Wittrup, Dane

Abstract α-PD-1 checkpoint blockade is a promising immunotherapeutic approach for many solid tumors; however, this strategy is minimally effective for GBM patients as a monotherapy. One potential reason why α-PD-1 checkpoint blockade is ineffective is the tumor microenvironment and systemic derangements of the immune system which are prevalent in GBM patients. We have successfully modeled peripheral immune derangements in experimental murine GBM models. These include low peripheral blood CD4 T cell counts, reduced MHC class II expression on monocytes, and atrophy of primary immune organs in animals harboring gliomas. We therefore hypothesized that extended half-life IL-2, a potent cytokine which promotes the proliferation, differentiation, and killing activity of T cells, could overcome immune derangements and could potentially synergize with α-PD-1 checkpoint blockade therapy. In cohorts of C57Bl/6 mice, we supplemented α-PD-1 checkpoint blockade with multiple bio-engineered extended half-life IL-2 molecules to treat GL261 and CT2A orthotopic glioma models which are normally resistant to monotherapy. We observe a statistically significant increase in survival in GL261-bearing animals receiving the combination of extended half-life IL-2 reagents and αPD-1 therapy relative to control-treated mice. Some animals receiving this combination therapy had a reduction in tumor burden to levels below detection. These long-term survivors underwent a rechallenge experiment with a second inoculation of GL261-Luc and effectively cleared tumor without further therapeutic intervention. This intervention causes a significant shift in the immune profile, including the formation of mature T cell responses, as well as restoring the diminished peripheral immune cell counts in GL261-bearing animals. Finally, combining extended half-life IL-2 with α-PD-1 checkpoint blockade is effective independently of the CD8 T cell response. Together, these data suggest that combination immunotherapies employing extended half-life IL-2 fusion proteins are translational to the clinic and do not require the identification of tumor specific antigens for efficacy

Abstract Glioblastoma (GBM) is the most common malignant brain tumor in adults, responsible for approximately 225,000 deaths per year. Despite pre-clinical successes, therapeutic interventions have failed to extend patient survival by more than a few months. Anti-PD-1 checkpoint inhibition monotherapy has had efficacy against some tumor types but not GBM. The aim of this study was to determine whether supplementing anti-PD-1 checkpoint blockade with an engineered extended half-life IL-2 could improve outcomes in a preclinical model of disease. Our enhanced checkpoint blockade (ECB) strategy reliably cures approximately50% of C57BL/6 mice bearing orthotopic GL261 gliomas and extended median survival even in the mice that eventually succumbed. This therapy generates robust immunologic responses, features of which include secondary lymphoid organ enlargement and increased activation status of both CD4 and CD8 T cells. Further, many of the characteristics of brain-tumor mediated peripheral immunosuppression, including MHC class II downregulation on APCs, are prevented by ECB combination therapy. This immunity is durable, with long-term ECB survivors able to resist GL261 rechallenge. Notably, ECB’s efficacy is independent of host MHC class I restricted antigen presentation, being equally efficacious in MHC class I and CD8 T cell deficient mice. Conversely, ECB combination therapy is reliant on CD4 T cells and their depletion abrogates the therapy’s survival benefit. Our data shows ECB combination immunotherapy to be efficacious against the GL261 glioma model through an MHC class I independent mechanism, enhancing its off-the-shelf translational appeal relative to strategies requiring extensive knowledge of tumor-specific antigens.