Sensitivity of human fetal hemopoietic cells to NK cell-mediated lysis

Hemopoietic cells from human fetal livers at 11 to 18 weeks of gestational age were studied as to whether they were sensitive to adult and autologous fetal NK cells. Cell line K562 was used as control target in the 51Cr release assay and in the cold target competition assay. Adult peripheral blood NK cells did not kill liver-derived hemopoietic cells of four fetuses tested. Neither did fetal liver cells, whether or not expressing spontaneous cytotoxicity against K562 cells, destroy autologous hemopoietic liver cells. Hemopoietic liver cells from six fetuses were studied in the cold target competition assay. Liver cells of two fetuses clearly competed with lysis of K562 cells by adult NK cells. Thymus cells from one 18 week-old fetus had a weak capacity to compete with lysis of K562 cells by adult cells, whereas cells from the spleen and liver of the same fetus did not. It is concluded that early fetal liver hemopoietic cells are not susceptible to lysis by NK cells but an interaction between fetal cells and NK effector cells results in a depressed NK cell activity against NK-sensitive target cells.