Characterization of secreted and intracellular forms of a truncated hepatitis C virus E2 protein expressed by a recombinant herpes simplex virus.

A replication-defective herpes simplex virus type 1 (HSV-1) recombinant lacking the glycoprotein H (gH)-encoding gene and expressing a truncated form of the hepatitis C (HCV) E2 glycoprotein (E2-661) was constructed and characterized. We show here that cells infected with the HSV/HCV recombinant virus efficiently express the HCV E2-661 protein. Most importantly, cellular and secreted E2-661 protein were both readily detected by the E2-conformational mAb H53 and despite the high expression levels, only limited amounts of misfolded aggregates were detected in either the cellular or secreted fractions. Furthermore, cell-associated and secreted E2-661 protein bound to the major extracellular loop (MEL) of CD81 in a concentration-dependent manner and both were highly reactive with sera from HCV-infected patients. Finally, BALB/c mice immunized intraperitoneally with the recombinant HSV/HCV virus induced high levels of anti-E2 antibodies. Analysis of the induced immunoglobulin G (IgG) isotypes showed high levels of IgG2a while the levels of the IgG1 isotype were significantly lower, suggesting a Th1-type of response. We conclude that the HSV-1 recombinant virus represents a promising tool for production of non-aggregated, immunologically active forms of the E2-661 protein and might have potential applications in vaccine development.

Induction of anti-mammary cancer immunity by engaging the OX-40 receptor in vivo.

The OX-40 receptor (OX-40R) is a member of the tumor necrosis factor receptor (TNF-R) superfamily that is expressed on activated CD4+ T cells. The OX-40R is a costimulatory molecule that induces CD4+ T cell activation when engaged by its ligand (OX-40 L; found on antigen presenting cells). In human and murine tumors, we have shown upregulation of the OX-40R on CD4+ T cells from tumor-infiltrating lymphocytes (TIL) and tumor-draining lymph node cells (TDLNC) but not on systemic CD4+ T cells, such as peripheral blood lymphocytes (PBL) or splenocytes. In order to examine potentially heightened anti-tumor immunity through enhanced costimulation when engaging OX-40R in vivo, we inoculated mice with a murine mammary cancer cell line (SM1) and then treated with a soluble form of the OX-40 L. Mice injected with a lethal inoculum of SM1 cells were given two intraperitoneal injections (days 3 and 7 post-inoculation) of 100 microg soluble OX-40 L. Seven of 28 treated mice survived the lethal tumor inoculum, as compared to one of 28 control mice, demonstrating a significant survival benefit with treatment (p = 0.0136, log rank analysis). Mice that did not develop tumor by day 90 were rechallenged; all remained tumor-free. Mice were also injected with a second mammary tumor line (4T1) and treated with OX-40L:Ig with similar therapeutic results. Activation of OX-40R+ CD4+ T cells during mammary cancer priming stimulated an antitumor immune response resulting in enhanced survival and protective anti-tumor immunity. These results should have practical applications for treatment modalities for patients with breast cancer.

Combination gene therapy using multiple immunomodulatory genes transferred by a defective infectious single-cycle herpes virus in squamous cell cancer.

Herpes simplex type 2-defective infectious single-cycle (DISC) viruses are attenuated viruses that were originally produced as viral vaccines; however, these viruses are also efficient gene transfer vehicles. The main goals of this study were to examine determinants of the gene transfer by using DISC virus for squamous cancer and to evaluate the antitumoral efficacy of vaccination with tumor cells modified by DISC viruses carrying a combination of immunomodulatory genes (interleukin-2 (IL-2), granulocyte-macrophage colony-stimulating factor (GM-CSF), B7-1) in a model of squamous cell cancer (SCCVII) in C3H/HeJ mice. SCCVII cells transduced by DISC viruses (multiplicity of infection of 10) carrying the IL-2 or GM-CSF gene produced nanogram quantities of IL-2 or GM-CSF per 10(6) cells. Irradiated (5,000 cGy, 10,000 cGy) cells secreted levels of GM-CSF or IL-2 that were comparable with nonirradiated cells. In vivo vaccination using tumor cells transduced ex vivo with DISC-IL2 or DISC-GMCSF resulted in protection against subsequent tumor challenge (P < .01), with DISC-GMCSF-transduced, irradiated tumor cells showing the greatest effects (P < .001). Marked growth arrest also was noted in established tumors after direct injection of DISC-GMCSF (P < .001). These data demonstrate that (a) DISC virus is capable of efficient gene transfer, (b) GM-CSF-secreting genetically modified tumor vaccine protects against tumor cell challenge and suppresses tumor growth, and (c) intratumoral injection of DISC-GMCSF significantly suppresses the growth of established tumors. These results not only confirm clinically relevant gene transfer but also demonstrate that the gene transfer is an effective anti-cancer therapy.

