Wittrup, K Dane

Abstract Glioblastoma (GBM) is the most common malignant brain tumor in adults, responsible for approximately 225,000 deaths per year. Despite preclinical successes, most interventions have failed to extend patient survival by more than a few months. Treatment with anti—programmed cell death protein 1 (anti–PD-1) immune checkpoint blockade (ICB) monotherapy has been beneficial for malignant tumors such as melanoma and lung cancers but has yet to be effectively employed in GBM. This study aimed to determine whether supplementing anti–PD-1 ICB with engineered extended half-life IL2, a potent lymphoproliferative cytokine, could improve outcomes. This combination therapy, subsequently referred to as enhanced checkpoint blockade (ECB), delivered intraperitoneally, reliably cures approximately 50% of C57BL/6 mice bearing orthotopic GL261 gliomas and extends median survival of the treated cohort. In the CT2A model, characterized as being resistant to CBI, ECB caused a decrease in CT2A tumor volume in half of measured animals similar to what was observed in GL261-bearing mice, promoting a trending survival increase. ECB generates robust immunologic responses, features of which include secondary lymphoid organ enlargement and increased activation status of both CD4 and CD8 T cells. This immunity is durable, with long-term ECB survivors able to resist GL261 rechallenge. Through employment of depletion strategies, ECB's efficacy was shown to be independent of host MHC class I–restricted antigen presentation but reliant on CD4 T cells. These results demonstrate ECB is efficacious against the GL261 glioma model through an MHC class I–independent mechanism and supporting further investigation into IL2-supplemented ICB therapies for tumors of the central nervous system.

Abstract Glioblastoma multiforme (GBM) is a deadly CNS malignancy with an average survival of ~12–18 months post diagnosis. The unique immune environment of the brain and the immunosuppressive features of GBM complicate the use of immunotherapies against these tumors. We aimed to promote the efficacy of αPD-1 against the GL261 murine model of GBM by supplementing this therapy with an engineered IL-2 cytokine. IL-2 therapy has been used clinically for metastatic melanoma and renal cancer, but its short half-life in circulation necessitated high doses to keep the drug concentration sufficiently high. Fusing IL-2 to the mouse serum albumin molecule (MSA-IL-2), extends the cytokine’s half-life. Neither αPD-1 nor MSA-IL-2 are effective monotherapies for GL261 tumors, but the combination provides durable tumor clearance and prevents subsequent rechallenge. Most strikingly, this combination therapy cleared established GL261 tumors even in mice incapable of MHC class I restricted antigen presentation. Instead, therapeutic efficacy was abrogated by the depletion of CD4 T cells. Our combination therapy also reversed multiple key features of GBM-associated peripheral immune suppression, including depressed CD4 T cell counts and dampened MHC class II expression. Our combination therapy’s ability to overcome these immune derangements associated with glioma growth and to function independent of MHC class I restricted antigen presentation enhance the appeal of this therapy for future translational adaptation. This work was supported by the National Institutes of Health (R01 NS103212) and the Mayo Clinic-Koch Institute Cancer Solutions Team Grant

Abstract Glioblastoma multiforme (GBM) is a deadly CNS malignancy with an average survival of ~12 months post diagnosis despite aggressive treatment. Immunotherapy approaches to treat GBM are being developed, but the unique immune environment of the brain and the immunosuppressive features of GBM have complicated early efforts. Even αPD-1 checkpoint blockade, highly useful in the context of melanoma, has proved ineffective in the treatment of GBM. In order to promote the efficacy of αPD-1 against the GL261 murine model of GBM, we supplemented this therapy with an engineered IL-2 cytokine. IL-2 therapy has been used clinically for metastatic melanoma and renal cancer, but its short half-life in circulation necessitated dangerously high doses to keep the drug concentration sufficiently high. Fusing IL-2 to the mouse serum albumin molecule (MSA-IL-2), extends the cytokine’s half-life. While neither αPD-1 nor MSA-IL-2 are effective monotherapies against the GL261 model tumor, we have found this combination immunotherapy to provide durable tumor clearance and to create immunologic memory capable of resisting GL261 rechallenge. Most strikingly, this combination therapy is independent of the CD8 T cell function, clearing established GL261 tumors in mice incapable of MHC class I restricted antigen presentation. Independence of MHC class I restricted antigen presentation makes this combination immunotherapy using αPD-1 checkpoint blockade both highly novel and translatable to clinical use.