Biochemical transformation of mouse cells by varicella-zoster virus

Oncolytic varicella-zoster virus engineered with ORF8 deletion and armed with drug-controllable interleukin-12

BACKGROUND

The varicella-zoster virus (VZV), belonging to the group of human α-herpesviruses, has yet to be developed as a platform for oncolytic virotherapy, despite indications from clinical case reports suggesting a potential association between VZV infection and cancer remission.

METHODS

Here, we constructed oncolytic VZV candidates based on the vaccine strain vOka and the laboratory strain Ellen. These newly engineered viruses were subsequently assessed for their oncolytic properties in the human MeWo melanoma xenograft model and the mouse B16-F10-nectin1 melanoma syngeneic model.

RESULTS

In the MeWo xenograft model, both vOka and Ellen exhibited potent antitumor efficacy. However, it was observed that introducing a hyperfusogenic mutation into glycoprotein B led to a reduction in VZV's effectiveness. Notably, the deletion of ORF8 (encodes viral deoxyuridine triphosphatase) attenuated the replication of VZV both in vitro and in vivo, but it did not compromise VZV's oncolytic potency. We further armed the VZV Ellen-ΔORF8 vector with a tet-off controlled mouse single-chain IL12 (scIL12) gene cassette. This augmented virus was validated for its oncolytic activity and triggered systemic antitumor immune responses in the immunocompetent B16-F10-nectin1 model.

CONCLUSIONS

These findings highlight the potential of using Ellen-ΔORF8-tet-off-scIL12 as a novel VZV-based oncolytic virotherapy.

Addition of exogenous protease facilitates reovirus infection in many restrictive cells

Virion uncoating is a critical step in the life cycle of mammalian orthoreoviruses. In cell culture, and probably in extraintestinal tissues in vivo, reovirus virions undergo partial proteolysis within endosomal or/or lysosomal compartments. This process converts the virion into a form referred to as an intermediate subvirion particle (ISVP). In natural enteric reovirus infections, proteolytic uncoating takes place extracellularly within the intestinal lumen. The resultant proteolyzed particles, unlike intact virions, have the capacity to penetrate cell membranes and thereby gain access to cytoplasmic components required for viral gene expression. We hypothesized that the capacity of reovirus outer capsid proteins to be proteolyzed is a determinant of cellular host range. To investigate this hypothesis, we asked if the addition of protease to cell culture medium would expand the range of cultured mammalian cell lines that can be productively infected by reoviruses. We identified many transformed and nontransformed cell lines, as well as primary cells, that restrict viral infection. In several of these restrictive cells, virion uncoating is inefficient or blocked. Addition of proteases to the cell culture medium generates ISVP-like particles and promotes viral growth in nearly all cell lines tested. Interestingly, we found that some cell lines that restrict reovirus uncoating still express mature cathepsin L, a lysosomal protease required for virion disassembly in murine L929 cells. This finding suggests that factors in addition to cathepsin L are required for efficient intracellular proteolysis of reovirus virions. Our results demonstrate that virion uncoating is a critical determinant of reovirus cellular host range and that many cells which otherwise support productive reovirus infection cannot efficiently mediate this essential early step in the virus life cycle.

Social epidemiology of chickenpox in two British national cohorts

STUDY OBJECTIVE

To provide a quantitative description of factors independently predictive of reported chickenpox infections in two national cohorts of British children.

DESIGN

Longitudinal cohort study design employing logistic regression analysis of data obtained in the 1970 British Births Survey (later to become the Child Health and Education Study, CHES), and the 1958 British Perinatal Mortality Survey (later to become the National Child Development Survey, NCDS).

SETTINGS

One-week birth cohorts covering the whole of the United Kingdom.

PARTICIPANTS

Data were obtained from questionnaires administered to the carers of 10,196 children born in the UK between 5 and 11 April 1970 (CHES) and 10,927 children born in the UK between 3 and 9 March 1958 (NCDS). These numbers consist of the whole of the surviving cohorts excluding those for whom data were incomplete.

MEASUREMENTS

Biological, social, and medical factors in the parents and children, as recorded by the child's principle carer or from clinical notes.

MAIN RESULTS

Chickenpox by the age of 10 years was reported to be more common in the children of advantaged families (higher social class, higher parental education levels), with a higher prevalence in those parts of the United Kingdom normally associated with affluence, such as the South East and South West of England, and lower rates in Wales and Scotland. Chickenpox by 10 years was also associated with more crowding in the home. A similar but less marked pattern occurred for chickenpox by the age of 11 years in the 1958 NCDS cohort. This social distribution apparently reflected overall rather than age-specific susceptibility.

CONCLUSIONS

The national and international pattern of chickenpox epidemiology indicate that both social and climatological factors may be important in defining groups at risk. Further research is indicated if a vaccination service is to be implemented in this country.

Regulation of thymidine kinase activity in mouse L cells biochemically transformed by varicella-zoster virus

Regulation of thymidine kinase (TK) activity was examined in L(O)c133 and L(H3) cells carrying varicella-zoster virus-TK gene. TK activity of L(O)c133 cells was similarly high in either medium but that of L(H3) cells was high in HAT medium and low in non-HAT medium. Cell growth was well correlated with TK activities of L(O)c133 and L(H3) cells in medium conditions. Regulation of the TK gene in L cells carrying the VZV-TK gene is discussed.

