Beneficial effect of short-term exposure of human NK cells to IL15/IL12 and IL15/IL18 on cell apoptosis and function.

Monokines IL12, IL15, and IL18 have been shown to activate NK cell function, however with high apoptosis induced by their combination within 48 h. Here, we demonstrate for the first time that CD56+ cells incubated for only 18 h with the combination of IL15/IL12 or IL15/IL18, then washed, and further cultured in plain medium, exhibit low levels of apoptosis. These shortly activated CD56+ cells show high killer activity against NK- and LAK-sensitive tumor targets that persists over a culture period of 18 days after two additional 6 h cycles of exposure to the monokines applied every 8 days and also retain their ability for high cytokine production during each exposure. Moreover, these repetitive short-term exposures of CD56+ cells to the monokine combinations result in long-lived CD56+ cells with slower rates of FcgammaRIII receptor (CD16) decline, therefore exhibiting higher antibody depended cytotoxicity, as opposed to the continuous incubation with the monokine combinations. In conclusion, short-term exposure of CD56+ cells to IL15/IL12 or IL15/IL18 at 8-day intervals may hold a promise for improved clinical results in cellular adoptive cancer immunotherapy and for the in vivo injections of the monokines.