Establishment of a novel overlay culture method that enables immune response assessment using gastric cancer organoids.

Organoid technology, a novel 3D cell culture system, can reproduce a patient's cancer and may be a novel immunotherapy experimental model. However, currently no gastric cancer organoid (GCO) models in which the organoid and immune cells are in free contact and sufficiently react with each other exist. In this study, we aimed to create a coculture model in which immune cells can move freely and stay in contact with GCOs. We coated the bottom surface of the plate with Matrigel and adhered stem cells to the Matrigel surface, instead of completely embedding them in Matrigel to culture organoids. This method allowed GCOs to grow on the Matrigel surface while maintaining a three-dimensional structure and reproducing the characteristics of the patient's cancer. We cocultured GCOs and immune cells. Using this model, immune cells could freely move and were in sufficient contact with the cultured GCOs. Our model allowed real-time observation of the immune response and tumor destruction with time. In addition, the GCO killing assay was assessed with natural killer cells from the same patient. This organoid culture model enabled repeated evaluation of the GCO killing assay with various immune cells . We established a new experimental model that allowed free movement of immune cells and sufficient contact with GCOs. Using this model, it may be possible to predict the effects of immune checkpoint inhibitors (using GCOs) before administering them to patients.