Subtype Of Acute Myelogenous Leukemia Research Articles

Role of c/ebpα in granulocytic differentiation and myeloid leukemogenesis

Abstract C/EBPα plays a critical role in myeloid differentiation. Specifically, induced expression of C/EBPα in early myeloid cells directed differentiation along the granulocytic pathway. In addition, C/EBPα knockout mice demonstrate a block in granulocyte differentiation. For this reason, we investigated abnormalities in C/EBPα in human acute myelogenous leukemia (AML). We identified eleven heterozygous mutations in C/EBPα in ten patients, mostly AML-M2 subtype without the t(8;21). The mutations resulted in production of mutant alleles which blocked DNA binding, transactivation of granulocyte target genes, and induction of granulocytic differentiation mediated by the wild type allele in a dominant negative manner. This is the first report of mutations in C/EBPα in human neoplasia, and such mutations are likely to induce the differentiation block found in AML. The hallmark of acute promyelocytic leukemia (APL), another subtype of AML, is the translocation t(15;17) and a block in promyelocytic differentiation. Treatment with A ll- T rans- R etinoic A cid (ATRA) induces blast differentiation and clinical remission. In primary human APL cells, we did not find mutations in C/EBPα, but the fusion protein PML/RARα physically interacts with C/EBPα to block its function in an ATRA reversible manner. These studies implicate disruption of C/EBPα DNA binding and function by physical interaction with PML/RARα as a mechanism contributing to the block in differentiation following expression of the fusion protein in APL. In summary, these results implicate abnormalities in function of C/EBPα as a major target leading to the block in myeloid differentiation found in AML.

Acute Promyelocytic Leukemia: From Morphology to Molecular Lesions

Acute promyelocytic leukemia is a unique subtype of acute myelogenous leukemia characterized by distinct morphologic, cytogenetic, and clinical characteristics. The t(15;17) translocation, which is a hallmark of this disease, results in a transcriptionally active fusion gene-derived from the PML gene from chromosome 15 and the retinoic acid receptor alpha (RARa) gene from chromosome 17. The PML/RARa protein product is responsible for the leukemic phenotype in these patients, but is also able to respond to pharmacologic levels of retinoic acid and induce cell differentiation. Treatment of this leukemia by retinoic acid represents the first example of gene-directed differentiation therapy for acute leukemia and has lead to greater understanding of the pathogenesis of this disease at the molecular level.

Signaling in leukemia: which messenger to kill?

Chromosomal translocations can activate oncogenes either by juxtaposing an inappropriate enhancer or promoter with a proto-oncogene or by fusing different genes to create novel combinations of protein-coding domains (1). The former mechanism is typical of lymphoid leukemias; in such cases, the regulatory region involved determines which cell types are at risk of transformation. For example, follicular lymphoma, a class of B-cell tumor, arises in cells containing a t(14;18) chromosomal translocation that places the Bcl2 gene under the control of immunoglobulin regulatory sequences. When novel fusion proteins drive oncogenesis, on the other hand, cell specificity may have other sources: new activities resulting from gain or loss of specific sequences, protein relocalization leading to both gain and loss of substrate access, or modulation of activity by 1 of the fusion partners. Such fusion proteins are typically found in myeloid leukemias. For example, the t(8;21) translocation creates the AML1/ETO fusion gene associated with the M2 subtype of acute myelogenous leukemia, and t(9;22) creates the bcr/abl oncogene which causes chronic myeloid leukemia. In this issue of the JCI, Tomasson et al. report an in vivo mutation analysis of another chimeric oncoprotein of this class, the TEL/PDGFβR fusion protein found in a subset of patients with chronic myelomonocytic leukemia (2). These new data indicate that the oncotropicity of TEL/PDGFβR depends critically on interactions between specific phosphotyrosine residues in the cytoplasmic portion of the oncoprotein, and a variety of signaling proteins containing the SH2 domain.

