Comprehensive mapping of poxvirus vCCI chemokine-binding protein. Expanded range of ligand interactions and unusual dissociation kinetics

Efficient production of fluorophore-labeled CC chemokines for biophysical studies using recombinant enterokinase and recombinant sortase

Chemokines are important immune system proteins, many of which mediate inflammation due to their function to activate and cause chemotaxis of leukocytes. An important anti-inflammatory strategy is therefore to bind and inhibit chemokines, which leads to the need for biophysical studies of chemokines as they bind various possible partners. Because a successful anti-chemokine drug should bind at low concentrations, techniques such as fluorescence anisotropy that can provide nanomolar signal detection are required. To allow fluorescence experiments to be carried out on chemokines, a method is described for the production of fluorescently labeled chemokines. First, a fusion-tagged chemokine is produced in Escherichia coli, then efficient cleavage of the N-terminal fusion partner is carried out with lab-produced enterokinase, followed by covalent modification with a fluorophore, mediated by the lab-produced sortase enzyme. This overall process reduces the need for expensive commercial enzymatic reagents. Finally, we utilize the product, vMIP-fluor, in binding studies with the chemokine binding protein vCCI, which has great potential as an anti-inflammatory therapeutic, showing a binding constant for vCCI:vMIP-fluor of 0.37 ± 0.006 nM. We also show how a single modified chemokine homolog (vMIP-fluor) can be used in competition assays with other chemokines and we report a Kd for vCCI:CCL17 of 14 μM. This work demonstrates an efficient method of production and fluorescent labeling of chemokines for study across a broad range of concentrations.

Genetic analysis of two viroceptor genes of orf virus

In the present study, we analyzed the chemokine-binding protein (CBP) and the GM-CSF/IL-2 inhibition factor (GIF) of orf virus (ORFV) isolates of sheep and goat origin from different geographical regions of India. Both are immunomodulatory proteins known for their unique strategy of establishing short-term immunity and re-infection in their host. The GIF gene is highly conserved, whereas the CBP gene is highly variable. Both the proteins have conserved potential N-glycosylation sites. The GIF protein contains the "WDPWV" motif responsible for receptor activation. In addition, the SUSHI/short consensus repeats (SCR) domain is reported for the first time in ORFV. Both proteins could potentially be used as immunotherapeutic agents in inflammatory diseases related to the overexpression of specific cytokines.

The binding and specificity of chemokine binding proteins, through the lens of experiment and computation

Chemokines are small proteins that are critical for immune function, being primarily responsible for the activation and chemotaxis of leukocytes. As such, many viruses, as well as parasitic arthropods, have evolved systems to counteract chemokine function in order to maintain virulence, such as binding chemokines, mimicking chemokines, or producing analogs of transmembrane chemokine receptors that strongly bind their targets. The focus of this review is the large group of chemokine binding proteins (CBP) with an emphasis on those produced by mammalian viruses. Because many chemokines mediate inflammation, these CBP could possibly be used pharmaceutically as anti-inflammatory agents. In this review, we summarize the structural properties of a diverse set of CBP and describe in detail the chemokine binding properties of the poxvirus-encoded CBP called vCCI (viral CC Chemokine Inhibitor). Finally, we describe the current and emerging capabilities of combining computational simulation, structural analysis, and biochemical/biophysical experimentation to understand, and possibly re-engineer, protein–protein interactions.

Injection site vaccinology of a recombinant vaccinia-based vector reveals diverse innate immune signatures

Poxvirus systems have been extensively used as vaccine vectors. Herein a RNA-Seq analysis of intramuscular injection sites provided detailed insights into host innate immune responses, as well as expression of vector and recombinant immunogen genes, after vaccination with a new multiplication defective, vaccinia-based vector, Sementis Copenhagen Vector. Chikungunya and Zika virus immunogen mRNA and protein expression was associated with necrosing skeletal muscle cells surrounded by mixed cellular infiltrates. The multiple adjuvant signatures at 12 hours post-vaccination were dominated by TLR3, 4 and 9, STING, MAVS, PKR and the inflammasome. Th1 cytokine signatures were dominated by IFNγ, TNF and IL1β, and chemokine signatures by CCL5 and CXCL12. Multiple signatures associated with dendritic cell stimulation were evident. By day seven, vaccine transcripts were absent, and cell death, neutrophil, macrophage and inflammation annotations had abated. No compelling arthritis signatures were identified. Such injection site vaccinology approaches should inform refinements in poxvirus-based vector design.

Poxvirus vector systems have been widely developed for vaccine applications. Despite considerable progress, so far only one recombinant poxvirus vectored vaccine has to date been licensed for human use, with ongoing efforts seeking to enhance immunogenicity whilst minimizing reactogenicity. The latter two characteristics are often determined by early post-vaccination events at the injection site. We therefore undertook an injection site vaccinology approach to analyzing gene expression at the vaccination site after intramuscular inoculation with a recombinant, multiplication defective, vaccinia-based vaccine. This provided detailed insights into inter alia expression of vector-encoded immunoregulatory genes, as well as host innate and adaptive immune responses. We propose that such injection site vaccinology can inform rational vaccine vector design, and we discuss how the information and approach elucidated herein might be used to improve immunogenicity and limit reactogenicity of poxvirus-based vaccine vector systems.

Flavonoids as P-gp Inhibitors: A Systematic Review of SARs

P-glycoprotein, also known as ABCB1 in the ABC transporter family, confers the simultaneous resistance of metastatic cancer cells towards various anticancer drugs with different targets and diverse chemical structures. The exploration of safe and specific inhibitors of this pump has always been the pursuit of scientists for the past four decades. Naturally occurring flavonoids as benzopyrone derivatives were recognized as a class of nontoxic inhibitors of P-gp. The recent advent of synthetic flavonoid dimer FD18, as a potent P-gp modulator in reversing multidrug resistance both in vitro and in vivo, specifically targeted the pseudodimeric structure of the drug transporter and represented a new generation of inhibitors with high transporter binding affinity and low toxicity. This review concerned the recent updates on the structure-activity relationships of flavonoids as P-gp inhibitors, the molecular mechanisms of their action and their ability to overcome P-gp-mediated MDR in preclinical studies. It had crucial implications on the discovery of new drug candidates that modulated the efflux of ABC transporters and also provided some clues for the future development in this promising area.

Evasins: Tick Salivary Proteins that Inhibit Mammalian Chemokines

Ticks are hematophagous arachnids that parasitize mammals and other hosts, feeding on their blood. Ticks secrete numerous salivary factors that enhance host blood flow or suppress the host inflammatory response. The recruitment of leukocytes, a hallmark of inflammation, is regulated by chemokines, which activate chemokine receptors on the leukocytes. Ticks target this process by secreting glycoproteins called Evasins, which bind to chemokines and prevent leukocyte recruitment. This review describes the recent discovery of numerous Evasins produced by ticks, their classification into two structural and functional classes, and the efficacy of Evasins in animal models of inflammatory diseases. The review also proposes a standard nomenclature system for Evasins and discusses the potential of repurposing or engineering Evasins as therapeutic anti-inflammatory agents.

The Virology of Taterapox Virus In Vitro

Taterapox virus (TATV) is phylogenetically the closest related virus to variola—the etiological agent of smallpox. Despite the similarity, few studies have evaluated the virus. In vivo, TATV can infect several animals but produces an inapparent infection in wild-type mice; however, TATV does cause morbidity and mortality in some immunocompromised strains. We employed in vitro techniques to compare TATV to ectromelia (ECTV) and vaccinia (VACV) viruses. Both ECTV and TATV replicate efficiently in primate cell lines but TATV replicates poorly in murine cells lines. Furthermore, TATV induces cytopathic effects, but to a lesser extent than ECTV, and changes cytoskeletal networks differently than both ECTV and VACV. Bioinformatic studies revealed differences in several immunomodulator open reading frames that could contribute to the reduced virulence of TATV, which were supported by in vitro cytokine assays.

