Immunoadhesins as research tools and therapeutic agents

Recent Advancements in AAV-Vectored Immunoprophylaxis in the Nonhuman Primate Model

Monoclonal antibodies (mAbs) are important treatment modalities for preventing and treating infectious diseases, especially for those lacking prophylactic vaccines or effective therapies. Recent advances in mAb gene cloning from naturally infected or immunized individuals has led to the development of highly potent human mAbs against a wide range of human and animal pathogens. While effective, the serum half-lives of mAbs are quite variable, with single administrations usually resulting in short-term protection, requiring repeated doses to maintain therapeutic concentrations for extended periods of time. Moreover, due to their limited time in circulation, mAb therapies are rarely given prophylactically; instead, they are generally administered therapeutically after the onset of symptoms, thus preventing mortality, but not morbidity. Adeno-associated virus (AAV) vectors have an established record of high-efficiency in vivo gene transfer in a variety of animal models and humans. When delivered to post-mitotic tissues such as skeletal muscle, brain, and heart, or to organs in which cells turn over slowly, such as the liver and lungs, AAV vector genomes assume the form of episomal concatemers that direct transgene expression, often for the lifetime of the cell. Based on these attributes, many research groups have explored AAV-vectored delivery of highly potent mAb genes as a strategy to enable long-term expression of therapeutic mAbs directly in vivo following intramuscular or intranasal administration. However, clinical trials in humans and studies in nonhuman primates (NHPs) indicate that while AAVs are a powerful and promising platform for vectored immunoprophylaxis (VIP), further optimization is needed to decrease anti-drug antibody (ADA) and anti-capsid antibody responses, ultimately leading to increased serum transgene expression levels and improved therapeutic efficacy. The following review will summarize the current landscape of AAV VIP in NHP models, with an emphasis on vector and transgene design as well as general delivery system optimization. In addition, major obstacles to AAV VIP, along with implications for clinical translation, will be discussed.

Denaturing and Native Mass Spectrometric Analytics for Biotherapeutic Drug Discovery Research: Historical, Current, and Future Personal Perspectives

Mass spectrometry (MS) plays a key role throughout all stages of drug development and is now as ubiquitous as other analytical techniques such as surface plasmon resonance, nuclear magnetic resonance, and supercritical fluid chromatography, among others. Herein, we aim to discuss the history of MS, both electrospray and matrix-assisted laser desorption ionization, specifically for the analysis of antibodies, evolving through to denaturing and native-MS analysis of newer biologic moieties such as antibody-drug conjugates, multispecific antibodies, and interfering nucleic acid-based therapies. We discuss challenging therapeutic target characterization such as membrane protein receptors. Importantly, we compare and contrast the MS and hyphenated analytical chromatographic methods used to characterize these therapeutic modalities and targets within biopharmaceutical research and highlight the importance of appropriate MS deconvolution software and its essential contribution to project progression. Finally, we describe emerging applications and MS technologies that are still predominantly within either a development or academic stage of use but are poised to have significant impact on future drug development within the biopharmaceutic industry once matured. The views reflected herein are personal and are not meant to be an exhaustive list of all relevant MS performed within biopharmaceutical research but are what we feel have been historically, are currently, and will be in the future the most impactful for the drug development process.

Current progress and limitations of AAV mediated delivery of protein therapeutic genes and the importance of developing quantitative pharmacokinetic/pharmacodynamic (PK/PD) models

While protein therapeutics are one of the most successful class of drug molecules, they are expensive and not suited for treating chronic disorders that require long-term dosing. Adeno-associated virus (AAV) mediated in vivo gene therapy represents a viable alternative, which can deliver the genes of protein therapeutics to produce long-term expression of proteins in target tissues. Ongoing clinical trials and recent regulatory approvals demonstrate great interest in these therapeutics, however, there is a lack of understanding regarding their cellular disposition, whole-body disposition, dose-exposure relationship, exposure-response relationship, and how product quality and immunogenicity affects these important properties. In addition, there is a lack of quantitative studies to support the development of pharmacokinetic-pharmacodynamic models, which can support the discovery, development, and clinical translation of this delivery system. In this review, we have provided a state-of-the-art overview of current progress and limitations related to AAV mediated delivery of protein therapeutic genes, along with our perspective on the steps that need to be taken to improve clinical translation of this therapeutic modality.

Optimization of the human colorectal carcinoma antigen GA733-2 production in tobacco plants

The colorectal carcinoma-associated protein GA733-2 is one of the representative candidate protein for the development of plant-derived colorectal cancer vaccine. Despite of its significant importance for colorectal vaccine development, low efficiency of GA733-2 production limits its wide applications. To improve productivity of GA733-2 in plants, we here tested multiple factors that affect expression of recombinant GA733-2 (rGA733-2) and rGA733 fused to fragment crystallizable (Fc) domain (rGA733-Fc) protein. The rGA733-2 and rGA733-Fc proteins were highly expressed when the pBINPLUS vector system was used for transient expression in tobacco plants. In addition, the length of interval between rGA733-2 and left border of T-DNA affected the expression of rGA733 protein. Transient expression analysis using various combinations of Agrobacterium tumefaciens strains (C58C1, LBA4404, and GV3101) and tobacco species (Nicotiana tabacum cv. Xanthi nc and Nicotiana benthamiana) revealed that higher accumulation of rGA733-2 and rGA733-Fc proteins were obtained by combination of A. tumefaciens LBA4404 and Nicotiana benthamiana. Transgenic plants generated by introduction of the rGA733-2 and rGA733-Fc expression cassettes also significantly accumulated corresponding recombinant proteins. Bioactivity and stability of the plant-derived rGA733 and rGA733-Fc were evaluated by further in vitro assay, western blot and N-glycosylation analysis. Collectively, we here suggest the optimal condition for efficient production of functional rGA733-2 protein in tobacco system.

Designed variants of ACE2-Fc that decouple anti-SARS-CoV-2 activities from unwanted cardiovascular effects

Angiotensin-converting enzyme 2 (ACE2) is the entry receptor for SARS-CoV-2, and recombinant ACE2 decoys are being evaluated as new antiviral therapies. We designed and tested an antibody-like ACE2-Fc fusion protein, which has the benefit of long pharmacological half-life and the potential to facilitate immune clearance of the virus. Out of a concern that the intrinsic catalytic activity of ACE2 may unintentionally alter the balance of its hormonal substrates and cause adverse cardiovascular effects in treatment, we performed a mutagenesis screening for inactivating the enzyme. Three mutants, R273A, H378A and E402A, completely lost their enzymatic activity for either surrogate or physiological substrates. All of them remained capable of binding SARS-CoV-2 and could suppress the transduction of a pseudotyped virus in cell culture. This study established new ACE2-Fc candidates as antiviral treatment for SARS-CoV-2 without potentially harmful side effects from ACE2's catalytic actions toward its vasoactive substrates.

Modulation of Signaling Mediated by TSLP and IL-7 in Inflammation, Autoimmune Diseases, and Cancer

Thymic Stromal Lymphopoietin (TSLP) and Interleukin-7 (IL-7) are widely studied cytokines within distinct branches of immunology. On one hand, TSLP is crucially important for mediating type 2 immunity at barrier surfaces and has been linked to widespread allergic and inflammatory diseases of the airways, skin, and gut. On the other hand, IL-7 operates at the foundations of T-cell and innate lymphoid cell (ILC) development and homeostasis and has been associated with cancer. Yet, TSLP and IL-7 are united by key commonalities in their structure and the structural basis of the receptor assemblies they mediate to initiate cellular signaling, in particular their cross-utilization of IL-7Rα. As therapeutic targeting of TSLP and IL-7 via diverse approaches is reaching advanced stages and in light of the plethora of mechanistic and structural data on receptor signaling mediated by the two cytokines, the time is ripe to provide integrated views of such knowledge. Here, we first discuss the major pathophysiological roles of TSLP and IL-7 in autoimmune diseases, inflammation and cancer. Subsequently, we curate structural and mechanistic knowledge about receptor assemblies mediated by the two cytokines. Finally, we review therapeutic avenues targeting TSLP and IL-7 signaling. We envision that such integrated view of the mechanism, structure, and modulation of signaling assemblies mediated by TSLP and IL-7 will enhance and fine-tune the development of more effective and selective approaches to further interrogate the role of TSLP and IL-7 in physiology and disease.

