Evaluation of PDL1 positive cancer cell-specific binding activity of recombinant anti-PDL1 scFv

Programmed cell death-ligand 1 (PDL1) is a transmembrane protein that is characterized as an immune regulatory molecule. We recently developed a recombinant single-chain fragment of variable domain (scFv) against PDL1, which showed high binding efficiency to purified recombinant PDL1 protein. However, at that time, proof-of-concept data for the effect of scFv using PDL1-expressing cells was lacking. In this study, we conducted two kinds of cell-based immunoassays, western blotting and enzyme-linked immunosorbent assay, using anti-PDL1 scFv. The results indicate that scFv can selectively and sensitively detect PDL1 from PDL1 positive human cancer cell lines. Our findings suggest that scFv could be used as a potential PDL1 inhibitor agent and probe for cell-based immunoassays to detect PDL1.

Development and characterization of phospho-ubiquitin antibodies to monitor PINK1-PRKN signaling in cells and tissue

The selective removal of dysfunctional mitochondria, a process termed mitophagy, is critical for cellular health and impairments have been linked to aging, Parkinson disease, and other neurodegenerative conditions. A central mitophagy pathway is orchestrated by the ubiquitin (Ub) kinase PINK1 together with the E3 Ub ligase PRKN/Parkin. The decoration of damaged mitochondrial domains with phosphorylated Ub (p-S65-Ub) mediates their elimination though the autophagy system. As such p-S65-Ub has emerged as a highly specific and quantitative marker of mitochondrial damage with significant disease relevance. Existing p-S65-Ub antibodies have been successfully employed as research tools in a range of applications including western blot, immunocytochemistry, immunohistochemistry, and ELISA. However, physiological levels of p-S65-Ub in the absence of exogenous stress are very low, therefore difficult to detect and require reliable and ultrasensitive methods. Here we generated and characterized a collection of novel recombinant, rabbit monoclonal p-S65-Ub antibodies with high specificity and affinity in certain applications that allow the field to better understand the molecular mechanisms and disease relevance of PINK1-PRKN signaling. These antibodies may also serve as novel diagnostic or prognostic tools to monitor mitochondrial damage in various clinical and pathological specimens.

A strong case for third-party testing

A strategy to identify high-quality commercially available antibodies for research reveals extensive use of non-specific antibodies and offers solutions for future large-scale testing.

Generation of an Ovomucoid-Immune scFv Library for the Development of Novel Immunoassays in Hen's Egg Detection

Hen's egg allergy is the second most common food allergy among infants and young children. The possible presence of undeclared eggs in foods poses a significant risk to sensitized individuals. Therefore, reliable egg allergen detection methods are needed to ensure compliance with food labeling and improve consumer protection. This work describes for the first time the application of phage display technology for the generation of a recombinant antibody aimed at the specific detection of hen's ovomucoid. First, a single-chain variable fragment (scFv) library was constructed from mRNA isolated from the spleen of a rabbit immunized with ovomucoid. After rounds of biopanning, four binding clones were isolated and characterized. Based on the best ovomucoid-binding candidate SR-G1, an indirect phage enzyme-linked immunosorbent assay (phage-ELISA) was developed, reaching limits of detection and quantitation of 43 and 79 ng/mL of ovomucoid, respectively. The developed ELISA was applied to the analysis of a wide variety of food products, obtaining a good correlation with a commercial egg detection assay used as a reference. Finally, in silico modeling of the antigen-antibody complex revealed that the main interactions most likely occur between the scFv heavy chain and the ovomucoid domain-III, the most immunogenic region of this allergen.

Generation of a Recombinant scFv against Deoxycholic Acid and Its Conversion to a Quenchbody for One-Step Immunoassay

Development of a rapid detection method for deoxycholic acid (DCA) is crucial for its diagnosis in the early stages of inflammation and cancer. In this study, we expressed a soluble recombinant anti-DCA single-chain variable fragment (scFv) in Escherichia coli. To convert scFv into a Quenchbody (Q-body), we labeled scFv using commercially available maleimide-linked fluorophores. The TAMRA-C5-maleimide-conjugated Q-body showed the highest response within a few minutes of DCA addition, indicating its applicability as a wash-free immunoassay probe for onsite DCA detection.

Targeted delivery of oral vaccine antigens to aminopeptidase N protects pigs against pathogenic E. coli challenge infection

Oral subunit vaccines are an interesting alternative strategy to traditional live-attenuated or inactivated vaccines for conferring protection against gut pathogens. Despite being safer and more cost-effective, the development of oral subunit vaccines remains challenging due to barriers imposed by the gastrointestinal tract, such as digestive enzymes, a tolerogenic immune environment and the inability of larger proteins to cross the epithelial barrier. Recent advances have focused on overcoming these barriers by using potent mucosal adjuvants or pH-responsive delivery vehicles to protect antigens from degradation and promote their release in the intestinal lumen. A promising approach to allow vaccine antigens to pass the epithelial barrier is by their targeting towards aminopeptidase N (APN; CD13), an abundant membrane protein present on small intestinal enterocytes. APN is a peptidase involved in digestion, but also a receptor for several enteric pathogens. In addition, upon antibody-mediated crosslinking, APN facilitated the transport of antibody-antigen fusion constructs across the gut epithelium. This epithelial transport resulted in antigen-specific immune responses. Here, we present evidence that oral administration of APN-specific antibody-antigen fusion constructs comprising the porcine IgA Fc-domain and the FedF tipadhesin of F18-fimbriated E. coli elicited both mucosal and systemic immune responses and provided at least partial protection to piglets against a subsequent challenge infection with an F18-fimbriated STEC strain. Altogether, these findings will contribute to the further development of new oral subunit vaccines and provide a first proof-of-concept for the protective efficacy of APN-targeted vaccine antigens.

Improving African Swine Fever Surveillance Using Fluorescent Rapid Tests

African swine fever (ASF) is a viral disease of swine with a huge impact due to its high mortality. Lately, the disease has actively spread around the world, affecting new areas from which it had been eradicated long ago. To date, ASF control is carried out by the implementation of strict biosecurity measures such as the early identification of infected animals. In this work, two fluorescent rapid tests were developed to improve the sensitivity of point-of-care diagnosis of ASF. For antigen (Ag) detection in blood, a double-antibody sandwich fluorescent lateral flow assay (LFA) was developed, employing a newly developed recombinant antibody to the VP72 of the virus. To complement the diagnosis, a double-recognition fluorescent LFA was developed using the VP72 for the detection of specific antibodies (Ab) in sera or blood. Both assays statistically improved the detection of the disease when compared to the commercial colorimetric assays INgezim^® ASFV CROM Ag and INgezim^® PPA CROM Anticuerpo, respectively, with higher statistical significance between 11 and 39 days post-infection. From the observation of results, it can be concluded that the combination of both Ag-LFA and Ab-LFA assays would facilitate the identification of infected animals, regardless of post-infection time.

A Novel Rabbit Anti-Myoglobin Monoclonal Antibody's Potential Application in Rhabdomyolysis Associated Acute Kidney Injury

Myoglobin (Mb) is the main constituent of vertebrate skeletal muscle and myocardium and plays an essential role in oxygen binding, storage, transport, and earliest disease diagnosis. This study focuses on preparing the novel recombinant rabbit anti-Mb monoclonal antibody and applying it to a diagnosis of Mb deposition in rhabdomyolysis-associated acute kidney injury (RM-AKI). The full-length coding sequence of rat Mb was cloned and expressed, and the high-quality and titer rabbit anti-Mb polyclonal antibodies were produced by the immunogen His-Mb fusion protein. A new hybridoma cell was obtained by hybridoma screening technology. With the help of DNA sequencing and a molecular clonal, anti-Mb monoclonal antibody heavy and light chains expression plasmid was constructed. Finally, the recombinant rabbit anti-Mb monoclonal antibody with extraordinarily high affinity (K_D = 1.21 pM) was obtained. Meanwhile, it had broad species reactivity (mouse, rat, human, and horse) and good tissue specificity (skeletal muscle and myocardium). It also had a very good performance in western blotting, immunohistochemistry, and immunofluorescence assay to detect the Mb level in the kidney, myocardium, and skeletal muscle of RM-AKI. This study will be significantly helpful for Mb-associated disease diagnosis, and pathogenesis exploration, and further may act as a neutralizing antibody for disease treatment.

