A Two-Step Approach for the Design and Generation of Nanobodies

Unlocking the Gates: Therapeutic Agents for Noninvasive Drug Delivery Across the Blood-Brain Barrier

The blood-brain barrier (BBB) is a highly selective network of various cell types that acts as a filter between the blood and the brain parenchyma. Because of this, the BBB remains a major obstacle for drug delivery to the central nervous system (CNS). In recent years, there has been a focus on developing various modifiable platforms, such as monoclonal antibodies (mAbs), nanobodies (Nbs), peptides, and nanoparticles, as both therapeutic agents and carriers for targeted drug delivery to treat brain cancers and diseases. Methods for bypassing the BBB can be invasive or noninvasive. Invasive techniques, such as transient disruption of the BBB using low pulse electrical fields and intracerebroventricular infusion, lack specificity and have numerous safety concerns. In this review, we will focus on noninvasive transport mechanisms that offer high levels of biocompatibility, personalization, specificity and are regarded as generally safer than their invasive counterparts. Modifiable platforms can be designed to noninvasively traverse the BBB through one or more of the following pathways: passive diffusion through a physio-pathologically disrupted BBB, adsorptive-mediated transcytosis, receptor-mediated transcytosis, shuttle-mediated transcytosis, and somatic gene transfer. Through understanding the noninvasive pathways, new applications, including Chimeric Antigen Receptors T-cell (CAR-T) therapy, and approaches for drug delivery across the BBB are emerging.

Advancements in nanobody generation: Integrating conventional, in silico, and machine learning approaches

Nanobodies, derived from camelids and sharks, offer compact, single-variable heavy-chain antibodies with diverse biomedical potential. This review explores their generation methods, including display techniques on phages, yeast, or bacteria, and computational methodologies. Integrating experimental and computational approaches enhances understanding of nanobody structure and function. Future trends involve leveraging next-generation sequencing, machine learning, and artificial intelligence for efficient candidate selection and predictive modeling. The convergence of traditional and computational methods promises revolutionary advancements in precision biomedical applications such as targeted drug delivery and diagnostics. Embracing these technologies accelerates nanobody development, driving transformative breakthroughs in biomedicine and paving the way for precision medicine and biomedical innovation.

CDR grafting and site-directed mutagenesis approach for the generation and affinity maturation of Anti-CD20 nanobody

BACKGROUND

Recently, new and advanced techniques have been adopted to design and produce nanobodies, which are used in diagnostic and immunotherapy treatments. Traditionally, nanobodies are prepared from camelid immune libraries that require animal treatments. However, such approaches require large library sizes and complicated selection procedures. The current study has employed CDR grafting and site-directed mutagenesis techniques to create genetically engineered nanobodies against the tumor marker CD20 (anti-CD20 nanobodies) used in leukemia treatment.

METHODS AND RESULTS

In this study, we utilized the swapping method to graft CDRs from the VH Rituximab antibody to VHH CDRs. We aimed to enhance the binding affinity of the nanobodies by substituting the amino acids (Y101R-Y102R-Y107R) in the VHH-CDR3. To assess the binding capacity of the mutated nanobodies, we conducted an ELISA test. Moreover, through flow cytometry analysis, we compared the fluorescence intensity of the grafted CD20 and mutant nanobodies with that of the commercially available human anti-CD20 in Raji cells. The results showed a significant difference in the fluorescence intensity of the grafted nanobodies and mutant nanobodies when compared to the commercially available human anti-CD20.

CONCLUSION

The approach we followed in this study makes it possible to create multiple anti-CD20 nanobodies with varying affinities without the need for extensive selection efforts. Additionally, our research has demonstrated that computational tools are highly reliable in designing functional nanobodies.

Design and Production of a Novel Anti-PD-1 Nanobody by CDR Grafting and Site-Directed Mutagenesis Approach

