Generation of a Novel Bacteriophage Library Displaying scFv Antibody Fragments from the Natural Buffalo Host to Identify Antigens from Adult Schistosoma japonicum for Diagnostic Development

Principles of antibodies with ultralong complementarity-determining regions and picobodies

In contrast to other species, cattle possess exceptional antibodies with ultra-long complementarity-determining regions (ulCDRs) that can consist of 40-70 amino acids. The bovine ulCDR is folded into a stalk and a disulfide-rich knob domain. The binding to the antigen is via the 3-6 kDa knob. There exists an immense sequence and structural diversity in the knob that enables binding to different antigens. Here we summarize the current knowledge of the ulCDR structure and provide an overview of the approaches to discover ulCDRs against novel antigens. Furthermore, we outline protein engineering approaches inspired by the natural ulCDRs. Finally, we discuss the enormous potential of using isolated bovine knobs, also named picobodies, as the smallest antigen-binding domains derived from natural antibodies.

Developing Recombinant Antibodies by Phage Display Against Infectious Diseases and Toxins for Diagnostics and Therapy

Antibodies are essential molecules for diagnosis and treatment of diseases caused by pathogens and their toxins. Antibodies were integrated in our medical repertoire against infectious diseases more than hundred years ago by using animal sera to treat tetanus and diphtheria. In these days, most developed therapeutic antibodies target cancer or autoimmune diseases. The COVID-19 pandemic was a reminder about the importance of antibodies for therapy against infectious diseases. While monoclonal antibodies could be generated by hybridoma technology since the 70ies of the former century, nowadays antibody phage display, among other display technologies, is robustly established to discover new human monoclonal antibodies. Phage display is an in vitro technology which confers the potential for generating antibodies from universal libraries against any conceivable molecule of sufficient size and omits the limitations of the immune systems. If convalescent patients or immunized/infected animals are available, it is possible to construct immune phage display libraries to select in vivo affinity-matured antibodies. A further advantage is the availability of the DNA sequence encoding the phage displayed antibody fragment, which is packaged in the phage particles. Therefore, the selected antibody fragments can be rapidly further engineered in any needed antibody format according to the requirements of the final application. In this review, we present an overview of phage display derived recombinant antibodies against bacterial, viral and eukaryotic pathogens, as well as microbial toxins, intended for diagnostic and therapeutic applications.

Generation of a single-chain variable fragment phage display antibody library from naïve mice panned against Fasciola hepatica antigens

Monoclonal antibodies have a wide range of applications in basic and applied research as well as in the medical and pharmaceutical industries. Phage display antibody libraries offer an alternative to hybridoma technology for the generation of monoclonal antibodies and can be applied to high-throughput screening and facilitate the generation of novel antibodies. Despite their utility in several fields of research there has been limited application of antibody libraries in the study of trematode parasites. Fasciola hepatica causes considerable loss to the agriculture sector and is also a human pathogen. The parasite's excretory/secretory material contains numerous molecules that facilitate its invasion and survival within the mammalian host, including cathepsin B and L proteases. F. hepatica cathepsin B2 is expressed during the initial weeks of infection and has suspected roles in immune evasion and as a digestive enzyme in the parasite's gut; it is considered a good target for vaccination or therapeutic inhibitors. In this study, we produced a single-chain variable fragment (scFv) phage display library from naïve mice. The library was used to identify several scFv that can bind to antigens from adult F. hepatica homogenate, and a scFv that can bind to F. hepatica cathepsin B2. The results highlight the potential applicability of such a library to facilitate the study of F. hepatica and other parasites. This is the first report of the application of a naïve phage display antibody library to the study of F. hepatica.

Camelid Single-Domain Antibodies As an Alternative to Overcome Challenges Related to the Prevention, Detection, and Control of Neglected Tropical Diseases

Due mainly to properties such as high affinity and antigen specificity, antibodies have become important tools for biomedical research, diagnosis, and treatment of several human diseases. When the objective is to administer them for therapy, strategies are used to reduce the heterologous protein immunogenicity and to improve pharmacokinetic and pharmacodynamic characteristics. Size minimization contributes to ameliorate these characteristics, while preserving the antigen-antibody interaction site. Since the discovery that camelids produce functional antibodies devoid of light chains, studies have proposed the use of single domains for biosensors, monitoring and treatment of tumors, therapies for inflammatory and neurodegenerative diseases, drug delivery, or passive immunotherapy. Despite an expected increase in antibody and related products in the pharmaceutical market over the next years, few research initiatives are related to the development of alternatives for helping to manage neglected tropical diseases (NTDs). In this review, we summarize developments of camelid single-domain antibodies (VHH) in the field of NTDs. Particular attention is given to VHH-derived products, i.e., VHHs fused to nanoparticles, constructed for the development of rapid diagnostic kits; fused to oligomeric matrix proteins for viral neutralization; and conjugated with proteins for the treatment of human parasites. Moreover, paratransgenesis technology using VHHs is an interesting approach to control parasite development in vectors. With enormous biotechnological versatility, facility and low cost for heterologous production, and greater ability to recognize different epitopes, VHHs have appeared as an opportunity to overcome challenges related to the prevention, detection, and control of human diseases, especially NTDs.