Functional characterization of two scFv-Fc antibodies from an HIV controller selected on soluble HIV-1 Env complexes: a neutralizing V3- and a trimer-specific gp41 antibody

Comprehensive profiling of pre-infection antibodies identifies HIV targets associated with viremic control and viral load

Background

High HIV viral load (VL) is associated with increased transmission risk and faster disease progression. HIV controllers achieve viral suppression without antiretroviral (ARV) treatment. We evaluated viremic control in a community-randomized trial with >48,000 participants.

Methods

A massively multiplexed antibody profiling system, VirScan, was used to quantify pre- and post-infection antibody reactivity to HIV peptides in 664 samples from 429 participants (13 controllers, 135 viremic non-controllers, 64 other non-controllers, 217 uninfected persons). Controllers had VLs <2,000 copies/mL with no ARV drugs detected at the first HIV-positive visit and one year later. Viremic non-controllers had VLs 2,000 copies/mL with no ARV drugs detected at the first HIV-positive visit. Other non-controllers had either ARV drugs detected at the first HIV-positive visit (n=47) or VLs <2,000 copies/mL with no ARV drugs detected at only one HIV-positive visit (n=17).

Results

We identified pre-infection HIV antibody reactivities that correlated with post-infection VL. Pre-infection reactivity to an epitope in the HR2 domain of gp41 was associated with controller status and lower VL. Pre-infection reactivity to an epitope in the C2 domain of gp120 was associated with non-controller status and higher VL. Different patterns of antibody reactivity were observed over time for these two epitopes.

Conclusion

These studies suggest that pre-infection HIV antibodies are associated with controller status and modulation of HIV VL. These findings may inform research on antibody-based interventions for HIV treatment.

Antibody Selection in Solution Using Magnetic Beads

Antibody phage display is a valuable in vitro technology to generate recombinant, sequence-defined antibodies for research, diagnostics, and therapy. Up to now (autumn 2022), 14 FDA/EMA-approved therapeutic antibodies were developed using phage display, including the world best-selling antibody adalimumab. Additionally, recombinant, sequence-defined antibodies have significant advantages over their polyclonal counterparts.For a successful in vitro antibody generation by phage display, a suitable panning strategy is highly important. We present in this book chapter the panning in solution and its advantages over panning with immobilized antigens and give detailed protocols for the panning and screening procedure.

Antibody Selection via Phage Display in Microtiter Plates

The most common and robust in vitro technology to generate monoclonal human antibodies is phage display. This technology is a widely used and powerful key technology for recombinant antibody selection. Phage display-derived antibodies are used as research tools, in diagnostic assays, and by 2022, 14 phage display-derived therapeutic antibodies were approved. In this review, we describe a fast high-throughput antibody (scFv) selection procedure in 96-well microtiter plates. The given detailed protocol allows the antibody selection ("panning"), screening, and identification of monoclonal antibodies in less than 2 weeks. Furthermore, we describe an on-rate panning approach for the selection of monoclonal antibodies with fast on-rates.

Construction of Human Immune and Naive scFv Phage Display Libraries

Antibody phage display is a widely used in vitro selection technology for the generation of human recombinant antibodies and has yielded thousands of useful antibodies for research, diagnostics, and therapy. In order to successfully generate antibodies using phage display, the basis is the construction of high-quality antibody gene libraries. Here, we describe detailed methods for the construction of such high-quality immune and naive scFv gene libraries of human origin. These protocols were used to develop human naive (e.g., HAL9/10) and immune libraries, which resulted in thousands of specific antibodies for all kinds of applications.