Genetically engineered two-warhead evasins provide a method to achieve precision targeting of disease-relevant chemokine subsets

Both CC and CXC-class chemokines drive inflammatory disease. Tick salivary chemokine-binding proteins (CKBPs), or evasins, specifically bind subsets of CC- or CXC-chemokines, and could precisely target disease-relevant chemokines. Here we have used yeast surface display to identify two tick evasins: a CC-CKBP, P1243 from Amblyomma americanum and a CXC-CKBP, P1156 from Ixodes ricinus. P1243 binds 11 CC-chemokines with Kd < 10 nM, and 10 CC-chemokines with Kd between 10 and 100 nM. P1156 binds two ELR + CXC-chemokines with Kd < 10 nM, and four ELR + CXC-chemokines with Kd between 10 and 100 nM. Both CKBPs neutralize chemokine activity with IC50 < 10 nM in cell migration assays. As both CC- and CXC-CKBP activities are desirable in a single agent, we have engineered "two-warhead" CKBPs to create single agents that bind and neutralize subsets of CC and CXC chemokines. These results show that tick evasins can be linked to create non-natural proteins that target subsets of CC and CXC chemokines. We suggest that "two-warhead" evasins, designed by matching the activities of parental evasins to CC and CXC chemokines expressed in disease, would achieve precision targeting of inflammatory disease-relevant chemokines by a single agent.

Biophysical and Computational Studies of the vCCI:vMIP-II Complex

Certain viruses have the ability to subvert the mammalian immune response, including interference in the chemokine system. Poxviruses produce the chemokine binding protein vCCI (viral CC chemokine inhibitor; also called 35K), which tightly binds to CC chemokines. To facilitate the study of vCCI, we first provide a protocol to produce folded vCCI from Escherichia coli (E. coli.) It is shown here that vCCI binds with unusually high affinity to viral Macrophage Inflammatory Protein-II (vMIP-II), a chemokine analog produced by the virus, human herpesvirus 8 (HHV-8). Fluorescence anisotropy was used to investigate the vCCI:vMIP-II complex and shows that vCCI binds to vMIP-II with a higher affinity than most other chemokines, having a K_d of 0.06 ± 0.006 nM. Nuclear magnetic resonance (NMR) chemical shift perturbation experiments indicate that key amino acids used for binding in the complex are similar to those found in previous work. Molecular dynamics were then used to compare the vCCI:vMIP-II complex with the known vCCI:Macrophage Inflammatory Protein-1β/CC-Chemokine Ligand 4 (MIP-1β/CCL4) complex. The simulations show key interactions, such as those between E143 and D75 in vCCI/35K and R18 in vMIP-II. Further, in a comparison of 1 μs molecular dynamics (MD) trajectories, vMIP-II shows more overall surface binding to vCCI than does the chemokine MIP-1β. vMIP-II maintains unique contacts at its N-terminus to vCCI that are not made by MIP-1β, and vMIP-II also makes more contacts with the vCCI flexible acidic loop (located between the second and third beta strands) than does MIP-1β. These studies provide evidence for the basis of the tight vCCI:vMIP-II interaction while elucidating the vCCI:MIP-1β interaction, and allow insight into the structure of proteins that are capable of broadly subverting the mammalian immune system.

Mechanisms of Regulation of the Chemokine-Receptor Network

The interactions of chemokines with their G protein-coupled receptors promote the migration of leukocytes during normal immune function and as a key aspect of the inflammatory response to tissue injury or infection. This review summarizes the major cellular and biochemical mechanisms by which the interactions of chemokines with chemokine receptors are regulated, including: selective and competitive binding interactions; genetic polymorphisms; mRNA splice variation; variation of expression, degradation and localization; down-regulation by atypical (decoy) receptors; interactions with cell-surface glycosaminoglycans; post-translational modifications; oligomerization; alternative signaling responses; and binding to natural or pharmacological inhibitors.

Evasins: Therapeutic Potential of a New Family of Chemokine-Binding Proteins from Ticks

Blood-sucking parasites, such as ticks, remain attached to their hosts for relatively long periods of time in order to obtain their blood meal without eliciting an immune response. One mechanism used to avoid rejection is the inhibition of the recruitment of immune cells, which can be achieved by a class of chemokine-binding proteins (CKBPs) known as Evasins. We have identified three distinct Evasins produced by the salivary glands of the common brown dog tick, Rhipicephalus sanguineus. They display different selectivities for chemokines, the first two identified show a narrow selectivity profile, while the third has a broader binding spectrum. The Evasins showed efficacy in animal models of inflammatory disease. Here, we will discuss the potential of their development for therapeutic use, addressing both the advantages and disadvantages that this entails.

Hydrodynamic Gene Delivery of CC Chemokine Binding Fc Fusion Proteins to Target Acute Vascular Inflammation In Vivo

Blockade of CC chemokines is an attractive yet under utilized therapeutic strategy. We report the in vivo pharmacokinetics of a broad-spectrum vaccinia virus CC chemokine binding protein (35 K) fused to human IgG1 Fc. We demonstrate that the in vivo efficacy of the protein can be interrogated using hydrodynamic gene delivery of a standard mammalian expression plasmid. High plasma levels of the 35 K-Fc protein are maintained for at least 14 days post gene transfer, with the protein still detectable at 5 weeks. We confirm that the protein has biological activity in acute inflammation, causing a significant reduction in monocyte recruitment during zymosan induced peritonitis. The ability of 35 K-Fc to block more complex pathologies is demonstrated using aortic digests to assess angiotensin II mediated leukocyte recruitment to the aorta. Angiotensin II causes upregulation of mCCL2 in the aorta causing the accumulation of CCR2+ cells. Peak monocyte recruitment to the aorta occurs within 3 days and this process is CC chemokine dependent, being significantly reduced by hydrodynamic delivery of 35 K-Fc.

Structural Conservation and Functional Diversity of the Poxvirus Immune Evasion (PIE) Domain Superfamily

Poxviruses encode a broad array of proteins that serve to undermine host immune defenses. Structural analysis of four of these seemingly unrelated proteins revealed the recurrent use of a conserved beta-sandwich fold that has not been observed in any eukaryotic or prokaryotic protein. Herein we propose to call this unique structural scaffolding the PIE (Poxvirus Immune Evasion) domain. PIE domain containing proteins are abundant in chordopoxvirinae, with our analysis identifying 20 likely PIE subfamilies among 33 representative genomes spanning 7 genera. For example, cowpox strain Brighton Red appears to encode 10 different PIEs: vCCI, A41, C8, M2, T4 (CPVX203), and the SECRET proteins CrmB, CrmD, SCP-1, SCP-2, and SCP-3. Characterized PIE proteins all appear to be nonessential for virus replication, and all contain signal peptides for targeting to the secretory pathway. The PIE subfamilies differ primarily in the number, size, and location of structural embellishments to the beta-sandwich core that confer unique functional specificities. Reported ligands include chemokines, GM-CSF, IL-2, MHC class I, and glycosaminoglycans. We expect that the list of ligands and receptors engaged by the PIE domain will grow as we come to better understand how this versatile structural architecture can be tailored to manipulate host responses to infection.

Process of hepatic metastasis from pancreatic cancer: biology with clinical significance

PURPOSE

Pancreatic cancer shows a remarkable preference for the liver to establish secondary tumors. Selective metastasis to the liver is attributed to the development of potential microenvironment for the survival of pancreatic cancer cells. This review aims to provide a full understanding of the hepatic metastatic process from circulating pancreatic cancer cells to their settlement in the liver, serving as a basic theory for efficient prediction and treatment of metastatic diseases.