Mapping of the varicella zoster virus deoxypyrimidine kinase gene and preliminary identification of its transcript

The varicella-zoster virus (VZV) deoxypyrimidine kinase (dPK) gene was mapped by transfection of cloned viral DNA fragments into thymidine kinase-deficient mouse L (LTK-) cells and subsequent biochemical transformation of these cells to the LTK+ phenotype. Such transforming activity was limited to the BamHI-H and EcoRI-D fragments of the VZV genome, which overlap by 2.2 kb between map units 0.50 and 0.52. Biochemically transformed cells were shown to contain a high copy number of viral DNA sequences that had integrated into the cellular DNA. Extracts of these cells showed a higher level of dPK activity than did extracts of parental LTK- cells. With the use of Northern hybridization analysis of transformed and VZV-infected cell RNAs, it was possible to tentatively assign a 1.8-kb transcript to the VZV dPK.

Virus-related pathology: is the continued presence of the virus necessary?

This chapter examines the effect of viruses in inducing modifications in chromosomes, immune system interactions, and cell metabolism to support such a hypothesis that virus may no longer be present when the pathology appears. When vaccines were available to protect the population against the major epidemics, then chronic, recurrent, or persistent infections came into focus. Viruses are everywhere and all organisms are permanently exposed to them. The result of this contact depends on the particular moment a t which a given cell is exposed to the virus. Rubella, for example, provokes a very benign disease in adults, but can induce abnormalities in the differentiating fetus. Although interferon is active against virus aggression, excess interferon has a toxic effect and can block differentiation. The capacity of several viruses to act as cellular mutagens by modifying chromosomes is well established, whatever the molecular mechanism may be. Mutations at the cellular level were carefully analyzed for their tumorigenic potential.

Transcription mapping of the varicella-zoster virus genome

RNA was isolated from varicella-zoster virus-infected Flow 5000 cells (diploid fibroblasts) at late times after infection. With the use of overlapping DNA probes representing all regions of the varicella-zoster genome, an extensive Northern blot analysis of the RNA was carried out. The analysis revealed at least 58 discrete transcripts ranging in size from approximately 0.8 to 6.5 kilobases. RNAs were found to be homologous to all probes used except for those mapping at approximately map unit 0.3, where no RNA transcripts could be detected. Comparison of the sizes and locations of RNA transcripts mapping in the right-hand ends of the varicella-zoster virus and the herpes simplex virus DNAs shows a number of striking analogies, suggesting their similar genomic organization.

Varicella-zoster virus-induced transformation of mammalian cells in vitro

A mixture of varicella-zoster virus-infected human embryonic lung fibroblasts and hamster embryo cells produced foci of morphologically transformed cells after several weeks of incubation. These transformed cells exhibited virus-specific antigens by immunofluorescence and developed surface Fc receptors. They induced aggressive fibrosarcomas when injected back into inbred hamsters. Cells derived from hamster tumor tissue exhibited similar properties. The tumor-bearing hamsters develop antibodies specific for varicella-zoster virus (VZV) antigens. Cell lines derived from both the original transformants and explanted hamster tumor tissue have varying growth properties. All maintain indefinite growth. All eventually lose varicella-zoster virus-specific immunofluorescence. None retain VZV-specific DNA sequences as determined by dot blot and Southern blot hybridization using radiolabeled whole VZV DNA and cloned VZV DNA fragments as a probe. A few transformed and tumor cell lines frozen relatively soon after isolation and stored in liquid nitrogen were also thawed, replicated to mass culture, and analyzed for VZV-specific DNA sequences. Hybridization with radiolabeled whole VZV DNA initially suggested that some of these cell lines did contain virus-specific DNA sequences. However, hybridization with cloned VZV DNA fragments radiolabeled in vitro and representing greater than 95% of the virus genome was negative. Karyotyping of these "positive" transformed cells indicated that they are of human and not hamster origin. The positive hybridization with whole VZV DNA therefore most likely represented contamination of the probe by host DNA sequences. The cells that survived freezing then were predominantly transformants of human origin. Attempts to repeat the transformation of hamster embryo and baby hamster kidney cells with laboratory-passaged VZV strains have been unsuccessful. Similarly, we have been unable to transform cells with whole VZV DNA or cloned VZV DNA fragments, although whole VZV DNA is demonstrably infectious. Apparently, transformation of cells by the varicella-zoster virus is a very rare event and one that may require a recent clinical isolate. Fresh clinical isolates of varicella-zoster virus are seemingly able to transform mammalian cells in vitro. The transformed cells have malignant properties and are capable of indefinite growth. Although VZV gene function can be detected early after transformation, there is no evidence that a VZV-specific protein product is required. Transformation of mammalian cells by varicella-zoster virus apparently occurs through a "hit-and-run" mechanism.

Symposium on infectious complications of neoplastic disease (Part II). Immunoprophylaxis of varicella-zoster infections

Because it is possible to identify groups of persons with a high risk of varicella development and also because it is possible to anticipate when an attack may occur, immunoprophylaxis for varicella has met with great success. In contrast, the nature of zoster--its unpredictability and low attack rate--makes immunoprophylaxis much more difficult to implement. Varicella may be modified by administration of varicella-zoster immune globulin within three days of a known exposure to the virus. Although interferon has not yet been used in an attempt to prevent or modify varicella in humans, it has been used successfully to abort an outbreak of simian varicella in a monkey colony. Thus it might be clinically useful, particularly for those who cannot be given varicella-zoster immune globulin within three days of exposure. Transfer factor has also been shown to induce at least partial immunity to varicella in children with leukemia. The duration of this protection is unknown, and further study of the efficacy of transfer factor against both varicella and possibly even against zoster seems warranted. Live attenuated varicella vaccine, although still experimental, seems now to be the most practical way to prevent severe varicella in high-risk persons. The vaccine is safe and immunogenic, even in children with underlying leukemia who are still receiving chemotherapy. Studies in Japan, Europe, and the United States have shown that most vaccinated leukemic children who are exposed are protected against severe disease, although mild breakthrough cases have been reported. Varicella vaccine's potential to cause zoster remains under study.