P08.21.a Reinvigorating Exhausted T Cells in Glioblastoma via Pd1-Il2v Immunocytokine Therapy

BACKGROUND Glioblastoma (GBM) remains one of the most lethal primary brain tumors, characterized by profound immunosuppression and resistance to conventional immunotherapy. A hallmark of the GBM microenvironment is the prevalence of functionally exhausted T cells, marked by sustained expression of inhibitory receptors such as PD-1 and impaired effector function. These exhausted T cells represent a major barrier to durable anti-tumor immunity and effective immunotherapeutic intervention. To overcome this, we investiagated the therapeutic potential of PD1-IL2v, a novel immunocytokine designed to selectively deliver IL-2 signaling to PD1-1+ cells while avoiding expansion of regulatory T cells (Tregs). MATERIAL AND METHODS We employed two murine models of glioblastoma: GL261, a commonly used immunogenic model, and SB28, an aggressive, poorly immunogenic model that is resistant to immune checkpoint blockade. PD1-IL2v was administered either systemically or intratumorally. Flow cytometry was used to phenotypically characterize tumor-infiltrating lymphocytes (TILs), with a focus on exhaustion markers and effector phenotypes. In the SB28 model, we additionally evaluated the combination of PD1-IL2v with radiotherapy and temozolomide to reflect the current clinical standard of care. RESULTS Local administration of PD1-Il2v, but not systemic delivery, effectively reactivated CD8⁺ T cells within the tumor microenvironment. Treated mice exhibited enhanced cytokine production, increased proliferation, and restoration of cytotoxic activity in T cells. Phenotypic profiling revealed an expansion of a stem-like subset of exhausted T cells (PD-1⁺TCF1⁺), alongside the emergence of a novel, differentiated population with superior effector functions—termed “better-effector” T cells. Therapeutic intervention with PD1-IL2v led to prolonged survival, complete tumor rejection in a subset of animals, and increased infiltration of functional T cells into the tumor core. Furthermore, we evaluated the efficacy of PD1-IL2v in combination with radiotherapy and temozolomide—the standard of care for glioblastoma—in the SB28 model. CONCLUSION Our findings underscore T cell exhaustion as an untapped reservoir of tumor-reactive T cells that can be therapeutically reinvigorated using PD1-IL2v. This approach not only restores anti-tumor immunity but also induces superior effector populations capable of driving tumor regression.