Infection of cultured murine brain cells by Semliki Forest virus: effects of interferon-alpha beta on viral replication, viral antigen display, major histocompatibility complex antigen display and lysis by cytotoxic T lymphocytes

Oncolytic Semliki forest virus vector as a novel candidate against unresectable osteosarcoma

Oncolytic viruses are a promising tool for treatment of cancer. We studied an oncolytic Semliki Forest virus (SFV) vector, VA7, carrying the enhanced green fluorescent protein gene (EGFP), as a novel virotherapy candidate against unresectable osteosarcoma. The efficiency and characteristics of the VA7-EGFP treatment were compared with a widely studied oncolytic adenovirus, Ad5Delta24, both in vitro and in vivo. VA7-EGFP resulted in more rapid oncolysis and was more efficient at low multiplicities of infection (MOI) when compared with Ad5Delta24 in vitro. Yet, in MG-63 cells, a subpopulation resistant to the VA7-EGFP vector emerged. In subcutaneous human osteosarcoma xenografts in nude mice treatment with either vector reduced tumor size, whereas tumors in control mice expanded quickly. The VA7-EGFP-treated tumors were either completely abolished or regressed to pinpoint size. The efficacy of VA7-EGFP vector was studied also in an orthotopic osteosarcoma nude mouse model characterized by highly aggressive tumor growth. Treatment with oncolytic SFV extended survival of the animals significantly (P < 0.01), yet none of the animals were finally cured. Sera from SFV-treated mice contained neutralizing antibodies, and as nude mice are not able to establish IgG response, the result points out the role of IgM class antibodies in clearance of virus from peripheral tumors. Furthermore, biodistribution analysis at the survival end point verified the presence of virus in some of the brain samples, which is in line with previous studies demonstrating that IgG is required for clearance of SFV from central nervous system.

Evaluation of cancer virotherapy with attenuated replicative Semliki forest virus in different rodent tumor models

Semliki Forest virus (SFV) is one of the latest candidates for a virotherapeutic agent against cancer, and recent studies have demonstrated its efficacy in tumor models. In the present study, we examined the antitumor efficacy of an avirulent SFV strain A7(74) and its derivative, a replication-competent SFV vector VA7-EGFP, in a partially immunodeficient mouse tumor model (subcutaneous A549 human lung adenocarcinoma in NMRI nu/nu mouse) and in an immunocompetent rat tumor model (intracranial BT4C glioma in BDIX rat). When subcutaneous mouse tumors were injected 3 times with VA7-EGFP, intratumorally treated animals showed almost complete inhibition of tumor growth, while systemically treated mice displayed only delayed tumor growth (intravenous injection) or no response at all (intraperitoneal injection). This was at least partially due to a strong type I interferon (IFN) response in the tumors. The animals did not display any signs of abnormal behavior or encephalitis, even though SFV-positive foci were detected in the brain after the initial blood viremia. Intracranial rat tumors were injected directly with SFV A7(74) virus and monitored with magnetic resonance imaging. Tumor growth was significantly reduced (p < 0.05) with one virus injection, but the tumor size continued to increase after a lag period and none of the treated animals survived. Three virus injections or T-cell suppression with dexamethasone did not significantly improve treatment efficacy. It appeared that the local virotherapy induced extensive production of neutralizing anti-SFV antibodies that most likely contributed to the insufficient treatment efficacy. In conclusion, we show here that SFV A7(74) is a potential oncolytic agent for cancer virotherapy, but major immunological hurdles may need to be overcome before the virus can be clinically tested.

Oncolytic capacity of attenuated replicative semliki forest virus in human melanoma xenografts in severe combined immunodeficient mice

Oncolytic viruses have gained attention as a novel form of cancer treatment. Many viral vectors in use today have been rendered safe by deletion of genes encoding viral structural proteins, thus making them unable to spread beyond the first infected cells. Hence, such replication-deficient constructs may lack efficacy. Here, we analyzed the oncolytic potential of the replication-competent vector VA7-EGFP, based on the avirulent Semliki Forest virus (SFV) strain A7(74), to kill cancer cells in culture as well as to target s.c. human melanoma xenografts in severe combined immunodeficient (SCID) mice. VA7-EGFP was able to infect most cancer cell lines studied, leading to complete lysis of the cells within 72 hours after infection. In SCID mice grafted with A2058 human melanoma, marked regression of the xenografts was observed following a single injection of 10(6) plaque-forming units of virus given either i.p., i.v., or intratumorally. Histologic analysis revealed the presence of virus not only in all treated tumors but also in the brains of the treated mice, causing progressing neuropathology beginning at day 16 after infection. Following initial oncolysis, clusters of viable tumor cells were observed embedded in connective tissue, and at later stages, encapsulated tumor nodules had formed. Infection of melanoma cells from explant cultures of these nodules revealed that a portion of the cells were resistant to virus. To be eligible for use in virotherapy, the ability of avirulent SFV to spread within tumor tissue may have to be improved and the biological safety of the virus may have to be addressed thoroughly in higher animals.

