2 Immunophenotypic classification of acute lymphoblastic leukaemia

Abstract

Recent advances in immunophenotyping of acute leukaemias have led to important insights into normal haematopoietic differentiation as well as into the cellular diversity and origins of leukaemic blasts, especially in acute lymphoblastic leukaemia (ALL). These advances include the production and standardization of monoclonal antibodies (mAbs) to a variety of lymphoidand myeloid-lineage-associated antigens, the characterization of reactivity patterns of these reagents with leukaemic blasts, the establishment of an internationally accepted cluster of differentiation (CD) nomenclature and, finally, technical innovations in the evaluation of antigen expression on individual leukaemic cells. Immunophenotyping has become an important element in the modern diagnosis of acute leukaemia for several reasons. First, use of a standardized panel of mAbs to B-cell, T-cell and myeloid as well as non-lineage-restricted antigens permits allocation of more than 98% of acute leukaemias to their respective lineage (Janossy et at, 1989; Campana et al, 1990a). Secondly, in ALL, immunophenotyping has established a solid basis for precise and biologically oriented classification of the disease (Foon and Todd, 1986; Greaves, 1986); and, in acute myeloid leukaemia (AML), immunologic markers are particularly important for identifying acute leukaemia with minimal myeloid or megakaryoblastic differentiation (Bennett et al, 1985; Bennett et al, 1991; Buccheri et al, 1992). Thirdly, based on recent observations that leukaemic blasts frequently disclose aberrant or asynchronous antigen expression compared with normal haematopoietic cell differentiation, leukaemia-associated phenotypic features have been used to detect minimal residual disease (MRD) in both ALL and AML (reviewed in Campana et al, 1991a; van Dongen et al, •992). Finally, immunophenotyping alone or in conjunction with more recently developed cytogenetic and molecular-biological techniques has identified biologically and clinically distinct subsets within the major diagnostic groups and has been essential for