Abstract 124: Autocrine signaling extends PD-L1 expression in NSCLC following an active immune response

Abstract Checkpoint inhibitors disrupting the PD-1/PD-L1 axis are used in multiple cancer subtypes. However, not all patients respond, and predictive biomarkers are needed to better stratify patients. PD-L1, the most studied biomarker, has given mixed results. The complexity of the immune response and plastic nature of PD-L1 expression on tumor and immune cells contributes to the heterogeneity of success. Not all malignant epithelial cells express PD-L1: some express it only when the correct signal is present, while others have constitutive expression. Additionally, the PD-L1 protein has multiple functions outside immune regulation, making its dynamics difficult to predict. In this study, we investigate these complex PD-L1 dynamics through a unique combination of in vitro studies and mathematical modeling simulations. IFN-γ, a pleotropic cytokine released by activated immune cells, induces PD-L1 expression in some tumor cells. Chronic IFN-γ results in long-term PD-L1 expression. However, relaxation dynamics following removal of IFN-γ remains unexplored. We show that PD-L1 relaxation depends on autocrine signaling, demonstrated by multiple in vitro assays seeded with varying population densities. Following 48h IFN-γ treatment, sub-confluent tumor cell populations demonstrated increased duration of PD-L1 expression, linking cell density to PD-L1 expression. Conditioned-media from A549 cells previously treated with IFN-γ induced PD-L1 on IFN-γ naïve tumor cell populations, indicative of autocrine signaling not previously identified. To reinforce our in vitro findings, we develop a hybrid agent-based model (ABM) to study PD-L1 dynamics. Tumor cells have variable PD-L1 expression and IFN-γ is modeled via reaction-diffusion. IFN-γ triggers tumor cells to secrete a diffusible factor that promotes PD-L1 expression. Initial fits of the ABM capture in vitro data dynamics for different conditions. In this ongoing project, we plan to identify the underlying mechanism responsible for extended PD-L1 expression in NSCLC cells, including investigation into specific molecular pathways. Identifying the cause for this phenomenon could help clinicians improve targeted therapy and introduce a potential avenue to enhance treatment in patients responsive to checkpoint inhibitors. Citation Format: Taylor M. Bursell, Sandhya Prabhakaran, Kimberly Luddy, Julian Pineriro, Rafael Bravo, Jeffrey West, Mark Robertson-Tessi, Aner Beg, Jhanelle Gray, Scott Antonia, Robert Gatenby, Alexander Anderson. Autocrine signaling extends PD-L1 expression in NSCLC following an active immune response [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 124.