The analogy in cell immunophenotype and parameters of cell cycle of ectopic thymus, normal thymus, and some acute lymphoblastic leukemia of T-phenotype

Abstract

In our study we described the immunophenotypic characteristics of an ectopic thymus found in an eight month old male baby. Comparing with the results of normal thymic cells we did not found any difference or abnormalities in the phenotype. A brief discussion of theories of histogenesis and possible differential diagnosis of ectopic thymus is included. The most common immune pattern of both, ectopic and normal thymuses, was expression of TdT,CD7,cCD3,CD1 and dual CD4/CD8. Early results of immunological examination confirmed by histopathology stated the diagnosis of ectopic thymus and excluded other causes (infection, trauma, neoplasm and congenital abnormalities). The study of both, ectopic and normal thymic tissue provides a perfect model for comparative analysis of some T-acute lymphoblastic leukemia (T-ALL). Both, thymocytes and some cases of our T-ALL (20 of 48 examined T-ALL) had a specific late cortical T-cell phenotype. We observed new qualities of both, thymic cells and T-ALL cells of a late cortical phenotype that resulted in cell populations localized in the so-called "empty spaces", in fluorescence histograms, that might be discriminated from internal T-cell populations with normal antigen expression. An important sign of T-ALL in common is to display aberrant marker combinations and the tendency to drop specific normal T-cell antigens. Aberrant markers were present in our study in a phenotypic group of a late cortical T-ALL in 11 cases (55.0%) of the 20 studied. As aberrant markers we observed mostly CD10, CD34, HLA-DR and CD13. Furthermore, the tendency to drop specific normal T-cell markers could be recognized in one case of a late cortical T-ALL in the form of TCRab and TCRgd absence. DNA analysis did not reveal any changes in proliferation index either in thymocytes (normal or ectopic), or in T-ALL of a late cortical T-cell phenotype. Based on our findings the clinical utility of comparing the results obtained from the immunophenotypic characterization of healthy hematopoietic and leukemia cells can be concluded. An exact and early diagnosis of hematopoietic disorders (ectopic thymus, T-ALL and T-NHL) and identification of identical phenotypic patterns at different times (for more exact minimal residual disease detection during and after therapy) could be obtained.