Replicating retroviral delivery of an IL-15 superagonist improves antitumor immunity and long-term survival in poorly immunogenic glioblastoma models

Glioblastoma (GBM) is the most lethal primary brain neoplasm due to its highly immunosuppressive microenvironment and resistance to conventional therapies. To overcome this challenge, we engineered a replicating retrovirus (RRV) to deliver a superagonist interleukin-15 receptor-linked fusion protein (RLI) directly to tumor cells, engineering them into local immunotherapy biofactories. This strategy leverages the tumor-selective replication of RRV to achieve localized and sustained RLI expression within the tumor microenvironment. In two orthotopic poorly immunogenic GBM mouse models, intratumoral administration of RRV RLI significantly reduced tumor growth and prolonged survival compared to controls, with some mice achieving long-term remission and demonstrating immunological memory upon rechallenge. Transcriptomic and flow cytometric analyses revealed that RRV RLI treatment enhanced infiltration and activation of CD8⁺ T cells and NK cells, and upregulated antigen presentation pathways within the tumor microenvironment. Depletion studies indicated that the therapeutic efficacy of RRV RLI is dependent on both CD4⁺ and CD8⁺ T cells. Notably, combining RRV RLI with the GBM standard of care chemotherapeutic agent temozolomide (TMZ) synergistically improved survival outcomes. Subsequent single-cell RNA and T-cell receptor sequencing identified enhanced effector cell activation, antigen presentation, and clonal T-cell expansion in the combination therapy group. Our findings suggest that RRV-mediated delivery of RLI effectively transforms GBM tumors into immunostimulatory hubs, eliciting potent anti-tumor immune responses. This novel viral immunotherapy holds significant promise for clinical translation in the treatment of GBM and other difficult-to-treat solid tumors.