Programmed cell death protein-1 (PD-1) is a membrane protein expressed on the surface of activated T-cells, B-cells, natural killer cells, dendritic cells, macrophages, and monocytes. Inhibition of the PD-1/PD-L1 interaction by monoclonal antibodies (mAbs) has many therapeutic benefits and has led to a major advance in the treatment of various types of tumors. Due to the large size and immunogenicity of the antibodies (Abs), using small molecules such as nanobodies (nanobodies or VHH) is more appropriate for this purpose. In this research, the complementarity determining regions (CDR) grafting method was used to produce anti-PD-1 nanobody. For producing the grafted anti-PD-1 nanobody, CDRs from the tislelizumab mAb were grafted into the frameworks of a nanobody whose sequence is similar to the tislelizumab mAb. Also, the site-directed mutagenesis method was used to produce two mutated anti-PD-1 nanobodies which increased the affinity of grafted anti-PD-1 nanobodies. Two amino acid substitutions (Tyr97Arg and Tyr102Arg) in the VHH-CDR3 were used to improve grafted nanobody affinity and the binding capacity of the mutated nanobodies. The binding of the anti-PD-1 nanobodies and PD-1 antigen (Ag) was confirmed by Dot blot, western blot, and indirect ELISA analysis. According to the results of these in silico and in vitro studies, the binding between grafted and mutated nanobodies with PD-1 was confirmed. Also, our findings show that site-directed mutagenesis can increase the affinity of nanobodies.

Computational Chemistry in Structure-Based Solute Carrier Transporter Drug Design: Recent Advances and Future Perspectives

Solute carrier transporters (SLCs) are a class of important transmembrane proteins that are involved in the transportation of diverse solute ions and small molecules into cells. There are approximately 450 SLCs within the human body, and more than a quarter of them are emerging as attractive therapeutic targets for multiple complex diseases, e.g., depression, cancer, and diabetes. However, only 44 unique transporters (∼9.8% of the SLC superfamily) with 3D structures and specific binding sites have been reported. To design innovative and effective drugs targeting diverse SLCs, there are a number of obstacles that need to be overcome. However, computational chemistry, including physics-based molecular modeling and machine learning- and deep learning-based artificial intelligence (AI), provides an alternative and complementary way to the classical drug discovery approach. Here, we present a comprehensive overview on recent advances and existing challenges of the computational techniques in structure-based drug design of SLCs from three main aspects: (i) characterizing multiple conformations of the proteins during the functional process of transportation, (ii) identifying druggability sites especially the cryptic allosteric ones on the transporters for substrates and drugs binding, and (iii) discovering diverse small molecules or synthetic protein binders targeting the binding sites. This work is expected to provide guidelines for a deep understanding of the structure and function of the SLC superfamily to facilitate rational design of novel modulators of the transporters with the aid of state-of-the-art computational chemistry technologies including artificial intelligence.

Molecular Evolution of Antiparathion Nanobody with Enhanced Sensitivity and Specificity Based on Structural Analysis

Nanobody (Nb) has gained significant attention in immunoassays owing to its numerous advantages, particularly its ease of molecular evolution. However, the limited understanding of how high sensitivity and specificity attained for antihapten Nbs hamper the development of high-performance Nbs. Herein, the antiparathion Nb (Nb9) we prepared previously was chosen as the model, and an approach based on X-ray crystallography, molecular docking, and rational site-directed saturation mutation for constructing a rapid and effective platform for nanobody evolution was described. Based on the structural analysis, two mutants, namely Nb-D5 (IC50 = 2.4 ± 0.2 ng/mL) and Nb-D12 (IC50 = 2.7 ± 0.1 ng/mL), were selected out from a six-sites directed saturation mutation library, 3.5-fold and 3.1-fold sensitivity enhancement over Nb9 to parathion, respectively. Besides, Nb-D12 exhibited improved sensitivity for quinalphos, triazophos, and coumaphos (5.4-35.4 ng/mL), indicating its broader detection potential. Overall, our study advances an effective strategy for the future rational evolution of Nbs with desirable performance.

Revolutionizing antiviral therapy with nanobodies: Generation and prospects

As the world continues to grapple with infectious diseases, scientists are constantly searching for effective ways to combat these deadly pathogens. One promising avenue of research is the use of nanobodies as neutralization agents. These small proteins, derived from camelid antibodies, have several unique advantages over traditional antibodies, including their small size. Nanobodies are much smaller than conventional antibodies, typically weighing in at around 15 kDa compared to the 150 kDa of a typical human antibody. This small size allows them to penetrate into tight spaces that larger molecules cannot reach, such as the crevices on the surface of viruses or bacteria. This makes them highly effective at neutralizing viruses by binding to and blocking their key functional sites. In this mini-review we discuss the construction approaches of nanobodies, and some methods to increase the half-life of nanobodies. Moreover, we discuss Nanobodies and their therapeutic potential for infectious agents.