Design of a Diagnostic Immunoassay for Aflatoxin M1 Based on a Plant-Produced Antibody

A new green competitive ELISA for aflatoxin M1 quantification in raw milk was developed. This diagnostic tool is based on an anti AFM1 mAb produced by plant molecular farming in alternative to classical systems. Our assay, showing an IC₅₀ below 25 ng/L, fits with the requirements of EU legislation limits for AFM1 (50 ng/L). Optimal accuracy was achieved in correspondence of the decision levels (25 and 50 ng/L), and the assay enabled AFM1 quantification in the range 5-110 ng/L, with limit of detection 3 ng/L. Moreover, to evaluate a real applicability in diagnostics, raw milk-spiked samples were analysed, achieving satisfactory recovery rates of AFM1. In conclusion, an efficient and ready-to-use diagnostic assay for the quantification of aflatoxin M1 in milk, based on a plant-produced recombinant mAb, has been successfully developed.

Rapid-format recombinant antibody-based methods for the diagnosis of Clostridioides difficile infection: Recent advances and perspectives

Clostridioides difficile, the most common cause of nosocomial diarrhea, has been continuously reported as a worldwide problem in healthcare settings. Additionally, the emergence of hypervirulent strains of C. difficile has always been a critical concern and led to continuous efforts to develop more accurate diagnostic methods for detection of this recalcitrant pathogen. Currently, the diagnosis of C. difficile infection (CDI) is based on clinical manifestations and laboratory tests for detecting the bacterium and/or its toxins, which exhibit varied sensitivity and specificity. In this regard, development of rapid diagnostic techniques based on antibodies has demonstrated promising results in both research and clinical environments. Recently, application of recombinant antibody (rAb) technologies like phage display has provided a faster and more cost-effective approach for antibody production. The application of rAbs for developing ultrasensitive diagnostic tools ranging from immunoassays to immunosensors, has allowed the researchers to introduce new platforms with high sensitivity and specificity. Additionally, DNA encoding antibodies are directly accessible in these approaches, which enables the application of antibody engineering to increase their sensitivity and specificity. Here, we review the latest studies about the antibody-based ultrasensitive diagnostic platforms for detection of C. difficile bacteria, with an emphasis on rAb technologies.

Development of a Novel Anti-EpCAM Monoclonal Antibody for Various Applications

The epithelial cell adhesion molecule (EpCAM) is a cell surface glycoprotein, which is widely expressed on normal and cancer cells. EpCAM is involved in cell adhesion, proliferation, survival, stemness, and tumorigenesis. Therefore, EpCAM is thought to be a promising target for cancer diagnosis and therapy. In this study, we established anti-EpCAM monoclonal antibodies (mAbs) using the Cell-Based Immunization and Screening (CBIS) method. We characterized them using flow cytometry, Western blotting, and immunohistochemistry. One of the established recombinant anti-EpCAM mAbs, recEpMab-37 (mouse IgG₁, kappa), reacted with EpCAM-overexpressed Chinese hamster ovary-K1 cells (CHO/EpCAM) or a colorectal carcinoma cell line (Caco-2). In contrast, recEpMab-37 did not react with EpCAM-knocked out Caco-2 cells. The K_D of recEpMab-37 for CHO/EpCAM and Caco-2 was 2.0 × 10⁻⁸ M and 3.2 × 10⁻⁸ M, respectively. We observed that EpCAM amino acids between 144 to 164 are involved in recEpMab-37 binding. In Western blot analysis, recEpMab-37 detected the EpCAM of CHO/EpCAM and Caco-2 cells. Furthermore, recEpMab-37 could stain formalin-fixed paraffin-embedded colorectal carcinoma tissues by immunohistochemistry. Taken together, recEpMab-37, established by the CBIS method, is useful for detecting EpCAM in various applications.

In vitro evolution of myc-tag antibodies: in-depth specificity and affinity analysis of Myc1-9E10 and Hyper-Myc

One of the most widely used epitope tags is the myc-tag, recognized by the anti-c-Myc hybridoma antibody Myc1-9E10. Combining error-prone PCR, DNA shuffling and phage display, we generated an anti-c-Myc antibody variant (Hyper-Myc) with monovalent affinity improved to 18 nM and thermal stability increased by 37%. Quantification of capillary immunoblots and by flow cytometry demonstrated improved antigen detection by Hyper-Myc. Further, three different species variants of this antibody were generated to allow the use of either anti-human, anti-mouse or anti-rabbit Fc secondary antibodies for detection. We characterized the specificity of both antibodies in depth: individual amino acid exchange mapping demonstrated that the recognized epitope was not changed by the in vitro evolution process. A laser printed array of 29,127 different epitopes representing all human linear B-cell epitopes of the Immune Epitope Database allowing to chart unwanted reactivities with mimotopes showed these to be very low for both antibodies and not increased for Hyper-Myc despite its improved affinity. The very low background reactivity of Hyper-Myc was confirmed by staining of myc-tag transgenic zebrafish whole mounts. Hyper-Myc retains the very high specificity of Myc1-9E10 while allowing myc-tag detection at lower concentrations and with either anti-mouse, anti-rabbit or anti human secondary antibodies.

Investigating Alternative Container Formats for Lyophilization of Biological Materials Using Diphtheria Antitoxin Monoclonal Antibody as a Model Molecule

When preparing biological reference materials, the stability of the lyophilized product is critical for long-term storage, particularly in order to meet WHO International Standards, which are not assigned expiry dates but are expected to be in use for several decades. Glass ampoules are typically used by the National Institute for Biological Standards and Control (NIBSC) for the lyophilization of biological materials. More recently, a clear need has arisen for the filling of smaller volumes, for which ampoules may not be optimal. We investigated the use of plastic microtubes as an alternative container for small volume fills. In this study, a recombinant diphtheria antitoxin monoclonal antibody (DATMAB) was used as a model molecule to investigate the suitability of plastic microtubes for filling small volumes. The stability and quality of the dried material was assessed after an accelerated degradation study using a toxin neutralization test and size exclusion HPLC. While microtubes have shown some promise in the past for use in the lyophilization of some biological materials, issues with stability may arise when more labile materials are freeze-dried. We demonstrate here that the microtube format is unsuitable for ensuring the stability of this monoclonal antibody.

Shelf-Life Extension of Fc-Fused Single Chain Fragment Variable Antibodies by Lyophilization

Generation of sequence defined antibodies from universal libraries by phage display has been established over the past three decades as a robust method to cope with the increasing market demand in therapy, diagnostics and research. For applications requiring the bivalent antigen binding and an Fc part for detection, phage display generated single chain Fv (scFv) antibody fragments can rapidly be genetically fused to the Fc moiety of an IgG for the production in eukaryotic cells of antibodies with IgG-like properties. In contrast to conversion of scFv into IgG format, the conversion to scFv-Fc requires only a single cloning step, and provides significantly higher yields in transient cell culture production than IgG. ScFv-Fcs can be effective as neutralizing antibodies in vivo against a panel of pathogens and toxins. However, different scFv fragments are more heterologous in respect of stability than Fab fragments. While some scFv fragments can be made extremely stable, this may change due to few mutations, and is not predictable from the sequence of a newly selected antibody. To mitigate the necessity to assess the stability for every scFv-Fc antibody, we developed a generic lyophilization protocol to improve their shelf life. We compared long-term stability and binding activity of phage display-derived antibodies in the scFv-Fc and IgG format, either stored in liquid or lyophilized state. Conversion of scFv-Fcs into the full IgG format reduced protein degradation and aggregation, but in some cases compromised binding activity. Comparably to IgG conversion, lyophilization of scFv-Fc resulted in the preservation of the antibodies' initial properties after storage, without any drop in affinity for any of the tested antibody clones.

