Fig. 4.

Target-cell killing is mediated via interaction of the chimeric scFv(Leu-16)-ζ antigen receptor with CD20. a Surface expression of human CD20 on NIH3T3 murine fibroblasts stably transfected with a CD20 cDNA construct (NIH3T3-CD20 cells) was determined by flow cytometry using CD20-specific Mab L27 and a secondary PE-labeled antibody. Parental NIH3T3 cells served as a control. b Cytotoxic activity of NK-92 and NK-92-scFv(Leu-16)-ζ toward CD20 expressing NIH3T3-CD20 and CD20-negative NIH3T3 cells at the indicated effector to target ratios was analyzed in a 3 h MTT cytotoxicity assay as described in the methods section. The relative number of viable target cells is expressed in % of untreated controls (set to 100%). Mean values of triplicate samples are shown. The standard deviation is indicated by error bars. c Cytotoxic activity of NK-92 and NK-92-scFv(Leu-16)-ζ toward NIH3T3-CD20 cells was also investigated by microscopical analysis after 16 h. Control cells were incubated in the absence of NK cells, or were treated with 8 μM of the apoptosis-inducing drug staurosporine as indicated. Representative fields are shown