Novel multiparameter flow cytometry assay using Syto16 for the simultaneous detection of early apoptosis and apoptosis-corrected P-glycoprotein function in clinical samples

BACKGROUND

The fluorescent probe Syto16 has been used successfully to measure P-glycoprotein (Pgp) function and, separately, early apoptosis and cell death. The present study was designed to evaluate whether the combined use of Syto16, the Pgp blocker PSC833, and 7-AAD allows simultaneous detection of all parameters, with emphasis on applications in acute myeloid leukemia (AML).

METHODS

Pgp negative/positive KB cell lines treated with tumor necrosis factor alpha/hyperthermia and frozen-thawed AML samples were used as apoptosis/Pgp models.

RESULTS

For the accurate assessment of apoptosis in samples with unknown Pgp status, it was essential to include a sample with PSC833: in such samples, viable cells always show a Syto16(high) and apoptotic cells a Syto16(low) fluorescence. Apoptotic cells loose their Pgp activity early on; in Pgp-positive cells, the Syto16(low) apoptotic cells then colocalize with the Syto16(low) viable cells in the situation minus PSC833. We have developed a gating strategy that, apart from quantifying apoptosis, allowed gating out these apoptotic cells for proper Pgp assessment. By using this strategy, no differences in Pgp activity were found in the treated versus the untreated samples (KB cells: P = 0.779, n = 10; AML cells: P = 0.525, n = 45).

CONCLUSIONS

The use of the combination Syto16/PSC833/7-AAD provides a sensitive multiparameter flow cytometry method that enables accurate assessment of both apoptosis, cell death, and Pgp function in clinical samples.

Assessment of the normal or leukemic nature of CD34+ cells in acute myeloid leukemia with low percentages of CD34 cells

BACKGROUND AND OBJECTIVES

The percentages of CD34+ cells in the bone marrow of patients with acute myeloid leukemia (AML) vary widely. Especially in the low range (<5% CD34+ cells), the nature (normal or malignant) of the CD34+ cells is uncertain. Since only in a minority of cases are molecular techniques applicable, in this study we explored a multiparameter approach using phenotypic and functional characteristics to discriminate normal CD34+ cells from malignant ones.

DESIGN AND METHODS

CD34+ cells from 24 AML patients with <5% CD34+ cells and from 3 patients with >50% CD34+ cells were studied immunophenotypically for aberrant phenotypes, CD133 and CD90 expression and for P-glycoprotein activity.

RESULTS

In the low (0.02-0.7%) CD34+ range, our approach offered strong evidence for a normal origin of the CD34+ cells in 18/19 cases, which was confirmed by interphase fluorescent in situ hybridization on sorted CD34+ cells in 3 cases, which had concomitant presence of cytogenetic abnormalities in the CD34- blasts. In contrast, in the intermediate (1.6-3.5%) CD34+ range, the CD34+ cells appeared as normal in only 1/5 cases. In the high (51-67%) CD34+ range, as expected the majority of CD34+ cells were malignant, although in 2/3 cases a small subpopulation (i.e. 0.15% and 0.20%) of CD34+ cells were of normal origin.

INTERPRETATION AND CONCLUSIONS

Our multiparameter approach enabled us to define the nature of CD34+ cells in AML. This has implications for studies dealing with the characterization of primitive malignant cells. Moreover, it enabled identification of truly CD34 negative AML, which would be eligible for CD34-based immunological purging of autologous stem cell transplants.

Differences between the CD34+ and CD34- blast compartments in apoptosis resistance in acute myeloid leukemia

BACKGROUND AND OBJECTIVES

Altered expression of members of the Bcl-2 family might account for the observed apoptosis resistance to chemotherapy in acute myeloid leukemia (AML). Given the poor prognosis associated with CD34+ expression in AML, we studied the role of spontaneous apoptosis and apoptosis regulatory proteins in sorted CD34+ and CD34- primary AML fractions.