Effect of Thrombopoietin on Acute Myelogenous Leukemia Blasts

It has been shown that the expression of c-mpl, which is a specific receptor for thrombopoietin (TPO), is restricted to the surface of megakaryocytes, platelets, human CD34+ progenitor cells and human erythroid/megakaryocytic leukemic cell lines. Recently, however, it has been reported that some acute myelogenous leukemia (AML) blasts expressed c-mpl on their cell surface and proliferated in response to TPO. We therefore investigated the effect of thrombopoietin on the growth of leukemic blasts from patients with CD7-positive acute myelogenous leukemia (AML), which is a distinct biological and clinical subtype of AML. Significant growth responses of leukemic blasts to TPO were seen in 10/10 CD7+ and 7/20 CD7 AML cases using 3H-thymidine incorporation, while synergistic stimulatory effects of TPO with stem cell factor (SCF), interleukin-3 (IL-3), granulocyte colony-stimulating factor, and granulocyte-macrophage colony-stimulating factor were observed in both groups. In a leukemic blast colony assay, significant growth response to TPO was observed in 5/6 CD7+ and 4/17 CD7− AML cases examined. Furthermore, the expression of c-mpl seemed to be higher in CD7+ AML cases than in CD7− cases, suggesting a relationship between the expression of c-mpl and the proliferative response to TPO. These findings imply that CD7+ leukemic blasts express functional TPO receptors and proliferate in response to TPO. Thus CD7 expression on AML blasts may indicate the involvement of leukemic progenitors at an early stage of multipotent hemopoietic stem cells. In this review, we discuss the effect of TPO on AML blasts, especially in CD7+ AML cases.

Assessment of Coagulation Disorders in Patients with Acute Leukemia Before and After Cytostatic Treatment

Coagulation disorders are often the reason for fatal bleeding in acute promyelocytic leukemia. Their occurrence as well as pathogenesis and prognostic significance in other subtypes of acute myelogenous leukemia and acute lymphoblastic leukemia is less known. Tests were carried out in 70 patients including 49 with AML and 21 with ALL. In all patients throm-bin-antithrombin complexes (TAT), D-dimer (DD) and plasmin-antiplasmin complexes (PAP), antithrombin 111 activity, fibrinogedfibrin degradation products, AFlT and PT were determined. The tests were performed on diagnosis and after cytostatic treatment.The level of TAT, DD and PAP was elevated in 83% of the patients on diagnosis and in 90% after treatment. The highest values were observed in AML M3 patients. Among leuke-mic patients with normal levels of TAT, DD and PAP at diagnosis, cytostatic treatment had a negligible effect on the level of these markers. During remission the levels of these markers returned to the normal values while in patients without remission they were either elevated or returned to normal values. No correlation between the levels of activation markers and remission rate was reported. DIC was diagnosed in 13 patients including three after chemotherapy. The DIC was acute or subacute in AML and chronic in ALL patients.In the majority of acute leukemia patients there were already changes on diagnosis indicating coagulation activation. Except for AML M3, these usually had a subclinical course. The TAT, DD and PAP tests are not reliable markers of remission in acute leukemias.

Combined analysis of differentiation inhibitory factor nm23-H1 and nm23-H2 as prognostic factors in acute myeloid leukaemia.

Differentiation inhibitory factor (nm23 protein) inhibited the induction of the differentiation of various leukaemic cell lines. We previously reported that nm23 genes (H1 and H2) were overexpressed in acute myelogenous leukaemia (AML) and nm23-H1 expression predicted the prognosis of AML, especially AML-M5. To clarify the correlation between French-American-British (FAB) classification and nm23 expression level and to clarify the involvement of nm23-H2 and nm23-H1 in patient survival, we investigated the relative levels of nm23-H1 and -H2 mRNA in 76 AML samples using the reverse transcriptase-polymerase chain reaction. We confirmed that the expression of both nm23-H1 and -H2 genes in AML samples from three different hospitals was significantly higher than that in normal blood cells (P < 0.0005). Overexpression of nm23-H1 was observed in each FAB AML-M1, -M2, -M3, -M4 or -M5 subtype, and the predictive effect of nm23-H1 expression on AML prognosis was shown in FAB AML-M2 and -M5 cases. Although overexpression of nm23-H2 was also found in each FAB subtype, the expression of nm23-H2 in AML-M1 and -M3 cells was not significantly higher than that in normal cells. Among AML subtypes, AML-M3 showed the lowest expression levels of both nm23 genes. To understand the relationship between nm23-H1 and -H2 expression levels, nm23 expression levels for all the AML cases were plotted and divided into four groups (group A, nm23-H1 and -H2 both high; B, both low; C, only nm23-H1 high; D, only nm23-H2 high). A statistically significant correlation between the levels of expression of nm23-H1 and -H2 was observed (r= 0.726). Most AML-M3 cases belonged to group B, but not other types of AML. Analysis of survival probability between the groups showed that group B survived for significantly longer compared with group A. Furthermore, AML-M3 cases survived for significantly longer compared with non-M3 cases in the same group B. These data suggest that low expression levels of both nm23-H1 and -H2 are associated with good prognosis in AML patients.

