Fas receptor-Fas ligand system is independent of both CD34 status and chemosensitivity in acute myeloid leukemia

Abstract

Objective To determine whether the Fas receptor-Fas ligand (FasR-FasL) system, which triggers apoptosis in sensitive cells, is an important mechanism of cytotoxicity in acute myeloblastic leukemia (AML). Materials and Methods We investigated FasR expression in primary AML cells and its upregulation by tumor necrosis factor (TNF), as well as the apoptosis induced by anti-Fas antibody and the potential interaction between the FasR-FasL system and the cytotoxic drug daunorubicin (DNR). Results FasR was expressed on all 25 AML samples and three normal bone marrow harvests. The intensity of expression was variable (range 1.6–2.1 in normal bone marrow CD34 + cells and 1.5–5.1 in AML cells, median 2.4) and was related to the morphologic FAB classification, with the highest expression in FAB types M4 and M5 (range 1.6–5.1, median 3.2). No relationship was found between FasR expression and expression of the CD34 antigen. FasR was heterogeneously upregulated in all AML cells on treatment with TNF-α. The degree of FasR upregulation induced was found to be related to the FAB subtype, with the greatest response observed in immature FAB types M1, M2, and M6 (range 11.0–207.1%, median 48.7%). Apoptosis could be induced in all AML samples, but not in normal bone marrow CD34 + ve cells, by the CH11 anti-FasR antibody, although the response was variable (range 4.1–37.6%, median 16.5%). The monocytic differentiated M4 and M5 AML cells exhibited the greatest sensitivity to Fas-mediated apoptosis (range 4.4–37.6, median 20.65%); however, no relationship was found between sensitivity to Fas-mediated apoptosis and FasR expression or CD34 positivity. Apoptosis in response to DNR was observed in all AML cases; however, sensitivity was heterogeneous and found to be unrelated to FasR expression or sensitivity to Fas-mediated apoptosis. The blocking anti-FasR antibody ZB4 blocked anti-FasR-mediated apoptosis but had no inhibitory effect on DNR-induced apoptosis in AML blasts. No cytotoxic synergistic effect was demonstrated when anti-FasR antibody was used in combination with DNR. Conclusion In AML, DNR induces apoptosis through an Fas-independent pathway. However, the induction of apoptosis through the Fas pathway might be a novel and effective approach for leukemia immunotherapy, particularly because Fas-mediated apoptosis was noted in CD34 + and CD34 − cases.