Characterization of interleukin-15 gene-modified human natural killer cells: implications for adoptive cellular immunotherapy.

BACKGROUND AND OBJECTIVES Natural killer (NK)-92 cells are effective against a broad range of malignant targets both in vitro and in vivo. Interleukin-15 (IL-15) is an important cytokine for NK cell development and differentiation. IL-15 gene-modified NK-92 cells need to be characterized and their clinical implications investigated. DESIGN AND METHODS IL-15 cDNA was inserted into a pcDNA3 eukaryotic expression vector and the recombinant vector (pcDNA3-IL15) was tranfected into NK-92 cells. The IL-15 gene-modified NK-92 cells (NK92-IL15) were cloned and characterized with regard to their cytokine production, proliferation, cytotoxicity and surface phenotype. RESULTS NK92-IL15 cells continuously produced a high level of IL-15 in culture supernatant, which made the cells proliferate significantly more rapidly in response to stimulation with low doses of IL-2 or IL-15; the cumulative number of cells in long-term culture was also significantly higher. NK92-IL15 cells became adherent to plastic and their expression of CD54 increased, which may explain their improved proliferating potential, like adherent NK cells. NK92-IL15 cells were more strongly cytotox against a broad range of target tumor cells than the parent NK-92 cells, and this increased cytotoxicity was correlated to the increased expression of cytotoxic effector molecules, such as perforin, Fas ligand and IFNgamma, and up- or down-regulated expression of activating or inhibitory NK cell receptors (NKG2D or NKG2A/CD94). INTERPRETATION AND CONCLUSIONS These results demonstrate that NK92-IL15 cells are promising for adoptive cellular immunotherapy.