A Real-Time Image-Based Co-Culture Assay to Quantify Tumor-Infiltrating Lymphocyte-Mediated Apoptotic Killing of Patient-Derived Tumor Organoids

Understanding the functional capacity of tumor-infiltrating lymphocytes (TILs) to recognize and eliminate autologous tumor cells is central to advancing personalized immunotherapy. The goal of this method is to provide an image-based, live-cell imaging protocol that measures TIL-mediated, caspase-3-dependent apoptotic killing against patient-derived tumor organoids (PDTOs) in real time. This method integrates established procedures for isolation and expansion of PDTOs and TILs with a standardized three-dimensional co-culture system and automated fluorescence-based apoptosis detection. Tumor organoids are plated in imaging-compatible 96-well plates and labeled with a red tumor marker, while expanded TILs are added at defined effector-to-target ratios in the presence of a caspase-3 activated green fluorescent substrate. Co-cultures are imaged every 4 h using a live-cell analysis system to capture phase-contrast and dual-fluorescence channels. Quantitative image analysis identifies red-positive tumor structures and calculates the proportion of red/green double-positive apoptotic tumor objects over time. Appropriate technical and biological replicates are incorporated, along with baseline, spontaneous apoptosis, negative and positive killing controls to ensure assay rigor. By preserving tumor heterogeneity within the PDTOs' three-dimensional architecture while enabling longitudinal quantification, this protocol provides a physiologically relevant system for functionally profiling patient-specific tumor-TIL interactions and investigating immunomodulatory agents that augment anti-tumor immunity.