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). Furthermore, its functional activity was studied by analysis of the influence of CD 54 on homologous interaction of the blasts. Prior to culture only a minority of the blasts displayed CD 54 positivity. Timed incubation of the blasts in RPMI-1640/FCS or serum-free medium 'spontaneously' 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 enhanced CD 54 positivity in 6/11 cases. In 2/13 cases neither a 'spontaneous' 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 cases 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 the 'spontaneous' and IFN-gamma induced cluster formation in a majority of the cases. Taken together, ICAM-1 expression on AML blasts is heterogenous with respect to (1) its 'constitutional' expression and (2) its 'spontaneous' and IFN-gamma-induced upregulation, while it seems to be functionally active once expressed on the surface membrane. The reason for the heterogenity, which did not correlate with the FAB subtype, and its importance remain unclear.