ChlVPP/ABV-VP16 hybrid regimen for advanced Hodgkin's disease: a study in 36 patients

Prolonged remission can now be induced in the majority of patients with advanced Hodgkin's disease (HD) by the use of non-cross-resistant regimens. The aim of this retrospective analysis was to evaluate the efficacy and tolerability of a hybrid chemotherapy regimen (ChlVPP/ABV-VP16) in this unfavorable subset of patients. From 1982 to 1997 thirty-six previously untreated patients with advanced HD, Stages IIB to IV according to the Ann Arbor classification, were treated with the ChlVPP/ABV-VP16 regimen. The median age of the group was 29 years (range, 18 to 74), and 50% of them had bulky disease. Complete remission (CR) was induced in 31 patients (86%); 3 patients achieved partial responses and 2 had progressive disease. The median follow-up duration is 5.7 years, with a 5-year overall survival rate of 80%. At 5 years, the time to progression (TTP) and event-free survival (EFS) were 71% and 64%, respectively. Acute toxicity was quite acceptable, and there were no treatment-related deaths. A total of 3 second malignancies (8%) were documented. In conclusion, the ChlVPP/ABV-VP16 hybrid is an active regimen for use in advanced HD. Its overall survival, TTP and CR rates make this regimen an attractive alternative to MOPP/ABVD. However, the possibility of the development of second tumors is worrisome, although the relatively brief interval between the end of treatment and tumor detection may imply caution about the possible relationship.

Adverse events occurring during bone marrow or peripheral blood progenitor cell infusion: analysis of 126 cases

Bone marrow (BM) and/or peripheral blood progenitor cells (PBPC) given after high-dose chemo-radiotherapy are commonly cryopreserved. Re-infusion of the thawed product can cause cardiovascular and other complications. We compared two groups of adult patients receiving autologous BM or PBPC transplant to assess the incidence of adverse events occurring during infusion. Fifty-one patients received BM, and 75 PBPC. The two groups were comparable in respect of age, total volume infused, quantity of dimethylsulfoxide (DMSO) and number of polymorphonuclear neutrophils. Patients receiving PBPC had a higher number of nucleated cells per kg of body weight; those in the BM group received a significantly greater quantity of red cells. Non-cardiovascular complications occurred in 19% and 8% of patients rescued by BM and PBPC respectively. The incidence of hypertension was 21% in the BM and 36% in the PBPC group. Asymptomatic hypotension was more frequent in PBPC patients (P<0.001). Bradyarrhythmia was noticed in two of 75 PBPC patients and in 14 of 51 BM patients (P<0.001). In the former group one patient had heart block; he died of renal failure 10 days later. Bradycardia and hemoglobinuria were more common in patients receiving BM where a higher concentration of red cells was present (P<0.001). Since bradyarrhythmias may be a life-threatening complication we advise continuous careful monitoring during infusion of thawed BM. The strong correlation between bradycardia and red blood cell contamination suggests the use of purified products with a very low red cell content.

Chemotherapy and donor peripheral blood progenitor cells for acute leukemia in early relapse after allogeneic bone marrow transplantation

Ten patients with acute leukemia (AL) in early relapse after allo-BMT were treated with a modified MEC (mitoxantrone, etoposide and Ara-C) regimen followed by donor PBPC collected after mobilization with G-CSF. Seven patients achieved CR or had normal hemopoietic reconstitution: two had an early relapse at days +53 and +48, two patients died from acute GVHD at days +31 and +96, one died of interstitial pneumonia at day +55, and two patients experienced long-term survival. One patient with refractory disease and nodal involvement who did not respond to the first BMT had overt expansion of the leukemia at day +36; one patient with Ph+ ALL and one with ANLL evolving from MDS, both with skin involvement, had blast cells in peripheral blood at day +27 and +26, respectively. Transient cytopenia occurred in all patients; a normal granulocyte and platelet count was achieved within 3 weeks in all patients but one; acute GVHD occurred in six patients, and four had chronic GVHD. This approach is feasible in patients in early relapse after allo-BMT. It assists prompt re-establishment of normal donor hematopoiesis avoiding the prolonged cytopenia observed after donor lymphocyte infusion in AL patients relapsed after allo-BMT.

