Characterisation of blast cells during blastic phase of chronic myeloid leukaemia by immunophenotyping--experience in 60 patients

BCR-ABL but not JAK2 V617F inhibits erythropoiesis through the Ras signal by inducing p21CIP1/WAF1

BCR-ABL is a causative tyrosine kinase (TK) of chronic myelogenous leukemia (CML). In CML patients, although myeloid cells are remarkably proliferating, erythroid cells are rather decreased and anemia is commonly observed. This phenotype is quite different from that observed in polycythemia vera (PV) caused by JAK2 V617F, whereas both oncogenic TKs activate common downstream molecules at the level of hematopoietic stem cells (HSCs). To clarify this mechanism, we investigated the effects of BCR-ABL and JAK2 V617F on erythropoiesis. Enforced expression of BCR-ABL but not of JAK2 V617F in murine LSK (Lineage(-)Sca-1(hi)CD117(hi)) cells inhibited the development of erythroid cells. Among several signaling molecules downstream of BCR-ABL, an active mutant of N-Ras (N-RasE12) but not of STAT5 or phosphatidylinositol 3-kinase (PI3-K) inhibited erythropoiesis, while N-RasE12 enhanced the development of myeloid cells. BCR-ABL activated Ras signal more intensely than JAK2 V617F, and inhibition of Ras by manumycin A, a farnesyltransferase inhibitor, ameliorated erythroid colony formation of CML cells. As for the mechanisms of Ras-induced suppression of erythropoiesis, we found that GATA-1, an erythroid-specific transcription factor, blocked Ras-mediated mitogenic signaling at the level of MEK through the direct interaction. Furthermore, enforced expression of N-RasE12 in LSK cells derived from p53-, p16(INK4a)/p19(ARF)-, and p21(CIP1/WAF1)-null/wild-type mice revealed that suppressed erythroid cell growth by N-RasE12 was restored only by p21(CIP1/WAF1) deficiency, indicating that a cyclin-dependent kinase (CDK) inhibitor, p21(CIP1/WAF1), plays crucial roles in Ras-induced suppression of erythropoiesis. These data would, at least partly, explain why respective oncogenic TKs cause different disease phenotypes.

Phenotype of blasts in chronic myeloid leukemia in blastic phase-Analysis of bone marrow trephine biopsies and correlation with cytogenetics

We identified different phenotypic subsets among 62 cases of chronic myeloid leukemia (CML) in blast crisis (BC) (26% B-lymphoblastic, and 74% various myeloblastic subsets) on bone marrow trephines and correlated the blast-phenotype with cytogenetics. Five of myeloid-BC had an associated 3q26 abnormality and two of these showed a megakaryoblastic-phenotype. While myeloid-BC was associated with additional copies of Philadelphia (Ph) (29%) (p=0.08), numerical abnormalities (51%) (p=0.007), trisomy-8 (29%) (p=0.08) and 17p-loss (22%), none of lymphoid-BC showed these abnormalities. Among myeloid-BC, CD34-negative cases were more often associated with trisomy-8, 17p-loss and numerical abnormalities, and the CD117-negative subset with additional copies of Ph (p<0.05).

Concurrent megakaryocytic and erythroid chronic myelogenous leukemia blast crisis

Chronic myelogenous leukemia with blast crisis is seen in 15% to 20% of patients with chronic myelogenous leukemia. Chronic myelogenous leukemia with either erythroid or megakaryocytic blast crisis is not uncommon in the clinical setting. The incidence ranges from 0% to 33% in accordance with literature reports. The diagnosis of erythroid or megakaryocytic blast phase is often challenging because the percentage of blasts in the blood or bone marrow required for diagnosis has not been firmly established. Also, some myeloblasts can have aberrant expression of either erythroid or megakaryocytic markers by flow cytometry during clonal evolution. Early recognition of this entity is crucial because either megakaryocytic or erythroid blast crisis predicts an aggressive clinical course. To our knowledge, the coexistence of megakaryocytic and erythroid blasts has not been reported. We report a unique case of chronic myelogenous leukemia with this rare bilineage blast crisis in the background of dysplasia and marked myelofibrosis. Related literature is also reviewed.

[Erythroleukemic blast crisis of chronic myeloid leukemia.]

