Abstract 6444: Assessing cytotoxic T cell responses to immune checkpoint inhibitors in murine and human tumor samples using metabolic imaging
Authors: Ouellette Jonathan , Degnan Janey , Kellner Anna , Flietner Evan , Doebert Lindsay , Swider Zachary , Wait Eric , Pope Victoria , Hrycyniak Laura , Caenepeel Sean , Eliceiri Kevin , Ramasubramanian T S. , Korrer Michael J. 
Published: March 2024

Abstract
Background   Immune checkpoint inhibitors (ICI) have revolutionized cancer treatment. Unfortunately, existing FDA approved biomarkers do not accurately predict which patients will respond. The Elephas Cybrid™ platform aims to improve ICI response prediction by imaging a patient’s biopsy treated with ICI ex vivo.   Multiphoton microscopy (MPM) is a powerful imaging technique to interrogate the biological changes in live tumor fragments (LTFs) following ICI treatment. MPM allows rapid visualization of biological processes in 3D living tissues in a non-destructive fashion allowing for longitudinal assessment of a sample. We and others have used label-free metabolic imaging to demonstrate that changes in T cell metabolism and activation status are correlated. Using MPM imaging we successfully demonstrated T cell activation and T cell mediated cytotoxicity in response to ICI in LTFs and tumor biopsies.
Methods   Tumors were cut into LTFs, sorted, and cultured using the Cybrid platform. LTF structure and metabolic status were assessed using intrinsically fluorescent NAD(P)H and FAD. Anti-CD8 nanobodies and cleaved caspase 3/7 dye were used to characterize T cell cytotoxicity. Multi-channel fluorescence intensity and lifetime were obtained over 48 hours using MPM.
Results   Murine CT26 LTFs generated with the Cybrid platform were treated with ICI and cytotoxicity was assessed in the intact LTFs by monitoring caspase 3/7 activity using MPM over 48 hours. We found that ICI treatment resulted in a significant increase in caspase 3/7 activity compared to control treated LTFs. By blocking the interaction of T cells with tumor cells through antibody blockade, we demonstrated that the cytotoxicity observed was T cell mediated. As additional confirmation, we measured changes in cytotoxicity in the ICI resistant LLC1 tumor model. As expected, we did not observe an increase in cytotoxicity in LLC1 LTFs treated with ICI. MPM allows for the tracking of labeled T cells and characterization of their metabolism as a means of assessing changes in their activation state. We used a CD8 nanobody to label T cells in CT26 LTFs and then characterized the shift in metabolism following ICI treatment. Finally, we applied the Cybrid platform to human biopsies treated with ICI and characterized the cytotoxicity and shifts in T cell metabolism in living tissue. These data show that the Cybrid platform can measure changes in T cell metabolism and T cell cytotoxicity in response to ICI in 3D living tissue.
Conclusions  The methods presented herein will advance the field of cancer diagnostics by progressing from fixed tissue imaging and genetic characterization to the assessment of clinically relevant ICI-treated biopsies. Understanding the response of biopsies to immunotherapies will allow clinicians to make more informed treatment decisions and improve the lives of those with cancer.
Citation Format: Jonathan Ouellette, Janey Degnan, Anna Kellner, Evan Flietner, Lindsay Doebert, Zachary Swider, Eric Wait, Victoria Pope, Laura Hrycyniak, Sean Caenepeel, Kevin Eliceiri, T S. Ramasubramanian, Michael J. Korrer. Assessing cytotoxic T cell responses to immune checkpoint inhibitors in murine and human tumor samples using metabolic imaging [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2024; Part 1 (Regular Abstracts); 2024 Apr 5-10; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2024;84(6_Suppl):Abstract nr 6444.