Partial duplication of the MLL gene in acute myelogenous leukemia without karyotypic aberration

Partial duplication of the MLL gene is a recently characterized novel genetic mechanism for leukemogenesis. A close association with trisomy 11 has been observed. A case of acute myelogenous leukemia (AML) M6 without karyotypic abnormality was found to have rearrangement of the MLL gene. Southern analysis with an MLL exon 2 probe revealed partial duplication of the MLL gene, with a duplicated MLL transcript amplified by reverse transcription polymerase chain reaction (RT = PCR). The presence of trisomy 11 was excluded by fluorescence in situ hybridization (FISH). Few cases of AML with MLL gene duplication have been reported, and they showed involvement of the M1, M2, and M4 subtypes. This case is the first reported case with an M6 phenotype, and highlights the importance of investigating for MLL gene mutations in all subtypes of AML, as they may carry prognostic significance.

Retinoid Induced Apoptosis in Leukemia Cells Through a Retinoic Acid Nuclear Receptor-Independent Pathway

AbstractTrans retinoic acid (RA) has proven to be a potent therapeutic agent in the treatment of acute promyelocytic leukemia. Unfortunately, other subtypes of acute myelogenous leukemia are resistant to the antiproliferative and differentiating effects of RA. In this report, we describe a novel retinoid 6-[3-(1-adamantyl)-4-hydroxyphenyl]-2-naphthalene carboxylic acid (AHPN; CD437) that not only totally inhibits the proliferation of RA-resistant leukemic cell lines HL-60R and K562 but also induces apoptosis in these cells. Exposure of HL-60R to CD437 results in the rapid (within 30 minutes) increase of the cyclin-dependent kinase inhibitor p21waf1/cip1 as well as GADD45 mRNA. Manifestations of CD437-mediated programmed cell death are noted within 2 hours, as indicated by both the cleavage and activation of the CPP32 protease and cleavage of poly (ADP-ribose) polymerase. This is followed by cleavage of bcl-2 and internucleosomal DNA degradation. HL-60R cells do not express the retinoid nuclear receptor RARβ and RARγ and express a truncated RARα. Thus, CD437 induction of p21waf1/cip1 and GADD45 mRNAs and apoptosis occurs through a unique mechanism not involving the retinoid nuclear receptors. CD437 represents a unique retinoid with therapeutic potential in the treatment of myeloid leukemia.

DEK, an autoantigen involved in a chromosomal translocation in acute myelogenous leukemia, binds to the HIV-2 enhancer.

The product of the dek oncogene is the 43-kDa DEK nuclear protein. DEK was first identified in a fusion with the CAN nucleoporin protein in a specific subtype of acute myelogenous leukemia. DEK has also been shown to be an autoantigen in patients with pauciarticular onset juvenile rheumatoid arthritis. Further, the last 65 amino acids of DEK can partially reverse the mutation-prone phenotype of cells from patients with ataxia-telangiectasia. However, in spite of these significant disease associations, the function of DEK has remained unclear. The HIV-2 peri-ets (pets) site is a TG-rich element found between the two Elf-1 binding sites in the HIV-2 enhancer. The pets element mediates transcriptional activation whether the enhancer is stimulated by phorbol 12-myristate 13-acetate (PMA) alone, phytohemagluttinin (PHA) alone, PMA plus PHA, soluble antibodies to the T cell receptor, immobilized antibodies to the T cell receptor, or by antigen. Previously, we purified and characterized the pets factor, demonstrating that it is a 43-kDa nuclear protein. We now describe the identification of DEK as this 43-kDa pets factor. Using a modified Southwestern screening procedure, we find that DEK can recognize the pets element. We demonstrate the ability of recombinant DEK to bind specifically to the pets site using the electrophoretic mobility shift assay (EMSA) and DNase I footprinting. "Supershift" EMSA further confirms that DEK is the dominant protein binding to the pets site in T cell extracts. Our findings show that DEK is a site-specific DNA binding protein that is likely involved in transcriptional regulation and signal transduction. This has implications for multiple pathogenic processes, including hematologic malignancies, arthritis, ataxia-telangiectasia, and AIDS caused by HIV-2.