Photoinscription of Bragg gratings within a germanosilicate fiber subjected to a high static electric field

The kinetics of Bragg grating growth in germanosilicate fibers subjected to a high static electric field are compared with those obtained without any electric field. The gratings were written by exposure of the fiber core to laser light at 244 or 193 nm. These experiments gave some clues about the mechanisms responsible for both the photosensitivity in germanosilicate fibers and the nonlinear second-order UV-induced susceptibility in silica glasses. The refractive-index modulation proved to be significantly higher in the fibers subjected to an electric field. Furthermore, the change in the fiber's mean effective refractive index as a function of exposure time was not monotonic. This evolution can be explained by the assumption that some electric-field-induced diffusion of electron trapped centers [Ge(1) and Ge(2)] from the fiber core is involved.

Autologous peripheral blood stem cell transplantation in acute myeloblastic leukaemia and myelodysplastic syndrome patients: evaluation of tumour cell contamination of leukaphereses by cytogenetic and molecular methods

We evaluated 18 acute myeloblastic leukaemia (AML) and myelodysplastic syndrome (MDS) patients with abnormal karyotype at diagnosis who underwent peripheral blood stem cell (PBSC) transplantation. To evaluate the presence of residual tumour cells, bone marrow (BM) samples and PBSC collections were analysed by cytogenetics and in selected cases also by fluorescence in situ hybridisation (FISH) and molecular studies. All patients were considered to be in morphologic and cytogenetic complete remission (CR) at the time of mobilisation. Seven patients showed neoplastic cells in PBSC harvest and/or BM specimen before reinfusion. Cytogenetic studies revealed contamination in apheretic collections in one patient only, while three patients had BM but not PBSC contamination. Three more patients had leukaemic cells both in the BM and PBSC. All but one (with only BM contamination) of these patients relapsed within 9 months. However, five more patients relapsed after transplantation: in four cases there was no cytogenetic sign of contamination either in PBSC or BM cells and in one case no molecular evidence was revealed either. This study suggests that, whereas the presence of leukaemic cells in autologous grafts correlates with a poor prognosis, the lack of detection of tumour cells is not always predictive of long-term disease-free survival. More importantly, PBSC collections from AML patients are not contaminated by leukaemic cells if the BM is disease-free.

Fournier's gangrene: a clinical presentation of necrotizing fasciitis after bone marrow transplantation

Three patients with ANLL developed Fournier's gangrene as an early complication after allo-BMT (two cases) and auto-BMT (one case); two patients were in first CR, the third had resistant disease. Patients developed fever, perineal pain, swelling and blistering of the genital area. Pseudomonas aeruginosa was isolated from the lesions and patients received systemic antibiotic therapy, surgical debridement and medication with potassium permanganate solution. Two patients made a complete recovery although one died of sepsis. The third had progressive involvement of the abdominal wall and later died of leukemia. Early diagnosis of this disorder and prompt initiation of appropriate therapy can prevent progression of this acute necrotizing infection.

Role of autologous bone marrow transplantation as consolidation therapy in acute promyelocytic leukemia patients in complete remission

Autologous bone marrow transplantation (ABMT), which consents a low mortality rate, has been proposed as an alternative approach to maintenance chemotherapy in patients with acute promyelocytic leukemia (APL) in first complete remission irrespective of the patients' molecular status. Sixteen patients with acute APL in complete remission were submitted to ABMT and were analyzed for the presence of the PML-RARa fusion gene by reverse transcription-polymerase chain reaction (RT-PCR). Our study demonstrated that continued positivity of PCR analysis before ABMT could predict subsequent relapse in patients who undergo un-purged ABMT procedures.

Disappearance of PML/RAR alpha acute promyelocytic leukemia-associated transcript during consolidation chemotherapy

BACKGROUND AND OBJECTIVE

Acute promyelocytic leukemia (APL) (M3 according to FAB classification) is a subtype of acute myelogenous leukemia characterized by a specific t(15;17) (q22;q12) chromosomal translocation. The majority of APL patients achieve morphologic remission after induction chemotherapy. They can be followed from this point by cytogenetic and molecular analysis of the persistence of the PML/RAR alpha transcript. In order to determine the influence of successive courses of consolidation chemotherapy on clinical and molecular outcome, APL patients treated with all-trans retinoic acid (ATRA) and chemotherapy (AIDA-GIMEMA-LAP0493 protocol) were investigated.

