CD-54 EXPRESSION AND ITS ROLE IN HOMOTYPIC AGGREGATION OF THE BLASTS OF ACUTE MYELOBLASTIC LEUKEMIAS (AML)

CD 54 (ICAM-1) expression was studied on blasts of 13 cases of de-novo AML prior to and after stimulation by interferon-gamma (IFN-gamma). F urthermore, its functional activity was studied by analysis of the inf luence of CD 54 on homologous interaction of the blasts. Prior to cult ure only a minority of the blasts displayed CD 54 positivity. Timed in cubation of the blasts in RPMI-1640/FCS or serum-free medium 'spontane ously' increased the percentage of CD 54 positive cells in 11/13 cases with a main increase after 24 h. IFN-gamma (500 IU/ml) further enhanc ed CD 54 positivity in 6/11 cases. In 2/13 cases neither a 'spontaneou s' nor an IFN-gamma induced CD 54 upregulation occurred. The homotypic aggregation of the AML blasts paralleled ICAM-1 expression in that (1 ) in all but the two CD 54 negative cases autologous cluster formation could be detected, (2) IFN-gamma enhanced cluster formation in 5/6 ca ses in which it had enhanced CD 54 upregulation, (3) incubation of the blasts in the presence of an anti-CD 54 MoAb (clone 84H10) reduced th e 'spontaneous' and IFN-gamma induced cluster formation in a majority of the cases. Taken together, ICAM-1 expression on AML blasts is heter ogenous with respect to (1) its 'constitutional' expression and (2) it s 'spontaneous' and IFN-gamma-induced upregulation, while it seems to be functionally active once expressed on the surface membrane. The rea son for the heterogenity, which did not correlate with the FAB subtype , and its importance remain unclear.