Population pharmacokinetic-pharmacodynamic modeling of PB2452, a monoclonal antibody fragment being developed as a ticagrelor reversal agent, in healthy volunteers.

PB2452, a neutralizing monoclonal antibody fragment that binds the antiplatelet drug ticagrelor with high affinity, is being developed as a ticagrelor reversal agent. To identify a clinically useful intravenous (i.v.) reversal regimen, a semimechanistic exposure-response model was developed during the PB2452 first-in-human phase I study. From a randomized, double-blind, placebo-controlled, single-dose trial to evaluate the safety, efficacy, and pharmacokinetics (PKs) of PB2452 in 61 healthy volunteers pretreated with ticagrelor, sequential dose cohort data were used to build and refine an exposure-response model that combined population PK models for ticagrelor (TICA), ticagrelor active metabolite (TAM), and PB2452, and related their binding relationships to the PK of uncomplexed TICA and TAM which is predictive of platelet inhibition. Platelet function was assessed by multiple assays. The model was developed using Bayesian methods in NONMEM. Human PK and pharmacodynamic data from sequential dose cohorts were used to initially define and then refine model parameters. Model simulations indicated that an initial i.v. bolus of PB2452, followed by a high-rate infusion, and then a slower-rate infusion would provide immediate and sustained reversal of the antiplatelet effects of ticagrelor. Based on model predictions, a 6 g i.v. bolus followed by 6 g infused over 4 h and then 6 g over 12 h was identified and tested in study subjects and shown to provide complete reversal within 5 min of infusion onset that was sustained for 20-24 h. The model is predictive of the reversal profile of PB2452 and will inform future trials of PB2452.

A Novel and Potent Thrombolytic Fusion Protein Consisting of Anti-Insoluble Fibrin Antibody and Mutated Urokinase.

Tissue plasminogen activator (tPA) is used clinically because it has a higher binding specificity for insoluble fibrin (IF) than urokinase (UK), but even pro-tPA has catalytic activity against substrates other than IF. UK has the advantage that it is specifically activated on IF; however, it binds IF weakly. Previously, we established a monoclonal antibody (mAb) that recognizes a pit structure formed only in IF. Here, we developed a new mAb against the pit, 1101, that does not affect coagulation or fibrinolysis, and prepared a fusion protein of UK with humanized 1101 Fab to transport UK selectively to IF. In IF-containing lesions, UK is cleaved by plasmin at two sites, Lys158/Ile159 and Lys135/Lys136. Cleavage of the former leads to activation of UK; however, because activated UK is linked by S-S bonds before and after cleavage, it is not released from the fusion. Cleavage at the latter site causes UK to leave the fusion protein; hence, we mutated Lys135/Lys136 to Gly135/Gly136 to prevent release of UK. This engineered UK-antibody fusion, AMU1114, significantly decreased the reduction of plasma plasminogen levels in vivo relative to UK. In a photochemically induced mouse model of thrombus, the vascular patency rate was 0% (0/10) in the control, 50% (5/10) in the tPA treatment group, and 90% (9/10) in the AMU1114 treatment group. Although no death was observed 1 hour after administration of each thrombolytic agent, some mice died within 24 hours in all treatment groups, including control. These data indicate the need for further basic studies of AMU1114.

Human Antibody Domains and Fragments Targeting Neutrophil Elastase as Candidate Therapeutics for Cancer and Inflammation-Related Diseases.

