Flow cytometry immunophenotyping has been efficiently employed for diagnosis of Acute Lymphoblastic Leukemia (ALL) almost for a decade. We succeeded to perform immunodiagnosis in 32 of 41 consecutive children with ALL admitted to our department between January 1995 - December 1996, using an extensive panel of monoclonal antibodies in FACScan flow cytometer (Becton Dickinson, Heidelberg, Germany). 24 patients (75%) had precursor-B ALL (2 cases of pro-B ALL and 22 cases of CD10+ precursor-B ALL) and 8 (25%) had T-ALL (one case with biphenotypic features). We were looking for abnormal antigen expression patterns i. e. cross-lineage, asynchronous maturation, antigen over- or underexpression. It was possible to find “leukemia specific” phenotypes in 18 patients (75%) including CD45 negativity (9 patients), myeloid antigen (CD13 and/or CD33) coexpression (4 patients), T-cell antigen (CD7) coexpression (2 cases), CD10 overexpression (2 cases) and asynchronous maturation CD34+/ CD20+ (2 cases) and CD34+/CD22+ (2 cases). Based on the assumption that the majority of T-ALLs express ectopic terminal deoxynucleotidyl transferase (TdT), minimal residual disease (MRD) could be monitored in virtually all our patients with T-ALL, due to additional expression of CD5, CD3 or T-cell receptors αβ. Additionally we found 3 cases of T-ALL with myeloid antigen coexpression as a second target for MRD monitoring.

Our results indicate that flow cytometry immunophenotyping of acute leukemias could be applied for MRD detection in 70-80% of precursor-B ALLs and>90% of T-ALL cases. Further studies should be performed to confirm clinical significance of these findings.