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Classification of acute lymphoblastic and myeloid leukemias (ALL and AML) remains heavily based on phenotypic resemblance to normal hematopoietic precursors. This framework can provide diagnostic challenges for immunophenotypically heterogeneous immature leukemias, and ignores recent advances in understanding of developmental multipotency of diverse normal hematopoietic progenitor populations that are identified by transcriptional signatures. We performed transcriptional analyses of a large series of acute myeloid and lymphoid leukemias and detected significant overlap in gene expression between cases in different diagnostic categories. Bioinformatic classification of leukemias along a continuum of hematopoietic differentiation identified leukemias at the myeloid/T-lymphoid interface, which shared gene expression programs with a series of multi or oligopotent hematopoietic progenitor populations, including the most immature CD34+CD1a-CD7- subset of early thymic precursors. Within these interface acute leukemias (IALs), transcriptional resemblance to early lymphoid progenitor populations and biphenotypic leukemias was more evident in cases originally diagnosed as AML, rather than T-ALL. Further prognostic analyses revealed that expression of IAL transcriptional programs significantly correlated with poor outcome in independent AML patient cohorts. Our results suggest that traditional binary approaches to acute leukemia categorization are reductive, and that identification of IALs could allow better treatment allocation and evaluation of therapeutic options.

According to French and European experience, hyperleukocytosis occurs during ATRA differentiation therapy in about 70% of de novo and 25% of relapsed APL cases. The most frequently suggested cause for this side-effect is an ATRA-induced proliferation of APL cells. However, no definite explanation for such a proliferative effect has been clearly established. Another mechanism directly related to the differentiation of marrow leukemic cells could be a change in their microrheology, allowing their release from the bone marrow and their transfer toward peripheral blood (PB) and tissues. Using a single cell aspiration assay into a glass restrictive channel, we measured APL cell viscosity values in five de novo APL patients. A deformability index (DI) was defined as the ratio of mean normal neutrophil viscosity x 100/mean APL cell viscosity. Results were the following: (1) at diagnosis, two patients had high marrow DI (96 and 250%) and three patients had low marrow DI (16, 17, and 40%); (2) when PB and marrow APL cells were simultaneously tested, PB APL cells display higher DI than marrow APL-cells; (3) the two patients with high initial marrow DI experienced an ATRA-induced hyperleukocytosis after only 1 day of treatment; (4) in the three patients with low initial marrow DI, the DI was increasing during ATRA therapy and hyperleukocytosis seemed to occur when a large amount of maturing APL cells reached a viscosity value similar to that of mature neutrophils. These results suggest that an asynchronism between rheological and morphological maturation in each APL cell might explain the occurrence of hyperleukocytosis in some patients during ATRA differentiation therapy.

APL-associated hemostasis disorders result from at least two distinct mechanisms due to the release of procoagulant activities and plasminogen activators from the leukemic cells. These two mechanisms (thrombin activation and plasmin activation) may cleave the fibrinogen molecule, but their respective roles in low fibrinogen levels and bleeding diathesis genesis remain in dispute. In vivo ATRA therapy induces a rapid correction of both low fibrinogen level and bleeding tendency, but no clear explanation of this beneficial effect has been proposed. We prospectively investigated 27 APL patients at presentation for diffuse intravascular coagulation (DIC) markers (prothrombin activation fragment and thrombin/antithrombin complexes) and plasmin-dependent primary fibrinogenolysis markers (alpha 2 plasmin inhibitor consumption +/- plasmin/alpha 2 plasmin inhibitor complexes). Fourteen of these patients were then serially studied during the first 2 weeks of ATRA therapy. Four of them, however, developed an hyperleukocytosis requiring additional chemotherapy before the end of the 2nd week. At presentation, low level of fibrinogen was clearly associated with alpha 2 plasmin inhibitor deficiency (p < 0.01), while DIC was equally present in fibrinogenopenic and non-fibrinogenopenic patients. Moreover, was observed a rapid simultaneous correction of low fibrinogen levels and plasmin activation markers in APL patients undergoing ATRA therapy (before day 5), but a more prolonged persistence of DIC markers (until day 14). Initial bleeding syndrome seemed more frequent in patients with initial low fibrinogen level. These data indicate that plasmin-dependent primary fibrinogenolysis is the major etiologic factor of low fibrinogen level in APL patients. In vivo differentiation ATRA therapy induces a rapid decrease in the plasmin activation and a normalization of fibrinogen level, while DIC may in vivo persist for several weeks. Prospective studies evaluating antifibrinolytic agents as therapy of APL-associated hemostasis disorders should be considered. Additionally, prophylactic heparin therapy might be useful after day 5 in patients undergoing ATRA therapy, since they present a prolonged procoagulant tendency.

