Whole-body PET imaging of T cell response to Glioblastoma.

PURPOSE Immunotherapy is a promising approach for many oncological malignancies, including glioblastoma, however, there are currently no available tools or biomarkers to accurately assess whole-body immune responses in glioblastoma patients treated with immunotherapy. Here, the utility of OX40, a co-stimulatory molecule mainly expressed on activated effector T cells known to play an important role in eliminating cancer cells, was evaluated as a positron emission tomography (PET) imaging biomarker to quantify and track response to immunotherapy. EXPERIMENTAL DESIGN A subcutaneous vaccination approach of CpG oligodeoxynucleotide, OX40 mAb, and tumor lysate at a remote site in a murine orthotopic glioma model was developed to induce activation of T cells distantly while monitoring their distribution in stimulated lymphoid organs with respect to observed therapeutic effects. To detect OX40-positive T cells we utilized our in-house developed 89Zr-DFO-OX40 mAb and in vivo PET/CT imaging. RESULTS ImmunoPET with 89Zr-DFO-OX40 mAb revealed strong OX40-positive responses with high specificity, not only in the nearest lymph node from vaccinated area (mean, 20.8%ID/cc) but also in the spleen (16.7%ID/cc) and the tumor draining lymph node (11.4%ID/cc). When the tumor was small (< 106 p/sec/cm2/sr in bioluminescence imaging), a high number of responders and % shrinkage in tumor signal was indicated after only a single cycle of vaccination. CONCLUSIONS The results highlight the promise of clinically translating cancer vaccination as a potential glioma therapy, as well as the benefits of monitoring efficacy of these treatments using immunoPET imaging of T cell activation.