Oncolytic virus infected tumors drive AP-1 and IRF signaling in NK cells to sustain anti tumor activity

Background: Natural killer (NK) cells play a crucial role in cancer immunosurveillance. They infiltrate the tumor microenvironment and kill tumor cells by integrating activating signals from stress-induced ligands on cancer cells and inhibitory signals, mediated by the major histocompatibility immune complex (HLA), that preserve self-tolerance. However, their effectiveness against solid tumors is limited by tumor-driven immune-suppression. Oncolytic viruses (OV) can potentially overcome this barrier by selectively infecting tumor cells and stimulating antitumor immunity. We thus combined the oncolytic adenovirus Delta24-RGD with NK cells to target aggressive solid tumors, aiming to define the mechanisms underlying virus-induced NK cell hyperactivation and supporting clinical translation of this approach. Methods: We conducted in vitro and in vivo studies to evaluate the cytotoxicity of ex vivo-expanded cord blood-derived NK cells against Delta24-RGD-infected pancreatic ductal adenocarcinoma and glioblastoma cells. In vitro, OV-infected tumor cells were co-cultured with NK cells, followed by CyTOF phenotyping and cytotoxicity evaluation using xCelligence and Incucyte. Long-term cytotoxic capacity was assessed by first co-culturing NK cells with OV-infected or non-infected tumor cells, isolating NK cells and then testing their serial killing against fresh tumor targets. In vivo efficacy was tested using patient-derived xenograft glioblastoma mouse models. Mechanistic workup included ATAC-seq, bulk RNA-seq, CUT&RUN, and CRISPR-Cas9 knockout of JUNB and FOS. Results: NK cells exhibited synergistic cytotoxicity against OV-infected PDAC and glioblastoma cells and acquired an enhanced activation phenotype with increased expression of DNAM-1, NKG2D, CD94, NKp30, CD25, CD69, ICOS, T-bet, TRAIL, and CD107a. OV-infected tumor cells upregulated stress ligands including B7-H6, MICA/B, and ULBP1 and downregulated HLA-I. In vivo, the combination therapy significantly reduced tumor growth and extended survival in glioblastoma models. NK hyperactivation required direct contact with OV-infected tumor cells, likely driven by virus-mediated modulation of NK-ligand expression on tumor cells. Robustly activated NK cells maintained enhanced cytotoxicity through repeated tumor rechallenges, indicating durable functional reprogramming. Mechanistic studies revealed AP-1 activation followed by type I interferon signaling. Disruption of JUNB and FOS, as well as chemical AP-1 inhibition reduced this effect. CUT&RUN confirmed AP-1 dependent transcriptional programs supporting cytotoxicity. Conclusion: Oncolytic viruses synergistically enhance sustained NK cell antitumor activity by reprogramming AP-1 driven transcriptional responses. This combination strategy provides a mechanistic foundation for advancing NK cell-based therapies against solid tumors.