Generation of a cloned NK cell line derived from the "null cell" fraction of human peripheral blood.

The present studies were designed to determine the conditions for generation of human NK clones. First the "null cell" (NC) fraction of human peripheral blood mononuclear cells, which contains the NK effectors, was purified using negative selection with anti-T3, anti-T8, anti-B1, and anti-Mo2 monoclonal antibodies. Subsequently, NC were cloned by limiting dilution using a combination of phytohemagglutinin (PHA) and lymphocyte-conditioned medium (LCM) as an initial stimulus. Colonies could be easily obtained with this procedure, but the maintenance of long-term growth of the cultures represented a major problem. A cloned cell line termed JT1 was generated and has been proliferating continuously in culture for more than 6 mo. The phenotype of JT1 cells was analyzed several times with a series of monoclonal antibodies. These cells did not express surface markers related to thymic (T3-, T4-, T8-, T11-), B cells (B1-, J5-), or myelomonocytic (Mo1-, Mo2-, MY7-) differentiation. In contrast, 95% of JT1 cells reacted with the anti-T10 monoclonal antibody. T9, Ia, and J2 antigens were also present on JT1 cells, but their expression appeared variable from one determination to another. This cloned cell line maintains a strong cytotoxicity against common NK targets, such as K562 and Molt 4 cell lines, and a moderate ADCC activity. In addition, after several months in culture, JT1 cells are still capable of being regulated by interferon, because this lymphokine rapidly enhances cytotoxicity against K562 cells.