Replication of poliovirus and measles virus in cultures of human lymphoblastoid and of Burkitt lymphoma cell lines

Measles virus in cancer therapy

Over the last years, the development of viruses to treat cancer patients has re-gained considerable attention. A genetically modified herpesvirus, Talimogene laherparepvec, has already been authorized for the treatment of melanoma patients. Also recombinant measles virus (MeV) is developed as an oncolytic virus. Because of its high genetic flexibility, a number of different MeV strains have been the basis for the generation of targeted, armed, or shielded viruses that are highly specific for a given tumor target, more effective, or protected against serum neutralization. Such MeV have been extensively tested in vitro and in vivo, whereby remarkable oncolytic potency is accompanied by safety also in non-human primates. Therefore, MeV has been introduced into 19 different clinical trials and has reached phase II against two different tumor entities, multiple myeloma and ovarian carcinoma. Remarkably, one patient with advanced stage myeloma experienced long-term remission after treatment, visualizing the potency of this approach.

Cellular tropism of human enterovirus D species serotypes EV-94, EV-70, and EV-68 in vitro: implications for pathogenesis

Enterovirus 94 (EV-94) is an enterovirus serotype described recently which, together with EV-68 and EV-70, forms human enterovirus D species. This study investigates the seroprevalences of these three serotypes and their abilities to infect, replicate, and damage cell types considered to be essential for enterovirus-induced diseases. The cell types studied included human leukocyte cell lines, primary endothelial cells, and pancreatic islets. High prevalence of neutralizing antibodies against EV-68 and EV-94 was found in the Finnish population. The virus strains studied had wide leukocyte tropism. EV-94 and EV-68 were able to produce infectious progeny in leukocyte cell lines with monocytic, granulocytic, T-cell, or B-cell characteristics. EV-94 and EV-70 were capable of infecting primary human umbilical vein endothelial cells, whereas EV-68 had only marginal progeny production and did not induce cytopathic effects in these cells. Intriguingly, EV-94 was able to damage pancreatic islet β-cells, to infect, replicate, and cause necrosis in human pancreatic islets, and to induce proinflammatory and chemoattractive cytokine expression in endothelial cells. These results suggest that HEV-D viruses may be more prevalent than has been thought previously, and they provide in vitro evidence that EV-94 may be a potent pathogen and should be considered a potentially diabetogenic enterovirus type.

Measles virus-induced disruption of the glial-fibrillary-acidic protein cytoskeleton in an astrocytoma cell line (U-251)

A recombinant measles virus which expresses enhanced green fluorescent protein (MVeGFP) has been used to infect two astrocytoma cell lines (GCCM and U-251) to study the effect of virus infection on the cytoskeleton. Indirect immunocytochemistry was used to demonstrate the cellular localization of the cytoskeletal components. Enhanced green fluorescent protein autofluorescence was used to identify measles virus-infected cells. No alteration of the actin, tubulin, or vimentin components of the cytoskeleton was observed in either cell type, whereas a disruption of the glial-fibrillary-acidic protein filament (GFAP) network was noted in MVeGFP-infected U-251 cells. The relative amounts of GFAP present in infected and uninfected U-251 cells were quantified by image analysis of data sets obtained by confocal microscopy by using vimentin, another intermediate filament on which MVeGFP has no effect, as a control.

Regulation of apoptosis resistance and ontogeny of age-dependent diseases

Diseases of the elderly, including neurodegenerative and cardiovascular disorders and cancer, may develop through the accumulation of "hits" composed of genetic and epigenetic risk factors. The "iceberg" buildup of these hits over time may exceed the tolerance threshold of a particular tissue, thus precipitating disease. Resistance to apoptosis, a self-eliminating cellular program, is one risk factor; it is attributed to persistent survival factors, or the absence of killer factors, which form a "Yin-Yang" mechanism directing cells to either live or die. Most apoptosis-associated genes can be categorized into four groups, providing signals, signal processors, activators, or substrates for the apoptotic pathway. Senescent human fibroblasts resist apoptosis, perhaps through the lack of key G1-phase gene expressions, also necessary for apoptosis initiation; they also lack key proteolytic activity, and maintain high levels of survival factor bcl2, reflecting a triple blockage to apoptosis. Accumulations of these apoptosis-resistant fibroblasts in aging individuals may impair proper tissue function, not only as noncontributing members, but also as the seed for the buildup of further hits. With time, these cells with multiple hits and apoptosis resistance may induce susceptibility to developing age-dependent diseases.

