Co-culture of natural killer cells and tumor spheroids on a heterogeneous multilayer paper stack.

Multilayer paper-based cell culture, as an in vitro three-dimensional (3D) cell culture method, has been frequently used to research drug bioavailability, therapeutic efficacy, and dose-limiting toxicity in malignant tumors. This paper proposes a heterogenous multilayer paper stacking co-culture system to establish a model of natural killer (NK) cells moving through the endothelium layer and attacking tumor spheroids. This system consists of three layers: a bottom tumor-spheroid layer, a middle invasion layer, and a top endothelium layer. NK-92 cells were placed in the supernatant on top of the three layers. After two days of co-culture, the attack of tumor spheroids by NK cells was observed. We additionally examined the infiltration of NK-92 cells within the tumor spheroids at different Z-axis depths using a confocal microscope, and the results suggested that the system successfully realizes NK cells traveling cross the endothelium layer to form tumor-infiltrating NK cells (TINKs). The potential application of multilayer paper for co-culture models involving cancer cells and immune cells holds great promise for exploring the interaction dynamics of these two cell types.