Recombinant vaccinia viruses. Design, generation, and isolation

Oncolytic Vaccinia Virus Expressing Aphrocallistes vastus Lectin as a Cancer Therapeutic Agent

Lectins display a variety of biological functions including insecticidal, antimicrobial, as well as antitumor activities. In this report, a gene encoding Aphrocallistes vastus lectin (AVL), a C-type lectin, was inserted into an oncolytic vaccinia virus vector (oncoVV) to form a recombinant virus oncoVV-AVL, which showed significant in vitro antiproliferative activity in a variety of cancer cell lines. Further investigations revealed that oncoVV-AVL replicated faster than oncoVV significantly in cancer cells. Intracellular signaling elements including NF-κB2, NIK, as well as ERK were determined to be altered by oncoVV-AVL. Virus replication upregulated by AVL was completely dependent on ERK activity. Furthermore, in vivo studies showed that oncoVV-AVL elicited significant antitumor effect in colorectal cancer and liver cancer mouse models. Our study might provide insights into a novel way of the utilization of marine lectin AVL in oncolytic viral therapies.

A rapid Orthopoxvirus purification protocol suitable for high-containment laboratories

Virus purification in a high-containment setting provides unique challenges due to barrier precautions and operational safety approaches that are not necessary in lower biosafety level (BSL) 2 environments. The need for high risk group pathogen diagnostic assay development, anti-viral research, pathogenesis and vaccine efficacy research necessitates work in BSL-3 and BSL-4 labs with infectious agents. When this work is performed in accordance with BSL-4 practices, modifications are often required in standard protocols. Classical virus purification techniques are difficult to execute in a BSL-3 or BSL-4 laboratory because of the work practices used in these environments. Orthopoxviruses are a family of viruses that, in some cases, requires work in a high-containment laboratory and due to size do not lend themselves to simpler purification methods. Current CDC purification techniques of orthopoxviruses uses 1,1,2-trichlorotrifluoroethane, commonly known as Genetron^®. Genetron^® is a chlorofluorocarbon (CFC) that has been shown to be detrimental to the ozone and has been phased out and the limited amount of product makes it no longer a feasible option for poxvirus purification purposes. Here we demonstrate a new Orthopoxvirus purification method that is suitable for high-containment laboratories and produces virus that is not only comparable to previous purification methods, but improves on purity and yield.

Role for the conserved N-terminal cysteines in the anti-chemokine activities by the chemokine-like protein MC148R1 encoded by Molluscum contagiosum virus

Molluscum contagiosum poxvirus (MCV) type 1 and type 2 encode two chemokine-like proteins MC148R1 and MC148R2. It is believed that MC148R proteins function by blocking the inflammatory response. However, the mechanism of the proposed biological activities of MC148R proteins and the role of the additional C-terminal cysteines that do not exist in other chemokines are not understood. Here, we demonstrated in two different assay systems that His-tagged MC148R1 displaces the interaction between CXCL12α and CXCR4. The N-terminal cysteines but not the additional C-terminal cysteines modulate this displacement. His-tagged MC148R1 blocked both CXCL12α-mediated and MIP-1α-mediated chemotaxis. In contrast, MC148R2 blocked MIP-1α-mediated but not CXCL12α-mediated chemotaxis. Immunoprecipitation by antibodies to MC148R1 or CXCL12α followed by immunoblotting and detection by antibodies to the other protein demonstrated physical interaction of His-tagged CXCL12α and His-tagged MC148R1. Interaction with chemokines might mask the receptor interaction site resulting in decreased binding and impairment of the biological activities.

IFN-alpha-mediated increase in cytolytic activity of maturing NK cell upon exposure to HSV-infected myelomonocytes

Impaired control of chronic pathogen replication may be associated to alterations of NK-cell function. Whether mechanisms underlying this dysfunction involve perturbations of differentiating NK cells is still unknown. We studied an "in vitro" model of differentiation from CD34(+)Lin(-) precursors growing only myelomonocytes and maturing NK cells and where myelomonocytes could be suitably infected with HSV, HIV, or vaccinia. Cultures were evaluated by cytofluorometry and cytotoxicity assays for perturbations in differentiating NK cells. Increased expression of natural cytotoxicity receptors on maturing NK cells with increased cytolytic activity was observed with HSV-1 infection, and with vaccinia while no modulation of NK-cell phenotype nor cytotoxic activity were evident with an ssRNA lentivirus (HIV-1). In the presence of constant IL-12 and IL-15 concentrations, the observed effect did not require cell contact, involved IFN-alpha and was not reproduced by the addition of TLR9 agonist, nor blocked by TLR9 antagonists. Virus replication at sites of NK-cell precursor development may have different outcomes depending on the interaction between invading viruses and maturing NK cells. Thus, NK-cell precursors may be involved in the immune response to dsDNA viruses and possibly contribute to efficient control of virus infection.