Characterization of an In Vivo Neutralizing Anti-Vaccinia Virus D8 Single-Chain Fragment Variable (scFv) from a Human Anti-Vaccinia Virus-Specific Recombinant Library

A panel of potent neutralizing antibodies are protective against orthopoxvirus (OPXV) infections. For the development of OPXV-specific recombinant human single-chain antibodies (scFvs), the IgG repertoire of four vaccinated donors was amplified from peripheral B-lymphocytes. The resulting library consisted of ≥4 × 10⁸ independent colonies. The immuno-screening against vaccinia virus (VACV) Elstree revealed a predominant selection of scFv clones specifically binding to the D8 protein. The scFv-1.2.2.H9 was engineered into larger human scFv-Fc-1.2.2.H9 and IgG1-1.2.2.H9 formats to improve the binding affinity and to add effector functions within the human immune response. Similar binding kinetics were calculated for scFv-1.2.2.H9 and scFv-Fc-1.2.2.H9 (1.61 nM and 7.685 nM, respectively), whereas, for IgG1-1.2.2.H9, the Michaelis-Menten kinetics revealed an increased affinity of 43.8 pM. None of the purified recombinant 1.2.2.H9 formats were able to neutralize VACV Elstree in vitro. After addition of 1% human complement, the neutralization of ≥50% of VACV Elstree was achieved with 0.0776 µM scFv-Fc-1.2.2.H9 and 0.01324 µM IgG1-1.2.2.H9, respectively. In an in vivo passive immunization NMRI mouse model, 100 µg purified scFv-1.2.2.H9 and the IgG1-1.2.2.H9 partially protected against the challenge with 4 LD₅₀ VACV Munich 1, as 3/6 mice survived. In contrast, in the scFv-Fc-1.2.2.H9 group, only one mouse survived the challenge.

Antibody-Mediated Targeting of Antigens to Intestinal Aminopeptidase N Elicits Gut IgA Responses in Pigs

Many pathogens enter the host via the gut, causing disease in animals and humans. A robust intestinal immune response is necessary to protect the host from these gut pathogens. Despite being best suited for eliciting intestinal immunity, oral vaccination remains a challenge due to the gastrointestinal environment, a poor uptake of vaccine antigens by the intestinal epithelium and the tolerogenic environment pervading the gut. To improve uptake, efforts have focused on targeting antigens towards the gut mucosa. An interesting target is aminopeptidase N (APN), a conserved membrane protein present on small intestinal epithelial cells shown to mediate epithelial transcytosis. Here, we aimed to further optimize this oral vaccination strategy in a large animal model. Porcine APN-specific monoclonal antibodies were generated and the most promising candidate in terms of epithelial transcytosis was selected to generate antibody fusion constructs, comprising a murine IgG1 or porcine IgA backbone and a low immunogenic antigen: the F18-fimbriated E. coli tip adhesin FedF. Upon oral delivery of these recombinant antibodies in piglets, both mucosal and systemic immune responses were elicited. The presence of the FedF antigen however appeared to reduce these immune responses. Further analysis showed that F18 fimbriae were able to disrupt the antigen presenting capacity of intestinal antigen presenting cells, implying potential tolerogenic effects of FedF. Altogether, these findings show that targeted delivery of molecules to epithelial aminopeptidase N results in their transcytosis and delivery to the gut immune systems. The results provide a solid foundation for the development of oral subunit vaccines to protect against gut pathogens.

Production of a Soluble Recombinant Antibody Fragment against MMP9 Using Escherichia coli

Matrix metalloproteinase 9 (MMP9) is involved in several aspects of the pathology of cancer, including invasion, metastasis, and angiogenesis. In this study, we expressed a recombinant scFv-type anti-MMP9 antibody in soluble form using Escherichia coli, purified it, and confirmed its antigen-binding ability. The convenient, rapid, inexpressive system used in this study for producing recombinant antibody fragments needs only five days, and thus can be used for the efficient production of scFv against MMP9, which can be used in a range of applications and industrial fields, including diagnosis and treatment of inflammatory and cancer-related diseases.

Antibody therapy against antibiotic-resistant diarrheagenic Escherichia coli: a systematic review

Over four billion episodes of diarrhea occur annually in developing countries with diarrheagenic Escherichia coli (DEC) outbreaks also being reported, until now bacterial diarrhea is conventionally addressed by the antibiotic treatment regimes. In recent decades, the emergence of antimicrobial-resistant strains has become a major obstacle in diarrheal treatment; hence, novel and ideal therapeutics are needed. Notably, 80% of DEC is resistant to first-class antibiotics. Among the existing strategies, passive immunization is considered as an alternative to combat drug-resistant bacteria. Antibodies specific to an antigen can be used for prophylactic and therapeutic purposes. In this review, we have systematically discussed the effect of passive immunotherapy to combat DEC and explored the types and advancements in antibodies used against antibiotic-resistant DEC.

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.

Effects of a Multimerized Recombinant Autoantibody Against Amyloid-β

Alzheimer's disease (AD) is the most common neurodegenerative disease; thus, the search for a cure or causal therapy has become necessary. Despite intense research on this topic in recent decades, there is no curative therapy up today, and also no disease-modifying treatment has been approved. As promising approach passive immunization strategies have thereby come forth. In this study, we focused on naturally occurring autoantibodies against the AD-associated peptide amyloid-β. These antibodies have already reported to show beneficial functions in vitro and in mouse models of AD. However, their availability is limited due to their low abundance in peripheral blood. In a recent study, we were able to generate four recombinant antibodies against amyloid-β. In the present study, we tested these antibodies in ELISA and SPR assays for their binding behavior and by aggregation- and phagocytosis assays as functional evidences to characterize their amyloid-β-related neutralizing and clearance abilities. Further ex vivo assay on organotypic hippocampal slice cultures gave first evidence of microglial activation and inflammatory features. The tested recombinant antibodies in IgG format showed, in comparison to naturally occurring autoantibodies against amyloid-β, insufficient binding capacities and -affinities. However, after conversion of one antibody into a single chain format multimerization of the scFv-Fc construct, the investigated binding capacity and -affinity showed improvements. Further functional assays predict a protective effect of this antibody. Although, all four recombinant antibodies showed binding to amyloid-β, promising features were only detectable after conversion into a multimeric format. The multimeric scFv-Fc antibody exhibited thereby strong impact on amyloid-β clearance and inhibition of oligomerization.

