scFv antibody: principles and clinical application

Targeted small interfering RNA-immunoliposomes as a promising therapeutic agent against highly pathogenic Avian Influenza A (H5N1) virus infection

This study describes a proof-of-concept study on the use of small interfering RNA (siRNA)-immunoliposomes as a therapeutic agent against H5N1 influenza virus infection. siRNA specific for influenza virus nucleoprotein (NP) mRNA was employed as the key antiviral agent to inhibit viral replication in this study. A humanized single-chain Fv antibody (huscFv) against the hemagglutinin (HA) of H5N1 highly pathogenic avian influenza virus (HPAI) was used as the targeting molecule to HA of H5N1 virus, which is abundantly expressed on the surface of infected cells (the HA target cells). The huscFv was applied to cationic polyethylene glycol-conjugated 3β-[N-(N',N'-dimethylaminoethane) carbamoyl] cholesterol-dioleoylphosphatidyl ethanolamine (PEGylated DC-Chol-DOPE) liposomes to generate immunoliposomes for siRNA delivery. The immunoliposomes were shown to specifically bind HA-expressing Sf9 cells and demonstrated enhanced siRNA transfection efficiency. The siRNA transfection efficiency was significantly reduced after preincubation of the HA target cells with an excess amount of free huscFv. These results therefore demonstrated that the enhanced siRNA delivery by use of immunoliposomes was mediated via targeting by huscFv. Furthermore, the siRNA silencing effect was more pronounced when the immunoliposomes were administered 6 to 12 h post-H5N1 infection in MDCK cells compared with the nontargeted liposomes. This proof-of-concept study may contribute to the future design and development of an siRNA delivery system for combating viral infectious diseases in humans.

Technical and ethical limitations in making human monoclonal antibodies (an overview)

In the broadest sense there are no longer any technical limitations to making human mAbs. Biological issues involving the type and nature of either a synthetic or a natural antibody, advantages of various B cell immunological compartments, and various assays needed to qualitate and quantitate mAbs have essentially been solved. If the target antigen is known then procedures to optimize antibody development can be readily planned out and implemented. When the antigen or target is unknown and specificity is the driving force in generating a human mAb then considerations about the nature and location of the B cell making the sought after antibody become important. And, therefore, the person the B cell is obtained from can be an ethical challenge and a limitation. For the sources of B cells special considerations must be taken to insure the anonymity and privacy of the patient. In many cases informed consent is adequate for antibody development as well as using discarded tissues. After the antibody has been generated then manufacturing technical issues become important that greatly depend upon the amounts of mAb required. For kilogram quantities then special considerations for manufacturing that include FDA guidelines will be necessary.

Therapeutic antibody engineering by high efficiency cell screening

In recent years, several cell-based screening technologies for the isolation of antibodies with prescribed properties emerged. They rely on the multi-copy display of antibodies or antibody fragments on a cell surface in functional form followed by high through put screening and isolation of cell clones that carry an antibody variant with the desired affinity, specificity, and stability. Particularly yeast surface display in combination with high-throughput fluorescence-activated cell sorting has proven successful in the last fifteen years as a very powerful technology that has some advantages over classical generation of monoclonals using the hybridoma technology or bacteriophage-based antibody display and screening. Cell-based screening harbours the benefit of single-cell online and real-time analysis and characterisation of individual library candidates. Moreover, when using eukaryotic expression hosts, intrinsic quality control machineries for proper protein folding and stability exist that allow for co-selection of high-level expression and stability simultaneously to the binding functionality. Recently, promising technologies emerged that directly rely on antibody display on higher eukaryotic cell lines using lentiviral transfection or direct screening on B-cells. The combination of immunisation, B-cell screening and next generation sequencing may open new avenues for the isolation of therapeutic antibodies with prescribed physicochemical and functional characteristics.

Microbials for the production of monoclonal antibodies and antibody fragments

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Glycosylated full length antibodies are currently produced in mammalian cells.

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Antibody fragments can be produced in microbial organisms.

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Strain engineering allows production of full length antibodies in microbials.

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Microbials provide several advantages over mammalian cells.

Monoclonal antibodies (mAbs) and antibody fragments represent the most important biopharmaceutical products today. Because full length antibodies are glycosylated, mammalian cells, which allow human-like N-glycosylation, are currently used for their production. However, mammalian cells have several drawbacks when it comes to bioprocessing and scale-up, resulting in long processing times and elevated costs. By contrast, antibody fragments, that are not glycosylated but still exhibit antigen binding properties, can be produced in microbial organisms, which are easy to manipulate and cultivate. In this review, we summarize recent advances in the expression systems, strain engineering, and production processes for the three main microbials used in antibody and antibody fragment production, namely Saccharomyces cerevisiae, Pichia pastoris, and Escherichia coli.