Engineering an enhanced thrombin-based GLP-1 analog with long-lasting glucose-lowering and efficient weight reduction

Peptides are considered as potent therapeutic drugs primarily due to the exquisite potency and selectivity to targets. However, the development and clinical application of peptide drugs were severely limited by the poor in vivo lifespans. Here, we designed an improved small albumin-binding polypeptide that can associate with human serum albumin (HSA) and liberate the bioactive peptide. Using glucagon-like peptide-1 (GLP-1) as a model, two new long-lasting GLP-1 analogs (termed XTS1 and XTS2) containing an albumin-binding domain, a protease-cleavable linker and a mutated GLP-1(A8Aib) were designed to demonstrate the sustained release of GLP-1 due to the plasma thrombin (TBN) digestion. Two XTS peptides were prepared of high purity (>99%) and accurate molecular weight determined by reversed high-performance liquid chromatography and mass spectrometry, respectively. In vitro measurements of surface plasmon resonance indicated that XTS1 associate with serum albumins of all species with higher affinity compared with XTS2. Metabolic stability of XTS1 in vitro in human plasma was also better than that of XTS2. Protease cleavage assay results of XTS peptides demonstrated the controlled-release of transient GLP-1 from the XTS1 and XTS2 mixture after thrombin-catalyzed hydrolysis. Then the intraperitoneal glucose tolerance test (IPGTT) showed that the glucose-lowering efficacies of XTS1 were in a dosage-dependent manner within the range of 0.1–0.9 mg kg⁻¹. In addition, XTS1 showed similar hypoglycemic intensity and significantly longer action duration compared to Liraglutide in both multiple IPGTTs and hypoglycemic duration test. Apparently extended plasma half-lives of ∼2.3 and ∼3.5 days were observed after a single subcutaneous administration of XTS1 (0.9 mg kg⁻¹) in rats and cynomolgus monkeys, respectively. Furthermore, twice-weekly subcutaneously dosed XTS1 in db/db mice achieved long-term beneficial effects on body weight, hemoglobin A1C (HbA1C) lowering and the function of pancreatic beta cells. These studies support that XTS1 exerts potential as a therapeutic drug for the treatment of T2DM.

Peptides are considered as potent therapeutic drugs primarily due to the exquisite potency and selectivity to targets.

Novel approaches in preclinical HIV vaccine research

PURPOSE OF REVIEW

The purpose is to review recent novel approaches in HIV vaccine research and development being undertaken in the preclinical and early clinical space, as well as related and novel nonvaccine approaches such as genetic delivery of broadly neutralizing antibodies for protection from HIV infection and AIDS.

RECENT FINDINGS

We review novel HIV envelope immunogen design, including native trimer and germline targeting approaches as well as genetic delivery of broadly neutralizing antibodies and replicating vector vaccinesSUMMARY: Despite 30+ years of research and development, and billions of dollars spent, a well tolerated and effective HIV vaccine remains a public health priority for any chance of ending the AIDS pandemic. It has become very clear that significant investments in novel technologies, innovation, and multidisciplinary science will be necessary to accelerate progress.

Engineered Expression of Broadly Neutralizing Antibodies Against Human Immunodeficiency Virus

This review discusses recent progress made in developing a vaccine and novel treatments for human immunodeficiency virus (HIV). It highlights the shortcomings of the RV144 vaccination trial [ALVAC-HIV (vCP1521) and AIDSVAX B/E] and the current standard of care and proposes that engineered expression of broadly neutralizing antibodies (bNAbs) against HIV-1 could overcome these shortcomings. Current developments in three major lines of research on HIV prevention and treatment using bNAbs are reviewed: firstly, the use of sequential immunogens to activate B cells to express bNAbs; secondly, the delivery of novel and extremely potent bNAbs through passive administration; and finally, the use of gene transfer using adeno-associated viral vectors to deliver bNAbs.

Expression, Purification, and Biophysical Characterization of a Secreted Anthrax Decoy Fusion Protein in Nicotiana benthamiana

Anthrax toxin receptor-mediated drug development for blocking anthrax toxin action has received much attention in recent decades. In this study, we produced a secreted anthrax decoy fusion protein comprised of a portion of the human capillary morphogenesis gene-2 (CMG2) protein fused via a linker to the fragment crystallizable (Fc) domain of human immunoglobulin G1 in Nicotiana benthamiana plants using a transient expression system. Using the Cauliflower Mosaic Virus (CaMV) 35S promoter and co-expression with the p19 gene silencing suppressor, we were able to achieve a high level of recombinant CMG2-Fc-Apo (rCMG2-Fc-Apo) protein accumulation. Production kinetics were observed up to eight days post-infiltration, and maximum production of 826 mg/kg fresh leaf weight was observed on day six. Protein A affinity chromatography purification of the rCMG2-Fc-Apo protein from whole leaf extract and apoplast wash fluid showed the homodimeric form under non-reducing gel electrophoresis and mass spectrometry analysis confirmed the molecular integrity of the secreted protein. The N-glycosylation pattern of purified rCMG2-Fc-Apo protein was analysed; the major portion of N-glycans consists of complex type structures in both protein samples. The most abundant (>50%) N-glycan structure was GlcNAc₂(Xyl)Man₃(Fuc)GlcNAc₂ in rCMG2-Fc-Apo recovered from whole leaf extract and apoplast wash fluid. High mannose N-glycan structures were not detected in the apoplast wash fluid preparation, which confirmed the protein secretion. Altogether, these findings demonstrate that high-level production of rCMG2-Fc-Apo can be achieved by transient production in Nicotiana benthamiana plants with apoplast targeting.

Vector-Mediated In Vivo Antibody Expression

This article focuses on a novel vaccine strategy known as vector-mediated antibody gene transfer, with a particular focus on human immunodeficiency virus (HIV). This strategy provides a solution to the problem of current vaccines that fail to generate neutralizing antibodies to prevent HIV-1 infection and AIDS. Antibody gene transfer allows for predetermination of antibody affinity and specificity prior to "immunization" and avoids the need for an active humoral immune response against the HIV envelope protein. This approach uses recombinant adeno-associated viral (rAAV) vectors, which have been shown to transduce muscle with high efficiency and direct the long-term expression of a variety of transgenes, to deliver the gene encoding a broadly neutralizing antibody into the muscle. Following rAAV vector gene delivery, the broadly neutralizing antibodies are endogenously synthesized in myofibers and passively distributed to the circulatory system. This is an improvement over classical passive immunization strategies that administer antibody proteins to the host to provide protection from infection. Vector-mediated gene transfer studies in mice and monkeys with anti-HIV and simian immunodeficiency virus (SIV)-neutralizing antibodies demonstrated long-lasting neutralizing activity in serum with complete protection against intravenous challenge with virulent HIV and SIV. These results indicate that existing potent anti-HIV antibodies can be rapidly moved into the clinic. However, this methodology need not be confined to HIV. The general strategy of vector-mediated antibody gene transfer can be applied to other difficult vaccine targets such as hepatitis C virus, malaria, respiratory syncytial virus, and tuberculosis.

Full Length Single Chain Fc Protein (FLSC IgG1) as a Potent Antiviral Therapy Candidate: Implications for In Vivo Studies

We have previously shown that FLSC, a chimeric protein containing HIV-1BAL gp120 and the D1 and D2 domains of human CD4, blocks the binding and entry of HIV-1 into target cells by occluding CCR5, the major HIV-1 coreceptor. In an effort to improve the antiviral potential of FLSC, we fused it with the hinge-CH2-CH3 region of human IgG1. The IgG moiety should increase both the affinity and stability in vivo of FLSC, due to the resultant bivalency and an extended serum half-life, thereby increasing its antiviral potency. We previously showed that (FLSC) IgG1 indeed had greater antiviral activity against T cell infections. Here we extend these results to macrophages, for which (FLSC) IgG1 has a more potent antiviral activity than FLSC alone, due in part to its higher binding affinity for CCR5. We also test both compounds in a relevant humanized mouse model and show that, as anticipated, the IgG1 moiety confers a greatly extended half-life. These data, taken together with previous results, suggest potential clinical utility for (FLSC) IgG1 and support further developmental work toward eventual clinical trials.