Preclinical evaluation of "whole" cell vaccines for prophylaxis and therapy using a disabled infectious single cycle-herpes simplex virus vector to transduce cytokine genes.

The development of genetically modified "whole" tumor cell vaccines for cancer therapy relies on the efficient transduction and expression of genes by vectors. In the present study, we have used a disabled infectious single cycle-herpes simplex virus 2 (DISC-HSV-2) vector constructed to express cytokine or marker genes upon infection. DISC-HSV-2 is able to infect a wide range of tumor cells and efficiently express the beta-galactosidase reporter gene, granulocyte-macrophage colony-stimulating factor (GM-CSF), or IL-2 genes. Gene expression occurred rapidly after infection of tumor cells, and the level of production of the gene product (beta-galactosidase, GM-CSF, or IL-2) was shown to be both time-and dose-dependent. Vaccination with irradiated DISC-mGM-CSF or DISC-hIL-2-infected murine tumor cells resulted in greatly enhanced immunity to tumor challenge with live parental tumor cells compared with control vaccines. When used therapeutically to treat existing tumors, vaccination with irradiated DISC-mGM-CSF-infected tumor cells significantly reduced the incidence and growth rates of tumors when administered locally adjacent to the tumor site, providing up to 90% protection. The prophylactic and therapeutic efficacy of DISC-mGM-CSF-infected cells was shown initially using a murine renal cell carcinoma model (RENCA), and the results were confirmed in two additional murine tumor models: the M3 melanoma and 302R sarcoma. Therapy with DISC-infected RENCA "whole" cell vaccines failed to reduce the incidence or growth of tumor in congenitally T-cell deficient (Nu+/Nu+) mice or mice depleted of CD4+ and/or CD8+ T-lymphocytes, confirming that both T-helper and T-cytotoxic effector arms of the immune response are required to promote tumor rejection. These preclinical results suggest that this "novel" DISC-HSV vector may prove to be efficacious in developing genetically modified whole-cell vaccines for clinical use.

An efficient selection system for packaging herpes simplex virus amplicons.

Due to their simplicity and flexibility of genomic construction, herpes simplex virus (HSV) amplicon-based vectors are attractive vehicles for gene delivery. However, a significant problem faced in the generation of amplicon stocks is the low amplicon to helper virus (A/H) ratio. In order to improve the proportion of amplicons generated, a selection system for amplicon production was developed in which the HSV thymidine kinase (TK) gene is inserted into an amplicon plasmid and an HSV mutant with both TK and glycoprotein H (gH) genes deleted is used as a helper virus. Using a protocol in which amplicon stocks are passaged 2-3 times in BHK cells of TK- and gH+ genotype in the presence of selection medium containing methotrexate, stock preparations with high A/H ratio (up to 5:1) and high amplicon titre (>1 x 10(9) infectious units/ml) were generated. In vitro characterization demonstrated that a high level of biologically functional products can be efficiently produced from these amplicon constructs.

Construction and Use of Cell Lines Expressing HSV Genes.

