Practical application of monoclonal antibodies to the diagnosis and classification of acute leukaemias

Monoclonal antibodies in the management of acute leukemia

This report reviews the diagnostic significance of immune markers, their relationship to patient outcome, and the therapeutic uses of monoclonal antibodies (MoAbs) in acute leukemia. Immunophenotyping allows for rapid and reproducible diagnosis in the majority of cases of acute leukemia. It is of particular importance in recognizing the major immunologic subclasses of acute lymphoblastic leukemia (ALL), and in identifying subtypes of acute myeloblastic leukemia (AML) which cannot be differentiated by morphology and cytochemistry alone, such as FAB M0 or M7. Immune marker analysis has been used to detect minimal residual disease in patients' bone marrow and CSF after treatment. However, the presence of leukemia-associated phenotypes on small numbers of normal cells may reduce the sensitivity of detection in some cases. The prognostic value of immune markers in AML is limited. In ALL, the prognostic significance of the different immunophenotypic subtypes has been lessened by modern treatment protocols. The relationship of mixed-lineage or biphenotypic antigen expression to patient outcome in both AML and ALL is unclear. Therapeutic applications of MoAbs in acute leukemia include immunologic techniques for purging malignant cells from autografts prior to transplantation, T-lymphocyte depletion from allografts as a strategy to reduce graft-versus-host disease, and the use of flow cytometry to monitor the timing and extent of leukapheresis in peripheral stem cell transplantation. MoAbs have also enabled the recent development of transplantation protocols using positively-selected CD34+ stem cells.

Where does transformation occur in acute leukemia?

We studied 43 consecutive cases of acute leukemia for evidence of hybrid leukemia including biphenotypic or bilineal involvement. Twenty-two were initially diagnosed as acute lymphoblastic leukemia (ALL) and 21 as acute myelogenous leukemia (AML). Techniques included morphology, cytochemistry, immune phenotyping and cytogenetics. Thirty-one cases seemed restricted to one lineage. Twelve cases showed involvement of both lymphoid and myeloid cells. Dual staining immune phenotyping showed coexpression of diverse lineage markers. These data indicate a considerable proportion of unselected cases of acute leukemia are hybrid leukemias. These data are consistent with the notion that transformation frequently occurs in a stem or progenitor cell.

Immunophenotype of blast cells in acute myeloid leukemia may be a useful predictive factor for outcome

The immunophenotype of peripheral blood blast cells was tested in 92 patients with acute myeloid leukemia (AML), who were diagnosed and treated at single centre, St Bartholomew's Hospital, from 1978-1987 with a standard adriamycin, cytosine arabinoside and 6-thioguanine regimen. Immunological analysis involved standard fluorescence flow cytometry and utilized 31 monoclonal antibodies to known myeloid antigens (of CD groups 11b, 11c, 13, 14, 15, 16, w17, 31, w32, 33, 34, 35 and 36), a number of relatively less well studied antibodies with potential specificity for AML, and a series of control antibodies to T and B lymphocytes, platelets, erythrocytes and of widespread distribution (CD45, leucocyte common; HLA-DR). The results highlighted a number of antibodies with wide myeloid reactivity, in addition to CD13 and 33 (present in 66 per cent and 76 per cent of cases, respectively), which may be of immunodiagnostic use. A number of correlations between AML cell immunophenotype and FAB morphology subtype were found; in particular five antibodies (CD11c, 10.1, Tu3, CD15 and CD16), of both predominant granulocytic and monocytic reactivity, reacted with cells of AML-M5 subtype (p less than 0.05). There was no significant correlation between immunophenotype and clinical and pathological features at presentation. Correlation with clinical outcome was not a prominent feature, in contrast to some reports based on multicentre data. However, of particular note was the strong association between early death (at less than 2 months) and the coexpression of Leucocyte Function Associated (LFA) antigens, CD11b and 11c, on patient's blast cells (p = 0.003). The relationship was independent of clinical features and persisted even if AML-M5 cases were excluded. The significance of this latter finding is unclear, but may be related to the known role of CD11b and 11c LFA antigens in the cellular response to infection.

Classification of acute leukaemias

Acute leukaemias have traditionally been classified according to the nature of the predominating cells as judged by cytomorphology and cytochemistry. A codification of this classification into L1-L3 subdivisions for lymphoblastic cases (ALL) and M1-M7 for myeloid cases (AML), proposed by the FAB group of haematologists, has been used extensively in the past decade. Some criticisms of this codification are presented and other approaches to classification are discussed. Among these are included the potential importance of multiple lineage expression, measurements of cell differentiation using cytochemical criteria, the relevance of isoenzyme biochemistry of leukaemic cell populations, their surface antigenic differences as demonstrated by the use of monoclonal antibodies and the growing contribution of cytogenetics. The development and complexity of combined classifications which attempt to incorporate most of these features is illustrated. A simplified classification into broad groups is proposed, ALL being divided by surface antigenic and cytogenetic criteria and AML by morphology and cytochemistry. These groups may be further elaborated as appropriate.