Increase in gammadelta T cells in the blood of cattle persistently infected with bovine leukemia virus following administration of recombinant bovine IFN-gamma

To examine the effect of recombinant bovine interferon-gamma (rbIFN-gamma) on cattle persistently infected with bovine leukemia virus (BLV), BLV-infected cattle were inoculated intraperitoneally with IFN-gamma. All cattle were febrile after inoculation with IFN-gamma and then recovered within 48 h. Flow cytometric analysis showed that the numbers of CD4+ and CD8+ T cells were decreased for 2-3 days and then their numbers were recovered. The number of gammadelta T cells increased after the fever. In contrast, the number of IgM+ lymphocytes remained low for about 1 week. Moreover, the numbers of syncytia produced by peripheral blood lymphocytes decreased and remained low compared to that before IFN-gamma administration. These results suggest that IFN-gamma induces the up-regulation of gammadelta T cells, decreases the number of IgM+ lymphocytes and suppresses the growth of BLV in BLV-infected cattle in vivo.

Treatment of adult T-cell leukemia-lymphoma with a combination of interferon alfa and zidovudine

BACKGROUND

Infection with the human T-cell lymphotropic virus type I, a retrovirus, can cause a distinctive cancer, adult T-cell leukemia-lymphoma. The median survival of patients with the acute and lymphomatous forms of the disease is short, despite the use of cytotoxic chemotherapy.

METHODS

We treated 19 patients with acute or lymphomatous forms of adult T-cell leukemia-lymphoma with oral zidovudine (200 mg five times daily) and interferon alfa (Intron A, 5 to 10 million units subcutaneously each day). Seven of these patients had either relapsed after multiagent cytotoxic chemotherapy or failed to respond to that treatment.

RESULTS

Major responses were achieved in 58 percent of the patients (11 of 19), including complete remission in 26 percent (5 of 19). Four patients in whom prior cytotoxic therapy had failed had major responses, two of which were complete remissions. Six patients have survived for more than 12 months, with the longest remission since the discontinuation of treatment lasting more than 59 months.

CONCLUSIONS

The combination of zidovudine and interferon alfa has activity against adult T-cell leukemia-lymphoma, even in patients in whom prior cytotoxic therapy has failed. This regimen should be evaluated further for its role in the treatment of adult T-cell leukemia-lymphoma.

Pathogenesis of virus-induced demyelination

Demyelination is a component of several viral diseases of humans. The best known of these are subacute sclerosing panencephalitis (SSPE) and progressive multifocal leukoencephalopathy (PML). There are a number of naturally occurring virus infections of animals that involve demyelination and many of these serve as instructive models for human demyelinating diseases. In addition to the naturally occurring diseases, many viruses have been shown to be capable of producing demyelination in experimental situations. In discussing virus-associated demyelinating disease, the chapter reviews the architecture and functional organization of the CNS and considers what is known of the interaction of viruses with CNS cells. It also discusses the immunology of the CNS that differs in several important aspects from that of the rest of the body. Experimental models of viral-induced demyelination have also been considered. Viruses capable of producing demyelinating disease have no common taxonomic features; they include both DNA and RNA viruses, enveloped and nonenveloped viruses. The chapter attempts to summarize the important factors influencing viral demyelination, their common features, and possible mechanisms.

Paralysis of street rabies virus-infected mice is dependent on T lymphocytes

Street rabies virus (SRV)-infected T-lymphocyte-deficient (nude) mice, in contrast to euthymic mice, did not develop hindlimb paralysis prior to death. To document the role of T lymphocytes in rabies virus-associated paralysis, 10(8) spleen cells from normal immunocompetent euthymic mice were transferred to nude mice and the recipient mice were challenged with SRV. One hundred percent of the reconstituted mice developed paralysis and died. Depletion of T cells from the donor spleen suspension prior to transfer abrogated the development of paralysis but did not prevent the deaths of the recipient animals. Mice receiving 10(8) rabies virus-immune spleen cells did not become paralyzed and did not die. Nude mice inoculated with either rabies virus-immune or normal mouse serum prior to and following SRV inoculation did not develop paralysis. Immune serum protected the mice, whereas animals inoculated with normal serum died. Central nervous system inflammatory responses in nude mice immunologically reconstituted with normal spleen cells were characterized by diffuse cellular infiltrates in the parenchyma and extensive perivascular cuffing. Perivascular infiltrates included CD8+ and CD4+ T lymphocytes and Mac-1+ macrophage-microglial cells. Inflammatory cells in the parenchyma were limited to CD8+ lymphocytes and Mac-1+ cells. These observations indicate that paralysis of SRV-infected mice is dependent on T lymphocytes. Whether injury leading to paralysis is mediated by T lymphocytes or by an influence of T lymphocytes on macrophage-microglial cells or other cells remains to be determined.

