Molecular studies of chronic myelogenous leukemia using the polymerase chain reaction

Philadelphia chromosome and/or bcr-abl mRNA-positive primary thrombocytosis: morphometric evidence for the transition from essential thrombocythaemia to chronic myeloid leukaemia type of myeloproliferation

AIMS

The incidence, bone marrow morphology and genetic features of bcr+ essential thrombocythaemia were investigated.

METHODS AND RESULTS

Sixty-four consecutive patients meeting the criteria of essential thrombocythaemia have been investigated for bcr-abl rearrangement and chimera mRNA expression. Reverse transcriptase-polymerase chain reaction indicated bcr-abl expression in six patients, in two of whom large fraction of the blood and bone marrow cells proved to be positive for Philadelphia chromosome (Ph) by fluorescent in-situ hybridization (FISH) and conventional cytogenetic analysis. In the remaining four patients FISH analysis could not detect Ph+ cells among the blood cells, but in one of these four patients conventional cytogenetic analysis indicated a very small fraction (2%) of Ph+ mitoses in the bone marrow (bcr+ essential thrombocythaemia patients). In three of these four patients, X-chromosome-linked clonality assay showed that the disease is of uncommitted stem cell origin. During an average of 57 month long follow-up no transformation to chronic myeloid leukaemia type of disease or acceleration/blastic crisis could be observed in the four bcr+ essential thrombocythaemia patients. They did not differ significantly from typical essential thrombocythaemia patients in quantitative indices of bone marrow cellularity or the size of megakaryocytes. In these two parameters as well as in the total nucleolus organizer region area per nucleus, however, significant differences could be detected between these four as well as typical chronic myeloid leukaemia patients. Statistical analysis of the morphometric data obtained from all six Ph+ and bcr+ essential thrombocythaemia patients combined indicated a shift of the bone marrow morphology towards the chronic myeloid leukaemia type of myeloproliferation.

CONCLUSIONS

These investigations indicate that bcr+ essential thrombocythaemia is infrequent among essential thrombocythaemia patients, and this condition resembles essential thrombocythaemia more than chronic myeloid leukaemia. Various expansions of the Ph+ clone appear to lead to either essential thrombocythaemia or, rather, chronic myeloid leukaemia type of myeloproliferation; however, data in the present study do not indicate that bcr+ essential thrombocythaemia would be a form fruste variant of chronic myeloid leukaemia.

The existence of lymphoid lineage restricted Philadelphia chromosome-positive acute lymphoblastic leukemia with heterogeneous bcr-abl rearrangement

Analysis of lineage involvement was performed in 17 Philadelphia chromosome-positive acute lymphoblastic leukemia patients with no history of chronic myeloproliferative disorder. The percentage of blastic cells as defined by flow cytometry matched that of the Ph-positive cells in 14 out of 17 patients. The bcr-abl rearrangement was investigated by fluorescent in situ hybridization in morphologically identified blastic cells, myeloid elements, lymphocytes and erythroblasts using a combined light and fluorescent microscopical imaging. Lymphoid lineage restriction could be determined in all but three of the patients. These 14 patients exhibited heterogeneity in terms of m-bcr and M-bcr types of translocation as revealed by reverse transcription polymerase chain reaction. The three patients with multilineage involvement and M-bcr type of translocation reverted to chronic phase and the percentage of Ph-positive cells remained high. Thus, we could identify an uncommitted stem cell origin among Ph-positive ALLs only in those patients whose disease subsequently proved to be a lymphoid blastic crisis with clinically silent chronic phase.

Silent Philadelphia chromosome: a distinct developmental stage in a philadelphia chromosome-positive chronic myeloproliferation?

In this paper, a patient is described who presented with peripheral blood and bone marrow features uncharacteristic of chronic granulocytic leukemia, which proved to be Philadelphia (Ph) chromosome-positive by metaphase and interphase cytogenetic analyses but lacked the p210 type of BCR/ABL fusion gene mRNA product by two different sensitive RT-PCR assays. In the course of the 32-month follow-up with a termination into a myeloblastic crisis, molecular investigations were performed four times. They indicated a constantly high rate of Ph positive cells and lack of BCR/ABL mRNA expression, except in the second investigation, when the patient showed reverse transcription polymerase chain reaction positivity with b3/a2 type of chimera, fusion gene mRNA expression, and a striking change in the bone marrow histology. Our findings might indicate that the dormant Ph chromosome state may exist not only at the primitive progenitor, but also at the entire peripheral blood cell compartment level.

Analysis of mRNA transcripts in chronic myeloid leukemia patients

The nature of BCR/ABL hybrid mRNA was analyzed by RT-PCR in cells from 33 patients (22 males, 11 females) with chronic myeloid leukemia (CML). b3a2 mRNA was found in 14 cases, whereas 13 patients had b2a2 mRNA and six had both kinds of mRNA, with a predominance of the b3a2 type. The type of mRNA present showed no significant correlation with age, hemoglobin level, number of leukocytes and platelets, percentage of blasts or basophils or the presence of splenomegaly at diagnosis. There was also no correlation with sex or duration of the chronic phase. When these results were combined with those reported by other groups, a significant association (P = 0.029) was observed for mRNA type vs. sex, with a predominance of men in the groups expressing b2a2 (2.68:1) and b3a2 (1.33:1). We conclude that the classification of patients according to mRNA type does not homogenize the clinical and hematological data within groups, where variance is large, nor does it allow a differentiation between groups.