Erythroleukemic blast crisis of chronic myeloid leukemia (CML) is very rare. We report two cases of erythroleukemic blast crisis of CML resistant to imatinib treatment. Both patients made a rapid progression to blast crisis 6 and 4 months after diagnosis while being treated with imatinib 400 mg/day. Bone marrow aspiration revealed predominant erythroid precursors with 65.4% and 54.8% each. There were significant proportions (more than 20%) of myeloblasts among non-erythroid cells. Immunophenotyping revealed expression of glycophorin A confirming erythroleukemic blast crisis. The karyotyping result of patient 1 was 46,XX,t(9;22)(q34;q11.2)[3]/52,idem,+8,+12,+18,+21,+22,+der(22)t(9;22)[17] and that of patient 2 was 46,XX,inv(3)(q21q26.2),t(9;22)(q34;q11.2)[20]. Patient 1 showed no response to imatinib and BMS-354825 in the following bone marrow study. She died of septic shock as a complication of an infection after 69 days of blast crisis. Patient 2 received allogeneic bone marrow transplantation (BMT) in the cytogenetically no response state, but she also died of graft-versus-host disease 9 weeks after BMT. The poor prognosis and rapid progression of disease in both cases were correspondent to most of the reported cases. During the course of the disease of the two patients, we monitored the BCR-ABL chimeric mRNA with real-time quantitative polymerase chain reaction (RT-PCR), and it was found useful in predicting the imatinib response and progression to blast crisis of CML. Although both of our cases showed the typical bad prognosis and findings of erythroleukemic blast crisis of CML, the karyotypes were different from the expected type of t(3;21)(q26;q22). But the relationship between additional changes of EVI1 on chromosome 3q26 shown in case 2, and progression to the erythroleukemic blast crisis need further investigation.

p210(BCR-ABL) reprograms transformed and normal human megakaryocytic progenitor cells into erythroid cells and suppresses FLI-1 transcription

The BCR-ABL oncoprotein exhibits deregulated protein tyrosine kinase activity and is implicated in the pathogenesis of Philadelphia chromosome (Ph)-positive human leukemias. Here, we report that ectopic expression of p210(BCR-ABL) in the megakaryoblastic Mo7e cell line and in primary human CD34(+) progenitors trigger erythroid differentiation at the expense of megakaryocyte (MK) differentiation. Clonal culture of purified CD41(+)CD42(-) cells, a population highly enriched in MK progenitors, combined with the conditional expression of p210(BCR-ABL) tyrosine kinase activity by imatinib identified a true lineage reprogramming. In both Mo7e or CD41(+)CD42(-) cells transduced with p210(BCR-ABL), lineage switching was associated with a downregulation of the friend leukemia Integration 1 (FLI-1) transcription factor. Re-expression of FLI-1 in p210(BCR-ABL)-transduced Mo7e cells rescued the megakaryoblastic phenotype. Altogether, these results demonstrate that alteration of signal transduction via p210(BCR-ABL) reprograms MK cells into erythroid cells by a downregulation of FLI-1. In addition, our findings underscore the role of kinases in lineage choice and infidelity in pathology and suggest that downregulation of FLI-1 may have important implications in CML pathogenesis.

New insights into the pathobiology and treatment of chronic myelogenous leukemia

Chronic myelogenous leukemia (CML) is one of the most frequently diagnosed forms of leukemia. Recent advances in the understanding of the molecular mechanisms involved in the pathogenesis of this disorder led to new diagnostic and therapeutic approaches. From a disease that used to be diagnosed purely on morphologic grounds, CML is now an entity that cannot be diagnosed in the absence of relevant cytogenetic or molecular data. Identification of the characteristic t(9;22) cytogenetic abnormality or of the BCR-ABL molecular abnormality is mandatory, as current treatment approaches rely on the use of agents active against this specific molecular target. This article presents the evolution in the understanding of the pathogenic mechanisms involved in CML, as well as the methods and the criteria currently in use in its diagnosis and treatment.