Differentiation of normal myeloid cells is accompanied by the increase of high-affinity GM-CSF receptors necessary for progenitor proliferation/differentiation and mature neutrophil function. All-trans retinoic acid (ATRA) induces terminal differentiation of acute promyelocytic leukemia cells (AML3 subtype). We report in this study that AML3 cells, like other AML subtypes, harbor high-affinity GM-CSF R (n = 138.3 +/- 69.3 sites/cell, Kd = 76.9 +/- 68.8 pM). In all cases, incubation with ATRA induces either an increase in the number of affinity of GM-CSF R (n = 212.7 +/- 116.2 sites/cell, Kd = 43.2 +/- 22.5 pM). The data presented show that modulation of GM-CSF receptors cells is correlated to the degree of ATRA-induced granulocytic differentiation but not to increased cell growth.

Acute promyelocytic leukemia (APL) is a homogeneous subgroup of acute myeloid leukemias (AML) characterized by the presence of the t(15;17) translocation and the resulting PML/RAR alpha fusion proteins. To date APL is the only AML which is sufficiently sensitive to all-trans retinoic acid (ATRA) differentiating effect. We have recently reported that APL express and secrete hematopoietic growth factors (HGF) such as IL-1 beta, TNF alpha, and IL-6. In vivo ATRA alone allows achievement of complete remission in APL patients. One of ATRA therapy's drawbacks is the increase of peripheral blast cells often associated with the ATRA leukocyte activation syndrome. To determine if this specific side-effect was linked to an increase of HGF release by APL cells, we studied the modulation of cytokine production by APL cells, we studied the modulation of cytokine production by APL samples (n = 12) before and after incubation with ATRA. ATRA failed to modulate TNF alpha, IL-6 or GM-CSF secretion levels; however, IL-8 levels decreased in 11 cases, and in four cases up-regulation of IL-1 beta and G-CSF protein expression was observed. These modulations were found to be linked to ATRA sensitivity as ATRA failed to modulate cytokine production in non-APL cells (n = 8). Interestingly, the increase of IL-1 beta and G-CSF production in the presence of ATRA was highly correlated to an increase in APL cell count in vitro and in vivo hyperleukocytosis, resulting in fatal outcome. IL-1 beta, TNF alpha, IL-6, and IL-8 are known to be implicated in leukocyte activation. The results of this study suggest that ATRA-induced hyperleukocytosis and ATRA leukocyte activation syndrome in APL may be inherent to the secretion of specific hematopoietic growth factors by the APL cells.

The current treatment of acute promyelocytic leukemia (APL, also called AML3 subtype) is focused on differentiating agents such as the vitamin A derivative all-trans retinoic acid (ATRA). This agent is a novel and very promising therapy for this disease characterized cytogenetically by a translocation t(15;17)(q21;q22) involving the alpha retinoic acid receptor on chromosome 17 and the PML gene on chromosome 15. Clinical trials have demonstrated that ATRA followed by or combined with conventional chemotherapy may be more beneficial than chemotherapy for inducing complete remission. Unfortunately, ATRA as a single agent, does not appear able to maintain patients in remission (median 5 months), and when relapse occurs resistance to a second induction of ATRA therapy is observed in almost all cases. Recently our laboratory investigated whether specific features of the AML3 cells at relapse could explain the in vivo resistance observed. We have demonstrated that AML3 patients' cells (from four patients) at relapse show high levels of CRABP, a cytosolic retinoic acid binding protein and this protein was not detected prior to ATRA therapy. Relapse-AML3 cells (n = 12) showed reduced differentiation induction when compared with 'virgin'-AML3 cells. Results from this study suggest that CRABP could modulate ATRA cellular concentrations reaching the nucleus. This induced ATRA hypercatabolytic state should be monitored during consolidation therapy and at relapse by evaluating CRABP and RA metabolite levels, in order to detect ATRA resistance in patients with AML3.

