Leukemia cells are targets for NK cell alloreactivity. NK cell clones which lysed allogeneic PHA lymphoblasts or BLCLs from leukemia patients () were tested for their ability to lyse pretransplant crypreserved leukemic cells from the same individuals (▪), (□ shows autologous targets). CML, AML, and ALL (calla⁺) cells were used as targets (E:T ratio = 10:1). The alloreactive NK clones killed all the CML and AML targets (top panel). Only a minority of the ALLs were killed (bottom left panel). None of 50 nonalloreactive NK clones killed any allogeneic leukemia (not shown). Bottom right panel: immunofluorescence analysis LFA-1 expression of allogeneic NK cell susceptible and resistant leukemic targets.