The activity of a number of therapeutic antibodies is mediated in part by antibody-dependent cell-mediated cytotoxicity (ADCC). An engineered effector cell line expressing the low affinity Fc receptor, FcγR111a (CD16), that responds to ligation of the Fc moiety of antibody bound to the specific antigen expressed on target cells by activation of a NFAT responsive reporter gene is described. In this cell line the firefly luciferase (FL) reporter gene is regulated by a novel synthetic chimeric promoter containing binding sites for NF-AT, AP1, NFkB, and STAT5 that confers improved sensitivity, an improved dynamic range, an improved tolerance to human serum and a reduced incubation time, relative to engineered effector cell lines that express a NFAT regulated reporter-gene, when used in an ADCC assay together with engineered target cells. The target cells have been engineered to over-express a constant high level of the specific antigen recognized by the therapeutic antibody, and homologous control cells have been developed in which the gene encoding the specific drug target has been invalidated by genomic editing. Target cells that have been engineered to over-express a constant level of CD20 together with homologous control cell line, in which the gene encoding CD20 has been invalidated, have been used to quantify the ADCC activity of Rituxan with a high degree of precision and with minimal interference from human serum.