Formatting antibody fragments to mediate specific therapeutic functions

In vivo Phage Display: A promising selection strategy for the improvement of antibody targeting and drug delivery properties

The discovery of hybridoma technology, described by Kohler and Milstein in 1975, and the resulting ability to generate monoclonal antibodies (mAbs) initiated a new era in antibody research and clinical development. However, limitations of the hybridoma technology as a routine antibody generation method in conjunction with high immunogenicity responses have led to the development of alternative approaches for the streamlined identification of most effective antibodies. Within this context, display selection technologies such as phage display, ribosome display, yeast display, bacterial display, and mammalian cell surface display have been widely promoted over the past three decades as ideal alternatives to traditional hybridoma methods. The display of antibodies on phages is probably the most widespread and powerful of these methods and, since its invention in late 1980s, significant technological advancements in the design, construction, and selection of antibody libraries have been made, and several fully human antibodies generated by phage display are currently approved or in various clinical development stages. With evolving novel disease targets and the emerging of a new generation of therapeutic antibodies, such as bispecific antibodies, antibody drug conjugates (ADCs), and chimeric antigen receptor T (CAR-T) cell therapies, it is clear that phage display is expected to continue to play a central role in antibody development. Nevertheless, for non-standard and more demanding cases aiming to generate best-in-class therapeutic antibodies against challenging targets and unmet medical needs, in vivo phage display selections by which phage libraries are directly injected into animals or humans for isolating and identifying the phages bound to specific tissues offer an advantage over conventional in vitro phage display screening procedures. Thus, in the present review, we will first summarize a general overview of the antibody therapeutic market, the different types of antibody fragments, and novel engineered variants that have already been explored. Then, we will discuss the state-of-the-art of in vivo phage display methodologies as a promising emerging selection strategy for improvement antibody targeting and drug delivery properties.

P-glycoprotein targeted photodynamic therapy of chemoresistant tumors using recombinant Fab fragment conjugates

P-glycoprotein (Pgp) has been considered as a major cause of cancer multidrug resistance; however, clinical solutions to overcome this drug resistance do not exist despite the tremendous endeavors. The lack of cancer specificity is a main reason for clinical failure of conventional approaches. Targeted photodynamic therapy (PDT) is highly cancer specific by combining antibody targeting and locoregional light irradiation. We aimed to develop Pgp-targeted PDT using antibody-photosensitizer conjugates made of a recombinant Fab fragment. We prepared the photosensitizer conjugates by expressing a recombinant Fab fragment and specifically linking IR700-maleimide at the C-terminal of the Fab heavy chain. In vitro studies showed that the Fab conjugates specifically bind to Pgp. Their phototoxicity was comparable to full antibody conjugates when assayed with conventional 2-D cell culture, but they outperformed the full antibody conjugates in a 3-D tumor spheroid model. In a mouse xenograft model of chemoresistant tumors, Fab conjugates showed Pgp specific delivery to chemoresistant tumors. Upon irradiation with near-infrared light, they caused rapid tumor shrinkage and significantly prolonged the survival of tumor-bearing mice. Compared to the full antibody conjugates, Fab conjugates took a shorter time to reach peak tumor levels and achieved a more homogeneous tumor distribution. This allows light irradiation to be initiated at a shorter time interval after the conjugate injection, and thus may facilitate clinical translation. We conclude that our targeted PDT approach provides a highly cancer-specific approach to combat chemoresistant tumors, and that the conjugates made of recombinant antibody fragments are superior to full antibody conjugates for targeted PDT.

Therapeutic Antibody Engineering and Selection Strategies

Antibody drugs became an increasingly important element of the therapeutic landscape. Their accomplishment has been driven by many unique properties, in particular by their very high specificity and selectivity, in contrast to the off-target liabilities of small molecules (SMs). Antibodies can bring additional functionality to the table with their ability to interact with the immune system, and this can be further manipulated with advances in antibody engineering.The expansion of strategies related to discovery technologies of monoclonal antibodies (mAbs) (phage display, yeast display, ribosome display, bacterial display, mammalian cell surface display, mRNA display, DNA display, transgenic animal, and human B cell derived) opened perspectives for the screening and the selection of therapeutic antibodies for, theoretically, any target from any kind of organism. Moreover, antibody engineering technologies were developed and explored to obtain chosen characteristics of selected leading candidates such as high affinity, low immunogenicity, improved functionality, improved protein production, improved stability, and others. This chapter contains an overview of discovery technologies, mainly display methods and antibody humanization methods for the selection of therapeutic humanized and human mAbs that appeared along the development of these technologies and thereafter. The increasing applications of these technologies will be highlighted in the antibody engineering area (affinity maturation, guided selection to obtain human antibodies) giving promising perspectives for the development of future therapeutics.

Calibrated flux measurements reveal a nanostructure-stimulated transcytotic pathway

Transport of therapeutic agents across epithelial barriers is an important element in drug delivery. Transepithelial flux is widely used as a measure of transit across an epithelium, however it is most typically employed as a relative as opposed to absolute measure of molecular movement. Here, we have used the calcium switch approach to measure the maximum rate of paracellular flux through unencumbered intercellular junctions as a method to calibrate the flux rates for a series of tracers ranging in 0.6-900kDa in size across barriers composed of human colon epithelial (Caco-2) cells. We then examined the effects of nanostructured films (NSFs) on transepithelial transport. Two different NSF patterns were used, Defined Nanostructure (DN) 2 imprinted on polypropylene (PP) and DN3 imprinted on polyether ether ketone (PEEK). NSFs made direct contact with cells and decreased their barrier function, as measured by transepithelial resistance (TER), however cell viability was not affected. When NSF-induced transepithelial transport of Fab fragment (55kDa) and IgG (160kDa) was measured, it was unexpectedly found to be significantly greater than the maximum paracellular rate as predicted using cells cultured in low calcium. These data suggested that NSFs stimulate an active transport pathway, most likely transcytosis, in addition to increasing paracellular flux. Transport of IgG via transcytosis was confirmed by immunofluorescence confocal microscopy, since NSFs induced a significant level of IgG endocytosis by Caco-2 cells. Thus, NSF-induced IgG flux was attributable to both transcytosis and the paracellular route. These data provide the first demonstration that transcytosis can be stimulated by NSFs and that this was concurrent with increased paracellular permeability. Moreover, NSFs with distinct architecture paired with specific substrates have the potential to provide an effective means to regulate transepithelial transport in order to optimize drug delivery.