Serum Interleukin-6 Levels in Adult Acute Myelogenous Leukemia: Relationship with Disease Characteristics and Outcome

Serum interleukin-6 (IL-6) levels were measured in 58 adult patients with newly diagnosed acute myelogenous leukemia (AML) using an ELISA method in order to find potential clinical correlations. Detectable average levels were 57 ± 68 pg/ml and 52 patients (90%) had higher cytokine levels than normal donors. IL-6 levels (115 ± 102 pg/ml versus 36 ± 40 pg/ml, p = 0.0001) were higher in patients with fever of apparently non infectious origin, and higher levels were associated with higher percentage of blasts in the peripheral blood (R = 0.29, p = 0.04) and in the bone marrow (R = 0.39, p = 0.003), elevated serum LDH level (R = 0.36, p = 0.01), hyperbilirubinemia (R = 0.36, p = 0.008), elevated serum GGT level (R = 0.46, p = 0.003), and elevated serum GOT (R = 0.36, p = 0.008) and GPT levels (R = 0.44, p = 0.004). Highest IL-6 levels were observed in FAB M1 (86 ± 112 pg/ml), M3 (73 ± 69 pg/ml), and M6 (92 ± 60 pg/ml) AML subtypes. Serum IL-6 levels in AML might be related to both non specific inflammatory reactions and the specific biology of the disease.

A family inheriting different subtypes of acute myelogenous leukemia

Rare inherited cancer syndromes have proven invaluable for the identification of genes involved in the more frequent corresponding noninherited cases. We report on a family with an adult onset, incompletely penetrant, autosomal dominant syndrome of myelodysplasia and acute myelogenous leukemia, affecting at least eight, and probably ten, individuals from three generations. The patients have developed leukemias differing in morphologic subtype, tumor cytogenetics, and abruptness of presentation. Some have presented with acute onset and others with protracted myelodysplasia. This family does not have an unusual incidence of other malignancies; however, one person at 50% risk of inheriting this gene developed atypical mycobacterium infection in the absence of leukemia, but also without appreciable risk factors for acquired deficiencies in cellular immunity. Features common to affected family members, including the individual with mycobacterium infection, are the early presence in the bone marrow of red cell and platelet maturation defects. A search for mutations in diseased marrows fails to detect abnormalities of p53 or N-ras. Two of the affected family members, third degree relatives, have co-inherited a constitutional chromosomal banding variation of 9p21-22, potentially suggesting linkage to this locus. The variable penetrance and expressivity of this syndrome support a multistep model of leukemia evolution, in which the gene defined by this family's syndrome is the signal step.

CD117/CD34 expression in leukemic blasts.