Genomic structure of the human prototype strain H of hepatitis C virus: comparison with American and Japanese isolates

Genomic RNA from the human prototype strain H of the hepatitis C virus (HCV-H) has been molecularly cloned and sequenced. The HCV-H sequence reported consists of 9416 nucleotides including the 5' and 3' untranslated regions. HCV-H shows 96% amino acid identity with the American isolate HCV-1 but only 84.9% with the Japanese isolates HCV-J and HCV-BK. In addition to the hypervariable region (region V) previously identified in the putative E2 domain, three other variable domains were identified: region V1 (putative E1), region V2 (putative E2), and region V3 (putative NS5). These regions appear rather conserved (86-100%) among the American isolates (HCV-1 and HC-J1) or among various Japanese isolates (HCV-J, HCV-BK, HCV-JH, and HC-J4) but show striking heterogeneity when the two subgroups are compared (42-87.5% amino acid difference). A structural similarity between the 5'-terminal hairpin structure of HCV and of poliovirus was observed. This study further suggests the existence of at least two genomic subtypes of HCV and confirms a distant relationship between HCV and pestiviruses.

Suppressive effects of interferons on the production and release of human T-lymphotropic virus type-I (HTLV-I)

The effects of human alpha-, beta-, or gamma-interferon (IFN) on the replication and production of human T-lymphotrophic virus type-I (HTLV-I) were investigated in a human T-cell line, MT-2. Virus transmission and production estimated by syncytium formation and HTLV-I-associated reverse transcriptase (RT) activity were strongly suppressed in the presence of alpha- and beta-IFN, but not gamma-IFN. However, the expression of virus specific proteins gp46 but not p19, p24, p28, p36, and gp68 was affected with IFNs as revealed by Western blotting analysis. Electron microscopic observations showed that some of the HTLV-I particles were trapped in the intracellular vacuoles in the presence of high doses of alpha- or beta-IFN. Continuous supply of IFNs appeared to be essential for the constant suppression of RT activity. These results suggest that alpha- and beta-IFN do not inhibit HTLV-I gene expression strikingly but suppress processing or assembly of virus proteins and/or releasing of virions in the late phase of maturation.

Interaction of v-Ki-ras oncogene and interferon-gamma in the control of histocompatibility antigen expression in mouse fibroblasts

C3H10T1/2 fibroblasts when transformed with Kirsten murine sarcoma virus lose the ability to be induced to express class II major histocompatibility complex antigens when induced with interferon-gamma (IFN-gamma). Sublines were derived from transformed lines by cell sorting after treatment with IFN-gamma, sorting for low or high expression of H-2Ak. These sublines remained stably noninducible or inducible for class II antigen for several passages after sorting. In all other respects tested, viz, sensitivity to IFN-gamma for the generation of an antiviral state or the induction of class I antigen, content of ras gene products, the sorted sublines were very similar. We conclude that ras oncogene expression in these cells can influence the induction of class II antigen but that because ras expression in the sorted lines is similar the effect of ras expression is indirect and presumably involves interaction with other cellular factors.

Flavivirus infection up-regulates the expression of class I and class II major histocompatibility antigens on and enhances T cell recognition of astrocytes in vitro

West Nile virus (WNV) infection of astrocytes can up-regulate their expression of both class I and class II major histocompatibility complex (MHC) antigens as determined by flow cytometry with monoclonal antibodies specific for class I and class II MHC antigens. The up-regulation of class I MHC antigen expression could be partly caused by interferon secreted after WNV infection because the synthetic interferon inducer polyinosinic-polycytidylic acid (poly I:C) has similar effects. In contrast the up-regulation of class II MHC antigen expression was not induced by poly I:C. The increased MHC antigen expression by WNV infection had significant effects on T cell recognition. Thus, WNV and influenza virus A/WSN double-infected astrocytes but not astrocytes infected by A/WSN alone were lysed by influenza virus-immune cytotoxic T cells. Similarly, WNV-infected astrocytes were better stimulators than normal astrocytes for a class II MHC-reactive T cell line, both in terms of T cell proliferation and interleukin release.

Kirsten murine sarcoma virus abolishes interferon gamma-induced class II but not class I major histocompatibility antigen expression in a murine fibroblast line

The effect of infecting fibroblasts with Kirsten murine sarcoma virus/murine leukemia virus (Ki-MSV/MLV) on constitutive and IFN-gamma-induced H-2 antigen expression was investigated. The fibroblasts used were two established cell lines (C3H10T1/2 and BALB/c3T3) and fresh embryo fibroblasts from C3H mice. Class I antigens were expressed constitutively by BALB/c3T3; infection with MLV, MSV or the two together had little effect on this constitutive expression. Class I antigens (H-2K, H-2D) were strongly induced on all three types of fibroblast by rIFN-gamma, and infection had little effect on this. None of the fibroblasts expressed constitutively detectable levels of class II antigen; however, C3H10T1/2 fibroblasts could be induced for both H-2A and H-2E by IFN-gamma. Infection of C3H10T1/2 with helper-free Ki-MSV, or MSV together with MLV, completely abolished this induction of class II antigens, while infection with MLV alone had little effect, implying that the abolition of class II induction was due to genomic regions of Ki-MSV not shared with Ki-MLV, probably the v-Ki-ras gene.