PROJECT SUMMARY – PROJECT 1 The combination of oncolytic virotherapy (OV) and monoclonal antibody (mAb) immunotherapy has great potential for the treatment of glioblastoma (GBM), the most common malignant brain tumor without a cure. An OV carrying a mAb-coding gene can produce and release the mAb drug specifically at the tumor site as a safe, effective, and innovative delivery system. Prior to our study, this approach has not been previously explored using herpes simplex virus 1-based OV (oHSV). CD47 is a transmembrane protein widely expressed on cancer cells including GBM. It acts as a “don’t eat me” signal by functioning as a ligand to signal regulatory protein-α (SIRPα) expressed on macrophages, resulting in inhibition of phagocytosis. We have generated an oHSV that expresses a full-length anti-CD47 mAb on an IgG1 scaffold (OV-αCD47-G1) that is capable of inducing antibody- dependent cellular phagocytosis (ADCP) by macrophages and antibody-dependent cellular cytotoxicity (ADCC) by natural killer cells to eradicate GBM cells in vitro and in vivo, in addition to blockade of the CD47-SIRPα “don’t eat me” signaling pathway in macrophages. We have demonstrated that our novel OV-αCD47-G1 significantly improves the survival of GBM-bearing mice in orthotopic, immunocompetent, and immunodeficient models. Our central hypothesis is that OV-αCD47-G1 will be safe and effective at improving GBM treatment and its anti- tumor activity in the brain will be reflected by markers in the peripheral blood. Importantly, we have optimized and manufactured GMP-grade OV-αCD47-G1 to conduct the proposed studies and will initiate a phase I clinical trial for adults with GBM. In this proposal, we will evaluate both the systemic and regional immune responses in vivo following clinical-grade OV-αCD47-G1 administration and identify markers in the circulation that correlate with anti-tumor activity in the brain in GBM animal models (Aim 1); we will perform Investigational New Drug (IND)-enabling in vivo safety and efficacy studies using clinical-grade OV-αCD47-G1 (Aim 2); and we will determine the safety of administering a single intracerebral infusion of OV-αCD47-G1 in adult patients with recurrent GBM (Aim 3). To accomplish these objectives, we will utilize immunocompetent and immunocompromised GBM mouse models for our correlative and preclinical studies evaluating OV-αCD47-G1 prior to the phase I clinical trial. Upon conclusion, we will understand how to optimize OV-αCD47-G1 therapy to cure GBM. Further insight into this process, as will result from the implementation and completion of this proposal, is impactful as it will ultimately lead to a reduction in mortality for adults suffering from GBM.