Constitutive expression levels of CD95 and Bcl‐2 as well as CD95 function and spontaneous apoptosis in vitro do not predict the response to induction chemotherapy and relapse rate in childhood acute lymphoblastic leukaemia

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Abstract
CD95 (Fas/APO‐1) expression and function and Bcl‐2 expression, as well as spontaneous apoptosis in vitro, have been shown to be predictive markers for the in vivo response to chemotherapy in acute myeloid leukaemia (AML). To determine the clinical significance of apoptosis‐regulating factors in acute lymphoblastic leukaemia (ALL), we investigated cell samples of children with ALL who had been included in the German ALL Berlin–Frankfurt–Münster (BFM) study using flow cytometry for constitutive expression levels of CD95 (n = 110) and Bcl‐2 (n = 110). Furthermore, we determined the extent of spontaneous apoptosis in vitro (n = 102) and susceptibility to anti‐CD95‐induced apoptosis (CD95‐sensitivity) (n = 97). We correlated these findings with the functional activity of the multidrug resistance (MDR)‐associated P‐glycoprotein (P‐gp), as detected by the rhodamine123 efflux test, immunophenotype, cytogenetics and clinical data of the patients examined. Good responders to initial prednisone therapy (‘prednisone response’) revealed significantly higher Bcl‐2 expression levels [5·4 ± 3·4 relative fluorescence intensity (RFI), n = 68] than poor responders (3·7 ± 2·6 RFI, n = 42; P = 0·002). There was no significant correlation between the other investigated parameters and prednisone response. Moreover, neither the CD95 and Bcl‐2 expression levels nor the extent of spontaneous apoptosis in vitro, CD95 sensitivity or P‐gp function were correlated with the response to induction chemotherapy or relapse rate, either for B‐cell precursor ALL or T‐cell ALL. No consistent pattern of change in CD95 (n = 10) and Bcl‐2 expression (n = 9) was noted in cases studied at both initial diagnosis and relapse. In conclusion, our findings underline the different cell biological features of primary AML and ALL cells.