An overview on display systems (phage, bacterial, and yeast display) for production of anticancer antibodies; advantages and disadvantages

Antibodies as ideal therapeutic and diagnostic molecules are among the top-selling drugs providing considerable efficacy in disease treatment, especially in cancer therapy. Limitations of the hybridoma technology as routine antibody generation method in conjunction with numerous developments in molecular biology led to the development of alternative approaches for the streamlined identification of most effective antibodies. In this regard, display selection technologies such as phage display, bacterial display, and yeast display have been widely promoted over the past three decades as ideal alternatives to traditional methods. The display of antibodies on phages is probably the most widespread of these methods, although surface display on bacteria or yeast have been employed successfully, as well. These methods using various sizes of combinatorial antibody libraries and different selection strategies possessing benefits in screening potency, generating, and isolation of high affinity antibodies with low risk of immunogenicity. Knowing the basics of each method assists in the design and retrieval process of antibodies suitable for different diseases, including cancer. In this review, we aim to outline the basics of each library construction and its display method, screening and selection steps. The advantages and disadvantages in comparison to alternative methods, and their applications in antibody engineering will be explained. Finally, we will review approved or non-approved therapeutic antibodies developed by employing these methods, which may serve as therapeutic antibodies in cancer therapy.

Perspectives on passive antibody therapy and peptide-based vaccines against emerging pathogens like SARS-CoV-2

The current epidemic of the severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) is raising awareness of the need to act faster when dealing with new pathogens. Exposure to an emerging pathogen generates an antibody response that can be used for preventing and treating the infection. These antibodies might have a high specificity to a target, few side effects, and are useful in the absence of an effective vaccine for treating immunocompromised individuals. The approved antibodies against the receptor-binding domain (RBD) of the viral spike protein of SARS-CoV-2 (e.g., regdanvimab, bamlanivimab, etesevimab, and casirivimab/imdevimab) have been selected from the antibody repertoire of B cells from convalescent patients using flow cytometry, next-generation sequencing, and phage display. This encourages use of these techniques especially phage display, because it does not require expensive types of equipment and can be performed on the lab bench, thereby making it suitable for labs with limited resources. Also, the antibodies in blood samples from convalescent patients can be used to screen pre-made peptide libraries to identify epitopes for vaccine development. Different types of vaccines against SARS-CoV-2 have been developed, including inactivated virus vaccines, mRNA-based vaccines, non-replicating vector vaccines, and protein subunits. mRNA vaccines have numerous advantages over existing vaccines, such as efficacy, ease of manufacture, safety, and cost-effectiveness. Additionally, epitope vaccination may constitute an attractive strategy to induce high levels of antibodies against a pathogen and phages might be used as immunogenic carriers of such peptides. This is a point worth considering further, as phage-based vaccines have been shown to be safe in clinical trials and phages are easy to produce and tolerate high temperatures. In conclusion, identification of the antibody repertoire of recovering patients, and the epitopes they recognize, should be an attractive alternative option for developing therapeutic and prophylactic antibodies and vaccines against emerging pathogens.

A SARS-CoV-2 neutralizing antibody selected from COVID-19 patients binds to the ACE2-RBD interface and is tolerant to most known RBD mutations

The novel betacoronavirus severe acute respiratory syndrome-coronavirus-2 (SARS-CoV-2) causes a form of severe pneumonia disease called coronavirus disease 2019 (COVID-19). To develop human neutralizing anti-SARS-CoV-2 antibodies, antibody gene libraries from convalescent COVID-19 patients were constructed and recombinant antibody fragments (scFv) against the receptor-binding domain (RBD) of the spike protein were selected by phage display. The antibody STE90-C11 shows a subnanometer IC50 in a plaque-based live SARS-CoV-2 neutralization assay. The in vivo efficacy of the antibody is demonstrated in the Syrian hamster and in the human angiotensin-converting enzyme 2 (hACE2) mice model. The crystal structure of STE90-C11 Fab in complex with SARS-CoV-2-RBD is solved at 2.0 Å resolution showing that the antibody binds at the same region as ACE2 to RBD. The binding and inhibition of STE90-C11 is not blocked by many known emerging RBD mutations. STE90-C11-derived human IgG1 with FcγR-silenced Fc (COR-101) is undergoing Phase Ib/II clinical trials for the treatment of moderate to severe COVID-19.

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.

Antibody display technologies: selecting the cream of the crop

Antibody display technologies enable the successful isolation of antigen-specific antibodies with therapeutic potential. The key feature that facilitates the selection of an antibody with prescribed properties is the coupling of the protein variant to its genetic information and is referred to as genotype phenotype coupling. There are several different platform technologies based on prokaryotic organisms as well as strategies employing higher eukaryotes. Among those, phage display is the most established system with more than a dozen of therapeutic antibodies approved for therapy that have been discovered or engineered using this approach. In recent years several other technologies gained a certain level of maturity, most strikingly mammalian display. In this review, we delineate the most important selection systems with respect to antibody generation with an emphasis on recent developments.

