Definition of Early Progenitors and Functional Maturation of Human Natural Killer Cells: Requirements for Cytocidal Activity

We examined the in vitro development of human natural killer (NK) cells to define the earliest hematopoietic progenitors which could give rise to NK cells. Our data indicates that NK cells arise from the Thy 1+ subpopulations of CD34+ marrow cells. In cultures with IL2 we generated up to 96.5% NK cells from CD34+ Thy 1+ and in cultures with IL7, cells bearing NK cell surface markers were also observed but were devoid of functional activity. We also addressed the functional integrity of these cultured cells by examining the appearance of granzyme A, serine esterase, Met-ase and perforin and correlating these with lytic activity. Granzyme A mRNA could be detected in IL-2-cultured cells and serine esterase activity as well as perforin were also found at the single cell level. Human Met-ase (Hu-Met-1) was not detected at any time of analysis. Granzyme expression occurs early in cells cultured with IL2 but its presence did not correlate with lytic function; CD56+ cells grown in the presence of IL7 express these enzymes and perforin after longer periods of culture, but lack the ability to lyse NK targets.