NorthWest Biotherapeutics Inc (NWBO)

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Detection of immune responses after immunotherapy in glioblastoma using PET and MRI

Joseph P. Antoniosa, Horacio Sotoa, Richard G. Eversona, Diana L. Moughon, Anthony C. Wang, Joey Orpilla, Caius Radub, Benjamin M. Ellingson, Jason T. Lee, Timothy Cloughesy, Michael E. Phelps, Johannes Czernin,, Linda M. Liau, and Robert M. Prins

The inability to accurately monitor glioblastoma tumor progression vs. pseudoprogression has severely limited clinical treatment decisions, especially in the setting of immunotherapy. We have identified a novel noninvasive imaging combination that could distinguish intracranial immune responses from tumor progression in mice bearing orthotopic gliomas and in patients with glioblastomas. We combined the use of advanced MRI with PET imaging of deoxycytidine kinase, an enzyme overexpressed in immune cells. This combination resulted in superior differentiation between immune responses and tumors within the brain, and identified peripheral lymph nodes in which immune responses occurred after immunotherapy combinations. This combined imaging approach may provide a useful method to clinically monitor patients with glioblastomas treated with immune-based therapies, and to distinguish tumor progression from pseudoprogression.

http://www.pnas.org/content/early/2017/08/30/1706689114.abstract


Abstract

Contrast-enhanced MRI is typically used to follow treatment response and progression in patients with glioblastoma (GBM). However, differentiating tumor progression from pseudoprogression remains a clinical dilemma largely unmitigated by current advances in imaging techniques. Noninvasive imaging techniques capable of distinguishing these two conditions could play an important role in the clinical management of patients with GBM and other brain malignancies. We hypothesized that PET probes for deoxycytidine kinase (dCK) could be used to differentiate immune inflammatory responses from other sources of contrast-enhancement on MRI. Orthotopic malignant gliomas were established in syngeneic immunocompetent mice and then treated with dendritic cell (DC) vaccination and/or PD-1 mAb blockade. Mice were then imaged with [18F]-FAC PET/CT and MRI with i.v. contrast. The ratio of contrast enhancement on MRI to normalized PET probe uptake, which we term the immunotherapeutic response index, delineated specific regions of immune inflammatory activity. On postmortem examination, FACS-based enumeration of intracranial tumor-infiltrating lymphocytes directly correlated with quantitative [18F]-FAC PET probe uptake. Three patients with GBM undergoing treatment with tumor lysate-pulsed DC vaccination and PD-1 mAb blockade were also imaged before and after therapy using MRI and a clinical PET probe for dCK. Unlike in mice, [18F]-FAC is rapidly catabolized in humans; thus, we used another dCK PET probe, [18F]-clofarabine ([18F]-CFA), that may be more clinically relevant. Enhanced [18F]-CFA PET probe accumulation was identified in tumor and secondary lymphoid organs after immunotherapy. Our findings identify a noninvasive modality capable of imaging the host antitumor immune response against intracranial tumors.