In vitro generation of NK-like activity in human PBL co-cultured with fresh T leukaemia cells.

Generation of cytotoxic activity attributable to natural killer (NK)-like effector cells, against the NK-sensitive erythroleukaemia cell line K562 was estimated in peripheral blood lymphocytes (PBL) from normal donors, following stimulation with fresh leukaemic cells (FLC) of T-origin. One of 9 FLC induced anti-K562 cytotoxicity which was considerably higher than that of unstimulated control PBL. Cells derived from this patient possessed acid phosphatase (AP) and TdT activity. The reacted with the monoclonal antibodies RFA1 (directed against early and mature T cells) and A10 (specific for lymphohaemopoietic precursors). However, the cells did not form E rosettes, nor did they react with the monoclonal antibodies OKT3, OKT4, OKT8 and OKT11 to human T cell surface antigens. OKT6, which recognizes 70% of thymic lymphocytes was also negative. The high stimulatory activity of these cells may be related to the expression of surface determinants characteristic of early stages of the T-cell pathway, detected only by the monoclonal antibody RFA1.