In vitro antitumor effect of LAK cells and alpha interferon in combination on tumor cell lines.

In vitro antitumor effects of LAK cells and alpha-2b-Interferon (IFN) either alone or in combination were evaluated on NK resistant (K562) and NK sensitive (Namalwa, Raji) cell lines. Tumor cells were incubated with LAK cells for 4, 8 and 24 hours at a LAK: tumor cell ratio of 1:1, 10:1, 100:1, or with IFN for 48 and 96 h at the concentrations of 100, 1000, 10,000, 100,000 IU/ml. A clonogenic assay was utilised to enumerate residual cells after in vitro treatment. A positive correlation was found between tumor cell killing and effector: target ratio, IFN of 100:1 incubated for 4 h, and 100 IU/ml of IFN incubated for 48 h were further chosen. A synergistic effect was found when IFN was incubated before LAK cells or contemporarily, but not when IFN was incubated after LAK cells. These findings demonstrate that an additive or a synergistic effect in vitro can be obtained by adding the two agents in different sequences and suggest that a potential utility of LAK cells and IFN in vivo should be tested in clinical trials.