Heavy chain single-domain antibodies to detect native human soluble epoxide hydrolase

The Generation of a Nanobody-Based ELISA for Human Microsomal Epoxide Hydrolase

A microsomal epoxide hydrolase (mEH) metabolizes in vivo in both xenobiotic and endogenous epoxides associated with signaling function. Findings in patients suggest that mEH might be a biomarker for several diseases, including metastatic cancer and viral hepatitis. To easily quantify mEH, nanobodies specific to the human mEH were isolated from a phage library of llama VHHs. Four unique clones were obtained and used for developing ELISAs. Three formats of double antibody sandwich assays were investigated using different detection strategies. Using PolyHRP, the signal was strongly amplified, yielding a 22-fold lower LOD (12 pg mL-1) than the 'conventional'. To further validate the performance of the immunoassays, human tissue samples were analyzed by nanobody-based ELISAs and compared to the enzyme activities (R2 > 0.95). The results demonstrate that these nanobodies are powerful tools for the quantification of human mEH and could eventually result in a bedside assay.

Mix-and-Read Nanobody-Based Sandwich Homogeneous Split-Luciferase Assay for the Rapid Detection of Human Soluble Epoxide Hydrolase

The soluble epoxide hydrolase (sEH) is possibly both a marker for and target of numerous diseases. Herein, we describe a homogeneous mix-and-read assay for the detection of human sEH based on using split-luciferase detection coupled with anti-sEH nanobodies. Selective anti-sEH nanobodies were individually fused with NanoLuc Binary Technology (NanoBiT), which consists of a large and small portion of NanoLuc (LgBiT and SmBiT, respectively). Different orientations of the LgBiT and SmBiT-nanobody fusions were expressed and investigated for their ability to reform the active NanoLuc in the presence of the sEH. After optimization, the linear range of the assay could reach 3 orders of magnitude with a limit of detection (LOD) of 1.4 ng/mL. The assay has a high sensitivity to human sEH and reached a similar detection limit to our previously reported conventional nanobody-based ELISA. The procedure of the assay was faster (30 min total) and easy to operate, providing a more flexible and simple way to monitor human sEH levels in biological samples. In general, the immunoassay proposed here offers a more efficient detection and quantification approach that can be easily adapted to numerous macromolecules.

Novel application of anti-human Fc nanobody for screening high-producing CHO cells for monoclonal antibody

Animal-derived anti-IgG secondary antibodies are currently employed to stain and screen of human monoclonal antibody(mAb)-producing cells, but using animal-derived antibodies may raise the concerns of high cost, complicated operations and biological safety issues in biopharmaceutical manufacturing. Nanobodies(VHHs) are attractive forms of antibodies for their straightforward engineering and expression in both eukaryotic and prokaryotic systems. Using phage-displayed immune llama VHH library, we identified new anti-Fc VHHs that could bind to human Fc with high affinity. In GFP fusion format, the anti-Fc VHH-GFP generated dramatically stronger FACS signals than AF488 conjugated anti-IgG antibodies when used for staining mAb-producing CHO cells. Furthermore, preparative sorting of CHO cells based on anti-Fc VHH-GFP staining resulted in the enrichment of cell lines capable of synthesizing mAb at high productivity. This safe and cost-efficient anti-Fc VHH-GFP may optimize the process of generating highly productive cell lines for therapeutic mAb production compared to conventional animal-derived fluorescent antibodies.

Nanobodies targeting immune checkpoint molecules for tumor immunotherapy and immunoimaging (Review)

The immune checkpoint blockade is an effective strategy to enhance the anti-tumor T cell effector activity, thus becoming one of the most promising immunotherapeutic strategies in the history of cancer treatment. Several immune checkpoint inhibitor have been approved by the FDA, such as anti-CTLA-4, anti-PD-1, anti-PD-L1 monoclonal antibodies. Most tumor patients benefitted from these antibodies, but some of the patients did not respond to them. To increase the effectiveness of immunotherapy, including immune checkpoint blockade therapies, miniaturization of antibodies has been introduced. A single-domain antibody, also known as nanobody, is an attractive reagent for immunotherapy and immunoimaging thanks to its unique structural characteristic consisting of a variable region of a single heavy chain antibody. This structure confers to the nanobody a light molecular weight, making it smaller than conventional antibodies, although remaining able to bind to a specific antigen. Therefore, this review summarizes the production of nanobodies targeting immune checkpoint molecules and the application of nanobodies targeting immune checkpoint molecules in immunotherapy and immunoimaging.