Neutrophil elastase (NE) is a serine protease released during neutrophil maturation. High levels of NE are related to lung tissue damage and poor prognosis in cancer; thus, NE is a potential target for therapeutic immunotherapy for multiple lung diseases and cancers. Here, we isolate and characterize two high-affinity, specific, and noncompetitive anti-NE antibodies Fab 1C10 and VH 1D1.43 from two large phage-displayed human Fab and VH libraries. After fusion with human IgG1 Fc, both of them (VH-Fc 1D1.43 and IgG1 1C10) inhibit NE enzymatic activity with VH-Fc 1D1.43 showing comparable inhibitory effects to that of the small molecule NE inhibitor SPCK and IgG1 1C10 exhibiting even higher (2.6-fold) activity than SPCK. Their epitopes, as mapped by peptide arrays combined with structural modeling, indicate different mechanisms for blocking NE activity. Both VH-Fc and IgG1 antibodies block NE uptake by cancer cells and fibroblast differentiation. VH-Fc 1D1.43 and IgG1 1C10 are promising for the antibody-based immunotherapy of cancer and inflammatory diseases.

The Chemical Synthesis of Knob Domain Antibody Fragments.

Cysteine-rich knob domains found in the ultralong complementarity determining regions of a subset of bovine antibodies are capable of functioning autonomously as 3-6 kDa peptides. While they can be expressed recombinantly in cellular systems, in this paper we show that knob domains are also readily amenable to a chemical synthesis, with a co-crystal structure of a chemically synthesized knob domain in complex with an antigen showing structural equivalence to the biological product. For drug discovery, following the immunization of cattle, knob domain peptides can be synthesized directly from antibody sequence data, combining the power and diversity of the bovine immune repertoire with the ability to rapidly incorporate nonbiological modifications. We demonstrate that, through rational design with non-natural amino acids, a paratope diversity can be massively expanded, in this case improving the efficacy of an allosteric peptide. As a potential route to further improve stability, we also performed head-to-tail cyclizations, exploiting the proximity of the N and C termini to synthesize functional, fully cyclic antibody fragments. Lastly, we highlight the stability of knob domains in plasma and, through pharmacokinetic studies, use palmitoylation as a route to extend the plasma half-life of knob domains in vivo. This study presents an antibody-derived medicinal chemistry platform, with protocols for solid-phase synthesis of knob domains, together with the characterization of their molecular structures, in vitro pharmacology, and pharmacokinetics.

Development of a human antibody fragment directed against the alpha folate receptor as a promising molecule for targeted application.

Alpha folate receptor (FRα) is currently under investigation as a target for the treatment of patients with non-small-cell lung cancer (NSCLC), since it is highly expressed in tumor cells but is largely absent in normal tissue. In this study, a novel human variable domain of a heavy-chain (VH) antibody fragment specific to FRα was enriched and selected by phage bio-planning. The positive phage clone (3A102 VH) specifically bound to FRα and also cross-reacted with FRß, as tested by ELISA. Clone 3A102 VH was then successfully expressed as a soluble protein in an E. coli shuffle strain. The obtained soluble 3A102 VH demonstrated a high affinity for FRα with affinity constants (Kaff) values around 7.77 ± 0.25 × 107 M-1, with specific binding against both FRα expressing NSCLC cells and NSCLC patient-derived primary cancer cells, as tested by cell ELISA. In addition, soluble 3A102 VH showed the potential desired property of a targeting molecule by being internalized into FRα-expressing cells, as observed by confocal microscopy. This study inspires the use of phage display to develop human VH antibody (Ab) fragments that might be well suited for drug targeted therapy of NSCLC and other FRα-positive cancer cells.

A Two-Pore Physiologically Based Pharmacokinetic Model to Predict Subcutaneously Administered Different-Size Antibody/Antibody Fragments.

