Nanobodies and their potential applications

A Nanobody Targeting Viral Nonstructural Protein 9 Inhibits Porcine Reproductive and Respiratory Syndrome Virus Replication

Porcine reproductive and respiratory syndrome (PRRS) is of great concern to the swine industry due to pandemic outbreaks of the disease, current ineffective vaccinations, and a lack of efficient antiviral strategies. In our previous study, a PRRSV Nsp9-specific nanobody, Nb6, was successfully isolated, and the intracellularly expressed Nb6 could dramatically inhibit PRRSV replication in MARC-145 cells. However, despite its small size, the application of Nb6 protein in infected cells is greatly limited, as the protein itself cannot enter the cells physically. In this study, a trans-activating transduction (TAT) peptide was fused with Nb6 to promote protein entry into cells. TAT-Nb6 was expressed as an inclusion body in Escherichia coli, and indirect enzyme-linked immunosorbent assays and pulldown assays showed that E. coli-expressed TAT-Nb6 maintained the binding ability to E. coli-expressed or PRRSV-encoded Nsp9. We demonstrated that TAT delivered Nb6 into MARC-145 cells and porcine alveolar macrophages (PAMs) in a dose- and time-dependent manner, and TAT-Nb6 efficiently inhibited the replication of several PRRSV genotype 2 strains as well as a genotype 1 strain. Using a yeast two-hybrid assay, Nb6 recognition sites were identified in the C-terminal part of Nsp9 and spanned two discontinuous regions (Nsp9_aa454-551 and Nsp9_aa599-646). Taken together, these results suggest that TAT-Nb6 can be developed as an antiviral drug for the inhibition of PRRSV replication and controlling PRRS disease.IMPORTANCE The pandemic outbreak of PRRS, which is caused by PRRSV, has greatly affected the swine industry. We still lack an efficient vaccine, and it is an immense challenge to control its infection. An intracellularly expressed Nsp9-specific nanobody, Nb6, has been shown to be able to inhibit PRRSV replication in MARC-145 cells. However, its application is limited, because Nb6 cannot physically enter cells. Here, we demonstrated that the cell-penetrating peptide TAT could deliver Nb6 into cultured cells. In addition, TAT-Nb6 fusion protein could suppress the replication of various PRRSV strains in MARC-145 cells and PAMs. These findings may provide a new approach for drug development to control PRRS.

Challenges in the Structural-Functional Characterization of Multidomain, Partially Disordered Proteins CBP and p300: Preparing Native Proteins and Developing Nanobody Tools

The structural and functional characterization of large multidomain signaling proteins containing long disordered linker regions represents special methodological and conceptual challenges. These proteins show extreme structural heterogeneity and have complex posttranslational modification patterns, due to which traditional structural biology techniques provide results that are often difficult to interpret. As demonstrated through the example of two such multidomain proteins, CREB-binding protein (CBP) and its paralogue, p300, even the expression and purification of such proteins are compromised by their extreme proteolytic sensitivity and structural heterogeneity. In this chapter, we describe the effective expression of CBP and p300 in a eukaryotic host, Sf9 insect cells, followed by their tandem affinity purification based on two terminal tags to ensure their structural integrity. The major focus of this chapter is on the development of novel accessory tools, single-domain camelid antibodies (nanobodies), for structural-functional characterization. Specific nanobodies against full-length CBP and p300 can specifically target their different regions and can be used for their marking, labeling, and structural stabilization in a broad range of in vitro and in vivo studies. Here, we describe four high-affinity nanobodies binding to the KIX and the HAT domains, either mimicking known interacting partners or revealing new functionally relevant conformations. As immunization of llamas results in nanobody libraries with a great sequence variation, deep sequencing and interaction analysis with different regions of the proteins provide a novel approach toward developing a panel of specific nanobodies.

Single-molecule labeling for studying trafficking of renal transporters

The ability to detect and track single molecules presents the advantage of visualizing the complex behavior of transmembrane proteins with a time and space resolution that would otherwise be lost with traditional labeling and biochemical techniques. Development of new imaging probes has provided a robust method to study their trafficking and surface dynamics. This mini-review focuses on the current technology available for single-molecule labeling of transmembrane proteins, their advantages, and limitations. We also discuss the application of these techniques to the study of renal transporter trafficking in light of recent research.

Detecting Biothreat Agents: From Current Diagnostics to Developing Sensor Technologies

Although a fundamental understanding of the pathogenicity of most biothreat agents has been elucidated and available treatments have increased substantially over the past decades, they still represent a significant public health threat in this age of (bio)terrorism, indiscriminate warfare, pollution, climate change, unchecked population growth, and globalization. The key step to almost all prevention, protection, prophylaxis, post-exposure treatment, and mitigation of any bioagent is early detection. Here, we review available methods for detecting bioagents including pathogenic bacteria and viruses along with their toxins. An introduction placing this subject in the historical context of previous naturally occurring outbreaks and efforts to weaponize selected agents is first provided along with definitions and relevant considerations. An overview of the detection technologies that find use in this endeavor along with how they provide data or transduce signal within a sensing configuration follows. Current "gold" standards for biothreat detection/diagnostics along with a listing of relevant FDA approved in vitro diagnostic devices is then discussed to provide an overview of the current state of the art. Given the 2014 outbreak of Ebola virus in Western Africa and the recent 2016 spread of Zika virus in the Americas, discussion of what constitutes a public health emergency and how new in vitro diagnostic devices are authorized for emergency use in the U.S. are also included. The majority of the Review is then subdivided around the sensing of bacterial, viral, and toxin biothreats with each including an overview of the major agents in that class, a detailed cross-section of different sensing methods in development based on assay format or analytical technique, and some discussion of related microfluidic lab-on-a-chip/point-of-care devices. Finally, an outlook is given on how this field will develop from the perspective of the biosensing technology itself and the new emerging threats they may face.

Therapeutics and Immunoprophylaxis Against Noroviruses and Rotaviruses: The Past, Present, and Future

Background:

Noroviruses and rotaviruses are important viral etiologies of severe gastroenteritis. Noroviruses are the primary cause of nonbacterial diarrheal outbreaks in humans, whilst rotaviruses are a major cause of childhood diarrhea. Although both enteric pathogens substantially impact human health and economies, there are no approved drugs against noroviruses and rotaviruses so far. On the other hand, whilst the currently licensed rotavirus vaccines have been successfully implemented in over 100 countries, the most advanced norovirus vaccine has recently completed phase-I and II trials.

Methods:

We performed a structured search of bibliographic databases for peer-reviewed research litera-ture on advances in the fields of norovirus and rotavirus therapeutics and immunoprophylaxis.