DESIGN AND METHODS

Twenty-four APL patients (pts) (15 males; 9 females) were studied by RT-PCR and cytogenetic analysis at diagnosis, after induction chemotherapy, at each point after any of three consolidation courses, and every 3 months during the first years of maintenance therapy. The median follow-up was 24 months (mths) (range 7-40 mths).

RESULTS

All pts achieved hematologic remission after induction chemotherapy. Our results demonstrate that the majority (87%) of APL patients were still molecularly positive for the APL associated transcript after induction chemotherapy, while the majority (80%) of APL patients became PCR-after the second consolidation chemotherapy.

INTERPRETATION AND CONCLUSIONS

The role of the third consolidation chemotherapy course in converting patients with persistent molecular evidence of disease from PCR+ to PCR- was minimal. We confirm the validity of molecular follow-up after single courses of chemotherapy in monitoring the role of molecular remission.

Long-term disease-free acute promyelocytic leukemia patients really can be cured at molecular level

The characteristic t(15;17) translocation involving chromosomes 15 and 17 is specifically associated with both the common and the variant subtypes of acute promyelocytic leukemia (APL) (M3 according to FAB classification). At the molecular level, it fuses genes encoding PML on chromosome 15 and the nuclear retinoic acid receptor-alpha (RAR alpha) on chromosome 17. The subsequent expression of PML/RAR alpha fusion mRNA provides a potential molecular marker that can be detected in leukemic cells taken from patients with APL. Using PML and RARa sequence specific primers, reverse transcription-polymerase chain reaction (RT-PCR) assays have been developed for detection of PML/RAR alpha transcript in leukemic cells obtained from patients; these RT-PCR assays are more sensitive than conventional cytogenetic analysis.

Maintenance and recovery characteristics of sevoflurane anaesthesia in adult patients. A multicenter, randomized comparison with isoflurane

BACKGROUND

The goal of the present multicenter, prospective, randomized clinical investigation was to compare the clinical efficacy and safety of sevoflurane and isoflurane during maintenance of and recovery from general anaesthesia in adult patients.

METHODS

With the approval of the Ethical Committee and the patient informed consent, 143 ASA physical status I-II patients, aged 18-65 years, were randomized in order to receive either isoflurane (n = 71) or sevoflurane (n = 72) as the main general anaesthetic. After an oral diazepam (0.1-0.2 mg kg-1) and atropine (0.007-0.01 mg kg-1) premedication and a standardized intravenous induction, general anaesthesia was maintained by adjusting the end-tidal concentrations of the inhalational agent for the maintainance of cardiovascular stability. At the end of surgery the anaesthetic vapours were discontinued, and the neuromuscular block was reversed; the following times were recorded: time of eyes opening, time of command response and suitability for discharge from the recovery area. The occurrence of any untoward event was also recorded. Preoperatively and 24 hr after surgery, blood was collected in order to assess renal an hepatic functions.

RESULTS

No differences in demography, duration of surgery, exposure to the inhalational agent and haemodynamic effects were observed between the two groups. Patients receiving sevoflurane showed shorter times for the achievement of extubation (median: 9 min versus 13 min, p = 0.002), eyes opening (median: 10 min versus 13 min, p = 0.002), command response (11 min versus 15 min, p = 0.002) and suitability for discharge from recovery room (median: 19 min versus 22 min, p < 0.05) than those receiving isofluorane. No intra- and intergroup differences were observed in pre- and post-operative laboratory testing of renal and hepatic function.

DISCUSSION

We conclude that sevoflurane, when compared to isoflurane, provides a similarly safe maintenance but allows for a more rapid emergence from general anaesthesia.

Early detection of relapse by prospective reverse transcriptase-polymerase chain reaction analysis of the PML/RARalpha fusion gene in patients with acute promyelocytic leukemia enrolled in the GIMEMA-AIEOP multicenter "AIDA" trial. GIMEMA-AIEOP Multicenter "AIDA" Trial