Quantitative modeling of the subcutaneous absorption processes of protein therapeutics is challenging. Here we have proposed a "two-pore" PBPK model that is able to simultaneously characterize plasma PK of different-size protein therapeutics in mice. The skin compartment is evolved to mechanistically account for the absorption pathways through lymph and blood capillaries, as well as local degradation at the SC injection site. The model is developed using in-house plasma PK data generated following subcutaneous administration of 6 different-size protein therapeutics (13-150 kDa) in mice. The model was able to capture plasma PK of all molecules following intravenous and subcutaneous administration relatively well. From the observed plasma PK profiles, as well as from the model simulation result, several important PK descriptors were found to be dependent on protein size for FcRn nonbinding molecules. A positive correlation was found between Tmax and protein size. A "U" shape relationship was found between Cmax and protein size. Negative correlations were observed between bioavailability (F) and local degradation rate (kdeg,SC), and F and protein size. Pathway analysis of the model was conducted for the subcutaneous absorption process, and continuous relationships were established between the percentage of absorption through lymphatic and vascular pathways and protein size. This PBPK model could serve as a platform for the development of different-size protein therapeutics and will be scaled up to humans for translational studies in the future.

Comparative evaluation of affibody- and antibody fragments-based CAIX imaging probes in mice bearing renal cell carcinoma xenografts.

Carbonic anhydrase IX (CAIX) is a cancer-associated molecular target for several classes of therapeutics. CAIX is overexpressed in a large fraction of renal cell carcinomas (RCC). Radionuclide molecular imaging of CAIX-expression might offer a non-invasive methodology for stratification of patients with disseminated RCC for CAIX-targeting therapeutics. Radiolabeled monoclonal antibodies and their fragments are actively investigated for imaging of CAIX expression. Promising alternatives are small non-immunoglobulin scaffold proteins, such as affibody molecules. A CAIX-targeting affibody ZCAIX:2 was re-designed with the aim to decrease off-target interactions and increase imaging contrast. The new tracer, DOTA-HE3-ZCAIX:2, was labeled with 111In and characterized in vitro. Tumor-targeting properties of [111In]In-DOTA-HE3-ZCAIX:2 were compared head-to-head with properties of the parental variant, [99mTc]Tc(CO)3-HE3-ZCAIX:2, and the most promising antibody fragment-based tracer, [111In]In-DTPA-G250(Fab')2, in the same batch of nude mice bearing CAIX-expressing RCC xenografts. Compared to the 99mTc-labeled parental variant, [111In]In-DOTA-HE3-ZCAIX:2 provides significantly higher tumor-to-lung, tumor-to-bone and tumor-to-liver ratios, which is essential for imaging of CAIX expression in the major metastatic sites of RCC. [111In]In-DOTA-HE3-ZCAIX:2 offers significantly higher tumor-to-organ ratios compared with [111In]In-G250(Fab')2. In conclusion, [111In]In-DOTA-HE3-ZCAIX:2 can be considered as a highly promising tracer for imaging of CAIX expression in RCC metastases based on our results and literature data.

A Novel Cell-Penetrating Antibody Fragment Inhibits the DNA Repair Protein RAD51.

DNA damaging chemotherapies are successful in cancer therapy, however, the damage can be reversed by DNA repair mechanisms that may be up-regulated in cancer cells. We hypothesized that inhibiting RAD51, a protein involved in homologous recombination DNA repair, would block DNA repair and restore the effectiveness of DNA damaging chemotherapy. We used phage-display to generate a novel synthetic antibody fragment that bound human RAD51 with high affinity (KD = 8.1 nM) and inhibited RAD51 ssDNA binding in vitro. As RAD51 is an intracellular target, we created a corresponding intrabody fragment that caused a strong growth inhibitory phenotype on human cells in culture. We then used a novel cell-penetrating peptide "iPTD" fusion to generate a therapeutically relevant antibody fragment that effectively entered living cells and enhanced the cell-killing effect of a DNA alkylating agent. The iPTD may be similarly useful as a cell-penetrating peptide for other antibody fragments and open the door to numerous intracellular targets previously off-limits in living cells.

Pharmacokinetic parameters and mechanism of action of an efficient anti-Aß single chain antibody fragment.

