Figure 6. TYRO3-expressing K562 feeder cells expand NK cells with similar in vivo antitumor activity.

(A-C) Primary human NK cells were incubated with inactivated APC K562 cells or APC K562^Tyro3 cells in the presence of IL2 (50 IU/ml) for 7 days. Summary data from 3 different donors showing the expression of surface markers on NK cells expanded with APC K562 cells or APC K562^Tyro3 cells (A). Representative flow cytometry plots and summary data from 3 different donors showing the expression of CD107a on NK cells expanded with APC K562 cells or APC K562^Tyro3 cells for 4 h at an E/T ratio of 4:1 (B). NK cells expanded with APC K562 cells or APC K562^Tyro3 cells were co-cultured with ⁵¹Cr-labeled K562 cell line for 4 h, followed by quantification of specific K562 cell lysis. Data are summarized from 3 different donors (C). (D) Primary human NK cells were incubated with APC K562^Tyro3 or APC K562 cells in the presence of IL2 (50 IU/ml) for 4 days. Then cells were transduced with a retrovirus vector expressing soluble IL15 (sIL15) for 48 h. On day 6, transduced NK cells were stimulated with APC K562^Tyro3 cells or APC K562 cells in the presence of IL2 (50 IU/ml) for another 7 days prior to harvest and storage for following usage. On day 0, mice were injected with 1×10⁶ K562_Luc cells and then treated with 10×10⁶ sIL15 NK cells expanded with APC K562 (APC K562_sIL15 NK) or APC K562^Tyro3 (APC K562^Tyro3_sIL15 NK). On day 1, mice were treated with a 2nd dose of these NK cells. Bioluminescence imaging was performed on days 9 and 14. Five mice in each group. Two-way ANOVA was used for A. **, P<0.01; ***, P<0.001. Data are presented as mean ± SD.