DESIGN AND METHODS

The expression levels of apoptosis regulatory proteins and spontaneous apoptosis were measured in primary AML samples by Western blot analysis and flow cytometry. To determine the role of CD34+ cells in apoptosis resistance, spontaneous apoptosis in serum-free conditions and apoptosis regulatory protein levels were measured in CD34+ and CD34- sorted cells from CD34+ primary AML samples.

RESULTS

We show that CD34+ AML fractions are more resistant to apoptosis than are corresponding CD34- AML fractions, and that this is paralleled by higher Bcl-2, Bcl-xL, Mcl-1, Pgp and lower Bax expression levels. Interestingly, as the percentage of CD34 cells increased in the primary AML sample, so too did the apoptosis resistance in the corresponding CD34- fraction, which was reflected by an increasing anti-apoptosis protein profile.

INTERPRETATION AND CONCLUSIONS

The data show that the CD34+ fraction is more resistant to apoptosis than is the corresponding CD34- fraction and secondly that the AML as a whole is more apoptosis resistant with increasing CD34 percentage.

A flow cytometric method to detect apoptosis-related protein expression in minimal residual disease in acute myeloid leukemia

Minimal residual disease (MRD) cells are thought to be responsible for the persistence and relapse of acute myeloid leukemia (AML). Flow cytometric MRD detection by the establishment of a leukemia-associated phenotype (LAP) at diagnosis can be used in 80% of AML patients, allowing detection and functional characterization of MRD in follow-up bone marrow. One of the mechanisms contributing to inefficient chemotherapy is apoptosis resistance. Measuring apoptosis parameters in MRD cells will help to unravel the importance of apoptosis resistance in AML. We therefore developed a four-color flow cytometry method that enables establishment of apoptosis-related protein expression such as Bcl-2, Bcl-x(L), Mcl-1 and Bax at diagnosis and in MRD. Firstly, validation of this assay using Western blot analysis in five leukemia cell lines showed a significant correlation (R=0.70: P<0.0001). Secondly, the influence of the permeabilization procedure on LAP expression was investigated in 38 AML samples at diagnosis and in 42 MRD samples. Quantification of the frequency of LAP+ cells with and without permeabilization showed no significant differences (diagnosis: P= 0.57, follow-up: P= 0.43). The flow cytometric protocol thus enables analysis of apoptosis-related proteins at different stages of the disease, which will lead to a better understanding of the role of apoptosis resistance in the emergence of MRD in AML.

Function of the ABC transporters, P-glycoprotein, multidrug resistance protein and breast cancer resistance protein, in minimal residual disease in acute myeloid leukemia

BACKGROUND AND OBJECTIVES

Relapse is common in acute myeloid leukemia (AML) because of persistence of minimal residual disease (MRD). ABC-transporters P-glycoprotein (Pgp) and multidrug resistance protein (MRP), are thought to contribute to treatment failure, while it is unknown whether breast cancer resistance protein (BCRP) does so. However, whether up-regulation of pump activity or selection of subpopulations with higher pump activity occurs during chemotherapy is unclear. The aim of this study was to elucidate whether ABC-transporter function changes during the course of disease.

DESIGN AND METHODS

MRD cells were identified using leukemia-associated phenotypes combined with a fluorescent probe assay with substrate/modulator: Syto16/ PSC833 (Pgp), calcein-AM/probenecid (MRP) and BODIPY-prazosin/Ko143 (BCRP); efflux profiles were directly compared with blasts at diagnosis and relapse from the same patient.

RESULTS

At diagnosis BCRP activity was undetectable in AML blasts from 23/26 cases, while Pgp activity was present in 36/45 and MRP activity in 26/44 of the cases. Furthermore, no subpopulations of blasts with considerably higher drug efflux capacities were found. Overall, no consistent changes were observed at follow-up [during chemotherapy (n=20), MRD (n=37), relapse (n=26))] in forty-five patients, the mean activities (as percentages of values at diagnosis) were 97% (Pgp), 103% (MRP) and 102% (BCRP).

INTERPRETATION AND CONCLUSIONS

Emergence of MRD is thus not accompanied by either upregulation of ABC-transporter function during or after chemotherapy or by selection of pre-existing highly resistant subpopulations. The prognostic value of Pgp and MRP is, therefore, likely related to drug efflux capacity homogeneously distributed in the whole blast population, while BCRP probably has a limited function in drug efflux-related resistance in AML.