CD117 is a transmembrane protein receptor encoded by the c-kit proto-oncogene. The CD117 ligand is stem cell factor, an important hematopoietic regulator. CD117 is present on approximately 4% of normal bone marrow mononuclear cells and in acute myelogenous leukemia (AML) and chronic myelogenous leukemia in myeloid blast crisis, but rarely in acute lymphoblastic leukemia (ALL). Initially viewed as a primitive myeloid marker, CD117 has been identified in all FAB subtypes of AML and may predict poor outcome. CD34, a primitive stem cell marker, may also predict poor outcome. The aim of this study was to examine the relationship between CD117 and CD34 expression on leukemic blasts and to determine whether CD117 is related to lymphoid-associated antigen (LAA) expression in AML. Consecutive bone marrow samples were studied from cases of AML (30 cases), myelodysplastic syndromes (MDS) (4 cases), myeloproliferative disorders in blast crisis (MPD-BC) (6 cases), and ALL (5 cases). Cases were diagnosed according to FAB criteria and included M0 (3 cases), M1 (2 cases), M2 (13 cases), M3 (1 case), M4 (6 cases), M5 (3 cases), M6 (1 case), AML NOS (1 case), RAEB (3 cases), and RAEB-T (1 case). CD117 and CD34 were analyzed by multiparameter flow cytometry. Blasts in 10 de novo AML samples were CD117+/CD34+ in 4 cases, CD117+/CD34-in 3 cases, CD117-/CD34+ in 1 case, and CD117-/ CD34- in 2 cases. Blasts in 20 cases of relapsed AML were CD117+/ CD34+ in 13 cases, CD117+/CD34- in 6 cases, and CD117-/CD34+ in 1 case. Blasts in MDS were CD117+/CD34+ in 3 cases, CD117-/ CD34+ in 1 case. Blasts in MPD-BC were CD117+/CD34+ in 4 cases, CD117-/CD34+ in 2 cases. Blasts in ALL were CD117+/CD34+ in 1 case, CD117-/CD34+ in 1 case, CD117-/CD34- in 3 cases. Of 26 cases of CD117+ AML, CD4 was expressed in 15 (58%) cases, CD7 in 7 (27%) cases, and CD2 in 2 (8%) cases. CD117/CD34 expression did not correlate with FAB subtype of AML. CD117 is borne on most leukemic blasts of myeloid origin (in this study, 87% of AML, 80% of MPD-myeloid BC, and 75% of MDS) and does not exclude expression of LAA. Although CD117 is a receptor for stem cell factor, its expression does not appear to correlate with CD34 positivity.

Neutrophilic Dermatoses During Granulocytopenia

Noninfectious cutaneous neutrophilic lesions can occur during granulocytopenia, but their mechanism remains unknown. We undertook a retrospective study of the neutrophilic dermatoses that developed during granulocytopenia induced by chemotherapy for acute myelogenous leukemia. Seven men and one woman were included (2.6% of treated cases of acute myelogenous leukemia); half had acute myelogenous leukemia subtypes 4 and 5. The male-to-female ratio was 7:1. Neutrophilic eccrine hidradenitis was diagnosed in five cases, Sweet's syndrome in two cases, and difficult-to-classify neutrophilic dermatoses in one case. Cutaneous lesions appeared 12.5 days after the start of chemotherapy, and the mean leukocyte count was 0.426 x 10(9)/L. Three patients needed corticosteroids systemically. Neutrophilic dermatoses during chemotherapy-induced granulocytopenia seem to occur more frequently in men with acute myelogenous leukemia subtypes 4 and 5.

Low incidence of MDR1 expression in acute promyelocytic leukaemia

The MDR1 gene product, P-glycoprotein, functions as a transmembrane efflux pump for certain cytotoxic agents including anthracyclines. Based upon the clinical observation that patients with acute promyelocytic leukaemia (APL) respond favourably to anthracyclines, we hypothesized that APL cells may have low levels of MDR1 expression. We therefore investigated MDR1 expression in 10 patients with APL and compared results with those obtained in 18 patients with other subtypes of acute myelogenous leukaemia (AML). Prior to reverse transcriptase polymerase chain reaction with MDR1 specific primers, leukaemic cells were purified by fluorescence activated cell sorting to exclude normal haemopoietic cells, in particular lymphocytes, from the MDR1 analysis. In sorted APL cells, MDR1 expression was detected in only two of 10 patients, which was significantly different from findings in other AML subtypes (MDR1 expression in 14/18 patients; P < 0.01). When unsorted specimens from APL patients were studied, five of six cases were MDR1 positive, whereas sorted APL cells were shown to express MDR1 mRNA in only one of these cases. MDR1 mRNA levels expressed as MDR1/beta-2 microglobulin ratios were significantly lower in APL (0.24 +/- 0.2, mean +/- SD) than in AML (0.75 +/- 0.48; P < 0.01). We conclude that low or absent expression of MDR1 in APL cells may contribute to the efficacy of anthracyclines in the treatment of APL.

Expression of MDR1 by normal bone marrow cells and its implication for leukemic hematopoiesis.

