Single domain antibodies from camelids in the treatment of microbial infections.

Infectious diseases continue to pose significant global health challenges. In addition to the enduring burdens of ailments like malaria and HIV, the emergence of nosocomial outbreaks driven by antibiotic-resistant pathogens underscores the ongoing threats. Furthermore, recent infectious disease crises, exemplified by the Ebola and SARS-CoV-2 outbreaks, have intensified the pursuit of more effective and efficient diagnostic and therapeutic solutions. Among the promising options, antibodies have garnered significant attention due to their favorable structural characteristics and versatile applications. Notably, nanobodies (Nbs), the smallest functional single-domain antibodies of heavy-chain only antibodies produced by camelids, exhibit remarkable capabilities in stable antigen binding. They offer unique advantages such as ease of expression and modification and enhanced stability, as well as improved hydrophilicity compared to conventional antibody fragments (antigen-binding fragments (Fab) or single-chain variable fragments (scFv)) that can aggregate due to their low solubility. Nanobodies directly target antigen epitopes or can be engineered into multivalent Nbs and Nb-fusion proteins, expanding their therapeutic potential. This review is dedicated to charting the progress in Nb research, particularly those derived from camelids, and highlighting their diverse applications in treating infectious diseases, spanning both human and animal contexts.

Design and construction of a phage-displayed Camelid nanobody library using a simple bioinformatics method.

BACKGROUND: Rational design of synthetic phage-displayed libraries requires the identification of the most appropriate positions for randomization using defined amino acid sets to recapitulate the natural occurrence. The present study uses position-specific scoring matrixes (PSSMs) for identifying and randomizing Camelidae nanobody (VHH) CDR3. The functionality of a synthetic VHH repertoire designed by this method was tested for discovering new VHH binders to recombinant coagulation factor VII (rfVII). METHODS: Based on PSSM analysis, the CDR3 of cAbBCII10 VHH framework was identified, and a set of amino acids for the substitution of each PSSM-CDR3 position was defined. Using the Rosetta design SwiftLib tool, the final repertoire was back-translated to a degenerate nucleotide sequence. A synthetic phage-displayed library was constructed based on this repertoire and screened for anti-rfVII binders. RESULTS: A synthetic phage-displayed VHH library with 1 × 108 variants was constructed. Three VHH binders to rfVII were isolated from this library with estimated dissociation constants (KD) of 1 × 10-8 M, 5.8 × 10-8 M and 2.6 × 10-7 M. CONCLUSION: PSSM analysis is a simple and efficient way to design synthetic phage-displayed libraries.

Production and characterization of a camelid single domain anti-CD22 antibody conjugated to DM1.

Antibody drug conjugates (ADCs) with twelve FDA approved drugs, known as a novel category of anti-neoplastic treatment created to merge the monoclonal antibody specificity with cytotoxicity effect of chemotherapy. However, despite many undeniable advantages, ADCs face certain problems, including insufficient internalization after binding, complex structures and large size of full antibodies especially in targeting of solid tumors. Camelid single domain antibody fragments (Nanobody®) offer solutions to this challenge by providing nanoscale size, high solubility and excellent stability, recombinant expression in bacteria, in vivo enhanced tissue penetration, and conjugation advantages. Here, an anti-human CD22 Nanobody was expressed in E.coli cells and conjugated to Mertansine (DM1) as a cytotoxic payload. The anti-CD22 Nanobody was expressed and purified by Ni-NTA resin. DM1 conjugated anti-CD22 Nanobody was generated by conjugation of SMCC-DM1 to Nanobody lysine groups. The conjugates were characterized using SDS-PAGE and Capillary electrophoresis (CE-SDS), RP-HPLC, and MALDI-TOF mass spectrometry. Additionally, flow cytometry analysis and a competition ELISA were carried out for binding evaluation. Finally, cytotoxicity of conjugates on Raji and Jurkat cell lines was assessed. The drug-to-antibody ratio (DAR) of conjugates was calculated 2.04 using UV spectrometry. SDS-PAGE, CE-SDS, HPLC, and mass spectrometry confirmed conjugation of DM1 to the Nanobody. The obtained results showed the anti-CD22 Nanobody cytotoxicity was enhanced almost 80% by conjugation with DM1. The binding of conjugates was similar to the non-conjugated anti-CD22 Nanobody in flow cytometry experiments. Concludingly, this study successfully suggest that the DM1 conjugated anti-CD22 Nanobody can be used as a novel tumor specific drug delivery system.

INDI-integrated nanobody database for immunoinformatics.