Anti-infective immunoadhesins from plants

Immunoadhesins are recombinant proteins that combine the ligand-binding region of a receptor or adhesion molecule with immunoglobulin constant domains. All FDA-approved immunoadhesins are designed to modulate the interaction of a human receptor with its normal ligand, such as Etanercept (Enbrel(®) ), which interferes with the binding of tumour necrosis factor (TNF) to the TNF-alpha receptor and is used to treat inflammatory diseases such as rheumatoid arthritis. Like antibodies, immunoadhesins have long circulating half-lives, are readily purified by affinity-based methods and have the avidity advantages conferred by bivalency. Immunoadhesins that incorporate normal cellular receptors for viruses or bacterial toxins hold great, but as yet unrealized, potential for treating infectious disease. As decoy receptors, immunoadhesins have potential advantages over pathogen-targeted monoclonal antibodies. Planet Biotechnology has specialized in developing anti-infective immunoadhesins using plant expression systems. An immunoadhesin incorporating the cellular receptor for anthrax toxin, CMG2, potently blocks toxin activity in vitro and protects animals against inhalational anthrax. An immunoadhesin based on the receptor for human rhinovirus, ICAM-1, potently blocks infection of human cells by one of the major causes of the common cold. An immunoadhesin targeting the MERS coronavirus is in an early stage of development. We describe here the unique challenges involved in designing and developing immunoadhesins targeting infectious diseases in the hope of inspiring further research into this promising class of drugs.

Emerging Vaccine Technologies

Vaccination has proven to be an invaluable means of preventing infectious diseases by reducing both incidence of disease and mortality. However, vaccines have not been effectively developed for many diseases including HIV-1, hepatitis C virus (HCV), tuberculosis and malaria, among others. The emergence of new technologies with a growing understanding of host-pathogen interactions and immunity may lead to efficacious vaccines against pathogens, previously thought impossible.

TRAF2 is a biologically important necroptosis suppressor

Tumor necrosis factor α (TNFα) triggers necroptotic cell death through an intracellular signaling complex containing receptor-interacting protein kinase (RIPK) 1 and RIPK3, called the necrosome. RIPK1 phosphorylates RIPK3, which phosphorylates the pseudokinase mixed lineage kinase-domain-like (MLKL)-driving its oligomerization and membrane-disrupting necroptotic activity. Here, we show that TNF receptor-associated factor 2 (TRAF2)-previously implicated in apoptosis suppression-also inhibits necroptotic signaling by TNFα. TRAF2 disruption in mouse fibroblasts augmented TNFα-driven necrosome formation and RIPK3-MLKL association, promoting necroptosis. TRAF2 constitutively associated with MLKL, whereas TNFα reversed this via cylindromatosis-dependent TRAF2 deubiquitination. Ectopic interaction of TRAF2 and MLKL required the C-terminal portion but not the N-terminal, RING, or CIM region of TRAF2. Induced TRAF2 knockout (KO) in adult mice caused rapid lethality, in conjunction with increased hepatic necrosome assembly. By contrast, TRAF2 KO on a RIPK3 KO background caused delayed mortality, in concert with elevated intestinal caspase-8 protein and activity. Combined injection of TNFR1-Fc, Fas-Fc and DR5-Fc decoys prevented death upon TRAF2 KO. However, Fas-Fc and DR5-Fc were ineffective, whereas TNFR1-Fc and interferon α receptor (IFNAR1)-Fc were partially protective against lethality upon combined TRAF2 and RIPK3 KO. These results identify TRAF2 as an important biological suppressor of necroptosis in vitro and in vivo.

Vector-mediated antibody gene transfer for infectious diseases

This chapter discusses the emerging field of vector-mediated antibody gene transfer as an alternative vaccine for infectious disease, with a specific focus on HIV. However, this methodology need not be confined to HIV-1; the general strategy of vector-mediated antibody gene transfer can be applied to other difficult vaccine targets like hepatitis C virus, malaria, respiratory syncytial virus, and tuberculosis. This approach is an improvement over classical passive immunization strategies that administer antibody proteins to the host to provide protection from infection. With vector-mediated gene transfer, the antibody gene is delivered to the host, via a recombinant adeno-associated virus (rAAV) vector; this in turn results in long-term endogenous antibody expression from the injected muscle that confers protective immunity. Vector-mediated antibody gene transfer can rapidly move existing, potent broadly cross-neutralizing HIV-1-specific antibodies into the clinic. The gene transfer products demonstrate a potency and breadth identical to the original product. This strategy eliminates the need for immunogen design and interaction with the adaptive immune system to generate protection, a strategy that so far has shown limited promise.

The Ephrin-A5/EphA4 Interaction Modulates Neurogenesis and Angiogenesis by the p-Akt and p-ERK Pathways in a Mouse Model of TLE

Studies have shown that neurogenesis and angiogenesis do exist in temporal lobe epilepsy (TLE). The ephrin ligands and Eph receptors are the largest members of receptor tyrosine kinases, and their interaction via cell-cell contact participates in cell proliferation, differentiation, migration, and tissue remodeling. However, there is little information about the function of the ephrin-A5/EphA4 complex in TLE. In the current study, we found that ephrin-A5 was expressed in astrocytes, while EphA4 existed in endothelial cells in the hippocampus in a mouse model of TLE. Furthermore, the messenger RNA (mRNA) and protein levels of both ephrin-A5 and EphA4 and the binding capacity of ephrin-A5/EphA4 showed gradual increase in spatiotemporal course. When ephrin-A5-Fc was injected into the hippocampus at 3 days post-status epilepticus (SE) for 7 days, the spontaneous recurrent seizure (SRS) frequency and intensity of the mice attenuated in the following 2 weeks. Furthermore, doublecortin-positive neuronal progenitor cells were reduced in the subgranular zone, and the density of microvessels decreased in the hilus. The molecular mechanism was attributed to ephrin-A5-Fc-induced inhibition of phosphorylated ERK (p-ERK) and phosphorylated Akt (p-Akt), and also EphA4 and VEGF reduction. In summary, interaction between ephrin-A5 and EphA4 could mediate the ERK and Akt signaling pathways in pilocarpine-induced epilepsy, and intervention of the ephrin/Eph interaction may play an essential role in the suppression of newborn neuron generation, microvessel remodeling, and SRS in a mouse model of TLE. The ephrin-A5/EphA4 communication may provide a potential therapy for the treatment of TLE.

Adeno-associated virus delivery of broadly neutralizing antibodies

PURPOSE OF REVIEW

In the present review, we will discuss the emerging field of vector-mediated antibody gene transfer as an alternative HIV vaccine. This approach is an improvement over classical passive immunization strategies that administer antibodies to the host to provide protection from infection. With vector-mediated gene transfer, the antibody gene is delivered to the host, resulting in long-term endogenous antibody expression from the injected muscle that confers protective immunity.

RECENT FINDINGS

Large numbers of very potent and broadly neutralizing HIV antibodies have recently been isolated and characterized. Vector-mediated antibody gene transfer allows one to immediately use these antibodies as a vaccine. Gene transfer studies in both mice and monkeys demonstrate long-term antibody expression in serum from a single injection at concentrations that provide sterilizing immunity.

SUMMARY

Vector-mediated antibody gene transfer can rapidly move existing, potent anti-HIV molecules into the clinic. The gene transfer products demonstrate a potency and breadth identical to the original product. This strategy eliminates the need for immunogen design and interaction with the adaptive immune system to generate protection, a strategy that so far has shown little promise.