Results:

Technological advances coupled with a proper understanding of viral morphology and replication over the past decade has facilitated pioneering research on therapeutics and immunoprophylaxis against noroviruses and rotaviruses, with promising outcomes in human clinical trials of some of the drugs and vaccines. This review focuses on the various developments in the fields of norovirus and rotavirus thera-peutics and immunoprophylaxis, such as potential antiviral drug molecules, passive immunotherapies (oral human immunoglobulins, egg yolk and bovine colostral antibodies, llama-derived nanobodies, and anti-bodies expressed in probiotics, plants, rice grains and insect larvae), immune system modulators, probiot-ics, phytochemicals and other biological substances such as bovine milk proteins, therapeutic nanoparti-cles, hydrogels and viscogens, conventional viral vaccines (live and inactivated whole virus vaccines), and genetically engineered viral vaccines (reassortant viral particles, virus-like particles (VLPs) and other sub-unit recombinant vaccines including multi-valent viral vaccines, edible plant vaccines, and encapsulated viral particles).

Conclusions:

This review provides important insights into the various approaches to therapeutics and im-munoprophylaxis against noroviruses and rotaviruses..

In planta expression of nanobody-based designer chicken antibodies targeting Campylobacter

Campylobacteriosis is a widespread infectious disease, leading to a major health and economic burden. Chickens are considered as the most common infection source for humans. Campylobacter mainly multiplies in the mucus layer of their caeca. No effective control measures are currently available, but passive immunisation of chickens with pathogen-specific maternal IgY antibodies, present in egg yolk of immunised chickens, reduces Campylobacter colonisation. To explore this strategy further, anti-Campylobacter nanobodies, directed against the flagella and major outer membrane proteins, were fused to the constant domains of chicken IgA and IgY, combining the benefits of nanobodies and the effector functions of the Fc-domains. The designer chimeric antibodies were effectively produced in leaves of Nicotiana benthamiana and seeds of Arabidopsis thaliana. Stable expression of the chimeric antibodies in seeds resulted in production levels between 1% and 8% of the total soluble protein. These in planta produced antibodies do not only bind to their purified antigens but also to Campylobacter bacterial cells. In addition, the anti-flagellin chimeric antibodies are reducing the motility of Campylobacter bacteria. These antibody-containing Arabidopsis seeds can be tested for oral passive immunisation of chickens and, if effective, the chimeric antibodies can be produced in crop seeds.

Use of camel single-domain antibodies for the diagnosis and treatment of zoonotic diseases

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VHHs provide many advantages over complete IgG in diagnostics and therapy.

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Toxins and viruses are more efficiently neutralized by multivalent VHHs.

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Camelids could be a source of broadly neutralizing antibodies (bNAbs) to treat zoonotic diseases.

Camelids produce both conventional heterotetrameric antibodies and homodimeric heavy-chain only antibodies. The antigen-binding region of such homodimeric heavy-chain only antibodies consists of one single domain, called VHH. VHHs provide many advantages over conventional full-sized antibodies and currently used antibody-based fragments (Fab, scFv), including high specificity, stability and solubility, and small size, allowing them to recognize unusual antigenic sites and deeply penetrate tissues. Since their discovery, VHHs have been used extensively in diagnostics and therapy. In recent decades, the number of outbreaks of diseases transmissible from animals to humans has been on the rise. In this review, we evaluate the status of VHHs as diagnostic and therapeutic biomolecular agents for the detection and treatment of zoonotic diseases, such as bacterial, parasitic, and viral zoonosis. VHHs show great adaptability to inhibit or neutralize pathogenic agents for the creation of multifunctional VHH-based diagnostic and therapeutic molecules against zoonotic diseases.

Anti-Multiple Myeloma Activity of Nanobody-Based Anti-CD38 Chimeric Antigen Receptor T Cells

Chimeric antigen receptor T cells (CAR-Ts) are a promising strategy for the treatment of many cancers, including multiple myeloma (MM), a hematological malignancy characterized by the high expression of CD38. To broaden the applications of using CD38 as a therapeutic target for the disease, we developed a new nanobody against CD38 and constructed a CD38-CAR that was composed of this nanobody as the targeting domain, and 4-1BB and CD3ζ as the costimulatory and activating domains, in a lentiviral vector. CD3⁺ T cells from healthy individuals were transduced with the CD38-CAR at an efficiency higher than 60%, as determined by CD38-CAR expression using flow cytometry. The CD38-CAR-Ts proliferated efficiently and produced more inflammatory cytokines, such as IL-2, IFN-γ, and TNF-α, when activated. The CD38-CAR-Ts effectively lysed CD38⁺ MM cell lines, including LP-1, RPMI 8226, OPM2, and MOLP8, and primary MM cells from multiple myeloma patients. The specificity was demonstrated by the fact that CD38-CAR-Ts showed little cytotoxicity on LP-1 cells with CD38 knocked out or on K562 cells, which do not express CD38. CD38-CAR-Ts appeared to have a very slight cytotoxicity against CD38⁺ fractions of T cells, B cells, and natural killer cells. In addition, the lysis of CD34⁺ hematopoietic progenitor cells did not completely inhibit the development of colony-forming units. In vivo, CD38-CAR-Ts inhibited tumor growth in NOD/SCID mice that were subcutaneously inoculated with RPMI 8226 cells. These results demonstrate that the CD38-CAR-Ts constructed with the anti-CD38 nanobody are a promising approach for the treatment of multiple myeloma.

Sandwich pair nanobodies, a potential tool for electrochemical immunosensing serum prostate-specific antigen with preferable specificity

Prostate-Specific Antigen (PSA) is a crucial biomarker for screening prostate cancer, but a sensitive and selective immunosensor for rapid quantification of serum PSA remains to be developed. In this study, a sandwich pair of nanobodies (Nbs) (i.e., Nb2 and Nb40) against PSA surface antigen was obtained from an alpaca-derived immune phage display library. A sandwich-type immunosensor for the sensitive and selective detection of PSA in serum samples was ingeniously designed based on the pair of Nbs. The small size of Nb40 allowed high capture densities on the surface of reduced graphene oxide (rGO) nanocomposed with massive Au nanoparticles (rGO@AuNPs), which significantly improved the conductivity and provided a large area to anchor many primary antibodies. The secondary antibody Nb2 fused with streptavidin -binding peptide (SBP) cooperated with Nb40 for PSA sandwiching. Accompanying introduction of horseradish peroxidase-streptavidin (HRP-SA) coupled with Nb2-SBP, the faradaic current was linearly correlated with the logarithm of PSA concentration in a range of 0.1-100 ng mL-1. More importantly, this immunosensor exhibited excellent selectivity, stability, and reproducibility due to the sandwich pair Nbs. The proposed immunosensor was successfully applied in determining PSA in serum samples and could be used for the sensitive and specific detection of PSA.

