The immune checkpoint inhibitor anti-PD-1, commonly used in cancer immunotherapy, has not been successful as a monotherapy for the highly aggressive brain cancer glioblastoma. However, when used in conjunction with a CC-chemokine receptor-2 (CCR2) antagonist that targets myeloid-derived suppressor cells (MDSCs), anti-PD-1 has shown efficacy in preclinical studies. We develop a glioblastoma-immune dynamics ODE model and include interventions with anti-PD-1 and the CCR2 antagonist. Using optimal control theory, we optimize combination immunotherapy treatment regimens for an average mouse and then scale the approach to a virtual murine cohort to evaluate mortality and quality of life concerns during treatment, and predict survival, tumor recurrence, or death after treatment.