Expression of MDR1 is a well-characterized mechanism leading to resistance of tumor cells to drugs like vinca-alkaloids, anthracyclines, and epipodophyllotoxins. In hematopoiesis, recent data indicate that not only leukemic cells, but also some populations of normal hematopoietic cells, particularly CD34+ progenitor cells as well as peripheral blood lymphocytes, express a functional multidrug-resistant phenotype. Among CD34+ cells, we found evidence that myeloid committed precursor cells (CD34+/CD33+) have lower levels of MDR1 expression than earlier CD34+ cell populations, but there was no difference in MDR1 expression between CD34+/HLA-DR- and CD34+/HLA-DR+ subpopulations. During normal myeloid differentiation, MDR1 expression is down-regulated, which is similar to our observations in acute myelogenous leukemia (AML): MDR1 expression was only rarely detected in acute promyelocytic leukemia, which was in contrast to other subtypes of AML; also, within leukemic subpopulations of the same patient, higher MDR1 levels were correlated with a more immature immunophenotype. Regarding regulation of MDR1 expression, we did not observe changes of MDR1 expression in normal CD34+ cells in response to various cytokines. However, in 2 patients with AML treated with interleukin-3 and granulocyte-colony stimulating factor, respectively, a significant down-regulation of MDR1 expression was found after 24 hours. In conclusion, there is evidence that the pattern of MDR1 expression observed in leukemias reflects the distribution of MDR1 in normal hematopoiesis. In contrast to normal CD34+ cells, leukemic cells from some AML patients can respond to cytokines with a down-regulation of MDR1, which may contribute to response to cytokine/chemotherapy combinations.

Terapêutica da Leucemia promielocítica aguda com ácido Trans-Retinóico. Experiência do Hospital de Santa Maria, Faculdade de Medicina de Lisboa.

Acute promyelocytic leukemia (APL) is a rare subtype of acute myelogenous leukemia that is usually associated with a fatal hemorrhagic diathesis. All trans-retinoic acid (ATRA) is an active metabolite of vitamin A that differentiates the malignant cell clone, corrects the coagulopathy, and induces complete remission in the vast majority of patients with APL. Between June 1992 and September 1993, 8 patients with APL (4 previously untreated, 3 in first relapse and 1 in second relapse) received ATRA. Complete remission was achieved in 7 patients; in 5 with ATRA alone and in 2 with ATRA followed by cytotoxic chemotherapy due to the development of asymptomatic hyperleukocytosis. The earliest signs of response were the correction of the coagulopathy and an increase in the white blood cell count. Sequential morphological and immunophenotypical analyses of the bone marrow revealed differentiation of the malignant cell clone, in the absence of bone marrow hypoplasia. 4 of 5 patients treated only with ATRA until complete remission had late leukopenia. The most frequent adverse effects were dryness of skin and mucosae, hypertrigliceridemia and hypercholesterolemia, and a moderate increase in liver transaminases. An increase in the white blood cell count was common, and in two cases exceeded 35.0 x 10(9)/l. One of these patients developed multiple thrombosis of the extremities after cytotoxic chemotherapy. We frequently observed an increase in lactic dehydrogenase levels that was concomitant with the peak in the white blood cell count. The only patient on whom complete remission was not achieved was 60 years old, had chronic obstructive pulmonary disease, and died in the third week of therapy with a pulmonary distress syndrome.(ABSTRACT TRUNCATED AT 250 WORDS)

Acute promyelocytic leukemia. The therapeutic advances

Acute promyelocytic leukemia (APL) is a rare subtype of acute myelogenous leukemia. It is frequently associated with a life-threatening hemorrhagic diathesis, often aggravated by induction cytotoxic chemotherapy. Patients with APL have bone marrow infiltration by abnormal promyelocytes, usually with prominent cytoplasmic granulation. These patients have a unique cytogenetic abnormality, a balanced reciprocal translocation between the long arms of chromosomes 15 and 17. The nuclear retinoic acid receptor alpha gene, on chromosome 17, is translocated to the PML gene region, on chromosome 15, resulting in the synthesis of two fusion messenger ribonucleic acids, PML/RAR-alpha and RAR-alpha/PML, easily detected by the reverse transcriptase polymerase chain reaction. This assay is extremely useful in the diagnosis and detection of minimal residual disease in APL patients. All trans-retinoic acid (ATR) differentiates the malignant cell clone and corrects the coagulopathy associated with this disease. The most important adverse effect is a respiratory distress syndrome, treatable with steroids, if detected at its onset. ATR yields durable remissions in patients with APL, after consolidation with cytotoxic chemotherapy.