Inhibitory Monoclonal Antibodies and Their Recombinant Derivatives Targeting Surface-Exposed Carbonic Anhydrase XII on Cancer Cells

Monoclonal and recombinant antibodies are widely used for the diagnostics and therapy of cancer. They are generated to interact with cell surface proteins which are usually involved in the development and progression of cancer. Carbonic anhydrase XII (CA XII) contributes to the survival of tumors under hypoxic conditions thus is considered a candidate target for antibody-based therapy. In this study, we have generated a novel collection of monoclonal antibodies (MAbs) against the recombinant extracellular domain of CA XII produced in HEK-293 cells. Eighteen out of 24 MAbs were reactive with cellular CA XII on the surface of live kidney and lung cancer cells as determined by flow cytometry. One MAb 14D6 also inhibited the enzymatic activity of recombinant CA XII as measured by the stopped-flow assay. MAb 14D6 showed the migrastatic effect on human lung carcinoma A549 and renal carcinoma A498 cell lines in a ‘wound healing’ assay. It did not reduce the growth of multicellular lung and renal cancer spheroids but reduced the cell viability by the ATP Bioluminescence assay. Epitope mapping revealed the surface-exposed amino acid sequence (35-FGPDGENS-42) close to the catalytic center of CA XII recognized by the MAb 14D6. The variable regions of the heavy and light chains of MAb 14D6 were sequenced and their complementarity-determining regions were defined. The obtained variable sequences were used to generate recombinant antibodies in two formats: single-chain fragment variable (scFv) expressed in E. coli and scFv fused to human IgG1 Fc fragment (scFv-Fc) expressed in Chinese Hamster Ovary (CHO) cells. Both recombinant antibodies maintained the same specificity for CA XII as the parental MAb 14D6. The novel antibodies may represent promising tools for CA XII-related cancer research and immunotherapy.

Phage Displayed Domain Antibodies (dAb) for Detection of Allergenic Pistachio Proteins in Foods

Pistachio nuts (Pistacia vera) have been consumed by past and present-day civilizations because of their organoleptic characteristics and potential health benefits. However, they can also produce moderate to severe IgE-mediated reactions in allergic individuals. In this work, we report the isolation of the first recombinant antibodies against pistachio nut, produced without animal immunization, to be used in immunoassays for detection of allergenic pistachio in food products. Several phage display biopanning strategies were evaluated to screen the human-based domain antibody library (dAb) in search for pistachio-specific probes. The clone producing the PVF4 phage-dAb was finally selected, and it does not cross-react with cashew despite the phylogenetic proximity with pistachio. Western blot and matrix-assisted laser desorption/ionization tandem mass spectrometry (MALDI-TOF/TOF) analysis demonstrated that this clone recognised a unique band of ∼22 kDa related to the basic subunit of pistachio 11S globulin (allergen Pis v 2). The PVF4 phage-dAb allowed detection of pistachio in a food matrix with a limit of detection (LOD) of 3983 mg kg⁻¹ in an indirect phage-enzyme-linked immunosorbent assay (ELISA). The ELISA method developed was used to assess applicability of the PVF4 phage-dAb for analysis of 77 commercial food products.

A phage-displayed single-chain Fab library optimized for rapid production of single-chain IgGs

Phage-displayed synthetic antibody (Ab) repertoires have become a major source of affinity reagents for basic and clinical research. Specific Abs identified from such libraries are often screened as fragments antigen binding (Fabs) produced in bacteria, and those with desired biochemical characteristics are reformatted for production as full-length immunoglobulin G (IgG) in mammalian cells. The conversion of Fabs to IgGs is a cumbersome and often rate-limiting step in the development of Abs. Moreover, biochemical properties required for lead IgG development are not always shared by the Fabs, and these issues are not uncovered until a significant effort has been spent on Abs that ultimately will not be useful. Thus, there is a need for simple and rapid techniques to convert phage-displayed Fabs to IgGs at an early stage of the Ab screening process. We report the generation of a highly diverse phage-displayed synthetic single-chain Fab (scFab) library, in which the light and heavy chains were tethered with an optimized linker. Following selection, pools of scFabs were converted to single-chain IgGs (scIgGs) en masse, enabling facile screening of hundreds of phage-derived scIgGs. We show that this approach can be used to rapidly screen for and select scIgGs that target cell-surface receptors, and scIgGs behave the same as conventional IgGs.

Camel nanobodies: Promising molecular tools against leishmaniasis

AIM

To characterize several anti-Leishmania tropica nanobodies and to investigate their effect on Leishmania infection.

METHODS

Several immunological tests were implied to characterize five different (as confirmed by sequencing) anti-L tropica nanobodies (NbLt05, NbLt06, NbLt14, NbLt24 and NbLt36) against parasite lysates or intact cells from different stages, promastigotes and amastigotes. Direct inhibitory effect of these nanobodies on parasite infection cycle on macrophages was tested in cell culture.

RESULTS

All the five nanobodies (with distinguished characteristics) were more specific to L tropica than to L major, but could equally recognize the lysate and the outer surface of the intact cells from the two main stages of the parasite. Nanobodies recognized several leishmania antigens (majorly between 75 and 63 kDa), and their proteinaceous nature was confirmed. Because of its role in leishmania life cycle, gp63 was considered a potential antigen candidate for nanobodies, and bioinformatics predicted such interaction. All nanobodies have a negative effect on the infectivity of L tropica, as they decreased the number of infected macrophages and the amastigotes inside those macrophages.

CONCLUSION

Such anti-leishmania nanobodies, with outstanding characteristics and important target, can be of great use in the development of promising treatment strategies against leishmaniasis.

Understanding microcystin-LR antibody binding interactions using in silico docking and in vitro mutagenesis

Microcystins (MCs) are a group of highly potent cyanotoxins that are becoming more widely distributed due to increased global temperatures and climate change. Microcystin-leucine-arginine (MC-LR) is the most potent and most common variant, with a guideline limit of 1 μg/l in drinking water. We previously developed a novel avian single-chain fragment variable (scFv), designated 2G1, for use in an optical-planar waveguide detection system for microcystin determination. This current work investigates interactions between 2G1 and MC-LR at the molecular level through modelling with an avian antibody template and molecular docking by AutoDock Vina to identify key amino acid (AA) residues involved. These potential AA interactions were investigated in vitro by targeted mutagenesis, specifically, by alanine scanning mutations. Glutamic acid (E) was found to play a critical role in the 2G1-MC-LR binding interaction, with the heavy chain glutamic acid (E) 102 (H-E102) forming direct bonds with the arginine (R) residue of MC-LR. In addition, alanine mutation of light chain residue aspartic acid 57 (L-D57) led to an improvement in antigen-binding observed using enzyme-linked immunosorbent assay (ELISA), and was confirmed by surface plasmon resonance (SPR). This work will contribute to improving the binding of recombinant anti-MC-LR to its antigen and aid in the development of a higher sensitivity harmful algal toxin diagnostic.

Preparation of a highly specific single chain variable fragment antibody targeting miroestrol and its application in quality control of Pueraria candollei by enzyme-linked immunosorbent assay

INTRODUCTION

Miroestrol is the potent phytoestrogen isolated from White Kwao Krua (Pueraria candollei var. mirifica (Airy Shaw & Suvat.) Niyomdham, a Thai traditional medicinal plant. Nowadays, various health supplementary products featuring White Kwao Krua are available worldwide. A sensitive and rapid analytical method for quantification of miroestrol is necessary for quality control of these products.

OBJECTIVES

To prepare a single-chain variable fragment (scFv) antibody specific to miroestrol and develop a scFv-based enzyme-linked immunosorbent assay (ELISA) for quantitative analysis of miroestrol in plant materials and health supplementary products.

METHODS

A gene encoding anti-miroestrol scFv antibody was constructed and expressed in Escherichia coli SHuffle T7 strain. Anti-miroestrol scFv antibody was characterised and applied to ELISA. The developed scFv-based ELISA method was validated for its sensitivity, specificity, accuracy and precision.

RESULTS

Anti-miroestrol scFv antibody was highly specific to miroestrol. The scFv-based ELISA was applied to determine miroestrol in the range 0.06-7.81 μg/mL, with the limit of quantification of 0.06 μg/mL miroestrol. The accuracy of the assay was validated by its 95.08-103.99% recovery from the spiked miroestrol recovery experiment and in good correlation with the results from the monoclonal antibody-based ELISA. The relative standard deviation of the intra- and inter-assay were less than 6.0%.

