Analysis of neoplastic leukocyte surface antigens in unfractionated blood

The detection of leukemic cells in peripheral blood is based on cytologic and cytochemical methods. Recently, the characterization of leukemic cells has been improved by the analysis of cell surface antigens. Abundant leukemic cells are relatively easy to identify. Small numbers of circulating leukemic cells, however, may be difficult to recognize by conventional or immunological techniques. This is of particular importance in treated patients in whom the presence of low levels of circulating leukemic cells may have considerable clinical relevance. We used multiparameter correlated flow cytometric analysis to detect and characterize human leukemia/lymphoma cells in small samples of unfractionated peripheral blood. Leukocyte surface antigens were labeled with monoclonal antibodies and simultaneous forward and right-angle light scatter and fluorescence signals were measured from each cell. An interactive computer program was written that permitted the two light scatter measurements to be displayed on the screen on a cell-by-cell basis (dot-plot). Subpopulations of interest could then be selected on the dot-plot for analysis of their fluorescence distribution. On the basis of their dual scatter properties and their antigenic profile, neoplastic leukocytes were recognized even in cases in which leukemic cells were infrequent and not detectable by conventional cytologic methods.