Quantitative flow cytometric selection of tau conformational nanobodies specific for pathological aggregates

Single-domain antibodies, also known as nanobodies, are broadly important for studying the structure and conformational states of several classes of proteins, including membrane proteins, enzymes, and amyloidogenic proteins. Conformational nanobodies specific for aggregated conformations of amyloidogenic proteins are particularly needed to better target and study aggregates associated with a growing class of associated diseases, especially neurodegenerative disorders such as Alzheimer's and Parkinson's diseases. However, there are few reported nanobodies with both conformational and sequence specificity for amyloid aggregates, especially for large and complex proteins such as the tau protein associated with Alzheimer's disease, due to difficulties in selecting nanobodies that bind to complex aggregated proteins. Here, we report the selection of conformational nanobodies that selectively recognize aggregated (fibrillar) tau relative to soluble (monomeric) tau. Notably, we demonstrate that these nanobodies can be directly isolated from immune libraries using quantitative flow cytometric sorting of yeast-displayed libraries against tau aggregates conjugated to quantum dots, and this process eliminates the need for secondary nanobody screening. The isolated nanobodies demonstrate conformational specificity for tau aggregates in brain samples from both a transgenic mouse model and human tauopathies. We expect that our facile approach will be broadly useful for isolating conformational nanobodies against diverse amyloid aggregates and other complex antigens.

Nanobodies as Diagnostic and Therapeutic Tools for Cardiovascular Diseases (CVDs)

The aim of this review is to summarize some of the most recent work in the field of cardiovascular disease (CVD) diagnosis and therapy, focusing mainly on the role of nanobodies in the development of non-invasive imaging methods, diagnostic devices, and advanced biotechnological therapy tools. In the context of the increased number of people suffering from CVDs due to a variety of factors such as sedentariness, poor nutrition, stress, and smoking, there is an urgent need for new and improved diagnostic and therapeutic methods. Nanobodies can be easily produced in prokaryotes, lower eukaryotes, and plant and mammalian cells, and offer great advantages. In the diagnosis domain, they are mainly used as labeled probes that bind to certain surface receptors or other target molecules and give important information on the severity and extent of atherosclerotic lesions, using imaging methods such as contrast-enhanced ultrasound molecular imaging (CEUMI), positron emission tomography (PET), single-photon emission computed tomography coupled with computed tomography (SPECT/CT), and PET/CT. As therapy tools, nanobodies have been used either for transporting drug-loaded vesicles to specific targets or as inhibitors for certain enzymes and receptors, demonstrated to be involved in various CVDs.

Significance of antibody numbering systems in the development of antibody engineering

Immunotherapy has become increasingly popular in recent years for treating a variety of diseases including inflammatory, neurological, oncological, and auto-immune disorders. The significant interest in antibody development is due to the high binding affinity and specificity of an antibody against a specific antigen. Recent advances in antibody engineering have provided a different view on how to engineer antibodies in silico for therapeutic and diagnostic applications. In order to improve the clinical utility of therapeutic antibodies, it is of paramount importance to understand the various molecular properties which impact antigen targeting and its potency. In antibody engineering, antibody numbering (AbN) systems play an important role to identify the complementarity determining regions (CDRs) and the framework regions (FR). Hence, it is crucial to accurately define and understand the CDR, FR and the crucial residues of heavy and light chains that aid in the binding of the antibody to the antigenic site. Detailed understanding of amino acids positions are useful for modifying the binding affinity, specificity, physicochemical features, and half-life of an antibody. In this review, we have summarized the different antibody numbering systems that are widely used in antibody engineering and highlighted their significance. Here, we have systematically explored and mentioned the various tools and servers that harness different AbN systems.

Screening and identification of an anti-PD-1 nanobody with antitumor activity

Blocking of PD-1 or PD-L1 with corresponding antibody to enhance T cell response and mediate antitumor activity has been successfully applied in clinical practice. Several immune checkpoint inhibitors including monoclonal antibodies targeting PD-1 have been approved by the Food and Drug Administration (FDA) in cancer immunotherapy. However, the application of traditional antibodies has limited due to their drawbacks of large molecular weight and low tissue penetration. As the high specificity and strong tissue penetration of nanobodies (Nbs), efforts have been taken to develop Nbs for cancer therapy. Herein, we aim to screen a specific Nb against human PD-1 derived from a naïve camel Nb phage display library and further study its biological characteristic and anti-tumor activity. Finally, an anti-PD-1 Nb with high specificity and affinity was screened and generated, its cytotoxicity and antitumor effect was also confirmed in vitro and vivo. All of these indicate that the anti-PD-1 Nb may provide an alternative and appealing therapeutic agent for cancer immunotherapy.