CONCLUSION

The developed scFv-based ELISA was sensitive, specific, accurate, and precise for determination of miroestrol and useful for quality control of P. candollei plant raw materials and supplementary products.

Pharmacokinetics of Human Recombinant Anti-Botulinum Toxin Antibodies in Rats

Botulinum neurotoxins (BoNT) are potential biothreat agents due to their high lethality, potency, and ease of distribution, thus the development of antitoxins is a high priority to the US government. This study examined pre-clinical pharmacokinetic studies in rats of four oligoclonal anti-BoNT mAb-based therapeutics (NTM-1631, NTM-1632, NTM-1633, NTM-1634) for five BoNT serotypes (A, B, E, C, and D). NTM-1631, NTM-1632, and NTM-1633 each consist of three IgG1 mAbs, each with a distinct human or humanized variable region which bind to distinct epitopes on BoNT serotype A, B, or E respectively. NTM-1634 consists of four human immunoglobulin G1 (IgG1) mAbs binding BoNT C/D mosaic toxins. The mechanism of these antitoxins requires that three antibodies simultaneously bind toxin to achieve rapid clearance. Rats (total 378) displayed no adverse clinical signs attributed to antibody treatment from any of the antitoxins. Pharmacokinetic evaluation demonstrated that the individual mAbs are slowly eliminated, exhibiting dose-dependent exposure and long elimination half-lives ranging from 6.5 days to 10 days. There were no consistent differences observed between males and females or among the individual antibodies in each formulation in half-life. Anti-drug antibodies (ADA) were observed, as expected for human antibodies administered to rats. The results presented were used to support the clinical investigation of antibody-based botulism antitoxins.

Recombinant Antibodies against Mycolactone

In the past, it has proved challenging to generate antibodies against mycolactone, the primary lipidic toxin A of Mycobacterium ulcerans causing Buruli ulcer, due to its immunosuppressive properties. Here we show that in vitro display, comprising both phage and yeast display, can be used to select antibodies recognizing mycolactone from a large human naïve phage antibody library. Ten different antibodies were isolated, and hundreds more identified by next generation sequencing. These results indicate the value of in vitro display methods to generate antibodies against difficult antigenic targets such as toxins, which cannot be used for immunization unless inactivated by structural modification. The possibility to easily generate anti-mycolactone antibodies is an exciting prospect for the development of rapid and simple diagnostic/detection methods.

Rapid production of a chimeric antibody-antigen fusion protein based on 2A-peptide cleavage and green fluorescent protein expression in CHO cells

To enable large-scale antibody production, the creation of a stable, high producer cell line is essential. This process often takes longer than 6 months using standard limited dilution techniques and is very labor intensive. The use of a tri-cistronic vector expressing green fluorescent protein (GFP) and both antibody chains, separated by a GT2A peptide sequence, allows expression of all proteins under a single promotor in equimolar ratios. By combining the advantages of 2A peptide cleavage and single cell sorting, a chimeric antibody-antigen fusion protein that contained the variable domains of mouse IgG with a porcine IgA constant domain fused to the FedF antigen could be produced in CHO-K1 cells. After transfection, a strong correlation was found between antibody production and GFP expression (r = 0.69) using image analysis of formed monolayer patches. This enables the rapid selection of GFP-positive clones using automated image analysis for the selection of high producer clones. This vector design allowed the rapid selection of high producer clones within a time-frame of 4 weeks after transfection. The highest producing clone had a specific antibody productivity of 2.32 pg/cell/day. Concentrations of 34 mg/L were obtained using shake-flask batch culture. The produced recombinant antibody showed stable expression, binding and minimal degradation. In the future, this antibody will be assessed for its effectiveness as an oral vaccine antigen.

ScFv Improvement Approaches

The most common recombinant antibody format is the single chain fragment variable (scFv) which it contains the complete antigen-binding domains of an intact antibody. ScFv fragments have found vast medical and non-medical applications. Several approaches have been employed to increase the affinity, avidity and structural stability related to these antibody fragments. Most approaches related to scFv improvement have been included in this review.

Efficient Development of Stable Recombinant Chinese Hamster Ovary (rCHO) Cell Lines to Produce Antibodies by Using Dimethyl Sulfoxide (DMSO) in Electroporation

Development of stable rCHO cell lines is still time consuming and labor intensive, although it is a critical step in the commercial development of recombinant antibodies. The current work demonstrates, for the first time, that electroporation of CHO cells with DMSO can enhance stable expression of recombinant antibodies in rCHO cells. Electroporation with DMSO resulted in an average 3.7-fold and 2.8-fold increases in expression levels of aflibercept and pembrolizumab, respectively, in pools of stable rCHO cells. It also resulted in an average of 2.2-fold and 2.6-fold increases in the expression of aflibercept and pembrolizumab, respectively, in single-cell derived rCHO clones. Simple batch cultures of rCHO cell clones with the highest expression produced 1.0 g/l for aflibercept and 1.4 g/l for pembrolizumab without a time-consuming gene amplification process. Electroporation with DMSO also shortened the development of rCHO cell lines to 2-3 months, allowing rapid establishment of stable rCHO cell lines with a desirable expression level antibodies.

Targeting the Post-translational Proteome with Intrabodies

The complexity of the proteome exceeds that of the genome. Post-translational modifications (PTMs) and conformational changes of proteins trigger new molecular interactions whose systematic elucidation is hampered by the lack of specific tools. PTMs are particularly relevant for epigenetic regulation of gene expression; a field of translational interest. However, state-of-the-art inhibitors used in epigenetic studies and therapies target modifier enzymes such as acetylases and deacetylases, rather than a single PTM protein per se. The systematic development of anti-PTM intrabodies, which allow targeting of intracellular proteins in the context of living cells, will help reaching a new level of precision and specificity in the description of epigenetics, paving the way to new therapeutic opportunities.

Development of Neutralizing and Non-neutralizing Antibodies Targeting Known and Novel Epitopes of TcdB of Clostridioides difficile

Clostridioides difficile is the causative bacterium in 15-20% of all antibiotic associated diarrheas. The symptoms associated with C. difficile infection (CDI) are primarily induced by the two large exotoxins TcdA and TcdB. Both toxins enter target cells by receptor-mediated endocytosis. Although different toxin receptors have been identified, it is no valid therapeutic option to prevent receptor endocytosis. Therapeutics, such as neutralizing antibodies, directly targeting both toxins are in development. Interestingly, only the anti-TcdB antibody bezlotoxumab but not the anti-TcdA antibody actoxumab prevented recurrence of CDI in clinical trials. In this work, 31 human antibody fragments against TcdB were selected by antibody phage display from the human naive antibody gene libraries HAL9/10. These antibody fragments were further characterized by in vitro neutralization assays. The epitopes of the neutralizing and non-neutralizing antibody fragments were analyzed by domain mapping, TcdB fragment phage display, and peptide arrays, to identify neutralizing and non-neutralizing epitopes. A new neutralizing epitope within the glucosyltransferase domain of TcdB was identified, providing new insights into the relevance of different toxin regions in respect of neutralization and toxicity.