Resistance to human immunodeficiency virus type 1 (HIV-1) generated by lentivirus vector-mediated delivery of the CCR5{Delta}32 gene despite detectable expression of the HIV-1 co-receptors

It has previously been demonstrated that there are two distinct mechanisms for genetic resistance to human immunodeficiency virus type 1 (HIV-1) conferred by the CCR5Delta32 gene: the loss of wild-type CCR5 surface expression and the generation of CCR5Delta32 protein, which interacts with CXCR4. To analyse the protective effects of long-term expression of the CCR5Delta32 protein, recombinant lentiviral vectors were used to deliver the CCR5Delta32 gene into human cell lines and primary peripheral blood mononuclear cells that had been immortalized by human T-cell leukemia virus type 1. Blasticidin S-resistant cell lines expressing the lentivirus-encoded CCR5Delta32 showed a significant reduction in HIV-1 Env-mediated fusion assays. It was shown that CD4(+) T lymphocytes expressing the lentivirus-encoded CCR5Delta32 gene were highly resistant to infection by a primary but not by a laboratory-adapted X4 strain, suggesting different infectivity requirements. In contrast to previous studies that analysed the CCR5Delta32 protective effects in a transient expression system, this study showed that long-term expression of CCR5Delta32 conferred resistance to HIV-1 despite cell-surface expression of the HIV co-receptors. The results suggest an additional unknown mechanism for generating the CCR5Delta32 resistance phenotype and support the hypothesis that the CCR5Delta32 protein acts as an HIV-suppressive factor by altering the stoichiometry of the molecules involved in HIV-1 entry. The lentiviral-CCR5Delta32 vectors offer a method of generating HIV-resistant cells by delivery of the CCR5Delta32 gene that may be useful for stem cell- or T-cell-based gene therapy for HIV-1 infection.

Preparation of recombinant viral glycoproteins for novel and therapeutic antibody discovery

Neutralizing antibodies are a critical component in the protection or recovery from viral infections. In the absence of available vaccines or antiviral drugs for many important human viral pathogens, the identification and characterization of new human monoclonal antibodies (hmAbs) that are able to neutralize viruses offers the possibility for effective pre- and/or post-exposure therapeutic modalities. Such hmAbs may also help in our understanding of the virus entry process, the mechanisms of virus neutralization, and in the eventual development of specific entry inhibitors, vaccines, and research tools. The majority of the more recently developed antiviral hmAbs have come from the use of antibody phage-display technologies using both naïve and immune libraries. Many of these agents are also enveloped viruses possessing important neutralizing determinants within their membrane-anchored envelope glycoproteins, and the use of recombinant, soluble versions of these viral glycoproteins is often critical in the isolation and development of antiviral hmAbs. This chapter will detail several methods that have been successfully employed to produce, purify, and characterize soluble and secreted versions of several viral envelope glycoproteins which have been successfully used as antigens to capture and isolate human phage-displayed monoclonal antibodies.

Targeted strategies for henipavirus therapeutics

Hendra and Nipah viruses are related emergent paramyxoviruses that infect and cause disease in animals and humans. Disease manifests as a generalized vasculitis affecting multiple organs, but is the most severe in the respiratory and central nervous systems. The high case fatality and person-to-person transmission associated with the most recent NiV outbreaks, and the recent re-emergence of HeV, emphasize the importance and necessity of effective therapeutics for these novel agents. In recent years henipavirus research has revealed a more complete understanding of pathogenesis and, as a consequence, viable approaches towards vaccines and therapeutics have emerged. All strategies target early steps in viral replication including receptor binding and membrane fusion. Animal models have been developed, some of which may prove more valuable than others for evaluating the efficacy of therapeutic agents and regimes. Assessments of protective host immunity and drug pharmacokinetics will be crucial to the further advancement of therapeutic compounds.

