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 γ34.5 neurovirulence gene and the US12 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 NECTIN1, NECTIN2, and ITGB6. 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.