Hybridoma technology: is it still useful?

The isolation of single monoclonal antibodies (mAbs) against a given antigen was only possible with the introduction of the hybridoma technology, which is based on the fusion of specific B lymphocytes with myeloma cells. Since then, several mAbs were described for therapeutic, diagnostic, and research purposes. Despite being an old technique with low complexity, hybridoma-based strategies have limitations that include the low efficiency on B lymphocyte-myeloma cell fusion step, and the need to use experimental animals. In face of that, several methods have been developed to improve mAb generation, ranging from changes in hybridoma technique to the advent of completely new technologies, such as the antibody phage display and the single B cell antibody ones. In this review, we discuss the hybridoma technology along with emerging mAb isolation approaches, taking into account their advantages and limitations. Finally, we explore the usefulness of the hybridoma technology nowadays.

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Hybridoma technology is the most popular technique to obtain monoclonal antibodies.

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Hybridoma technology variants include B cell and stereospecific targeting protocols.

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Phage display and single B cell methods are hybridoma technology alternatives.

Infectious disease antibodies for biomedical applications: A mini review of immune antibody phage library repertoire

Antibody phage display is regarded as a critical tool for the development of monoclonal antibodies for infectious diseases. The different classes of antibody libraries are classified based on the source of repertoire used to generate the libraries. Immune antibody libraries are generated from disease infected host or immunization against an infectious agent. Antibodies derived from immune libraries are distinct from those derived from naïve libraries as the host's in vivo immune mechanisms shape the antibody repertoire to yield high affinity antibodies. As the immune system is constantly evolving in accordance to the health state of an individual, immune libraries can offer more than just infection-specific antibodies but also antibodies derived from the memory B-cells much like naïve libraries. The combinatorial nature of the gene cloning process would give rise to a combination of natural and un-natural antibody gene pairings in the immune library. These factors have a profound impact on the coverage of immune antibody libraries to target both disease-specific and non-disease specific antigens. This review looks at the diverse nature of antibody responses for immune library generation and discusses the extended potential of a disease-specified immune library in the context of phage display.

Antibody Phage Display: Antibody Selection in Solution Using Biotinylated Antigens

Antibody phage display is the most used in vitro technology to generate recombinant, mainly human, antibodies as tools for research, for diagnostic assays, and for therapeutics. Up to now (autumn 2018), eleven FDA/EMA-approved therapeutic antibodies were developed using phage display, including the world best-selling antibody adalimumab.A key to generate successfully human antibodies in vitro is the choice of the most appropriate antibody selection method, for our goal. In this book chapter, we describe the antibody selection process (panning) in solution and its advantages over panning on immobilized antigens. Detailed protocols on the panning procedure and the screening of monoclonal binders are given.

Development of Protein- and Peptide-Based HIV Entry Inhibitors Targeting gp120 or gp41

Application of highly active antiretroviral drugs (ARDs) effectively reduces morbidity and mortality in HIV-infected individuals. However, the emergence of multiple drug-resistant strains has led to the increased failure of ARDs, thus calling for the development of anti-HIV drugs with targets or mechanisms of action different from those of the current ARDs. The first peptide-based HIV entry inhibitor, enfuvirtide, was approved by the U.S. FDA in 2003 for treatment of HIV/AIDS patients who have failed to respond to the current ARDs, which has stimulated the development of several series of protein- and peptide-based HIV entry inhibitors in preclinical and clinical studies. In this review, we highlighted the properties and mechanisms of action for those promising protein- and peptide-based HIV entry inhibitors targeting the HIV-1 gp120 or gp41 and discussed their advantages and disadvantages, compared with the current ARDs.