Although the majority of patients with acute promyelocytic leukemia (APL) are potentially cured by treatments combining all-trans retinoic acid (ATRA) and chemotherapy (CHT), a sizable proportion (around 30%) will relapse during follow-up. Retrospective molecular monitoring studies using reverse transcriptase-polymerase chain reaction (RT-PCR) for the specific PML/RARalpha fusion gene, have shown that a positive test usually precedes the occurrence of hematologic relapse. Prospective RT-PCR analyses were performed since 1993 at diagnosis and at preestablished time intervals during follow-up in bone marrow (BM) samples of 163 patients with PML/RARalpha+ APL enrolled in the multicenter Gruppo Italiano Malattie Ematologiche Maligne dell' Adulto (GIMEMA) trial AIDA (All-trans retinoic acid plus Idarubicin). Treatment consisted of ATRA and idarubicin for induction followed by three polychemotherapy courses as consolidation. The sensitivity level of the RT-PCR assay for PML/RARalpha, as assessed by serial dilution experiments, was 10(-4). All patients were in hematologic remission and tested PCR- at the end of consolidation. Of 21 who converted to PCR-positive thereafter, 20 underwent hematologic relapse at a median time of 3 months (range, 1 to 14) from the first PCR+ result. Seventeen of these 21 (81%) PCR+ conversions were recorded within the first 6 months postconsolidation. Of 142 who tested persistently PCR- in >/=2 tests after consolidation, 8 had hematologic relapse and 134 remained in complete remission (CR) after a median follow-up of 18 months (range, 6 to 38) postconsolidation. Using a time-dependent Cox model, the relative risk of hematologic relapse of patients who converted to PCR+ was 31.8 (confidence limits 95%, 12.9 to 78.3). Our results indicate that conversion to PCR positivity for PML/RARalpha during remission is highly predictive of subsequent hematologic relapse and highlight the prognostic value of stringent molecular monitoring during the early postconsolidation phase in APL. As a result of the present study, salvage treatment in patients enrolled in the GIMEMA trial AIDA is now anticipated at the time of molecular relapse, defined as the conversion to PCR positivity in two successive BM samplings during follow-up.

Hematopoietic progenitor cell collection and neoplastic cell contamination in breast cancer patients receiving chemotherapy plus granulocyte-colony stimulating factor (G-CSF) or G-CSF alone for mobilization

BACKGROUND

We compared hematopoietic progenitor cell (HPC) collection and neoplastic cell contamination in breast cancer patients given cyclophosphamide (CTX) plus granulocyte-colony stimulating factor (G-CSF) or G-CSF alone for mobilization.

PATIENTS AND METHODS

In 57 stage II-III breast cancer patients, CD34+ cells, colony-forming units-granulocyte macrophage (CFU-GM), early HPC and breast cancer cells were counted in HPC collections obtained after CTX plus G-CSF (n = 27) or G-CSF-alone mobilization (n = 30).

RESULTS

The CD34+ cell collection was about two-fold greater after CTX plus G-CSF mobilization (11.0 +/- 7.9 vs. 5.8 +/- 3.5 x 10(6)/kg, P < 0.001). Similarly, the total number of CFU-GM, CD34+CD38- cells and of week-5 cobblestone area forming cells (CAFC) collected was significantly higher in patients mobilized with CTX plus G-CSF. Breast cancer cells were found in the apheresis products of 22% of patients mobilized with CTX plus G-CSF and in 10% of patients mobilized with G-CSF alone (P = 0.36). Of seven patients who failed G-CSF-alone mobilization and eventually underwent chemotherapy plus G-CSF mobilization, none had cytokeratin-positive cells after G-CSF mobilization, whereas four out of seven had cytokeratin-positive cells after chemotherapy plus G-CSF (P = 0.07 by chi 2 test).

CONCLUSION

The CTX plus G-CSF mobilization protocol was associated with a significantly higher HPC collection. However, this benefit was not accompanied by a reduction in the incidence of tumor-contaminated HPC graft.

Detection of bcr-abl transcript in chronic myelogenous leukemia patients by reverse-transcription-polymerase chain reaction and capillary electrophoresis

BACKGROUND AND OBJECTIVE

Capillary electrophoresis (CE) has become an attractive alternative to SLAB gel analysis for direct and accurate detection of amplified product, and a few cycles of polymerase chain reactions (PCRs) could be sufficient for both quantitative and qualitative analysis. We try to assess: 1) whether CE could be a practical, non-isotopic method for direct detection of the presence of amplified bcr-abl obtained by a reverse transcription (RT)-PCR (qualitative analysis) and 2) whether it is possible to quantify PCR products using a competitive RT-PCR measuring peak areas of CE electropherograms (quantitative analysis).

