Identification of distinct target-specific subsets of NK cells in peripheral blood of normal donors

One major issue in studies on natural killer activities centers around the concept of heterogeneity of effector cells in the NK population. In this study Ficoll-Hypaque fractionated PBL from normal adult donors were used as effectors against a variety of tumor targets in in vitro chromium release assays with the goal of substantiation of the existence of NK subsets. Effectors with common or distinct specificities were demonstrated by the cold target inhibition assays as well as by immunoadsorption studies using tumor cell monolayers. In particular, a distinct subset of NK effectors, with the unique ability of killing a myeloma cell line (FRV), hitherto an NK-resistant tumor target, was demonstrated with the PBL of one normal donor (LP). Separation of this unique subpopulation based on differential light scatter property was achieved using flow cytometry (FACS III). The unique FRV killers were larger than the effectors which lyse K562 and they resemble the activated NK cells in the mouse system.