Improved Ordering in Low Molecular Weight Protein-Polymer Conjugates Through Oligomerization of the Protein Block

The self-assembly of protein-polymer conjugates incorporating oligomers of a small, engineered high-affinity binding protein, rcSso7d.SA, is studied to determine the effect of protein oligomerization on nanoscale ordering. Oligomerization enables a systematic increase in the protein molar mass without changing its overall folded structure, leading to a higher driving force for self-assembly into well-ordered structures. Though conjugates of monomeric rcSso7d.SA are found to only exist in disordered states, oligomers of this protein linked to a poly( N-isopropylacrylamide) (PNIPAM) block self-assemble into lamellar nanostructures. Conjugates of trimeric and tetrameric rcSso7d.SA are observed to produce the strongest ordering in concentrated solution, displaying birefringent lamellae at concentrations as low as 40 wt %. In highly concentrated solution, the oligomeric rcSso7d.SA-PNIPAM block copolymers exhibit ordering and domain spacing trends atypical from that of most block copolymers. Fluorescent binding assays indicate that oligomerized protein blocks retain binding functionality and exhibit limits of detection up to three times lower than that of surface-immobilized protein sensors. Therefore, oligomerization of the protein block in these block copolymers serves as an effective method to improve both nanoscale ordering and biosensing capabilities.

Chimeric camel/human heavy-chain antibodies protect against MERS-CoV infection

Middle East respiratory syndrome coronavirus (MERS-CoV) continues to cause outbreaks in humans as a result of spillover events from dromedaries. In contrast to humans, MERS-CoV-exposed dromedaries develop only very mild infections and exceptionally potent virus-neutralizing antibody responses. These strong antibody responses may be caused by affinity maturation as a result of repeated exposure to the virus or by the fact that dromedaries-apart from conventional antibodies-have relatively unique, heavy chain-only antibodies (HCAbs). These HCAbs are devoid of light chains and have long complementarity-determining regions with unique epitope binding properties, allowing them to recognize and bind with high affinity to epitopes not recognized by conventional antibodies. Through direct cloning and expression of the variable heavy chains (VHHs) of HCAbs from the bone marrow of MERS-CoV-infected dromedaries, we identified several MERS-CoV-specific VHHs or nanobodies. In vitro, these VHHs efficiently blocked virus entry at picomolar concentrations. The selected VHHs bind with exceptionally high affinity to the receptor binding domain of the viral spike protein. Furthermore, camel/human chimeric HCAbs-composed of the camel VHH linked to a human Fc domain lacking the CH1 exon-had an extended half-life in the serum and protected mice against a lethal MERS-CoV challenge. HCAbs represent a promising alternative strategy to develop novel interventions not only for MERS-CoV but also for other emerging pathogens.

Nanobody-Antigen Conjugates Elicit HPV-Specific Antitumor Immune Responses

High-risk human papillomavirus-associated cancers express viral oncoproteins (e.g., E6 and E7) that induce and maintain the malignant phenotype. The viral origin of these proteins makes them attractive targets for development of a therapeutic vaccine. Camelid-derived single-domain antibody fragments (nanobodies or VHHs) that recognize cell surface proteins on antigen-presenting cells (APC) can serve as targeted delivery vehicles for antigens attached to them. Such VHHs were shown to induce CD4⁺ and CD8⁺ T-cell responses against model antigens conjugated to them via sortase, but antitumor responses had not yet been investigated. Here, we tested the ability of an anti-CD11b VHH (VHH_CD11b) to target APCs and serve as the basis for a therapeutic vaccine to induce CD8⁺ T-cell responses against HPV⁺ tumors. Mice immunized with VHH_CD11b conjugated to an H-2D^b-restricted immunodominant E7 epitope (E7_49-57) had more E7-specific CD8⁺ T cells compared with those immunized with E7_49-57 peptide alone. These CD8⁺ T cells acted prophylactically and conferred protection against a subsequent challenge with HPV E7-expressing tumor cells. In a therapeutic setting, VHH_CD11b-E7_49-57 vaccination resulted in greater numbers of CD8⁺ tumor-infiltrating lymphocytes compared with mice receiving E7_49-57 peptide alone in HPV⁺ tumor-bearing mice, as measured by in vivo noninvasive VHH-based immune-positron emission tomography (immunoPET), which correlated with tumor regression and survival outcome. Together, these results demonstrate that VHHs can serve as a therapeutic cancer vaccine platform for HPV-induced cancers. Cancer Immunol Res; 6(7); 870-80. ©2018 AACR.

Delivery of an anti-transthyretin Nanobody to the brain through intranasal administration reveals transthyretin expression and secretion by motor neurons

Transthyretin (TTR) is a transport protein of retinol and thyroxine in serum and CSF, which is mainly secreted by liver and choroid plexus, and in smaller amounts in other cells throughout the body. The exact role of TTR and its specific expression in Central Nervous System (CNS) remains understudied. We investigated TTR expression and metabolism in CNS, through the intranasal and intracerebroventricular delivery of a specific anti-TTR Nanobody to the brain, unveiling Nanobody pharmacokinetics to the CNS. In TTR deficient mice, we observed that anti-TTR Nanobody was successfully distributed throughout all brain areas, and also reaching the spinal cord. In wild-type mice, a similar distribution pattern was observed. However, in areas known to be rich in TTR, reduced levels of Nanobody were found, suggesting potential target-mediated effects. Indeed, in wild-type mice, the anti-TTR Nanobody was specifically internalized in a receptor-mediated process, by neuronal-like cells, which were identified as motor neurons. Whereas in KO TTR mice Nanobody was internalized by all cells, for late lysosomal degradation. Moreover, we demonstrate that in vivo motor neurons also actively synthesize TTR. Finally, in vitro cultured primary motor neurons were also found to synthesize and secrete TTR into culture media. Thus, through a novel intranasal CNS distribution study with an anti-TTR Nanobody, we disclose a new cell type capable of synthesizing TTR, which might be important for the understanding of the physiological role of TTR, as well as in pathological conditions where TTR levels are altered in CSF, such as amyotrophic lateral sclerosis.

Fenobody: A Ferritin-Displayed Nanobody with High Apparent Affinity and Half-Life Extension

Nanobodies consist of a single domain variable fragment of a camelid heavy-chain antibody. Nanobodies have potential applications in biomedical fields because of their simple production procedures and low cost. Occasionally, nanobody clones of interest exhibit low affinities for their target antigens, which, together with their short half-life limit bioanalytical or therapeutic applications. Here, we developed a novel platform we named fenobody, in which a nanobody developed against H5N1 virus is displayed on the surface of ferritin in the form of a 24mer. We constructed a fenobody by substituting the fifth helix of ferritin with the nanobody. TEM analysis showed that nanobodies were displayed on the surface of ferritin in the form of 6 × 4 bundles, and that these clustered nanobodies are flexible for antigen binding in spatial structure. Comparing fenobodies with conventional nanobodies currently used revealed that the antigen binding apparent affinity of anti-H5N1 fenobody was dramatically increased (∼360-fold). Crucially, their half-life extension in a murine model was 10-fold longer than anti-H5N1 nanobody. In addition, we found that our fenobodies are highly expressed in Escherichia coli, and are both soluble and thermo-stable nanocages that self-assemble as 24-polymers. In conclusion, our results demonstrate that fenobodies have unique advantages over currently available systems for apparent affinity enhancement and half-life extension of nanobodies. Our fenobody system presents a suitable platform for various large-scale biotechnological processes and should greatly facilitate the application of nanobody technology in these areas.

