Granzyme B PET imaging of immune-mediated tumor killing as a tool for understanding immunotherapy response

Abstract

BackgroundCancer immunotherapy research is expanding to include a more robust understanding of the mechanisms of treatment response and resistance. Identification of drivers of pro-tumor and anti-tumor immunity during treatment offers new strategies for effective alternative or combination immunotherapies. Currently, tissue or blood samples are collected and analyzed, then dichotomized based on clinical end points that may occur months or years after tissue is collected. While overall survival is ultimately the desired clinical outcome, this dichotomization fails to incorporate the nuances that may occur during an anti-tumor response. By failing to directly measure immune activation at the time of sampling, tumors may be misclassified and potentially obscure important biological information. Non-invasive techniques, such as positron emission tomography (PET), allow for global and quantitative measurements of cancer specific processes and are widely used clinically to help manage disease.MethodsWe have previously developed a novel PET agent that can non-invasively quantify granzyme B release in tumors and have demonstrated its ability to predict response to checkpoint inhibitor therapy in multiple murine models of cancer. Here, we used the quantitative measurement of granzyme B release as a direct and time-matched marker of immune cell activation in order to determine immune cell types and cytokines that correlate with effective checkpoint inhibitor therapy in both tumors and tumor-draining lymph nodes.ResultsThrough PET imaging, we were able to successfully distinguish distinct microenvironments, based on tumor type, which influenced immune cell subpopulations and cytokine release. Although each tumor was marked by functionally distinct pathways of immune cell activation and inflammation, they also shared commonalities that ultimately resulted in granzyme B release and tumor killing.ConclusionsThese results suggest that discrete tumor immune microenvironments can be identified in both responsive and non-responsive tumors and offers strategic targets for intervention to overcome checkpoint inhibitor resistance.

Off-tumor IDO1 target engagements determine the cancer-immune set point and predict the immunotherapeutic efficacy

“…30 Unexpectedly, we identified the MLNs as a robust offtumor IDO1 site for active immune response monitoring (figures 3 and 4), different from currently known methods that focus on tumor sites (online supplemental table 4). [31][32][33][34][35][36][37][38][39][40][41][42][43][44] These findings enabled us to distinguish l-1MTrp+CPA as a more effective regimen than l-1MTrp+PTX for treating murine B16F10 melanoma (figure 3), simplifying the assessment of immunotherapy effectiveness, and allowing oncologists to rapidly analyze and screen more effective combination regimens on a common platform. Although various studies have indicated that the combination of an IDO1 inhibitor with chemotherapy induces antitumor immunity, which leads to immune-mediated clearance of IDO1-expressing and nonexpressing poorly immunogenic tumors, including melanoma, 1-3 11 19 failed clinical trials with IDO1 inhibitors have set back the development of this approach.…”

Imaging Beyond Seeing: Early Prognosis of Cancer Treatment

“…[ 81 ] Indeed, granzymeB‐based imaging applications are attracting increasing interest. [ 82 ] A similar approach to detecting antigen‐specific T lymphocytes has been developed by Ploegh et al. [ 83 ] Unlike targeting to Granzyme B, the different peptides provided a variable platform to identify different antigen‐activated T cells.…”

Multi-parameter optical imaging of immune cell activity in chimeric antigen receptor T-cell and checkpoint blockade therapies

“…A handful of fluorogenic (35)(36)(37), photoacoustic (37), chemiluminescent (29), and PET (28) probes have been developed for imaging gzmB activity or its distribution in vivo. These studies focused on probing gzmB in different preclinical models and have supported gzmB as a reliable biomarker of cytotoxic cell activation in anti-cancer responses (28,38,39).…”