Figure 3. Maintenance of a memory-like phenotype after NK cell expansion.

Cytokine-activated or control treated congenic NK cells enriched from Rag1^−/− mice were adoptively transferred into Rag-2^−/− γ_c^−/− hosts. (A) Seven days after adoptive transfer, pre-activated NK cells were more likely to produce IFN-γ following a 4 hour in vitro stimulation with IL-12 + IL-15 as shown in a representative intracellular flow plot gating on NK1.1⁺ CD45.1⁺ control or CD45.1⁻ pre-activated NK cells. (B) Adoptively transferred cells were re-stimulated in vitro with IL-12 + IL-15 (black bars) or cultured with media alone (grey bars). Pre-activated NK cells had a primed phenotype with very high IFN-γ production 1d after adoptive transfer and spontaneous production of low levels of IFN-γ. By 7d, pre-activated NK cells exhibited a memory-like phenotype and were more likely to produce IFN-γ than control cells. Results represent the mean +/− SEM of 3-5 independent experiments. *p=0.01; **p=0.007.