METHODS

A systematic search of relevant original articles and reviews was performed on PubMed, EMBASE and Cochrane Library for the purpose of this review.

RESULTS

Three interrelated phases are delineated as the contributions of the interaction between pancreatic cancer cells and the liver to hepatic metastasis process. Chemotaxis of disseminated pancreatic cancer cells and simultaneous defensive formation of platelets or neutrophils facilitate specific metastasis toward the liver. Remodeling of extracellular matrix and stromal cells in hepatic lobules and angiogenesis induced by proangiogenic factors support the survival and growth of clinical micrometastasis colonizing the liver. The bimodal role of the immune system or prevalence of cancer cells over the immune system makes metastatic progression successfully proceed from micrometastasis to macrometastasis.

CONCLUSIONS

Pancreatic cancer is an appropriate research object of cancer metastasis representing more than a straight cascade. If any of the successive or simultaneous phases, especially tumor-induced immunosuppression, is totally disrupted, hepatic metastasis will be temporarily under control or even cancelled forever. To shrink cancers on multiple fronts and prolong survival for patients, novel oral or intravenous anti-cancer agents covering one or different phases of metastatic pancreatic cancer are expected to be integrated into innovative strategies on the premise of safety and efficacious biostability.

Immune modulation by virus-encoded secreted chemokine binding proteins

Chemokines are chemoattractant cytokines that mediate the migration of immune cells to sites of infection which play an important role in innate and adaptive immunity. As an immune evasion strategy, large DNA viruses (herpesviruses and poxviruses) encode soluble chemokine binding proteins that bind chemokines with high affinity, even though they do not show sequence similarity to cellular chemokine receptors. This review summarizes the different secreted viral chemokine binding proteins described to date, with special emphasis on the diverse mechanisms of action they exhibit to interfere with chemokine function and their specific contribution to virus pathogenesis.

Targeting chemokines: Pathogens can, why can't we?

Chemoattractant cytokines, or chemokines, are the largest sub-family of cytokines. About 50 distinct chemokines have been identified in humans. Their principal role is to stimulate the directional migration of leukocytes, which they achieve through activation of their receptors, following immobilization on cell surface glycosaminoglycans (GAGs). Chemokine receptors belong to the G protein-coupled 7-transmembrane receptor family, and hence their identification brought great promise to the pharmaceutical industry, since this receptor class is the target for a large percentage of marketed drugs. Unfortunately, the development of potent and efficacious inhibitors of chemokine receptors has not lived up to the early expectations. Several approaches to targeting this system will be described here, which have been instrumental in establishing paradigms in chemokine biology. Whilst drug discovery programs have not yet elucidated how to make successful drugs targeting the chemokine system, it is now known that certain parasites have evolved anti-chemokine strategies in order to remain undetected by their hosts. What can we learn from them?

Contrasting in vitro vs. in vivo effects of a cell membrane-specific CC-chemokine binding protein on macrophage chemotaxis

Abstract

Chemokines (CK) provide directional cues that mediate the recruitment of leukocytes to sites of inflammation. Broad-spectrum blockade of the CC-CK family, using the vaccinia virus 35K protein, has been shown to cause a potent reduction of systemic inflammation in models of atherosclerosis, vein graft disease and arthritis. We have used a cell membrane-targeted form of 35K, Mem35K, to probe whether cell-associated blockade of chemokine response is sufficient to reduce cell recruitment in inflammation. In Tie2cre mice, activation of a flox-stop Mem35K transgene directed conditional expression of Mem35K in leukocytes and endothelial cells, confirmed by Western blotting, flow cytometry and immunofluorescence microscopy. This conditional Mem35K expression was sufficient to increase cell surface CCL5 binding and reduce chemotaxis in vitro to CCL5, CCL2 and CCL3 but not to non-CC-CK chemoattractants, LTB4, C5a or chemerin. However, in vivo monocyte recruitment into the peritoneum driven by zymosan or CC-chemokine injection, which was demonstrated to be CC-CK dependent using CCR2−/− mice, was not reduced by Mem35K expression, despite the expression of functional Mem35K protein. These findings highlight differing requirements for cell-associated anti-inflammatory activity in in vitro and in vivo models.

Key message

Mem35K is a cell-associated CC-chemokine binding protein.

Conditional Mem35K transgenic mice show expression Mem35K in leukocytes.

Mem35K blocks in vitro primary macrophage chemotaxis specifically towards CC-chemokines.

Mem35K expression is not sufficient to reduce inflammation in vivo.

The requirements for anti-inflammatory activity in vitro and in vivo are different.

Electronic supplementary material

The online version of this article (doi:10.1007/s00109-014-1194-6) contains supplementary material, which is available to authorized users.

Chemokine (C-C Motif) receptor 1 is required for efficient recruitment of neutrophils during respiratory infection with modified vaccinia virus Ankara

Modified vaccinia virus Ankara (MVA) serves as a versatile platform in vaccine development. This highly attenuated orthopoxvirus, which cannot replicate in mammalian cells, triggers strong innate immune responses, including cell migration. Previously, we have shown that induction of chemokine (C-C motif) ligand 2 (CCL2) by MVA is necessary for the recruitment of monocytes and T cells, but not neutrophils, to the lung. Here, we identified neutrophil-attracting chemokines produced by MVA-infected primary murine lung fibroblasts and murine bone marrow-derived macrophages. We demonstrate that MVA, but not vaccinia virus (VACV) strain WR, induces chemokine expression, which is independent of Toll-like receptor 2 (TLR2) signaling. Additionally, we show that both chemokine (C-C motif) receptor 1 (CCR1) and chemokine (C-X-C motif) receptor 2 (CXCR2) are involved in MVA-induced neutrophil chemotaxis in vitro. Finally, intranasal infection of Ccr1(-/-) mice with MVA, as well as application of the CCR1 antagonist J-113863, revealed a role for CCR1 in leukocyte recruitment, including neutrophils, into the lung.

IMPORTANCE

Rapid attraction of leukocytes to the site of inoculation is unique to MVA in comparison to other VACV strains. The findings here extend current knowledge about the regulation of MVA-induced leukocyte migration, particularly regarding neutrophils, which could potentially be exploited to improve other VACV strains currently in development as oncolytic viruses and viral vectors. Additionally, the data presented here indicate that the inflammatory response may vary depending on the cell type infected by MVA, highlighting the importance of the site of vaccine application. Moreover, the rapid recruitment of neutrophils and other leukocytes can directly contribute to the induction of adaptive immune responses elicited by MVA inoculation. Thus, a better understanding of leukocyte migration upon MVA infection is particularly relevant for further development and use of MVA-based vaccines and vectors.

Structural insights into the interaction between a potent anti-inflammatory protein, viral CC chemokine inhibitor (vCCI), and the human CC chemokine, Eotaxin-1

Chemokines play important roles in the immune system, not only recruiting leukocytes to the site of infection and inflammation but also guiding cell homing and cell development. The soluble poxvirus-encoded protein viral CC chemokine inhibitor (vCCI), a CC chemokine inhibitor, can bind to human CC chemokines tightly to impair the host immune defense. This protein has no known homologs in eukaryotes and may represent a potent method to stop inflammation. Previously, our structure of the vCCI·MIP-1β (macrophage inflammatory protein-1β) complex indicated that vCCI uses negatively charged residues in β-sheet II to interact with positively charged residues in the MIP-1β N terminus, 20s region and 40s loop. However, the interactions between vCCI and other CC chemokines have not yet been fully explored. Here, we used NMR and fluorescence anisotropy to study the interaction between vCCI and eotaxin-1 (CCL11), a CC chemokine that is an important factor in the asthma response. NMR results reveal that the binding pattern is very similar to the vCCI·MIP-1β complex and suggest that electrostatic interactions provide a major contribution to binding. Fluorescence anisotropy results on variants of eotaxin-1 further confirm the critical roles of the charged residues in eotaxin-1. In addition, the binding affinity between vCCI and other wild type CC chemokines, MCP-1 (monocyte chemoattractant protein-1), MIP-1β, and RANTES (regulated on activation normal T cell expressed and secreted), were determined as 1.1, 1.2, and 0.22 nm, respectively. To our knowledge, this is the first work quantitatively measuring the binding affinity between vCCI and multiple CC chemokines.

