In vivo augmentation of natural killer cell activity with a deoxyribonucleic acid fraction of BCG.

A fraction extracted from BCG and designated MY-1, which was composed of 70.0% DNA and 28.0% RNA, was previously reported to possess strong antitumor activities against various syngeneic mouse and guinea pig tumors. An intraperitoneal injection of MY-1 (100 micrograms) 1 day before rendered mouse peritoneal cells cytotoxic to YAC-1 cells. The effector cells were nonadherent to plastic dishes, and the activity was destroyed by treatment with anti-asialo GM1 antiserum plus complement or carrageenan in vitro, but not with carbonyl-iron or anti-Thy 1.2, suggesting that the cells are natural killer (NK) cells. In vivo augmentation of NK activity was dependent on MY-1 dose, and reached the peak 1 day after MY-1 injection. Since NK activity in lipopolysaccharide (LPS)-nonresponder mice could be augmented by MY-1, the possibility that LPS contaminated the MY-1-augmented NK was excluded. MY-1 digested preliminarily with DNase lost its NK-inducing activity, suggesting that the DNA entity of MY-1 was essential for the activity. When mice were pretreated with anti-asialo GM1 or carrageenan, MY-1 could not render the peritoneal cells cytotoxic. Antitumor activities of MY-1 were also abolished if the animals were pretreated with anti-asialo GM1 antiserum or carrageenan, suggesting that the activities can be ascribed mainly to activated NK cells.