Cell-cell adhesion-independent killing due to lymphokine-activated killer cells against glioblastoma cell lines

Lymphokine-activated killer (LAK) cells can kill several tumor cells. Their killing activity is generally due to cell-cell adhesion. Cell-cell adhesion of the LAK cells to the target cells is essential for LAK lysis. In this report, however, we describe that the LAK cells can also kill the target cells by cell-cell adhesion-independent killing. Killing occurred after the target cells were exposed to the LAK cells. When the LAK cells were added to glioblastoma cell lines T98G and U373MG (which proliferate by adhering to the bottom of a culture flask), the LAK cells killed them by cell-cell adhesion killing within 4 h (early killing). On the other hand, when small numbers of the LAK cells were added, some of the target cells escaped from the early killing. At 4 and 6 h after the adding the LAK cells, when the LAK cells were discarded from the flask by washing with PBS, the escaped cells still adhered and were alive. However, they ultimately died over the next 24-96 h (late killing). The late killing was the cell-cell adhesion-independent killing, because it occurred after the LAK cells were removed. In this killing, numerous granules and vacuoles appeared in the cytoplasm of the cells. The vacuoles enlarged and then the cells died. The cell death was different from apoptosis, because the nucleus was intact until the late stage and no DNA fragment laddering in the degenerated cells was recognized. The vacuoles were stained with acid phosphatase and the cell death was inhibited with 3-methyladenine (an inhibitor of lysosome), suggesting that the late killing may be autophagic cell death due to activated lysosome. Induction of late killing in tumor cells using the LAK cells may become one approach for cancer therapy.