DESIGN AND METHODS

The two types of bcr-abl chronic myelogenous leukemia (CML) associated transcript products were generated by RT-PCR (qualitative analysis) from 1 microgram of total RNA extracted from bone marrow samples of 34 CML patients at diagnosis (median age 47.5; range 18-65; median Sokal's score 0.9; range 0.53-2.78). The PCR products were analyzed by SLAB-gel electrophoresis (SGE) on 2% agarose gels and by CE (128 runs; median 3.3 times for each sample). Furthermore, we assessed the amount of PCR product (quantitative analysis) by a competitive RT-PCR approach and by CE (bcr-abl transcripts were expressed as transcript per microgram of total RNA examined).

RESULTS

CE separation of PCR products obtained by qualitative RT-PCR showed baseline resolution for the two peaks corresponding to the two types of bcr-abl junctions: the b2-a2 type (343 base pairs, 10 patients) was revealed at 9.33 min [standard deviation (SD) = 0.1] and the b3-a2 type (418 base pair, 24 patients) at 10.03 min (SD = 0.25). By quantitative analysis we found that there is great interpatient variability in bcr-abl expression at diagnosis: the median value of the amount of bcr-abl transcript was 78,000 bcr-abl transcript/microgram total RNA ranging from 17,300 to 750,000. The amount of bcr-abl transcript at diagnosis was related to the number of blast cells (mean value 128,859 vs. 331,722 in patients with 0% blast cells and > 1% blast cells, respectively; p = 0.004) and Sokal's score (mean value 156,865 vs. 408,800 in patients with Sokal's score < 0.8 and > 1.2, respectively; p = 0.003).

INTERPRETATION AND CONCLUSIONS

Our results confirm that CE analysis offers greater resolution and enhanced sensitivity for detection and quantification of bcr-abl PCR product in the study of this leukemia. Qualitative analysis by CE of bcr-abl product provides a rapid technique (less than 20 min) for the analysis of subnanogram amounts of DNA fragments. CE run times are short, the capillary can be re-used and full automation may be feasible with data acquisition by a computer-controlled step. Competitive/quantitative analysis of bcr-abl as analyzed by CE allowed fewer reactions and more precise quantification.

Incidence and prognostic significance of idiopathic thrombocytopenic purpura in patients with Hodgkin's disease in complete hematological remission

Idiopathic thrombocytopenic purpura (ITP) is a frequent and well recognized complication of lymphoproliferative diseases (especially chronic lymphatic leukemia), but it is an unusual and poorly documented disease in the acute phase (1-2%). We report on two female patients with Hodgkin's disease (HD) followed between 1970 and 1995 at the institute of Hematology and Medical Oncology "Seràgnoli" in Bologna, who developed ITP unrelated to bone marrow failure, 26 and 15 months after achievement of complete hematologic remission from HD.

Intracavitary chemotherapy with thiotepa in malignant pericardial effusions: an active and well-tolerated regimen

PURPOSE

Malignant pericardial effusion, although highly variable, is an uncommon complication of cancer. It is often associated with symptoms like dyspnea, chest pain, and cough, which may be severe and disabling. We analyzed the results of our current treatment policy to evaluate the effectiveness and tolerance of a new approach for this disorder.

PATIENTS AND METHODS

Patients with malignant pericardial effusions were treated with intracavitary thiotepa (15 mg on days 1, 3, and 5) through an indwelling pericardial cannula after extraction of as much pericardial fluid as possible on day 0. Responses were assessed by clinical examination, computed tomographic (CT) scan, and echocardiography before treatment, 1 month after treatment, and every 2 months thereafter. Twenty-three patients with malignant symptomatic pericardial effusion were treated and all were assessable for effectiveness and tolerance of the procedure.

RESULTS

Nine patients with breast cancer, 11 with lung cancer, two with an unknown primary tumor, and one with metastatic melanoma were treated. In all but three patients, systemic medical treatment was started after completion of intracavitary therapy. Nineteen patients responded to treatment (83%; 95% confidence interval, 61% to 95%) with a rapid improvement of symptoms. The median time to pericardial effusion progression was 8.9 months (range, 1 to 26). No significant side effects were registered, except one patient who had transient grade III thrombocytopenia and leukopenia and one patient who had grade I leukopenia.