The success of the targeting of amyloid-ß (Aß) oligomers through immunotherapy in Alzheimer's disease (AD) mouse models has not been translated into the clinics. The use of single-chain variable fragments (scFvs) has been proposed to prevent the potential severe effects of full-length mAbs by precluding crystallizable fraction-mediated microglia activation. The efficacy of scFv-h3D6, a bapineuzumab-derived anti-Aß scFv, has been extensively proven. In this work, we compared scFv-h3D6-EL, an elongated variant of the scFv-h3D6, with its original version to assess whether its characteristic higher thermodynamic stability improved its pharmacokinetic parameters. Although scFv-h3D6-EL had a longer half-life than its original version, its absorption from the peritoneal cavity into the systemic compartment was lower than that of the original version. Moreover, we attempted to determine the mechanism underlying the protective effect of scFv-h3D6. We found that scFv-h3D6 showed compartmental distribution and more interestingly crossed the blood-brain barrier. In the brain, scFv-h3D6 was engulfed by glial cells or internalized by Aß peptide-containing neurons in the early phase post-injection, and was colocalized with the Aß peptide almost exclusively in glial cells in the late phase post-injection. Aß peptide levels in the brain decreased simultaneously with an increase in scFv-h3D6 levels. This observation in addition to the increased tumor necrosis factor-α levels in the late phase post-injection suggested that the engulfment of Aß peptide/scFv-h3D6 complex extruded from large neurons by phagocytic cells was the mechanism underlying Aß peptide withdrawal. The mechanism of action of scFv-h3D6 demonstrates the effectivity of Aß-immunotherapy and lays the background for other studies focused on the finding of a treatment for AD.

High antitumor activity of Sortase A-generated anti-CD20 antibody fragment drug conjugates.

Antibody fragments, as the products of engineered antibodies, exhibit great potential for cancer therapy and imaging. Antibody fragment drug conjugates (AFDCs), which conjugate the highly specific, low-immunity and small-sized antibody fragments with cytotoxic payloads, can overcome the limitations of traditional IgG format drugs in cancer therapy. In this study, a commercialized anti-CD20 monoclonal antibody, ofatumumab (OFA), was applied to generate two site-specific monomethyl auristain E (MMAE)-conjugated AFDCs (Fab-vcMMAE, Fab-CH3mut-vcMMAE) by Sortase A mediated transpeptidation. Compared with OFA-vcMMAE, the two AFDCs maintained most of the binding affinity and the ability of internalization. In vitro studies revealed that Fab-vcMMAE and OFA-vcMMAE had almost identical IC50 values against CD20-positive cell lines, while Fab-CH3-vcMMAE had a lower anti-tumor activity. In vivo studies showed that Fab-vcMMAE had a significantly higher maximum tolerated dose (MTDs), a 30-fold shorter half-life, and slightly lower antitumor activity within the MTDs than OFA-vcMMAE. The distribution study showed that both of the Fab and Fab-CH3mut had higher penetration rates into the tumors than OFA in a xenograft model. Additionally, no obvious difference in tumor drug accumulation was found between the Fab and OFA groups after the penetration process, but the Fab-CH3mut group exhibited less tumor drug accumulation, possibly contributing to the inferior anti-tumor activity of Fab-CH3mut-vcMMAE in vivo. Overall, we preliminarily demonstrated the characteristics of AFDCs by studying OFA-based AFDCs. Our results revealed that Fab is a promising carrier of MMAE to enhance the anti-tumor activity and increase the safety profile compared with OFA.

Distinctive Activation Mechanism for Angiotensin Receptor Revealed by a Synthetic Nanobody.

The angiotensin II (AngII) type 1 receptor (AT1R) is a critical regulator of cardiovascular and renal function and is an important model for studies of G-protein-coupled receptor (GPCR) signaling. By stabilizing the receptor with a single-domain antibody fragment ("nanobody") discovered using a synthetic yeast-displayed library, we determined the crystal structure of active-state human AT1R bound to an AngII analog with partial agonist activity. The nanobody binds to the receptor's intracellular transducer pocket, stabilizing the large conformational changes characteristic of activated GPCRs. The peptide engages the AT1R through an extensive interface spanning from the receptor core to its extracellular face and N terminus, remodeling the ligand-binding cavity. Remarkably, the mechanism used to propagate conformational changes through the receptor diverges from other GPCRs at several key sites, highlighting the diversity of allosteric mechanisms among GPCRs. Our structure provides insight into how AngII and its analogs stimulate full or biased signaling, respectively.