Studying the characteristics of nanobody CDR regions based on sequence analysis in combination with 3D structures

Background

Single-domain antibodies or nanobodies have recently attracted much attention in research and applications because of their great potential and advantage over conventional antibodies. However, isolation of candidate nanobodies in the lab has been costly and time-consuming. Screening of leading nanobody candidates through synthetic libraries is a promising alternative, but it requires prior knowledge to control the diversity of the complementarity-determining regions (CDRs) while still maintaining functionality. In this work, we identified sequence characteristics that could contribute to nanobody functionality by analyzing three datasets, CDR1, CDR2, and CDR3.

Results

By classification of amino acids based on physicochemical properties, we found that two different amino acid groups were sufficient for CDRs. The nonpolar group accounted for half of the total amino acid composition in these sequences. Observation of the highest occurrence of each amino acid revealed that the usage of some important amino acids such as tyrosine and serine was highly correlated with the length of the CDR3. Amino acid repeat motifs were also under-represented and highly restricted as 3-mers. Inspecting the crystallographic data also demonstrated conservation in structural coordinates of dominant amino acids such as methionine, isoleucine, valine, threonine, and tyrosine and certain positions in the CDR1, CDR2, and CDR3 sequences.

Conclusions

We identified sequence characteristics that contributed to functional nanobodies including amino acid groups, the occurrence of each kind of amino acids, and repeat patterns. These results provide a simple set of rules to make it easier to generate desired candidates by computational means; also, they can be used as a reference to evaluate synthetic nanobodies.

Structural Insights into the Design of Synthetic Nanobody Libraries

Single domain antibodies from camelids, or nanobodies, are a unique class of antibody fragments with several advantageous characteristics: small monomeric size, high stability and solubility and easy tailoring for multiple applications. Nanobodies are gaining increasing acceptance as diagnostic tools and promising therapeutic agents in cancer and other diseases. While most nanobodies are obtained from immunized animals of the camelid family, a few synthetic nanobody libraries constructed in recent years have shown the capability of generating high quality nanobodies in terms of affinity and stability. Since this synthetic approach has important advantages over the use of animals, the recent advances are indeed encouraging. Here we review over a dozen synthetic nanobody libraries reported so far and discuss the different approaches followed in their construction and validation, with an emphasis on framework and hypervariable loop design as critical issues defining their potential as high-class nanobody sources.

Molecular probes for cellular imaging of post-translational proteoforms

Specific post-translational modification (PTM) states of a protein affect its property and function; understanding their dynamics in cells would provide deep insight into diverse signaling pathways and biological processes. However, it is not trivial to visualize post-translational modifications in a protein- and site-specific manner, especially in a living-cell context. Herein, we review recent advances in the development of molecular imaging tools to detect diverse classes of post-translational proteoforms in individual cells, and their applications in studying precise roles of PTMs in regulating the function of cellular proteins.

Structural Biology of Nanobodies against the Spike Protein of SARS-CoV-2

Nanobodies are 130 amino acid single-domain antibodies (V_HH) derived from the unique heavy-chain-only subclass of Camelid immunogloblins. Their small molecular size, facile expression, high affinity and stability have combined to make them unique targeting reagents with numerous applications in the biomedical sciences. The first nanobody agent has now entered the clinic as a treatment against a blood disorder. The spread of the SARS-CoV-2 virus has seen the global scientific endeavour work to accelerate the development of technologies to try to defeat a pandemic that has now killed over four million people. In a remarkably short period of time, multiple studies have reported nanobodies directed against the viral Spike protein. Several agents have been tested in culture and demonstrate potent neutralisation of the virus or pseudovirus. A few agents have completed animal trials with very encouraging results showing their potential for treating infection. Here, we discuss the structural features that guide the nanobody recognition of the receptor binding domain of the Spike protein of SARS-CoV-2.

