Terminal transferase expression in acute myeloid leukaemia: biology and prognosis

Inhibiting DNA Polymerases as a Therapeutic Intervention against Cancer

Inhibiting DNA synthesis is an important therapeutic strategy that is widely used to treat a number of hyperproliferative diseases including viral infections, autoimmune disorders, and cancer. This chapter describes two major categories of therapeutic agents used to inhibit DNA synthesis. The first category includes purine and pyrmidine nucleoside analogs that directly inhibit DNA polymerase activity. The second category includes DNA damaging agents including cisplatin and chlorambucil that modify the composition and structure of the nucleic acid substrate to indirectly inhibit DNA synthesis. Special emphasis is placed on describing the molecular mechanisms of these inhibitory effects against chromosomal and mitochondrial DNA polymerases. Discussions are also provided on the mechanisms associated with resistance to these therapeutic agents. A primary focus is toward understanding the roles of specialized DNA polymerases that by-pass DNA lesions produced by DNA damaging agents. Finally, a section is provided that describes emerging areas in developing new therapeutic strategies targeting specialized DNA polymerases.

Terminal deoxynucleotidyl transferase expression in acute myelogenous leukemia and myelodysplasia as determined by flow cytometry

The significance of terminal deoxynucleotidyl transferase (TdT) expression in acute myelogenous leukemia (AML) remains controversial. Therefore, we studied TdT expression by flow cytometry in 120 previously untreated patients with AML or myelodysplastic syndrome (MDS) to determine the distribution of TdT-positive blasts and the intensity of TdT expression and to seek clinically significant associations. TdT expression measured by flow cytometry (flow TdT%) was heterogeneous, ranging from 0.1% to 87% (median, 8.5%), and 74 patients (62%) had at least 5% TdT-positive blasts. TdT positivity was associated with the M0 or M1 subtype and with expression of CD34 and CD7. No significant correlation was found between TdT expression and type of cytogenetic abnormality or rearrangement of immunoglobulin or T-cell receptor genes. Remission lasted longer in patients with a flow TdT% < 5 than in patients with a flow TdT% > 5 (median, 95 weeks vs 55 weeks, p = 0.02); however, complete remission rates did not differ when patients were classified by initial flow TdT%. Survival was slightly better for patients with flow TdT% less than 5%. Among patients with a flow TdT% > 5%, those with a higher TdT intensity survived longer than those with a lower intensity. These data suggest that quantitative TdT measurement may contribute to prognostic estimate in AML patients.

V(D)J recombination activity in human hematopoietic cells: correlation with developmental stage and genome stability

V(D)J recombinase activity was measured in an array of human cell lines derived from hematopoietic malignancies representing various lineages and developmental stages. The level of recombinase activity was found to vary over a 2000-fold range between different cell lines. Several myeloid cell lines were positive for V(D)J recombinase activity, providing additional insight into the relationship between myeloid and lymphoid differentiation. Despite high levels of V(D)J recombination in two human acute lymphoblastic leukemia cell lines, the cytogenetic karyotype has remained essentially constant over several years of continuous cell culture. Silencing of recombination of chromosomal and minichromosomal targets has been strongly correlated with the replication of CpG methylated DNA in murine cells. Here, in human cells, we show that human minichromosomes bearing V(D)J recombination signals are protected well over 100-fold from recombination if they are CpG methylated, providing a rational basis for the karyotypic stability in cells with high levels of V(D)J recombination activity.

Terminal transferase expression in the differential diagnosis of acute leukemias. Eastern Cooperative Oncology Group

While the clinical significance of terminal transferase (TdT) detection in acute lymphoblastic leukemia (ALL) is uncontested, conflicting evidence exists for the prognostic relevance of this enzyme in blast cells from patients with acute myeloid leukemia (AML). The technical challenge of determining TdT in myeloid blast cells may be primarily responsible for those discrepancies in the literature. We present here the relative values of various standard approaches to the detection of TdT in ALL versus AML, including the slide staining technique, which served as the reference method, flow cytometry, and the biochemical enzyme assay.

Acute leukemia with t(10;11)(p11-p15;q13-q23)

We report six patients with acute leukemia characterized by the presence of a t(10;11)(p11-15;q13-q23), either as sole cytogenetic abnormality (three patients) or as part of a complex abnormal karyotype. The morphologic and cytochemical features of four patients were consistent with FAB-M5A, while two patients presented with FAB-L1 characteristics. By immunophenotyping, myeloid leukemia was diagnosed in five patients, including one patient with FAB-L1 leukemia who typed as terminal transferase (TdT)+, CD7 T-cell antigen+ acute myelomonocytic leukemia. Differentiated acute myeloid leukemia (AML) with expression of terminal transferase was found in two of the other cases and monocytic leukemia in two, with co-expression of T-cell antigens in one of them. The second FAB-L1 patient typed as undifferentiated acute lymphocytic leukemia (ALL) expressing myeloid antigens. Serial phenotypic studies in patient 3 during the course of the disease demonstrated a switch from monocytic to lymphoid morphology at the time of first and second relapse, which was paralleled by the appearance of a pre-T ALL immunophenotype with co-expression of the myeloid antigen CD33. These phenotypic changes occurred without apparent alteration in the genotype since t(10;11)(p11.2;q23) remained the only cytogenetic aberration at all stages of the disease. Our observations suggest that the (10;11) variant of 11q aberrations occurs in a bipotential myelomonocytic/T-lymphoid stem cell.