Antibody Fragments Humanization: Beginning with the End in Mind.

Molecular engineering has made possible to reformat monoclonal antibodies into smaller antigen-binding structures like scFvs, diabodies, Fabs with new potential in vivo applications because they do not induce Fc-mediated functions. However, most of these molecules are from rodent origin. As a consequence, they are immunogenic and approval for administration to humans requires prior humanization. Today, there is no well-identified strategy to create recombinant humanized antibody V-domains that preserve the antigen-binding characteristics of the parental antibody associated with high stability and solubility. Here, we propose a strategy that consists in grafting CDRs onto properly chosen human antibody frameworks in order to reduce immunogenicity. A flowchart indicates the way to proceed in order to introduce an internal affinity purification tag while structural refinements are proposed to maintain antigen-binding characteristics. The best humanized candidates are identified through selection steps including in silico analysis, research scale production followed by early functional evaluation, purification assays, aggregation, and stability assessment.

An antibody fragment against human delta-like ligand-4 for inhibition of cell proliferation and neovascularization.

OBJECTIVES: Angiogenesis targeting is an attractive approach for cancer treatment. Delta-like ligand 4 (DLL4) plays a pivotal role in neovascular development and its inhibitors have recently entered clinical trials for solid tumors. The aim of this study was to evaluate the possibilities of using anti-DLL4 antibody fragment as an angiogenesis maturation inhibitor. MATERIALS AND METHODS: In this study, a DLL4-specific Nanobody, named 3Nb3, was selected and assessed by western blotting and internalization assays. Functional assessments included MTT, apoptosis, and chicken chorioallantoic membrane (CAM) assays. RESULTS: Based on the results, 3Nb3 specifically binds to DLL4 and internalizes into MKN cell. Furthermore, 3Nb3 significantly inhibited the proliferation of cells and also neovascularization in the CAM. CONCLUSIONS: These data demonstrated the potential of Nanobody for application in targeting DLL4. Our findings may provide a basis for the development of novel therapeutic techniques to inhibit growth and neovascularization of tumors.

Emerging Paradigm of Intracellular Targeting of G Protein-Coupled Receptors.

G protein-coupled receptors (GPCRs) recognize a diverse array of extracellular stimuli, and they mediate a broad repertoire of signaling events involved in human physiology. Although the major effort on targeting GPCRs has typically been focused on their extracellular surface, a series of recent developments now unfold the possibility of targeting them from the intracellular side as well. Allosteric modulators binding to the cytoplasmic surface of GPCRs have now been described, and their structural mechanisms are elucidated by high-resolution crystal structures. Furthermore, pepducins, aptamers, and intrabodies targeting the intracellular face of GPCRs have also been successfully utilized to modulate receptor signaling. Moreover, small molecule compounds, aptamers, and synthetic intrabodies targeting ß-arrestins have also been discovered to modulate GPCR endocytosis and signaling. Here, we discuss the emerging paradigm of intracellular targeting of GPCRs, and outline the current challenges, potential opportunities, and future outlook in this particular area of GPCR biology.

Influence of Molecular size on the clearance of antibody fragments.