Binding of fusion protein FLSC IgG1 to CCR5 is enhanced by CCR5 antagonist Maraviroc

The CCR5 chemokine receptor is crucial for human immunodeficiency virus type 1 (HIV-1) infection, acting as the principal coreceptor for HIV-1 entry and transmission and is thus an attractive target for antiviral therapy. Studies have suggested that CCR5 surface density and its conformational changes subsequent to virion engagement are rate limiting for entry, and consequently, infection. Not all CCR5 antibodies inhibit HIV-1 infection, suggesting a need for more potent reagents. Here we evaluated full length single chain (FLSC) IgG1, a novel IgG-CD4-gp120(BAL) fusion protein with several characteristics that make it an attractive candidate for treatment of HIV-1 infections, including bivalency and a potentially increased serum half-life over FLSC, the parental molecule. FLSC IgG1 binds two domains on CCR5, the N-terminus and the second extracellular loop, lowering the levels of available CCR5 viral attachment sites. Furthermore, FLSC IgG1 synergizes with Maraviroc (MVC), the only licensed CCR5 antagonist. In this study, we used both microscopy and functional assays to address the mechanistic aspects of the interactions of FLSC IgG1 and MVC in the context of CCR5 conformational changes and viral infection. We used a novel stochastic optical reconstruction microscopy (STORM), based on high resolution localization of photoswitchable dyes to visualize direct contacts between FLSC IgG1 and CCR5. We compared viral entry inhibition by FLSC IgG1 with that of other CCR5 blockers and showed FLSC IgG1 to be the most potent. We also showed that lower CCR5 surface densities in HIV-1 infected primary cells result in lower FLSC IgG1 EC50 values. In addition, CCR5 binding by FLSC IgG1, but not CCR5 Ab 2D7, was significantly increased when cells were treated with MVC, suggesting MVC allosterically increases exposure of the FLSC IgG1 binding site. These data have implications for future antiviral therapy development.

Novel exenatide analogs with peptidic albumin binding domains: potent anti-diabetic agents with extended duration of action

The design, synthesis and pharmacology of novel long-acting exenatide analogs for the treatment of metabolic diseases are described. These molecules display enhanced pharmacokinetic profile and potent glucoregulatory and weight lowering actions compared to native exenatide. [Leu(14)]exenatide-ABD is an 88 residue peptide amide incorporating an Albumin Binding Domain (ABD) scaffold. [Leu(14)]exenatide-ABP is a 53 residue peptide incorporating a short Albumin Binding Peptide (ABP). [Leu(14)]exenatide-ABD and [Leu(14)]exenatide-ABP exhibited nanomolar functional GLP-1 receptor potency and were metabolically stable in vitro in human plasma and in a pancreatic digestive enzyme mixture. Both molecules displayed picomolar and nanomolar binding association with albumin across multiple species and circulating half lives of 16 and 11 hours, respectively, post a single IV dose in rats. Unlike exenatide, both molecules elicited robust glucose lowering when injected 1 day prior to an oral glucose tolerance test, indicative of their extended duration of action. [Leu(14)]exenatide-ABD was compared to exenatide in a Lep (ob/ob) mouse model of diabetes. Twice-weekly subcutaneously dosed [Leu(14)]exenatide-ABD displayed superior glucose lowering and weight loss in diabetic mice when compared to continuously infused exenatide at the same total weekly dose. A single oral administration of each molecule via an enteric coated capsule to cynomolgus monkeys showed superior pharmacokinetics for [Leu(14)]exenatide-ABD as compared to [Leu(14)]exenatide-ABP with detectable exposure longer than 14 days. These studies support the potential use of these novel long acting exenatide analogs with different routes of administration for the treatment of type 2 diabetes.

Expression of GA733-Fc fusion protein as a vaccine candidate for colorectal cancer in transgenic plants

The tumor-associated antigen GA733 is a cell-surface glycoprotein highly expressed in colorectal carcinomas. In this study, 3 recombinant genes were constructed as follows: GA733 tagged to the ER retention sequence KDEL (GA733K), GA733 fused to the immunoglobulin Fc fragment (GA733-Fc), and GA733-Fc fused to the ER retention sequence (GA733-FcK). Agrobacterium-mediated transformation was used to generate transgenic plants expressing recombinant genes. The presence of transgenes was confirmed by genomic PCR. Western blot, confocal immunofluorescence, and sandwich ELISA showed the expression of recombinant proteins. The stability, flexibility, and bioactivity of recombinant proteins were analyzed and demonstrated through N-glycosylation analysis, animal trials, and sera ELISA. Our results suggest that the KDEL retained proteins in ER with oligomannose glycan structure and enhanced protein accumulation level. The sera of mice immunized with GA733-FcK purified from plants contained immunoglobulins which were at least as efficient as the mammalian-derived GA733-Fc at recognizing human colorectal cancer cell lines. Thus, a plant system can be used to express the KDEL fusion protein with oligomannose glycosylation, and this protein induces an immune response which is comparable to non-KDEL-tagged, mammalian-derived proteins.

Two decades of plant-based candidate vaccines: a review of the chimeric protein approaches

Genetic engineering revolutionized the concept of traditional vaccines since subunit vaccines became reality. Additionally, over the past two decades plant-derived antigens have been studied as potential vaccines with several advantages, including low cost and convenient administration. More specifically, genetic fusions allowed the expression of fusion proteins carrying two or more components with the aim to elicit immune responses against different targets, including antigens from distinct pathogens or strains. This review aims to provide an update in the field of the production of plant-based vaccine, focusing on those approaches based on the production of chimeric proteins comprising antigens from human pathogens, emphasizing the case of cholera toxin/E. coli enterotoxin fusions, chimeric viruses like particles approaches as well as the possible use of adjuvant-producing plants as expression hosts. Challenges for the near future in this field are also discussed.

Pathway-specific engagement of ephrinA5-EphA4/EphA5 system of the substantia nigra pars reticulata in cocaine-induced responses

The nucleus accumbens (NAc) serves as a key neural substrate that controls acute and adaptive behavioral responses to cocaine administration. In this circuit, inputs from the NAc are transmitted through two parallel pathways, named the direct and indirect pathways, and converge at the substantia nigra pars reticulata (SNr). Our previous study using reversible neurotransmission blocking (RNB) of each pathway revealed that the dual stimulation of the SNr by both pathways is necessary for the acute response, but that the direct pathway predominantly controls the adaptive response to repeated cocaine administration. This study aimed at exploring the pathway-specific mechanism of cocaine actions at the convergent SNr. We examined a genome-wide expression profile of the SNr of three types of experimental mice: the direct pathway-blocked D-RNB mice, the indirect pathway-blocked I-RNB mice, and wild-type mice. We identified the up-regulation of ephrinA5, EphA4, and EphA5 specific to D-RNB mice during both acute and adaptive responses to cocaine administration. The activation by EphA4 and EphA5 in the SNr of wild-type mice by use of the immunoadhesin technique suppressed the adaptive response to repeated cocaine administration. Furthermore, cocaine exposure stimulated the phosphorylation of Erk1/2 in ephrinA5-expressing SNr cells in a direct pathway-dependent manner. The results have demonstrated that the ephrinA5-EphA4/EphA5 system plays an important role in the direct pathway-dependent regulation of the SNr in both acute and adaptive cocaine responses and would provide valuable therapeutic targets of cocaine addiction.

Recombinant anthrax toxin receptor-Fc fusion proteins produced in plants protect rabbits against inhalational anthrax

Inhalational anthrax, a zoonotic disease caused by the inhalation of Bacillus anthracis spores, has a ∼50% fatality rate even when treated with antibiotics. Pathogenesis is dependent on the activity of two toxic noncovalent complexes: edema toxin (EdTx) and lethal toxin (LeTx). Protective antigen (PA), an essential component of both complexes, binds with high affinity to the major receptor mediating the lethality of anthrax toxin in vivo, capillary morphogenesis protein 2 (CMG2). Certain antibodies against PA have been shown to protect against anthrax in vivo. As an alternative to anti-PA antibodies, we produced a fusion of the extracellular domain of human CMG2 and human IgG Fc, using both transient and stable tobacco plant expression systems. Optimized expression led to the CMG2-Fc fusion protein being produced at high levels: 730 mg/kg fresh leaf weight in Nicotiana benthamiana and 65 mg/kg in N. tabacum. CMG2-Fc, purified from tobacco plants, fully protected rabbits against a lethal challenge with B. anthracis spores at a dose of 2 mg/kg body weight administered at the time of challenge. Treatment with CMG2-Fc did not interfere with the development of the animals' own immunity to anthrax, as treated animals that survived an initial challenge also survived a rechallenge 30 days later. The glycosylation of the Fc (or lack thereof) had no significant effect on the protective potency of CMG2-Fc in rabbits or on its serum half-life, which was about 5 days. Significantly, CMG2-Fc effectively neutralized, in vitro, LeTx-containing mutant forms of PA that were not neutralized by anti-PA monoclonal antibodies.

