Cord Blood–Derived and Peripheral Blood–Derived Cytokine-Induced Killer Cells Are Sensitive to Fas-Mediated Apoptosis

Fas-mediated apoptosis is one of the mechanisms used by tumor cells to escape the cytotoxicity of tumor-infiltrating lymphocytes. It has been suggested that cytokine-induced killer (CIK) cells are resistant to Fas-mediated apoptosis, thereby rendering them more attractive for use in cellular immunotherapy. Unlike what was observed by others, here we show that CIK cells are sensitive to Fas-mediated apoptosis. We have observed an increase in Fas expression in the different CIK cell subpopulations (CD3+CD56−, CD3+CD56+, and CD3−CD56+) isolated from both cord blood (CB) and peripheral blood (PB). We also show that the bulk, as well as the CD3+CD56− and CD56+ CB- and PB-CIK cell subpopulations were sensitive to Fas-mediated apoptosis induced by both CH11 and APO-1 antibodies, albeit with a weaker effect for the CH11 antibody on CB-CIK cells. In addition, in the presence of the APO-1 and CH11 inducers, Fas engagement inhibited the cytotoxic activity of CB- and PB-CIK cells. This new contradictory result may help explain the variable efficacy observed with CIK cells in the clinic.