Myeloperoxidase cytochemical negativity: an unexpected but intrinsic property of blasts of all phases of chronic myeloid leukemia

Myeloperoxidase (MPO) cytochemical activity, recognized as a very important hallmark of myeloblasts, is generally negative in chronic myeloid leukemia (CML) blast crisis (BC). Because this finding is unexpected, being not in keeping with the myeloproliferative nature of CML, we tried to ascertain if MPO cytochemical negativity could be an intrinsic property of blasts of CML and hence present in the preblastic phases as well. Myeloperoxidase cytochemistry of peripheral blood blasts in 161 cases of CML, including 103 in chronic phase (CP) and 29 each in accelerated phase (AP) and BC, was assessed and compared with that of 30 cases of acute myeloid leukemia, AML-M2. Blasts of 97 (94.2%) of 103 cases of CP, 28 (96.6%) of 29 cases of AP, and 22 (75.9%) of 29 cases of BC were negative for MPO (<3% MPO-positive blasts). Compared with the strong MPO positivity, both in terms of intensity and proportion, in the AML-M2 cases, the positivity in the CML cases was generally weak and was seen in a small number of blasts (5-15%), except in one case of BC with 20% positive blasts. Absence or, at times, weak MPO cytochemical activity is an intrinsic property of blasts of all phases of CML, and use of the term myeloblast in CML should be understood to refer to a cell with this property. This also explains why MPO cytochemistry, despite its high reputation as a myeloid-lineage marker, generally does not help in CML BC. CML BC should therefore be considered as a possible diagnosis along with acute lymphoblastic leukemia, AML-M0, AML-M7, etc., in the setting of MPO-negative blasts. Similarity between MPO expression pattern in CML, i.e., negative in blasts and positive in the more mature cells, and that during maturation of normal myeloid series of cells shows the deranged myelopoiesis of CML to be undisturbed at least with respect to MPO expression. There is need for a more comprehensive study of blasts of preblastic phases.

Detection of BCR/ABL fusion product in normoblasts in a case of chronic myelogenous leukemia

Erythroblast phase of chronic myelogenous leukemia (CML) and Philadelphia chromosome-positive acute erythroid leukemia are rare events. The distinction between these two entities is poorly defined. The World Health Organization (WHO) classification requires the presence of more than 50% of erythroblasts in the bone marrow for the diagnosis of both the erythroid/myeloid or pure erythroid subtypes of acute erythroid leukemia. However, in previous studies of erythroblast crisis CML, the percentage of erythroid series in the bone marrow is seldom mentioned and the direct relationship of the erythroblasts and the Philadelphia chromosome has never been established. We report a well-documented case of acute erythroid leukemia transformed from CML. The studies in morphology, immunohistochemistry, and flow cytometry fulfill the WHO criteria for the diagnosis of acute erythroid leukemia, and yet the complex karyotype containing Philadelphia chromosome indicates genetic evolution. Finally, the direct demonstration of the BCR/ABL fusion product by fluorescence in situ hybridization in the erythroblasts provides concrete evidence that the erythroblasts are part of the leukemic process and not an innocent bystander.

Myelodysplastic syndromes, chronic myeloproliferative diseases, and myelodysplastic/myeloproliferative diseases

This article reviews the major diagnostic criteria for the myelodysplastic syndromes, chronic myeloproliferative diseases, and myelodysplastic/myeloproliferative diseases. Perhaps the most important message this article intends to convey is that the proper diagnosis and classification of myelodysplastic syndromes, chronic myeloproliferative diseases, and myelodysplastic/myeloproliferative diseases requires a multidisciplinary approach that correlates morphologic findings with clinical, genetic, and other laboratory information. Thus, the pathologist is central to the diagnosis of these disorders. Not only do pathologists have the morphologic skills to interpret peripheral blood and bone marrow aspirate smears and bone marrow biopsy specimens properly, but they often are responsible for interpretation of flow-cytometry and molecular genetic data as well. Pathologists are therefore in the best position to determine whether all the individual pieces of data fit together for the diagnosis under consideration. An additional important theme in the paper is that "well-prepared" blood and bone marrow aspirate smears and "adequate, well-processsed" bone marrow biopsy specimens are essential for the diagnosis. In the author's opinion, inadequate specimens usually account for most of the difficulties encountered in the proper diagnosis of these diseases. It is hoped that when an excellent specimen is available, the guidelines contained in this article may provide the pathologist with assistance in arriving at the most appropriate diagnosis.