Development of a fluvoxamine detection system using a Quenchbody, a novel fluorescent biosensor

The misuse of psychotropic drugs intended for medical treatment represents a recent worldwide public health concern. Quenchbody (Q-body) is a novel fluoroimmunosensor that can detect an antigen immediately without additional reagents or washing steps. Here, we describe creating Q-bodies for the detection of the antidepressant fluvoxamine (FLV) and determining optimal conditions to achieve the highest fluorescence intensity (FI). We prepared five Q-bodies with the fluorophore labeled at either the N- or C- terminus and with different linker lengths. Fluorescence was measurable within minutes, indicating the interaction of Q-bodies with FLV. The normalized FI (FI ratio) of the N-terminus labeled Q-body increased approximately 1.5-fold upon FLV addition; Q-bodies labeled at the C-terminus did not significantly increase FI. Among the fluorescence dyes used in this study, Rhodamine 6G labeled Q-body showed the best FI ratio. EC₅₀ values of the N-terminus labeled Q-bodies were similar (23.2-224nM) regardless of linker length or labeling dye. We examined whether the Q-body could be applicable to serum matrix instead of phosphate-buffered saline. The intact serum interfered strongly with the Q-body fluorescence. However, the FI ratios of the Q-body for FLV-spiked serum filtrate, for which proteins were removed by filtration, showed a dose-dependency for detecting FLV levels. Deproteinization, which does not interfere with Q-body fluorescence measurements, is likely necessary to detect serum FLV with high sensitivity. This study demonstrates the potential of Q-body probes as a tool towards developing creative immunoassay applications.

Real-time monitoring of antibody glycosylation site occupancy by in situ Raman spectroscopy during bioreactor CHO cell cultures

The glycosylation of therapeutic monoclonal antibodies (mAbs), a known critical quality attribute, is often greatly modified during the production process by animal cells. It is essential for biopharmaceutical industries to monitor and control this glycosylation. However, current glycosylation characterization techniques involve time- and labor-intensive analyses, often carried out at the end of the culture when the product is already synthesized. This study proposes a novel methodology for real-time monitoring of antibody glycosylation site occupancy using Raman spectroscopy. It was first observed in CHO cell batch culture that when low nutrient concentrations were reached, a decrease in mAb glycosylation was induced, which made it essential to rapidly detect this loss of product quality. By combining in situ Raman spectroscopy with chemometric tools, efficient prediction models were then developed for both glycosylated and nonglycosylated mAbs. By comparing variable importance in projection profiles of the prediction models, it was confirmed that Raman spectroscopy is a powerful method to distinguish extremely similar molecules, despite the high complexity of the culture medium. Finally, the Raman prediction models were used to monitor batch and feed-harvest cultures in situ. For the first time, it was demonstrated that the concentrations of glycosylated and nonglycosylated mAbs could be successfully and simultaneously estimated in real time with high accuracy, including their sudden variations due to medium exchanges. Raman spectroscopy can thus be considered as a promising PAT tool for feedback process control dedicated to on-line optimization of mAb quality. © 2018 American Institute of Chemical Engineers Biotechnol. Prog., 34:486-493, 2018.

Therapeutic targeting in nanomedicine: the future lies in recombinant antibodies

The unique chemical and functional properties of nanoparticles can be harnessed for the delivery of large quantities of various therapeutic biomolecules. Active targeting of nanoparticles by conjugating ligands that bind to target cells strongly facilitates accumulation, internalization into target cells and longer retention at the target site, with consequent enhanced therapeutic effects. Recombinant antibodies with high selectivity and availability for a vast range of targets will dominate the future. In this review, we systematically outline the tremendous progress in the conjugation of antibodies to nanoparticles and the clear advantages that recombinant antibodies offer in the therapeutic targeting of nanoparticles. The demonstrated flexibility of recombinant antibody coupling to nanoparticles highlights the bright future of this technology for modern therapeutic nanomedicine.

Utilization of Multi-Immunization and Multiple Selection Strategies for Isolation of Hapten-Specific Antibodies from Recombinant Antibody Phage Display Libraries

Phage display technology provides a powerful tool for the development of novel recombinant antibodies. In this work, we optimized and streamlined the recombinant antibody discovery process for haptens as an example. A multi-immunization approach was used in order to avoid the need for construction of multiple antibody libraries. Selection methods were developed to utilize the full potential of the recombinant antibody library by applying four different elution conditions simultaneously. High-throughput immunoassays were used to analyse the binding properties of the individual antibody clones. Different carrier proteins were used in the immunization, selection, and screening phases to avoid enrichment of the antibodies for the carrier protein epitopes. Novel recombinant antibodies against mycophenolic acid and ochratoxin A, with affinities up to 39 nM and 34 nM, respectively, were isolated from a multi-immunized fragment antigen-binding (Fab) library.

Exploiting Nanobodies in the Detection and Quantification of Human Growth Hormone via Phage-Sandwich Enzyme-Linked Immunosorbent Assay

BACKGROUND

Monitoring blood levels of human growth hormone (hGH) in most children with short stature deficiencies is crucial for taking a decision of treatment with extended course of daily and expensive doses of recombinant hGH (rhGH or Somatropin^®). Besides, misusing of rhGH by sportsmen is banned by the World Anti-Doping Agency and thus sensitive GH-detecting methods are highly welcome in this field. Nanobodies are the tiniest antigen-binding entity derived from camel heavy chain antibodies. They were successfully generated against numerous antigens including hormones.

METHODS

A fully nanobody-based sandwich ELISA method was developed in this work for direct measurement of GH in biological samples.

RESULTS

Two major characteristics of nanobody were exploited for this goal: the robust and stable structure of the nanobody (NbGH04) used to capture hGH from tested samples, and the great ability of tailoring, enabling the display of the anti-GH detector nanobody (NbGH07) on the tip of M13-phage. Such huge, stable, and easy-to-prepare phage-Nb was used in ELISA to provide an amplified signal. Previously, NbGH04 was retrieved on immobilized hGH by phage display from a wide "immune" cDNA library prepared from a hGH-immunized camel. Here, and in order to assure epitope heterogeneity, NbGH07 was isolated from the same library using NbGH04-captured hGH as bait. Interaction of both nanobodies with hGH was characterized and compared with different anti-GH nanobodies and antibodies. The sensitivity (~0.5 ng/ml) and stability of the nanobody-base sandwich ELISA were assessed using rhGH before testing in the quantification of hGH in blood sera and cell culture supernatants.

CONCLUSION

In regard to all advantages of nanobodies; stability, solubility, production affordability in Escherichia coli, and gene tailoring, nanobody-based phage sandwich ELISA developed here would provide a valuable method for hGH detection and quantification.

Microbial platform technology for recombinant antibody fragment production: A review

Recombinant antibody fragments are being used for the last few years as an important therapeutic protein to cure various critical and life threatening human diseases. Several expression platforms now days employed for the production of these recombinant fragments, out of which bacterial system has emerged a promising host for higher expression. Since, a small antibody fragment unlike full antibody does not require human-like post-translational modification therefore it is potentially expressed in prokaryotic production system. Recently, small antibody fragments such as scFvs (single-chain variable fragments) and Fabs (antibody fragments) which does not require glycosylation are successfully produced in bacteria and have commercially launched for therapeutic use as these fragments shows better tissue penetration and less immunogenic to human body compared to full-size antibody. Recently developed Wacker's ESETEC secretion technology is an efficient technology for the expression and secretion of the antibody fragment (Fab) exceeded up to 4.0 g/L while scFv up to 3.5 g/L into the fermentation broth. The Pfenex system and pOP prokaryotic expression vector are another platform used for the considerably good amount of antibody fragment production successfully. In this review, we summarize the recent progress on various expression platforms and cloning approaches for the production of different forms of antibody fragments in E. coli.

