Oncolytic virotherapy in glioblastoma patients induces a tumor macrophage phenotypic shift leading to an altered glioblastoma microenvironment

Abstract

Background

Immunosuppressive pro-tumorous M2 macrophages are important in pathogenesis, progression and therapy resistance in glioblastoma (GBM) and provide a target for therapy. Recently oncolytic virotherapy in murine models was shown to change these M2 macrophages towards the pro-inflammatory and anti-tumorous M1 phenotype. Here we study the effects of the oncolytic virotherapy Delta24-RGD in humans using both in vitro models and patient material.

Methods

Human monocyte-derived macrophages were co-cultured with Delta24-RGD-infected primary glioma stem cells (GSCs) and were analyzed for their immunophenotype, cytokine expression and secretion profiles. Cerebrospinal fluid (CSF) from 18 Delta24-RGD-treated patients was analyzed for inflammatory cytokine levels and the effects of these CSF samples on macrophage phenotype in vitro were determined. In addition, tumor macrophages in resected material from a Delta-24-RGD-treated GBM patient were compared to 5 control GBM patient samples by flow cytometry.

Results

Human monocyte-derived M2 macrophages co-cultured with Delta24-RGD-infected GSCs shifted towards an M1-immunophenotype, coinciding with pro-inflammatory gene expression and cytokine production. This phenotypic switch was induced by the concerted effects of a change in tumor-produced soluble factors and the presence of viral particles. CSF samples from Delta24-RGD-treated GBM patients revealed cytokine levels indicative of a pro-inflammatory microenvironment. Furthermore, tumoral macrophages in a Delta24-RGD-treated patient showed significantly greater M1 characteristics then in control GBM tissue.

Conclusion

Together these in vitro and patient studies demonstrate that local Delta24-RGD therapy may provide a therapeutic tool to promote a prolonged shift in the pro-tumoral M2 macrophages towards M1 in human GBM, inducing a pro-inflammatory and potentially tumor-detrimental microenvironment.