Abstract 6378: An in vitro human CD8 T cell exhaustion model for the functional screening of immune checkpoint inhibitors
Authors: Carrio Roberto , Cucchetti Margot , Devonish Mikielia , Poisson Louis , Babiceanu Mihaela , Kettring Andrew , Liu Yingchun , Jackson Donald , Gomes Evan , Baudhuin Jeremy , Drake Donald R. , Fantin Valeria , Byers Anthony , Sassoon Ingrid 
Published: April 2023

Abstract
T cell exhaustion is a state of dysfunction that frequently occurs during chronic infections and cancer due to persistent antigen stimulation and inflammation. It is defined by poor effector function, sustained expression of inhibitory receptors, and a transcriptional state distinct from that of functional effector or memory T cells. In this state, cells remain in the local environment but lack effector functions necessary to combat the tumor or infection. In the current study, we developed an in vitro human antigen-specific CD8 T cell exhaustion model to evaluate the ability of immune checkpoint inhibitors to restore functionality to exhausted T cells. Using the fully human, autologous MIMIC (Modular IMmune In vitro Construct) effector CD8 T cell assay as a framework, we assessed the effect of antigen dose, timing, and frequency of repeated antigen stimulation with antiviral HLA Class I-restricted peptides to drive the development of Ag-specific CD8 T cells toward an exhausted state. Epitope-specific CD8 T cell responses were monitored by HLA class I-restricted pentamers and establishment of an exhausted profile was evaluated by increased expression of inhibitory co-stimulatory receptors and decreased intracellular expression of antiviral effector cytokine via flow cytometry relative to functional Ag-specific CD8 T cells from the same donor. Repeated antigen exposure led to decreased production of IFN-γ and TNF-α and increased expression of inhibitory co-stimulation markers on antigen-specific CD8 T cells. After establishment of an exhausted phenotype, treatment with various immune checkpoint inhibitor molecules restored functionality to Ag-specific CD8 T cells upon an additional antigen re-stimulation. Moreover, here using this model we characterized distinct transcriptomic signatures of functional and exhausted MIMIC CD8 T cells. Development of an in vitro human viral antigen-specific CD8 T cell exhaustion model with characteristic features of dysfunctional CD8 T cells as observed in vivo and the ability to restore effector function by treatment with immune checkpoint inhibitors, provides a platform to assess the effectiveness of therapeutic mono-specific or bi-specific “checkpoint blockade” antibody candidates and, in general, the potential to evaluate a myriad of immunotherapeutic approaches for cancer treatment.
Citation Format: Roberto Carrio, Margot Cucchetti, Mikielia Devonish, Louis Poisson, Mihaela Babiceanu, Andrew Kettring, Yingchun Liu, Donald Jackson, Evan Gomes, Jeremy Baudhuin, Donald R. Drake, Valeria Fantin, Anthony Byers, Ingrid Sassoon. An in vitro human CD8 T cell exhaustion model for the functional screening of immune checkpoint inhibitors [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2023; Part 1 (Regular and Invited Abstracts); 2023 Apr 14-19; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2023;83(7_Suppl):Abstract nr 6378.