Insights into maleimide-thiol conjugation chemistry: Conditions for efficient surface functionalization of nanoparticles for receptor targeting

Maleimide-thiol chemistry is widely used for the design and preparation of ligand-decorated drug delivery systems such as poly(lactide-co-glycolide) (PLGA) based nanoparticles (NPs). While many publications on nanocarriers functionalized exploiting this strategy are available in the literature, the conditions at which this reaction takes place vary among publications. This paper presents a comprehensive study on the conjugation of the peptide cRGDfK and the nanobody 11A4 (both containing a free thiol group) to maleimide functionalized PLGA NPs by means of the maleimide-thiol click reaction. The influence of different parameters, such as the nanoparticles preparation method and storage conditions as well as the molar ratio of maleimide to ligand used for conjugation, on the reaction efficiency has been evaluated. The NPs were prepared by a single or double emulsion method using different types and concentrations of surfactants and stored at 4 or 20 °C before reaction with the targeting moieties. Several maleimide to ligand molar ratios and different reaction times were studied and the conjugation efficiency was determined by quantification of the not-bound ligand by liquid chromatography. The kind of emulsion used to prepare the NPs as well as the type and concentration of surfactant used had no effect on the conjugation efficiency. Reaction between the maleimide groups present in the NPs and cRGDfK was optimal at a maleimide to thiol molar ratio of 2:1, reaching a conjugation efficiency of 84 ± 4% after 30 min at room temperature in 10 mM HEPES pH 7.0. For 11A4 nanobody the optimal reaction efficiency, 58 ± 12%, was achieved after 2 h of incubation at room temperature in PBS pH 7.4 using a 5:1 maleimide to protein molar ratio. Storage of the NPs at 4 °C for 7 days prior to their exposure to the ligands resulted in approximately 10% decrease in the reactivity of maleimide in contrast to storage at 20 °C which led to almost 40% of the maleimide being unreactive after the same storage time. Our findings demonstrate that optimization of this reaction, particularly in terms of reactant ratios, can represent a significant increase in the conjugation efficiency and prevent considerable waste of resources.

Structural Basis for the Specific Neutralization of Stx2a with a Camelid Single Domain Antibody Fragment

BACKGROUND

Shiga toxin-producing Escherichia coli (STEC) are a subset of pathogens leading to illnesses such as diarrhea, hemolytic uremic syndrome and even death. The Shiga toxins are the main virulence factors and divided in two groups: Stx1 and Stx2, of which the latter is more frequently associated with severe pathologies in humans.

RESULTS

An immune library of nanobodies (Nbs) was constructed after immunizing an alpaca with recombinant Shiga toxin-2a B subunit (rStx2aB), to retrieve multiple rStx2aB-specific Nbs. The specificity of five Nbs towards rStx2aB was confirmed in ELISA and Western blot. Nb113 had the highest affinity (9.6 nM) and its bivalent construct exhibited a 100-fold higher functional affinity. The structure of the Nb113 in complex with rStx2aB was determined via X-ray crystallography. The crystal structure of the Nb113-rStx2aB complex revealed that five copies of Nb113 bind to the rStx2aB pentamer and that the Nb113 epitope overlaps with the Gb3 binding site, thereby providing a structural basis for the neutralization of Stx2a by Nb113 that was observed on Vero cells. Finally, the tandem-repeated, bivalent Nb113₂ exhibits a higher toxin neutralization capacity compared to monovalent Nb113.

CONCLUSIONS

The Nb of highest affinity for rStx2aB is also the best Stx2a and Stx2c toxin neutralizing Nb, especially in a bivalent format. This lead Nb neutralizes Stx2a by competing for the Gb3 receptor. The fusion of the bivalent Nb113₂ with a serum albumin specific Nb is expected to combine high toxin neutralization potential with prolonged blood circulation.

The current perspectives of dromedary camel stem cells research

Camels have cultural value in the Arab society and are considered one of the most important animals in the Arabian Peninsula and arid environments, due to the distinct characteristics of their meat and milk. Moreover, there is a great interest in camel racing and beauty shows. Therefore, treatment of elite animals, increasing the number of camels as well as genetic improvement is an essential demand. Because there are unique camels for milk production, meat, or in racing, the need to propagate genetically superior camels is urgent. Recent biotechnological approaches such as stem cells hold great promise for biomedical research, genetic engineering, and as a model for studying early mammalian developmental biology. Establishment of stem cells lines from camels would tremendously facilitate regenerative medicine for genetically superior camels, permit the gene targeting of the camel genome and the generation of genetically modified animal and be a mean for genome conservation for the elite breeds. In this mini-review, we show the current research, future horizons and potential applications for camel stem cells.

Novel half-life extended anti-MIF nanobodies protect against endotoxic shock

Sepsis-leading to septic shock-is the leading cause of death in intensive care units. The systemic inflammatory response to infection, which is initiated by activated myeloid cells, plays a key role in the lethal outcome. Macrophage migration inhibitory factor (MIF) is an upstream immunoregulatory mediator, released by myeloid cells, that underlies a common genetic susceptibility to different infections and septic shock. Accordingly, strategies that are aimed at inhibiting the action of MIF have therapeutic potential. Here, we report the isolation and characterization of tailorable, small, affinity-matured nanobodies (Nbs; single-domain antigen-binding fragments derived from camelid heavy-chain Abs) directed against MIF. Of importance, these bioengineered Nbs bind both human and mouse MIFs with nanomolar affinity. NbE5 and NbE10 inhibit key MIF functions that can exacerbate septic shock, such as the tautomerase activity of MIF (by blocking catalytic pocket residues that are critical for MIF's conformation and receptor binding), the TNF-inducing potential, and the ability of MIF to antagonize glucocorticoid action. A lead NbE10, tailored to be a multivalent, half-life extended construct (NbE10-NbAlb8-NbE10), attenuated lethality in murine endotoxemia when administered via single injection, either prophylactically or therapeutically. Hence, Nbs, with their structural and pharmacologic advantages over currently available inhibitors, may be an effective, novel approach to interfere with the action of MIF in septic shock and other conditions of inflammatory end-organ damage.-Sparkes, A., De Baetselier, P., Brys, L., Cabrito, I., Sterckx, Y. G.-J., Schoonooghe, S., Muyldermans, S., Raes, G., Bucala, R., Vanlandschoot, P., Van Ginderachter, J. A., Stijlemans, B. Novel half-life extended anti-MIF nanobodies protect against endotoxic shock.