Vaccinia virus immune evasion: mechanisms, virulence and immunogenicity

Virus infection of mammalian cells is sensed by pattern recognition receptors and leads to an innate immune response that restricts virus replication and induces adaptive immunity. In response, viruses have evolved many countermeasures that enable them to replicate and be transmitted to new hosts, despite the host innate immune response. Poxviruses, such as vaccinia virus (VACV), have large DNA genomes and encode many proteins that are dedicated to host immune evasion. Some of these proteins are secreted from the infected cell, where they bind and neutralize complement factors, interferons, cytokines and chemokines. Other VACV proteins function inside cells to inhibit apoptosis or signalling pathways that lead to the production of interferons and pro-inflammatory cytokines and chemokines. In this review, these VACV immunomodulatory proteins are described and the potential to create more immunogenic VACV strains by manipulation of the gene encoding these proteins is discussed.

Chemokine binding protein vCCI attenuates vaccinia virus without affecting the cellular response elicited by immunization with a recombinant vaccinia vector carrying the HPV16 E7 gene

Viral CC chemokine inhibitor (vCCI) of the clone P13 vaccinia virus (VACV) strain PRAHA lacks eight amino acids in the signal peptide sequence. To study the influence of vCCI on virus biology, a virus with the vCCI gene coding for a prolonged signal sequence was prepared. We found that secreted vCCI attenuated the virus in vivo, and that it correlated with decreased levels of RANTES, eotaxin, TARC, and MDC in the blood in comparison with the parental virus. We determined the influence of vCCI on the CTL response against VACV E3((140-148)) (VGPSNSPTF) and HPV16 E7((49-57)) (RAHYNIVTF) H-2D(b)-restricted epitopes. The examination of the specific CTL response elicited by immunization with the recombinant VACV-expressing tumor-associated HPV16 E7 antigen by IFN-γ ELISPOT showed that the immunogenicity of the recombinant VACV-producing secretory vCCI was similar to that of the parent virus or deletion mutant in the C23L/B29R locus. Immunization with the secretory vCCI-producing recombinant virus has a lower therapeutic anti-tumor effect against TC-1 tumors. Viral CCI downregulated the E7-specific response induced by gene gun immunization with the DNA vaccines pBSC-SigE7 LAMP and pBSC-vCCI. We also observed that the immune response against vCCI elicited by the DNA vaccine did not affect the multiplication of VACV in vivo.

A novel highly potent therapeutic antibody neutralizes multiple human chemokines and mimics viral immune modulation

Chemokines play a key role in leukocyte recruitment during inflammation and are implicated in the pathogenesis of a number of autoimmune diseases. As such, inhibiting chemokine signaling has been of keen interest for the development of therapeutic agents. This endeavor, however, has been hampered due to complexities in the chemokine system. Many chemokines have been shown to signal through multiple receptors and, conversely, most chemokine receptors bind to more than one chemokine. One approach to overcoming this complexity is to develop a single therapeutic agent that binds and inactivates multiple chemokines, similar to an immune evasion strategy utilized by a number of viruses. Here, we describe the development and characterization of a novel therapeutic antibody that targets a subset of human CC chemokines, specifically CCL3, CCL4, and CCL5, involved in chronic inflammatory diseases. Using a sequential immunization approach, followed by humanization and phage display affinity maturation, a therapeutic antibody was developed that displays high binding affinity towards the three targeted chemokines. In vitro, this antibody potently inhibits chemotaxis and chemokine-mediated signaling through CCR1 and CCR5, primary chemokine receptors for the targeted chemokines. Furthermore, we have demonstrated in vivo efficacy of the antibody in a SCID-hu mouse model of skin leukocyte migration, thus confirming its potential as a novel therapeutic chemokine antagonist. We anticipate that this antibody will have broad therapeutic utility in the treatment of a number of autoimmune diseases due to its ability to simultaneously neutralize multiple chemokines implicated in disease pathogenesis.

Structural basis of chemokine sequestration by CrmD, a poxvirus-encoded tumor necrosis factor receptor

Pathogens have evolved sophisticated mechanisms to evade detection and destruction by the host immune system. Large DNA viruses encode homologues of chemokines and their receptors, as well as chemokine-binding proteins (CKBPs) to modulate the chemokine network in host response. The SECRET domain (smallpox virus-encoded chemokine receptor) represents a new family of viral CKBPs that binds a subset of chemokines from different classes to inhibit their activities, either independently or fused with viral tumor necrosis factor receptors (vTNFRs). Here we present the crystal structures of the SECRET domain of vTNFR CrmD encoded by ectromelia virus and its complex with chemokine CX3CL1. The SECRET domain adopts a β-sandwich fold and utilizes its β-sheet I surface to interact with CX3CL1, representing a new chemokine-binding manner of viral CKBPs. Structure-based mutagenesis and biochemical analysis identified important basic residues in the 40s loop of CX3CL1 for the interaction. Mutation of corresponding acidic residues in the SECRET domain also affected the binding for other chemokines, indicating that the SECRET domain binds different chemokines in a similar manner. We further showed that heparin inhibited the binding of CX3CL1 by the SECRET domain and the SECRET domain inhibited RAW264.7 cell migration induced by CX3CL1. These results together shed light on the structural basis for the SECRET domain to inhibit chemokine activities by interfering with both chemokine-GAG and chemokine-receptor interactions.

Chemokines are a family of small proteins that help the immune system fight against invading pathogens by inducing the white blood cells to the areas of infection and inflammation. Due to the important roles of chemokines in immune response, the pathogens evolve diverse mechanisms to neutralize their activities. One example is that large DNA viruses, such as poxviruses and herpesviruses can produce chemokine binding proteins (CKBPs) to sequester chemokines during the infection. The SECRET domain represents a new family of viral CKBPs that was originally identified as a C-terminal extension of the viral tumor necrosis factor receptors (vTNFRs). We determined the three-dimensional structures of the SECRET domain and its complex with chemokine CX3CL1, revealing a new chemokine-binding manner of viral CKBPs. We also showed that other chemokines from different classes may be bound by the SECRET domain in a way similar to that observed in the SECRET/CX3CL1 complex structure. Our biochemical and chemotaxis assays also suggest that the SECRET domain is able to interfere with both chemokine-GAG and chemokine-receptor interactions, both of which are essential for chemokine activities in vivo.