PURPOSE: To establish a continuous relationship between the size of various antibody fragments and their systemic clearance (CL) in mice. METHODS: Two different orthogonal approaches have been used to establish the relationship. First approach uses CL values estimated by non-compartmental analysis (NCA) to establish a correlation with protein size. The second approach simultaneously characterizes the PK data for all the proteins using a 2-compartment model to establish a relationship between protein size and pharmacokinetic (PK) parameters. RESULTS: Simple mathematical functions (e.g. sigmoidal, power law) were able to characterize the CL vs. protein size relationship generated using the investigated proteins. The relationship established in mouse was used to predict rat, rabbit, monkey, and human relationships using allometric scaling. The predicted relationships were found to capture the available spares data from each species reasonably well. CONCLUSIONS: The CL vs. protein size relationship is important for establishing a robust quantitative structure-PK relationship (QSPKR) for protein therapeutics. The relationship presented here can help in a priori predicting plasma exposure of therapeutic proteins, and together with our previously established relationship between plasma and tissue concentrations of proteins, it can predict the tissue exposure of non-binding proteins simply based on molecular weight/radius and dose.

An Anti-VEGF-B Antibody Fragment Induces Regression of Pre-Existing Blood Vessels in the Rat Cornea.

Purpose: We tested the ability of an antibody fragment with specificity for vascular endothelial growth factor-B (VEGF-B) to regress nascent and established corneal blood vessels in the rat. Methods: A single chain variable antibody fragment (scFv) with specificity for VEGF-B was engineered from the 2H10 hybridoma. Binding to rat, mouse, and human VEGF-B was confirmed by surface plasmon resonance. Activity of the anti-VEGF-B scFv on developing and established corneal blood vessels was assessed following unilateral superficial cautery in male and female outbred Sprague Dawley rats. Groups (untreated, control scFv-treated, or anti-VEGF-B scFv-treated) comprised 6 to 22 rats. Treatment consisted of 5 µL scFv, 1 mg/mL, applied topically five times per day for 14 days, or two subconjunctival injections, 50 µg scFv each, applied 7 days apart, or combined topical and subconjunctival treatment. Corneal vessel area was quantified on hematoxylin-stained corneal flat-mounts, and groups were compared using the Mann-Whitney U test, with post hoc Bonferroni correction. Immunohistochemistry for cleaved caspase-3 was performed. Results: Topical anti-VEGF-B scFv therapy alone did not regress corneal blood vessels significantly (P > 0.05). Subconjunctival injection and combined treatment regressed 14-day established corneal blood vessels (25% reduction in vessel area [P = 0.04] and 37% reduction in vessel area [P < 0.001], respectively, compared to results in untreated controls). Cleaved caspase-3 was identified in vascular endothelial cells of anti-VEGF-B scFv-treated corneas. In scFv-treated rats, corneal endothelial cell function was maintained to 12 weeks after treatment and a normal blink reflex was present. Conclusions: The anti-VEGF-B scFv significantly regressed established but not developing corneal blood vessels in rats.

The antigen-binding fragment of human gamma immunoglobulin prevents amyloid ß-peptide folding into ß-sheet to form oligomers.

The amyloid beta-peptide (Aß) plays a leading role in Alzheimer's disease (AD) physiopathology. Even though monomeric forms of Aß are harmless to cells, Aß can aggregate into ß-sheet oligomers and fibrils, which are both neurotoxic. Therefore, one of the main therapeutic approaches to cure or delay AD onset and progression is targeting Aß aggregation. In the present study, we show that a pool of human gamma immunoglobulins (IgG) protected cortical neurons from the challenge with Aß oligomers, as assayed by MTT reduction, caspase-3 activation and cytoskeleton integrity. In addition, we report the inhibitory effect of IgG on Aß aggregation, as shown by Thioflavin T assay, size exclusion chromatography and atomic force microscopy. Similar results were obtained with Palivizumab, a human anti-sincitial virus antibody. In order to dissect the important domains, we cleaved the pool of human IgG with papain to obtain Fab and Fc fragments. Using these cleaved fragments, we functionally identified Fab as the immunoglobulin fragment inhibiting Aß aggregation, a result that was further confirmed by an in silico structural model. Interestingly, bioinformatic tools show a highly conserved structure able to bind amyloid in the Fab region. Overall, our data strongly support the inhibitory effect of human IgG on Aß aggregation and its neuroprotective role.