Phenotypic and genotypic analyses of blastic cell population suggest that pure B-lymphoblastic leukemia may arise from myelodysplastic syndrome

The case history of a 70-year-old man with myelodysplastic syndrome terminated into acute leukemia in 22 months is presented. The leukemic cells exhibited multifocal acid phosphatase positivity and expressed TdT, CD45, CD34 and HLA-DR but not myeloid, monocytic or megakaryocytic differentiation antigenes. The genotypic analysis revealed clonal immunoglobulin heavy chain gene rearrangement. These phenotypic and genotypic analyses of the blastic cell population suggest that myelodysplastic syndrome may transform to pure acute lymphoblastic leukemia of B-cell origin.

Interferon response in chronic myeloid leukaemia correlates with ABL/BCR expression: a preliminary study

alpha-Interferon (IFN) has been used to induce cytogenetic remission in chronic myeloid leukaemia (CML), but there are few indicators to predict IFN response. The role of the chimaeric BCR/ABL gene in the malignant process is undisputed. There are, however, conflicting views as to whether the breakpoint site within the BCR gene, and the type of mRNA produced determine disease prognosis and progression. The function and clinical significance of the newly discovered ABL/BCR mRNA has not been investigated for a correlation with CML prognosis or response to therapy. We have used a two-step reverse transcriptase polymerase chain reaction (RT-PCR) to detect the transcripts of the chimaeric genes BCR/ABL, ABL/BCR, as well as the normal ABL and BCR genes in 24 CML patients treated with IFN. Because of the variable expression of the four transcripts at presentation, a correlation between gene expression, prognosis and clinical progression was examined. No correlation between prognosis and gene expression was seen. Also, no correlation was found between expression of BCR, ABL or BCR/ABL mRNA and response to treatment with IFN. However, 7/10 ABL/BCR mRNA positive patients achieved a major cytogenetic response to IFN; but of the 13 ABL/BCR mRNA negative patients, only two achieved a major cytogenetic response (P = 0.013). Further studies are required to confirm these findings.

Influence of M-BCR breakpoint sites on the duration of chronic phase in 100 patients with chronic myelocytic leukemia

Rearrangements of the bcr (M-BCR) gene were studied in 100 patients with chronic myelocytic leukemia (CML). To determine the significance of a chimeric gene expression in the progression of CML, we analyzed 43 patients for bcr-ABL chimeric mRNA expression. Both DNA and RNA analyses revealed a possible influence of breakpoint sites in the bcr region on the duration of the chronic phase. Patients with the breakpoint located at about the 1-kb region between BamHI and HindIII in bcr exon 3 (region C2) had a significantly shorter chronic phase (31 months) (p = 0.028) than patients in whom the breakpoint was located in other regions. When the bcr locus was divided into 5' and 3' regions as for the BamHI cleavage site located near the 5' region of bcr exon 3, the chronic phase duration in patients with the 5' site (HindIII-BamHI) and 3' site (BamHI-EcoRI site) was 75 and 38 months, respectively. However, the difference was not statistically significant (p = 0.128). These results suggest that only the breakpoint site at C2 on the bcr locus, rather than breakpoint sites in other regions, has an important role in the progression of CML.

A long-term suppression by alpha-interferon of Philadelphia chromosome in children with chronic myelogenous leukemia

An 8 year old girl with adult type Philadelphia (Ph1)-positive chronic myelogenous leukemia received natural alpha-interferon therapy in the chronic phase. Complete suppression of the Ph1 clone of bone marrow cells was achieved after 1 month of therapy, which was determined by disappearance of rearranged breakpoint cluster region (BCR) gene in Southern blot analysis. Complete hematological remission was also attained following 2 months of therapy. Both the suppression and the hematological remission have been sustained for 24 months with alpha-interferon, in spite of the detection of the chimeric BCR/ABL mRNA in her bone marrow by polymerase chain reaction assay 12 months after therapy.

Immunological classification of childhood acute lymphoblastic leukemia

Seven hundred and forty-four newly diagnosed patients with acute leukemias between 1978 and 1990 were classified on the basis of immunological phenotypes. The majority of the patients were enrolled in the Tokyo Children's Cancer Study Group (TCCSG) studies. The incidence of subclassification of acute leukemias in this study was as follows: 522 patients with ALL (70%), 139 patients with ANLL (18%), 29 patients with biphenotypic leukemia, 8 patients with Ph1-positive acute leukemia (Ph1-AL), and 45 patients with infant leukemia. ALLs were classified into common ALL (cALL, 77%), T-ALL (15%), B-ALL (4%), and unclassified ALL (3%). The incidence of ALL subtypes in this study reflected those of TCCSG. Biphenotypic leukemias were categorized into 4 groups as follows; 1) cALL with positive myelomonocytic antigen(s) (N = 11), 2) unclassified ALL with positive myelomonocytic antigen(s) (N = 5), 3) ANLL with positive B-lymphoid antigen(s) (N = 4), and 4) acute leukemia with positive T-lymphoid and myeloid antigen(s). Infant leukemias were classified into ALL type (N = 27) and ANLL type (N = 18). In this present study, clinical features and immunological phenotypes of the acute leukemias with a poor prognosis, i.e. biphenotypic leukemia, Ph1-AL, and infant leukemia are analyzed and discussed.