TdT expression in acute myeloid leukaemia. Haemopoietic immaturity or maturational asynchrony?

TCR delta gene rearrangements in acute myeloid leukemia with T-lymphoid antigen expression

In this review we present our data concerning T-cell receptor (TCR) delta gene rearrangements in acute myeloid leukemia with coexpression of T-lymphoid features (CD2/CD4/CD7; Ly+ AML). We found a correlation between TCR delta gene rearrangements and coexpression of these T-lymphoid features. Ten of 66 Ly+ AML and only one of 44 AML cases without this coexpression exhibited TCR delta gene rearrangements (p = .028). In contrast, no correlation was observed between terminal deoxynucleotidyl transferase (TdT) expression and the occurrence of TCR delta gene rearrangements in AML. Rearrangements were found in two of 25 AML with and seven of 71 AML cases without TdT expression. Interestingly, nucleotide sequencing of junctional sites revealed up to 36 N-nucleotides in cases without or with only weak TdT expression indicating downregulation of TdT expression after the TCR rearrangement took place. Complete V delta 1J delta 1 and incomplete D delta 2J delta 1 gene rearrangements were observed most frequently in Ly+ AML. These recombination patterns were similar to patterns observed in acute T-lymphoblastic leukemia with coexpression of myeloid features (My+ T-ALL) suggesting transformation of a common myeloid/T-lymphoid progenitor cell in these cases.

Terminal acute myelogenous leukemia in a patient with congenital agranulocytosis

Congenital agranulocytosis terminating in acute myelogenous leukemia has been previously reported in only two cases of adolescent males. We describe the clinical and laboratory features of a 13-year-old male with congenital agranulocytosis, treated with G-CSF with initial good neutrophil response, who subsequently developed acute myeloid leukemia. This rare complication may define a preleukemic subset of patients for whom G-CSF therapy is ineffective. The diagnostic challenges of this case are presented.

Combined flow cytometric assessment of cell surface antigens and nuclear TdT for the detection of minimal residual disease in acute leukaemia

To define more precisely the immunophenotype of lymphoid blast cells, a new flow cytometric technique for the simultaneous detection of surface antigens and nuclear terminal deoxynucleotidyl transferase (TdT) was established. After staining for the cell surface marker, mononuclear cells were treated with paraformaldehyde (1%) and methanol to permeabilize the cell membrane. Then the cells were stained by indirect immunofluorescence using a rabbit anti-human TdT antibody. Dilution experiments were performed to reveal the sensitivity of the described flow cytometric assay: 0.02% leukaemic cells could reliably be detected above background level among normal peripheral blood lymphocytes. It is concluded that the double-staining procedure described here is a sensitive tool that contributes to the detection of minimal residual disease in a substantial proportion of acute leukaemias.

Diagnostic application of monoclonal antibody KB90 (CD11c) in acute myeloid leukaemia

The expression of membrane CD11c by leukaemic blast cells was examined (indirect immunorosetting) in 75 cases of acute leukaemia (myeloid, n = 60; lymphoid, n = 15) and evaluated as a potential marker for the diagnostic discrimination between monocytic (AMML-M4 and AMoL-M5) and non-monocytic (M1, M2 and M3) AML subtypes. Preliminary studies of normal bone marrow cells indicated that CD11c expression was not restricted to cells of monocytic lineage but was also present, with apparent lower density, on significant proportions of mature and immature granulocytes. Examination of acute myeloid leukaemia (AML) subtypes revealed that the non-monocytic leukaemias (n = 33) were CD11c-, defined as less than 30% positive cells, whereas all but one of the AMML-M4 (n = 13) and AMoL-M5 (n = 14) cases were CD11c+. All 15 cases of lymphoblastic leukaemia (ALL) showed less than 5% CD11c+ blasts. Membrane CD11c expression was also compared to the more widely used markers of monocytic differentiation; cytoplasmic alpha-naphthyl acetate esterase (ANAE) and membrane CD14 expression. This analysis showed that all 13 AMML-M4 leukaemias studied, including seven cases that were CD14- and eight that were ANAE-, were CD11c+. In addition, the AMoL-M5 cases (all of which were ANAE+) could be phenotypically subdivided into CD11c+ CD14+ (n = 9), CD11c+ CD14- (n = 4) and CD11c- CD14- (n = 1) subgroups. The study also confirmed that the discriminitive ability and sensitivity of the immunorosetting procedure for the detection of membrane CD11c compared favourably to immunofluorescent staining intensities as measured by flow cytometry.

Immunophenotyping of acute myeloid leukaemia: relevance of analysing different lineage-associated markers

The immunophenotype of 135 previously untreated patients with FAB defined acute myeloid leukaemia (AML) was studied at diagnosis. The panel of reagents included monoclonal antibodies (MoAb) recognising myeloid-associated determinants (CD11, CD13, CD14, CD33 and others) as well as MoAb directed towards lymphoid antigens (CD7, CD10, CD19) and TdT. The results indicate that CD13 and/or CD33 are consistently expressed in AML and only rarely in ALL blasts (131/135 + ve cases, versus 4/130 in ALL). Lymphoid antigen expression was rarely detected when CD10 and CD19 were investigated in AML (0.9% and 2% + ve cases, respectively), whereas significant positivities were found for TdT and CD7 (20% and 10% respectively). Concerning FAB subtypes, two new MoAb (LAM3 and LAM7) proved very useful in the specific recognition of AML with monocytic features. The phenotype CD13+ and/or CD33+, CD9+, HLA-DR- was found to be almost exclusive for M3 AML. The response to induction chemotherapy was analysed in CD7+ and in TdT+ patients. In the latter group a statistically significant lower response rate was found with respect to TdT-ve-AML patients.