High percentage of CD34-positive cells in autologous AML peripheral blood stem cell products reflects inadequate in vivo purging and low chemotherapeutic toxicity in a subgroup of patients with poor clinical outcome

In this study, a high CD34% in autologous peripheral blood stem cell (PBSC) products from 71 AML patients was associated directly with a high relapse rate (P = 0.006) and inversely with disease-free survival (P = 0.003), irrespective whether patients were transplanted or not. The relapse rate at 12 months was 67% in a group with >0.8% CD34+ cells and 34% in a group with < or = 0.8% CD34+ cells. Although the percentage of malignant CD34+ cells in the CD34+ compartment in the relapses of the first group was not high (median 8%), the total number of malignant cells as a percentage of WBC was about 13 times higher than for the patients remaining >12 months in remission. When all patients evaluable were taken together, this frequency of malignant cells correlated strongly with disease-free survival (P < 0.001). Both this massive mobilization of normal CD34+ cells and high frequency of malignant cells in the subgroup of patients with CD34 >0.8% and relapse within 12 months indicate an insufficient in vivo purging, as well as low chemotherapeutic bone marrow toxicity. This was confirmed by an inverse correlation between hypoplasia period after the induction therapy and CD34% in PBSC products (P < 0.002). It is concluded that a subgroup of patients has been identified that might benefit from a more intensive chemotherapeutic treatment.

Early apoptosis largely accounts for functional impairment of CD34+ cells in frozen-thawed stem cell grafts

Quality assessment of stem cell grafts is usually performed by flow cytometric CD34(+) enumeration or assessment of clonogenic output of fresh material. Previously, we identified the occurrence of early apoptosis, not detectable with the permeability marker 7-amino actinomycin D (7-AAD), in purified frozen-thawed CD34(+) cells, using the vital stain Syto16. Syto(high)/7-AAD(-) cells were defined as viable, Syto16(low)/7-AAD(-) cells as early apoptotic and Syto16(low)/7-AAD(+) as dead. This was confirmed in a subsequent study using frozen-thawed transplants of lymphoma patients. In the present study on grafts from multiple myeloma and lymphoma patients, we investigated the functional consequences of the early apoptotic process. The mean Syto16-defined viability was 41 and 42%, respectively, for both graft groups, compared to 78% and 72%, respectively, using 7-AAD only. The established early apoptosis marker annexin V missed roughly 50% of the early apoptosis detected with Syto16. In contrast, viability of CD34(+) cells in nonmanipulated whole blood transplants from a matched group of lymphoma patients, after 72 h of storage at 4 degrees C, was more than 90%, even with the Syto16 assay. CFU recovery (median 26-33%) after cryopreservation matched CD34(+) recovery after Syto16, but not 7-AAD correction. In contrast, colony-forming unit (CFU) recovery in the whole blood transplant was close to 100%. Furthermore, early apoptotic CD34(+) cells had lost migratory ability toward stromal cell derived factor-1alpha (SDF-1alpha). The establishment of a Syto16(high)/7-AAD(-) proportion of CD34(+) cells offers a new approach for a more correct determination of the number of viable nonapoptotic CD34(+) cells in stem cell grafts. Further development of this assay should allow its incorporation into the routine CD34(+) assessment of post-thawed samples in clinical flow cytometry laboratories.

Granulocyte colony-stimulating factor mobilized whole blood containing over 0.3 x 106/kg CD34+ cells is a sufficient graft in autologous transplantation for relapsed non-Hodgkin's lymphoma