Development of a Highly Sensitive Enzyme-Linked Immunosorbent Assay for Mouse Soluble Epoxide Hydrolase Detection by Combining a Polyclonal Capture Antibody with a Nanobody Tracer

Enzyme-linked immunosorbent assays (ELISA) for the detection of soluble epoxide hydrolase (sEH), a key enzyme in the metabolism of fatty acids and a biomarker, may increasingly represent an important diagnostic tool. However, there is a lack of ELISAs for mouse sEH quantification, thus resulting in a bottleneck in understanding the pathogenesis of many diseases related to sEH based on mouse models. In this work, nanobodies recognizing mouse sEH were obtained through rebiopanning against mouse sEH in the previous phage display library of human sEH. Later, we developed four ELISAs involving a combination of anti-mouse sEH polyclonal antibodies (pAbs) and nanobodies. It was found that the double antibodies worked as dual filters and had a huge impact on both the sensitivity and selectivity of sandwich immunoassays. The switch from anti-human sEH pAbs to anti-mouse sEH pAbs led to over a 100-fold increase in the sensitivity and a dramatic decrease of the limit of detection to a picogram per milliliter range in format B (pAb/biotin-VHH/streptavidin-poly-horseradish peroxidase). Moreover, we found that the four sandwich ELISAs might demonstrate excellent selectivities to mouse sEH, despite the antibodies alone showing significant cross-reactivity to the matrix, indicating the enhanced selectivity of double antibodies as dual filters. Eventually, for the first time, the ELISA (format B) was successfully used to measure the mouse sEH level in cancer cells with ultralow abundances. The ELISAs proposed here represent a sensitive tool for tracking sEH in various biological processes and also provide deep insights into developing sandwich immunoassays against various targets in terms of both the sensitivity and selectivity.

Development of Improved Double-Nanobody Sandwich ELISAs for Human Soluble Epoxide Hydrolase Detection in Peripheral Blood Mononuclear Cells of Diabetic Patients and the Prefrontal Cortex of Multiple Sclerosis Patients

Nanobodies have been progressively replacing traditional antibodies in various immunological methods. However, the use of nanobodies as capture antibodies is greatly hampered by their poor performance after passive adsorption to polystyrene microplates, and this restricts the full use of double nanobodies in sandwich enzyme-linked immunosorbent assays (ELISAs). Herein, using the human soluble epoxide hydrolase (sEH) as a model analyte, we found that both the immobilization format and the blocking agent have a significant influence on the performance of capture nanobodies immobilized on polystyrene and the subsequent development of double-nanobody sandwich ELISAs. We first conducted epitope mapping for pairing nanobodies and then prepared a horseradish-peroxidase-labeled nanobody using a mild conjugation procedure as a detection antibody throughout the work. The resulting sandwich ELISA using a capture nanobody (A9, 1.25 μg/mL) after passive adsorption and bovine serum albumin (BSA) as a blocking agent generated a moderate sensitivity of 0.0164 OD·mL/ng and a limit of detection (LOD) of 0.74 ng/mL. However, the introduction of streptavidin as a linker to the capture nanobody at the same working concentration demonstrated a dramatic 16-fold increase in sensitivity (0.262 OD·mL/ng) and a 25-fold decrease in the LOD for sEH (0.03 ng/mL). The streptavidin-bridged double-nanobody ELISA was then successfully applied to tests for recovery, cross-reactivity, and real samples. Meanwhile, we accidentally found that blocking with skim milk could severely damage the performance of the capture nanobody by an order of magnitude compared with BSA. This work provides guidelines to retain the high effectiveness of the capture nanobody and thus to further develop the double-nanobody ELISA for various analytes.