A cDNA Immunization Strategy to Generate Nanobodies against Membrane Proteins in Native Conformation

Nanobodies (Nbs) are soluble, versatile, single-domain binding modules derived from the VHH variable domain of heavy-chain antibodies naturally occurring in camelids. Nbs hold huge promise as novel therapeutic biologics. Membrane proteins are among the most interesting targets for therapeutic Nbs because they are accessible to systemically injected biologics. In order to be effective, therapeutic Nbs must recognize their target membrane protein in native conformation. However, raising Nbs against membrane proteins in native conformation can pose a formidable challenge since membrane proteins typically contain one or more hydrophobic transmembrane regions and, therefore, are difficult to purify in native conformation. Here, we describe a highly efficient genetic immunization strategy that circumvents these difficulties by driving expression of the target membrane protein in native conformation by cells of the immunized camelid. The strategy encompasses ballistic transfection of skin cells with cDNA expression plasmids encoding one or more orthologs of the membrane protein of interest and, optionally, other costimulatory proteins. The plasmid is coated onto 1 µm gold particles that are then injected into the shaved and depilated skin of the camelid. A gene gun delivers a helium pulse that accelerates the DNA-coated particles to a velocity sufficient to penetrate through multiple layers of cells in the skin. This results in the exposure of the extracellular domains of the membrane protein on the cell surface of transfected cells. Repeated immunization drives somatic hypermutation and affinity maturation of target-specific heavy-chain antibodies. The VHH/Nb coding region is PCR-amplified from B cells obtained from peripheral blood or a lymph node biopsy. Specific Nbs are selected by phage display or by screening of Nb-based heavy-chain antibodies expressed as secretory proteins in transfected HEK cells. Using this strategy, we have successfully generated agonistic and antagonistic Nbs against several cell surface ecto-enzymes and ligand-gated ion channels.

Biophysical insights from a single chain camelid antibody directed against the Disrupted-in-Schizophrenia 1 protein

Accumulating evidence suggests an important role for the Disrupted-in-Schizophrenia 1 (DISC1) protein in neurodevelopment and chronic mental illness. In particular, the C-terminal 300 amino acids of DISC1 have been found to mediate important protein-protein interactions and to harbor functionally important phosphorylation sites and disease-associated polymorphisms. However, long disordered regions and oligomer-forming subdomains have so far impeded structural analysis. VHH domains derived from camelid heavy chain only antibodies are minimal antigen binding modules with appreciable solubility and stability, which makes them well suited for the stabilizing proteins prior to structural investigation. Here, we report on the generation of a VHH domain derived from an immunized Lama glama, displaying high affinity for the human DISC1 C region (aa 691-836), and its characterization by surface plasmon resonance, size exclusion chromatography and immunological techniques. The VHH-DISC1 (C region) complex was also used for structural investigation by small angle X-ray scattering analysis. In combination with molecular modeling, these data support predictions regarding the three-dimensional fold of this DISC1 segment as well as its steric arrangement in complex with our VHH antibody.

Covalent functionalization of graphene oxide with d-mannose: evaluating the hemolytic effect and protein corona formation

Graphene oxide mannosylation impacts on RBCs toxicity and plasma protein interactions.

Nanobodies As Novel Agents for Targeting Angiogenesis in Solid Cancers

Solid cancers are dependent on angiogenesis for sustenance. The FDA approval of Bevacizumab in 2004 inspired many scientists to develop more inhibitors of angiogenesis. Although several monoclonal antibodies (mAbs) are being administered to successfully combat various pathologies, the complexity and large size of mAbs seem to narrow the therapeutic applications. To improve the performance of cancer therapeutics, including those blocking tumor angiogenesis, attractive strategies such as miniaturization of the antibodies have been introduced. Nanobodies (Nbs), small single-domain antigen-binding antibody fragments, are becoming promising therapeutic and diagnostic proteins in oncology due to their favorable unique structural and functional properties. This review focuses on the potential and state of the art of Nbs to inhibit the angiogenic process for therapy and the use of labeled Nbs for non-invasive in vivo imaging of the tumors.

Screening and antitumor effect of an anti‑CTLA‑4 nanobody

Cytotoxic T-lymphocyte antigen-4 (CTLA-4) is a critical negative regulator of immune responses. CTLA-4 is rapidly upregulated following T-cell activation, and then binds to B7 molecules with a higher affinity than CD28. CTLA-4 may abolish the initiation of the responses of T cells by raising the threshold of signals required for full activation of T cells, and it also may terminate ongoing T-cell responses. This regulatory role has led to the development of monoclonal antibodies (mAbs) designed to block CTLA-4 activity for enhancing immune responses against cancer. mAbs have several disadvantages including high production cost and unstable behavior. Nanobodies (Nbs) are single-domain antigen-binding fragments derived from the camelid heavy-chain antibodies, which are highly attractive in cancer immunotherapy due to their small size, high specificity, and stability. We selected CTLA-4-specific Nbs from a high quality dromedary camel immune library by phage display technology. Four positive colonies were sequenced and classified based on the amino acids sequences in the CDR3 region. These Nbs recognized unique epitopes on CTLA-4 and displayed high binding rates when used on PHA-stimulated human T cells. Treatment of B16 melanoma-bearing C57BL/6 mice with anti-CTLA-4 nanobody 16 (Nb16) delayed melanoma growth and prolonged the survival time of mice. These data indicate that anti-CTLA-4 Nbs selected from a high quality phage display library may be effective for the treatment of patients with tumors.

Synthesis, Functionalization, and Design of Magnetic Nanoparticles for Theranostic Applications

In order to translate nanotechnology into medical practice, magnetic nanoparticles (MNPs) have been presented as a class of non-invasive nanomaterials for numerous biomedical applications. In particular, MNPs have opened a door for simultaneous diagnosis and brisk treatment of diseases in the form of theranostic agents. This review highlights the recent advances in preparation and utilization of MNPs from the synthesis and functionalization steps to the final design consideration in evading the body immune system for therapeutic and diagnostic applications with addressing the most recent examples of the literature in each section. This study provides a conceptual framework of a wide range of synthetic routes classified mainly as wet chemistry, state-of-the-art microfluidic reactors, and biogenic routes, along with the most popular coating materials to stabilize resultant MNPs. Additionally, key aspects of prolonging the half-life of MNPs via overcoming the sequential biological barriers are covered through unraveling the biophysical interactions at the bio-nano interface and giving a set of criteria to efficiently modulate MNPs' physicochemical properties. Furthermore, concepts of passive and active targeting for successful cell internalization, by respectively exploiting the unique properties of cancers and novel targeting ligands are described in detail. Finally, this study extensively covers the recent developments in magnetic drug targeting and hyperthermia as therapeutic applications of MNPs. In addition, multi-modal imaging via fusion of magnetic resonance imaging, and also innovative magnetic particle imaging with other imaging techniques for early diagnosis of diseases are extensively provided.

