Cytokine-armed vaccinia virus infects the mesothelioma tumor microenvironment to overcome immune tolerance and mediate tumor resolution

Our plain-English summary of Cytokine-armed vaccinia virus infects the mesothelioma tumor microenvironment to overcome immune tolerance and mediate tumor resolution, by C. Jackaman, D.J. Nelson (Cancer Gene Therapy, 2010).

The study

• Authors: C. Jackaman, D.J. Nelson
• Journal: Cancer Gene Therapy
• Published: 2010;17(6):429-40
• Cited by: 13 articles, as counted by NIH iCite
• Read it: PubMed · Publisher

Abstract

Intratumoral (i.t.) administration of cytokine genes expressed by viral vectors represents a rational approach that induces cytokine secretion at the site they are needed, and i.t. vaccinia virus (VV) has shown promise in mesothelioma patients. However, we and others have shown that the mesothelioma tumor microenvironment includes macrophages, dendritic cells (DCs), and T cells. Therefore, we investigated which of these cell types are infected after exposure to VV or Fowlpox virus (FPV)-cytokine gene constructs. In vitro studies showed that mesothelioma tumor cells were resistant to FPV infection yet highly permissive to infection by VV vectors resulting in significant cytokine production and impaired proliferation. Macrophages secreted low levels of cytokine suggestive of resistance to overt infection. DCs transiently secreted virally derived cytokines, but did not mature during VV infection. VV inhibition of T cell proliferation was rescued by the interleukin (IL)-2 and IL-12 VV constructs. In vivo studies of murine mesotheliomas showed that i.t. injection of the parent VV could not hinder tumor progression. In contrast, the VV-cytokine constructs induced profound tumor regression. These data suggest that i.t. VV-cytokine gene constructs retard tumor growth by infecting mesothelioma cells and targeting the immune system through tumor-infiltrating DC and T cells.

In plain English

This laboratory study compared Fowlpox virus (FPV) and vaccinia virus (VV) vectors carrying hemagglutinin (HA) alone or with interleukin (IL)-2 or IL-12 genes in murine AE17 mesothelioma cells, derived from crocidolite asbestos-injected mice. In vitro, FPV-cytokine constructs infected under 30 percent of AE17 cells at any time point, whereas all VV constructs infected more than 80 percent by 72 hours. VV cytokine constructs made AE17 cells secrete that cytokine (none after VV-HA) and blocked proliferation, which returned at lower viral doses. Macrophages and spleen cells secreted low cytokine levels; dendritic cells secreted cytokine but showed no MHC class II upregulation at 10 million plaque-forming units, with maturation partially improved at a tenfold lower load. ConA-stimulated splenic T cell proliferation was significantly inhibited at a high multiplicity of infection (10:1) of VV-HA, and this was ameliorated by the cytokine constructs. In mice given weekly intratumoral injections for three weeks, VV-HA gave no benefit, VV-IL-2 cured 20 percent and VV-IL-12 cured 80 percent of mice, five mice in each of those groups. The authors described these as proof-of-principle studies supporting VV vectors for cytokine delivery into the mesothelioma tumour site.

We wrote this plain-English summary from the full article with the help of AI, and a second AI model checked each sentence against the article. It is not the authors' wording; the abstract and the article are their own account.

What the study did and found

• Design: Laboratory study combining in vitro infection/cytokine/proliferation experiments with an in vivo mouse tumour experiment
• Who was studied: Murine AE17 mesothelioma cells (asbestos-induced, C57BL/6J origin), 143BTK human osteosarcoma cells, mouse peritoneal macrophages, bone marrow-derived dendritic cells and splenocytes; and female C57BL/6J mice aged 6-8 weeks bearing subcutaneous AE17 tumours (five mice per single-construct group, six in the combination group), Perth, Western Australia
• Exposure: Recombinant Fowlpox virus and vaccinia virus vectors expressing hemagglutinin alone or with IL-2 or IL-12 genes, given at varying plaque-forming unit doses in vitro and as weekly intratumoral injections for 3 weeks in vivo (not an asbestos exposure study)
• Main results:
  • AE17 mesothelioma cells were poorly infected by FPV-cytokine constructs: fewer than 30 percent of cells at any time point, with FPV-HA reaching at most 60 percent by 72 hours at a multiplicity of infection of 10:1
  • All VV constructs infected more than 80 percent of AE17 mesothelioma cells after 72 hours in culture
  • VV-infected AE17 and 143BTK cells secreted IL-2 or IL-12, but no cytokine was detected after infection with the VV-HA control vector
  • VV vectors reduced AE17 viability by about 20 percent
  • Each VV construct prevented AE17 proliferation in vitro, and the proliferative response was restored when the viral dose was reduced by a log fold
  • Macrophages infected with VV cytokine constructs secreted low cytokine levels (at 5 million pfus: IL-12 65.6±6.3 ng/ml for VV-HA-IL-12; IL-2 22.2±2.3 ng/ml for VV-HA-IL-2)
  • Dendritic cells exposed to the VV constructs secreted cytokine (at 10 million pfus, 24 h: 77.1±6.3 ng/ml IL-2; 267.7±38.0 ng/ml IL-12) but showed no upregulation of MHC class II at that dose at 24 or 48 hours
  • Reducing the viral load tenfold partially improved dendritic cell maturation
  • ConA-stimulated splenic T cell proliferation was significantly inhibited at high multiplicity of infection (10:1) by VV-HA, and this inhibition was ameliorated by the IL-2 or IL-12 constructs
  • Intratumoral VV-HA gave no benefit, with tumours continuing to grow at a similar or faster rate than the PBS controls
  • VV-IL-2 cured 20 percent of mice and VV-IL-12 cured 80 percent of mice (five mice in each of these groups)
  • The combination of both cytokine constructs appeared to slow tumour growth further, but not significantly compared with VV-IL-12 alone
• The authors' conclusion: The authors concluded that VV vectors infect mesothelioma tumour cells but also impair dendritic cell maturation and T cell proliferation, and that arming VV with IL-2 or IL-12 rescues these immune cells and restrains tumour growth, supporting the concept of VV vectors for cytokine delivery into the mesothelioma tumour site
• Limitations the authors state:
  • The authors used peritoneal macrophages as surrogates for tumour-infiltrating macrophages
  • Splenic cells were used only as an indicator of T cell responses, and the cytokine data could reflect other splenic components
  • Whether reduced tumour cell turnover leads to increased tumour antigen presentation and tumour-specific cytotoxic T cell induction was not determined and was left to future studies

Topics

The National Library of Medicine indexes this study under subjects our site covers: Lung cancer, Mesothelioma.

Medical terms in this study, explained in our Lexicon: Cytokine, Mesothelioma, Tumor Microenvironment, Macrophage.

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