Detection of terminal transferase in acute myeloid leukemia by flow cytometry

The purpose of this study was twofold: (1) to develop an optimized, reliable method for the flow cytometric analysis of the intranuclear DNA polymerase, terminal deoxynucleotidyl transferase (TdT) in acute myeloid leukemia, and (2) to establish the usefulness of a novel, fluorescein-isothiocyanate conjugated monoclonal anti-TdT antibody (HT-6) in double-fluorescence staining for surface antigens in the characterization of leukemic cells. Inclusion of an aldehyde blocking buffer in the staining protocol reduced background fluorescence sufficiently to allow for the detection of the low-level fluorescent TdT+ myeloblasts. When admixed to normal peripheral blood mononuclear cells, 0.4-0.5% of HLA-DR+ or myeloid surface antigen+, TdT+ double-stained myeloblasts could be reliably detected above background levels. Flow cytometric TdT measurements using the HT-6 antibody in 55 patients with TdT+ acute lymphocytic or myelocytic leukemia or blast crisis of chronic myelogenous leukemia were equal or superior to the results obtained with a mixture of monoclonal anti-TdT antibodies (anti-HTDT-Mix) and comparable to those obtained by the conventional slide method employing polyclonal rabbit anti-human TdT antiserum. This flow cytometric TdT determination in combination with surface antigen staining using a novel anti-TdT monoclonal antibody (HT-6) allows for the recognition of minimal leukemic blast cells during clinical remission in acute myeloid leukemia.

Acute myeloblastic leukemia with minimal myeloid differentiation (FAB AML-M0): a study of eleven cases

The main clinical, morphological, cytochemical, immunological features and therapy results of eleven patients diagnosed as acute myeloblastic leukemia M0 (AML-M0) are reported here. There were no clinical characteristics, abnormalities on physical examination or initial laboratory parameters that distinguished these eleven patients. Bone marrow aspirates were hypocellular in four patients. The leukemic cells were undifferentiated by light microscopy and myeloperoxidase (MPO) and/or Sudan Black B (SBB) stains were negative in all cases. Myeloid differentiation antigens were present on the leukemic cells of all eleven patients, whereas B and T cell markers were clearly negative except for CD4 and CD7 antigens. Whatever the treatment employed survival was very short. Eight of the eleven patients were treated and two achieved complete remission (CR) but only one of them is alive in continuous CR. Our results like those previously reported, suggest that AML-M0 patients have a very poor prognosis with standard induction therapies and should perhaps be considered for experimental therapeutic approaches.

Differential expression of terminal transferase (TdT) in acute lymphocytic leukaemia expressing myeloid antigens and TdT positive acute myeloid leukaemia as compared to myeloid antigen negative acute lymphocytic leukaemia

We examined whether the allegedly aberrant expression of the lymphoid lineage associated DNA polymerase, terminal deoxynucleotidyl transferase (TdT), in acute myeloid leukaemia (AML) is associated with alterations of the enzyme at the cellular, biochemical or transcriptional level when compared to lymphoid leukaemia (ALL), either lacking or expressing myeloid antigens. By flowcytometric analysis, the intensity of TdT staining with monoclonal anti-TdT antibody was considerably weaker in TdT+ AML and myeloid+ ALL (M+ ALL) than in myeloid- ALL (M- ALL). TdT enzyme activity in TdT+ AML was on an average 10%, and in M+ ALL 25% of that measured in M- ALL. Anti-TdT antibodies precipitated a major specific protein of identical relative molecular mass (58 kD) from metabolically labelled TdT+ myeloblasts and lymphoblasts. By Northern blot analysis and ribonuclease protection assay, TdT transcript levels were significantly lower in TdT+ myeloblasts and M+ lymphoblasts than in M- ALL (P < 0.0001). The level of TdT transcription in AML was independent of the simultaneous expression of lymphoid-specific antigens, such as CD2 and CD19. Our data demonstrate that TdT expression is downregulated in association with myeloid features, not only in AML but also in ALL. This observation may provide the molecular basis for the differential therapeutic responsiveness, particularly to glucocorticoids, in these various leukaemia subtypes.

