The Oncolytic Adenovirus XVir-N-31 Joins Forces with CDK4/6 Inhibition Augmenting Innate and Adaptive Antitumor Immunity in Ewing Sarcoma

Purpose: Ewing sarcoma (EwS) is a highly malignant pediatric tumor characterized by a non-T-cell-inflamed immune-evasive phe-notype. When relapsed or metastasized, survival is poor, emphasizing the need for novel treatment strategies. Here, we analyze the novel combination approach using the YB-1-driven oncolytic adenovirus XVir-N-31 and CDK4/6 inhibition to augment EwS immunogenicity.Experimental Design: In vitro, viral toxicity, replication, and immunogenicity were studied in several EwS cell lines. In vivo tumor xenograft models with transient humanization were applied to evaluate tumor control, viral replication, immunogenicity, and dynamics of innate as well as human T cells after treatment with XVir-N-31 combined with CDK4/6 inhibition. Furthermore, immunologic features of dendritic cell maturation and T-cell -stimulating capacities were assessed.Results: The combination approach significantly increased viral replication and oncolysis in vitro, induced HLA-I upregulation, and IFNy-induced protein 10 expression and enhanced mat-uration of monocytic dendritic cells with superior capacities to stimulate tumor antigen-specific T cells. These findings were confirmed in vivo showing tumor infiltration by (i) monocytes with antigen-presenting capacities and M1 macro-phage marker genes, (ii) TReg suppression in spite of adeno-virus infection, (iii) superior engraftment, and (iv) tumor infiltration by human T cells. Consequently, survival was improved over controls with signs of an abscopal effect after combination treatment.Conclusions: The joint forces of the YB-1-driven oncolytic adenovirus XVir-N-31 and CDK4/6 inhibition induce therapeu-tically relevant local and systemic antitumor effects. Innate as well as adaptive immunity against EwS is boosted in this pre -clinical setting, pointing toward high therapeutic potential in the clinic.