Glioblastoma (GBM) is the most common and aggressive primary brain tumor in adults. Current therapies remain unsuccessful in improving overall survival; thus, the identification of novel therapies for GBM is critical. We have pioneered a novel, targeted immunotoxin (IT)-based cytotoxic therapy, D2C7-IT, that targets epidermal growth factor receptor (EGFR) and mutant EGFR variant III (EGFRvIII), established driver oncogenes of GBM. In preclinical studies, D2C7-IT targets and kills a substantial number of tumor cells and prolongs survival but is unable to generate cures in all treated animals because of the presence of a highly immunosuppressive GBM microenvironment. The majority of the immune cells in the GBM microenvironment are tumor-associated macrophages (TAMs), which promote tumor cell growth and inhibit antitumor T cell responses. Therefore, eliminating TAM-mediated immunosuppression is anticipated to enhance D2C7-IT-induced antitumor immune responses. CD40 is an immune co-stimulatory molecule whose activation is known to re-educate TAMs, and also induce T cell responses. Thus, the central hypothesis driving the present proposal is that overcoming TAM immunosuppression and tumor-promoting activities via CD40 co-stimulation will improve the efficacy of the cytotoxic D2C7-IT therapy. Accordingly, our preliminary studies have demonstrated that (1) in a mouse glioma model, D2C7-IT+?CD40 functions synergistically to prolong survival and generate significant cures, (2) brain resident microglia is the principal antigen-presenting cells (APCs) activated by the combination therapy, and (3) ?CD40 treatment engages CD8+ effector T cells that are antitumorigenic only when combined with cytotoxic D2C7-IT. Our results strongly imply that ?CD40 alters either the development or activity of TAMs in GBM and activates microglia/T cells. Demonstrating the antitumor efficacy of the D2C7-IT+?CD40 therapy in relevant brain tumor models and gaining insights into their mechanism of action will greatly aid in the clinical translation of D2C7-IT+?CD40 therapy. Therefore, we propose to pursue three Specific Aims to characterize D2C7-IT+?CD40 antitumor efficacy, TAM re-education, and microglia/T cell activation mechanisms:
Aim 1 : Evaluate whether ?CD40 overcomes TAM immunosuppression and enhances D2C7-IT efficacy in two preclinical immunocompetent glioma models.
Aim 2 : Define whether microglial CD40/MHCII molecules are the mediators of D2C7-IT+?CD40 antitumor immune response.
Aim 3 : Determine whether D2C7-IT+?CD40 therapy stimulates CD8+ effector T cell response capable of eliminating antigen-positive as well as antigen-negative tumors. The proposed research is significant because it will result in the development of a therapeutic strategy for simultaneous tumor cell killing, reversal of TAM immunosuppression, activation of microglia and T cells, and ultimately could be translated and tested in the clinic.
Glioblastoma (GBM) is the most common and aggressive type of brain cancer in adults, and effective treatment for GBM remains an unmet need. Therefore, it is critical to evaluate novel therapeutic approaches that will be beneficial for individuals afflicted with this debilitating disease. To develop protective antitumor immunity and improve GBM patient survival, we propose to simultaneously destroy tumor cells and activate microglia/macrophages, specialized immune cells in the tumor microenvironment. This study should result in the development of a novel therapeutic combination that will improve GBM patient survival.