An engineered oncolytic vaccinia virus expressing PD-L1 inhibitor exerts anti-tumor effects on glioblastoma by activating T cell responses.

BACKGROUND

Glioblastoma represents the most aggressive primary brain malignancy, with median survival of only 14-16 months despite standard therapy. Immune checkpoint inhibitors show limited efficacy due to the immunologically "cold" tumor microenvironment.

OBJECTIVE

To develop and evaluate an engineered oncolytic vaccinia virus co-expressing a PD-L1 inhibitor and GM-CSF (VV-iPDL1/GM), and assess its synergy with systemic anti-PD-1 therapy.

METHODS

VV-iPDL1/GM was engineered to express a soluble PD-1 extracellular domain-IgG-Fc fusion protein and GM-CSF. Immunomodulatory effects were assessed using glioblastoma-T cell co-cultures. Antitumor efficacy was evaluated in orthotopic GL261 glioblastoma models.

RESULTS

VV-iPDL1/GM demonstrated potent PD-L1 inhibition (IC₅₀ = 145 ± 23 nM) and enhanced CD8+ T cell activation while reducing regulatory T cells. In vivo, VV-iPDL1/GM monotherapy achieved 94.5% tumor growth inhibition, doubled median survival (47.5 vs. 22.5 days), and resulted in 30% long-term survivors. Combination with systemic anti-PD-1 therapy further improved tumor inhibition to 99.7%, extended median survival to 71.5 days (3.2-fold increase), and achieved 60% long-term survival. Treatment produced 4.8-fold increased CD8+ T cell infiltration and favorable CD8/Treg ratios (19.8:1 vs. 1.7:1). Mechanistic analysis revealed synergistic interactions with Hill coefficients of 1.8-2.3.

CONCLUSIONS

VV-iPDL1/GM effectively remodels the glioblastoma immune microenvironment through integrated oncolysis, immune activation, and checkpoint inhibition. Localized delivery circumvents blood-brain barrier limitations while minimizing systemic toxicity, highlighting its clinical translation potential.