High-level secretory production of recombinant single-chain variable fragment (scFv) in Corynebacterium glutamicum

We describe the development of a new secretory production system for the enhanced production of a single-chain variable fragment (scFv) against the anthrax toxin in Corynebacterium glutamicum. For efficient secretory production of the antibody fragment, the following components were examined: (1) signal peptides, (2) codon usage of antibody fragment, (3) promoters, (4) 5' untranslated region (5' UTR) sequence, and (5) transcriptional terminator. Among all the systems examined, the use of a codon-optimized gene sequence, a Sec-dependent PorB signal peptide, and a fully synthetic H36 promoter, allowed the highest production of antibody fragments in a culture medium. For large-scale production, fed-batch cultivations were also conducted in a 5-L lab-scale bioreactor. When cells were cultivated in semi-defined media, cells could grow up to an OD600 of 179 for 32 h and an antibody fragment concentration as high as 68 mg/L could be obtained in a culture medium with high purity. From the culture medium, the secreted antibody was successfully purified using a simple purification procedure, with correct binding activity confirmed by enzyme-linked immunosorbent assay. To the best of our knowledge, this is the first report of a fed-batch cultivation for antibody fragment production in C. glutamicum.

Phage display as a technology delivering on the promise of peptide drug discovery

Phage display represents an important approach in the development pipeline for producing peptides and peptidomimetics therapeutics. Using randomly generated DNA sequences and molecular biology techniques, large diverse peptide libraries can be displayed on the phage surface. The phage library can be incubated with a target of interest and the phage which bind can be isolated and sequenced to reveal the displayed peptides' primary structure. In this review, we focus on the 'mechanics' of the phage display process, whilst highlighting many diverse and subtle ways it has been used to further the drug-development process, including the potential for the phage particle itself to be used as a drug carrier targeted to a particular pathogen or cell type in the body.

Single-chain fragment variable passive immunotherapies for neurodegenerative diseases

Accumulation of misfolded proteins has been implicated in a variety of neurodegenerative diseases including prion diseases, Alzheimer’s disease (AD), Parkinson’s disease (PD), and Huntington’s disease (HD). In the past decade, single-chain fragment variable (scFv) -based immunotherapies have been developed to target abnormal proteins or various forms of protein aggregates including Aβ, SNCA, Htt, and PrP proteins. The scFvs are produced by fusing the variable regions of the antibody heavy and light chains, creating a much smaller protein with unaltered specificity. Because of its small size and relative ease of production, scFvs are promising diagnostic and therapeutic reagents for protein misfolded diseases. Studies have demonstrated the efficacy and safety of scFvs in preventing amyloid protein aggregation in preclinical models. Herein, we discuss recent developments of these immunotherapeutics. We review efforts of our group and others using scFv in neurodegenerative disease models. We illustrate the advantages of scFvs, including engineering to enhance misfolded conformer specificity and subcellular targeting to optimize therapeutic action.

New engineered antibodies against prions

A number of recently developed and approved therapeutic agents based on highly specific and potent antibodies have shown the potential of antibody therapy. As the next step, antibody-based therapeutics will be bioengineered in a way that they not only bind pathogenic targets but also address other issues, including drug targeting and delivery. For antibodies that are expected to act within brain tissue, like those that are directed against the pathogenic prion protein isoform, one of the major obstacles is the blood-brain barrier which prevents efficient transfer of the antibody, even of the engineered single-chain variants. We recently demonstrated that a specific prion-specific antibody construct which was injected into the murine tail vein can be efficiently transported into brain tissue. The novelty of the work was in that the cell penetrating peptide was used as a linker connecting both specificity-determining domains of the antibody peptide, thus eliminating the need for the standard flexible linker, composed of an arrangement of three consecutive (Gly 4Ser) repeats. This paves the road toward improved bioengineered antibody variants that target brain antigens.