The feasibility of unprocessed, granulocyte colony-stimulating factor (G-CSF)-mobilized whole blood (WB) as an alternative stem cell source for autologous stem cell transplantation was studied. Forty-seven relapsed non-Hodgkin's lymphoma (NHL) patients entered the study. After two or three ifosfamide, methotrexate and etoposide (IMVP) courses, 1 l of G-CSF-mobilized WB was collected and stored refrigerated for 72 h. Meanwhile, BAM conditioning was given: BCNU (carmustine) 300 mg/m(2), high-dose cytarabine 6000 mg/m(2) and melphalan 140 mg/m(2). Toxicity, haematological recovery and survival were assessed and compared with peripheral blood stem cell transplantation (PBSCT) and bone marrow transplantation (BMT) reference groups. High-dose G-CSF (2 x 12 microg/kg/d) gave the best mobilization results. Haematological recovery was related to the WB CD34+ content. A CD34+ threshold of >or= 0.3 10(6)/kg, obtained in 90% of patients using high-dose G-CSF, correlated with adequate recovery: absolute neutrophil count (ANC) > 0.5 x 10(9)/l: median 12 d (range 9-19). Platelet recovery > 20 and > 50 x 10(9)/l was 19 (11-59) and 30 d (14 not reached) respectively. Overall survival of patients < 60 years was 57% at 4 years and event-free survival was 32%. Survival was comparable with PBSCT and BMT after BEAM (BCNU, etoposide, cytarabine, melphalan). Remarkably, haematological recovery after BAM + WB was rapid and comparable (ANC) or slightly prolonged (platelets) in comparison with BEAM + PBSCT, despite a 10-20 times lower CD34+ cell dose in the WB graft. In conclusion, transplantation of WB containing >or= 0.3 x 10(6)/kg CD34+ cells after BAM conditioning is a safe procedure, and offers a fully equivalent and less costly alternative for PBSC.

In vitro safety profile of G-CSF-mobilized whole blood after storage for 7 days in an infusable-grade L15 medium

BACKGROUND

G-CSF-mobilized whole blood (WB) is a cost-reducing and simple alternative for peripheral blood progenitor cell transplantation. Recently, it was demonstrated that mobilized WB supplemented with Leibovitz's L15 medium permitted prolonged preservation of clonogenic cells at ambient temperature. In this study, an infusable-grade L15 medium (IG-L15) was developed, and the safety profile of mobilized WB after 7 days of storage was investigated.

STUDY DESIGN AND METHODS

IG-L15 was manufactured in a closed system under good manufacturing practice conditions. Proinflammatory cytokine levels and hemolysis in mobilized WB were determined after 7 days of storage in different containers and were compared with current clinical mobilized WB values after 1 to 3 days of storage at 4 degrees C.

RESULTS

IG-L15 and L15 maintained clonogenic cells equally. In the samples of mobilized WB that were returned to the patient, cytokine levels were not elevated in comparison with freshly collected mobilized WB. By using IG-L15 in polystyrene-coated cell culture bags, median (range) levels of 9.4 (2.2-69.8) pg per mL (IL-1beta), 31.6 (6.1-146.5) pg per mL (TNF-alpha), 76.9 (15.5-934.9) pg per mL (IL-6), and 7195 (104-205,600) pg per mL (IL-8) were found after 7 days. Higher cytokine levels were found with L15 and different containers. He- molysis was less than 0.5 g per dL in all cases.

CONCLUSION

The storage of mobilized WB for 7 days in IG-L15 at ambient temperature is possible with adequate preservation of clonogenic cells, but cytokine levels may require plasma removal before return.

Extensive early apoptosis in frozen-thawed CD34-positive stem cells decreases threshold doses for haematological recovery after autologous peripheral blood progenitor cell transplantation

Stem cell doses necessary for engraftment after myelo-ablative therapy as defined for fresh transplants vary largely. Loss of CD34+ cell quality after cryopreservation might contribute to this variation. With a new early apoptosis assay including the vital stain Syto16, together with the permeability marker 7-AAD, CD34+ cell viability in leucapheresis samples of 49 lymphoma patients receiving a BEAM regimen was analysed. After freeze-thawing large numbers of non-viable, early apoptotic cells appeared, leading to only 42% viability compared to 72% using 7-AAD only. Based on this Syto16 staining in the frozen-thawed grafts, threshold numbers for adequate haematological recovery of 2.8-3.0 x 10(6) CD34+ cells/kg body weight determined for fresh grafts, now decreased to 1.2-1.3 x 10(6) CD34+ cells/kg. In whole blood transplantation of lymphoma patients (n = 45) receiving a BEAM-like regimen, low doses of CD34+ cells were sufficient for recovery (0.3-0.4 x 10(6)CD34+ cells/kg). In contrast to freeze-thawing of leucapheresis material, a high viability of CD34+ cells was preserved during storage for 3 days at 4 degrees C, leaving threshold doses for recovery unchanged. In conclusion, the Syto16 assay reveals the presence of many more non-functional stem cells in frozen-thawed transplants than presumed thus far. This led to a factor 2.3-fold adjustment downward of viable CD34+ threshold doses for haematological recovery.

