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. 2023 Mar 5;13(5):1506–1519. doi: 10.7150/thno.79942

Figure 3.

Figure 3

In vitro proliferation and expansion of NK cells by MBP IL-2 engineering and the IL-2 signal transmission in a cis-acting mechanism. (A) Proliferation of NK-92 cells (gray color) and MBP NK cells (red color) in the presence or absence of IL-2 were investigated by an MTS assay. Means ± SDs of triplicate determinations are shown. (B) Viability of the parental and the MBP NK cells over time in the absence of IL-2 supplement in growth medium. The MBP NK cells were continuously maintained, with approximately 70% viability. (C) Expansion of parental NK-92 and MBP NK cells without exogenous IL-2 addition. While the parental NK-92 cells did not proliferate and exhibited a reduced cell number, the MBP NK cells proliferated appropriately, with an estimated doubling time of 42 hours. (D) Evaluation of the autocrine effect of MBP IL-2 engineering. IL-2 signal reporter HEK cells were purchased from InvivoGen (# hkb-il2) to monitor the activation of the JAK-STAT pathway induced by IL-2. The level of secreted embryonic alkaline phosphatase (SEAP) from reporter HEK cells did not increase proportionally even when the proportion of cocultured MBP NK cells was increased, which confirmed that the MBP IL-2 on the MBP NK cells mainly acts in a cis manner dominantly.