Antibody engineering of a cytotoxic monoclonal antibody 84 against human embryonic stem cells: Investigating the effects of multivalency on cytotoxicity

Antibody fragments have shown targeted specificity to their antigens, but only modest tissue retention times in vivo and in vitro. Multimerization has been used as a protein engineering tool to increase the number of binding units and thereby enhance the efficacy and retention time of antibody fragments. In this work, we explored the effects of valency using a series of self-assembling polypeptides based on the GCN4 leucine zipper multimerization domain fused to a single-chain variable fragment via an antibody upper hinge sequence. Four engineered antibody fragments with a valency from one to four antigen-binding units of a cytotoxic monoclonal antibody 84 against human embryonic stem cells (hESC) were constructed. We hypothesized that higher cytotoxicity would be observed for fragments with increased valency. Flow cytometry analysis revealed that the trimeric and tetrameric engineered antibody fragments resulted in the highest degree of cytotoxicity to the undifferentiated hESC, while the engineered antibody fragments were observed to have improved tissue penetration into cell clusters. Thus, a trade off was made for the trimeric versus tetrameric fragment due to improved tissue penetration. These results have direct implications for antibody-mediated removal of undifferentiated hESC during regenerative medicine and cell therapy.

Adeno-associated virus-mediated expression of myostatin propeptide improves the growth of skeletal muscle and attenuates hyperglycemia in db/db mice

Inhibition of myostatin, a negative growth modulator for muscle, can functionally enhance muscle mass and improve glucose and fat metabolism in myostatin propeptide (MPRO) transgenic mice. This study was to investigate whether myostatin inhibition by adeno-associated virus (AAV)-mediated gene delivery of MPRO could improve muscle mass and achieve therapeutic effects on glucose regulation and lipid metabolism in the db/db mice and the mechanisms involved in that process. Eight-week-old male db/db mice were administered saline, AAV-GFP and AAV-MPRO/Fc vectors and monitored random blood glucose levels and body weight for 36 weeks. Body weight gain was not different during follow-up among the groups, but AAV-MPRO/Fc vectors resulted high level of MPRO in the blood companied by an increase in skeletal muscle mass and muscle hypertrophy. In addition, AAV-MPRO/Fc-treated db/db mice showed significantly lower blood glucose and insulin levels and significantly increased glucose tolerance and insulin sensitivity compared with the control groups (P<0.05). Moreover, these mice exhibited lower triglyceride (TG) and free fatty acid (FFA) content in the skeletal muscle, although no difference was observed in fat pad weights and serum TG and FFA levels. Finally, AAV-MPRO/Fc-treated mice had enhanced insulin signaling in the skeletal muscle. These data suggest that AAV-mediated MPRO therapy may provide an important clue for potential clinical applications to prevent type II diabetes, and these studies confirm that MPRO is a therapeutic target for type II diabetes.

Exploring the affinity binding of alkylmaltoside surfactants to bovine serum albumin and their effect on the protein stability: A spectroscopic approach

Steady-state and time-resolved fluorescence together with circular dichroism (CD) spectroscopic studies was performed to examine the interactions between bovine serum albumin (BSA) and two alkylmaltoside surfactants, i.e. n-decyl-β-D-maltoside (β-C10G2) and n-dodecyl-β-D-maltoside (β-C12G2), having identical structures but different tail lengths. Changes in the intrinsic fluorescence of BSA from static as well as dynamic measurements revealed a weak protein-surfactant interaction and gave the corresponding binding curves, suggesting that the binding mechanism of surfactants to protein is essentially cooperative in nature. The behavior of both surfactants is similar, so that the differences detected were attributed to the more hydrophobic nature of β-C12G2, which favors the adsorption of micelle-like aggregates onto the protein surface. These observations were substantially demonstrated by data derived from synchronous, three-dimensional and anisotropy fluorescence experiments. Changes in the secondary structure of the protein induced by the interaction with surfactants were analyzed by CD to determine the contents of α-helix and β-strand. It was noted that whereas the addition of β-C10G2 appears to stabilize the secondary structure of the protein, β-C12G2 causes a marginal denaturation of BSA for a protein:surfactant molar ratio as high as 1 to 100.

Antibody Isotype Switching in Vertebrates

The humoral or antibody-mediated immune response in vertebrates has evolved to respond to diverse antigenic challenges in various anatomical locations. Diversification of the immunoglobulin heavy chain (IgH) constant region via isotype switching allows for remarkable plasticity in the immune response, including versatile tissue distribution, Fc receptor binding, and complement fixation. This enables antibody molecules to exert various biological functions while maintaining antigen-binding specificity. Different immunoglobulin (Ig) classes include IgM, IgD, IgG, IgE, and IgA, which exist as surface-bound and secreted forms. High-affinity autoantibodies are associated with various autoimmune diseases such as lupus and arthritis, while defects in components of isotype switching are associated with infections. A major route of infection used by a large number of pathogens is invasion of mucosal surfaces within the respiratory, digestive, or urinary tract. Most infections of this nature are initially limited by effector mechanisms such as secretory IgA antibodies. Mucosal surfaces have been proposed as a major site for the genesis of adaptive immune responses, not just in fighting infections but also in tolerating commensals and constant dietary antigens. We will discuss the evolution of isotype switching in various species and provide an overview of the function of various isotypes with a focus on IgA, which is universally important in gut homeostasis as well as pathogen clearance. Finally, we will discuss the utility of antibodies as therapeutic modalities.