A single-step colony-forming unit assay for unseparated mobilized peripheral blood, cord blood, and bone marrow

The colony-forming unit (CFU) assay is exposed to a lot of variation, part of which is introduced by several enrichment strategies that are routinely performed before assessment of clonogenic capacity in mobilized peripheral blood (PB), bone marrow (BM), or cord blood (CB). We investigated the possibility to perform a single-step CFU assay by direct plating of PB, BM, or CB into CFU culture medium to obtain more reproducible results than after a standard Ficoll or lysis procedure. Direct plating implies the presence of red blood cells (RBC), white blood cells (WBC), and plasma in the CFU assay, which could possibly influence the outcome of the assay. Of all components, only the RBC was found to negatively influence CFU-GM growth if a concentration of > 0.02 x 10(9)/ml was present in the CFU culture medium. Subsequently, depending on the RBC concentration PB, BM, and CB samples were prediluted in triplicate or quadruplicate and plated into CFU medium. Lysis and/or Ficoll procedures were also performed in triplicate or quadruplicate on the same samples, and the mean colony number and coefficient of variation (CV) of the three techniques were compared. Significantly smaller CV values were found using the direct plating technique (all assays, mean 7.5%, range 1.6-15.6%) than after Ficoll separation (mean 18.0%, range 2.2-62.5%). Intermediate results were obtained with the lysis method (mean CV 11.6%, range 3.3-29%). In most samples, and especially in those with a very low number of clonogenic cells per milliliter, more colonies were detected with the direct plating method than with either the lysis or Ficoll method. In conclusion, the single-step direct plating method significantly enhances reproducibility of the CFU assay for PB, BM, and CB samples in comparison with standard techniques by circumvention of loss of colony formation and by decreasing variability. Furthermore, the direct plating technique is a timesaving assay.

Functional characterization of minimal residual disease for P-glycoprotein and multidrug resistance protein activity in acute myeloid leukemia

Relapse is common in acute myeloid leukemia (AML) due to persistence of residual leukemia cells: minimal residual disease (MRD). In 102 out of 127 patients (80%), cells at diagnosis displayed one or more leukemia-associated phenotypes (LAP), ie combinations of cell surface markers which are absent in normal cells and can thus be used to detect MRD at follow-up. Functional characterization of MRD cells for P-glycoprotein (Pgp) and multidrug resistance protein (MRP) activity is essential to investigate the role of these drug transport proteins in multidrug resistance in AML. A fluorescent probe assay using Syto16/PSC833 and calcein-AM/probenecid as substrate/modulator of the Pgp and MRP pump, respectively, and subsequent labeling of cells with monoclonal antibodies for LAP detection allowed simultaneous detection of LAP and Pgp or MRP activity. Validation of this assay is shown for 30 newly diagnosed AML and 11 MRD situations. In addition, no significant differences were found when comparing fresh and cryopreserved de novo AML for LAP expression (n = 43), Pgp (n = 30) and MRP (n = 24) function and for MRD samples for simultaneous LAP expression and Pgp/MRP activity (n = 10). This approach enables longitudinal and multicenter studies on the detection, quantification and functional characterisation of MRD cells.