Site-directed mutagenesis of the CC chemokine binding protein 35K-Fc reveals residues essential for activity and mutations that increase the potency of CC chemokine blockade

Chemokines of the CC class are key mediators of monocyte recruitment and macrophage differentiation and have a well documented role in many inflammatory diseases. Blockade of chemokine activity is therefore an attractive target for anti-inflammatory therapy. 35K (vCCI) is a high-affinity chemokine binding protein expressed by poxviruses, which binds all human and murine CC chemokines, preventing their interaction with chemokine receptors. We developed an Fc-fusion protein of 35K with a modified human IgG1 Fc domain and expressed this construct in human embryonic kidney 293T cells. Purified 35K-Fc is capable of inhibiting CC chemokine-induced calcium flux, chemotaxis, and β-arrestin recruitment in primary macrophages and transfected cells. To elucidate the residues involved in chemokine neutralization, we performed site-directed mutagenesis of six key amino acids in 35K and expressed the mutant Fc-fusion proteins in vitro. We screened the mutants for their ability to block chemokine-induced β-arrestin recruitment in transfected cells and to inhibit primary macrophage signaling in an electric cell substrate impedance sensing assay. Using a sterile model of acute inflammation, zymosan-induced peritonitis, we confirmed that wild-type 35K-Fc can reduce monocyte recruitment, whereas one mutant (R89A) showed a more pronounced blockade of monocyte influx and another mutant (E143K) showed total loss of function. We believe that 35K-Fc will be a useful tool for exploring the role of CC chemokines in chronic inflammatory pathologies, and we have identified a higher potency form of the molecule that may have potential therapeutic applications in chronic inflammatory disease.

Pan-CC chemokine neutralization restricts splenocyte egress and reduces inflammation in a model of arthritis

Chemokines are key regulators of leukocyte trafficking and play a crucial role under homeostatic and inflammatory conditions. Because chemokines are involved in multiple pathologies, they represent an attractive class of therapeutic targets. However, because of the redundancy of this system, neutralizing a single chemokine may be insufficient to achieve therapeutic benefit. Our strategy was to use a Fc-fusion recombinant protein form of the poxvirus-derived viral CC chemokine inhibitor protein (vCCI-Fc) that has the ability to specifically bind to multiple CC chemokines and neutralize their activity. In this study, we demonstrate first that, in vivo, vCCI-Fc prevents CC chemokine-dependent migration of macrophages into inflamed tissue of carageenan-challenged mice. We next studied this effect of inhibiting CC chemokine activity in a model more relevant to human disease, collagen-induced arthritis. Mice receiving vCCI-Fc revealed a striking retention of splenocytes, including activated and IFN-gamma-secreting CD4(+) and CD8(+) T cells, that was associated with a concomitant decrease of cells in the draining lymph nodes. These phenomena resulted in a significant decrease in the incidence of disease and a reduction in clinical score, joint inflammation, and cartilage destruction as compared with mice receiving isotype control. Taken together, these results define a role for CC chemokines in the control of disease, as interfering with their function leads to a previously unappreciated role of controlling inflammatory cell trafficking in and out of secondary lymphoid organs.

Structural basis of chemokine sequestration by a tick chemokine binding protein: the crystal structure of the complex between Evasin-1 and CCL3

Background

Chemokines are a subset of cytokines responsible for controlling the cellular migration of inflammatory cells through interaction with seven transmembrane G protein-coupled receptors. The blocking of a chemokine-receptor interaction results in a reduced inflammatory response, and represents a possible anti-inflammatory strategy, a strategy that is already employed by some virus and parasites. Anti-chemokine activity has been described in the extracts of tick salivary glands, and we have recently described the cloning and characterization of such chemokine binding proteins from the salivary glands, which we have named Evasins.

Methodology/Principal Findings

We have solved the structure of Evasin-1, a very small and highly selective chemokine-binding protein, by x-ray crystallography and report that the structure is novel, with no obvious similarity to the previously described structures of viral chemokine binding proteins. Moreover it does not possess a known fold. We have also solved the structure of the complex of Evasin-1 and its high affinity ligand, CCL3. The complex is a 1∶1 heterodimer in which the N-terminal region of CCL3 forms numerous contacts with Evasin-1, including prominent π-π interactions between residues Trp89 and Phe14 of the binding protein and Phe29 and Phe13 of the chemokine.

Conclusions/Significance

However, these interactions do not appear to be crucial for the selectivity of the binding protein, since these residues are found in CCL5, which is not a ligand for Evasin-1. The selectivity of the interaction would appear to lie in the N-terminal residues of the chemokine, which form the “address” whereas the hydrophobic interactions in the rest of the complex would serve primarily to stabilize the complex. A thorough understanding of the binding mode of this small protein, and its other family members, could be very informative in the design of potent neutralizing molecules of pro-inflammatory mediators of the immune system, such as chemokines.

CCR1 and CCR5 promote hepatic fibrosis in mice

Hepatic fibrosis develops as a response to chronic liver injury and almost exclusively occurs in a proinflammatory environment. However, the role of inflammatory mediators in fibrogenic responses of the liver is only poorly understood. We therefore investigated the role of CC chemokines and their receptors in hepatic fibrogenesis. The CC chemokines MIP-1alpha, MIP-1beta, and RANTES and their receptors CCR1 and CCR5 were strongly upregulated in 2 experimental mouse models of fibrogenesis. Neutralization of CC chemokines by the broad-spectrum CC chemokine inhibitor 35k efficiently reduced hepatic fibrosis, and CCR1- and CCR5-deficient mice displayed substantially reduced hepatic fibrosis and macrophage infiltration. Analysis of fibrogenesis in CCR1- and CCR5-chimeric mice revealed that CCR1 mediates its profibrogenic effects in BM-derived cells, whereas CCR5 mediates its profibrogenic effects in resident liver cells. CCR5 promoted hepatic stellate cell (HSC) migration through a redox-sensitive, PI3K-dependent pathway. Both CCR5-deficient HSCs and CCR1- and CCR5-deficient Kupffer cells displayed strong suppression of CC chemokine-induced migration. Finally, we detected marked upregulation of RANTES, CCR1, and CCR5 in patients with hepatic cirrhosis, confirming activation of the CC chemokine system in human fibrogenesis. Our data therefore support a role for the CC chemokine system in hepatic fibrogenesis and suggest distinct roles for CCR1 and CCR5 in Kupffer cells and HSCs.

Disruption of CCR5-dependent homing of regulatory T cells inhibits tumor growth in a murine model of pancreatic cancer

Tumors evade immune destruction by actively inducing immune tolerance through the recruitment of CD4(+)CD25(+)Foxp3(+) regulatory T cells (Treg). We have previously described increased prevalence of these cells in pancreatic adenocarcinoma, but it remains unclear what mechanisms are involved in recruiting Tregs into the tumor microenvironment. Here, we postulated that chemokines might direct Treg homing to tumor. We show, in both human pancreatic adenocarcinoma and a murine pancreatic tumor model (Pan02), that tumor cells produce increased levels of ligands for the CCR5 chemokine receptor and, reciprocally, that CD4(+) Foxp3(+) Tregs, compared with CD4(+) Foxp3(-) effector T cells, preferentially express CCR5. When CCR5/CCL5 signaling is disrupted, either by reducing CCL5 production by tumor cells or by systemic administration of a CCR5 inhibitor (N,N-dimethyl-N-{{4-{[2-(4-methylphenyl)-6,7-dihydro-5H-benzocyclohepten-8-yl]carbonyl}amino}}benzyl]-N,N-dimethyl-N- {{{4-{{{[2-(4-methylphenyl)-6,7-dihydro-5H-benzocycloheptan-8-yl]carbonyl}amino}}benzyl}}}tetrahydro-2H-pyran-4-aminiumchloride; TAK-779), Treg migration to tumors is reduced and tumors are smaller than in control mice. Thus, this study demonstrates the importance of Tregs in immune evasion by tumors, how blockade of Treg migration might inhibit tumor growth, and, specifically in pancreatic adenocarcinoma, the role of CCR5 in the homing of tumor-associated Tregs. Selective targeting of CCR5/CCL5 signaling may represent a novel immunomodulatory strategy for the treatment of cancer.