Developments towards effective treatments for Nipah and Hendra virus infection

Hendra and Nipah virus are closely related emerging viruses comprising the Henipavirus genus of the subfamily Paramyxovirinae and are distinguished by their ability to cause fatal disease in both animal and human hosts. In particular, the high mortality and person-to-person transmission associated with the most recent Nipah virus outbreaks, as well as the very recent re-emergence of Hendra virus, has confirmed the importance and necessity of developing effective therapeutic interventions. Much research conducted on the henipaviruses over the past several years has focused on virus entry, including the attachment of virus to the host cell, the identification of the virus receptor and the membrane fusion process between the viral and host cell membranes. These findings have led to the development of possible vaccine candidates, as well as potential antiviral therapeutics. The common link among all of the possible antiviral agents discussed here, which have also been developed and tested, is that they target very early stages of the infection process. The establishment and validation of suitable animal models of Henipavirus infection and pathogenesis are also discussed as they will be crucial in the assessment of the effectiveness of any treatments for Hendra and Nipah virus infection.

Use ofin vitrotransporter assays to understand hepatic and renal disposition of new drug candidates

Hepatic and renal transporters contribute to the uptake, secretion and reabsorption of endogenous compounds, xenobiotics and their metabolites and have been implicated in drug-drug interactions and toxicities. Characterising the renal and hepatic disposition of drug candidates early in development would lead to more rational drug design, as chemotypes with 'ideal' pharmacokinetic characteristics could be identified and further refined. Because transporters are often organ specific, 'custom' transporter panels need to be identified for each major organ and chemotype to be evaluated, and appropriate studies planned. This review outlines the major renal and hepatic transporters and some of the in vitro transporter reagents, assays and processes that can be used to evaluate the renal and hepatic disposition of new chemical entities during drug discovery and development.

Protection of rhesus monkeys against infection with minimally pathogenic simian-human immunodeficiency virus: correlations with neutralizing antibodies and cytotoxic T cells

We studied the capacity of active immunization of rhesus monkeys with HIV-1 envelope protein (Env) to induce primary virus cross-reactive neutralizing antibodies to prevent infection following intravenous challenge with simian-human immunodeficiency virus (SHIV). Monkeys were immunized with the human immunodeficiency type 1 (HIV-1) strain R2 Env. Initially, the Env was expressed in vivo by an alphavirus replicon particle system, and then it was administered as soluble oligomeric gp140. Concurrently, groups of monkeys received expression vectors that encoded either simian immunodeficiency virus (SIV) gag/pol genes or no SIV genes in vivo to test the additional protective benefit of concurrent induction of virus-specific cell-mediated immune (CMI) responses. Groups of control monkeys received either the gag/pol regimen or sham immunizations. The antibodies induced by the Env immunization regimen neutralized diverse primary HIV-1 strains. Similarly, potent CMI responses were induced by the gag/pol regimen, as measured by gamma interferon enzyme-linked immunospot assays. Differences in the responses among groups of monkeys strongly suggested that there was interference between the Env and gag/pol immunization regimens. Complete protection of some of the monkeys against infection after intravenous challenge with the partially pathogenic SHIV(DH12R (Clone 7)) was associated independently with both neutralizing antibody and CMI responses. Protection was associated with SHIV(DH12 (Clone 7)) serum neutralizing antibody titers of > or =1:80 or with cellular immune responses corresponding to >2,000 spot forming cells per 10(6) peripheral blood mononuclear cells. Immunization was also associated with a reduction in the magnitude and duration of virus load. Induction of cross-reactive, primary HIV-1-neutralizing antibodies is feasible and, when potent, may result in complete protection against infection with a heterologous challenge virus strain.