Storage of unprocessed G-CSF-mobilized whole blood in a modified Leibovitz's L15 medium preserves clonogenic capacity for at least 7 days

Autologous stem cell transplantation using unprocessed, G-CSF-mobilized whole blood (WB) is a simple, cost-reducing procedure and supports high-dose chemotherapy regimens not exceeding 72 h. Thereafter, clonogenic capacity rapidly decreases if routine anticoagulants are used for storage. In order to increase clinical applicability, we investigated the requirements for optimal preservation of unprocessed WB for 7 days. During storage at 22 degrees C in CPDA-1, a decrease in pH was noted, which was at least partially responsible for the low recovery of clonogenic cells. Subsequently, WB cells were stored in various cell culture media (RPMI 1640, alpha-MEM, X-VIVO15, CellGro SCGM and Leibovitz's L15 medium) containing either serum, serum-free substitutes or no additives. Leibovitz's L15 showed significantly better CFU-GM recoveries than the other media. Using a calcium-free modification of L15 medium (added 3:10 to WB), 94 +/- 24% of CD34(+) cells, 41 +/- 14% of BFU-E, 56 +/- 17% CFU-GM and 90 +/- 14% of LTC-IC were preserved during storage for 7 days at 22 degrees C. Storage at 4 degrees C was also feasible, but showed less optimal recoveries of 52 +/- 29% (CD34), 32 +/- 10% (BFU-E), 13 +/- 7% (CFU-GM) and 58 +/- 9% (LTC-IC). The expression of CD38, Thy-1, c-kit, AC133, L-selectin and CXCR4 on CD34-positive cells remained unchanged. In conclusion, a modified Leibovitz's L15 medium better meets the metabolic requirements of a high-density cell culture and allows safe storage of G-CSF mobilized WB for at least 7 days. The results encourage further exploration of WB transplants stored for 7 days for clinical use.

High-dose melphalan with G-CSF-stimulated whole blood rescue followed by stem cell harvesting and busulphan/cyclophosphamide with autologous stem cell transplantation in multiple myeloma

In 90 consecutive patients with multiple myeloma, we investigated the feasibility of administering a tandem high-dose therapy regimen, using whole blood for rescue after the first and leucapheresis harvested between the two high doses, for rescue after the second high dose. After 5 days of G-CSF 1 litre of whole blood (WB) was obtained, left undisturbed at 4 degrees C and reinfused 24 h after HDM (140 mg/m(2)). Patients not in progression after 3-6 months were again mobilised, leucapheresed and treated with busulphan 16 mg/kg and cyclophosphamide 120 mg/kg (Bu/Cy) and reinfusion. In 90 patients, WB contained a mean (range) of 0.57 (0.02-3.22) x 10(6)/kg CD34(+) cells. Recovery after HDM was in 13 days for granulocytes and in 18 days for platelets, with 11 patients not recovering within 3 months. There were three toxic deaths. Sixty-six patients qualified for harvesting after HDM. In the first 11, marrow was harvested. The subsequent 55 patients were mobilised and in 45 the preset minimum of 1.5 x 10(6) CD34(+) cells was obtained. Forty-nine patients actually received Bu/Cy. Recovery after Bu/Cy and marrow reinfusion was in 35 days for granulocytes and 20 days for platelets, with two of five patients not recovering after 3 months. After Bu/Cy and leucapheresis reinfusion, recovery was in 17 days for granulocytes and in 34 days for platelets. Nine patients did not recover within 3 months. There were four toxic deaths. The median overall survival from diagnosis for patients receiving HDM was 49 months and for patients also receiving Bu/Cy, 84 months. We conclude that WB rescue after HDM followed by leucapheresis and a second transplant is feasible in the majority of patients. Better mobilisation techniques are required to increase the number of patients who can receive the second transplant.

Large populations of non-clonogenic early apoptotic CD34-positive cells are present in frozen-thawed peripheral blood stem cell transplants

