Enriched Environment Cues Suggest a New Strategy to Counteract Glioma: Engineered rAAV2-IL-15 Microglia Modulate the Tumor Microenvironment

Abstract

Several types of cancer grow differently depending on the environmental stimuli they receive. In glioma, exposure to an enriched environment (EE) increases the overall survival rate of tumor-bearing mice, acting on the cells that participate to define the tumor microenvironment. In particular, environmental cues increase the microglial production of interleukin (IL)-15 which promotes a pro-inflammatory (antitumor) phenotype of microglia and the cytotoxic activity of natural killer (NK) cells, counteracting glioma growth, thus representing a virtuous mechanism of interaction between NK cells and microglia. To mimic the effect of EE on glioma, we investigated the potential of creating engineered microglia as the source of IL-15 in glioma. We demonstrated that microglia modified with recombinant adeno-associated virus serotype 2 (rAAV2) carrying IL-15 (rAAV2-IL-15), to force the production of IL-15, are able to increase the NK cells viability in coculture. Furthermore, the intranasal delivery of rAAV2-IL-15 microglia triggered the interplay with NK cells in vivo, enhancing NK cell recruitment and pro-inflammatory microglial phenotype in tumor mass of glioma-bearing mice, and ultimately counteracted tumor growth. This approach has a high potential for clinical translatability, highlighting the therapeutic efficacy of forced IL-15 production in microglia: the delivery of engineered rAAV2-IL-15 microglia to boost the immune response paves the way to design a new perspective therapy for glioma patients.

Dialogue among Lymphocytes and Microglia in Glioblastoma Microenvironment

“…Consistently, AAVs are considered safe for human gene therapy and have been successfully used to target several cell types within the central (CNS) and peripheral (PNS) nervous systems, including neurons, oligodendrocytes, astrocytes, Müller glia, and Schwann cells [ 117 ]. On the other side, the AAV transduction of microglia is rare and challenging: indeed, in vivo, less than 20% of efficiency seems to be achieved, although some cases of microglial transductions, both in vitro and in vivo, have recently been reported, thanks to advances in the new strategies designed for recombinant viral vectors [ 113 , 118 , 119 ]. Furthermore, engineered microglial cells could be destined as a biologically active vehicle for the delivery of anti-tumoral molecules.…”

“…Furthermore, engineered microglial cells could be destined as a biologically active vehicle for the delivery of anti-tumoral molecules. Indeed, recently, the potential use of microglia engineered to express IL-15 upon infection with a recombinant AAV serotype 2 (rAAV2) carrying IL-15 (rAAV2-IL-15) was explored to counteract GBM growth in mouse models [ 119 ]. IL-15 is a crucial cytokine for the development, maturation, and activation of NK cells and CD8 + T-cells, with no effect on the expansion of the T regulatory cell population involved in suppressing immune responses, highlighting a potential therapeutic use in cancer immunotherapy [ 120 ].…”

“…Furthermore, IL-15 enhances the anti-tumor efficacy of the extracellular vesicles derived from NK cells, showing higher cytolytic activity against GBM [ 121 ]. Microglia infected with rAAV2-IL-15 functionally induce the release of IL-15, increasing the viability of NK cells without affecting their activation state in vitro [ 119 ]. In vivo, the rAAV2-IL-15 microglial cells infiltrate GBM mass and increase the recruitment of IFN-γ + NK cells in GBM-bearing mice, with effects on tumor growth [ 32 , 33 , 119 ], highlighting the fundamental role of IL-15 in the tumor core to boost immune reaction.…”

“…Microglia infected with rAAV2-IL-15 functionally induce the release of IL-15, increasing the viability of NK cells without affecting their activation state in vitro [ 119 ]. In vivo, the rAAV2-IL-15 microglial cells infiltrate GBM mass and increase the recruitment of IFN-γ + NK cells in GBM-bearing mice, with effects on tumor growth [ 32 , 33 , 119 ], highlighting the fundamental role of IL-15 in the tumor core to boost immune reaction. Moreover, rAAV2-IL-15 microglia consistently modulate the GAM state, with a reduction in arginase levels and an increased number of branches, and cover the parenchymal region [ 119 ], suggesting the switch to an anti-tumoral phenotype [ 122 ].…”

“…In vivo, the rAAV2-IL-15 microglial cells infiltrate GBM mass and increase the recruitment of IFN-γ + NK cells in GBM-bearing mice, with effects on tumor growth [ 32 , 33 , 119 ], highlighting the fundamental role of IL-15 in the tumor core to boost immune reaction. Moreover, rAAV2-IL-15 microglia consistently modulate the GAM state, with a reduction in arginase levels and an increased number of branches, and cover the parenchymal region [ 119 ], suggesting the switch to an anti-tumoral phenotype [ 122 ]. These data indicate that the recruited NK cells in the tumor core are activated and release pro-inflammatory cytokines (i.e., IFN-γ), thus explaining the modulation of the GAM phenotype [ 33 ].…”