Shiga toxin-induced apoptosis is more efficiently inhibited by dimeric recombinant hybrid-IgG/IgA immunoglobulins than by the parental IgG monoclonal antibodies

Shiga toxin 1 (Stx1) is a virulence factor of enterohaemorrhagic Escherichia coli strains such as O157:H7 and Shigella dysenteriae. To prevent entry of Stx1 from the mucosal surface, an immunoglobulin A (IgA) specific for Stx1 would be useful. Due to the difficulty of producing IgA monoclonal antibodies (mAb) against the binding subunit of Stx1 (Stx1B) in mice, we took advantage of recombinant technology that combines the heavy chain variable region from Stx1B-specific IgG1 mAb and the Fc region from IgA. The resulting hybrid IgG/IgA was stably expressed in Chinese hamster ovary cells as a dimeric hybrid IgG/IgA. We separated the dimeric hybrid IgG/IgA from the monomeric one by size-exclusion chromatography. The dimer fraction, confirmed by immunoblot analyses, was used for toxin neutralization assays. The dimeric IgG/IgA was shown to neutralize Stx1 toxicity toward Vero cells by assaying their viability. To compare the relative effectiveness of the dimeric hybrid IgG/IgA and parental IgG1 mAb, Stx1-induced apoptosis was examined using 2 different cell lines, Ramos and Vero cells. The hybrid IgG/IgA inhibited apoptosis more efficiently than the parental IgG1 mAb in both cases. The results indicated that the use of high affinity binding sites as variable regions of IgA would increase the utility of IgA specific for virulence factors.

A Highly Specific Monoclonal Antibody for Botulinum Neurotoxin Type A-Cleaved SNAP25

Botulinum neurotoxin type-A (BoNT/A), as onabotulinumtoxinA, is approved globally for 11 major therapeutic and cosmetic indications. While the mechanism of action for BoNT/A at the presynaptic nerve terminal has been established, questions remain regarding intracellular trafficking patterns and overall fate of the toxin. Resolving these questions partly depends on the ability to detect BoNT/A’s location, distribution, and movement within a cell. Due to BoNT/A’s high potency and extremely low concentrations within neurons, an alternative approach has been employed. This involves utilizing specific antibodies against the BoNT/A-cleaved SNAP25 substrate (SNAP25₁₉₇) to track the enzymatic activity of toxin within cells. Using our highly specific mouse monoclonal antibody (mAb) against SNAP25₁₉₇, we generated human and murine recombinant versions (rMAb) using specific backbone immunoglobulins. In this study, we validated the specificity of our anti-SNAP25₁₉₇ rMAbs in several different assays and performed side-by-side comparisons to commercially-available and in-house antibodies against SNAP25. Our rMAbs were highly specific for SNAP25₁₉₇ in all assays and on several different BoNT/A-treated tissues, showing no cross-reactivity with full-length SNAP25. This was not the case with other reportedly SNAP25₁₉₇-selective antibodies, which were selective in some, but not all assays. The rMAbs described herein represent effective new tools for detecting BoNT/A activity within cells.

Redirection of CD4+ and CD8+ T lymphocytes via a novel antibody-based modular targeting system triggers efficient killing of PSCA+ prostate tumor cells

BACKGROUND

There is still a need for new therapeutic options against prostate cancer. Conventional single-chain bispecific antibodies (bsAbs), that directly cross-link T cells and tumor cells, hold great potential for efficient tumor treatment. However, rapid development of novel bsAbs is hampered by laborious optimization to improve their efficacy and reduce potential side effects. To accelerate the development of a novel antibody tool for the redirection of T cells to different tumor-associated antigens, we recently introduced a modular targeting system.

METHODS

We here describe a novel modular system for treatment of prostate cancer by retargeting of T cells to the prostate stem cell antigen (PSCA). Functionality of the novel PSCA-specific modular system was investigated in vitro by T cell activation and chromium release assays as well as in immunodeficient mice.

RESULTS

Similar to a conventional bsAb CD3-PSCA, the novel PSCA-specific modular system induces activation of both CD4+ and CD8+ T cells leading to secretion of pro-inflammatory cytokines and highly efficient target-specific tumor cell lysis. The novel TM was ready-to-use from the time point of construction and functional at low E:T ratios and picomolar concentrations without further optimization. In addition, the PSCA-specific modular system delays outgrowth of s.c. tumors in mice comparable to bsAb CD3-PSCA.

CONCLUSIONS

We have developed a novel PSCA-specific modular system which triggers an efficient T cell-mediated killing of PSCA+ tumor cells in vitro and in vivo. The new Ab-based targeting strategy can functionally replace conventional bsAbs and allows a flexible redirection of T cells to different tumor-associated antigens.

Simultaneous targeting of prostate stem cell antigen and prostate-specific membrane antigen improves the killing of prostate cancer cells using a novel modular T cell-retargeting system

BACKGROUND

Recently, we described a novel modular platform technology in which T cell-recruitment and tumor-targeting domains of conventional bispecific antibodies are split to independent components, a universal effector module (EM) and replaceable monospecific/monovalent target modules (TMs) that form highly efficient T cell-retargeting complexes. Theoretically, our unique strategy should allow us to simultaneously retarget T cells to different tumor antigens by combining the EM with two or more different monovalent/monospecific TMs or even with bivalent/bispecific TMs, thereby overcoming limitations of a monospecific treatment such as the selection of target-negative tumor escape variants.

METHODS

In order to advance our recently introduced prostate stem cell antigen (PSCA)-specific modular system for a dual-targeting of prostate cancer cells, two additional TMs were constructed: a monovalent/monospecific TM directed against the prostate-specific membrane antigen (PSMA) and a bivalent/bispecific TM (bsTM) with specificity for PSMA and PSCA. The functionality of the novel dual-targeting strategies was analyzed by performing T cell activation and chromium release assays.

RESULTS

Similar to the PSCA-specific modular system, the novel PSMA-specific modular system mediates an efficient target-dependent and -specific tumor cell lysis at low E:T ratios and picomolar Ab concentrations. Moreover, by combination of the EM with either the bispecific TM directed to PSMA and PSCA or both monospecifc TMs directed to either PSCA or PSMA, dual-specific targeting complexes were formed which allowed us to kill potential escape variants expressing only one or the other target antigen.

CONCLUSIONS

Overall, the novel modular system represents a promising tool for multiple tumor targeting.

Expression of recombinant antibodies

Recombinant antibodies are highly specific detection probes in research, diagnostics, and have emerged over the last two decades as the fastest growing class of therapeutic proteins. Antibody generation has been dramatically accelerated by in vitro selection systems, particularly phage display. An increasing variety of recombinant production systems have been developed, ranging from Gram-negative and positive bacteria, yeasts and filamentous fungi, insect cell lines, mammalian cells to transgenic plants and animals. Currently, almost all therapeutic antibodies are still produced in mammalian cell lines in order to reduce the risk of immunogenicity due to altered, non-human glycosylation patterns. However, recent developments of glycosylation-engineered yeast, insect cell lines, and transgenic plants are promising to obtain antibodies with "human-like" post-translational modifications. Furthermore, smaller antibody fragments including bispecific antibodies without any glycosylation are successfully produced in bacteria and have advanced to clinical testing. The first therapeutic antibody products from a non-mammalian source can be expected in coming next years. In this review, we focus on current antibody production systems including their usability for different applications.

The art of blocking ADP-ribosyltransferases (ARTs): nanobodies as experimental and therapeutic tools to block mammalian and toxin ARTs

In 1901, the first Nobel Prize in Physiology or Medicine was awarded to Emil von Behring for his ground-breaking discovery of serum therapy: serum from horses vaccinated with toxin-containing culture medium of Corynebacterium diphtheriae contained life-saving 'antitoxins'. The molecular nature of the ADP-ribosylating toxin and the neutralizing antibodies were unraveled only 50 years later. Today, von Behring's antibody therapy is being refined with a new generation of recombinant antibodies and antibody fragments. Nanobodies, which are single-domain antibodies derived from the peculiar heavy-chain antibodies of llamas and other camelids, are emerging as a promising new class of highly specific enzyme inhibitors. In this review, we illustrate the potential of nanobodies as tools to block extracellular and intracellular ADP-ribosyltransferases (ARTs), using the toxin-related membrane-bound mammalian ecto-enzyme ARTC2 and the actin-ADP-ribosylating Salmonella virulence plasmid factor B toxin of Salmonella enterica as examples.