Bispecific T-cell engagers for cancer immunotherapy

Bispecific T-cell engagers (BiTEs) are a new class of immunotherapeutic molecules intended for the treatment of cancer. These molecules enhance the patient's immune response to tumors by retargeting T cells to tumor cells. BiTEs are constructed of two single-chain variable fragments (scFv) connected in tandem by a flexible linker. One scFv binds to a T-cell-specific molecule, usually CD3, whereas the second scFv binds to a tumor-associated antigen. This structure and specificity allows a BiTE to physically link a T cell to a tumor cell, ultimately stimulating T-cell activation, tumor killing and cytokine production. BiTEs have been developed, which target several tumor-associated antigens, for a variety of both hematological and solid tumors. Several BiTEs are currently in clinical trials for their therapeutic efficacy and safety. This review examines the salient structural and functional features of BiTEs, as well as the current state of their clinical and preclinical development.

Prion protein-specific antibodies-development, modes of action and therapeutics application

Prion diseases or Transmissible Spongiform Encephalopathies (TSEs) are lethal neurodegenerative disorders involving the misfolding of the host encoded cellular prion protein, PrP^C. This physiological form of the protein is expressed throughout the body, and it reaches the highest levels in the central nervous system where the pathology occurs. The conversion into the pathogenic isoform denoted as prion or PrP^Sc is the key event in prion disorders. Prominent candidates for the treatment of prion diseases are antibodies and their derivatives. Anti-PrP^C antibodies are able to clear PrP^Sc from cell culture of infected cells. Furthermore, application of anti-PrP^C antibodies suppresses prion replication in experimental animal models. Major drawbacks of immunotherapy are immune tolerance, the risks of neurotoxic side effects, limited ability of compounds to cross the blood-brain barrier and their unfavorable pharmacokinetic. The focus of this review is to recapitulate the current understanding of the molecular mechanisms for antibody mediated anti-prion activity. Although relevant for designing immunotherapeutic tools, the characterization of key antibody parameters shaping the molecular mechanism of the PrP^C to PrP^Sc conversion remains elusive. Moreover, this review illustrates the various attempts towards the development of anti-PrP antibody compounds and discusses therapeutic candidates that modulate PrP expression.

Biological therapies for rheumatoid arthritis: progress to date

Biologic drugs for the management of rheumatoid arthritis (RA) have revolutionized the therapeutic armamentarium with the development of several novel monoclonal antibodies, which include murine, chimeric, humanized, fully human antibodies and fusion proteins. These biologics bind to their targets with high affinity and specificity. Since 1998, nine different biologics have been approved by the US Food and Drug Administration (FDA) and European Medicines Agency (EMA) for the treatment of RA, and several others are in different stages of clinical trials. This field is in continuous evolution and new biologics are tested every year. Therefore a precise analysis is required in order to have a detailed and updated state of the art of this field. In this review, our main aim is to analyse all available biological therapies that are FDA and EMA approved for the treatment of RA and also those that are in clinical trials for the management of RA patients.

With or without sugar? (A)glycosylation of therapeutic antibodies

Antibodies and antibody-based drugs are currently the fastest-growing class of therapeutics. Over the last three decades, more than 30 therapeutic monoclonal antibodies and derivatives thereof have been approved for and successfully applied in diverse indication areas including cancer, organ transplants, autoimmune/inflammatory disorders, and cardiovascular disease. The isotype of choice for antibody therapeutics is human IgG, whose Fc region contains a ubiquitous asparagine residue (N297) that acts as an acceptor site for N-linked glycans. The nature of these glycans can decisively influence the therapeutic performance of a recombinant antibody, and their absence or modification can lead to the loss of Fc effector functions, greater immunogenicity, and unfavorable pharmacokinetic profiles. However, recent studies have shown that aglycosylated antibodies can be genetically engineered to display novel or enhanced effector functions and that favorable pharmacokinetic properties can be preserved. Furthermore, the ability to produce aglycosylated antibodies in lower eukaryotes and bacteria offers the potential to broaden and simplify the production platforms and avoid the problem of antibody heterogeneity, which occurs when mammalian cells are used for production. In this review, we discuss the importance of Fc glycosylation focusing on the use of aglycosylated and glyco-engineered antibodies as therapeutic proteins.

Industrial production of recombinant therapeutics in Escherichia coli and its recent advancements

Nearly 30% of currently approved recombinant therapeutic proteins are produced in Escherichia coli. Due to its well-characterized genetics, rapid growth and high-yield production, E. coli has been a preferred choice and a workhorse for expression of non-glycosylated proteins in the biotech industry. There is a wealth of knowledge and comprehensive tools for E. coli systems, such as expression vectors, production strains, protein folding and fermentation technologies, that are well tailored for industrial applications. Advancement of the systems continues to meet the current industry needs, which are best illustrated by the recent drug approval of E. coli produced antibody fragments and Fc-fusion proteins by the FDA. Even more, recent progress in expression of complex proteins such as full-length aglycosylated antibodies, novel strain engineering, bacterial N-glycosylation and cell-free systems further suggests that complex proteins and humanized glycoproteins may be produced in E. coli in large quantities. This review summarizes the current technology used for commercial production of recombinant therapeutics in E. coli and recent advances that can potentially expand the use of this system toward more sophisticated protein therapeutics.

