Phenotypic heterogeneity and aberrant markers expression in T-cell leukemia

For exact determination of lineage assessment there is a need of surface membrane and intracellular (cytoplasmic and nuclear) immunophenotyping performed by flow cytometry. We evaluated in detail the results of surface and intracellular immunophenotyping of 34 T-ALL cases. The great heterogeneity of T-cell differentiation markers has been observed which did not allow relevant subclassification of T-ALL according to the existing subclassification schemes and the proposed three-stage model of physiological T-cell differentiation. Therefore, a simplified classification based on the CD3 marker expression either on cell membrane or in cytoplasm has been created with allocation of T-ALL into two main phenotypic groups. From 34 in detail examined T-ALL cases a great deal-27 (79%) belonged to an immature phenotype (Stage I) and only 7 (21%) expressed more mature phenotype (Stage II). Simultaneously the presence of atypical/aberrant T-cell phenotypes has been studied. We showed that in T-ALL it was possible to specify some cases with leukemia-associated phenotype with coexistence of atypical markers which are absent in nonleukemic cells. In a majority of cases early B-lineage marker (CD10) and in a smaller proportion of them non-lineage associated marker (CD34) were observed. Myeloid marker CD13 was observed in one case of the immature T-ALL, together with CD10 and CD34. As these atypical markers were present through all differentiation stages of T-ALL we obtained a strong evidence that they might represent an abnormal rather than an immature phenotype. The prognostic significance of T-ALL subtypes and aberrant markers coexpression have been discussed. Simultaneously it was shown that quantitative immunofluorescence could provide an additional important diagnostic marker also in T-ALL cases.