Inhibition of foam cell formation using a soluble CD68-Fc fusion protein

The appearance of lipid-rich foam cells is a major feature of vulnerable atherosclerotic plaque formation. The transformation of macrophages into foam cells results from excessive uptake of cholesterol-rich particles by scavenger receptors such as CD68. We cloned a CD68-Fc immunoadhesin, a fusion protein consisting of the extracellular domain of the human CD68 and a human Fc domain, and investigated the function in vitro. Specific binding of CD68-Fc to OxLDL with an affinity of 10 nmol/L was determined by surface plasmon resonance and increased binding to lipid-rich human and ApoE(-/-) mice plaque tissue. This was confirmed both by immunohistochemical staining of CD68-Fc-treated paraffin sections from human plaques and by ELISA-based quantification of CD68-Fc binding to human atherosclerotic plaque extracts. In an in vitro model of macrophage/foam cell formation, CD68-Fc reduced foam cell formation significantly. This was caused both by interference of CD68-Fc with OxLDL uptake into macrophages and platelets and by the inhibition of platelet/OxLDL phagocytosis. Finally, expression of metalloproteinases by macrophages/foam cells was inhibited by CD68-Fc. In conclusion, CD68-Fc seems to be a promising new tool for preventing macrophage/foam cell formation. Thus, CD68-Fc might offer a novel therapeutic strategy for patients with acute coronary syndrome by modulating the generation of vulnerable plaques.

Production of recombinant anthrax toxin receptor (ATR/CMG2) fused with human Fc in planta

Mass vaccination against anthrax with existing vaccines is costly and unsafe due to potential side effects. For post-infection treatment, passive immunotherapy measures are currently available, most based on anthrax protective antigen (PA)-specific therapeutic antibodies. Efficient against wild-type strains, these treatment(s) might fail to protect against infections caused by genetically engineered Bacillus anthracis strains. A recent discovery revealed that the von Willebrand factor A (VWA) domain of human capillary morphogenesis protein 2 (CMG2) is an exceptionally effective anthrax toxin receptor (ATR) proficient in helping to resolve this issue. Here we describe in planta production of chimeric recombinant protein (immunoadhesin) comprised of functional ATR domain fused with the human immunoglobulin Fc fragment (pATR-Fc). The fusion design allowed us to obtain pATR-Fc in plant green tissues in a soluble form making it fairly easy to purify by Protein-A chromatography. Standardized pATR-Fc preparations (purity>90%) were shown to efficiently bind anthrax PA as demonstrated by ELISA and Western blot analysis. Recombinant pATR-Fc was also shown to protect J774A1 macrophage cells against the anthrax toxin. This study confirmed that plant-derived pATR-Fc antibody-like protein is a prospective candidate for anthrax immunotherapy.

Molecular decoys: antidotes, therapeutics and immunomodulators

Receptor–ligand interactions are fundamental to the regulation of cell physiology, enabling the communication between cells and their environment via signal transduction. Receptors are also exploited by toxins and infectious agents to mediate pathogenesis. Over the past 20 years, however, this bi-partite paradigm for cellular regulation, that is, receptors and their ligands, has been revised to include an unforeseen participant namely, soluble receptors or molecular decoys. Decoys function as nature's modifiers of potent responses such as inflammation, stimulation of cell proliferation and triggering apoptosis. Decoys not only provide the means to fine tune the regulation of these phenomena; they also serve as potential leads for the development of recombinant anti-toxins, anti-viral agents and novel therapeutics for combating cancer and inflammatory disease.

Human soluble E-selectin immunoadhesin inhibits leukemic monocyte adhesion to endothelial cells

Immunoadhesins are immunoglobulin (Ig)-like chimeric proteins comprised of target-binding regions fused to the Fc-hinge region of Ig, and are designed to have a long half-life and antibody-like properties. In an effort to find a good candidate for therapeutic use for inflammatory responses, we constructed a soluble human E-selectin immunoadhesin containing the extracellular region of human E-selectin fused to the Fc-hinge region of human IgG, and determined its effects on leukocyte adhesion and rolling in vitro. Our results revealed that the adhesion of leukocytes to endothelial cells was efficiently inhibited in the presence of 50 nM E-selectin immunoadhesin. In addition, the E-selectin immunoadhesin significantly inhibited leukocyte rolling on endothelial cells in perfusion experiments performed at 1.0 dyne/cm(2) wall shear stress. These findings indicate that our E-selectin immunoadhesin decreases leukocyte attachment and rolling in vitro, suggesting that this immunoadhesin may be a promising candidate for therapeutic anti-inflammatory use.

A recombinant allosteric lectin antagonist of HIV-1 envelope gp120 interactions

The first, critical stage of HIV-1 infection is fusion of viral and host cellular membranes initiated by a viral envelope glycoprotein gp120. We evaluated the potential to form a chimeric protein entry inhibitor that combines the action of two gp120-targeting molecules, an allosteric peptide inhibitor 12p1 and a higher affinity carbohydrate-binding protein cyanovirin (CVN). In initial mixing experiments, we demonstrated that the inhibitors do not interfere with each other and instead show functional synergy in inhibiting viral cell infection. Based on this, we created a chimera, termed L5, with 12p1 fused to the C-terminal domain of CVN through a linker of five penta-peptide repeats. L5 revealed the same broad specificity as CVN for gp120 from a variety of clades and tropisms. By comparison to CVN, the L5 chimera exhibited substantially increased inhibition of gp120 binding to receptor CD4, coreceptor surrogate mAb 17b and gp120 antibody F105. These binding inhibition effects by the chimera reflected both the high affinity of the CVN domain and the allosteric action of the 12p1 domain. The results open up the possibility to form high potency chimeras, as well as noncovalent mixtures, as leads for HIV-1 envelope antagonism that can overcome potency limits and potential virus mutational resistance for either 12p1 or CVN alone.

An immunoglobulin fusion protein based on the gp120-CD4 receptor complex potently inhibits human immunodeficiency virus type 1 in vitro

Fusion proteins containing immunoglobulin Fc domains attached to bioactive moieties have been developed as therapeutic agents against several diseases. Here, we describe the development and characteristics of a novel fusion protein (FLSC R/T-IgG1) that targets CCR5, the major coreceptor for HIV-1 during primary infection. FLSC R/T-IgG1 was expressed from a synthetic gene that linked a single chain gp120-CD4 complex containing an R5 gp120 sequence with the hinge-CH2-CH3 portion of human immunoglobulin gamma subtype 1. Purified FLSC R/T-IgG1 exhibited a molecular mass of 189 kDa under reducing conditions, which matched the expected size of one polypeptide chain. Chemically crosslinked or untreated FLSC R/T-IgG1 exhibited a mass of a 360-kDa polypeptide under reducing and nonreducing conditions, which indicated that the molecule adopts a disulfide-linked bivalent structure. The chimeric molecule bound specifically to CCR5-expressing cells and to peptides derived from the CCR5 N-terminus. Such binding was more efficient than what was obtained with a monomeric single chain gp120-CD4 complex. FLSC R/T-IgG1 binding to CCR5 was blocked by preincubation of coreceptor-expressing cells with CCR5 ligands and by antibody to the coreceptor binding domain of gp120. Conversely, FLSC R/T-IgG1 blocked the binding of chemokine to CCR5. However, FLSC R/T-IgG1 did not trigger intracellular Ca2+ mobilization in peripheral blood mononuclear cells. FLSC R/T-IgG1 potently neutralized primary R5 HIV-1 in both a PBMC-based assay and cell line-based assays but did not affect the replication of X4 viruses. These findings suggest that FLSC R/T-IgG1 might be used as a possible therapeutic agent against HIV.