Biomedicals from a soil bug: expanding scFv production host range

Recombinant antibody fragments have a wide range of applications from research to diagnostics and therapy. Of special interest are small fragments like fragment antigen binding (Fab) or single chain fragment variables (scFv) fragments as they can be produced inexpensively in bacterial expression systems. However, recombinant production efficiencies from established production hosts vary significantly leading to inadequate yields. Gene sequences that have been synthetically adapted to match the codon preferences and respective genomic tRNA pool of the host have been used to improve yields but cannot resolve the principal problem. The development of inducible broad host range scFv expression plasmid constructs leads the way to an easy and efficient screening method for the identification of the optimal bacterial expression host.

Protein-based tumor molecular imaging probes

Molecular imaging is an emerging discipline which plays critical roles in diagnosis and therapeutics. It visualizes and quantifies markers that are aberrantly expressed during the disease origin and development. Protein molecules remain to be one major class of imaging probes, and the option has been widely diversified due to the recent advances in protein engineering techniques. Antibodies are part of the immunosystem which interact with target antigens with high specificity and affinity. They have long been investigated as imaging probes and were coupled with imaging motifs such as radioisotopes for that purpose. However, the relatively large size of antibodies leads to a half-life that is too long for common imaging purposes. Besides, it may also cause a poor tissue penetration rate and thus compromise some medical applications. It is under this context that various engineered protein probes, essentially antibody fragments, protein scaffolds, and natural ligands have been developed. Compared to intact antibodies, they possess more compact size, shorter clearance time, and better tumor penetration. One major challenge of using protein probes in molecular imaging is the affected biological activity resulted from random labeling. Site-specific modification, however, allows conjugation happening in a stoichiometric fashion with little perturbation of protein activity. The present review will discuss protein-based probes with focus on their application and related site-specific conjugation strategies in tumor imaging.

Developing the next generation of monoclonal antibodies for the treatment of rheumatoid arthritis

Rheumatoid arthritis is one of the commonest autoimmune diseases affecting 0.8% of the population. Over the last decade the treatment of this chronic disease has been revolutionized by the use of monoclonal antibodies and fusion proteins, targeting molecules like tumour necrosis factor alpha. Nevertheless, approximately one-third of subjects fail to respond to these therapies and therefore significant unmet medical need remains. Following a decade of use, clinical, government and regulatory agency expectations have changed for new antibodies therapies entering this highly competitive area. In this review, we discuss the current advances being made in antibody engineering and how they are being considered and used in the development of the next generation of antibodies to meet future expectations of healthcare providers, physicians and patients. Moreover, we discuss how pattern recognition receptors may provide new antibody tractable targets that may break the cycle of autoimmunity in rheumatoid arthritis.

Construction of divalent anti-keratin 8 single-chain antibodies (sc(Fv)(2)), expression in Pichia pastoris and their reactivity with multicellular tumor spheroids

Single-chain variable fragments (scFvs) are small monovalent recombinant antibody fragments that retain the specificity of their parent immunoglobulins. ScFvs are excellent building blocks for new and improved immunodiagnostic and therapeutic proteins. However, the monovalency and the rapid renal elimination of scFvs result in poor tumor accumulation and retention. Engineering divalent antibody fragments is an excellent way to address these shortcomings. In this study, covalent divalent single-chain variable fragments (sc(Fv)(2)s), were constructed from the monovalent anti-keratin 8 scFvs, TS1-218 and its mutant, HE1-Q. The scFvs and sc(Fv)(2)s were expressed in the methylotrophic yeast Pichia pastoris, utilizing the alpha-factor secretion signal (α-factor) for extracellular secretion. The immunoreactivity and specificity of the antibody fragments were analyzed with enzyme-linked immunosorbent assay (ELISA) and the uptake and retention of the (125)I labeled antibody fragments were evaluated using HeLa HEp-2 multicellular tumor spheroids (MCTSs). Analysis of the antibody fragments demonstrated that parts of the α-factor remained at the N-terminal of the antibody fragments. Despite incomplete processing of the α-factor, the antibody fragments were functional where the sc(Fv)(2)s gave a three-fold stronger signal in ELISA compared to their scFv counterparts and the mutant antibodies demonstrated a stronger signal than their initial wild types. In addition, the sc(Fv)(2)s DiTS1-218 and DiHE1-Q displayed an approximately two-fold higher uptake and were retained to a larger extent in the MCTS, demonstrating a 3.9 and 9.4-fold increase in half-life respectively compared to their corresponding scFvs. In conclusion, expression in P. pastoris improved the yield 20-fold and facilitated the purification of the antibody fragments. Furthermore, the sc(Fv)(2)s presented a higher functional affinity to K 8 both in ELISA and MCTS compared to the scFvs with DiHE1-Q being the best candidate for further studies.

Novel GLP-1 fusion chimera as potent long acting GLP-1 receptor agonist

GLP-1 has a variety of anti-diabetic effects. However, native GLP-1 is not suitable for therapy of diabetes due to its short half-life (t1/2<2 min). To circumvent this, we developed a long-lasting GLP-1 receptor agonist by the fusion of GLP-1 with human IgG2 Fc (GLP-1/hIgG2). ELISA-based receptor binding assay demonstrated that GLP-1/hIgG2 had high binding affinity to the GLP-1R in INS-1 cells (Kd = 13.90±1.52 nM). Upon binding, GLP-1/hIgG2 was rapidly internalized by INS-1 cells in a dynamin-dependent manner. Insulin RIA showed that GLP-1/IgG2 dose-dependently stimulated insulin secretion from INS-1 cells. Pharmacokinetic studies in CD1 mice showed that with intraperitoneal injection (i.p.), the GLP-1/hIgG2 peaked at 30 minutes in circulation and maintained a plateau for >168 h. Intraperitoneal glucose tolerance test (IPGTT) in mice showed that GLP-1/hIgG2 significantly decreased glucose excursion. Furthermore, IPGTT performed on mice one week after a single drug-injection also displayed significantly reduced glucose excursion, indicating that GLP-1/hIgG2 fusion protein has long-lasting effects on the modulation of glucose homeostasis. GLP-1/hIgG2 was found to be effective in reducing the incidence of diabetes in multiple-low-dose streptozotocin-induced type 1 diabetes in mice. Together, the long-lasting bioactive GLP-1/hIgG2 retains native GLP-1 activities and thus may serve as a potent GLP-1 receptor agonist.