Modulation of p210(BCR-ABL) activity in transduced primary human hematopoietic cells controls lineage programming

Retroviral transduction of primary hematopoietic cells with human oncogenes provides a powerful approach to investigating the molecular mechanisms controlling the normal proliferation and differentiation of these cells. Here we show that primitive human CD34(+) cord blood cells, including multipotent as well as granulopoietic- and erythroid-restricted progenitors, can be efficiently transduced with a MSCV-BCR-ABL-IRES-GFP retrovirus, resulting in the sustained expression by their progeny of very high levels of tyrosine phosphorylated p210(BCR-ABL). Interestingly, even in the presence of growth factors that supported the exclusive production of granulopoietic cells from green fluorescent protein (GFP)-transduced control cells, BCR-ABL-transduced progenitor subpopulations generated large numbers of erythropoietin-independent terminally differentiating erythroid cells and reduced numbers of granulopoietic cells. Analyses of individual clones generated by single transduced cells in both semisolid and liquid cultures showed this BCR-ABL-induced erythroid differentiation response to be elicited at a high frequency from all types of transduced CD34(+) cells independent of their apparent prior lineage commitment status. Additional experiments showed that this erythroid differentiation response was largely prevented when the cells were transduced and maintained in the presence of the BCR-ABL-specific tyrosine kinase inhibitor, STI-571. These findings indicate that overexpression of BCR-ABL in primary human hematopoietic cells can activate an erythroid differentiation program in apparently granulopoietic-restricted cells through a BCR-ABL kinase-dependent mechanism, thus providing a new molecular tool for elucidating mechanisms underlying lineage fate determination in human hematopoietic cells and infidelity in human leukemia.

Peripheral blood findings in chronic myeloproliferative disorders

Chronic myeloproliferative disorders are now frequently detected on routine total blood count. A careful analysis of PB smears allows the diagnosis in many cases, and helps to classify most of them. The peripheral blood parameters may be of prognostic value, especially in AMM. During the follow-up of CMPD, modifications of the PB are of great interest to detect an evolution toward a myelofibrosis or a blastic phase.

CD7 expression on CD34+ cells from chronic myeloid leukaemia in chronic phase

Thirty-seven patients with chronic phase chronic myeloid leukaemia and fourteen healthy controls have been evaluated for lineage differentiation with immunological markers on purified bone marrow CD34 positive cells by multiparameter flow cytometry. The myeloid-associated antigen CD33 and the stem cell factor receptor (CD117, c-kit) was expressed by 82.3% and 73.5% on CP-CML patients and by 57% and 57.5% on healthy donors, respectively (P < 0.005). CD34+/CD19+ or CD34+/CD10+ B-lymphoid cell population represented 9. 1% and 10.7% of the CD34+ cells in CML whereas in normal controls this subpopulation was expressed by 27.9% and 30.4% of the CD34+ cells, respectively (P< 0.005). The T-lineage associated markers (CD7 and CD2) were detected on a minor population of CD34+ BM cells of healthy controls (mean, 3.6% and 4.6%, respectively). The CD2 positive cells represented 1.5% of the CD34+ cells in CML patients. CP-CML patients co-expressed the CD7 antigen on a mean of 32.6% of the CD34+ BM cells. Moreover, 93% of this CD34/CD7 double positive subpopulation co-expressed CD33 antigen in CML patients. Co-expression of CD7 on CD34+ cells was induced to decrease significantly after short-term in vitro culture with the differentiation-inducing agent phorbol ester (PMA) and with a combination of cytokines (stem-cell factor, interleukin-3 and granulocyte colony-stimulating factor). In conclusion, a high co-expression of CD7 antigen is demonstrated on CD34+ cells of chronic phase-chronic myeloid leukaemia patients. The loss of CD7 marker following incubation with PMA and cytokines suggests that this antigen is expressed transiently in early myeloid leukaemic CML haemopoiesis.

Development of acute promyelocytic leukemia with isochromosome 17q after BCR/ABL positive chronic myeloid leukemia

We describe a pediatric case of acute promyelocytic leukemia with an i(17q) after treatment of BCR/ABL positive chronic myeloid leukemia (CML) for 3.5 years. The patient was treated with Busulphan, alpha-2a interferon, hydroxyurea, and cytosine arabinoside at various times in the course of the chronic phase of CML, because he had no HLA-identical donor for bone marrow transplantation. Hematologic remission was achieved for a short time, but cytogenetic remission was never possible. When promyelocytic blast crisis was diagnosed according to the French-American-British classification, cytogenetic studies revealed an i(17q) as a new feature in our patient. The promyelocytic transformation was associated with the appearance of an i(17q) preceding CML are discussed in the light of recent literature.