Integrating cell-level kinetic modeling into the design of engineered protein therapeutics

Functional genomics and proteomics are identifying many potential drug targets for novel therapeutic proteins, and both rational and combinatorial protein engineering methods are available for creating drug candidates. A central challenge is the definition of the most appropriate design criteria, which will benefit critically from computational kinetic models that incorporate integration from the molecular level to the whole systems level. Interpretation of these processes will require mathematical models that are refined in combination with relevant data derived from quantitative assays, to correctly set biophysical objectives for protein design.

Improving protein pharmacokinetics by genetic fusion to simple amino acid sequences

The role of primary amino acid sequences in protein pharmacokinetics, an issue of relevance in both basic knowledge and biotechnology, was addressed here using as a starting point two repetitive antigens from the hemoflagellate Trypanosoma cruzi that are known to stabilize their associated proteins in the bloodstream. A major drawback to their pharmacological application is that these repetitive sequences are highly immunogenic, being therefore the deletion of this characteristic desirable. Based on sequence homology and epitope mapping analyses, an artificial repetitive sequence (PSTAD) was engineered. This motif was tested by genetic fusion to the C terminus of both the trypanosomal trans-sialidase and the rat tyrosine aminotransferase and found to produce a 4.5-6-fold increase in the half-life of the associated proteins in blood while displaying significantly lower immunogenicity. Residues involved in the stabilizing properties of the novel peptide were mapped by a site-directed mutagenesis approach, allowing us to successfully identify another two motifs. Searching databases for sequences displaying some homology, embedded in proline frameworks and associated to shed virulence factors from unrelated microorganisms, resulted in the identification of four other protein extensions. Remarkably, three of them (from Streptococcus pneumoniae, Actinomyces viscosus, and Escherichia coli) revealed similar pharmacokinetic features, suggesting therefore an analogous evolutionarily acquired mechanism to ensure the biodistribution of their corresponding proteins. Our findings indicate that the insertion of defined motifs into a proline-rich framework constitutes a suitable alternative to construct a chimeric protein with extended half-life in blood.

Discovery of small molecule leads in a biotechnology datastream

A case study of the discovery of small molecule antagonists to the integrins GPIIbIIIa (alphaII(B)beta3), alphavbeta3, LFA-1 (alphaLbeta2), alpha4beta1 and alpha4beta7 is presented from the perspective of a biotechnology research organization. A strategy incorporating protein mutagenesis and structural studies to develop a structure-activity relationship (SAR) that described the 'epitope' of the integrin ligand was crucial to the identification of peptide analogs of these proteins, and subsequently, through parallel trends in SAR, to the identification of small molecule mimetics of these peptides, which are active analogs of the protein ligands themselves.

Albumin binding as a general strategy for improving the pharmacokinetics of proteins

Plasma protein binding can be an effective means of improving the pharmacokinetic properties of otherwise short lived molecules. Using peptide phage display, we identified a series of peptides having the core sequence DICLPRWGCLW that specifically bind serum albumin from multiple species with high affinity. These peptides bind to albumin with 1:1 stoichiometry at a site distinct from known small molecule binding sites. Using surface plasmon resonance, the dissociation equilibrium constant of peptide SA21 (Ac-RLIEDICLPRWGCLWEDD-NH(2)) was determined to be 266 +/- 8, 320 +/- 22, and 467 +/- 47 nm for rat, rabbit, and human albumin, respectively. SA21 has an unusually long half-life of 2.3 h when injected by intravenous bolus into rabbits. A related sequence, fused to the anti-tissue factor Fab of D3H44 (Presta, L., Sims, P., Meng, Y. G., Moran, P., Bullens, S., Bunting, S., Schoenfeld, J., Lowe, D., Lai, J., Rancatore, P., Iverson, M., Lim, A., Chisholm, V., Kelley, R. F., Riederer, M., and Kirchhofer, D. (2001) Thromb. Haemost. 85, 379-389), enabled the Fab to bind albumin with similar affinity to that of SA21 while retaining the ability of the Fab to bind tissue factor. This interaction with albumin resulted in reduced in vivo clearance of 25- and 58-fold in mice and rabbits, respectively, when compared with the wild-type D3H44 Fab. The half-life was extended 37-fold to 32.4 h in rabbits and 26-fold to 10.4 h in mice, achieving 25-43% of the albumin half-life in these animals. These half-lives exceed those of a Fab'(2) and are comparable with those seen for polyethylene glycol-conjugated Fab molecules, immunoadhesins, and albumin fusions, suggesting a novel and generic method for improving the pharmacokinetic properties of rapidly cleared proteins.

Vascular endothelial-junctional adhesion molecule (VE-JAM)/JAM 2 interacts with T, NK, and dendritic cells through JAM 3

Screening expressed sequence tag databases for endothelial-specific homologs to human junctional adhesion molecule (JAM) and A33-Ag, we identified a protein of 298 aa that represents the recently described vascular endothelial-JAM (VE-JAM)/JAM 2. We confirmed VE-JAM/JAM 2 expression to be restricted to the high endothelial venule of tonsil and lymph nodes, and we further expanded the localization to the endothelium of arterioles in and around inflammatory and tumor foci. In our functional characterizations of VE-JAM/JAM 2, we discovered that it can function as an adhesive ligand for the T cell line J45 and can interact with GM-CSF/IL-4-derived peripheral blood dendritic cells, circulating CD56(+) NK cells, circulating CD56(+)CD3(+) NK/T cells, and circulating CD56(+)CD3(+)CD8(+) cytolytic T cells. In the course of our studies, we also isolated and characterized the functional VE-JAM/JAM 2 receptor, which, upon cloning, turned out to be a submitted sequence representing JAM 3 (accession number NP 113658). With these understandings, we have characterized a protein-interacting pair that can be important in the role of T, NK, and dendritic cell trafficking and inflammation.

Recombinant canine IL-13 receptor alpha2-Fc fusion protein inhibits canine allergen-specific-IgE production in vitro by peripheral blood mononuclear cells from allergic dogs

Human IL-13, like IL-4, is involved in the regulation of B-cell development, IgE synthesis and allergic responses. However, because IL-13 does not affect either murine Ig class switching or IgE production in vitro, the use of murine models to study the role of IL-13 in IgE-mediated diseases has been limited. In this communication, we report that recombinant protein of canine IL-13 (rcaIL-13) stimulates production of allergen-specific-IgE in vitro by peripheral blood mononuclear cells (PBMC) from flea allergen-sensitized dogs, and that this stimulation activity is specifically inhibited by recombinant protein of canine IL-13Ralpha2 and Fc fragment of canine IgG heavy chain (rcaIL-13Ralpha2-Fc). The data suggest that the regulatory effects of IL-13 on IgE production in canine PBMC are similar to those reported in humans. Thus, canine IL-13 may be a central mediator of allergic diseases in dogs, and allergic dogs may be excellent models for research on IgE-mediated diseases in humans.

Molecular therapeutics of liver disease

Fundamental advances in biomedical research will revolutionize the prevention and treatment of liver disease during the early twenty-first century. Recent progress in gene-, cell-, and recombinant protein-based therapeutics will contribute to this revolution, although formidable obstacles currently prevent the clinical application of these novel therapies. Eventually, these obstacles will be overcome, and molecular therapeutics of liver disease will become a clinical reality. As a result, the new millennium will be a very interesting time to practice hepatology.