CONCLUSION

A short course of intracavitary treatment with thiotepa is highly effective and well tolerated in the treatment of malignant pericardial effusion.

Generation and functional characterization of human dendritic cells derived from CD34 cells mobilized into peripheral blood: comparison with bone marrow CD34+ cells

Dendritic cells (DCs) are the most powerful professional antigen-presenting cells (APC), specializing in capturing antigens and stimulating T-cell-dependent immunity. In this study we report the generation and characterization of functional DCs derived from both steady-state bone marrow (BM) and circulating haemopoietic CD34+ cells from 14 individuals undergoing granulocyte colony-stimulating factor (G-CSF) treatment for peripheral blood stem cells (PBSC) mobilization and transplantation. Clonogenic assays in methylcellulose showed an increased frequency and proliferation of colony-forming unit-dendritic cells (CFU-DC) in circulating CD34+ cells, compared to that of BM CD34+ precursors in response to GM-CSF and TNF-alpha with or without SCF and FLT-3L. Moreover, peripheral blood (PB) CD34+ cells generated a significantly higher number of fully functional DCs, as determined by conventional mixed lymphocyte reactions (MLR), than their BM counterparts upon different culture conditions. DCs derived from mobilized stem cells were also capable of processing and presenting soluble antigens to autologous T cells for both primary and secondary immune response. Replacement of the early-acting growth factors SCF and FLT-3L with IL-4 at day 7 of culture of PB CD34+ cells enhanced both the percentage of total CD1a+ cells and CD1a+ CD14- cells and the yield of DCs after 14 d of incubation. In addition, the alloreactivity of IL-4-stimulated DCs was significantly higher than those generated in the absence of IL-4. Furthermore, autologous serum collected during G-CSF treatment was more efficient than fetal calf serum (FCS) or two different serum-free media for large-scale production of DCs. Thus, our comparative studies indicate that G-CSF mobilizes CD34+ DC precursors into PB and circulating CD34+ cells represent the optimal source for the massive generation of DCs. The sequential use of early-acting and intermediatelate-acting colony-stimulating factors (CSFs) as well as the use of autologous serum greatly enhanced the growth of DCs. These data may provide new insights for manipulating immunocompetent cells for cancer therapy.

Selective expansion of normal haemopoietic progenitors from chronic myelogenous leukaemia marrow

CD34+ and CD34+ DR- cells from the bone marrow (BM) of chronic-phase chronic myelogenous leukaemia (CML) patients at diagnosis were tested for their colony-forming ability in response to early and intermediate-late colony stimulating factors (CSFs). Molecular analysis revealed that 55.6+/-9% SD of CD 34+ DR- colonies, in which actin and ABL mRNA were detectable, expressed the product of the BCR-ABL gene. The percentage and the clonogenic efficiency of CML DR- cells were significantly lower than those of comparable DR- cells from normal donors. However, clonogenic assays using recombinant human CSFs demonstrated a remarkable proliferation of CML cells when stimulated by SCF, IL-11 and IL-3, used as single factors in the presence of erythropoietin (EPO) and was almost entirely due to erythroid progenitors. Conversely, optimal stimulation of CD34 +DR- cells from normal donors required co-incubation with three or more CSFs. Stroma-noncontact long-term cultures were then established in the presence of exogenous CSFs and human irradiated allogeneic stromal layers or the murine stromal cell line M2-10B4, engineered to produce G-CSF and IL-3. In these cultures the combination of SCF and IL-3 induced a 25.4 +/- 5 SD, 40 +/- 6 SD and 20.5 +/- 6 SD fold increase of colony-forming unit cells (CFU-C), at weeks 2, 4 and 5, respectively. At the same time-points the number of primitive long-term culture initiating cells (LTC-IC) showed a 4 +/- 2 SD, 3.3 +/- 1.5 SD and 2.3 +/-1 SD fold increase compared to baseline values. BCR-ABL mRNA analysis of single colonies demonstrated that 27 +/- 9% SD and 7 +/- 3% SD CFU-C at weeks 4 and 5, respectively, expressed the fusion gene, whereas leukaemic LTC-IC disappeared from the culture by week 2. These results suggest that leukaemic CD34+ DR- cells have a different pattern of response to CSFs than normal cells. In addition, we established culture conditions which allow selective expansion of benign haemopoietic cells coexisting with leukaemic progenitors.