The promoters for human and monkey poliovirus receptors. Requirements for basic and cell type-specific activity

The cellular receptors for poliovirus (PVR) are glycoproteins belonging to the immunoglobulin superfamily. Functional receptors for poliovirus are only expressed by primates; known rodent homologues lack the ability to bind virus due to amino acid differences. Human poliovirus infections are targeted to the gastrointestinal tract and, rarely, to motor neurons in the central nervous system. Available evidence suggests that poliovirus uses only one cellular receptor, implying that the tissue tropism of poliovirus is likely to be related to the expression of the human PVR (hPVR). However, low levels of expression of hPVR-specific mRNAs can be detected in many human tissues other than the apparent target cells. The nonpathogenic function of hPVR is unknown. For a study of the transcriptional control of hPVR expression, we have isolated and characterized the promoter of the hPVR gene. Deletion analysis defined an approximately 280 base pair minimal promoter fragment that: 1) lacks TATA- and CAAT-like elements, 2) is distinguished by a high GC content, and 3) promotes transcription at multiple start sites. The pattern of activity caused by transfection of serial 5'- and 3'-promoter deletions is almost identical in HEp2, HeLa, COS-1, and mouse L929 cells, indicating a similar transcriptional regulation of the hPVR promoter in these cell lines. However, on transfection of Raji cells, a Burkitt's lymphoma cell line harboring a transcriptionally inactive hPVR gene, all promoter reporter constructs tested exerted only residual activity. These results suggest that the cis-element(s) governing cell type-specific hPVR expression resides in the minimal promoter region. We also report the sequences of the promoters of two monkey homologues to hPVR (AGMalpha1 and AGMalpha2). Transcripts encoding the monkey poliovirus receptors originate from a region analogous to that identified for hPVR transcripts.

Susceptibility of human bone marrow cells and hematopoietic cell lines to coxsackievirus B3 infection

Viremia is commonly observed in association with enterovirus infections, and during this phase viruses can be transmitted to secondary target organs in the body. It is not known, however, whether blood cells play a role in the pathogenesis of enterovirus infection supporting virus replication. Our earlier work (T. Vuorinen, R. Vainionpää, H. Kettinen, and T. Hyypiä, Blood 84:823-829, 1994) demonstrated that coxsackievirus B3 is able to replicate in representatives of B- and T-cell lines but not in a monocytic cell line or peripheral blood mononuclear cells, indicating that virus replication may depend on the differentiation and maturation stages of the cells. Therefore, we have broaden our studies and analyzed the susceptibility of granulocyte-macrophage CFU and hematopoietic cell lines with various differentiation and maturation stages to coxsackievirus B3 infection. Virus replication was detected in B- and T-cell lines with no direct correlation to the maturation stage. Granulocyte-macrophage CFU were also able to support virus multiplication.

Characterization of persistent poliovirus mutants selected in human neuroblastoma cells

Six Sabin-derived persistent poliovirus mutants were selected in human neuroblastoma IMR-32 cells. The mutants had a titer 30 to 10(5) times lower in nonneural HEp-2c cells than in IMR-32 cells. When the growth cycles of persistent viruses in the two cell lines were compared, the most striking feature was a delay of 2 to 4 hr in virus release from HEp-2c cells. In Hep-2c cells, type 1 mutants could spontaneously establish a persistent infection in the absence of any exogenous viral inhibitor. Mutations at a rate of 1 every 210 nucleotides had accumulated in the genome of the type 1 mutants selected in neuroblastoma cells, modifying cell specificity and conferring the ability to persist in some nonneural cells. These results indicate that mutants of poliovirus with highly modified biological properties can be selected in vitro in cells of neural origin.

Restriction of poliovirus RNA translation in a human monocytic cell line

The infection of the human monocytic cell line U-937 by poliovirus was characterized by a low level of virus production and a slow progression of the cytopathic effect. Infection took place in greater than 99% of the cells as revealed by a limiting dilution assay. No viral protein synthesis was evident in the infected U-937 cells when analyzed by polyacrylamide gel electrophoresis. However, a low level of poliovirus RNA translation was detected by immunofluorescence analysis using a mixture of polyclonal antisera against non-structural proteins. Although there was only a low level of viral protein synthesis, a gradual accumulation of viral mRNA took place in U-937 cells as revealed by RNA blot analysis. Similar results were obtained when the erythroleukemic cell line K-562 was used as a host cell for poliovirus. RNA extracted from infected U-937 cells was efficiently translated in rabbit reticulocyte extracts giving rise to a pattern of viral polypeptides similar to that detected when virion-purified RNA was the template used for the in vitro translation assay, suggesting that the poliovirus RNA present in infected U-937 cells is functional. The existence in U-937 cells of a discriminatory mechanism which differentially interferes with poliovirus RNA translation is discussed.