Camelid Single-Domain Antibodies: Historical Perspective and Future Outlook

Tremendous effort has been expended over the past two and a half decades to understand many aspects of camelid heavy chain antibodies, from their biology, evolution, and immunogenetics to their potential applications in various fields of research and medicine. In this article, I present a historical perspective on the development of camelid single-domain antibodies (sdAbs or V_HHs, also widely known as nanobodies) since their discovery and discuss the advantages and disadvantages of these unique molecules in various areas of research, industry, and medicine. Commercialization of camelid sdAbs exploded in 2001 with a flurry of patents issued to the Vrije Universiteit Brussel (VUB) and later taken on by the Vlaams Interuniversitair Instituut voor Biotechnologie (VIB) and, after 2002, the VIB-founded spin-off company, Ablynx. While entrepreneurial spirit has certainly catalyzed the exploration of nanobodies as marketable products, IP restrictions may be partially responsible for the relatively long time span between the discovery of these biomolecules and their entry into the pharmaceutical market. It is now anticipated that the first V_HH-based antibody drug, Caplacizumab, a bivalent anti-vWF antibody for treating rare blood clotting disorders, may be approved and commercialized in 2018 or shortly thereafter. This elusive first approval, along with the expiry of key patents, may substantially alter the scientific and biomedical landscape surrounding camelid sdAbs and pave the way for their emergence as mainstream biotherapeutics.

A nanobody-based tracer targeting DPP6 for non-invasive imaging of human pancreatic endocrine cells

There are presently no reliable ways to quantify endocrine cell mass (ECM) in vivo, which prevents an accurate understanding of the progressive beta cell loss in diabetes or following islet transplantation. To address this unmet need, we coupled RNA sequencing of human pancreatic islets to a systems biology approach to identify new biomarkers of the endocrine pancreas. Dipeptidyl-Peptidase 6 (DPP6) was identified as a target whose mRNA expression is at least 25-fold higher in human pancreatic islets as compared to surrounding tissues and is not changed by proinflammatory cytokines. At the protein level, DPP6 localizes only in beta and alpha cells within the pancreas. We next generated a high-affinity camelid single-domain antibody (nanobody) targeting human DPP6. The nanobody was radiolabelled and in vivo SPECT/CT imaging and biodistribution studies were performed in immunodeficient mice that were either transplanted with DPP6-expressing Kelly neuroblastoma cells or insulin-producing human EndoC-βH1 cells. The human DPP6-expressing cells were clearly visualized in both models. In conclusion, we have identified a novel beta and alpha cell biomarker and developed a tracer for in vivo imaging of human insulin secreting cells. This provides a useful tool to non-invasively follow up intramuscularly implanted insulin secreting cells.

Nanobody-Based Delivery Systems for Diagnosis and Targeted Tumor Therapy

The development of innovative targeted therapeutic approaches are expected to surpass the efficacy of current forms of treatments and cause less damage to healthy cells surrounding the tumor site. Since the first development of targeting agents from hybridoma’s, monoclonal antibodies (mAbs) have been employed to inhibit tumor growth and proliferation directly or to deliver effector molecules to tumor cells. However, the full potential of such a delivery strategy is hampered by the size of mAbs, which will obstruct the targeted delivery system to access the tumor tissue. By serendipity, a new kind of functional homodimeric antibody format was discovered in camelidae, known as heavy-chain antibodies (HCAbs). The cloning of the variable domain of HCAbs produces an attractive minimal-sized alternative for mAbs, referred to as VHH or nanobodies (Nbs). Apart from their dimensions in the single digit nanometer range, the unique characteristics of Nbs combine a high stability and solubility, low immunogenicity and excellent affinity and specificity against all possible targets including tumor markers. This stimulated the development of tumor-targeted therapeutic strategies. Some autonomous Nbs have been shown to act as antagonistic drugs, but more importantly, the targeting capacity of Nbs has been exploited to create drug delivery systems. Obviously, Nb-based targeted cancer therapy is mainly focused toward extracellular tumor markers, since the membrane barrier prevents antibodies to reach the most promising intracellular tumor markers. Potential strategies, such as lentiviral vectors and bacterial type 3 secretion system, are proposed to deliver target-specific Nbs into tumor cells and to block tumor markers intracellularly. Simultaneously, Nbs have also been employed for in vivo molecular imaging to diagnose diseased tissues and to monitor the treatment effects. Here, we review the state of the art and focus on recent developments with Nbs as targeting moieties for drug delivery systems in cancer therapy and cancer imaging.

Quantum-Dot-Based Theranostic Micelles Conjugated with an Anti-EGFR Nanobody for Triple-Negative Breast Cancer Therapy

A quantum-dot (QD)-based micelle conjugated with an anti-epidermal growth factor receptor (EGFR) nanobody (Nb) and loaded with an anticancer drug, aminoflavone (AF), has been engineered for EGFR-overexpressing cancer theranostics. The near-infrared (NIR) fluorescence of the indium phosphate core/zinc sulfide shell QDs (InP/ZnS QDs) allowed for in vivo nanoparticle biodistribution studies. The anti-EGFR nanobody 7D12 conjugation improved the cellular uptake and cytotoxicity of the QD-based micelles in EGFR-overexpressing MDA-MB-468 triple-negative breast cancer (TNBC) cells. In comparison with the AF-encapsulated nontargeted (i.e., without Nb conjugation) micelles, the AF-encapsulated Nb-conjugated (i.e., targeted) micelles accumulated in tumors at higher concentrations, leading to more effective tumor regression in an orthotopic triple-negative breast cancer xenograft mouse model. Furthermore, there was no systemic toxicity observed with the treatments. Thus, this QD-based Nb-conjugated micelle may serve as an effective theranostic nanoplatform for EGFR-overexpressing cancers such as TNBCs.

Models for discovery of targeted therapy in genetic epileptic encephalopathies

Epileptic encephalopathies are severe disorders emerging in the first days to years of life that commonly include refractory seizures, various types of movement disorders, and different levels of developmental delay. In recent years, many de novo occurring variants have been identified in individuals with these devastating disorders. To unravel disease mechanisms, the functional impact of detected variants associated with epileptic encephalopathies is investigated in a range of cellular and animal models. This review addresses efforts to advance and use such models to identify specific molecular and cellular targets for the development of novel therapies. We focus on ion channels as the best-studied group of epilepsy genes. Given the clinical and genetic heterogeneity of epileptic encephalopathy disorders, experimental models that can reflect this complexity are critical for the development of disease mechanisms-based targeted therapy. The convergence of technological advances in gene sequencing, stem cell biology, genome editing, and high throughput functional screening together with massive unmet clinical needs provides unprecedented opportunities and imperatives for precision medicine in epileptic encephalopathies.