Design and expression of polymeric immunoglobulin fusion proteins: a strategy for targeting low-affinity Fcgamma receptors

We have developed a family of cloning vectors that direct expression of fusion proteins that mimic aggregated immunoglobulin (IgG) (AIG) and immune complex function with respect to their interactions with FcgammaR and that allow for the inclusion and targeting of a second protein domain to cells expressing FcgammaR. This was accomplished by expressing multiple linear copies of the hinge and CH2 domains (HCH2) of human IgG(1) fused to the framework region of human IgG(1). Convenient restriction sites allow for the facile introduction of additional amino-terminal domains. The resulting molecule is tripartite. The carboxyl-IgG(1) framework domain provides stability and permits dimerization, and the intervening polymer provides increased effector function and targeting to FcgammaR while the amino-terminal domain can deliver an additional signal to cells expressing FcgammaR. To demonstrate the utility of the vectors, the extracellular domain of human CD8alpha was expressed as a HCH2 polymer fusion protein. The fusion proteins were secreted in useful amounts from polyclonal cell lines established in Sf9 cells following transfection and selection with G418. The biological activity of the recombinant CD8alpha-HCH2 polymers was determined and compared to those of AIG and an anti-CD16 monoclonal antibody using an in vitro assay. The activity of the fusion proteins positively correlates to the number of HCH2 units. The largest polymer tested was severalfold more potent than AIG at similar concentrations. The HCH2 polymers described here represent a new strategy in the design of recombinant proteins for the therapeutic targeting of FcgammaR in autoimmune disorders.

Expression of lymphotoxins and their receptor-Fc fusion proteins by baculovirus

The tumor necrosis factor (TNF) cytokine and receptor superfamily plays critical roles in immune physiology. Several members of this family, such as the lymphotoxins (LT alpha and LT beta), Fas ligand, and TNF, induce cell death in some normal and transformed cells, but also induce cell growth and differentiation. The receptors for these ligands, when expressed as fusion proteins with the Fc region of IgG, function as potent antagonists of biological activity. The receptor-Fc fusion protein is a highly versatile reagent that can be utilized in virtually all the formats designed for antibodies. In this chapter we describe the expression, purification, and assays for lymphotoxins and their receptors, using a recombinant baculovirus system.

Characterization of huJAM: evidence for involvement in cell-cell contact and tight junction regulation

Cell-cell interactions of the mucosal epithelia are important for the maintenance and establishment of epithelial barrier function. During events of inflammation, such cell-cell interactions are often disrupted, resulting in a leaky epithelial barrier, which in turn can lead to various inflammatory and infective dysfunctions. Human junctional adhesion molecule (huJAM), found on the mucosal epithelia and vascular endothelia of many major organ systems, is a membrane glycoprotein which resolves to a doublet band of approximately 40 and approximately 37 kDa under SDS-PAGE analysis, representing differentially glycosylated forms of the same protein. huJAM was localized to the lateral membrane of Caco-2 cells (a human colonic epithelial cell line) monolayers, in an area basolateral of the epithelial tight junctions (TJ). Through functional and biochemical assays, we show huJAM to be able to homotypically associate and to participate in TJ restitution after trypsin-EDTA disruption. Furthermore, we also observed a migration of huJAM expression toward areas of cell-cell contacts during events of cell adhesion and monolayer formation. These qualities makes huJAM a likely player in the regulation of cell-cell contacts and the subsequent formation of TJs.

Protein targeting: altering receptor kinase function in the brain

Gene targeting has proved to be one of the most powerful techniques with which one can investigate molecular mechanisms that underlie complex phenomena such as learning and memory. Despite its popularity, however, concerns have been raised about this technique and alternative approaches have been sought. One such approach is protein targeting, which is based on the application of immunoadhesins, genetically engineered fusion proteins that exhibit functionally relevant target specificity. These immunoadhesins modulate the activity of not only a single receptor but of all receptors with homologous binding sites, which thereby eliminates the possibility of compensation by sister receptors. Furthermore, immunoadhesins can be used not only to impair but also to improve receptor function in the brain. Initial studies using immunoadhesins suggest that protein targeting might be a useful approach for analyzing the molecular mechanisms of brain function and behavior.

An interleukin-2-IgG-Fas ligand fusion protein suppresses delayed-type hypersensitivity in mice by triggering apoptosis in activated T cells as a novel strategy for immunosuppression

BACKGROUND

Cell-mediated immune responses can be down-regulated by induction of apoptosis of immunoreactive lymphocytes. In the present study, we have tested the feasibility of a strategy for immunosuppression by the selective induction of apoptosis in activated, interleukin (IL)-2 receptor-positive lymphocytes, using a triple IL-2-IgG-FasL fusion protein. The IL-2-IgG-FasL fusion protein combines IL-2 for the selection of activated T cells, with the extracellular domain of the FasL molecule for inducing T-cell apoptosis. These components were separated by the Fc part of IgG1 serving as a spacer as well as for half-life prolongation.

METHODS

The gene for the chimeric protein was created by fusing DNA sequences encoding for the three functional components: human IL-2, the Fc part of human IgG1, and the extracellular domain of murine FasL. When the fusion gene was expressed in murine J558L cells, we obtained soluble dimeric immunoglobulin-like proteins in the supernatant. After analyzing the function of the IL-2 and FasL portions individually in vitro, a delayed-type hypersensitivity (DTH) reaction to sheep red blood cells as model for cell-mediated immune responses was investigated to evaluate the IL-2-IgG-FasL-mediated immunosuppression in vivo.

RESULTS

In vitro, the IL-2-IgG-FasL fusion protein supported IL-2-dependent proliferation of Fas-resistant CTLL-2 cells, whereas concanavalin A-T blasts were induced to undergo apoptosis by the FasL portion. In vivo, this fusion protein potently inhibited a murine DTH. This was associated with an increased rate of apoptosis in activated lymphocytes in the spleen, even at very low doses of the fusion protein. Furthermore, a second antigen challenge 10 days after IL-2-IgG-FasL treatment still failed to elicit a DTH response.

CONCLUSION

The abrogation of a standard T cell-dependent immune response in vivo demonstrates that IL-2-IgG-FasL can be successfully exploited to trigger the death of deleterious T cells, presenting a potentially useful strategy in the management of autoimmune diseases and allotransplant rejections.

Blocking the NGF-TrkA interaction rescues the developmental loss of LTP in the rat visual cortex: role of the cholinergic system

Although nerve growth factor (NGF) is a crucial factor in the activity-dependent development and plasticity of visual cortex, its role in synaptic efficacy changes is largely undefined. We demonstrate that the maintenance phase of long-term potentiation (LTP) is blocked by local application of exogenous NGF in rat visual cortex at an early stage of postnatal development. Long-term depression (LTD) and bidirectional plasticity are unaffected. At later postnatal ages, blockade of either endogenous NGF by immunoadhesin (TrkA-IgG) or TrkA receptors by monoclonal antibody rescues LTP. Muscarinic receptor activation/inhibition suggests that LTP dependence on NGF is mediated by the cholinergic system. These results indicate that NGF regulates synaptic strength in well-characterized cortical circuitries.

Complement activation and inhibition in experimental models of arthritis

Complement activation has been implicated as a pathological process in a number of inflammatory and autoimmune disorders including chronic rheumatoid arthritis (RA). Animal models of experimental arthritis have been widely used to investigate the pathogenesis of RA and also in the development of novel therapies. Many of these models are complement-dependent and both incidence and progression of disease can be influenced by complement inhibition. In certain situations, local inhibition is of greater therapeutic benefit than systemic decomplementation. An increasing awareness and availability of a wide range of naturally occurring complement regulatory proteins can now offer a more targeted approach to complement inhibition while the availability of novel engineering strategies has also improved the efficiency of this process. The success of complement inhibition in the experimental models described should offer a novel therapeutic approach to the treatment of human inflammatory arthritis.

Recombinant proteins for genetic disease

The era of molecular biology has led to the development of powerful tools capable of generating therapeutics for genetic disorders. Although there is much current emphasis placed on the development of 'gene therapy' for human disease, developments in the production and availability of recombinant proteins are likely to have a more substantial impact on genetic disease in the short term. The clinical evaluation of recombinant or purified proteins serves as an initial 'proof of principle' of gene-based therapies and thus should expedite advances in this area. Current examples include the use of bovine adenosine deaminase for a form of severe combined immune deficiency (SCID) (Hilman BC, Sorensen RU. Management options: SCIDS with adenosine deaminase deficiency. Ann Allergy 72: 1994: 395-403) and glucocerebrosidase for Gaucher disease (Niederau C, vom Dahl S, Haussinger D. First long-term results of imiglucerase therapy of type 1 Gaucher disease. Eur J Med Res 1998: 3: 25-30). The success of these two enzyme replacement regimes in human clinical trials has been a main impetus for the development of gene-based therapies for these disorders. The 'molecularization of medicine' has led to a more thorough understanding of the molecular basis of disease and disease pathogenesis. The availability of recombinant proteins and the development of appropriate delivery systems will result in more widespread use of these agents. Protein engineering will generate agents with novel functions as is already witnessed with the generation of fusion proteins. This review will highlight advances in the use of recombinant proteins for genetic disease and future potential uses of recombinant proteins.