Cloning and expression of an anti-LDL(-) single-chain variable fragment, and its inhibitory effect on experimental atherosclerosis

The in vivo modified forms of low-density lipoprotein (LDL) are important for the formation of foam cells and as mediators of the immuno-inflammatory process involved in the progression of atherosclerosis. Electronegative LDL, LDL(-), is a LDL subfraction with pro-inflammatory properties that is present in human blood. To investigate possible atheroprotective effects, an anti-LDL(-) single-chain variable fragment (scFv) was expressed in the methylotrophic yeast Pichia pastoris and its activity was evaluated in vitro against macrophages and in experimental atherosclerosis in Ldlr(-/-) mice. The recombinant 2C7 scFv was produced in a yield of 9.5 mg of protein/L. The specificity and affinity of purified 2C7 scFv against LDL(-) was confirmed by ELISA. To assess the activity of 2C7 scFv on foam cell formation, RAW 264.7 macrophages were exposed to LDL(-) in the presence or absence of 2C7 scFv. The 2C7 scFv inhibited the uptake of LDL(-) by macrophages in a dose-dependent manner, and internalization of LDL(-) by these cells was found to be mediated by the CD36 and CD14 receptor. In addition, compared with untreated cells, lipid accumulation in macrophages was decreased, and the expression of Cd36, Tlr-4 and Cox-2 was downregulated in macrophages treated with 2C7 scFv. Importantly, compared with untreated mice, the treatment of Ldlr(-/-) mice with 2C7 scFv decreased the atherosclerotic lesion area at the aortic sinus. In conclusion, our data show that 2C7 scFv inhibits foam cell formation and atherosclerotic plaque development by modulating the expression of genes relevant to atherogenesis. These results encourage further use of this antibody fragment in the development of new therapeutic strategies that neutralize the pro-atherogenic effects of LDL(-).

Development of MicroRNA Therapeutics for Hepatocellular Carcinoma

Hepatocellular carcinoma (HCC) is the most common form of liver cancer and is the third leading cause of cancer-related deaths worldwide. Treatment options for HCC are very limited, as it is often diagnosed at a late stage. Recent studies have demonstrated that microRNAs (miRNAs), a class of non-coding RNAs, are aberrantly expressed in HCC. Some of these were shown to be functionally involved in carcinogenesis and tumor progression, suggesting that miRNAs can serve as novel molecular targets for HCC therapy. Several promising studies have recently demonstrated the therapeutic potential of miRNAs in animal models and in reducing the viral load in hepatitis C patients. In this review, these advances and strategies for modulating miRNAs for in vivo therapeutic delivery and replacement therapy are discussed.

Recombinant single-chain antibody with the Trojan peptide penetratin positioned in the linker region enables cargo transfer across the blood-brain barrier

Delivery of therapeutic proteins into tissues and across the blood-brain barrier (BBB) is limited by the size and biochemical properties of the proteins. Efficient delivery across BBB is generally restricted to small, highly lipophilic molecules. However, in the last decades, several peptides that can pass cell membranes have been identified. It has been shown that these peptides are also capable of delivering large hydrophilic cargoes into cells and are therefore a powerful biological tool for transporting drugs across cell membranes and even into the brain. We designed and prepared a single-chain antibody fragment (scFvs), specific for the pathological form of the prion protein (PrP(Sc)), where a cell-penetrating peptide (CPP) was used as a linker between the two variable domains of the scFv. The intravenously administered recombinant scFv-CPP was successfully targeted to and delivered into mouse brain cells. Our single-chain antibody fragments are of special interest in view of possible therapeutic reagents design not only for prion diseases but also for other neurodegenerative diseases.

Development of anti-infectives using phage display: biological agents against bacteria, viruses, and parasites

The vast majority of anti-infective therapeutics on the market or in development are small molecules; however, there is now a nascent pipeline of biological agents in development. Until recently, phage display technologies were used mainly to produce monoclonal antibodies (MAbs) targeted against cancer or inflammatory disease targets. Patent disputes impeded broad use of these methods and contributed to the dearth of candidates in the clinic during the 1990s. Today, however, phage display is recognized as a powerful tool for selecting novel peptides and antibodies that can bind to a wide range of antigens, ranging from whole cells to proteins and lipid targets. In this review, we highlight research that exploits phage display technology as a means of discovering novel therapeutics against infectious diseases, with a focus on antimicrobial peptides and antibodies in clinical or preclinical development. We discuss the different strategies and methods used to derive, select, and develop anti-infectives from phage display libraries and then highlight case studies of drug candidates in the process of development and commercialization. Advances in screening, manufacturing, and humanization technologies now mean that phage display can make a significant contribution in the fight against clinically important pathogens.