A novel oncolytic herpes simplex virus type 2 induces polarization of tumor-associated macrophages and remodels the immune microenvironment in glioblastoma

BACKGROUND: Glioblastoma multiforme (GBM) is a highly aggressive primary malignant brain tumor with limited survival despite multimodal therapy. Its profoundly immunosuppressive tumor microenvironment severely restricts treatment efficacy. Oncolytic viruses represent a promising therapeutic strategy, yet the immunological mechanisms underlying the antitumor activity of OH2 (oncolytic herpes simplex virus type 2) remain poorly defined. METHODS: The effects of OH2 were evaluated in GBM cell lines (U251, LN229 and GL261) by assessing cell viability, migration, apoptosis, and cell cycle distribution. Modulation of tumor-associated macrophages (TAMs) was examined in RAW264.7 and THP-1 cells through functional assays, RNA sequencing, Western blotting and pharmacologic inhibition. In vivo studies were performed in subcutaneous and orthotopic GBM models to assess tumor growth and immune alterations. Exploratory clinical observations were conducted in seven recurrent GBM patients (NCT05235074), including peripheral blood monocyte profiling, longitudinal immune monitoring and cytokine analysis. RESULTS: OH2 induced apoptotic and oncolytic cell death in GBM cells, while inhibiting cell proliferation and migration in vitro. In macrophage models, exposure to OH2-conditioned media enhanced proliferation and phagocytic activity and promoted M1-like polarization, accompanied by activation of JAK-STAT1 signaling. In vivo, OH2 suppressed tumor growth, promoted M1-like TAM polarization, reduced immunosuppressive macrophage populations, and increased recruitment of bone marrow-derived macrophages into the brain. Exploratory clinical observation suggested that changes in peripheral monocyte profiles may be associated with clinical benefit. CONCLUSIONS: OH2 exerts antitumor activity in GBM through direct oncolysis and immune microenvironment modulation, highlighting its potential as an immunotherapeutic strategy.