Gene expression in INTERLEUKIN-7 differentiated natural killer cells derived from CD34+lin− bone marrow cells

Human NK cells can be generated in vitro from CD34+Lin− bone marrow (BM) cells in long term cultures supplemented with stem cell factor (SCF or c-kit ligand), Interleukin-1α (IL-1α), Interleukin-2 (IL-2) or Interleukin-7 (IL-7). However, only IL-2 differentiated cells show cytotoxicity against the NK-sensitive K562 cell line. The cytotoxic activity defect seen in IL-7 differentiated NK cells could be due in part to the: a) lack of expression of adhesion molecules essential for the formation of the effector:target conjugates or/and b) lack of perforin and granzymes mRNA and enzymatic activity. In previous studies our results shown that these cells express low levels of the adhesion molecules CD11a and CD18 when compared with IL-2 differentiated NK cells. The addition for one week of IL-2 or Interleukin-15 (IL-15) to IL-7 differentiated NK cells induced an increase in the expression of CD11a and CD18 to similar levels seen in IL-2 differentiated NK cells. This increase seems to be related with their increase inthe cytolytic activity suggesting that these cell surface markers are important for cell killing. NK cells have cytotoxic granules containing effector molecules like perforin and granzymes which are able to trigger pathways leading to DNA fragmentation and apoptosis on target cells. IL-7 differentiated NK cells express perforin and Granzyme A (GA) mRNA but not Hu-Met-1mRNA. We also detected by RT-PCR the expression of Granzyme B (GB) and Granzyme H (GH) mRNA in these cells. These results suggest that the defect seen in the cytotoxic activity in not due to lack of perforin or granzyme mRNA expression.