Monitoring of minimal residual disease in acute leukemia by multiparametric flow cytometry.

In this review, we discuss methodological principles and clinical applications of minimal residual disease (MRD) assays based on multiparameter flow cytometry (MFC). The introduction of methods for MRD detection has revolutionized monitoring of treatment response in acute leukemia. Great progress has been made in the development of wide array of flow cytometric techniques for rare event detection. This advance was accompanied by increasingly greater understanding of the immunophenotypic features of leukemic and normal lymphoid cells, and of the antigenic differences that make MRD studies possible. Immunologic testing of MRD relies on "leukemia-associated" immunophenotypes which can be identified by MFC in the most of acute leukemia cases. The recent technical innovations in routine MFC (3 lasers and≥8 colors) and the new developments in software for data analysis make this technology the most attractive for MRD diagnostics. The importance of MFC methodology will be further strengthened by the ongoing international standardization efforts. Results of MRD testing provide unique and clinically important information. The systematic application of immunologic techniques to study MRD in clinical samples has demonstrated the prognostic significance of MRD in patients, leading to the use of MRD to regulate treatment intensity in many contemporary protocols. The identification of new markers of MRD should increase the sensitivity of MRD testing by MFC and is required to widen the applicability of MRD studies.