Single-Domain Antibodies As Versatile Affinity Reagents for Analytical and Diagnostic Applications

With just three CDRs in their variable domains, the antigen-binding site of camelid heavy-chain-only antibodies (HcAbs) has a more limited structural diversity than that of conventional antibodies. Even so, this does not seem to limit their specificity and high affinity as HcAbs against a broad range of structurally diverse antigens have been reported. The recombinant form of their variable domain [nanobody (Nb)] has outstanding properties that make Nbs, not just an alternative option to conventional antibodies, but in many cases, these properties allow them to reach analytical or diagnostic performances that cannot be accomplished with conventional antibodies. These attributes include comprehensive representation of the immune specificity in display libraries, easy adaptation to high-throughput screening, exceptional stability, minimal size, and versatility as affinity building block. Here, we critically reviewed each of these properties and highlight their relevance with regard to recent developments in different fields of immunosensing applications.

Unravelling the Molecular Basis of High Affinity Nanobodies against HIV p24: In Vitro Functional, Structural, and in Silico Insights

Preventing the spread of infectious diseases remains an urgent priority worldwide, and this is driving the development of advanced nanotechnology to diagnose infections at the point of care. Herein, we report the creation of a library of novel nanobody capture ligands to detect p24, one of the earliest markers of HIV infection. We demonstrate that these nanobodies, one tenth the size of conventional antibodies, exhibit high sensitivity and broad specificity to global HIV-1 subtypes. Biophysical characterization indicates strong 690 pM binding constants and fast kinetic on-rates, 1 to 2 orders of magnitude better than monoclonal antibody comparators. A crystal structure of the lead nanobody and p24 was obtained and used alongside molecular dynamics simulations to elucidate the molecular basis of these enhanced performance characteristics. They indicate that binding occurs at C-terminal helices 10 and 11 of p24, a negatively charged region of p24 complemented by the positive surface of the nanobody binding interface involving CDR1, CDR2, and CDR3 loops. Our findings have broad implications on the design of novel antibodies and a wide range of advanced biomedical applications.

Nanobodies As Tools to Understand, Diagnose, and Treat African Trypanosomiasis

African trypanosomes are strictly extracellular protozoan parasites that cause diseases in humans and livestock and significantly affect the economic development of sub-Saharan Africa. Due to an elaborate and efficient (vector)–parasite–host interplay, required to complete their life cycle/transmission, trypanosomes have evolved efficient immune escape mechanisms that manipulate the entire host immune response. So far, not a single field applicable vaccine exists, and chemotherapy is the only strategy available to treat the disease. Current therapies, however, exhibit high drug toxicity and an increased drug resistance is being reported. In addition, diagnosis is often hampered due to the inadequacy of current diagnostic procedures. In the context of tackling the shortcomings of current treatment and diagnostic approaches, nanobodies (Nbs, derived from the heavy chain-only antibodies of camels and llamas) might represent unmet advantages compared to conventional tools. Indeed, the combination of their small size, high stability, high affinity, and specificity for their target and tailorability represents a unique advantage, which is reflected by their broad use in basic and clinical research to date. In this article, we will review and discuss (i) diagnostic and therapeutic applications of Nbs that are being evaluated in the context of African trypanosomiasis, (ii) summarize new strategies that are being developed to optimize their potency for advancing their use, and (iii) document on unexpected properties of Nbs, such as inherent trypanolytic activities, that besides opening new therapeutic avenues, might offer new insight in hidden biological activities of conventional antibodies.

Tools and limitations to study the molecular composition of synapses by fluorescence microscopy

The synapse is densely packed with proteins involved in various highly regulated processes. Synaptic protein copy numbers and their stoichiometric distribution have a drastic influence on neuronal integrity and function. Therefore, the molecular analysis of synapses is a key element to understand their architecture and function. The overall structure of the synapse has been revealed with an exquisite amount of details by electron microscopy. However, the molecular composition and the localization of proteins are more easily addressed with fluorescence imaging, especially with the improved resolution achieved by super-resolution microscopy techniques. Notably, the fast improvement of imaging instruments has not been reflected in the optimization of biological sample preparation. During recent years, large efforts have been made to generate affinity probes smaller than conventional antibodies adapted for fluorescent super-resolution imaging. In this review, we briefly discuss the current views on synaptic organization and necessary key technologies to progress in the understanding of synaptic physiology. We also highlight the challenges faced by current fluorescent super-resolution methods, and we describe the prerequisites for an ideal study of synaptic organization.

A novel immuno-gold labeling protocol for nanobody-based detection of HER2 in breast cancer cells using immuno-electron microscopy

Immuno-electron microscopy is commonly performed with the use of antibodies. In the last decade the antibody fragment indicated as nanobody (VHH or single domain antibody) has found its way to different applications previously done with conventional antibodies. Nanobodies can be selected to bind with high affinity and specificity to different antigens. They are small (molecular weight ca. 15kDa) and are usually easy to produce in microorganisms. Here we have evaluated the feasibility of a nanobody binding to HER2 for application in immuno-electron microscopy. To obtain highest labeling efficiency combined with optimal specificity, different labeling conditions were analysed, which included nanobody concentration, fixation and blocking conditions. The obtained optimal protocol was applied for post-embedment labeling of Tokuyasu cryosections and for pre-embedment labeling of HER2 for fluorescence microscopy and both transmission and scanning electron microscopy. We show that formaldehyde fixation after incubation with the anti-HER2 nanobody, improves labeling intensity. Among all tested blocking agents the best results were obtained with a mixture of cold water fish gelatine and acetylated bovine serum albumin, which prevented a-specific interactions causing background labeling while preserving specific interactions at the same time. In conclusion, we have developed a nanobody-based protocol for immuno-gold labeling of HER2 for Tokuyasu cryosections in TEM as well as for pre-embedment gold labeling of cells for both TEM and SEM.

An in-silico approach to find a peptidomimetic targeting extracellular domain of HER3 from a HER3 Nanobody

HER3 is an important therapeutic target in cancer treatments. HER3 Nanobodies (Nbs) are a novel class of antibodies with several competitive advantages over conventional antibodies. A peptidomimetic derived from these Nbs can be considered to be a small peptide mimicking some of the molecular recognition interactions of a natural peptide or protein in a three-dimensional (3D) space, with a receptor that has improved properties. In this study, we introduce a new approach to design a peptidomimetic derived from HER3 Nb through an in silico analysis. We propose that the complementarity determining region (CDR3) of HER3 Nb is large enough to effectively interact with HER3 antigen as well as with the entire Nb. A computational analysis has been performed using Nb models retrieved from SWISS-pdb Viewer 4.1.0 (spdbv) as a target spot and HER3 extracellular domain as its antigenic target to identify the interactions between them by the protein-protein docking method. Detailed analysis of selected models with docked complex help us to identify the interacting amino acid residues between the two molecules. The results of in silico analysis show that the CDR3 of HER3 Nb might be used by itself as a peptidomimetic drug instead of the full Nb. HER3 peptidomimetic-derived HER3 Nb may reduce Nb production costs and be used as a substitute for HER3 Nb after further experimental work. The paper demonstrates the feasibility of peptidomimetics designs using bioinformatic tools.

