Novel approaches to 3D cancer heterospheroid culture and assay development for immunotherapy screening

Advanced 3D heterospheroids, composed of cancer, fibroblast, and immune cells, serve as more physiologically relevant models for anticancer drug screening and immunotherapy research compared to traditional 2D cultures. This study aimed to optimize the culturing, dissociation, and analysis of heterospheroids, addressing limitations that restrict their broader use in immunotherapy research. Our study revealed significant effects of Human Plasma-Like culture medium on cell viability, necrotic core formation, and the spatial organization of cancer and fibroblast cells within heterospheroids compared to DMEM and RPMI media. In HT-29 heterospheroids, cell viability decreased from 75 % in DMEM to 20 % in HPLM, which was accompanied by increased necrotic core formation and elevated PD-L1 expression. TrypLE™ effectively dissociated heterospheroids but compromised immune cell viability and surface marker detection. In comparison, Accutase™ significantly reduced cell yield, while collagenase I preserved immune cell markers but affected those on cancer cells. Furthermore, we developed a luciferase-based assay to measure immune-mediated cancer cell killing in heterospheroids, excluding signals from non-target cells, such as dying fibroblasts and immune cells, without requiring spheroid lysis or dissociation. Our findings highlight the importance of tailoring experimental conditions to reflect specific tumor characteristics, thus enhancing the utility of heterospheroids in drug discovery and immunotherapy research.