Computational design and modeling of nanobodies toward SARS-CoV-2 receptor binding domain

The ongoing pandemic of coronavirus disease 2019 (COVID‐19) caused by severe acute respiratory syndrome coronavirus 2 (SARS‐CoV‐2) has become a global health concern and pose a serious threat to humanity. There is an urgent need for developing therapeutic drugs and (or) biologics to prevent the spread of the virus. The life cycle of SARS‐CoV‐2 shows that the virus enters host cells by first binding to angiotensin‐converting enzyme 2 (ACE2) through its spike protein receptor‐binding domain (RBD). Therefore, blocking the binding between of ACE2 and SARS‐CoV‐2 RBD can inhibit the virus infection in the host cells. In this study, by grafting the complementarity‐determining regions (CDRs) of developed SARS‐CoV, MERS‐CoVs specific neutralizing antibodies (nAbs) include monoclonal antibodies (mAbs) as well as SARS‐CoV‐2 mAbs onto a known stable nanobody (Nb) scaffold, and a total of 16 Nbs sequences were designed. Five Nbs, namely CS01, CS02, CS03, CS10, and CS16, were selected based on the free energy landscape of protein docking verified by the recently reported Nb‐RBD cocrystal structures. CS01, CS02, and CS03 occupied the ACE2 binding site of RBD, while CS10 and CS16 were proposed to inhibit the interaction between RBD and ACE2 through an allosteric mechanism. Based on the structures of the five Nbs in complex with RBD, seven brand‐new Nbs with enhanced binding affinities (CS02_RD01, CS03_RD01, CS03_RD02, CS03_RD03, CS03_RD04, CS16_RD01, and CS16_RD02) were generated by redesign of residues on the interface of the five Nbs contact with SARS‐CoV‐2 RBD. In addition, the identified “hot spots” on the interface of each complex provide useful information to understand the binding mechanism of designed Nbs to SARS‐CoV‐2 RBD. In sum, the predicted stabilities and high binding affinities of the 11 (re)designed Nbs indicating the potential of the developed computational framework in this work to design effective agents to block the infection of SARS‐CoV‐2.

Production, characterization and in-vitro applications of single-domain antibody against thyroglobulin selected from novel T7 phage display library

Single- domain antibodies (SdAbs) have been deployed in various biomedical applications in the recent past. However, there are no reports of their use in the immunoradiometric assays (IRMA) for thyroglobulin (Tg). Tg is the precursor molecule for the biosynthesis of thyroid hormones: thyroxine and triiodothyronine, which are essential for the regulation of normal metabolism in all vertebrates. Patients with differentiated thyroid cancer (DTC) require periodic monitoring of their serum thyroglobulin levels, as it serves as a prognostic marker for DTC. Here, we report a methodology to produce SdAbs against human-Tg, by a hybrid immunization/directed-evolution approach by displaying the SdAb gene-repertoire derived from a hyperimmune camel in the T7 phage display system. We have demonstrated the immunoreactivity of anti-Tg-SdAb (KT75) in immunoassays for thyroglobulin and measured its affinity by surface plasmon resonance (K_D ~ 18 picomolar). Additionally, we have shown the quantitative-binding property of SdAb for the first time in IRMA for thyroglobulin. The serum Tg values obtained from SdAb-Tg-IRMA and in-house assay using murine anti-Tg-monoclonal antibody as tracer significantly correlated, r = 0.81, p < 0.05. Our results highlight the scope of using the T7 phage display system as an alternative for the conventional M13-phage to construct single-domain antibody display libraries.

A platform for post-translational spatiotemporal control of cellular proteins

Mammalian cells process information through coordinated spatiotemporal regulation of proteins. Engineering cellular networks thus relies on efficient tools for regulating protein levels in specific subcellular compartments. To address the need to manipulate the extent and dynamics of protein localization, we developed a platform technology for the target-specific control of protein destination. This platform is based on bifunctional molecules comprising a target-specific nanobody and universal sequences determining target subcellular localization or degradation rate. We demonstrate that nanobody-mediated localization depends on the expression level of the target and the nanobody, and the extent of target subcellular localization can be regulated by combining multiple target-specific nanobodies with distinct localization or degradation sequences. We also show that this platform for nanobody-mediated target localization and degradation can be regulated transcriptionally and integrated within orthogonal genetic circuits to achieve the desired temporal control over spatial regulation of target proteins. The platform reported in this study provides an innovative tool to control protein subcellular localization, which will be useful to investigate protein function and regulate large synthetic gene circuits.