Molecular imaging of rheumatoid arthritis by radiolabelled monoclonal antibodies: new imaging strategies to guide molecular therapies

The closing of the last century opened a wide variety of approaches for inflammation imaging and treatment of patients with rheumatoid arthritis (RA). The introduction of biological therapies for the management of RA started a revolution in the therapeutic armamentarium with the development of several novel monoclonal antibodies (mAbs), which can be murine, chimeric, humanised and fully human antibodies. Monoclonal antibodies specifically bind to their target, which could be adhesion molecules, activation markers, antigens or receptors, to interfere with specific inflammation pathways at the molecular level, leading to immune-modulation of the underlying pathogenic process. These new generation of mAbs can also be radiolabelled by using direct or indirect method, with a variety of nuclides, depending upon the specific diagnostic application. For studying rheumatoid arthritis patients, several monoclonal antibodies and their fragments, including anti-TNF-alpha, anti-CD20, anti-CD3, anti-CD4 and anti-E-selectin antibody, have been radiolabelled mainly with (99m)Tc or (111)In. Scintigraphy with these radiolabelled antibodies may offer an exciting possibility for the study of RA patients and holds two types of information: (1) it allows better staging of the disease and diagnosis of the state of activity by early detection of inflamed joints that might be difficult to assess; (2) it might provide a possibility to perform 'evidence-based biological therapy' of arthritis with a view to assessing whether an antibody will localise in an inflamed joint before using the same unlabelled antibody therapeutically. This might prove particularly important for the selection of patients to be treated since biological therapies can be associated with severe side-effects and are considerably expensive. This article reviews the use of radiolabelled mAbs in the study of RA with particular emphasis on the use of different radiolabelled monoclonal antibodies for therapy decision-making and follow-up.

Curative properties of antibodies against prion protein: a comparative in vitro study of monovalent fragments and divalent antibodies

Prion diseases, which include Creutzfeldt-Jakob disease (CJD) in humans, are a group of devastating neurodegenerative disorders for which no therapy is yet available. However, passive immunotherapy appears to be a promising therapeutic approach, given that antibodies against the cellular prion protein (PrPc) have been shown in vitro to antagonize deposition of the disease-associated prion protein (PrPSc). Nevertheless, in vivo deleterious side effects of injected anti-PrP antibodies have been reported, mainly due to their Fc fragments and divalence. In this context, we examined here the ability of five Fabs (monovalent fragments devoid of the Fc part), prepared from antibodies already characterized in the laboratory, to inhibit prion replication in infected neuronal cells. We show that all Fabs (which all retain the same apparent affinity for PrPc as their whole antibody counterpart, as measured in EIA experiments) recognize quite well membrane bound-PrP in neuronal cells (as shown by flow cytometry analysis) and inhibit PrPSc formation in infected cells in a dose-dependent manner, most of them (four out of five) exhibiting a similar efficiency as whole antibodies. From a fundamental point of view, this report indicates that the in vitro curative effect of antibodies i) is epitope independent and only related to the efficiency of recognizing the native, membrane-inserted form of neuronal PrP and ii) probably occurs by directly or indirectly masking the PrPc epitopes involved in PrPSc interaction, rather than by cross-linking membrane bound PrPc. From a practical point of view, i.e. in the context of a possible immunotherapy of prion diseases, our data promote the use of monovalent antibodies (either Fabs or engineered recombinant fragments) for further in vivo studies.

Infusion reactions triggered by monoclonal antibodies treating solid tumors

Monoclonal antibodies (mAb) are potent agents with significant therapeutic advantages and represent the new standard of care in oncology. Although fairly well tolerated, a major health issue with mAbs is the development of infusion reactions that can range in severity from mild to life threatening. Therefore, it is critical to know how to manage these reactions when the first symptoms appear. Oncology nurses need to be proactive in monitoring, assessing, and managing infusion reactions throughout the entire course of therapy. Nurses are also instrumental in developing a protocol on how to address infusion reactions. Building a partnership with patients and caregivers ensures that patients are safely treated and can fully benefit from mAb therapy.

A human anti-Pseudomonas aeruginosa serotype O6ad immunoglobulin G1 expressed in transgenic tobacco is capable of recruiting immune system effector function in vitro

The production of a recombinant human IgG1 in transgenic tobacco was examined to determine whether a plant-derived antibody could recruit immune system effector function against a bacterial pathogen. A plant transformation vector was engineered to contain genes for a human kappa light chain and a human gamma-1 heavy chain with V(H) and V(L) sequences from a previously identified human IgG2 monoclonal antibody (MAb) that specifically binds to and opsonizes Pseudomonas aeruginosa serotype O6ad. Unique NcoI and NotI restriction sites were incorporated to flank these variable sequences, resulting in a plant transformation vector that could be engineered for expression of any other human IgG1 antibody, requiring only the substitution of other V(H) and V(L) antigen-binding coding sequences. The plant-produced IgG1 was determined to have high-mannose glycan content and to be capable of mediating opsonophagocytosis of P. aeruginosa serotype O6ad in vitro using human complement and human polymorphonuclear leukocytes. Thus, MAbs produced in plants from this vector could provide human IgG1 MAbs for targeting other pathogens that require the recruitment of immune system effector functions.

