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

Abstract

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.