Suspension culture promoted the expansion of NK-92 cells ex vivo by enhancing the expression of IL-2 receptor.

Vigorous ex vivo expansion of NK-92 cells is a pivotal step for clinical adoptive immunotherapy. Interleukin-2 (IL-2) is identified as a key cytokine for NK-92 cells, and it can stimulate cell proliferation after binding to the IL-2 receptor (IL-2R). In this work, the differences in IL-2 consumption and IL-2R expression were investigated between the two culture modes. The results showed that suspension culture favored ex vivo expansion of NK-92 cells compared with static culture. The specific consumption rate of IL-2 in suspension culture was significantly higher than that in static culture. It was further found that the mRNA levels of the two IL-2R subunits remained unchanged in suspension culture, but the proportion of NK-92 cells expressing IL-2Rβ was increased, and the fluorescence intensity of IL-2Rβ was remarkably enhanced. Meanwhile, the proportion of cells expressing IL-2R receptor complex also increased significantly. Correspondingly, the phosphorylation of STAT5, a pivotal protein in the downstream signaling pathway of IL-2, was up-regulated. Notably, the expression level and colocalization coefficient of related endosomes during IL-2/IL-2R complex endocytosis were markedly elevated, suggesting the enhancement of IL-2 endocytosis. Taken together, these results implied that more IL-2 was needed to support cell growth in suspension culture. Therefore, the culture process was optimized from the perspective of cytokine utilization to further improve the NK-92 cell's expansion ability and function. This study provides valuable insight into the efficient ex vivo expansion of NK-92 cells.