In vivo expression of GLP-1/IgG-Fc fusion protein enhances beta-cell mass and protects against streptozotocin-induced diabetes

Glucagon-like peptide 1 (GLP-1) and its analogue exendin-4 (Ex4) have displayed potent glucose homeostasis-modulating characteristics in type 2 diabetes (T2D). However, there are few reports of effectiveness in type 1 diabetes (T1D) therapy, where there is massive loss of beta cells. We previously described a novel GLP-1 analogue consisting of the fusion of active GLP-1 and IgG heavy chain constant regions (GLP-1/IgG-Fc), and showed that in vivo expression of the protein, via electroporation-enhanced intramuscular plasmid-based gene transfer, normalized blood glucose levels in T2D-prone db/db mice. In the present study, GLP-1/IgG-Fc and Ex4/IgG-Fc were independently tested in multiple low-dose streptozotocin-induced T1D. Both GLP-1/IgG-Fc and Ex4/IgG-Fc effectively reduced fed blood glucose levels in treated mice and ameliorated diabetes symptoms, where as control IgG-Fc had no effect. Treatment with GLP-1/IgG-Fc or Ex4/IgG-Fc improved glucose tolerance and increased circulating insulin and GLP-1 levels. It also significantly enhanced islet beta-cell mass, which is likely a major factor in the amelioration of diabetes. This suggests that GLP-1/IgG-Fc gene therapy may be applicable to diseases where there is either acute or chronic beta-cell injury.

Antibody structure, instability, and formulation

The number of therapeutic monoclonal antibody in development has increased tremendously over the last several years and this trend continues. At present there are more than 23 approved antibodies on the US market and an estimated 200 or more are in development. Although antibodies share certain structural similarities, development of commercially viable antibody pharmaceuticals has not been straightforward because of their unique and somewhat unpredictable solution behavior. This article reviews the structure and function of antibodies and the mechanisms of physical and chemical instabilities. Various aspects of formulation development have been examined to identify the critical attributes for the stabilization of antibodies.

Recombinant production of a VL single domain antibody in Escherichia coli and analysis of its interaction with peptostreptococcal protein L

A kappa-light chain from a Fab expression system was truncated by the insertion of a stop codon in the gene sequence to produce a variable light (VL) single domain antibody (dAb). Here, we describe the expression of dAb in the periplasm of Escherichia coli through fermentation in a defined media. Immunoglobulin binding domains from peptostreptococcal protein L (PpL) have been shown to bind specifically to kappa-light chains. We have produced recombinant PpL, at high yield, and this was used to custom-produce PpL-Sepharose affinity columns. Here, we show that the affinity purification of VL dAb by this method is simple and efficient with no apparent loss in protein at any stage. The truncated dAb protein product was confirmed by electrospray mass spectrometry and N-terminal sequencing. When analyzed by SDS-PAGE it was shown to be over 95% pure and produced at yields of 35-65 mg/L of culture medium. The dAb protein produced was shown by NMR and CD to be a folded beta-sheet domain. This domain is bound by PpL with a Kd of approximately 50 nM as determined by stopped-flow fluorimetry.

Gene therapy of diabetes using a novel GLP-1/IgG1-Fc fusion construct normalizes glucose levels in db/db mice

Glucagon-like peptide (GLP-1), a major physiological incretin, plays numerous important roles in modulating blood glucose homeostasis and has been proposed for the treatment of type 2 diabetes. The major obstacles for using native GLP-1 as a therapeutic agent are that it must be delivered by a parenteral route and has a short half-life. In an attempt to develop a strategy to prolong the physiological t(1/2) and enhance the potency of GLP-1, a fusion protein consisting of active human GLP-1 and mouse IgG(1) heavy chain constant regions (GLP-1/Fc) was generated. A plasmid encoding an IgK leader peptide-driven secretable fusion protein of the active GLP-1 and IgG(1)-Fc was constructed for mammalian expression. This plasmid allows for expression of bivalent GLP-1 peptide ligands as a result of IgG-Fc homodimerization. In vitro studies employing purified GLP-1/Fc indicate that the fusion protein is functional and elevates cAMP levels in insulin-secreting INS-1 cells. In addition, it stimulates insulin secretion in a glucose concentration-dependent manner. Intramuscular gene transfer of the plasmid in db/db mice demonstrated that expression of the GLP-1/Fc peptide normalizes glucose tolerance by enhancing insulin secretion and suppressing glucagon release. This strategy of using a bivalent GLP-1/Fc fusion protein as a therapeutic agent is a novel approach for the treatment of diabetes.

Ligand-Targeted Delivery of Therapeutic siRNA

RNA interference (RNAi) is a post-transcriptional gene-silencing phenomenon that is triggered by double-stranded RNA (dsRNA). Since many diseases are associated with the inappropriate production of specific proteins, attempts are being made to exploit RNAi in a clinical settings. However, before RNAi can be exploited as therapeutically, several obstacles must be overcome. For example, small interfering RNA (siRNA) is unstable in the blood stream so any effects of injected siRNA are only transient. Accordingly, methods must be developed to prolong its activity. Furthermore, the efficient and safe delivery of siRNA into target tissues and cells is critical for successful therapy. Any useful delivery method should be designed to target siRNA to specific cells and to promote gene-silencing activity once the siRNA is inside the cells. Recent chemical modifications of siRNA have overcome problems associated with the instability of siRNA, and various ligands, including glycosylated molecules, peptides, proteins, antibodies and engineered antibody fragments, appear to be very useful or have considerable potential for the targeted delivery of siRNA. The use of such ligands improves the efficiency, specificity and, as a consequence, the safety of the corresponding delivery systems.