'Lymphoid' blast crisis of chronic myeloid leukaemia is associated with distinct clinicohaematological features

It has been suggested that in blast crisis (BC) of chronic myeloid leukaemia (CML) the clinical and laboratory features of patients with 'lymphoid' phenotype differ from those of patients with non-lymphoid BC. In order to assess any differences, 97 patients consecutively diagnosed with BC that followed a known chronic phase of CML were analysed. 19 patients had 'lymphoid' BC: in 17 the blasts expressed a B-lineage phenotype: in the remaining two they corresponded to T lymphoblasts. Four cases of B-lineage phenotype BC were considered as biphenotypic, due to the co-expression of myeloperoxidase and one or two other myeloid markers (CD33, CD13 and CD68) on the blast cells; in the other six cases of B-lineage BC the blasts expressed one or both of the myeloid markers CD33 (n = 4) and CD13 (n = 3). Patients with 'lymphoid' BC seldom had an accelerated phase prior to BC (1/19 v 36/78 with non-lymphoid BC, P = 0.002), had less frequent splenomegaly (9/19 v 59/78, P = 0.03) and hepatomegaly (5/19 v 45/78, P = 0.02) and showed a higher degree of marrow blast infiltration (mean value 74 +/- 24% v 38 +/- 23%, P < 0.0001), lesser blood basophilia (2.2 +/- 2.5% v 8.2 +/- 7.8%, P < 0.0001), and higher serum albumin levels (P = 0.001) than those with non-lymphoid BC. 13 patients with 'lymphoid' BC (68.4%) showed a favourable response to chemotherapy regimens including vincristine and prednisone and, overall, 'lymphoid' BC patients survived significantly longer than the remainder (median survival 12 months v 4.7 months, P = 0.006). These results indicate that 'lymphoid' BC of CML has a distinct clinicohaematological profile and confirm the better prognosis of such patients.

Burkitt-like blast crisis in chronic myeloid leukemia

A case of Burkitt-like blast crisis in a patient with chronic myelocytic leukaemia (CML) is presented. To our knowledge, this is the first such case recorded to date. The patient had a useful response to combination chemotherapy.

Immunophenotype and ultrastructural studies in blast crisis of chronic myeloid leukemia

Thirty-four patients with chronic myeloid leukemia in blast crisis (CML-BC) were evaluated for lineage differentiation with immunological markers and the presence of ultrastructural peroxidase. Eighteen (52.9%) were found to have myeloid blast crisis. Cytochemically, myeloperoxidase (MPO) could be detected only in six patients on light microscopy while in the remaining 12 patients, myeloid differentiation was confirmed only by demonstration of MPO either at ultrastructural level or by the reactivity with anti myeloperoxidase (anti MPO) antibody. Six (17.6%) had lymphoid blast crisis as identified by lymphoid specific markers (CD19; CD10; CD7; CD4) along with the absence of myeloid markers. Heterogenous blast cell populations with mixed lineage differentiation were seen in 4 (11.7%) patients. These cases showed both lymphoid (CD19, CD10) and myeloid (anti MPO and ultrastructural MPO) characteristics. A single case of megakaryoblastic blast crisis was identified with positivity for CD41 and CD42 along with the presence of platelet peroxidase at the ultrastructural level. Five cases (14%) of CML blast crisis remained unclassifiable. These results suggest that blast crisis in CML show an arrest of differentiation at an early stage when compared to de novo acute leukemias. This is particularly evident from the fact that MPO could only be demonstrated ultrastructurally or with anti MPO antibody in the majority of patients with myeloid differentiation. It is expected that utilisation of molecular studies including immunoglobulin and T-cell receptor gene rearrangement and m-RNA expression for myeloperoxidase will provide a better insight into the level of differentiation for the presently unclassifiable cases of CML-blast crisis.

