Table 1.

Ex vivo cultivation of pure natural killer (NK) cells with cytokines only.

Protocol features	Starting material/culture system	NK cell expansion rate	NK cell purity	NK cell phenotype	NK cell function	Setting	Reference
IL-2 + IL-15	PBMC, CD3 depleted and CD56 enriched or PBMC, CD3/CD19 depleted in flasks	>1 (5 days)	75–100% NK ≤0.1% T cells	Upregulated: CD69, NKp30, and NKp44	Cytolysis of leukemia cell lines and primary acute leukemic blasts	In vitro	(51)
IL-2	PBMC, CD3 depleted, and CD56 enriched in bags and flasks	4–5 (12–14 days)	~92–95% NK <0.1% T cells	increased CD56+CD16− frequency; increased p-STAT3 and p-AKT; increased lytic activity, upregulation of CD69, NKG2D, and natural cytotoxicity receptors (NCRs); increasing amount of NK cells without killer cell immunoglobulin-likereceptors	Improved cytotoxic activity against leukemia and tumors	Clinical	(26, 52, 53)
IL-15	Isolated CD3−CD56+ cells	N/A (2–5 weeks)	94–99% NK	Enhanced killing via NCRs, DNAM-1 and NKG2D	Enhanced cytolysis of lymphoma and rhabdomyosarcoma cell lines via NCRs	In vitro	(54)
IL-2 + IL-21	PBMC, sorted for CD3−CD56+	None with IL-21 only; strongly with IL-2 + IL-21	N/A	Upregulated: CD69, CD25; activation of STAT3	Enhanced cytotoxicity against K562	In vitro	(55)
IL-12 + IL-15 + IL-18	PBMC, sorted for CD3−CD56+ cells PBMC, CD3 depleted and CD56 enriched	N/A (12–16 h)	≥90% NK	Upregulated: CD94, NKG2A, NKp30, NKp44, NKG2D, NKp46, CD69, and CD25 Downregulated: NKp80	Memory: increased IFN-γ production upon stimulation that is preserved during cell division Responsive to picomolar concentrations of IL-2	In vitro Clinical	(56–59)