Oncolytic HSV-1 expressing FLT3L kills melanoma, glioblastoma, and pancreatic cancer cells in vitro and induces immunogenic cell death

Oncolytic viruses (OVs) are promising anti-cancer agents designed to induce cancer cell death while simultaneously stimulating immune responses through encoded transgenes. FMS-like tyrosine kinase 3 ligand (FLT3L), a critical cytokine in dendritic cell (DC) biology, was incorporated into a genetically engineered OV derived from herpes simplex virus type 1. This virus was modified with deletions in the <i>γ34.5</i> neurovirulence gene and the <i>US12</i> gene. Treatment with the FLT3L-encoding OV resulted in a time- and dose-dependent increase in FLT3L secretion and inhibition of cell growth across all tested cell lines, although sensitivity varied among the lines. Susceptibility to oncolysis correlated with the expression levels of <i>NECTIN1</i>, <i>NECTIN2</i>, and <i>ITGB6</i>. OV-induced lysates from melanoma and ASPC1 cell lines showed minimal effects on the phenotype of conventional DCs (cDCs). However, oncolysates significantly increased the secretion of interferon (IFN)-λ1 and IFN-α-2a, particularly using BXPC3 oncolysates. Additionally, treatment of pancreatic cancer and 938-mel cell lines with the FLT3L-expressing OV elevated ATP levels but did not affect HMGB1 release. In conclusion, this study demonstrates the dual oncolytic and immunogenic potential of an FLT3L-encoding OV, particularly on cDCs. These findings support the further development of this approach as a novel cancer immunotherapy.