Enhancing Effect of Pokeweed Mitogen on the Proliferation and the Cytotoxicity of Lymphokine‐activated Killer Cells

In order to obtain more potent lymphokine‐activated killer (LAK) cells for use in adoptive immunotherapy, pokeweed mitogen (PWM) was added to the culture medium for the initial 24–48 h of culturing. The proliferation rate of PWM‐stimulated LAK cells reached about 1000‐fold after 3‐week culture. This rate was nearly the same as that of LAK cells stimulated by 10 ng/ml of OKT3, the mouse anti‐CD3 monoclonal antibody. However, the cytotoxicity of PWM‐stimulated LAK cells was significantly more potent than that of OKT3‐stimulated LAK cells. Phenotypic analysis revealed that PWM‐stimulated LAK cells were CD3(+)CD56(+)‐dominant while OKT3‐stimulated LAK cells were CD3(+)CD56(‐)‐dominant. About half of CD3+CD56+ PWM‐stimulated LAK cells was CD8(+). These results suggest that more efficient adoptive immunotherapy is possible by using high‐dose PWM‐stimulated LAK cells with more potent cytotoxicity. Interleukin‐1β and tumor necrosis factor a were significantly increased in the culture media after 24‐h incubation with 1 μg/ml of PWM. Secretion of interferon‐γ was not enhanced by this concentration of PWM within 24 h. Therefore, PWM is considered to activate monocytes or macrophages to produce these cytokines in advance, influencing the proliferation and the cytotoxicity of LAK cells.