Preactivation of human NK cells of reconstituted NSG mice in vivo. Splenocytes of untreated or poly I:C [p(I:C)]-injected reconstituted NSG mice were restimulated ex vivo with medium alone or the monokines IL-12 and IL-15, or K562 cells, or CEM cells. Both degranulation (B) and cytokine production (IFN-γ; A,C) were evaluated. One representative of 2 experiments (A) and composite data (B) from 8 mice are shown. CFSE-labeled LCL721.221 (HLA class I negative) and LCL721.45 (HLA class I positive) cells were injected intravenously into untreated or poly I:C–preactiveted hu-NSG mice. Twelve hours later, the composition of CFSE-labeled cells in the recipient spleens was analyzed by w6/32 (anti–HLA class I) staining. Analysis of HLA class I expression and CFSE prior to adoptive transfer (D) and after recovery after gating on CFSE⁺ cells (E). One representative of 3 experiments is shown. Numbers in plots represent frequencies within gates or marker regions.