Modified vaccinia virus ankara triggers chemotaxis of monocytes and early respiratory immigration of leukocytes by induction of CCL2 expression

Orthopoxviruses commonly enter into humans and animals via the respiratory tract. Herein, we show that immigration of leukocytes into the lung is triggered via intranasal infection of mice with modified vaccinia virus Ankara (MVA) and not with the vaccinia virus (VACV) Elstree, Wyeth, or Western Reserve (WR) strain. Immigrating cells were identified as monocytes, neutrophils, and CD4(+) lymphocytes by flow cytometry and could be detected 24 h and 48 h postinfection. Using an in vitro chemotaxis assay, we confirmed that infection with MVA induces the expression of a soluble chemotactic factor for monocytes, identified as CCL2 (monocyte chemotactic protein-1 [MCP-1]). In contrast to infection with several other VACV strains, MVA induced the expression of CCL2, CCL3, CCL4, and CXCL10 in the human monocytic cell line THP-1 as well as in primary human monocytes. Thus, MVA, and not the VACV Elstree, Wyeth, or WR strain, consistently triggered the expression of a panel of chemokines, including CCL2, in the murine lung, correlating considerably with the immigration of leukocytes. Using CCL2-deficient mice, we demonstrate that CCL2 plays a key role in MVA-triggered respiratory immigration of leukocytes. Moreover, UV irradiation of MVA prevented CCL2 expression in vitro and in vivo as well as respiratory immigration of leukocytes, demonstrating the requirement for an activated molecular viral life cycle. We propose that MVA-triggered chemokine expression causes early immigration of leukocytes to the site of infection, a feature that is important for rapid immunization and its safety and efficiency as a viral vector.

Chemokine binding proteins encoded by pathogens

Chemokines are chemoattractant cytokines that play an important role in immunity. The role of chemokines against invading pathogens is emphasized by the expression of chemokine inhibitors by many pathogens. A mechanims employed by poxviruses and herpesviruses is the secretion of chemokine bindingproteins unrelated to host receptors that bind chemokines with high affinity and block their activity. Soluble chemokine binding proteins have also been identified in the human parasite Schistosoma mansoni and in ticks. The binding specificity of these inhibitors of cell migration point at chemokines that contribute to host defense mechanisms against various pathogens. Chemokine binding proteins modulate the immune response and may lead to new therapeutic approaches to treat inflamatory diseases.

Lentiviral gene transfer to reduce atherosclerosis progression by long-term CC-chemokine inhibition

CC-chemokines are important mediators in the pathogenesis of atherosclerosis. Atherosclerosis progression is reduced by high-level, short-term inhibition of CC-chemokine activity, for example by adenoviral gene transfer. However, atherosclerosis is a chronic condition where short-term effects, while demonstrating proof-of-principle, are unlikely to provide maximum therapeutic benefit. Accordingly, we generated a recombinant lentivirus, lenti35K, encoding the broad-spectrum CC chemokine inhibitor, 35K, derived from the vaccinia virus. To investigate the effects of prolonged broad-spectrum chemokine inhibition on atherosclerosis, lenti35K, or lentiGFP or PBS were delivered to 6-week-old ApoE knockout (ApoE-KO) mice by hydrodynamic injection. Sustained lentiviral transduction and transgene expression were demonstrated by 35K mRNA and viral DNA in liver tissue, and recombinant 35K protein circulating in the plasma, 3 months after gene transfer. Plasma from lenti35K animals had reduced chemokine activity compared with plasma from lentiGFP or PBS-treated animals. Histologic analysis of aortic sinus sections revealed that atherosclerotic plaque area in lenti35K mice was significantly reduced compared with both lentiGFP and PBS controls. Furthermore, plaque macrophage content was substantially reduced in lenti35K mice. Lentiviral 35K gene transfer is a promising experimental strategy to reduce atherosclerosis progression, and demonstrates the potential of long-term CC-chemokine inhibition as a potential therapeutic target in atherosclerosis.

Structure and function of A41, a vaccinia virus chemokine binding protein

The vaccinia virus (VACV) A41L gene encodes a secreted 30 kDa glycoprotein that is nonessential for virus replication but affects the host response to infection. The A41 protein shares sequence similarity with another VACV protein that binds CC chemokines (called vCKBP, or viral CC chemokine inhibitor, vCCI), and strains of VACV lacking the A41L gene induced stronger CD8⁺ T-cell responses than control viruses expressing A41. Using surface plasmon resonance, we screened 39 human and murine chemokines and identified CCL21, CCL25, CCL26 and CCL28 as A41 ligands, with K_ds of between 8 nM and 118 nM. Nonetheless, A41 was ineffective at inhibiting chemotaxis induced by these chemokines, indicating it did not block the interaction of these chemokines with their receptors. However the interaction of A41 and chemokines was inhibited in a dose-dependent manner by heparin, suggesting that A41 and heparin bind to overlapping sites on these chemokines. To better understand the mechanism of action of A41 its crystal structure was solved to 1.9 Å resolution. The protein has a globular β sandwich structure similar to that of the poxvirus vCCI family of proteins, but there are notable structural differences, particularly in surface loops and electrostatic charge distribution. Structural modelling suggests that the binding paradigm as defined for the vCCI–chemokine interaction is likely to be conserved between A41 and its chemokine partners. Additionally, sequence analysis of chemokines binding to A41 identified a signature for A41 binding. The biological and structural data suggest that A41 functions by forming moderately strong (nM) interactions with certain chemokines, sufficient to interfere with chemokine-glycosaminoglycan interactions at the cell surface (μM–nM) and thereby to destroy the chemokine concentration gradient, but not strong enough to disrupt the (pM) chemokine–chemokine receptor interactions.

As part of the innate immune response (for example to virus infection), the body produces proteins called chemokines, which act by directing white blood cells (leukocytes) to the areas of infection and inflammation. Viruses have evolved mechanisms to fight this immune response. Indeed, so important is this need to protect themselves from the immune system that some viruses, such as poxviruses, devote up to half their genetic information to this battle. We have studied a protein called A41, one component of the response of vaccinia virus (the vaccine used to eradicate smallpox) to the immune system and shown that it interferes with the function of a group of chemokines. These chemokines function by forming concentration gradients along which the white blood cells migrate, and A41 sequesters the chemokines, thereby preventing formation of the gradient. Interestingly, we show also that A41 is very similar in structure to another group of proteins, called vCCIs, that bind chemokines more tightly, blocking their attachment to white blood cells, suggesting that both mechanisms are important for virus virulence.

An ectromelia virus protein that interacts with chemokines through their glycosaminoglycan binding domain

Poxviruses encode a number of secreted virulence factors that modulate the host immune response. The vaccinia virus A41 protein is an immunomodulatory protein with amino acid sequence similarity to the 35-kDa chemokine binding protein, but the host immune molecules targeted by A41 have not been identified. We report here that the vaccinia virus A41 ortholog encoded by ectromelia virus, a poxvirus pathogen of mice, named E163 in the ectromelia virus Naval strain, is a secreted 31-kDa glycoprotein that selectively binds a limited number of CC and CXC chemokines with high affinity. A detailed characterization of the interaction of ectromelia virus E163 with mutant forms of the chemokines CXCL10 and CXCL12alpha indicated that E163 binds to the glycosaminoglycan binding site of the chemokines. This suggests that E163 inhibits the interaction of chemokines with glycosaminoglycans and provides a mechanism by which E163 prevents chemokine-induced leukocyte migration to the sites of infection. In addition to interacting with chemokines, E163 can interact with high affinity with glycosaminoglycan molecules, enabling E163 to attach to cell surfaces and to remain in the vicinity of the sites of viral infection. These findings identify E163 as a new chemokine binding protein in poxviruses and provide a molecular mechanism for the immunomodulatory activity previously reported for the vaccinia virus A41 ortholog. The results reported here also suggest that the cell surface and extracellular matrix are important targeting sites for secreted poxvirus immune modulators.