All-trans retinoic acid (ATRA) in acute promyelocytic leukemia (APL) represents the leading example of targetted drugs for inducing an in vivo differentiation of malignancy (1,2). A fixed dose of 45 mg/m2/day was proposed for the treatment of patients (3), according to the results obtained by retinoic acid derivatives in skin diseases. We report that 25 mg (4), and even 15 mg/m2/day are still effective dosages. Absence of drug resistance, rapid correction of fibrinogenopenia and the absence of hypoplasia are the apparent major advantages and consequently high frequency of early mortality generally reported during chemotherapy is expected to be reduced. In fact the same risk of early death (10%) is recorded in all available data (5), due to coagulation disorders and to a leukocyte activation syndrome. Management of these side-effects is based on the prevention and treatment of the irreversible state as soon as first symptoms appear. Actually the major advantage of ATRA treatment in addition to chemotherapy is the decrease of relapse rate (6), the increase of event-free survival, and thus the increase of survival.

The bleeding diathesis in patients with acute promyelocytic leukemia (APL) is generally attributed to disseminated intravascular coagulation (DIC), initiated by the release of procoagulant activity from leukemic cells. Primary fibrinogenolysis, mediated by the release of leukocyte proteases, may also contribute to this disorder. We analyzed coagulation parameters in 15 non-septic APL patients. Before treatment, there was evidence of thrombin activation with DIC: increased levels of circulating thrombin-antithrombin III complexes, prothrombin fragments 1 + 2 and D-Dimer complexes. This DIC syndrome was probably limited, since no prothrombin time decrease, no significant factor V consumption, and normal levels of coagulation inhibitors (antithrombin III and protein C) were observed in APL patients when compared to normal controls. In this context, marked hypofibrinogenemia suggested primary fibrinogenolysis as the predominant etiology. Despite normal or high tissue plasminogen activator (tPA) and plasminogen activator inhibitor (PAI-1) antigen levels, the plasma PAI-1 activity and the formation of tPA/PAI-1 complexes were lower in APL patients than in normal controls, suggesting a proteolytic degradation of PAI-1, not able to complex tPA. Two other fibrinolytic inhibitor molecules (alpha-2 plasmin inhibitor antigen and histidine-rich glycoprotein antigen) were also significantly reduced, as well as the two subunits of fibrin stability factor XIII, although only subunit A is known to be susceptible to thrombin action. Evidence of degraded forms of von Willebrand factor in the plasma suggested an extended proteolytic activity. Four patients treated with all-trans-retinoic acid (ATRA) as a single differentiating agent were studied serially. A dissociation between these two syndromes--DIC and fibrinogenolysis/proteolysis--was observed. The rapid correction of the lysis markers contrasted with a more prolonged persistence of the procoagulant activity. We observed persistently high elastase/alpha 1-proteinase inhibitor complex levels during ATRA therapy, despite progressive correction of all lysis markers. Thus, the release of elastase from promyelocytic leukemic cells is probably not the only determinant of the fibrinogenolytic/proteolytic syndrome. In summary, the present findings provide new arguments for the association of DIC and proteolysis syndromes in APL-associated coagulation disorders. Further prospective studies are needed in order to confirm the persistence of thrombin activation in course of ATRA therapy.

Acute promyelocytic leukemia (APL) is associated with a high incidence of disseminated intravascular coagulation (DIC) and early hemorrhagic death. The risk of early fatal hemorrhage is increased when high peripheral-blood blast count and severe DIC accompanied by visceral hemorrhage are present at diagnosis. Progressive cytolysis induced by daily increased doses of chemotherapy, or differentiation all-trans-retinoic acid (ATRA) therapy have been proposed for initial control of DIC, but both are dangerous in hyperleukocytic APL patients. We report our results obtained in three high-risk APL patients treated with a combination of conventional chemotherapy and ATRA. All patients had documented hyperleukocytic APL [M3 or M3-variant subtype, (15, 17) translocation] with DIC, and all had critical clinical course before treatment. Patient 1 presented with cerebral hemorrhage, patients 2 and 3 had acute respiratory failure probably due to pulmonary leukemic infiltration and pulmonary hemorrhage. In order to minimize the severity of DIC during chemotherapy-induced acute cytolysis, ATRA (45 mg/m2 per day) was started on the first or second day of chemotherapy and withdrawn when complete remission (CR) was achieved. Despite adverse clinical features, CR was obtained in these three high-risk patients. Patient 1 showed no increase of cerebral bleeding during therapy. Patients 2 and 3 required transient intensive care, with mechanical ventilation from day 4 to day 11 for one of them. Differentiating granular cells were present in peripheral blood of all patients from the day 5, 12 and 8 of cytotoxic therapy. For the three patients, the number of days with white blood cell count < 1 x 10(9)/l was only 2, 7 and 11 days respectively. These results suggest that differentiation therapy with ATRA may be useful even in hyperleukocytic APL patients, when ATRA is used in combination with chemotherapy. The mechanisms of this putative beneficial effect are discussed.