Nanobodies, a subclass of antibodies found in camelids, are versatile molecular binding scaffolds composed of a single polypeptide chain. The small size of nanobodies bestows multiple therapeutic advantages (stability, tumor penetration) with the first therapeutic approval in 2018 cementing the clinical viability of this format. Structured data and sequence information of nanobodies will enable the accelerated clinical development of nanobody-based therapeutics. Though the nanobody sequence and structure data are deposited in the public domain at an accelerating pace, the heterogeneity of sources and lack of standardization hampers reliable harvesting of nanobody information. We address this issue by creating the Integrated Database of Nanobodies for Immunoinformatics (INDI, http://naturalantibody.com/nanobodies). INDI collates nanobodies from all the major public outlets of biological sequences: patents, GenBank, next-generation sequencing repositories, structures and scientific publications. We equip INDI with powerful nanobody-specific sequence and text search facilitating access to >11 million nanobody sequences. INDI should facilitate development of novel nanobody-specific computational protocols helping to deliver on the therapeutic promise of this drug format.

Unique aspects of adaptive immunity in camelids and their applications.

Members of the Camelidae have unique adaptive immunological features that are not widely observed in other species. All camelids are known to have three distinct IgG isotypes - IgG1, IgG2 and IgG3. While IgG1 has a conventional antibody structure, both IgG2 and IgG3 are devoid of light chains and instead possess hypervariable regions in their heavy chain (VHH), while lacking the typical CH1 domain found in heavy chains. VHH domains are increasingly being utilized as "next generation" antibodies, as they have unique biochemical and structural properties including high pH stability as well as a lower molecular weight allowing for increased tissue penetration. These features of VHH domains offer a number of advantages for both biotechnology and clinical applications and are commonly termed "nanobodies". A second unique aspect of the camelid adaptive response is involves T cell-mediated immunity. Characterization of gamma delta (ꝩδ) T cells in camelid species has found they use somatic hypermutation in their T cell receptor gamma (TRG) and delta (TRD) loci to increase the structural stability of their ꝩδ T receptor. The use of somatic hyper mutation to increase the diversity of their T cell repertoire, is a feature that has not been observed in other mammalian species. In addition, in alpacas there is a unique subset of ꝩδ T cells called Vꝩ9Vδ2 T cells. Activation of these cells is dependent upon phosphoantigen (PAg)-mediated interaction with B7-like butyrophilin molecules (BTN-3). This makes alpacas the first species outside of primates to be identified with this unique subset and activation mechanism. Here we review some fundamentals of camelid adaptive immunity that make them distinct from other vertebrate species and their potential applications to human therapies.

Applications of Nanobodies.

Unique, functional, homodimeric heavy chain-only antibodies, devoid of light chains, are circulating in the blood of Camelidae. These antibodies recognize their cognate antigen via one single domain, known as VHH or Nanobody. This serendipitous discovery made three decades ago has stimulated a growing number of researchers to generate highly specific Nanobodies against a myriad of targets. The small size, strict monomeric state, robustness, and easy tailoring of these Nanobodies have inspired many groups to design innovative Nanobody-based multi-domain constructs to explore novel applications. As such, Nanobodies have been employed as an exquisite research tool in structural, cell, and developmental biology. Furthermore, Nanobodies have demonstrated their benefit for more sensitive diagnostic tests. Finally, several Nanobody-based constructs have been designed to develop new therapeutic products.

A guide to: generation and design of nanobodies.

A nanobody (Nb) is a registered trademark of Ablynx, referring to the single antigen-binding domain of heavy chain-only antibodies (HCAbs) that are circulating in Camelidae. Nbs are produced recombinantly in micro-organisms and employed as research tools or for diagnostic and therapeutic applications. They were - and still are - also named single-domain antibodies (sdAbs) or variable domain of the heavy chain of HCAbs (VHH). A variety of methods are currently in use for the fast and efficient generation of target-specific Nbs. Such Nbs are produced at low cost and associate with high affinity to their cognate antigen. They are robust, strictly monomeric and easy to tailor into more complex entities to meet the requirements of their application. Here, we review the various sources and different strategies that have been developed to identify rapidly, target-specific Nbs. We further discuss a variety of engineering technologies that have been explored to broaden the application range of Nbs and summarise those applications where designed Nbs might offer a marked advantage over other affinity reagents.

[Construction of camelidae natural nanobody phage dispaly library and screening, production and identification of anti-CD19 nanobody].

