Natural killer cells. In vitro and in vivo.

A nonadherent, nonphagocytic mouse cell found in lymphoid organelles, but lacking characteristic surface markers of mature lymphocytes, is capable of lysing a wide spectrum of tumor cells but shows little cytolytic activity toward normal cells. This cytotoxic cell, termed a "natural killer" (NK) cell, shows a marked capacity to lyse lymphomas (syngeneic, allogeneic, or even xenogeneic) to the effector cell source. Its activity is inhibited by a variety of pharmacologic agents, eg, cytochalasins, cAMP-"active" drugs, and colchicine, over the same dose range at which these drugs inhibit other cytotoxic cells. We have no evidence that NK cell "specificities" are clonally distributed. Two sets of evidence are presented which suggest that the same NK cell population is responsible for lysing a variety of tumor target cells. Preliminary evidence suggests that modulation of NK cell levels in vivo is correlated with resistance to challenge with a syngeneic tumor, inferring that NK cells may play a salient role in host defenses against neoplasia.