It has been shown that patients with acute promyelocytic leukemia (AML3 subtype) treated with all-trans retinoic acid (all-trans RA), 45 mg/m2/day, achieve complete remission through differentiation of the leukemic clone to mature myeloid cells, which die spontaneously. The pharmacokinetics of all-trans RA given by mouth were studied in 15 AML3 patients. Blood samples were drawn for 24 h following a single oral dose of 45 mg/m2 and assayed for all-trans RA and 13-cis retinoic acid (13-cis RA) plasma concentrations by specific high-performance liquid chromatography. In one patient all-trans RA and 13-cis RA levels were below the detection limits at all times. In the other patients, the time to peak concentration of all-trans RA was between 60 and 210 min (median 90 min) after ingestion, with maximum concentrations between 0.03 and 2.5 micrograms/ml (median 0.4 micrograms/ml). These concentrations were within the in vitro differentiating concentration range of all-trans RA for these patients' cells. In nine patients, enterohepatic cycling was suggested by the presence on the concentration versus time curve of a secondary peak that occurred at meal times. The apparent plasma elimination half-life was between 16.8 and 77.4 min (median 30 min). Detectable plasma levels of 13-cis RA in 12 patients indicated in vivo isomerization of all-trans RA. Despite the high inter-individual variability of all-trans RA pharmacokinetics in these patients, high blast cell counts and failure to respond to differentiation treatment tended to be associated with low all-trans RA Cmax values and high clearance estimates.

Two recent reports have described major clinical benefits from all-trans-retinoic acid (tRA) therapy of patients with promyelocytic leukemia (APL). This paper describes the first patient with a blast crisis of chronic myelogenous leukemia (CML-BC) who responded to oral tRA therapy. In vitro marrow studies, including clonogenic assays, immunopheno-typing, cytogenetics and premature chromosome condensation together with chromosome painting provided evidence for the in vivo differentiation and maturation of the malignant cells. The patient achieved a partial remission with reversal of all clinical features of disease, including normalization of peripheral blood counts, complete resolution of fever, fatigue and splenomegaly, and marked maturation of the bone marrow. This response to tRA in CML-BC is unique, and broadens the spectrum of diseases which may respond to retinoids.

All-trans retinoic acid (RA), the active metabolite of vitamin A, has recently been demonstrated to be an efficient alternative to chemotherapy in the treatment of acute promyelocytic leukemia (M3 subtype of the French-American-British cytological classification). Complete remission is obtained by inducing terminal granulocytic differentiation of the leukemic cells. To elucidate whether the effect of retinoic acid on the differentiation of M3 leukemic cells was related to any specific characteristics of its receptor, we analyzed the structure and expression of retinoic acid receptor (RAR) genes in 16 M3 patients. Abnormal RAR alpha transcripts were detected in 13 cases. In nine patients, the genomic DNA was analyzed by Southern blotting and evidence for a rearranged RAR alpha gene was found generated in four cases. Normal RAR transcripts and germline restriction fragments were found in samples from normal or other leukemic cells, suggesting that this alteration of the RAR alpha gene is specifically seen in M3 leukemias. These results suggest that alteration of the retinoic acid receptor alpha may be implicated in M3 leukemogenesis.

Fifty-three hairy cell leukemia patients were treated with low dose recombinant and natural alpha-interferon for 7 or 13 months with a marked improvement in peripheral blood and bone marrow findings. Our results suggest that daily injections have no advantage over three weekly injections, but longer treatment (12-13 months) is better than shorter treatment (6-7 months). The possibility of a relapse raises the issue of the place of splenectomy in the treatment strategy. Since the definition of remission and of relapse is based on the histological changes in the bone marrow, the necessity for the quantification of the hairy cell infiltration on bone marrow sections is stressed.