Use of bacteriophage for discovery of therapeutically relevant antibodies against infectious diseases

Scientists George P Smith and Gregory Winter were recently awarded half of the 2018 Nobel Prize for Chemistry for developing a technology to display exogenous peptides and proteins on the surface of bacteriophage. ‘Phage display' has revolutionised the development of monoclonal antibodies, allowing fully human-derived antibodies to be isolated from large antibody libraries. It has been used for the discovery of many blockbuster drugs, including Humira (adalimumab), the highest selling drug yearly since 2012, with US$18.4b in sales globally in 20171. Phage display can be used to isolate antibodies to almost any antigen for a wide range of applications including clinical use (for cancer, inflammatory conditions and infectious diseases), diagnostic use or as research tools. The technology is accessible to any laboratory equipped for molecular biology and bacteria culture.

Parallelized Microscale Expression of Soluble scFv

Antibody phage display is a key technology to generate recombinant, mainly human, antibodies for diagnostic and therapy, but also as tools for basic research. After antibody selection by "panning," a crucial step is the screening of monoclonal binders to isolate those which show antigen specificity. For this screening procedure, a highly parallelized approach to produce soluble antibody fragments in microtiter plates is essential. In this chapter, we give the protocol for the parallelized microscale production of scFvs for the screening procedure or further assays.

Phage display-derived antibody fragments against conserved regions of VacA toxin of Helicobacter pylori

Infection with Helicobacter pylori may result in the emergence of gastric adenocarcinoma. Among various toxins assisting pathogenesis of H. pylori, the vacuolating cytotoxin A (VacA) is one of the most potent toxins known as the major cause of the peptic ulcer and gastric adenocarcinoma. To isolate single-chain variable fragments (scFvs) against two conserved regions of VacA, we capitalized on the phage display technology and a solution-phase biopanning (SPB). Characterization of scFvs was carried out by enzyme-linked immunosorbent assay (ELISA), immunoblotting, and surface plasmon resonance (SPR). Bioinformatics analyses were also performed in order to characterize the structural and functional properties of the isolated scFvs and the interaction(s) between the isolated antibodies (Ab)-antigen (Ag). After four rounds of biopanning, the positive colonies detected by scFv ELISA were harvested to extract the plasmids and perform sequencing. Of several colonies, three colonies showed high affinity to the VacA1 and two colonies for the VacA2. Further complementary examinations (e.g., sodium dodecyl sulfate polyacrylamide gel electrophoresis (SDS-PAGE), western blot, SPR, and flow cytometry) displayed the high affinity and specificity of the isolated scFvs to the VacA. Docking results revealed the interaction of the complementarity-determining regions (CDRs) with the VacA peptide. In conclusion, for the first time, we report on the isolation of several scFvs against conserved residues of VacA toxin with high affinity and specificity, which may be used as novel diagnostic/therapeutic tool in the H. pylori infection.

Optimization of the EC26-2A4 Epitope in the gp41 Membrane Proximal External Region Targeted by Neutralizing Antibodies from an Elite Controller

The analysis of patient derived HIV neutralizing antibodies (nAbs) and their target epitopes in the viral envelope (Env) protein provides important basic information for vaccine design. In this study we optimized an epitope, EC26-2A4, that is targeted by neutralizing antibodies from an elite controller (EC26) and localizes in the membrane-proximal external region from the gp41 transmembrane protein. Due to its overlap with the epitope of the first generation broadly neutralizing monoclonal Ab (mAb) 2F5 associated with autoreactivity, we first defined the minimal core epitope reacting with antibodies from EC26 plasma, but not with mAb 2F5. The optimized minimal epitope, EC26-2A4ΔM, was able to induce neutralizing antibodies in vaccinated mice. We further analyzed the frequency of antibodies against the EC26-2A4ΔM peptide in HIV-positive patient sera from a treated cohort and an untreated long-term nonprogressor (LTNP) cohort. Interestingly, 27% of the LTNP sera reacted with the peptide, whereas only 9% showed reactivity in the treated cohort. Although there was no association between the presence of antibodies against the EC26-2A4ΔM epitope and viral load or CD4 count in these patients, the CD4 nadir in the treated cohort was higher in patients positive for EC26-2A4ΔM antibodies, in particular in patients having such antibodies at an early and a late timepoint after infection.