Apoptosis is the common cell death pathway which is initiated by a variety of different stimuli. The recognition of early apoptotic events would markedly improve reliability and convenience of apoptosis assays. In the present study the vital stain SytoR 16 in combination with the permeability marker 7-amino actinomycin D, (7-AAD) has been used to identify an early stage of apoptosis, not detected with trypan blue or 7-AAD alone or with conventional apoptosis tests and not consistently and only partly detected by the early apoptosis marker annexin V. The method was established using solid tumour cell lines treated with TNF. Subsequently we applied it to determine apoptotic populations in CD34(+) peripheral blood progenitor cells obtained from growth factor and/or chemotherapy mobilised patients and frozen/thawed according to standard stem cell transplantation protocols. In a cell line model as well as CD34(+) progenitor cells, different subpopulations with decreased SytoR 16 fluorescence (SytoR 16int or SytoR 16low, compared with the normal SytoR 16high) appeared which are not, or only partly, apoptotic using conventional techniques including morphology or 7-AAD staining: eg percentages of SytoR 16(int)/7-AAD(-) and SytoR 16(low)/7-AAD(-) may amount to the majority of cells present in a particular CD34(+) sample. Second, upon further incubation these subpopulations become late apoptotic/secondary necrotic much faster than the unmodified SytoR 16high population, as determined with 7-AAD staining and morphology. Third, these cells have strongly or completely reduced clonogenic capacity for committed (CFU-GM) and early (LTC-IC, determined only for CD34(+) cells) progenitors. This technique needs the inclusion of a blocker of P-glycoprotein, which is highly active in CD34(+) progenitor cells. This prevents the interference of the detection of SytoR16(low) apoptotic cells by SytoR 16low cells resulting from P-glycoprotein activity. By comparison with other apoptosis markers we found that early apoptotic subpopulations were detected in the order SytoR 16 > annexin V > 7-AAD. In conclusion, the combination of SytoR 16 and 7-AAD detects apoptotic events earlier than conventional apoptosis techniques or annexin V. Compared to the presently available viability tests, it allows a much better estimation of the number of viable clonogenic CD34(+) cells after freeze/thawing.

Monocyte-chemoattractant-protein-1-mediated migration of human monocytes towards blasts from patients with acute myeloid leukemia

PURPOSE

In the present study the possible clinical relevance of monocyte chemoattractant protein (MCP)-1 in patients with acute myeloid leukemia (AML) was established.

METHODS

The pattern of migration of human monocytes towards the supernatants of blasts from 15 patients with AML was studied and the role of MCP-1, produced by these blasts, was assessed.

RESULTS

In 4 patients (group 1) the amount of monocyte migration was low and not inhibited by the addition of anti-hMCP-1. In 11 patients, the amount of monocyte migration was high; after addition of anti-hMCP-1, monocyte migration was either completely (8 patients, group 2), or partly or not (3 patients, group 3) inhibited to the level of chemokinesis. In groups 1 and 2, there was a good correlation (r = 0.67) between the concentration of MCP-1 in the supernatants and the amount of monocyte migration. In group 3, such a correlation was not evident, suggesting that another chemokine might be involved or MCP-1 function was impaired by an unknown substance. Finally, measurements of MCP-1 during culture of AML blasts showed that the time at which maximal amounts of MCP-1 are produced differs between the AML samples.

CONCLUSIONS

AML blasts produce different amounts of MCP-1, which plays an important role in monocyte migration towards most AML blasts. Therefore, in the context of adoptive immunotherapy, MCP-1 might be involved in future tumor vaccination programmes using autologous MCP-1-transfected irradiated AML blasts.

The phenotypic profile of CD34-positive peripheral blood stem cells in different mobilization regimens