Molecular Cloning and Characterization of a Highly Selective Chemokine-binding Protein from the Tick Rhipicephalus sanguineus

Ticks are blood-feeding parasites that secrete a number of immuno-modulatory factors to evade the host immune response. Saliva isolated from different species of ticks has recently been shown to contain chemokine neutralizing activity. To characterize this activity, we constructed a cDNA library from the salivary glands of the common brown dog tick, Rhipicephalus sanguineus. Pools of cDNA clones from the library were transfected into HEK293 cells, and the conditioned media from the transfected cells were tested for chemokine binding activity by chemical cross-linking to radiolabeled CCL3 followed by SDS-PAGE. By de-convolution of a single positive pool of 270 clones, we identified a full-length cDNA encoding a protein of 114 amino acids, which after signal peptide cleavage was predicted to yield a mature protein of 94 amino acids that we called Evasin-1. Recombinant Evasin-1 was produced in HEK293 cells and in insect cells. Using surface plasmon resonance we were able to show that Evasin-1 was exquisitely selective for 3 CC chemokines, CCL3 and CCL4 and the closely related chemokine CCL18, with K(D) values of 0.16, 0.81, and 3.21 nm, respectively. The affinities for CCL3 and CCL4 were confirmed in competition receptor binding assays. Analysis by size exclusion chromatography demonstrated that Evasin-1 was monomeric and formed a 1:1 complex with CCL3. Thus, unlike the other chemokine-binding proteins identified to date from viruses and from the parasitic worm Schistosoma mansoni, Evasin-1 is highly specific for a subgroup of CC chemokines, which may reflect a specific role for these chemokines in host defense against parasites.

Virus-encoded chemokines, chemokine receptors and chemokine-binding proteins: new paradigms for future therapy

Over millions of years of coevolution with their hosts, viruses have learned the finest artifices of the immune system defense mechanisms and developed a variety of strategies for evading them. The chemokine system has been a primary target of these viral efforts because of the critical role it plays in the development of effective immune responses. Not only do chemokines control cellular recruitment at the site of infection, they also regulate the magnitude and character of the immune responses. Several viruses, and large DNA viruses in particular, have exploited the chemokine system by hijacking and reprogramming chemokine or chemokine-receptor genes, and/or secreting chemokine-binding proteins. In the past few years there has been intense investigation in this area, driven not only by the prospect of gaining a better understanding of viral-immune evasion mechanisms, but also by the possibility of targeting these molecules as part of future antiviral therapeutic approaches, as well as exploiting viral strategies of chemokine interference as novel therapies for inflammatory or neoplastic diseases.

Gene therapy of fibroproliferative vasculopathies: current ideas in molecular mechanisms and biomedical technology

Intimal hyperplasia occurs primarily as a part of the pathogenesis of coronary artery disease or secondary to therapeutic intervention in relieving vascular occlusion. Intimal hyperplasia involving vascular smooth muscle cells is found in atherosclerosis, post-balloon angioplasty restenosis, in-stent restenosis and vein graft disease, predominantly involving the use of saphenous vein conduits in coronary artery bypass grafting procedures. One potentially exciting area is that of gene therapy. Gene and protein expression patterns at the site of vasculoproliferative lesions have been widely studied and several target areas have been identified on the basis of whether the gene has an antiproliferative, proapoptotic, matrix degrading or endothelial protective action. Blood vessels are easily accessible for the delivery of the gene product, and experimental studies using animal models have used catheter-delivered gene products at the site of vascular injury. Currently, the application of antisense technology and adenoviral vector-mediated delivery has shown significant promise, albeit in in vitro or animal model settings. In this review, we discuss the current knowledge in the application of gene therapy in fibroproliferative vasculopathies. We examine some of the cellular mechanisms and intermediaries which could be potential candidates for gene targeting. We also present some of the advances in biomedical technology that might provide useful vehicles for pinpoint delivery of the gene product. Could the future of restenosis treatment be in gene therapy or is it misplaced enthusiasm?

Membrane-bound CC chemokine inhibitor 35K provides localized inhibition of CC chemokine activity in vitro and in vivo

CC chemokines mediate mononuclear cell recruitment and activation in chronic inflammation. We have shown previously that gene transfer using recombinant adenoviruses, encoding a soluble CC chemokine-binding protein of vaccinia virus 35K, can dramatically reduce atherosclerosis and vein graft remodeling in apolipoprotein E knockout mice. In this study, we report the development of a membrane-bound form of 35K (m35K), tagged with GFP, which allows for localized, broad-spectrum CC chemokine blockade. In vitro experiments indicate that m35K-expressing cells no longer undergo CC chemokine-induced chemotaxis, and m35K-expressing cells can locally deplete the CC chemokines RANTES (CCL5) and MIP-1alpha (CCL3) from supernatant medium. This sequestration of CC chemokines can prevent chemotaxis of bystander cells to CC, but not CX(3)C chemokines. Intraperitoneal injection of mice with an adenovirus-encoding m35K leads to a significant (44%) decrease in leukocyte recruitment into the peritoneal cavity in a sterile peritonitis model. Intravenous adenovirus-encoding m35K delivery leads to m35K expression in hepatocytes, which confers significant protection against liver damage (75% reduction in liver enzymes) in a Con A-induced hepatitis model. In summary, we have generated a membrane-bound CC chemokine-binding protein (m35K) that provides localized broad-spectrum CC chemokine inhibition in vitro and in vivo. m35K may be a useful tool to study the role of CC chemokines in leukocyte trafficking and block the recruitment of monocytes in chronic inflammation.

Solution structure of the complex between poxvirus-encoded CC chemokine inhibitor vCCI and human MIP-1beta

Chemokines (chemotactic cytokines) comprise a large family of proteins that recruit and activate leukocytes, giving chemokines a major role in both immune response and inflammation-related diseases. The poxvirus-encoded viral CC chemokine inhibitor (vCCI) binds to many CC chemokines with high affinity, acting as a potent inhibitor of chemokine action. We have used heteronuclear multidimensional NMR to determine the structure of an orthopoxvirus vCCI in complex with a human CC chemokine, MIP-1beta (macrophage inflammatory protein 1beta). vCCI binds to the chemokine with 1:1 stoichiometry, forming a complex of 311 aa. vCCI uses residues from its beta-sheet II to interact with a surface of MIP-1beta that includes residues adjacent to its N terminus, as well as residues in the 20's region and the 40's loop. This structure reveals the strategy used by vCCI to tightly bind numerous chemokines while retaining selectivity for the CC chemokine subfamily.

Immune evasion by poxviruses

Through eons of co-evolution, poxviruses and their hosts have come to an elegant point of equilibrium whereby the host immune system is systematically modulated in favor of the virus. Owing to the large coding capacity of poxviruses, many gene products are dedicated as virulence factors. Key targets of these immunomodulators include mediators of inflammation, chemotaxis, apoptosis and the antiviral state. It is not surprising that these systems have become targets since they are crucial for mounting an effective immune response against poxviruses. The following discussion will focus on a select group of poxvirus proteins that are able to modulate particular components of the host response efficiently to ensure propagation of the virus.

Broad-Spectrum CC-Chemokine Blockade by Gene Transfer Inhibits Macrophage Recruitment and Atherosclerotic Plaque Formation in Apolipoprotein E–Knockout Mice

Background— The CC-chemokines (CKs) recruit monocytes/macrophages to sites of inflammation; several different CC-CKs play a role in the pathogenesis of atherosclerosis. The vaccinia virus expresses a 35-kDa soluble protein (35K) that binds to and inactivates nearly all of the CC-CKs, providing a potentially useful therapeutic strategy for broad-spectrum CC-CK inhibition in atherosclerosis. A recombinant adenovirus encoding soluble 35K (Ad35K) was generated to investigate the effect of 35K gene transfer on atherosclerosis in Western diet–fed apolipoprotein E–knockout (ApoE KO) mice.