Isolation and characterization of HeLa cell lines blocked at different steps in the poliovirus life cycle

Cotransfection of poliovirus RNA and R1, a poliovirus subgenomic RNA containing a deletion of nearly all of the capsid region, resulted in surviving cells, in contrast to the complete cell death observed after transfection with viral RNA. Cells that survived the cotransfection grew into colonies, produced infectious poliovirus, and underwent cycles of cell lysis (crisis periods) where less than 1% of the cells survived, followed by periods of growth. Poliovirus evolved during the persistent infection as judged by changes in plaque size. After passage for 6 months, a stable line called SOFIA emerged that no longer produced infectious virus and did not contain viral proteins or viral RNA. Cells frozen in liquid N2 while still in crisis and recultured 4 months later (named SOFIA N2) were also stabilized. After infection with poliovirus, SOFIA N2 cells showed a delay in the development of cytopathic effect, viral production, and cellular death when compared with HeLa cells. In contrast, SOFIA cells did not develop cytopathic effect and produced 10,000 times less virus than SOFIA N2 or HeLa cells. Viral production was delayed in SOFIA and SOFIA N2 cells transfected with poliovirus RNA when compared with HeLa cells, suggesting the presence of an intracellular block to poliovirus replication. Analysis of the cellular receptor for poliovirus by virus binding, an enzyme-linked immunosorbent assay, and in situ rosette assays with an antireceptor monoclonal antibody showed that receptors were expressed in SOFIA N2 cells but not in SOFIA cells. Echovirus 6, an enterovirus which uses a different cellular receptor, formed small plaques on SOFIA cells. Vesicular stomatitis virus formed plaques of similar size on SOFIA and HeLa cells, suggesting that the intracellular block was specific for enteroviruses. Cotransfection of the subgenomic replicon R1 with poliovirion RNA therefore resulted in the selection of HeLa cell variants containing blocks to poliovirus replication at the level of receptor and within the cell.

Poliovirus infection of established human blood cell lines: relationship between the differentiation stage and susceptibility of cell killing

The replication of type 1 poliovirus in 13 established human blood cell lines differing in the differentiation stage and cell lineage was investigated. Three T (CCRF-CEM, CCRF-HSB-2, and Molt-3) and three B (Raji, CCRF-SB, and RPMI 8226) cell lines showed no cytopathic effects (CPE) or virus production. CPE associated with virus production were detected in the other seven cell lines: HL-60, ML-1, and KG-1 (granulocytic lineage), U-937 and THP-1 (monocytic lineage), K-562 (erythroid lineage), and Molt-4 (T cell lineage). These susceptible cell lines greatly differed in the speed at which the CPE progressed. The progression of CPE was faster in relatively well-differentiated cell lines such as HL-60 and U-937, independently of the multiplicity of infection, than in less differentiated cell lines such as K-562, KG-1, and THP-1. Thus, for the same lineage, the speed at which CPE progressed became proportionally higher with subsequent differentiation stages. In the K-562 cell culture, CPE were not observed until at least 5 days postinfection (p.i.), while more than 80% of HL-60 cells were killed within 3 days p.i. There were no significant differences between infected HL-60 and K-562 cells in the efficiency of infection determined at 8 hr p.i. by the indirect immunofluorescent technique, the rate of virus growth, or the amount of viral capsid protein synthesized. This indicated that there were similar viral replication cycles in the two cell lines. These observations suggest that the killing function of the virus is expressed more slowly in K-562 cells than in HL-60 cells.

Propagation of large quantities of poliovirus in human lymphoblastoid cells grown in a serum-free medium

All three types of poliovirus replicated to good titers in Epstein-Barr virus-transformed human lymphoblastoid cells isolated from patients with infectious mononucleosis. Cells were grown in a serum-free medium, which consisted of enriched Eagle's medium with addition of 0.1% albumin, 0.1% Intralipid and 1 mg/l of transferrin. Large quantities of virus could be produced in 2- to 20-l roller flasks or in spinner flasks. The propagated poliovirus gave an antibody response that complies with requirements for vaccine production.