Intratumoral delivery of engineered recombinant modified vaccinia virus Ankara expressing Flt3L and OX40L generates potent antitumor immunity through activating the cGAS/STING pathway and depleting tumor-infiltrating regulatory T cells

Intratumoral (IT) delivery of immune-activating viruses can serve as an important strategy to turn cold tumors into hot tumors, resulting in overcoming resistance to immune checkpoint block-ade (ICB). Modified vaccinia virus Ankara (MVA) is a highly attenuated, non-replicative vaccinia virus that has a long history of human use. Here we report that IT recombinant MVA (rMVA), lacking E5R encoding an inhibitor of the DNA sensor cyclic GMP-AMP synthase (cGAS), ex-pressing a dendritic cell growth factor, Fms-like tyrosine kinase 3 ligand (Flt3L), and a T cell co-stimulator, OX40L, generates strong antitumor immunity, which is dependent on CD8+ T cells, the cGAS/STING-mediated cytosolic DNA-sensing pathway, and STAT1/STAT2-mediated type I IFN signaling. Remarkably, IT rMVA depletes OX40hi regulatory T cells via OX40L/OX40 inter-action and IFNAR signaling. Taken together, our study provides a proof-of-concept for improving MVA-based cancer immunotherapy, through modulation of both innate and adaptive immunity.