Methods and Results— ApoE KO mice received tail-vein injections of phosphate-buffered saline, Ad35K, or control adenovirus AdGFP encoding green fluorescence protein. Two weeks after Ad35K gene transfer, atherosclerotic lesion area was significantly reduced in aortic roots by 55% compared with PBS or AdGFP control mice ( P <0.05). Furthermore, 35K gene transfer strikingly reduced the macrophage content in aortic root lesions by 85% ( P <0.01) and reduced lipid deposition in descending aortas by more than half ( P <0.05). By an in vitro chemotaxis assay, plasma and aortic homogenates from 35K gene transfer mice promoted significantly less CC-CK–induced cell migration than did PBS or AdGFP controls.

Conclusions— These findings show that a single intravenous injection of a recombinant adenovirus encoding the broad-spectrum CC-CK inhibitor 35K can reduce atherosclerosis by inhibiting CC-CK–induced macrophage recruitment in atherosclerotic ApoE KO mice. These experiments suggest that CC-CKs play an important role in atherogenesis and are a rational target for therapeutic intervention.

The genomic sequence of ectromelia virus, the causative agent of mousepox

Ectromelia virus is the causative agent of mousepox, an acute exanthematous disease of mouse colonies in Europe, Japan, China, and the U.S. The Moscow, Hampstead, and NIH79 strains are the most thoroughly studied with the Moscow strain being the most infectious and virulent for the mouse. In the late 1940s mousepox was proposed as a model for the study of the pathogenesis of smallpox and generalized vaccinia in humans. Studies in the last five decades from a succession of investigators have resulted in a detailed description of the virologic and pathologic disease course in genetically susceptible and resistant inbred and out-bred mice. We report the DNA sequence of the left-hand end, the predicted right-hand terminal repeat, and central regions of the genome of the Moscow strain of ectromelia virus (approximately 177,500 bp), which together with the previously sequenced right-hand end, yields a genome of 209,771 bp. We identified 175 potential genes specifying proteins of between 53 and 1924 amino acids, and 29 regions containing sequences related to genes predicted in other poxviruses, but unlikely to encode for functional proteins in ectromelia virus. The translated protein sequences were compared with the protein database for structure/function relationships, and these analyses were used to investigate poxvirus evolution and to attempt to explain at the cellular and molecular level the well-characterized features of the ectromelia virus natural life cycle.

Adenoviral-mediated delivery of a viral chemokine binding protein blocks CC-chemokine activity in vitro and in vivo

Chemokines are important mediators of leukocyte recruitment and activation that play critical roles in the pathology of inflammatory diseases such as atherosclerosis, rheumatoid arthritis and asthma. The vaccinia virus (strain Lister) expresses a 35 kDa soluble protein ('35K') that binds and inactivates a wide range of CC chemokines. We generated a recombinant adenovirus encoding soluble 35K (Ad35K). Ad35K-infected cell culture medium, containing recombinant 35K, potently reduced migration of CCR5-transfected 293 cells by 95% in response to the CC-chemokine RANTES, but had no effect on cells transfected with the CX3CR1 fractalkine receptor. Delivery of Ad35K to mice in vivo via tail vein injection resulted in expression of recombinant 35K in plasma and increased serum RANTES and MIP-1alpha levels when quantified by ELISA. However, chemotaxis of both CCR5-transfected cells and primary macrophages was inhibited by more than 90% by plasma from Ad35K-infected animals compared with control plasma from animals injected with AdGFP. Furthermore, 35K delivered by intra-peritoneal injection more than halved biogel-induced inflammatory cell recruitment in peritoneal exudates compared to AdGFP medium. These studies identify broad-spectrum CC-chemokine blockade using in vivo adenoviral-mediated recombinant 35K expression as a promising strategy to reduce local and systemic inflammation.

Analysis of an orf virus chemokine-binding protein: Shifting ligand specificities among a family of poxvirus viroceptors

We identify a secreted chemokine inhibitor encoded by orf virus (ORFV), the prototypic poxvirus of the Parapoxvirus genus, and show that it is related to the poxvirus type II CC-chemokine-binding proteins (CBP-II) produced by members of the Orthopoxvirus and Leporipoxvirus genera. The ORFV chemokine-binding protein (CBP) is functionally similar to the CBP-II proteins in its ability to bind and inhibit many CC-chemokines with high affinity. However, unlike CBP-II, the ORFV CBP also binds with high affinity to lymphotactin, a member of the C-chemokine family, demonstrating that the ORFV CBP possesses an altered binding specificity. Interestingly, the amino acid sequence of ORFV CBP more closely resembles the granulocyte-macrophage colony-stimulating factor/IL-2 inhibitory factor also produced by ORFV, implicating the granulocyte-macrophage colony-stimulating factor/IL-2 inhibitory factor protein as a highly diverged, but related, member of the CBP-II protein family. Notably, these findings suggest that the genes that encode these proteins derive from a common poxvirus ancestral gene that has since been modified in binding specificity during speciation of the poxvirus genera. Overall, these findings illustrate the concept of evolution of viral proteins at the biophysical and molecular interface.

Characterization of the rhesus cytomegalovirus US28 locus

Human cytomegalovirus (CMV) US28 (and the related open reading frame [ORF] US27) are G-protein-coupled receptor homologs believed to play a role in viral pathogenesis. In vitro, US28 has been shown to bind and internalize ligands, as well as activate intracellular signaling in response to certain chemokines, and to initiate the migration of smooth muscle cells to chemokine gradients. To assess the role of US28 in vivo, we examined the rhesus model and sequenced and characterized the rhesus CMV US28 locus. We found that rhesus CMV carries five tandem homologs of US28, all widely divergent from US28 and from each other. By reverse transcription-PCR and Northern analysis, we demonstrated expression of these ORFs in infected cells. With stable cell lines expressing these ORFs, we analyzed the homolog's binding and signaling characteristics across a wide range of chemokines and found one (RhUS28.5) to have a ligand binding profile similar to that of US28. In addition, we localized US28 and the rhesus CMV homolog RhUS28.5 to the envelope of infectious virions, suggesting a role in viral entry or cell tropism.

Variola virus immune evasion proteins

Variola virus, the causative agent of smallpox, encodes approximately 200 proteins. Over 80 of these proteins are located in the terminal regions of the genome, where proteins associated with host immune evasion are encoded. To date, only two variola proteins have been characterized. Both are located in the terminal regions and demonstrate immunoregulatory functions. One protein, the smallpox inhibitor of complement enzymes (SPICE), is homologous to a vaccinia virus virulence factor, the vaccinia virus complement-control protein (VCP), which has been found experimentally to be expressed early in the course of vaccinia infection. Both SPICE and VCP are similar in structure and function to the family of mammalian complement regulatory proteins, which function to prevent inadvertent injury to adjacent cells and tissues during complement activation. The second variola protein is the variola virus high-affinity secreted chemokine-binding protein type II (CKBP-II, CBP-II, vCCI), which binds CC-chemokine receptors. The vaccinia homologue of CKBP-II is secreted both early and late in infection. CKBP-II proteins are highly conserved among orthopoxviruses, sharing approximately 85% homology, but are absent in eukaryotes. This characteristic sets it apart from other known virulence factors in orthopoxviruses, which share sequence homology with known mammalian immune regulatory gene products. Future studies of additional variola proteins may help illuminate factors associated with its virulence, pathogenesis and strict human tropism. In addition, these studies may also assist in the development of targeted therapies for the treatment of both smallpox and human immune-related diseases.