Acute lymphoid leukemias following either a previous chronic myelogenous leukemia or myelodysplastic syndrome: phenotypic and genomic differences

We have analyzed the immunological and genomic characteristics of the lymphoid blast cells present in secondary lymphoid leukemias following either a previous chronic myelogenous leukemia (CML) or myelodysplastic syndrome (MDS). Twenty-one of 107 secondary leukemias analyzed displayed a lymphoid phenotype (15 after a CML and 6 after a MDS). Most of the lymphoid blast crises of CML (73%) correspond to pure lymphoid transformation, all of them having a common acute lymphoblastic leukemia (ALL) phenotype (CD10+). By contrast, in all MDS cases, lymphoid blast cells coexisted with another myeloid component (hybrid leukemias) and showed an early B phenotype. IgH and TCR-gamma gene rearrangements were detected in the CML-lymphoid blast crisis (86% of cases) more frequently than in the MDS transformations (33%). The TCR-beta gene was in germ line configuration in all cases while TCR-delta gene rearrangements were detected in four cases, all of them corresponding to a previous diagnosis of CML. These results show the existence of both immunophenotypic and genomic differences between the lymphoid transformations of either CML or MDS, which could reflect differences at the stage of maturation of the target cell in these transformations.

High incidence of meningeal leukemia in lymphoid blast crisis of chronic myelogenous leukemia

Fifteen patients with lymphoid blast crisis of chronic myelogenous leukemia (LyBC-CML) and five patients with acute lymphoblastic leukemia converting to Philadelphia-positive (Ph+) chronic myeloid leukemia (ALL Ph + CML) were followed. Seven of 15 (46.7%) LyBC-CML patients developed meningeal leukemia within a median period of 6 months (range 2-11 months), while there was no medullary relapse. Five of these responded well to triple intrathecal therapy. In the ALL Ph + CML patients, in spite of central nervous system (CNS) prophylaxis with IT MTX and 18 Gy cranial radiation, two of five patients (40%) experienced meningeal leukemia, one isolated and the other with medullary relapse. The data confirm that LyBC-CML patients experience a high incidence of meningeal leukemia. The role of CNS prophylaxis is not very clear, but its use may delay development and reduce morbidity due to CNS disease.

Immunophenotypic, genomic and clinical characteristics of blast crisis of chronic myelogenous leukaemia

We have studied phenotypic and clinical features in a consecutive series of 45 patients with chronic myelogenous leukaemia (CML) in blast crisis (BC). In addition, in 22 of these patients we have analysed the genotypic characteristics including immunoglobulin, T-cell receptor (TCR) and major breakpoint cluster region (M-bcr) gene organization. The granulomonocytic and megakaryoblastic lineages are the most commonly involved in these BC of CML (33% and 33% of cases, respectively); only 18% of our cases displayed a lymphoid phenotype. Moreover, both morphological and immunophenotypic studies revealed the frequent coexistence of two or three cell populations, especially when the megakaryoblast component is involved. The lymphoid BC displayed the highest incidence of complete remissions although this was not associated with a longer survival. Only minor differences between the different myeloid subgroups were observed. Immunoglobulin heavy chain (IgH) gene rearrangement was found in five of the six lymphoid BC and in one myeloid BC. Only one case showed k light chain gene rearrangement. In all but one myeloid BC the TCR-beta gene was in germline configuration. The TCR-gamma gene was rearranged in all lymphoid and one myeloid BC, while TCR-delta gene rearrangement was detected in 67% and 16% of the lymphoid and myeloid BC, respectively. Most of the lymphoid BC (4/5) had the M-bcr breakpoint in subregion 3, while the myeloid BC had the breakpoint either in subregion 2 or 3. No differences between the different myeloid phenotypic subgroups were observed in relation to breakpoint.

A hypothetical model to explain the 'termination' of chronic myeloid leukemia into blastic crisis

Chronic myeloid leukemia is characterised by two discrete phases, a 'benign' phase which terminates into an 'acute' phase. Various explanations have been given to explain the cause of 'blastic' crisis in CML. But the consistency and regularity with which blast crisis occurs and the irregularity with which the factors which are ascribed to cause it (e.g. additional chromosomal abnormalities, change in bcr/abl rearrangement, etc. occur, suggests that CML-BC is not a stochastic process in the natural history of CML but is predetermined at the time of the first mutation in the stem cell. A hypothetical model is put forward proposing this. Different points supporting the model are discussed. The most important implication of this model would be to provide an insight that should lead to the development of more selective and appropriate treatment strategies for this disease.