Parallelized Antibody Selection in Microtiter Plates

The most common in vitro technology to generate human antibodies is phage display. This technology is a key technology to select recombinant antibodies for the use as research tools, in diagnostic tests, and for the development of therapeutics.In this review, the high-throughput compatible selection of antibodies (scFv) in microtiter plates is described. The given detailed protocols allow the antibody selection ("panning"), screening and identification of monoclonal antibodies in less than 1 week.

Construction of Macaque Immune-Libraries

Rapidly after the clinical success of the first murine therapeutic antibody licensed in 1985 (muromomab-CD3), the first limits of the therapeutic use of antibodies deriving from hybridoma technology appeared. Indeed, the nonhuman nature of these therapeutic antibodies makes them immunogenic when administrated to patients, which develop anti-drug antibodies (ADA). If repeated drug-administrations are needed, the immune response will accelerate the elimination of the drug, leading to a therapeutic failure, or in the worst case to an anaphylactic reaction against the murine protein. Several antibody generations were then developed to obtain better-tolerated molecules: chimeric, humanized, and fully human antibodies. The first antibody generation is fully based on cellular technology (mice hybridoma technology), but the next generations are improved by molecular engineering. Immune antibody phage-display libraries are one successful approach to isolating such engineered antibodies. One strategy to isolate high-affinity and well-tolerated antibodies when no immunized patients are available is based on the phage-display-screening of immune libraries deriving from immunized nonhuman primates, which are phylogenetically close to humans. This chapter presents the strategy for the construction of macaque antibody immune-libraries.

Construction of Human Immune and Naive scFv Libraries

Antibody phage display is the most commonly used in vitro selection technology for the generation of human recombinant antibodies and has yielded thousands of useful antibodies for research, diagnostics, and therapy. The prerequisite for successful generation of antibodies using phage display is the construction of high-quality antibody gene libraries. Here, we give the detailed methods for the construction of human immune and naive scFv gene libraries.

Designing Human Antibodies by Phage Display

With six approved products and more than 60 candidates in clinical testing, human monoclonal antibody discovery by phage display is well established as a robust and reliable source for the generation of therapeutic antibodies. While a vast diversity of library generation philosophies and selection strategies have been conceived, the power of molecular design offered by controlling the in vitro selection step is still to be recognized by a broader audience outside of the antibody engineering community. Here, we summarize some opportunities and achievements, e.g., the generation of antibodies which could not be generated otherwise, and the design of antibody properties by different panning strategies, including the adjustment of kinetic parameters.

Selection of nanobodies with broad neutralizing potential against primary HIV-1 strains using soluble subtype C gp140 envelope trimers

Broadly neutralizing antibodies (bnAbs) against HIV-1 protect from infection and reduce viral load upon therapeutic applications. However no vaccine was able so far to induce bnAbs demanding their expensive biotechnological production. For clinical applications, nanobodies (VHH) derived from heavy chain only antibodies from Camelidae, may be better suited due to their small size, high solubility/stability and extensive homology to human VH3 genes. Here we selected broadly neutralizing nanobodies by phage display after immunization of dromedaries with different soluble trimeric envelope proteins derived from HIV-1 subtype C. We identified 25 distinct VHH families binding trimeric Env, of which 6 neutralized heterologous primary isolates of various HIV-1 subtypes in a standardized in vitro neutralization assay. The complementary neutralization pattern of two selected VHHs in combination covers 19 out of 21 HIV-1 strains from a standardized panel of epidemiologically relevant HIV-1 subtypes. The CD4 binding site was preferentially targeted by the broadly neutralizing VHHs as determined by competition ELISAs and 3D models of VHH-Env complexes derived from negative stain electron microscopy. The nanobodies identified here are excellent candidates for further preclinical/clinical development for prophylactic and therapeutic applications due to their potency and their complementary neutralization patterns covering the majority of epidemiologically relevant HIV-1 subtypes.

