Autoreactive natural killer-like cells from agar-cloned murine bone marrow cells

Natural surveillance against malignant cells has been ascribed to so-called natural killer (NK) cells. These cells attack tumour cells without prior antigen stimulation and may also be cytotoxic to non-malignant cells. NK cells are routinely demonstrated by their cytotoxic activity against various types of tumour cell in vitro, but elucidation of the characteristics of the cytotoxic cells has hitherto been hampered by the lack of techniques by which NK cells can be isolated. Here we demonstrate murine NK-like activity from bone marrow cells cloned in semi-solid agar medium for granulocyte-macrophage colony formation. Data obtained indicate that such procedures considerably improve the possibility of obtaining quite pure NK cell populations by which the NK cell phenomenon may be studied in more detail.