Natural killer cells are potentially promising candidates for cancer cellular therapy and have been exploited in clinical trials for more than 20 years.However, overall success rotes were low and did not match expectations.Likely reasons are under-representation of NK cells in the graft (10% in lymphokine activated killer (LAK) cell grafts) and inefficient cytolytic potency of the NK effector cells.Novel approaches are warranted to overcome such limitations.More recently, application of a highly cytotoxic NK cell line, NK-92, was tested in clinical trials demonstrating safety for the procedure.Similarly, another highly cytotoxic NK cell line, KHYG-1, which expresses the glycoprotein CD8 α/α, could be a candidate for adoptive immunotherapy (AIT).However, application of primary NK cells instead of transformed cell lines would be preferable.Our laboratory studies cytolytic potential and mechanisms of action of long term IL-2 stimulated NK cells (CD56+CD3-) that express the CD8 marker as potential novel AIT candidates.