Complementary cell lines have become an accepted tool for the functional analysis of viral genes (1,2) and proteins, as well as an essential component in strategies for the construction of mutant viruses. More recent applications include the propagation of replication-defective virus products with potential as viral vaccines (3,4) or as vehicles for gene therapy (5,6). The perceived requirements for such systems are low recombination frequencies between complementing cell and recombinant virus, stable expression of the complementing protein within the cell, and efficient complementation. The standard techniques of eukaryotic cell transfection and clonal selection are routinely employed in the generation of complementary cell lines, and are described briefly in this chapter. Perhaps a more novel introduction to this field is the possibility of using transgenic technology. Transgenic animals have the potential to provide both an in vivo model of complementation (7) and a comprehensive library of novel complementing cell types, particularly cell types resistant to traditional transfection protocols.

A genetically inactivated herpes simplex virus type 2 (HSV-2) vaccine provides effective protection against primary and recurrent HSV-2 disease.

A glycoprotein H (gH)-deleted herpes simplex virus type 2 (HSV-2) was evaluated as a vaccine for the prevention of HSV-induced disease. This virus, which we term a DISC (disabled infectious single cycle) virus, can only complete one replication cycle in normal cells and should thus be safe yet still able to stimulate broad humoral and cell-mediated antiviral immune responses. A gH-deleted HSV-2 virus that has been tested as a vaccine in the guinea pig model of recurrent HSV-2 infection was constructed. Animals vaccinated with DISC HSV-2 showed complete protection against primary HSV-2-induced disease, even when challenged 6 months after vaccination. In addition, the animals were almost completely protected against recurrent disease. Even at low vaccination doses, there was a high degree of protection against primary disease. A reduction in recurrent disease symptoms was also observed following therapeutic vaccination of animals already infected with wild type HSV-2.

A recombinant, chimeric enzyme with a novel mechanism of action leading to greater potency and selectivity than tissue-type plasminogen activator.

BACKGROUND: Early intervention with thrombolytic agents has been shown unequivocally to reduce mortality after acute myocardial infarction. Presently used agents have disadvantages such as short half-life, immunogenicity, hypotension, and bleeding complications. Therefore, there is a need to develop improved thrombolytic drugs with novel mechanisms of action leading to improved properties. METHODS AND RESULTS: Hybrid plasminogen/tissue-type plasminogen activator (t-PA) complementary DNA was constructed and expressed in Chinese hamster ovary cells. The chimeric protein, comprising the fibrin-binding domains of plasminogen covalently linked to the catalytic domain of t-PA, was purified and evaluated in vitro and in vivo. The hybrid was inhibited rapidly in human and animal plasmas. The mediator of this rapid inhibition was shown to be alpha 2-antiplasmin. The active center of the hybrid could be protected by reversible active center acylation with a novel inverse acylating agent, 4'-amidinophenyl-4-chloroanthranilic acid (AP-CLAN). An acylated (CLAN-) hybrid was cleared from the bloodstream of guinea pigs at 0.35 +/- 0.02 ml/min.kg-1 compared with a clearance rate of 36 +/- 4 ml/min.kg-1 for t-PA. The CLAN-plasminogen/t-PA hybrid was evaluated in a quantitative, "humanized" guinea pig pulmonary embolism model and shown to be approximately threefold more potent when given by bolus than an infusion of t-PA. Furthermore, the acylated hybrid was more fibrin selective than t-PA as determined by the relation between clot lysis and fibrinogen degradation. CONCLUSIONS: An acylated, recombinant plasminogen/t-PA hybrid has sufficiently slow clearance to be administered by bolus and is more potent and fibrin selective than t-PA in vivo.

A tissue-type plasminogen activator mutant with prolonged clearance in vivo. Effect of removal of the growth factor domain.

The complete cDNA for human tissue-type plasminogen activator (t-PA) was cloned and sequenced. A mutant was constructed by using in vitro site-specific mutagenesis to delete the region encoding the growth factor domain (amino acids 51-87 inclusive). Normal and mutant t-PA species were produced using two mammalian expression systems (in human HeLa cells and mouse C127 cells). The clearance of mutant and normal t-PA from plasma was examined in vivo using a guinea pig model. Mutant t-PA derived from HeLa or C127 cells was cleared much more slowly than the cognate normal t-PA. The potential role of the growth factor domain in the recognition of t-PA by the hepatic clearance mechanism is discussed.