Immune Human Antibody Libraries for Infectious Diseases

The incident of two children in Europe who died of diphtheria due to a shortage of anti-toxin drugs has highlighted the need for alternative anti-toxins. Historically, antiserum produced from immunised horses have been used to treat diphtheria. Despite the potential of antiserum, the economical and medial concerns associated with the use of animal antiserum has led to its slow market demise. Over the years, new and emerging infectious diseases have grown to be a major global health threat. The emergence of drug-resistant superbugs has also pushed the boundaries of available therapeutics to deal with new infectious diseases. Antibodies have emerged as a possible alternative to combat the continuous onslaught of various infectious agents. The isolation of antibodies against pathogens of infectious diseases isolated from immune libraries utilising phage display has yielded promising results in terms of affinities and neutralizing activities. This chapter focuses on the concept of immune antibody libraries and highlights the application of immune antibody libraries to generate antibodies for various infectious diseases.

Phage display-derived human antibodies in clinical development and therapy

Over the last 3 decades, monoclonal antibodies have become the most important class of therapeutic biologicals on the market. Development of therapeutic antibodies was accelerated by recombinant DNA technologies, which allowed the humanization of murine monoclonal antibodies to make them more similar to those of the human body and suitable for a broad range of chronic diseases like cancer and autoimmune diseases. In the early 1990s in vitro antibody selection technologies were developed that enabled the discovery of “fully” human antibodies with potentially superior clinical efficacy and lowest immunogenicity.

Antibody phage display is the first and most widely used of the in vitro selection technologies. It has proven to be a robust, versatile platform technology for the discovery of human antibodies and a powerful engineering tool to improve antibody properties. As of the beginning of 2016, 6 human antibodies discovered or further developed by phage display were approved for therapy. In 2002, adalimumab (Humira®) became the first phage display-derived antibody granted a marketing approval. Humira® was also the first approved human antibody, and it is currently the best-selling antibody drug on the market. Numerous phage display-derived antibodies are currently under advanced clinical investigation, and, despite the availability of other technologies such as human antibody-producing transgenic mice, phage display has not lost its importance for the discovery and engineering of therapeutic antibodies.

Here, we provide a comprehensive overview about phage display-derived antibodies that are approved for therapy or in clinical development. A selection of these antibodies is described in more detail to demonstrate different aspects of the phage display technology and its development over the last 25 years.

Recombinant antibodies for diagnostics and therapy against pathogens and toxins generated by phage display

Antibodies are valuable molecules for the diagnostic and treatment of diseases caused by pathogens and toxins. Traditionally, these antibodies are generated by hybridoma technology. An alternative to hybridoma technology is the use of antibody phage display to generate recombinant antibodies. This in vitro technology circumvents the limitations of the immune system and allows—in theory—the generation of antibodies against all conceivable molecules. Phage display technology enables obtaining human antibodies from naïve antibody gene libraries when either patients are not available or immunization is not ethically feasible. On the other hand, if patients or immunized/infected animals are available, it is common to construct immune phage display libraries to select in vivo affinity‐matured antibodies. Because the phage packaged DNA sequence encoding the antibodies is directly available, the antibodies can be smoothly engineered according to the requirements of the final application. In this review, an overview of phage display derived recombinant antibodies against bacterial, viral, and eukaryotic pathogens as well as toxins for diagnostics and therapy is given.

Generation of Recombinant Antibodies Against Toxins and Viruses by Phage Display for Diagnostics and Therapy

Antibody phage display is an in vitro technology to generate recombinant antibodies. In particular for pathogens like viruses or toxins, antibody phage display is an alternative to hybridoma technology, since it circumvents the limitations of the immune system. Phage display allows the generation of human antibodies from naive antibody gene libraries when either immunized patients are not available or immunization is not ethically feasible. This technology also allows the construction of immune libraries to select in vivo affinity matured antibodies if immunized patients or animals are available.In this review, we describe the generation of human and human-like antibodies from naive antibody gene libraries and antibodies from immune antibody gene libraries. Furthermore, we give an overview about phage display derived recombinant antibodies against viruses and toxins for diagnostics and therapy.

