Quantitative Imaging for the Evaluation of High-Grade Glioma Changes During Novel Combination Immunotherapy

Novel immunotherapies for high-grade glioma (HGG), including immune checkpoint blockade (ICB) and oncolytic virotherapy, have shown remarkable potential in promoting antitumoral immune responses and allowing for long-term tumor remission. However, the complexity of the HGG tumor microenvironment and the dynamic immunological changes associated with immunotherapy response can limit the diagnostic utility of conventional magnetic resonance imaging (MRI). Consequently, distinguishing true tumor progression from immunotherapy-related effects often requires prolonged clinical follow-up over several months. During this period, patients may continue to receive ineffective therapies, increasing the risks of treatment-related toxicities without meaningful clinical benefit.

This dissertation explores the role of quantitative imaging to non-invasively evaluate changes in intratumoral heterogeneity and immune dynamics as early indicators of immunotherapy response in both preclinical and clinical settings. Initially, quantitative MRI was shown to be informative of improved outcomes in a Phase I/II clinical trial of M032, an IL-12 expressing oncolytic herpes simplex virus (oHSV), in recurrent HGG. Multiparametric evaluation of tumor heterogeneity revealed that increases in intratumoral hypoxia, defined by low vascularity and high cellularity, were associated with worse clinical outcomes. Furthermore, M032 infusions at regions with higher cellularity, vascularity, and hypoxia were linked with enhanced therapeutic effects and improved clinical outcomes, highlighting potential applications for treatment planning and response monitoring in HGG.

Immune-targeting molecular imaging using positron emission tomography (PET) allows for the characterization of immune recruitment and activation within the HGG tumor microenvironment. Preclinical studies evaluated [⁸⁹Zr]-CD8 minibody and [⁶⁴Cu]-GZP immune-PET imaging in response to combination M002, the murine equivalent of M032, and checkpoint inhibitors in orthotopic syngeneic HGG models. These studies demonstrated the importance of spatial intratumoral heterogeneity of cytotoxic T cell populations and effector molecule expression in mediating immunotherapy response. Additionally, a mathematical modeling framework was established to characterize immune-targeted PET tracer kinetics, with potential for translation to other tumor models and clinical applications.

These cumulative findings support the role of advanced, complementary quantitative MRI and PET imaging to evaluate intratumoral heterogeneity and predict responses to single-agent and combination immunotherapy. This work provides a foundation for clinically translatable, non-invasive biomarkers to guide clinical interventions and improve therapeutic outcomes for HGG patients.