Effects of ifosfamide on immunocompetent effector cells.

We analyzed the effects of ifosfamide, a chemotherapeutic agent that is broadly used within anticancer therapy, on immunocompetent effector cell subpopulations. For our in vitro studies we used 4-hydroperoxyifosfamide (4-OOH-IF), which rapidly gives rise to 4-OH-IF, the activated form of ifosfamide. Activated cytotoxic T lymphocytes and natural killer (NK) cells were used because of their antitumor activity and their antiviral or antibacterial activity. Our study demonstrated three major findings. (1) The capacity of cytotoxic T cells to lyse their specific target cells was substantially reduced by 4-OH-IF treatment. This inhibition of the lytic activity could be correlated with a substantial depletion of the intracellular glutathione (GSH) levels. A rapid reconstitution of the depleted GSH levels and of the cytotoxic activity was achieved by incubation of the T cells with thiols such as mercaptoethanesulfonate (mesna). (2) In contrast to T cells the lytic activity of NK cells was not substantially affected by 4-OH-IF treatment; this increased resistance of NK cells against 4-OH-IF treatment could be explained by their higher initial GSH levels and by their higher rate of GSH synthesis. Furthermore, we demonstrated that (3) NK cells, but not T cells, have the capacity to take up cystine, the oxidized form of cysteine, from the medium. In conclusion we can state that NK cells are much more resistant to ifosfamide treatment compared to T cells with respect to intracellular GSH levels and cytotoxic activity.