutical development programs

The last three decades have seen the biotherapeutic drug market evolve from promising concept to market dominance in a range of clinical indications. This growth has been spurred by the success of established drug classes like monoclonal antibodies, but also by the introduction of biosimilars, and more recently, multiple novel cell and gene therapies. Biotherapeutic drug development presents many unique challenges, but unintended immune responses are among the most common reasons for program attrition. Anti-drug antibodies can impact the safety and efficacy of drug products, and related immune responses, like the cytokine release syndrome that occurred in the infamous TGN-1412 clinical trial, can be challenging to predict with nonclinical models. For this reason, it is important that development programs proceed with a scientifically grounded and measured approach to these responses. This process begins at the discovery stage with the application of “quality by design,” continues into the clinic with the development of quality assays and management strategies, and culminates in the effective presentation of this information in regulatory documents. This review provides an overview of some of the key strategic and regulatory considerations for biotherapeutics as they pertain to immunogenicity and related responses.

HaloTag-based conjugation of proteins to barcoding-oligonucleotides

Highly sensitive protein quantification enables the detection of a small number of protein molecules that serve as markers/triggers for various biological phenomena, such as cancer. Here, we describe the development of a highly sensitive protein quantification system called HaloTag protein barcoding. The method involves covalent linking of a target protein to a unique molecule counting oligonucleotide at a 1:1 conjugation ratio based on an azido-cycloalkyne click reaction. The sensitivity of the HaloTag-based barcoding was remarkably higher than that of a conventional luciferase assay. The HaloTag system was successfully validated by analyzing a set of protein-protein interactions, with the identification rate of 44% protein interactions between positive reference pairs reported in the literature. Desmoglein 3, the target antigen of pemphigus vulgaris, an IgG-mediated autoimmune blistering disease, was used in a HaloTag protein barcode assay to detect the anti-DSG3 antibody. The dynamic range of the assay was over 104-times wider than that of a conventional enzyme-linked immunosorbent assay (ELISA). The technology was used to detect anti-DSG3 antibody in patient samples with much higher sensitivity compared to conventional ELISA. Our detection system, with its superior sensitivity, enables earlier detection of diseases possibly allowing the initiation of care/treatment at an early disease stage.

Bioluminescent Antibodies through Photoconjugation of Protein G-Luciferase Fusion Proteins

Bioluminescent antibodies represent attractive detection agents in both bioanalytical assays and imaging. Currently, their preparation relies on genetic fusion of luciferases to antibodies or nonspecific chemical conjugation strategies. Here, we report a generic method to generate well-defined covalent antibody-luciferase conjugates starting from commercially available monoclonal antibodies. Our approach uses fusion proteins consisting of the bright blue light-emitting luciferase NanoLuc (NL) and an Fc-binding protein domain (Gx) that can be photo-cross-linked to the antibody using UV light illumination. Green and red color variants were constructed by tight fusion of the NanoLuc with a green fluorescent acceptor domain and introduction of Cy3, respectively. To increase the already bright NanoLuc emission, tandem fusions were successfully developed in which the Gx domain is fused to two or three copies of the NanoLuc domain. The Gx-NL fusion proteins can be efficiently photo-cross-linked to all human immunoglobulin G (IgG) isotypes and most mammalian IgG's using 365 nm light, yielding antibodies with either one or two luciferase domains. The bioluminescent antibodies were successfully used in cell immunostaining and bioanalytical assays such as enzyme-linked immunosorbent assay (ELISA) and Western blotting.

GloBody Technology: Detecting Anti-Drug Antibody against VH/VL domains

The occurrence of anti-drug antibodies following administration of therapeutic monoclonal antibody to patients is a growing problem that is attracting attention from frontline clinicians. Ideally, an initial indicative point of care test would provide guidance to seek testing approved by the regulatory authorities. Here we describe a platform for the detection of IgG anti-drug antibodies that may provide an initial screen for all therapeutic monoclonal antibodies. Synthetic genes encoding Nanoluciferase polypeptides were inserted between the variable heavy and light domain encoding region of known antibody drugs (alemtuzumab and adalimumab) to generate recombinant single chain GloBodies, which retain the drug antibody paratopes and Nanoluciferase activity. In the presence of anti-drug antibodies, the GloBody is bound by specific IgG in the sample. These complexes are captured on immobilised Protein G and the luciferase activity determined. The amount of light generated being indicative of the anti-drug IgG antibody levels in serum. It should be possible to assemble GloBody reagents for all therapeutic monoclonal antibodies and adapt the capture phase to include additional specific isotypes. The assay has the potential to be developed for use with a drop of blood allowing initial pre-screening in a point of care setting.

