Soluble Fas variants block apoptosis of leukemic LGLs.

(A) PBMCs from a patient with LGL leukemia were stimulated with PHA and IL-2, then incubated with CH11 in the presence or absence of 40% concentration of supernatant harvested from COS cells transfected with control construct, pcDNA3.1, full-length Fas cDNA, or various Fas mutants. The concentration of soluble Fas in these supernatants is indicated as measured using soluble Fas ELISA. (B) The activated PBMCs from the same patient with LGL leukemia were incubated with CH11 in the presence of serial dilutions of supernatant obtained from COS cells transfected with the Exo4,6Del Fas mutant. The concentration of soluble Fas in this dilution series is indicated. The percentages of apoptotic cells are indicated at the left upper corner. Similar data were obtained in experiments using PBMCs from 3 other patients with LGL leukemia.