Modified Nanoantibodies Increase Sensitivity in Avidin-Biotin Immunohistochemistry

Revealing the spatial arrangement of molecules within a tissue through immunohistochemistry (IHC) is an invaluable tool in biomedical research and clinical diagnostics. Choosing both the appropriate antibody and amplification system is paramount to the pathologic interpretation of the tissue at hand. The use of single domain VHH nanoantibodies (nAbs) promise more robust and consistent results in IHC, but are rarely used as an alternative to conventional immunoglobulin G (IgG) antibodies. nAbs are originally obtained from llamas and are the smallest antigen-binding fragments available. To determine whether the unique biophysical properties of nAbs give them an advantage in IHC, we first compared a basic fibroblast growth factor nAb to polyclonal IgG antibodies using tissue isolated from pancreatic adenocarcinoma. The nAb was extremely effective in antigen signal detection and allowed for a more streamlined and reproducible protocol. Furthermore, because nAbs are expressed in Escherichia coli from a single gene, they are quite amenable to genetic engineering. As such, we then covalently bound a highly biotinylated amplifier protein to basic fibroblast growth factor and p16 nAbs (termed nAb Plus), resulting in improved IHC sensitivity. The use of a biotinylated nAb Plus not only achieved local, covalent signal amplification, but also eliminated the need for a secondary antibody and subsequent amplification steps. These results highlight nAbs as valuable alternatives to conventional IgG antibodies, decreasing overall processing time and costs of reagents while increasing sensitivity and reproducibility across individual IHC assays.

Exploiting Nanobodies in the Detection and Quantification of Human Growth Hormone via Phage-Sandwich Enzyme-Linked Immunosorbent Assay

BACKGROUND

Monitoring blood levels of human growth hormone (hGH) in most children with short stature deficiencies is crucial for taking a decision of treatment with extended course of daily and expensive doses of recombinant hGH (rhGH or Somatropin^®). Besides, misusing of rhGH by sportsmen is banned by the World Anti-Doping Agency and thus sensitive GH-detecting methods are highly welcome in this field. Nanobodies are the tiniest antigen-binding entity derived from camel heavy chain antibodies. They were successfully generated against numerous antigens including hormones.

METHODS

A fully nanobody-based sandwich ELISA method was developed in this work for direct measurement of GH in biological samples.

RESULTS

Two major characteristics of nanobody were exploited for this goal: the robust and stable structure of the nanobody (NbGH04) used to capture hGH from tested samples, and the great ability of tailoring, enabling the display of the anti-GH detector nanobody (NbGH07) on the tip of M13-phage. Such huge, stable, and easy-to-prepare phage-Nb was used in ELISA to provide an amplified signal. Previously, NbGH04 was retrieved on immobilized hGH by phage display from a wide "immune" cDNA library prepared from a hGH-immunized camel. Here, and in order to assure epitope heterogeneity, NbGH07 was isolated from the same library using NbGH04-captured hGH as bait. Interaction of both nanobodies with hGH was characterized and compared with different anti-GH nanobodies and antibodies. The sensitivity (~0.5 ng/ml) and stability of the nanobody-base sandwich ELISA were assessed using rhGH before testing in the quantification of hGH in blood sera and cell culture supernatants.

CONCLUSION

In regard to all advantages of nanobodies; stability, solubility, production affordability in Escherichia coli, and gene tailoring, nanobody-based phage sandwich ELISA developed here would provide a valuable method for hGH detection and quantification.

Screening and Characterization Strategies for Nanobodies Targeting Membrane Proteins

The study of membrane protein function and structure requires their successful detection, expression, solubilization, and/or reconstitution, which poses a challenging task and relies on the availability of suitable tools. Several research groups have successfully applied Nanobodies in the purification, as well as the functional and structural characterization of membrane proteins. Nanobodies are small, single-chain antibody fragments originating from camelids presenting on average a longer CDR3 which enables them to bind in cavities and clefts (such as active and allosteric sites). Notably, Nanobodies generally bind conformational epitopes making them very interesting tools to stabilize, dissect, and characterize specific protein conformations. In the clinic, several Nanobodies are under evaluation either as potential drug candidates or as diagnostic tools. In recent years, we have successfully generated high-affinity, conformation-sensitive anti-γ-secretase Nanobodies. γ-Secretase is a multimeric membrane protease involved in processing of the amyloid precursor protein with high clinical relevance as mutations in its catalytic subunit (Presenilin) cause early-onset Alzheimer's disease. Advancing our knowledge on the mechanisms governing γ-secretase intramembrane proteolysis through various strategies may lead to novel therapeutic avenues for Alzheimer's disease. In this chapter, we present the strategies we have developed and applied for the screening and characterization of anti-γ-secretase Nanobodies. These protocols could be of help in the generation of Nanobodies targeting other membrane proteins.

New agents in HSC mobilization

Mobilized peripheral blood (PB) is the most common source of hematopoietic stem cells (HSC) for autologous transplantation. Granulocyte colony stimulating factor (G-CSF) is the most commonly used mobilization agent, yet despite its widespread use, a considerable number of patients still fail to mobilize. Recently, a greater understanding of the interactions that regulate HSC homeostasis in the bone marrow (BM) microenvironment has enabled the development of new molecules that mobilize HSC through specific inhibition, modulation or perturbation of these interactions. AMD3100 (plerixafor), a small molecule that selectively inhibits the chemokine receptor CXCR4 is approved for mobilization in combination with G-CSF in patients with Non-Hodgkin's lymphoma and multiple myeloma. Nevertheless, identifying mobilization strategies that not only enhance HSC number, but are rapid and generate an optimal "mobilized product" for improved transplant outcomes remains an area of clinical importance. In recent times, new agents based on recombinant proteins, peptides and small molecules have been identified as potential candidates for therapeutic HSC mobilization. In this review, we describe the most recent developments in HSC mobilization agents and their potential impact in HSC transplantation.

A current perspective on applications of macrocyclic-peptide-based high-affinity ligands

Monoclonal antibodies can bind with high affinity and high selectivity to their targets. As a tool in therapeutics or diagnostics, however, their large size (∼150 kDa) reduces penetration into tissue and prevents passive cellular uptake. To overcome these and other problems, minimized protein scaffolds have been chosen or engineered, with care taken to not compromise binding affinity or specificity. An alternate approach is to begin with a minimal non-antibody scaffold and select functional ligands from a de novo library. We will discuss the structure, production, applications, strengths, and weaknesses of several classes of antibody-derived ligands, that is, antibodies, intrabodies, and nanobodies, and nonantibody-derived ligands, that is, monobodies, affibodies, and macrocyclic peptides. In particular, this review is focussed on macrocyclic peptides produced by the Random non-standard Peptides Integrated Discovery (RaPID) system that are small in size (typically ∼2 kDa), but are able to perform tasks typically handled by larger proteinaceous ligands.