Summary The goal of the proposed research is to develop a bacterial vector to deliver oncolytic viruses (OVs). As immunotherapies, OVs regress many cancers and have had clinical success treating externally accessible tumors. Despite the promise of this approach, poor delivery limits the efficacy of OVs for treating internal solid tumors. To address this issue, we developed virus-delivering Salmonella (VDS) to carry oncolytic viruses into cancer cells in tumors. By specifically colonizing tumors, VDS protects the viral genome from clearance in the blood and circumvents the difficulty of using OVs as immunotherapy for solid tumors. We propose to deliver H-1 parvovirus (H-1PV) with VDS to prevent sequestration of viral particles in non-tumor organs and increase delivery to tumors. We hypothesize that immunogenic cell death (ICD) caused by H-1PV induces the production of cytokines, triggers immune cell infiltration, and generates memory CD8 T cells. This newly formed antitumor immunity will eliminate cancer cells regardless of their location in the body. We have established the foundation for this research by showing that (1) deletion of homologous recombination genes (RecB, SbcB, SbcCD and RecF) from Salmonella preserves essential hairpins in the viral genome that are required for formation and replication; (2) delivery of H-1PV to cancer cells with VDS produces functional viral particles, and (3) the produced virus particles are infective and kill cancer cells. The proposed research plan has two Aims that will (Aim 1) measure bacterial virus delivery to tumors in mice and quantify tumor specificity, safety, and tissue amplification, and (Aim 2) quantify the induction of cytotoxic cell death by VDS-H1PV and its generation of antitumor immune responses. We hypothesize that when administered to mice, VDS-H1PV produces functional virions that spread throughout tumors by re-infecting neighboring cancer cells. We will test this hypothesis by delivering VDS-H1PV to mice with murine hepatocellular carcinoma tumors and measuring viral titers in tumors and healthy organs. We will also measure infiltration and activation of T cells, dendritic cells, macrophages and NK cells. We anticipate that VDS-H1PV induces cancer cell death, reduces tumor volume, generates T-cell-mediated antitumor immunity, and prevents tumor re-implantation. VDS has several distinct advantages over other therapeutic strategies. Compared to other cellular carriers, VDS has a significantly higher therapeutic index and tumor accumulation is not rate limiting. VDS-H1PV also has several advantages over other microbial therapies. It directs the immune induction of OV therapy specifically to tumors and it is not dependent on the extent of bacterial colonization in tumors. Only a small number of bacteria are required to initiate a tumor-localized infection that amplifies the therapeutic response. The combination of targeted intracellular delivery with Salmonella and immune induction with H-1PV ...