Lipid A OM-174 increases the natural killer activity of peripheral blood cells from breast cancer patients

Natural killer (NK) cells have been implicated in immune surveillance again st tumors, but their activity is often impaired in cancer patients. Lipopol ysaccharides (LPSs) are known to enhance NK activity, but their toxicity pr events their use in humans. OM-174, a purified 3,3'-O-deacylated Escherichi a coli lipid A, is able to cure established tumors in the rat with little t oxicity. We tested the ability of OM-174 to stimulate in vitro the lytic po tential of peripheral blood cells from patients with non-metastatic breast tumor (n = 48). After 24 h pre-incubation of nylon-non-adherent cells with OM-174, increased antitumor activity was observed toward the NK-sensitive t arget cells K562 but not the lymphokine-activated killer (LAK)-sensitive ta rget cells Daudi. Both NK cells and a non-NK population are involved in thi s cytotoxicity. So, although the basal NK activity of blood cells was lower in tumor-bearing patients than in healthy donors, OM-174 may increase thei r toxicity toward cancer cells.