Production of recombinant proteins by vaccinia virus in a microcarrier based mammalian cell perfusion bioreactor

The HeLa cell-vaccinia virus expression system was evaluated for the production of recombinant proteins (enhanced green fluorescent protein (EGFP) and HIV envelope coat protein, gp120) using microcarriers in 1.5 L perfused bioreactor cultures. Perfusion was achieved by use of an alternating tangential flow device (ATF), increasing the length of the exponential phase by 50 h compared to batch culture and increasing the maximum cell density from 1.5x10(6) to 4.4x10(6) cell/mL. A seed train expansion method using cells harvested from microcarrier culture and reseeding onto fresh carriers was developed. EGFP was first used as a model protein to study process parameters affecting protein yield, specifically dissolved oxygen (DO) and temperature during the production phase. The highest level of EGFP, 12+/-1.5 microg/10(6) infected cells, was obtained at 50% DO and 31 degrees C. These setpoints were then used to produce glycoprotein, gp120, which was purified and deglycosylated, revealing a significant amount of N-linked glycosylation. Also, biological activity was assayed, resulting in an ID50 of 3.1 microg/mL, which is comparable to previous reports.

Role for CCR5Delta32 protein in resistance to R5, R5X4, and X4 human immunodeficiency virus type 1 in primary CD4+ cells

CCR5Delta32 is a loss-of-function mutation that abolishes cell surface expression of the human immunodeficiency virus (HIV) coreceptor CCR5 and provides genetic resistance to HIV infection and disease progression. Since CXCR4 and other HIV coreceptors also exist, we hypothesized that CCR5Delta32-mediated resistance may be due not only to the loss of CCR5 function but also to a gain-of-function mechanism, specifically the active inhibition of alternative coreceptors by the mutant CCR5Delta32 protein. Here we demonstrate that efficient expression of the CCR5Delta32 protein in primary CD4(+) cells by use of a recombinant adenovirus (Ad5/Delta32) was able to down-regulate surface expression of both wild-type CCR5 and CXCR4 and to confer broad resistance to R5, R5X4, and X4 HIV type 1 (HIV-1). This may be important clinically, since we found that CD4(+) cells purified from peripheral blood mononuclear cells of individuals who were homozygous for CCR5Delta32, which expressed the mutant protein endogenously, consistently expressed lower levels of CXCR4 and showed less susceptibility to X4 HIV-1 isolates than cells from individuals lacking the mutation. Moreover, CD4(+) cells from individuals who were homozygous for CCR5Delta32 expressed the mutant protein in five of five HIV-exposed, uninfected donors tested but not in either of two HIV-infected donors tested. The mechanism of inhibition may involve direct scavenging, since we were able to observe a direct interaction of CCR5 and CXCR4 with CCR5Delta32, both by genetic criteria using the yeast two-hybrid system and by biochemical criteria using the coimmunoprecipitation of heterodimers. Thus, these results suggest that at least two distinct mechanisms may account for genetic resistance to HIV conferred by CCR5Delta32: the loss of wild-type CCR5 surface expression and the generation of CCR5Delta32 protein, which functions as a scavenger of both CCR5 and CXCR4.

Replication and expression of a swinepox virus vector delivering feline leukemia virus Gag and Env to cell lines of swine and feline origin

The host range of swinepox virus (SPV) is restricted to swine, although SPV has been shown to infect mammalian, non-swine cells, without recovery of infectious virus. SPV is a reasonable candidate for development as a non-productively replicating viral vector for use in non-swine, mammalian species, such as the cat. A novel SPV gene deletion (SPV 043) was created and found to be non-attenuating. This deletion was utilized to generate a stable recombinant virus expressing the Gag-Pro and Env proteins of feline leukemia virus (FeLV). Expression and replication of this vector was studied in embryonic swine kidney cells (ESK-4), and two feline cell lines, Crandell feline kidney cells (CRFK) and feline skin fibroblasts (FSF). Our results showed that feline cells were susceptible to infection by SPV and supported expression of foreign genes driven by synthetic poxvirus promoters, however, SPV viral DNA was not replicated in feline cells and infectious virus was not recovered. In addition, FeLV Gag virus-like particles were produced from both ESK-4 and CRFK cells and foreign antigens were incorporated into infectious SPV intracellular mature virions (IMV). These results suggest that SPV may have potential as a safe vaccine delivery vector for cats.