Nr-CAM promotes neurite outgrowth from peripheral ganglia by a mechanism involving axonin-1 as a neuronal receptor

Nr-CAM is a neuronal cell adhesion molecule (CAM) belonging to the immunoglobulin superfamily that has been implicated as a ligand for another CAM, axonin-1, in guidance of commissural axons across the floor plate in the spinal cord. Nr-CAM also serves as a neuronal receptor for several other cell surface molecules, but its role as a ligand in neurite outgrowth is poorly understood. We studied this problem using a chimeric Fc-fusion protein of the extracellular region of Nr-CAM (Nr-Fc) and investigated potential neuronal receptors in the developing peripheral nervous system. A recombinant Nr-CAM-Fc fusion protein, containing all six Ig domains and the first two fibronectin type III repeats of the extracellular region of Nr-CAM, retains cellular and molecular binding activities of the native protein. Injection of Nr-Fc into the central canal of the developing chick spinal cord in ovo resulted in guidance errors for commissural axons in the vicinity of the floor plate. This effect is similar to that resulting from treatment with antibodies against axonin-1, confirming that axonin-1/Nr-CAM interactions are important for guidance of commissural axons through a spatially and temporally restricted Nr-CAM positive domain in the ventral spinal cord. When tested as a substrate, Nr-Fc induced robust neurite outgrowth from dorsal root ganglion and sympathetic ganglion neurons, but it was not effective for tectal and forebrain neurons. The peripheral but not the central neurons expressed high levels of axonin-1 both in vitro and in vivo. Moreover, antibodies against axonin-1 inhibited Nr-Fc-induced neurite outgrowth, indicating that axonin-1 is a neuronal receptor for Nr-CAM on these peripheral ganglion neurons. The results demonstrate a role for Nr-CAM as a ligand in axon growth by a mechanism involving axonin-1 as a neuronal receptor and suggest that dynamic changes in Nr-CAM expression can modulate axonal growth and guidance during development.

Expression and characterization of a DNase I-Fc fusion enzyme

Recombinant human deoxyribonuclease I (DNase I) is an important clinical agent that is inhaled into the airways where it degrades DNA to lower molecular weight fragments, thus reducing the viscoelasticity of sputum and improving the lung function of cystic fibrosis patients. To investigate DNases with potentially improved properties, we constructed a molecular fusion of human DNase I with the hinge and Fc region of human IgG1 heavy chain, creating a DNase I-Fc fusion protein. Infection of Sf9 insect cells with recombinant baculovirus resulted in the expression and secretion of the DNase I-Fc fusion protein. The fusion protein was purified from the culture medium using protein A affinity chromatography followed by desalting by gel filtration and was characterized by amino-terminal sequence, amino acid composition, and a variety of enzyme-linked immunosorbent assays (ELISA) and activity assays. The purified fusion contains DNase I, as determined by a DNase I ELISA and an actin-binding ELISA, and an intact antibody Fc region, which was quantified by an Fc ELISA, in a 2:1 stoichiometric ratio, respectively. The dimeric DNase I-Fc fusion was functionally active in enzymatic DNA digestion assays, albeit about 10-fold less than monomeric DNase I. Cleavage of the DNase I-Fc fusion by papain resulted in a specific activity comparable to the monomeric enzyme. Salt was inhibitory for wild type monomeric DNase I but actually enhanced the activity of the dimeric DNase I-Fc fusion. The DNase I-Fc fusion protein was also less Ca2+-dependent than DNase I itself. These results are consistent with a higher affinity of the dimeric fusion protein to DNA than monomeric DNase I. The engineered DNase I-Fc fusion protein described herein has properties that may have clinical benefits.

Immunoadhesins of interleukin-6 and the IL-6/soluble IL-6R fusion protein hyper-IL-6

Signal transduction in response to interleukin-6 (IL-6) results from homodimerization of gp130. This dimerization occurs after binding of IL-6 to its surface receptor (IL-6R) and can also be triggered by the complex of soluble IL-6R and IL-6. We fused IL-6 to the constant region of a human IgG1 heavy chain (Fc). IL-6Fc was expressed in COS-7 cells and purified via Protein A Sepharose. Using three different assays we found that the biological activity of this dimeric IL-6 protein is comparable with monomeric IL-6. Recently, we described the designer cytokine Hyper-IL-6 (H-IL-6) in which soluble IL-6R and IL-6 are connected via a flexible peptide linker. This molecule turned out to be 100-1000 times more effective than unlinked IL-6 and soluble IL-6R. Hyper-IL-6 acts on cells only expressing gp130 and is a potent stimulator of in vitro expansion of early hematopoietic precursors. Here we show that a Fc fusion protein of H-IL-6 (H-IL-6Fc) has the same biological activity on BAF/gp130 cells as H-IL-6. Furthermore, both H-IL-6 forms have a similar ability to induce the synthesis of acute phase proteins in human hepatoma cells HepG2 and in mice in vivo. The introduction of a thrombin cleavage site between H-IL-6 and the Fc portion of H-IL-6Fc made it possible to specifically recover biologically active monomeric H-IL-6 by limited proteolysis of the fusion protein. A more general use of cleavable immunoadhesins expressed in mammalian cells is discussed.

Identification of a new member of the tumor necrosis factor family and its receptor, a human ortholog of mouse GITR

The tumor necrosis factor (TNF) and TNF receptor (TNFR) gene superfamilies regulate diverse biological functions, including cell proliferation, differentiation, and survival [1] [2] [3]. We have identified a new TNF-related ligand, designated human GITR ligand (hGITRL), and its human receptor (hGITR), an ortholog of the recently discovered murine glucocorticoid-induced TNFR-related (mGITR) protein [4]. The hGITRL gene mapped to chromosome 1q23, near the gene for the TNF homolog Fas/CD95 ligand [5]. The hGITR gene mapped to chromosome 1p36, near a cluster of five genes encoding TNFR homologs [1] [6]. We found hGITRL mRNA in several peripheral tissues, and detected hGITRL protein on cultured vascular endothelial cells. The levels of hGITR mRNA in tissues were generally low; in peripheral blood T cells, however, antigen-receptor stimulation led to a substantial induction of hGITR transcripts. Cotransfection of hGITRL and hGITR in embryonic kidney 293 cells activated the anti-apoptotic transcription factor NF-kappaB, via a pathway that appeared to involve TNFR-associated factor 2 (TRAF2) [7] and NF-kappaB-inducing kinase (NIK) [8]. Cotransfection of hGITRL and hGITR in Jurkat T leukemia cells inhibited antigen-receptor-induced cell death. Thus, hGITRL and hGITR may modulate T lymphocyte survival in peripheral tissues.

Genomic amplification of a decoy receptor for Fas ligand in lung and colon cancer

Fas ligand (FasL) is produced by activated T cells and natural killer cells and it induces apoptosis (programmed cell death) in target cells through the death receptor Fas/Apol/CD95. One important role of FasL and Fas is to mediate immune-cytotoxic killing of cells that are potentially harmful to the organism, such as virus-infected or tumour cells. Here we report the discovery of a soluble decoy receptor, termed decoy receptor 3 (DcR3), that binds to FasL and inhibits FasL-induced apoptosis. The DcR3 gene was amplified in about half of 35 primary lung and colon tumours studied, and DcR3 messenger RNA was expressed in malignant tissue. Thus, certain tumours may escape FasL-dependent immune-cytotoxic attack by expressing a decoy receptor that blocks FasL.