Abstract
Three-dimensional multicellular tumor spheroids are invaluable due to their ability to recapitulate major physiological characteristics of solid tumors. The lack of appropriate in vitro models to evaluate the effects of PD-1 blockade has restricted use of PD-1 inhibitors. Here, we established spheroids from a human gastric cell line to evaluate the cytotoxicity of the PD-1 blockade. Mature spheroids were formed 72 h after seeding tumor cells into ultra-low attachment microplates. We induced PD-L1 expression of spheroids using IFN-γ and TNF-α. Confocal images showed that PD-1 blockade enhanced T-cell cytotoxicity against PD-L1-expressing spheroids. Mechanistic studies revealed that PD-1 blockade increased expression of multiple chemokines. Altogether, our study demonstrates that tumor spheroids provide a novel platform to evaluate the effects of PD-1 blockade and might be further utilized to develop promising combination therapies.