OBJECTIVETo investigate the enhanced cytotoxicity against leukemia cells of natural Killer (NK) cells from cord blood (CB) after expansion in vitro.

METHODSNK cells was expanded on a layer of trophoblast cells with irradiated K562-mb15-41BBL cell line for 21 days. The levels of receptors on NK cells were detected by flow cytometry. Cytotoxicity of expanded NK cells against leukemia cells and specific ligand of immunoglobulin like(Ig- liKe)receptors were assessed using 51Cr released assay.

RESULTSThere were no differences of inhibitory receptors expression between fresh NK cells and expanded NK cells [CD158a:(16.77±11.65)% vs(14.37±11.12)%, P>0.05; CD158b: (42.48±18.11)% vs (40.92±19.02)%, P>0.05; NKG2A: (70.20±18.43)% vs (78.90±13.69)%, P>0.05], but higher activated receptors expression on expanded NK cells [NKp30: (54.10±13.27)% vs (4.14±2.05)%, P<0.05; NKp44: (72.10±17.30)% vs (0.52±1.16)%, P<0.05; NKp46: (80.63±14.01)% vs (44.19±6.19)%, P<0.05; NKG2D: (97.50±2.55)% vs (72.25±14.35)%, P<0.05]. Expanded NK cells showed higher cytotoxicity against leuKemia cell lines than fresh NK cells [K562: (74.3±3.6)% vs (55.3±4.2)%, P<0.05; Raji: (60.6±5.0)% vs (12.0±3.6)%, P<0.05]. CD158a⁻ CD158b⁻ NK cells had higher cytotoxicity on four types of target cells, but CD158a⁺CD158b⁻ CB-NK cell had lower cytotoxicity on 221-Cw4 and 221-Cw3Cw4 cells. CD158a⁻ CD158b⁺ CB- NK cells had lower cytotoxicity on 221-Cw3 and 221-Cw3Cw4, but CD158a⁺CD158b⁺ CB-NK cells had higher cytotoxicity on 721- 221 cells.

CONCLUSIONExpression of activated receptors of expanded NK cells were up-regulated, but no changes of inhibitory receptors. Expanded NK cells showed high cytotoxicity against leukemia cells and kept the specificity of ligand of Ig-like receptors, which could be beneficial to cell-therapy for tumor.