From Polyclonal Sera to Recombinant Antibodies: A Review of Immunological Detection of Gluten in Foodstuff

Gluten is the ethanol-soluble protein fraction of cereal endosperms like wheat, rye, and barley. It is widely used in the food industry because of the physical-chemical properties it gives to dough. Nevertheless, there are some gluten-related diseases that are presenting increasing prevalences, e.g., celiac disease, for which a strict gluten-free diet is the best treatment. Due to this situation, gluten labeling legislation has been developed in several countries around the world. This article reviews the gluten immune detection systems that have been applied to comply with such regulations. These systems have followed the development of antibody biotechnology, which comprise three major methodologies: polyclonal antibodies, monoclonal antibodies (mAbs) derived from hybridoma cells (some examples are 401.21, R5, G12, and α-20 antibodies), and the most recent methodology of recombinant antibodies. Initially, the main objective was the consecution of new high-affinity antibodies, resulting in low detection and quantification limits that are mainly achieved with the R5 mAb (the gold standard for gluten detection). Increasing knowledge about the causes of gluten-related diseases has increased the complexity of research in this field, with current efforts not only focusing on the development of more specific and sensitive systems for gluten but also the detection of protein motifs related to pathogenicity. New tools based on recombinant antibodies will provide adequate safety and traceability methodologies to meet the increasing market demand for gluten-free products.

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.

Antibodies, Nanobodies, or Aptamers-Which Is Best for Deciphering the Proteomes of Non-Model Species?

This planet is home to countless species, some more well-known than the others. While we have developed many techniques to be able to interrogate some of the "omics", proteomics is becoming recognized as a very important part of the puzzle, given how important the protein is as a functional part of the cell. Within human health, the proteome is fairly well-established, with numerous reagents being available to decipher cellular pathways. Recent research advancements have assisted in characterizing the proteomes of some model (non-human) species, however, in many other species, we are only just touching the surface. This review considers three main reagent classes-antibodies, aptamers, and nanobodies-as a means of continuing to investigate the proteomes of non-model species without the complications of understanding the full protein signature of a species. Considerations of ease of production, potential applications, and the necessity for producing a new reagent depending on homology are presented.

Engineering Bacillus subtilis as a Versatile and Stable Platform for Production of Nanobodies

There is a growing need for a highly stable system to allow the production of biologics for diagnoses and therapeutic interventions on demand that could be used in extreme environments. Among the variety of biologics, nanobodies (Nbs) derived from single-chain variable antibody fragments from camelids have attracted great attention in recent years due to their small size and great stability with translational potentials in whole-body imaging and the development of new drugs. Intracellular expression using the bacterium Escherichia coli has been the predominant system to produce Nbs, and this requires lengthy steps for releasing intracellular proteins for purification as well as removal of endotoxins. Lyophilized, translationally competent cell extracts have also been explored as offering portability and long shelf life, but such extracts may be difficult to scale up and suffer from batch-to-batch variability. To address these problems, we present a new system to do the following: (i) engineer the spore-forming bacterium Bacillus subtilis to secrete Nbs that can target small molecules or protein antigens on mammalian cells, (ii) immobilize Nbs containing a cellulose-binding domain on a cellulose matrix for long-term storage and small-molecule capturing, (iii) directly use Nb-containing bacterial supernatant fluid to perform protein detection on cell surfaces, and (iv) convert engineered B. subtilis to spores that are resistant to most environmental extremes. In summary, our work may open a new paradigm for using B. subtilis as an extremely stable microbial factory to produce Nbs with applications in extreme environments on demand.IMPORTANCE It is highly desirable to produce biologics for diagnoses and therapeutic interventions on demand that could be used in a variety of settings. Among the many biologics, Nbs have attracted attention due to their small size, thermal stability, and broad utility in diagnoses, therapies, and fundamental research. Nbs originate from antibodies found in camelids, and >10 companies have invested in Nbs as potential drugs. Here, we present a system using cells of the bacterium Bacillus subtilis as a versatile platform for production of Nbs and then antigen detection via customized affinity columns. Importantly, B. subtilis carrying engineered genes for Nbs can form spores, which survive for years in a desiccated state. However, upon rehydration and exposure to nutrients, spores rapidly transition to growing cells which secrete encoded Nbs, thus allowing their manufacture and purification.