Objective To construct and verify camelidae natural nanobody phage display library for selection of nanobodies against various antigens, and to obtain and identify the nanobody targeting CD19. Methods The total RNA of spleen of Bactrian camel was reverse transcribed and the variable region gene fragment of its heavy chain was obtained by nested PCR. It was constructed into the pCANTAB5e phagemid vector and electrotransformed into TG1 E. coli to develop the natural nanobody phage display library. After rescued by the KM13 helper phage, its capacity and diversity were analyzed and identified. Nanobody against CD19 was screened using biotinylated antigen combined with streptavidin magnetic beads, followed by ELISA, sequencing, exogenous expression and verification. Results The constructed natural phage nanobody display library had great diversity, and its fragment insertion rate was about 100%. The amino acid homology of 20 randomly selected clones was 65.85%, and the titer of the display library rescued by the helper phage was 9.0×1013 CFU/mL. After panning with CD19 as the antigen, the positive clones were sequenced and analyzed, and finally anti-CD19 nanobody sequences were obtained. The exogenously expressed anti-CD19 nanobody based on the sequences was verified having the ability to bind to CD19. Conclusion A camelidae natural nanobody phage display library with high titer and great diversity has been successfully constructed. Three anti-CD19 nanobody sequences have been obtained by panning with CD19. In addition, this study provides technical support for researching and developing diagnostic kits and antibody drugs targeting CD19, and it is a novel direction to improve CAR-T cells targeting CD19.

Generation of mWasabi fluorescent protein-binding nanobodies.

mWasabi is a bright monomeric green fluorescent protein. It can be used as a fusion tag to monitor various biological events, e.g. protein localization. Here we report the selection of camelid-derived single-domain antibody fragments (nanobodies) against mWasabi. In this work, phage-display approach was employed to select the high affinity mWasabi-specific Nb (nanobodies). These nanobodies were able to recognize mWasabi or in a fused fashion with PD1. The interesting binding characteristics of these two mWasabi-specific nanobodies could be valuable for design new tools for cellular tracing or targeting based on the mWasabi-fusing protein in many different biological research fields.

Nanobodies derived from Camelids represent versatile biomolecules for biomedical applications.

Nanobodies are antigen binding variable domains of heavy-chain antibodies without light-chains, and these biomolecules occur naturally in the serum of Camelidae species. Nanobodies have a compact structure and low molecular weight when compared with antibodies, and are the smallest active antigen-binding fragments. Because of their remarkable stability and manipulable characteristics, nanobodies have been incorporated into biomaterials and used as molecular recognition and tracing agents, drug delivery systems, molecular imaging tools and disease therapeutics. This review summarizes recent progress in this field focusing on nanobodies as versatile biomolecules for biomedical applications.

Evaluation of Laboratory Application of Camelid Sera Containing Heavy-Chain Polyclonal Antibody Against Recombinant Cytotoxic T-Lymphocyte-Associated Protein-4.

Cytotoxic T-lymphocyte-associated protein-4 (CTLA-4) is a critical negative immunomodulatory receptor that is normally expressed in activated T cells and noticeably, in many cancerous cells. Indeed, molecular detection of CTLA-4 protein is crucial in basic research. In this work, the extracellular domain of the human CTLA-4 (hCTLA-4) protein was cloned, expressed, and purified. Subsequently, this protein was used as an antigen for camel (Camelus dromedarius) immunization to obtain polyclonal camelid sera against this protein. Furthermore, we evaluated the benefits of applying camelid hyperimmune sera containing heavy-chain antibodies in different antibody-based techniques. Our results indicated that hCTLA-4 protein was successfully expressed in the prokaryotic system. The polyclonal antibody (pAb) that raised against recombinant hCTLA-4 protein was able to detect the CTLA-4 protein in antibody-based techniques, such as enzyme-linked immunosorbent assay, western blotting, flow cytometry and immunohistochemistry (IHC) staining. This study shows that, due to the advantages such as multi-epitope-binding ability, camelid pAbs are potent to efficiently apply for molecular detection of CTLA-4 receptors in fundamental antibody-based researches such as IHC.

Advances in the Production and Batch Reformatting of Phage Antibody Libraries.

Phage display antibody libraries have proven an invaluable resource for the isolation of diagnostic and potentially therapeutic antibodies, the latter usually being antibody fragments converted into IgG formats. Recent advances in the production of highly diverse and functional antibody libraries are considered here, including for Fabs, scFvs and nanobodies. These advances include codon optimisation during generation of CDR diversity, improved display levels using novel signal sequences, molecular chaperones and isomerases and the use of highly stable scaffolds with relatively high expression levels. In addition, novel strategies for the batch reformatting of scFv and Fab phagemid libraries, derived from phage panning, into IgG formats are described. These strategies allow the screening of antibodies in the end-use format, facilitating more efficient selection of potential therapeutics.

Perspectives for the Development of CD38-Specific Heavy Chain Antibodies as Therapeutics for Multiple Myeloma.