Recent Updates on Molecular Genetic Engineering Approaches and Applications of Human Therapeutic Proteins.

Therapeutic proteins are engineered proteins produced in the laboratory for pharmaceutical use. With the advent of recombinant DNA technology, the proteins can be generated in specific host cells under defined conditions. In the process of production of genetically engineered animals, the gene of interest can be added at a single cell stage to produce a cloned animal from genetically engineered cells. Several recombinant cytokines, clotting factors etc have been licensed and are currently being utilized for the treatment of cancer, infectious diseases, hemophilia, anemia, multiple sclerosis, and hepatitis B/C. Therapeutic proteins that are useful for human are successfully produced in poultry as well as in livestock animals. However, the fastest growing class of therapeutic proteins are antibodies especially monoclonal antibodies (mAb), the most important class of therapeutic protein with the potential to generate significant revolution in terms of clinical success rate. Here, we review the most recent clinical advances in the field of emerging and existing therapeutic proteins.

Inhibitors and Antibody Fragments as Potential Anti-Inflammatory Therapeutics Targeting Neutrophil Proteinase 3 in Human Disease.

Proteinase 3 (PR3) has received great scientific attention after its identification as the essential antigenic target of antineutrophil cytoplasm antibodies in Wegener's granulomatosis (now called granulomatosis with polyangiitis). Despite many structural and functional similarities between neutrophil elastase (NE) and PR3 during biosynthesis, storage, and extracellular release, unique properties and pathobiological functions have emerged from detailed studies in recent years. The development of highly sensitive substrates and inhibitors of human PR3 and the creation of PR3-selective single knockout mice led to the identification of nonredundant roles of PR3 in cell death induction via procaspase-3 activation in cell cultures and in mouse models. According to a study in knockout mice, PR3 shortens the lifespan of infiltrating neutrophils in tissues and accelerates the clearance of aged neutrophils in mice. Membrane exposure of active human PR3 on apoptotic neutrophils reprograms the response of macrophages to phagocytosed neutrophils, triggers secretion of proinflammatory cytokines, and undermines immune silencing and tissue regeneration. PR3-induced disruption of the anti-inflammatory effect of efferocytosis may be relevant for not only granulomatosis with polyangiitis but also for other autoimmune diseases with high neutrophil turnover. Inhibition of membrane-bound PR3 by endogenous inhibitors such as the α-1-protease inhibitor is comparatively weaker than that of NE, suggesting that the adverse effects of unopposed PR3 activity resurface earlier than those of NE in individuals with α-1-protease inhibitor deficiency. Effective coverage of PR3 by anti-inflammatory tools and simultaneous inhibition of both PR3 and NE should be most promising in the future.

Cytokine Activation by Antibody Fragments Targeted to Cytokine-Receptor Signaling Complexes.

Exogenous cytokine therapy can induce systemic toxicity, which might be prevented by activating endogenously produced cytokines in local cell niches. Here we developed antibody-based activators of cytokine signaling (AcCS), which recognize cytokines only when they are bound to their cell surface receptors. AcCS were developed for type I interferons (IFNs), which induce cellular activities by binding to cell surface receptors IFNAR1 and IFNAR2. As a potential alternative to exogenous IFN therapy, AcCS were shown to potentiate the biological activities of natural IFNs by ∼100-fold. Biochemical and structural characterization demonstrates that the AcCS stabilize the IFN-IFNAR2 binary complex by recognizing an IFN-induced conformational change in IFNAR2. Using IFN mutants that disrupt IFNAR1 binding, AcCS were able to enhance IFN antiviral potency without activating antiproliferative responses. This suggests AcCS can be used to manipulate cytokine signaling for basic science and possibly for therapeutic applications.