A homogeneous bioluminescent immunoassay to probe cellular signaling pathway regulation

Monitoring cellular signaling events can help better understand cell behavior in health and disease. Traditional immunoassays to study proteins involved in signaling can be tedious, require multiple steps, and are not easily adaptable to high throughput screening (HTS). Here, we describe a new immunoassay approach based on bioluminescent enzyme complementation. This immunoassay takes less than two hours to complete in a homogeneous "Add and Read" format and was successfully used to monitor multiple signaling pathways' activation through specific nodes of phosphorylation (e.g pIκBα, pAKT, and pSTAT3). We also tested deactivation of these pathways with small and large molecule inhibitors and obtained the expected pharmacology. This approach does not require cell engineering. Therefore, the phosphorylation of an endogenous substrate is detected in any cell type. Our results demonstrate that this technology can be broadly adapted to streamline the analysis of signaling pathways of interest or the identification of pathway specific inhibitors.

A novel luciferase immunosorbent assay performs better than a commercial enzyme-linked immunosorbent assay to detect MERS-CoV specific IgG in humans and animals

The Middle East respiratory syndrome (MERS) is a lethal zoonosis caused by MERS coronavirus (MERS-CoV) and poses a significant threat to public health worldwide. Therefore, a rapid, sensitive, and specific serologic test for detecting anti-MERS-CoV antibodies in both humans and animals is urgently needed for the successful management of this illness. Here, we evaluated various novel luciferase immunosorbent assays (LISA) based on nucleocapsid protein (NP) as well as fragments derived from spike protein (S) including subunit 1 (S1), N terminal domain (NTD), receptor-binding domain (RBD) and subunit 2 (S2) of S for the detection of MERS-CoV-specific IgG. Fusion proteins, including nanoluciferase (NLuc) and various fragments derived from the NP or S protein of MERS-CoV, were expressed in human embryonic kidney 293 T cells. LISAs that detected anti-MERS-CoV IgG were further developed using cell lysates expressing various fusion proteins. Panels of human or animal samples infected with MERS-CoV were used to analyze the sensitivity and specificity of various LISAs in reference to a MERS-CoV RT-PCR, commercial S1-based ELISA, and pseudovirus particle neutralization test (ppNT). Our results showed that the S1-, RBD-, and NP-LISAs were more sensitive than the NTD- and S2-LISAs for the detection of anti-MERS-CoV IgG. Furthermore, the S1-, RBD-, and NP-LISAs were more sensitive (by at least 16-fold) than the commercially available S1-ELISA. Moreover, the S1-, RBD-, and NP-LISA specifically recognized anti-MERS-CoV IgG and did not cross-react with samples derived from other human CoV (OC43, 229E, HKU1, NL63)-infected patients. More importantly, these LISAs proved their applicability and reliability for detecting anti-MERS-CoV IgG in samples from camels, monkeys, and mice, among which the RBD-LISA exhibited excellent performance. The results of this study suggest that the novel MERS-CoV RBD- and S1- LISAs are highly effective platforms for the rapid and sensitive detection of anti-MERS-CoV IgG in human and animal samples. These assays have the potential to be used as serologic tests for the management and control of MERS-CoV infection.

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Scientific question

This study evaluated novel luciferase immunosorbent assays (LISAs) based on nucleocapsid protein (NP) as well as fragments derived from spike protein (S) for detection of MERS-CoV-specific IgG in humans and animals.

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Evidence before this study

Enzyme-linked immunosorbent assay (ELISA), microneutralization (MN), immunofluorescence assay (IFA), and pseudovirus particle neutralization test (ppNT) have been performed to detect serum antibodies against MERS-CoV. There remains a need to develop novel serological assays independent of protein purification, special secondary antibody, virus cultivation and Biosafety Level 3 (BSL-3) laboratory.

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New findings

In this study, novel LISAs based on the MERS-CoV S fragments and NP were developed. Human and animal samples infected with MERS-CoV were measured by the newly developed LISAs as well as reference methods including commercial S1-ELISA and ppNT. The results showed that the S1-, RBD-, and NP-LISAs were able to specifically distinguish MERS-CoV-infected samples from samples infected by other HCoV as consistent as the reference methods. Comparing with the commercially available S1-ELISA, the S1- and RBD-LISAs were 64-folds more sensitive. Moreover, the applicability and reliability of the LISAs were verified by detecting anti-MERS-CoV IgG in samples from camels, monkeys, and mice. The RBD-LISA exhibited superior sensitivity and specificity.

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Significance of the study

The novel MERS-CoV RBD- and S1-LISAs were developed independent of protein purification and special secondary antibody, and showed super specificity and efficiency for the detection of anti-MERS-CoV IgG in human and animal samples. These assays are recommended for serological diagnosis of MERS-CoV infection in the investigation of epidemic characteristic, origin tracing and vaccine study of MERS-CoV, they would contribute to the scientific control and prevention of MERS.

Pharmacological Autophagy Regulators as Therapeutic Agents for Inflammatory Bowel Diseases

The arsenal of effective molecules to treat patients with chronic inflammatory bowel diseases (IBDs) remains limited. These remitting-relapsing diseases have become a global health issue and new therapeutic strategies are eagerly awaited to regulate the course of these disorders. Since the association between autophagy-related gene polymorphism and an increased risk of Crohn's disease (CD) has been discovered, a new domain of investigation has emerged, focused on the intracellular degradation system, with the objective of generating new medicines that are safer and more targeted. This review summarizes the drugs administered to IBD patients and describes recently emerged therapeutic agents. We compile evidence on the contribution of autophagy to IBD pathogenesis, give an overview of pharmacological autophagy regulators in animal models of colitis, and propose novel therapeutic avenues based on autophagy components.