Selection of Recombinant Human Antibodies

Since the development of therapeutic antibodies the demand of recombinant human antibodies is steadily increasing. Traditionally, therapeutic antibodies were generated by immunization of rat or mice, the generation of hybridoma clones, cloning of the antibody genes and subsequent humanization and engineering of the lead candidates. In the last few years, techniques were developed that use transgenic animals with a human antibody gene repertoire. Here, modern recombinant DNA technologies can be combined with well established immunization and hybridoma technologies to generate already affinity maturated human antibodies. An alternative are in vitro technologies which enabled the generation of fully human antibodies from antibody gene libraries that even exceed the human antibody repertoire. Specific antibodies can be isolated from these libraries in a very short time and therefore reduce the development time of an antibody drug at a very early stage.In this review, we describe different technologies that are currently used for the in vitro and in vivo generation of human antibodies.

A Novel Dual Expression Platform for High Throughput Functional Screening of Phage Libraries in Product like Format

High throughput screenings of single chain Fv (scFv) antibody phage display libraries are currently done as soluble scFvs produced in E.coli. Due to endotoxin contaminations from bacterial cells these preparations cannot be reliably used in mammalian cell based assays. The monovalent nature and lack of Fc in soluble scFvs prevent functional assays that are dependent on target cross linking and/or Fc functions. A convenient approach is to convert scFvs into scFv.Fc fusion proteins and express them in mammalian cell lines for screening. This approach is low throughput and is only taken after primary screening of monovalent scFvs that are expressed in bacteria. There is no platform at present that combines the benefits of both bacterial and mammalian expression system for screening phage library output. We have, therefore, developed a novel dual expression vector, called pSplice, which can be used to express scFv.Fc fusion proteins both in E.coli and mammalian cell lines. The hallmark of the vector is an engineered intron which houses the bacterial promoter and signal peptide for expression and secretion of scFv.Fc in E.coli. When the vector is transfected into a mammalian cell line, the intron is efficiently spliced out resulting in a functional operon for expression and secretion of the scFv.Fc fusion protein into the culture medium. By applying basic knowledge of mammalian introns and splisosome, we designed this vector to enable screening of phage libraries in a product like format. Like IgG, the scFv.Fc fusion protein is bi-valent for the antigen and possesses Fc effector functions. Expression in E.coli maintains the speed of the bacterial expression platform and is used to triage clones based on binding and other assays that are not sensitive to endotoxin. Triaged clones are then expressed in a mammalian cell line without the need for any additional cloning steps. Conditioned media from the mammalian cell line containing the fusion proteins are then used for different types of cell based assays. Thus this system retains the speed of the current screening system for phage libraries and adds additional functionality to it.

Generation and analysis of the improved human HAL9/10 antibody phage display libraries

BACKGROUND

Antibody phage display is a proven key technology that allows the generation of human antibodies for diagnostics and therapy. From naive antibody gene libraries - in theory - antibodies against any target can be selected. Here we describe the design, construction and characterization of an optimized antibody phage display library.

RESULTS

The naive antibody gene libraries HAL9 and HAL10, with a combined theoretical diversity of 1.5×10(10) independent clones, were constructed from 98 healthy donors using improved phage display vectors. In detail, most common phagemids employed for antibody phage display are using a combined His/Myc tag for detection and purification. We show that changing the tag order to Myc/His improved the production of soluble antibodies, but did not affect antibody phage display. For several published antibody libraries, the selected number of kappa scFvs were lower compared to lambda scFvs, probably due to a lower kappa scFv or Fab expression rate. Deletion of a phenylalanine at the end of the CL linker sequence in our new phagemid design increased scFv production rate and frequency of selected kappa antibodies significantly. The HAL libraries and 834 antibodies selected against 121 targets were analyzed regarding the used germline V-genes, used V-gene combinations and CDR-H3/-L3 length and composition. The amino acid diversity and distribution in the CDR-H3 of the initial library was retrieved in the CDR-H3 of selected antibodies showing that all CDR-H3 amino acids occurring in the human antibody repertoire can be functionally used and is not biased by E. coli expression or phage selection. Further, the data underline the importance of CDR length variations.

CONCLUSION

The highly diverse universal antibody gene libraries HAL9/10 were constructed using an optimized scFv phagemid vector design. Analysis of selected antibodies revealed that the complete amino acid diversity in the CDR-H3 was also found in selected scFvs showing the functionality of the naive CDR-H3 diversity.