Nanobodies as novel agents for cancer therapy

Nanobodies are the smallest fragments of naturally occurring heavy-chain antibodies that have evolved to be fully functional in the absence of a light chain. As such, the cloning and selection of antigen-specific nanobodies obviate the need for construction and screening of large libraries, and for lengthy and unpredictable in vitro affinity maturation steps. The unique and well-characterised properties enable nanobodies to excel conventional therapeutic antibodies in terms of recognising uncommon or hidden epitopes, binding into cavities or active sites of protein targets, tailoring of half-life, drug format flexibility, low immunogenic potential and ease of manufacture. Moreover, the favourable biophysical and pharmacological properties of nanobodies, together with the ease of formatting them into multifunctional protein therapeutics, leaves them ideally placed as a new generation of antibody-based therapeutics. This review describes the state of the art on nanobodies and illustrates their potential as cancer therapeutic agents.

Manufacturing of recombinant therapeutic proteins in microbial systems

Recombinant therapeutic proteins have gained enormous importance for clinical applications. The first recombinant products have been produced in E. coli more than 20 years ago. Although with the advent of antibody-based therapeutics mammalian expression systems have experienced a major boost, microbial expression systems continue to be widely used in industry. Their intrinsic advantages, such as rapid growth, high yields and ease of manipulation, make them the premier choice for expression of non-glycosylated peptides and proteins. Innovative product classes such as antibody fragments or alternative binding molecules will further expand the use of microbial systems. Even more, novel, engineered production hosts and integrated technology platforms hold enormous potential for future applications. This review summarizes current applications and trends for development, production and analytical characterization of recombinant therapeutic proteins in microbial systems.

Engineered antibody fragments and the rise of single domains

With 18 monoclonal antibody (mAb) products currently on the market and more than 100 in clinical trials, it is clear that engineered antibodies have come of age as biopharmaceuticals. In fact, by 2008, engineered antibodies are predicted to account for >30% of all revenues in the biotechnology market. Smaller recombinant antibody fragments (for example, classic monovalent antibody fragments (Fab, scFv)) and engineered variants (diabodies, triabodies, minibodies and single-domain antibodies) are now emerging as credible alternatives. These fragments retain the targeting specificity of whole mAbs but can be produced more economically and possess other unique and superior properties for a range of diagnostic and therapeutic applications. Antibody fragments have been forged into multivalent and multi-specific reagents, linked to therapeutic payloads (such as radionuclides, toxins, enzymes, liposomes and viruses) and engineered for enhanced therapeutic efficacy. Recently, single antibody domains have been engineered and selected as targeting reagents against hitherto immunosilent cavities in enzymes, receptors and infectious agents. Single-domain antibodies are anticipated to significantly expand the repertoire of antibody-based reagents against the vast range of novel biomarkers being discovered through proteomics. As this review aims to show, there is tremendous potential for all antibody fragments either as robust diagnostic reagents (for example in biosensors), or as nonimmunogenic in vivo biopharmaceuticals with superior biodistribution and blood clearance properties.

Modulation of CSF-1-regulated post-natal development with anti-CSF-1 antibody

Colony-stimulating factor-1 (CSF-1) regulates the survival, proliferation and differentiation of macrophages. CSF-1-deficient mice are osteopetrotic due to a lack of osteoclasts, while their tissue macrophage deficiencies and an absence of CSF-1 regulation of CSF-1 receptor-expressing cells in the female reproductive tract contribute to their pleiotropic phenotype. To further understand CSF-1 regulation of macrophages in vivo, we developed a neutralizing anti-mouse CSF-1 antibody which was expressed as a recombinant Fab' fragment and coupled to 40 kDa polyethylene glycol. As developmental regulation by CSF-1 is highest during the early post-natal period, the ability of this anti-CSF-1 reagent to inhibit development was tested by regular subcutaneous injection of mice from post-natal days 0.5-57.5. Antibody treatment decreased growth rate, decreased osteoclast number, induced osteopetrosis, decreased macrophage density in bone marrow, liver, dermis, synovium and kidney and decreased adipocyte size in adipose tissue, thereby inducing phenotypes shared by CSF-1- and CSF-1 receptor-deficient mice. While the antibody blocked macrophage development in some tissues, macrophage densities in other tissues were initially high and were reduced by treatment, proving that the antibody also blocked macrophage maintenance. Since cell surface CSF-1 is sufficient for the maintenance of normal synovial macrophage densities, these studies suggest that anti-CSF-1 Fab'-PEG efficiently neutralizes all three CSF-1 isoforms in vivo, namely the secreted proteoglycan, secreted glycoprotein and cell surface glycoprotein. Since CSF-1 has been shown to enhance chronic disease development in a number of mouse model systems, these studies demonstrate the feasibility of neutralizing CSF-1 effects in these models with an anti-CSF-1 antibody.

Protein PEGylation Decreases Observed Target Association Rates via a Dual Blocking Mechanism

PEGylation is an attractive strategy to enhance the therapeutic efficacy of proteins with a short serum half-life. It can be used to extend the serum persistence and to reduce the immunogenicity of proteins. However, PEGylation can also lead to a decrease in the functional activity of the molecule to which it is applied. We constructed site-specifically PEGylated variants of anti-p185(HER-2) antibody fragments in the format of a monovalent single-chain variable fragment and a divalent miniantibody and characterized the antigen binding properties in detail. Mass-transport limited BIAcore measurements and binding assays on HER-2-overexpressing cells demonstrated that the immunoreactivity of the antibody fragments is fully maintained after PEGylation. Nevertheless, we found that the attachment of a 20-kDa polyethylene glycol (PEG) moiety led to a reduction in apparent affinity of approximately 5-fold, although in both formats, the attachment site was most distal to the antigen binding regions. This decrease in affinity was observed in kinetic BIAcore measurements as well as in equilibrium binding assays on whole cells. By analysis of the binding kinetics, we could pinpoint this reduction exclusively to slower apparent on rates. Through both experimental and computational analyses, we demonstrate that these reduced on-rates do not arise from diffusion limitations. We show that a mathematical model accounting for both intramolecular and intermolecular blocking mechanisms of the PEG moiety can robustly explain the observed binding kinetics. The results suggest that PEGylation can significantly alter the binding-competent fraction of both ligands and receptors and may help to explain some of the beneficial effects of PEGylation in vivo.

