Multimodal glioma immunotherapy combining TLR9-targeted STAT3 antisense oligodeoxynucleotides with PD1 immune checkpoint blockade.

Abstract

Background: Therapeutic resistance in glioblastoma (GBM) is multifactorial and results from genetic heterogeneity, the immunoprivileged localization, and the potently tolerogenic microenvironment. Signal transducer and activator of transcription 3 (STAT3) plays a key role in both glioma cell survival and immune evasion, reinforcing GBM resistance.

Methods: Here, we describe a new cell-selective and double-stranded STAT3 antisense oligonucleotide (CpG-STAT3dsASO) for targeting human/mouse glioma cells and GAMs but not T cells. The oligonucleotide safety and efficacy against orthotopic GBM was assessed in immunocompetent or immunodeficient mice.

Results: CpG-STAT3dsASO injected intracranially/intratumorally was well-tolerated and reduced progression of human U251 GBM xenotransplants and mouse GL261 or neural cell-derived QPP8 gliomas. Unlike the single-stranded oligonucleotide, local CpG-STAT3dsASO administration did not trigger type-I IFN-dependent neurotoxicities in immunocompetent mice within the therapeutic dose range. CpG-STAT3dsASO activated intratumoral GAMs, such as dendritic cells, macrophages and microglia, thereby expanding CD4+ Th1 cells while reducing TREG numbers. CpG-STAT3dsASO monotherapy did not have curative effects as it led to recruitment of only limited numbers of mostly exhausted effector CD8+ T cells. However, when combined with systemic PD1 inhibition, CpG-STAT3dsASO/anti-PD1 treatments caused regression of GL261 as well as immunotherapy-resistant QPP8 gliomas and resulted in long-term survival of the majority of mice. The combination treatment boosted CD8+ effector T-cell activity, while promoting their intratumoral interaction with activated CD4+ Th1 cells and activated macrophages as indicated by spatial transcriptomics.

Conclusions: Our results suggest rationale for GBM immunotherapy using CpG-STAT3dsASO to disrupt GAMs-dependent immune evasion, thereby restoring sensitivity to PD1 blockade and facilitating T-cell-mediated antitumor immune responses.