A novel IgE antibody targeting the prostate-specific antigen as a potential prostate cancer therapy

BACKGROUND

Prostate cancer (PCa) is the second leading cause of cancer deaths in men in the United States. The prostate-specific antigen (PSA), often found at high levels in the serum of PCa patients, has been used as a marker for PCa detection and as a target of immunotherapy. The murine IgG1 monoclonal antibody AR47.47, specific for human PSA, has been shown to enhance antigen presentation by human dendritic cells and induce both CD4 and CD8 T-cell activation when complexed with PSA. In this study, we explored the properties of a novel mouse/human chimeric anti-PSA IgE containing the variable regions of AR47.47 as a potential therapy for PCa. Our goal was to take advantage of the unique properties of IgE in order to trigger immune activation against PCa.

METHODS

Binding characteristics of the antibody were determined by ELISA and flow cytometry. In vitro degranulation was determined by the release of β-hexosaminidase from effector cells. In vivo degranulation was monitored in human FcεRIα transgenic mice using the passive cutaneous anaphylaxis assay. These mice were also used for a vaccination study to determine the in vivo anti-cancer effects of this antibody. Significant differences in survival were determined using the Log Rank test. In vitro T-cell activation was studied using human dendritic cells and autologous T cells.

RESULTS

The anti-PSA IgE, expressed in murine myeloma cells, is properly assembled and secreted, and binds the antigen and FcεRI. In addition, this antibody is capable of triggering effector cell degranulation in vitro and in vivo when artificially cross-linked, but not in the presence of the natural soluble antigen, suggesting that such an interaction will not trigger systemic anaphylaxis. Importantly, the anti-PSA IgE combined with PSA also triggers immune activation in vitro and in vivo and significantly prolongs the survival of human FcεRIα transgenic mice challenged with PSA-expressing tumors in a prophylactic vaccination setting.

CONCLUSIONS

The anti-PSA IgE exhibits the expected biological properties and is capable of triggering immune activation and anti-tumor protection. Further studies on this antibody as a potential PCa therapy are warranted.

Simultaneous analysis of the non-canonical amino acids norleucine and norvaline in biopharmaceutical-related fermentation processes by a new ultra-high performance liquid chromatography approach

In this study, a precise and reliable ultra-high performance liquid chromatography (UHPLC) method for the simultaneous determination of non-canonical (norvaline and norleucine) and standard amino acids (aspartic acid, glutamic acid, serine, histidine, glycine, threonine, arginine, tyrosine, methionine, valine, phenylalanine, isoleucine, leucine) in biopharmaceutical-related fermentation processes was established. After pre-column derivatization with ortho-phthaldialdehyde and 2-mercaptoethanol, the derivatives were separated on a sub-2 μm particle C18 reverse-phase column. Identification and quantification of amino acids were carried out by fluorescence detection. To test method feasibility on standard HPLC instruments, the assay was properly transferred to a core-shell particle C18 reverse-phase column. The limits of detection showed excellent sensitivity by values from 0.06 to 0.17 pmol per injection and limits of quantification between 0.19 and 0.89 pmol. In the present study, the newly established UHPLC method was applied to a recombinant antibody Escherichia coli fermentation process for the analysis of total free amino acids. We were able to specifically detect and quantify the unfavorable amino acids in such complex samples. Since we observed trace amounts of norvaline and norleucine during all fermentation phases, an obligatory process monitoring should be considered to improve quality of recombinant protein drugs in future.

Aberrant localization and underglycosylation of highly accumulating single-chain Fv-Fc antibodies in transgenic Arabidopsis seeds

Production of high-value recombinant proteins in transgenic seeds is an attractive and economically feasible alternative to conventional systems based on mammalian cells and bacteria. In contrast to leaves, seeds allow high-level accumulation of recombinant proteins in a relatively small volume and a stable environment. We demonstrate that single-chain variable fragment (scFv)-Fc antibodies, with N-terminal signal sequence and C-terminal KDEL tag, can accumulate to very high levels as bivalent IgG-like antibodies in Arabidopsis thaliana seeds and illustrate that a plant-produced anti-hepatitis A virus scFv-Fc has similar antigen-binding and in vitro neutralizing activities as the corresponding full-length IgG. As expected, most scFv-Fc produced in seeds contained only oligomannose-type N-glycans, but, unexpectedly, 35-40% was never glycosylated. A portion of the scFv-Fc was found in endoplasmic reticulum (ER)-derived compartments delimited by ribosome-associated membranes. Additionally, consistent with the glycosylation data, large amounts of the recombinant protein were deposited in the periplasmic space, implying a direct transport from the ER to the periplasmic space between the plasma membrane and the cell wall. Aberrant localization of the ER chaperones calreticulin and binding protein (BiP) and the endogenous seed storage protein cruciferin in the periplasmic space suggests that overproduction of recombinant scFv-Fc disturbs normal ER retention and protein-sorting mechanisms in the secretory pathway.

Antibodies: an alternative for antibiotics?

In 1967, the success of vaccination programs, combined with the seemingly unstoppable triumph of antibiotics, prompted the US Surgeon General to declare that "it was time to close the books on infectious diseases." We now know that the prediction was overly optimistic and that the fight against infectious diseases is here to stay. During the last 20 yr, infectious diseases have indeed made a staggering comeback for a variety of reasons, including resistance against existing antibiotics. As a consequence, several alternatives to antibiotics are currently being considered or reconsidered. Passive immunization (i.e., the administration of more or less pathogen-specific antibodies to the patient) prior to or after exposure to the disease-causing agent is one of those alternative strategies that was almost entirely abandoned with the introduction of chemical antibiotics but that is now gaining interest again. This review will discuss the early successes and limitations of passive immunization, formerly referred to as "serum therapy," the current use of antibody administration for prophylaxis or treatment of infectious diseases in agriculture, and, finally, recent developments in the field of antibody engineering and "molecular farming" of antibodies in various expression systems. Especially the potential of producing therapeutic antibodies in crops that are routine dietary components of farm animals, such as corn and soy beans, seems to hold promise for future application in the fight against infectious diseases.

Regeneration of lesioned corticospinal tract fibers in the adult rat induced by a recombinant, humanized IN-1 antibody fragment

Axons in the CNS of higher vertebrates generally fail to regenerate after injury. This lack of regeneration is crucially influenced by neurite growth inhibitory protein constituents of CNS myelin. We have shown previously that a monoclonal antibody (mAb IN-1) capable of binding and neutralizing Nogo-A, a myelin-associated inhibitor of neurite growth, can induce long-distance axonal regeneration and increased structural plasticity with improved functional recovery in rat models of CNS injury. In this paper we demonstrate that a partially humanized, recombinant Fab fragment (rIN-1 Fab) derived from the original mAb IN-1, was able to promote long-distance regeneration of injured axons in the spinal cord of adult rats. When infused into a spinal cord injury site, regrowth of corticospinal fibers in 11 of 18 animals was observed after a survival time of 2 weeks. Regenerating fibers grew for >9 mm beyond the lesion site and arborized profusely in the distal cord. Regenerated fibers formed terminal arbors with varicosities in the spinal cord gray matter, strongly resembling synaptic points of contact to neurons in the spinal cord distal to the lesion. In animals that had received a bovine serum albumin solution or a recombinant IN-1 fragment that had been mutated in the antigen binding site (mutIN-1 Fab), no significant growth beyond normal lesion-induced sprouting was observed. Neutralization of endogenous nerve growth inhibitors represents a novel use of recombinant antibody technology with potential therapeutic applications after traumatic CNS lesions.