Classification of AML by morphologic, immunologic and cytogenetic criteria. Review with reference to subtypes in the AML-BFM-87 study

The current FAB classification of acute myelogenous leukemia (AML) by morphologic, immunologic and cytogenetic features is described and the incidence of subtypes and variant forms of AML in study AML-BFM-87 is given. In general, lymphoblastic or myeloid blast populations can be identified by morphologic, cytochemical and immunologic parameters, while immunophenotyping facilitates diagnosis in biphenotypic leukemia. Furthermore, the AML subtypes M0 and M7 (defined in 1985 and 1991) can only be ascertained by the presence of lineage-associated markers. Whereas chromosome aberrations provide an insight into the neoplastic process and assure diagnosis. Thus, next to morphologic findings, immunologic and cytogenetic studies are essential for a definite diagnosis of AML.

What is the Best Treatment for Acute Promyelocytic Leukemia?

The modern treatment of acute myelogenous leukemia (AML), consists of a polychemotherapeutic induction treatment followed by a post-remission therapy of variable intensity and duration and acute promyelocytic leukemia (APL) does not differ from this behavior. However, differently from the other AML subtypes, APL shows a high response rate to induction monochemotherapies with anthracycline drugs. This high response rate to anthracycline monochemotherapies is very peculiar of APL. Moreover, it has been suggested that maintenance treatment regimens incorporating the drugs Methotrexate and 6-Mercaptopurine, two drugs generally not utilized in the post-remission treatment of other AML subtypes, may be effective in prolonging the leukemia-free survival of APL. Furthermore, the results firstly obtained by a Chinese group in 1988 by using the vitamin A derivative all-trans retinoic acid (ATRA) have been successively confirmed by several other groups in the world. Therefore, at present the all-trans retinoic acid appears to be the best CR inducer in APL. However, these CRs are short lasting when maintained with ATRA alone and eventually all patients relapse. As a consequence, patients achieving CR with ATRA still require intensive post-remission chemotherapy to maintain the CR. As for bone marrow transplantation procedures, it is our opinion that they do not represent the treatment of choice of APL in first CR considering the very good results obtained with standard pharmacological approaches. In conclusion, only future randomized prospective trials will clarify which, among the several proposed therapeutic approaches, should be preferred in this very peculiar subtype of AML.

Biological characteristics of CD7 positive acute myelogenous leukaemia.

We studied the biological characteristics of CD7+ acute myelogenous leukaemia (AML). We diagnosed nine out of 88 consecutive AML cases as CD7+ AML based on myeloperoxidase positivity and surface antigen expression. In eight of these nine cases more than 20% of leukaemic blasts were found to coexpress both CD7 and a myeloid-associated antigen, CD33, by a two-colour flow-cytometric assay, while in the remaining case more than 90% of blasts were positive for CD7 and myeloperoxidase. CD7+ AML was most frequently observed in M1 among AML subtypes according to the FAB classification. An early stage-specific antigen, CD34 was also expressed on leukaemic blasts from eight of these nine cases. Neither the T-cell receptor (TcR)-beta nor the TcR-gamma gene was clonally rearranged in any of the cases. We then studied the proliferative responses to stimulation by various growth factors. Among interleukin-3 (IL-3), granulocyte/macrophage colony-stimulating factor (GM-CSF), and granulocyte-CSF (G-CSF), IL-3 showed the strongest stimulatory effect on DNA synthesis and leukaemic blast colony formation in 8/9 and 6/8 CD7+ AML cases examined, respectively. On the other hand, the strongest stimulatory effect exerted by IL-3 on blast colony formation was observed in only six out of the 33 CD7- AML cases examined. Furthermore, CD7+ AML blasts could proliferate in response to stem cell factor (SCF); SCF alone showed stimulatory effects on blast colony formation (7/8 cases), and in 5/7 SCF-responding cases, stimulatory effects of SCF were more potent than those of IL-3. In addition, SCF enhanced blast colony formation synergistically with IL-3 in four of these seven cases. These data suggest that progenitor cells of CD7+ AML may possess the biological properties characteristic of immature haematopoietic stem cells.