The NAD+-metabolizing ectoenzyme CD38 is an established therapeutic target in multiple myeloma. The CD38-specific monoclonal antibodies daratumumab and isatuximab show promising results in the clinic. Nanobodies correspond to the single variable domains (VHH) derived from heavy chain antibodies that naturally occur in camelids. VHHs display high solubility and excellent tissue penetration in vivo. We recently generated a panel of CD38-specific nanobodies, some of which block or enhance the enzymatic activity of CD38. Fusion of such a nanobody to the hinge, CH2, and CH3 domains of human IgG1 generates a chimeric llama/human hcAb of about half the size of a conventional moAb (75 vs. 150 kDa). Similarly, a fully human CD38-specific hcAb can be generated using a CD38-specific human VH3 instead of a CD38-specific camelid nanobody. Here we discuss the advantages and disadvantages of CD38-specific hcAbs vs. conventional moAbs and provide an outlook for the potential use of CD38-specific hcAbs as novel therapeutics for multiple myeloma.

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

Application of camelid heavy-chain variable domains (VHHs) in prevention and treatment of bacterial and viral infections.

Camelid heavy-chain variable domains (VHHs) are the smallest, intact, antigen-binding units to occur in nature. VHHs possess high degrees of solubility and robustness enabling generation of multivalent constructs with increased avidity - characteristics that mark their superiority to other antibody fragments and monoclonal antibodies. Capable of effectively binding to molecular targets inaccessible to classical immunotherapeutic agents and easily produced in microbial culture, VHHs are considered promising tools for pharmaceutical biotechnology. With the aim to demonstrate the perspective and potential of VHHs for the development of prophylactic and therapeutic drugs to target diseases caused by bacterial and viral infections, this review article will initially describe the structural features that underlie the unique properties of VHHs and explain the methods currently used for the selection and recombinant production of pathogen-specific VHHs, and then thoroughly summarize the experimental findings of five distinct studies that employed VHHs as inhibitors of host-pathogen interactions or neutralizers of infectious agents. Past and recent studies suggest the potential of camelid heavy-chain variable domains as a novel modality of immunotherapeutic drugs and a promising alternative to monoclonal antibodies. VHHs demonstrate the ability to interfere with bacterial pathogenesis by preventing adhesion to host tissue and sequestering disease-causing bacterial toxins. To protect from viral infections, VHHs may be employed as inhibitors of viral entry by binding to viral coat proteins or blocking interactions with cell-surface receptors. The implementation of VHHs as immunotherapeutic agents for infectious diseases is of considerable potential and set to contribute to public health in the near future.

[Application of nanobody in cancer treatment].

Camelidae can produce a unique antibody that lacks light chain called variable heavy chain domain, also known as nanobodies. This antibody contains only one variable region, with high affinity, high stability, strong tissue penetration, efficient expression. Besides, their toxicity and immunogenicity are both low to be used for both therapeutic and diagnostic applications, as well as research tools. In this review, we discuss how nanobody has been explored as therapeutics in oncology, and provide ideas for the further development of nanobody.

A camelid single-domain antibody neutralizes botulinum neurotoxin A by blocking host receptor binding.

Antibody treatment is currently the only available countermeasure for botulism, a fatal illness caused by flaccid paralysis of muscles due to botulinum neurotoxin (BoNT) intoxication. Among the seven major serotypes of BoNT/A-G, BoNT/A poses the most serious threat to humans because of its high potency and long duration of action. Prior to entering neurons and blocking neurotransmitter release, BoNT/A recognizes motoneurons via a dual-receptor binding process in which it engages both the neuron surface polysialoganglioside (PSG) and synaptic vesicle glycoprotein 2 (SV2). Previously, we identified a potent neutralizing antitoxin against BoNT/A1 termed ciA-C2, derived from a camelid heavy-chain-only antibody (VHH). In this study, we demonstrate that ciA-C2 prevents BoNT/A1 intoxication by inhibiting its binding to neuronal receptor SV2. Furthermore, we determined the crystal structure of ciA-C2 in complex with the receptor-binding domain of BoNT/A1 (HCA1) at 1.68 Å resolution. The structure revealed that ciA-C2 partially occupies the SV2-binding site on HCA1, causing direct interference of HCA1 interaction with both the N-glycan and peptide-moiety of SV2. Interestingly, this neutralization mechanism is similar to that of a monoclonal antibody in clinical trials, despite that ciA-C2 is more than 10-times smaller. Taken together, these results enlighten our understanding of BoNT/A1 interactions with its neuronal receptor, and further demonstrate that inhibiting toxin binding to the host receptor is an efficient countermeasure strategy.