[Advances in nanobody screening technology].

Nanobody (Nb) is a novel type of antibody discovered in the serum of Camelidae. It is characterized by its small size, high specificity, stability, and ease of preparation. Nanobodies exhibit the ability to identify hidden epitopes and have diverse applications across various fields. This review aims to introduce three key stages in the screening and optimization of nanobodies, including nanobody library construction, in vitro surface display, and affinity maturation. We provide a brief description of preparation and characteristics of natural, immunological, and semi-synthetic/synthetic libraries. Additionally, we systematically explain eight in vitro display methods, including phage display, yeast display, bacterial display, ribosome display/mRNA display, and eukaryotic cell display. Furthermore, we discuss the application of yeast two-hybrid system high-throughput sequencing and mass spectrometry identification. A thorough analysis of their advantages and limitations is presented in this protocols. Finally, we summarize the platforms for in vitro or computer-aided affinity maturation techniques aimed at enhancing the functional stability of nanobodies. Consequently, this review provides a comprehensive approach to the integrated utilization of various technologies for the rapid development of stable, reliable, and specific nanobody-based drugs or diagnostic agents.

A mammalian cell display platform based on scFab transposition.

In vitro display technologies have been successfully utilized for the discovery and evolution of monoclonal antibodies (mAbs) for diagnostic and therapeutic applications, with phage display and yeast display being the most commonly used platforms due to their simplicity and high efficiency. As their prokaryotic or lower eukaryotic host organisms typically have no or different post-translational modifications, several mammalian cell-based display and screening technologies for isolation and optimization of mAbs have emerged and are being developed. We report here a novel and useful mammalian cell display platform based on the PiggyBac transposon system to display mAbs in a single-chain Fab (scFab) format on the surface of HEK293F cells. Immune rabbit antibody libraries encompassing ~7 × 107 independent clones were generated in an all-in-one transposon vector, stably delivered into HEK293F cells and displayed as an scFab with rabbit variable and human constant domains. After one round of magnetic activated cell sorting and two rounds of fluorescence activated cell sorting, mAbs with high affinity in the subnanomolar range and cross-reactivity to the corresponding human and mouse antigens were identified, demonstrating the power of this platform for antibody discovery. We developed a highly efficient mammalian cell display platform based on the PiggyBac transposon system for antibody discovery, which could be further utilized for humanization as well as affinity and specificity maturation.

Biosynthetic Strategies for Macrocyclic Peptides.

Macrocyclic peptides are predominantly peptide structures bearing one or more rings and spanning multiple amino acid residues. Macrocyclization has become a common approach for improving the pharmacological properties and bioactivity of peptides. A variety of ribosomal-derived and non-ribosomal synthesized cyclization approaches have been established. The biosynthesis of backbone macrocyclic peptides using seven new emerging methodologies will be discussed with regard to the features and strengths of each platform rather than medicinal chemistry tools. The mRNA display variant, known as the random nonstandard peptide integrated discovery (RaPID) platform, utilizes flexible in vitro translation (FIT) to access macrocyclic peptides containing nonproteinogenic amino acids (NAAs). As a new discovery approach, the ribosomally synthesized and post-translationally modified peptides (RiPPs) method involves the combination of ribosomal synthesis and the phage screening platform together with macrocyclization chemistries to generate libraries of macrocyclic peptides. Meanwhile, the split-intein circular ligation of peptides and proteins (SICLOPPS) approach relies on the in vivo production of macrocyclic peptides. In vitro and in vivo peptide library screening is discussed as an advanced strategy for cyclic peptide selection. Specifically, biosynthetic bicyclic peptides are highlighted as versatile and attractive modalities. Bicyclic peptides represent another type of promising therapeutics that allow for building blocks with a heterotrimeric conjugate to address intractable challenges and enable multimer complexes via linkers. Additionally, we discuss the cell-free chemoenzymatic synthesis of macrocyclic peptides with a non-ribosomal catalase known as the non-ribosomal synthetase (NRPS) and chemo-enzymatic approach, with recombinant thioesterase (TE) domains. Novel insights into the use of peptide library tools, activity-based two-hybrid screening, structure diversification, inclusion of NAAs, combinatorial libraries, expanding the toolbox for macrocyclic peptides, bicyclic peptides, chemoenzymatic strategies, and future perspectives are presented. This review highlights the broad spectrum of strategy classes, novel platforms, structure diversity, chemical space, and functionalities of macrocyclic peptides enabled by emerging biosynthetic platforms to achieve bioactivity and for therapeutic purposes.

Amplification of a minimally biased antibody repertoire for in vitro display using a universal primer-based amplification method.

Immune hosts are valuable sources for antibody discovery. To construct in vitro display antibody libraries from immune repertoires, singleplex or multiplex PCR amplification were employed using primers targeting multiple immunoglobulin genes. However, during this process, the B cell receptor repertoire is distorted due to interactions between multiple target genes and primers. To minimize this alternation, we devised a new method for harvesting immunoglobulin genes and tested its performance in rabbit variable heavy chain (VH) and variable kappa light chain (VK) genes. Double-stranded cDNA was synthesized using primers containing V/J gene-specific regions and universal sequence parts for in vitro display. VH and VK gene libraries were obtained through subsequent PCR amplification using primers with universal sequences. Next-generation sequencing analysis confirmed that universal PCR libraries had more diverse VH and VK clonotypes, and a less biased clonal distribution, than conventional singleplex or multiplex gene-specific PCR libraries.

Monoclonal antibodies: technologies for early discovery and engineering.

Antibodies are essential in modern life sciences biotechnology. Their architecture and diversity allow for high specificity and affinity to a wide array of biochemicals. Combining monoclonal antibody (mAb) technology with recombinant DNA and protein expression links antibody genotype with phenotype. Yet, the ability to select and screen for high affinity binders from recombinantly-displayed, combinatorial libraries unleashes the true power of mAbs and a flood of clinical applications. The identification of novel antibodies can be accomplished by a myriad of in vitro display technologies from the proven (e.g. phage) to the emerging (e.g. mammalian cell and cell-free) based on affinity binding as well as function. Lead candidates can be further engineered for increased affinity and half-life, reduced immunogenicity and/or enhanced manufacturing, and storage capabilities. This review begins with antibody biology and how the structure and genetic machinery relate to function, diversity, and in vivo affinity maturation and follows with the general requirements of (therapeutic) antibody discovery and engineering with an emphasis on in vitro display technologies. Throughout, we highlight where antibody biology inspires technology development and where high-throughput, "big data" and in silico strategies are playing an increasing role. Antibodies dominate the growing class of targeted therapeutics, alone or as bioconjugates. However, their versatility extends to research, diagnostics, and beyond.

Development of Next-Generation Peptide Binders Using In vitro Display Technologies and Their Potential Applications.

During the last decade, a variety of monoclonal antibodies have been developed and used as molecular targeting drugs in medical therapies. Although antibody drugs tend to have intense pharmacological activities and negligible side effects, several issues in their development and prescription remain to be resolved. Synthetic peptides with affinities and specificities for a desired target have received significant attention as alternatives to antibodies. In vitro display technologies are powerful methods for the selection of such peptides from combinatorial peptide libraries. Various types of peptide binders are being selected with such technologies for use in a wide range of fields from bioscience to medicine. This mini review article focuses on the current state of in vitro display selection of synthetic peptide binders and compares the selected peptides with natural peptides/proteins to provide a better understanding of the target affinities and inhibitory activities derived from their amino acid sequences and structural frameworks. The potential of synthetic peptide binders as alternatives to antibody drugs in therapeutic applications is also reviewed.