LEUKEMIA-ASSOCIATED MARKER COMBINATIONS IN ACUTE-LEUKEMIA SUITABLE FOR DETECTION OF MINIMAL RESIDUAL DISEASE

In the absence of truly leukemia-specific antigen, antigen combination s were identified in leukemia cells that are absent or extremely rare among normal hemopoietic cells. Some of the studied combinations relat ed to the simultaneous surface and cytoplasmic marker expression, othe rs, expressed mainly on cell surface membrane, represented atypical or aberrant combinations. Comparing membrane (m) and cytoplasmic (c) ant igen expression (followed in 23 acute leukemia cases), we observed tha t CD3 could be detected in cytoplasm in the majority of T-ALL cells, w hile was absent on cell surface membrane, where simultaneous expressio n of more immature T cell markers, such as CD7 and CD5, could be detec ted. Combination of mCD7/cCD3 could be regarded as a suitable marker o f individual T-ALL cells. In cases of B-precursors of acute leukemia c ells leukemia-related combination of mCD19/cCD22 was found, which coul d characterize a single leukemia cell The cells in one of 11 AML follo wed cases were positive for CD13 in cytoplasm, but not on cell surface membrane, where CD33 and other myeloid antigens were expressed. The c ells in another two AML cases were positive for CD11 in cytoplasm but not on cell surface membrane, where CD13 or CD33 were expressed. Again , marker combinations of mCD33/cCD13 and mCD13 or mCD33/cCD11, respect ively, represent a leukemia-related feature, suitable for tracing sing le leukemia cells in double immunofluorescence. Acute leukemia defined by the coexpression on most blast cells of antigens classically attri buted to different lineages (referred as a typical/aberrant marker com binations) remains a rare event. We isolated a series of 27 (12%) such cases of 225 acute leukemia patients whose cells were immunophenotype d at diagnosis. Myeloid markers were present in T-ALL of two cease, T and B markers were coexpressed in 13 cases, markers of B and myeloid l ineage were associated in one case, and T cell and myeloid antigens we re found in 10 AML cases; in one AML case (M3 according to FAB classif ication) an aberrant nuclear coexpression of TdT was observed. In one case of the last group an interesting antigen combination of CD4/CD34 present in AML with monocytic differentiation was observed. When 5 pat ients with leukemia-associated (aberrant) markers were again analyzed at relapse, the relevant antigen combinations were retained in all of them. In summary, 44 of 50 cases (88%) from our acute leukemia series studied for leukemia-associated antigen combination, both with surface membrane and cytoplasmic marker combinations and those with aberrant markers coexpression allow the detection of minimal residual disease.