Nanobodies: a new approach for the diagnosis and treatment of viral infectious diseases

With the rise of viral infections and antibiotic resistance, there is a constant need for the development of more sensitive and effective treatment and diagnostic tools. Since their discovery in the early 1990s, Camelidae antibodies have been investigated as potential tools due to their unique structure and favorable characteristics. Members of this family produce conventional IgG antibodies as well as heavy-chain only IgG antibodies that do not possess light chains. The variable domain (VHH), or nanobody, demonstrates unique antigen-binding capabilities, enhanced stability, and its small size allows for delivery into the body using a nebulizer, thereby eliminating the unfavorable use of injections. In addition, the cost-effective and easy in vitro production of these antibodies are an attractive quality in terms of mass production. This review covers the past and current nanobody treatment and diagnostic developments aimed at viral infectious diseases, including a brief overview of protozoal, bacterial, and veterinary viral approaches.

Structure and development of single domain antibodies as modules for therapeutics and diagnostics

Since their discovery just over 25 years ago, the single variable domain from heavy-chain-only antibodies plays a role in an increasing number of antibody-based applications. Structural and biophysical studies have revealed that the small, ∼15 kDa, single variable domain found in camelids displays versatility in target recognition. Such insight has served as the foundation to develop and engineer VHH domains with enhanced properties capable of targeting a range of therapeutically relevant protein antigens or low-molecular weight haptens. Furthermore, the modular nature of VHH domains allows them to be introduced into constructs that are simply not possible with conventional antibodies. Here, we review the structural and biophysical properties of VHH domains, highlight recent VHH-based therapeutics and diagnostics, and provide insight into VHH engineering that may pave the way to next-generation single domain antibody applications.

Homology Modeling-Based in Silico Affinity Maturation Improves the Affinity of a Nanobody

Affinity maturation and rational design have a raised importance in the application of nanobody (VHH), and its unique structure guaranteed these processes quickly done in vitro. An anti-CD47 nanobody, Nb02, was screened via a synthetic phage display library with 278 nM of K_D value. In this study, a new strategy based on homology modeling and Rational Mutation Hotspots Design Protocol (RMHDP) was presented for building a fast and efficient platform for nanobody affinity maturation. A three-dimensional analytical structural model of Nb02 was constructed and then docked with the antigen, the CD47 extracellular domain (CD47^ext). Mutants with high binding affinity are predicted by the scoring of nanobody-antigen complexes based on molecular dynamics trajectories and simulation. Ultimately, an improved mutant with an 87.4-fold affinity (3.2 nM) and 7.36 °C higher thermal stability was obtained. These findings might contribute to computational affinity maturation of nanobodies via homology modeling using the recent advancements in computational power. The add-in of aromatic residues which formed aromatic-aromatic interaction plays a pivotal role in affinity and thermostability improvement. In a word, the methods used in this study might provide a reference for rapid and efficient in vitro affinity maturation of nanobodies.

High Expression Achievement of Active and Robust Anti-β2 microglobulin Nanobodies via E.coli Hosts Selection

Nanobodies (VHHs) overcome many of the drawbacks of conventional antibodies, and the related technologies represent state-of-the-art and advanced applications in scientific research, pharmaceuticals, and therapies. In terms of productivity and economic cost, the cytoplasmic expression of VHHs in Escherichia coli (E. coli) is a good process for their recombinant production. The cytoplasmic environment of the host is critical to the affinity and stability of the recombinant VHHs in soluble form, yet the effects have not been studied. For this purpose, recombinant anti-β2 microglobulin VHHs were constructed and expressed in four commercialized E. coli hosts, including BL21 (DE3), Rosetta-gami B (DE3) pLysS, Origami 2 (DE3) and SHuffle T7 Express. The results showed that anti-β2 microglobulin (β2MG) VHHs expressed in different hosts exhibited distinctive differences in the affinity and structural characteristics. The VHHs expressed in Rosetta-gami B (DE3) pLysS possessed not only the greatest affinity of (equilibrium dissociation constant) K_D = 4.68 × 10⁻⁸ M but also the highest yields compared with the VHHs expressed in BL21 (DE3), Origami 2 (DE3) and SHuffle T7 Express. In addition, the VHHs expressed in Rosetta-gami B (DE3) pLysS were more stable than the VHHs expressed in the rest three hosts. Thus far, we have successfully realized the high expression of the active and robust anti-β2MG VHHs in Rosetta-gami B (DE3) pLysS. The underlying principle of our study is able to guide the expression strategies of nanobodies on the context of industrial large-scale production.