635 Reprogramming the tumor microenvironment by a second-generation recombinant modified vaccinia virus Ankara

Immune checkpoint blockade (ICB) therapy has brought hope to many cancer patients, but the response rate is low in types, and acquired resistance ICB can develop over time. Oncolytic viruses are promising therapeutic agents for advanced cancers. Modified vaccinia virus Ankara (MVA) an attenuated, replication-deficient poxvirus safe human use, making it a favorable platform immunotherapy. Our first-generation recombinant MVA shown antitumor efficacy multiple murine tumor models due deletion of E5R gene (encoding inhibitor DNA sensor cGAS) from genome insertion two membrane-anchored transgenes – Flt3L OX40L, which leads activation host innate adaptive immunity. Here this study, we engineered our second-generation (MQ833) with more viral immune evasion genes E3L WR199, IL12 anchored extracellular matrix mitigate toxicity. Intratumoral (IT) delivery MQ833 resulted 80-100% cure mouse B16-F10 melanoma model, dependent on nucleic acid-sensing IFN signaling pathways. Single-cell RNA sequencing analysis revealed that IT injection reprogrammed microenvironment into immune-stimulating state, by activating CD8+ CD4+ T cells, depleting regulatory recruiting neutrophils, polarizing M1 macrophages. Interestingly, treatment cured 70% B2m knock-out melanomas likely combined effects IL-12 type I II IFN. Loss MHC-I most common mechanism ICB. Hence, results support use ICB-resistant tumors.