Small molecule-protein interactions in branch migration thermodynamics: modelling and application in the homogeneous detection of proteins and small molecules

We have disclosed the unique inhibition effect of small molecule-protein interactions toward the DNA branch migration process and constructed a complete thermodynamic model for it. The disclosed effect was further coupled with the steric hindrance effect to establish a homogeneous assay for proteins and small molecules with ultra-high inhibition factors and sensitivity.

Nanobody-based dual epitopes protein identification (DepID) assay for measuring soluble CD38 in plasma of multiple myeloma patients

BACKGROUND

CD38 is a surface membrane antigen highly expressed in malignant blood cells, such as multiple myeloma (MM). A soluble form of CD38 (sCD38) is also present in the plasma, deriving likely from the shedding from the cells. The plasma levels of sCD38 should thus correlate closely with the proliferation of the MM cells, allowing the development of a simple diagnostic blood test for monitoring the progress of the disease. However, the plasma sCD38 levels are extremely low, requiring the design of a highly sensitive and specific assay.

RESULTS

In this study, we developed an ultra-sensitive assay, based on two nanobodies (Nbs) targeting two distinct epitopes of sCD38. One Nb acts as a capturer, and the other is fused with the firefly luciferase serving as a reporter to ensure sensitivity. We showed that this Dual epitopes protein IDentification (DepID) assay has sensitivity reaching 10 pg/mL, which is 10 times higher than that of a commercial ELISA kit. By this method, we were able to precisely quantify the levels of sCD38 in the plasma of MM patients, which were significantly higher than those from healthy donors. We further showed that the increase plasma levels of sCD38 correlated with the progress of MM.

CONCLUSION

We have developed a Nb-based luminescence sandwich assay, named as DepID, for quantification of the soluble CD38 in MM patients' plasma and showed the potency of this method as a tool for general diagnosis of MM or companion diagnosis of the CD38-targeted therapies.

Dual-Color Bioluminescent Sensor Proteins for Therapeutic Drug Monitoring of Antitumor Antibodies

Monitoring the levels of therapeutic antibodies in individual patients would allow patient-specific dose optimization, with the potential for major therapeutic and financial benefits. Our group recently developed a new platform of bioluminescent sensor proteins (LUMABS; LUMinescent AntiBody Sensor) that allow antibody detection directly in blood plasma. In this study, we targeted four clinically important therapeutic antibodies, the Her2-receptor targeting trastuzumab, the anti-CD20 antibodies rituximab and obinutuzumab, and the EGFR-blocking cetuximab. A strong correlation was found between the affinity of the antibody binding peptide and sensor performance. LUMABS sensors with physiologically relevant affinities and decent sensor responses were obtained for trastuzumab and cetuximab using mimotope and meditope peptides, respectively, with affinities in the 10^-7 M range. The lower affinity of the CD20-derived cyclic peptide employed in the anti-CD20 LUMABS sensor ( K_d = 10^-5 M), translated in a LUMABS sensor with a strongly attenuated sensor response. The trastuzumab and cetuximab sensors were further characterized with respect to binding kinetics and their performance in undiluted blood plasma. For both antibodies, LUMABS-based detection directly in plasma compared well to the analytical performance of commercial ELISA kits. Besides identifying important design parameters for the development of new LUMABS sensors, this work demonstrates the potential of the LUMABS platform for point-of-care detection of therapeutic antibodies.

Construction and Potential Applications of Biosensors for Proteins in Clinical Laboratory Diagnosis

Biosensors for proteins have shown attractive advantages compared to traditional techniques in clinical laboratory diagnosis. In virtue of modern fabrication modes and detection techniques, various immunosensing platforms have been reported on basis of the specific recognition between antigen-antibody pairs. In addition to profit from the development of nanotechnology and molecular biology, diverse fabrication and signal amplification strategies have been designed for detection of protein antigens, which has led to great achievements in fast quantitative and simultaneous testing with extremely high sensitivity and specificity. Besides antigens, determination of antibodies also possesses great significance for clinical laboratory diagnosis. In this review, we will categorize recent immunosensors for proteins by different detection techniques. The basic conception of detection techniques, sensing mechanisms, and the relevant signal amplification strategies are introduced. Since antibodies and antigens have an equal position to each other in immunosensing, all biosensing strategies for antigens can be extended to antibodies under appropriate optimizations. Biosensors for antibodies are summarized, focusing on potential applications in clinical laboratory diagnosis, such as a series of biomarkers for infectious diseases and autoimmune diseases, and an evaluation of vaccine immunity. The excellent performances of these biosensors provide a prospective space for future antibody-detection-based disease serodiagnosis.