Lymphoid lineage-associated features in acute myeloid leukaemia: phenotypic and genotypic correlations

This study is intended to establish biological correlation between the expression of lymphoid associated features in acute myeloid leukaemia (AML). In 62 AML patients, predominantly enrolled on Eastern Cooperative Oncology Group (ECOG) treatment protocols, in whom immunoglobulin (Ig) as well as T-cell receptor beta chain (TCR-beta) gene rearrangement analyses had been performed, morphology, cytochemistry, antigen profile and karyotype were reviewed retrospectively. Nuclear reactivity with anti-TdT antibody was demonstrated in 34 patients (55%) and confirmed by ribonuclease protection assay in all patients tested. Five TdT-protein negative patients were TdT-transcript positive. Lymphoid antigens (lyA) were detected in 24 of 51 cases tested (47%) with B-cell antigens (CD19, CD10) being restricted to TdT+ AML (P = 0.03). Only two patients had Ig heavy, none had Ig light chain or TCR-beta gene rearrangements. Although both patients with rearranged Ig loci were TdT+, either by protein or RNA analysis, the low incidence of such rearrangement within the TdT+ AML group (6%) argues against a significant association between the presence of TdT and crosslineage Ig gene rearrangements in AML. While FAB-diagnoses did not differ between TdT+ and TdT- or lyA+ and lyA- AML, particular immunophenotypic features correlated with TdT positively, e.g. the presence of early antigens, CD34 and HLA-DR, and the absence of the more mature myelo-monocytic antigens, CDw65 and CD14. Certain cytogenetic abnormalities were associated with TdT+ AML such as inv(16) (p13q22) or t(16;16) (p12;q22) (five patients; P = 0.03) and t(8;21) (q22;q22) (three patients). A greater number of TdT- than TdT+ AML patients had only normal karyotypes (P = 0.06). Neither immunophenotypic nor karyotypic correlations could be established for lyA+ AML.

Role of blast cell immunophenotyping for the diagnosis and prognosis of acute myeloid leukemia

Bone marrow blast cell antigen expression from 86 patients with de novo acute myeloid leukemias (AML) was studied and correlated with FAB classification and clinical outcome. Among a panel of 14 monoclonal antibodies routinely used for the diagnosis of acute leukemias we studied the expression of six antibodies (CD13, CD15, VIM2, CD33, CD14, CD34) of the granulomonocytic lineage and found that some of them were useful for diagnosis and/or prognosis. For FAB subclassification of AML, the CD13 or VIM2 antigen expression was of no benefit. Monocytic leukemias (M4 + M5PD + M5WD) more frequently expressed CD34 antigen (28/31) than granulocytic (M1 + M2 + M3) subtypes (33/53) (P < 0.01). Finally, the most striking differences were found with CD14 antigen expression: CD14 antigen was more frequently expressed in M4 + M5 leukemias (21/31) than in M1 + M2 + M3 subtypes (12/33) (P < 0.01). The mean percentage of CD14 positive blast cells was accordingly higher in monocytic leukemias than in granulocytic leukemias and the difference was highly significant (P < 0.0001). The CD15 antigen was more frequently expressed in differentiated leukemias (M2 + M3 + M4 + M5WD) (35/44) than in poorly differentiated forms (M1 + M5PD) (17/37) (P < 0.001). The statistical difference was higher when the mean percentage of CD15 positive blast cells were compared (P < 0.0003). Moreover these latter percentages were different in M1 and M2 subtypes (P < 0.003). The blast cell expression of CD13, CD14, CD15 or CD33 was not predictive of the length of CR or survival. Moreover, our results support previously published findings suggesting a longer overall survival duration for patients whose leukemic cells do not express the CD34 antigen (P < 0.01). We also confirm that patients with the more differentiated subtypes of AML (CD13-, CD34+) tend to survive longer than patients with the less differentiated subtypes of AML (CD13-, CD34+) (P < 0.001).

Monosomy 7 in multilineage and acute lymphoblastic leukaemia

Monosomy 7 as the sole cytogenetic abnormality was detected in five of 310 consecutive adult patients with acute leukaemia who were characterized by morphological, immunophenotypic and cytogenetic analyses. Morphologically, blast cells were myelomonocytic (FAB M4) in three and lymphoid (FAB L2) in two patients. By immunophenotyping, two M4 patients expressed terminal transferase (TdT) in 15-90% of myelomonoblasts (patients 3 and 1, respectively), and in the third M4 patient (no. 2), a 10% TdT+ component was present distinct from the bulk of myelomonoblasts. In one L2 patient (no. 4), the blast cells had an undifferentiated phenotype only expressing TdT and HLA-DR but lacking specific lymphoid and myeloid antigens, and patient 5 was typed as CD10+ ALL. Two patients had developed leukaemia following radiotherapy and/or chemotherapy for multiple myeloma or breast cancer. In two patients, induction chemotherapy induced a lineage switch in the immunophenotype without change in karyotype. These observations support the concept that monosomy 7 leukaemia results from the transformation of a multipotential stem cell.