Membrane fusion tropism and heterotypic functional activities of the Nipah virus and Hendra virus envelope glycoproteins

Nipah virus (NiV) and Hendra virus (HeV) are novel paramyxoviruses from pigs and horses, respectively, that are responsible for fatal zoonotic infections of humans. The unique genetic and biological characteristics of these emerging agents has led to their classification as the prototypic members of a new genus within the Paramyxovirinae subfamily called HENIPAVIRUS: These viruses are most closely related to members of the genus Morbillivirus and infect cells through a pH-independent membrane fusion event mediated by the actions of their attachment (G) and fusion (F) glycoproteins. Understanding their cell biological features and exploring the functional characteristics of the NiV and HeV glycoproteins will help define important properties of these emerging viruses and may provide new insights into paramyxovirus membrane fusion mechanisms. Using a recombinant vaccinia virus system and a quantitative assay for fusion, we demonstrate NiV glycoprotein function and the same pattern of cellular tropism recently reported for HeV-mediated fusion, suggesting that NiV likely uses the same cellular receptor for infection. Fusion specificity was verified by inhibition with a specific antiserum or peptides derived from the alpha-helical heptads of NiV or HeV F. Like that of HeV, NiV-mediated fusion also requires both F and G. Finally, interactions between the glycoproteins of the paramyxoviruses have not been well defined, but here we show that the NiV and HeV glycoproteins are capable of highly efficient heterotypic functional activity with each other. However, no heterotypic activity was observed with envelope glycoproteins of the morbilliviruses Measles virus and Canine distemper virus.

Novel CD8+ T cell antagonists based on beta 2-microglobulin

The CD8 coreceptor of cytotoxic T lymphocytes binds to a conserved region of major histocompatibility complex class I molecules during recognition of peptide-major histocompatibility complex (MHC) class I antigens on the surface of target cells. This event is central to the activation of cytotoxic T lymphocyte (CTL) effector functions. The contribution of the MHC complex class I light chain, beta(2)-microglobulin, to CD8alphaalpha binding is relatively small and is mediated mainly through the lysine residue at position 58. Despite this, using molecular modeling, we predict that its mutation should have a dramatic effect on CD8alphaalpha binding. The predictions are confirmed using surface plasmon resonance binding studies and human CTL activation assays. Surprisingly, the charge-reversing mutation, Lys(58) --> Glu, enhances beta(2)m-MHC class I heavy chain interactions. This mutation also significantly reduces CD8alphaalpha binding and is a potent antagonist of CTL activation. These results suggest a novel approach to CTL-specific therapeutic immunosuppression.

Functional expression and membrane fusion tropism of the envelope glycoproteins of Hendra virus

Hendra virus (HeV) is an emerging paramyxovirus first isolated from cases of severe respiratory disease that fatally affected both horses and humans. Understanding the mechanisms of host cell infection and cross-species transmission is an important step in addressing the risk posed by such emerging pathogens. We have initiated studies to characterize the biological properties of the HeV envelope glycoproteins. Recombinant vaccinia viruses encoding the HeV F and G open reading frames were generated and glycoprotein expression was verified by metabolic labeling and detection using specific antisera. Glycoprotein function and cellular tropism were examined with a quantitative assay for HeV-mediated membrane fusion. Fusion specificity was verified through specific inhibition by anti-HeV antiserum and a peptide corresponding to one of the alpha-helical heptad repeats of F. HeV requires both F and G to mediate fusion. Permissive target cells have been identified, including cell lines derived from cat, bat, horse, human, monkey, mouse, and rabbit. Fusion negative cell types have also been identified. Protease treatments of the target cells abolished fusion activity, suggesting that the virus is employing a cell-surface protein as its receptor.

N-linked glycosylation of CXCR4 masks coreceptor function for CCR5-dependent human immunodeficiency virus type 1 isolates

The chemokine receptors CXCR4 and CCR5 are the principal coreceptors for infection of X4 and R5 human immunodeficiency virus type 1 (HIV-1) isolates, respectively. Here we report on the unexpected observation that the removal of the N-linked glycosylation sites in CXCR4 potentially allows the protein to serve as a universal coreceptor for both X4 and R5 laboratory-adapted and primary HIV-1 strains. We hypothesize that this alteration unmasks existing common extracellular structures reflecting a conserved three-dimensional similarity of important elements of CXCR4 and CCR5 that are involved in HIV envelope glycoprotein (Env) interaction. These results may have far-reaching implications for the differential recognition of cell type-dependent glycosylated CXCR4 by HIV-1 isolates and their evolution in vivo. They also suggest a possible explanation for the various observations of restricted virus entry in some cell types and further our understanding of the framework of elements that represent the Env-coreceptor contact sites.