Controlled-release and local delivery of therapeutic antibodies

Human and humanised antibodies are now poised to become a major new class of protein-based therapeutic agents. A significant fraction of new drugs in clinical testing (approximately 20% in 2002) are antibody classes. Monoclonal antibodies (mAbs) with high affinities against newly discovered disease targets, both cellularly and extracellularly, are now clinically proven to elicit high bioactivities against numerous diseases, including tumours, infections, asthma, inflammation, arthritis and osteoporosis. Clinical humanised antibody delivery is typically intravenous, with large multiple doses (grams) required for systemic volumes of distribution. Due to the relatively high costs of both this drug type, and its common mode of administration, alternatives are sought where doses might be reduced and the bioavailability and efficacy enhanced. Local, controlled-release methods that deliver antibodies locally to site of disease, offer new possibilities with these potential advantages. However, protein drugs frequently exhibit formulation challenges when packaged in delivery vehicles, and as globular proteins, antibodies are no exception. Several examples of mAb controlled-release and local delivery strategies against several disease targets are reviewed. Importantly, several antibody delivery methods work in tandem with existing clinically-accepted therapeutics, sometimes exhibiting potentiating or synergistic effects in animal models with small molecule, systemically administered drugs.

Domain Interactions in the Fab Fragment: A Comparative Evaluation of the Single-chain Fv and Fab Format Engineered with Variable Domains of Different Stability

Recombinant antibody fragments, most notably Fab and scFv, have become important tools in research, diagnostics and therapy. Since different recombinant antibody formats exist, it is crucial to understand the difference in their respective biophysical properties. We assessed the potential stability benefits of changing the scFv into the Fab format, the influence of the variable domains on the stability of the Fab fragment, and the influence of the interchain disulfide bond in the Fab fragment. To analyze domain interactions, the Fab fragment was broken down into its individual domains, several two-domain assemblies and one three-domain assembly. The equilibrium denaturation properties of these constructs were then compared to those of the Fab fragment. It was found that mutual stabilization occurred across the VH/VL and the CH1/CL interface, whereas the direct interaction between the V) and the CL domain had no influence on the stability of either domain. This observation can be explained by the different interfaces used for interaction. In contrast, the whole CH1CL and VHVL unit showed significant mutual stabilization, indicating a high degree of cooperation between the VH/VL and CH1/CL interface. The interchain disulfide bond in the Fab fragment plays an essential role in this stabilization. In addition to the effects of domain association on the thermodynamic (equilibrium) stability, Fab fragments differ from scFv fragments of similar equilibrium stability by having a very slow unfolding rate. This kinetic stabilization may increase significantly the resistance of Fab fragments against short time exposure to adverse conditions.

The therapeutic antibodies market to 2008

The therapeutic biologics market is currently dominated by recombinant protein products. However, many of these products are mature, and growth of the biologics market will increasingly rely on the expansion of the therapeutic monoclonal antibody sector. Successive technology waves have driven the growth of the monoclonal antibody sector, which is currently dominated by chimeric antibodies. Chimeric products, led by Remicade and Rituxan, will continue to drive market share through to 2008. However, over the forecast period, humanized and fully human monoclonal antibodies, together with technologies such as Fabs and conjugated antibodies, will play an increasingly important role, driving monoclonal antibody market growth at a forecast compound annual growth rate of 20.9%, to reach $16.7 billion by 2008. In terms of therapeutic focus, the monoclonal antibody market is heavily focused on oncology and arthritis, immune and inflammatory disorders, and products within these therapeutic areas are set to continue to be the key growth drivers over the forecast period. Underlying the growth of the market is the evolution of the monoclonal antibody company business model, set to transition towards the highly successful innovator model.

Effect of pegylation on pharmaceuticals

Protein and peptide drugs hold great promise as therapeutic agents. However, many are degraded by proteolytic enzymes, can be rapidly cleared by the kidneys, generate neutralizing antibodies and have a short circulating half-life. Pegylation, the process by which polyethylene glycol chains are attached to protein and peptide drugs, can overcome these and other shortcomings. By increasing the molecular mass of proteins and peptides and shielding them from proteolytic enzymes, pegylation improves pharmacokinetics. This article will review how PEGylation can result in drugs that are often more effective and safer, and which show improved patient convenience and compliance.

Therapeutic antibodies for human diseases at the dawn of the twenty-first century

Antibodies are highly specific, naturally evolved molecules that recognize and eliminate pathogenic and disease antigens. The past 30 years of antibody research have hinted at the promise of new versatile therapeutic agents to fight cancer, autoimmune diseases and infection. Technology development and the testing of new generations of antibody reagents have altered our view of how they might be used for prophylactic and therapeutic purposes. The therapeutic antibodies of today are genetically engineered molecules that are designed to ensure high specificity and functionality. Some antibodies are loaded with toxic modules, whereas others are designed to function naturally, depending on the therapeutic application. In this review, we discuss various aspects of antibodies that are relevant to their use as as therapeutic agents.