Nanobody-based binding assay for the discovery of potent inhibitors of CFTR inhibitory factor (Cif)

Lead identification and optimization are essential steps in the development of a new drug. It requires cost-effective, selective and sensitive chemical tools. Here, we report a novel method using nanobodies that allows the efficient screening for potent ligands. The method is illustrated with the cystic fibrosis transmembrane conductance regulator inhibitory factor (Cif), a virulence factor secreted by the opportunistic pathogen Pseudomonas aeruginosa. 18 nanobodies selective to Cif were isolated by bio-panning from nanobody-phage library constructed from immunized llama. 8 out of 18 nanobodies were identified as potent inhibitors of Cif enzymatic activity with IC₅₀s in the range of 0.3-6.4 μM. A nanobody VHH219 showed high affinity (K_D = 0.08 nM) to Cif and the highest inhibitory potency, IC₅₀ = 0.3 μM. A displacement sandwich ELISA (dsELISA) with VHH219 was then developed for classification of synthetic small molecule inhibitors according their inhibitory potency. The developed assay allowed identification of new inhibitor with highest potency reported so far (0.16 ± 0.02 μM). The results from dsELISA assay correlates strongly with a conventional fluorogenic assay (R = 0.9998) in predicting the inhibitory potency of the tested compounds. However, the novel dsELISA is an order of magnitude more sensitive and allows the identification and ranking of potent inhibitors missed by the classic fluorogenic assay method. These data were supported with Octet biolayer interferometry measurements. The novel method described herein relies solely on the binding properties of the specific neutralizing nanobody, and thus is applicable to any pharmacological target for which such a nanobody can be found, independent of any requirement for catalytic activity.

Nanobody Based Immunoassay for Human Soluble Epoxide Hydrolase Detection Using Polymeric Horseradish Peroxidase (PolyHRP) for Signal Enhancement: The Rediscovery of PolyHRP?

Soluble epoxide hydrolase (sEH) is a potential pharmacological target for treating hypertension, vascular inflammation, cancer, pain, and multiple cardiovascular related diseases. A variable domain of the heavy chain antibody (termed single domain antibody (sdAb), nanobody, or VHH) possesses the advantages of small size, high stability, ease of genetic manipulation, and ability for continuous manufacture, making such nanobody a superior choice as an immunoreagent. In this work, we developed an ultrasensitive nanobody based immunoassay for human sEH detection using polymeric horseradish peroxidase (PolyHRP) for signal enhancement. Llama nanobodies against human sEH were used as the detection antibody in sandwich enzyme linked immunosorbent assays (ELISA) with polyclonal anti-sEH as the capture antibody. A conventional sandwich ELISA using a horseradish peroxidase (HRP) labeled anti-hemeagglutinin (HA) tag as the tracer showed a marginal sensitivity (0.0015 optical density (OD)·mL/ng) and limit of detection (LOD) of 3.02 ng/mL. However, the introduction of the PolyHRP as the tracer demonstrated a 141-fold increase in the sensitivity (0.21 OD·mL/ng) and 57-fold decrease in LOD (0.05 ng/mL). Systematic comparison of three different tracers in four ELISA formats demonstrated the overwhelming advantage of PolyHRP as a label for nanobody based immunoassay. This enhanced sEH immunoassay was further evaluated in terms of selectivity against other epoxide hydrolases and detection of the target protein in human tissue homogenate samples. Comparison with an enzyme activity based assay and a Western blot for sEH detection reveals good correlation with the immunoassay. This work demonstrates increased competiveness of nanobodies for practical sEH protein detection utilizing PolyHRP. It is worthwhile to rediscover the promising potential of PolyHRP in nanobody and other affinity based methods after its low-profile existence for decades.

Method for Sorting and Pairwise Selection of Nanobodies for the Development of Highly Sensitive Sandwich Immunoassays

Single domain heavychain binders (nanobodies) obtained from camelid antibody libraries hold a great promise for immunoassay development. However, there is no simple method to select the most valuable nanobodies from the crowd of positive clones obtained after the initial screening. In this paper, we describe a novel nanobody-based platform that allows comparison of the reactivity of hundreds of clones with the labeled antigen, and identifies the best nanobody pairs for two-site immunoassay development. The output clones are biotinylated in vivo in 96-well culture blocks and then used to saturate the biotin binding capacity of avidin coated wells. This standardizes the amount of captured antibody allowing their sorting by ranking their reactivity with the labeled antigen. Using human soluble epoxide hydrolase (sEH) as a model antigen, we were able to classify 96 clones in four families and confirm this classification by sequencing. This provided a criterion to select a restricted panel of five capturing antibodies and to test each of them against the rest of the 96 clones. The method constitutes a powerful tool for epitope binning, and in our case allowed development of a sandwich ELISA for sEH with a detection limit of 63 pg/mL and four log dynamic range, which performed with excellent recovery in different tissue extracts. This strategy provides a systematic way to test nanobody pairwise combinations and would have a broad utility for the development of highly sensitive sandwich immunoassays.