The type of regimen used might result in mobilization of phenotypically and functionally different CD34(+) cells. We compared the phenotype of CD34(+) cells in leukapheresis products of three homogeneous groups: I, healthy individuals treated with granulocyte colony-stimulating factor (G-CSF) alone (n = 13); II, patients mobilized with G-CSF following chemotherapy (n = 16); and III, patients mobilized with G-CSF after high-dose chemotherapeutic pretreatment (n = 24). Multiparameter flow cytometry was performed for CD34(+) subpopulation analysis and focused on adhesion molecules, differentiation markers and megakaryocytic markers relevant for stem cell homing, with special reference to the importance of L-selectin expression. Regimens I and II led to higher numbers of mobilized CD34(+) cells (mean 468 x 10(6) and 491 x 10(6) CD34(+) cells per leukapheresis procedure respectively) than regimen III (mean 41 x 10(6) CD34(+) cells per leukapheresis procedure). Both the expression of L-selectin and CD54 on CD34(+) cells was significantly lower in group III, as was the percentage of megakaryocytic (CD41(+)) progenitors. A higher percentage of primitive (CD38(-) and/or HLA(-)DR(-)) CD34(+) cells was found in group III, correlating with a higher clonogenicity of the CD34(+) cells. However, when comparing the CD34(+)_ subpopulations that were also positive for L-selectin, there was no significant difference between the three regimens. A similar approach for the megakaryocytic CD34+ population resulted in an even worse quality of regimen III: 5.1% of CD34(+) being CD41(+)/L-selectin(+) compared with 9.2% and 8.9% in regimens I and II respectively. We concluded that the phenotypes of the CD34(+) cells in the G-CSF (group I) and G-CSF-chemotherapy (group II) regimens are similar, whereas the phenotype of the CD34(+) cells mobilized in the high-dose regimen (group III) displayed features that might negatively influence homing of the cells. Future studies will be directed towards regimens that will lead to the mobilization of a higher amount of CD34(+) cells with a phenotypically favourable phenotype.

Aberrant Fanconi anaemia protein profiles in acute myeloid leukaemia cells

Fanconi anaemia (FA) is an autosomal recessive disease strongly predisposing to bone marrow failure and acute myeloid leukaemia (AML). Four FA genes, corresponding to complementation groups A, C, F and G, have been cloned, but the molecular functions of the corresponding proteins are unknown. The high risk of AML in FA patients suggests that the 'FA pathway' helps to prevent AML in non-FA individuals. We examined 10 AML cell lines, as well as primary cells from 15 AML patients representing the French-American-British subclasses M1-M5a, for possible deficiencies in the 'FA pathway'. Cellular lysates were analysed for the presence of the FA proteins FANCA, FANCC, FANCF and FANCG, as well as the complexes reported to be formed between these proteins, using immunoprecipitation and Western blot analysis. Aberrant protein profiles were observed in five of the 10 cell lines and in 11 of the 15 primary AML samples. Aberrations, that included absence or reduced presence of FA proteins and/or their complexes, were noted in the subclasses M1-M4, but not in M5a (n = 3). Our results suggest that a significant proportion of general AML is characterized by a disturbance of the 'FA pathway' that may represent an early event in the development of this type of leukaemia.

In vitro drug resistance profiles of adult versus childhood acute lymphoblastic leukaemia

The difference in the current cure rates between adult and childhood acute lymphoblastic leukaemia (ALL) may be caused by differences in drug resistance. Earlier studies showed that in vitro cellular drug resistance is a strong independent adverse risk factor in childhood ALL. Knowledge about cellular drug resistance in adult ALL is still limited. The present study compared the in vitro drug resistance profiles of 23 adult ALL patients with that of 395 childhood ALL patients. The lymphoblasts were tested by the MTT assay. The group of adult ALL samples was significantly more resistant to cytosine arabinoside, L-asparaginase, daunorubicin, dexamethasone and prednisolone. The resistance ratio (RR) was highest for prednisolone (31.7-fold) followed by dexamethasone (6.9-fold), L-asparaginase (6. 1-fold), cytosine arabinoside (2.9-fold), daunorubicin (2.5-fold) and vincristine (2.2-fold). Lymphoblasts from adult patients were not more resistant to mercaptopurine, thioguanine, 4-HOO-ifosfamide, mitoxantrone and teniposide. There were no significant differences in drug resistance between adult T-cell (T-) ALL (n = 11) and adult common/pre-B-cell (B-) ALL (n = 10). Additionally, adult T-ALL did not differ from childhood T-ALL (n = 69). There were significant differences between adult common/pre-B-ALL and childhood common/pre-B-ALL (n = 310) for prednisolone (RR = 302, P = 0.008), dexamethasone (RR = 20.9, P = 0.017) and daunorubicin (RR = 2.7, P = 0.009). Lymphoblasts from adults proved to be relatively resistant to drugs commonly used in therapy. This might contribute to the difference in outcome between children and adults with ALL.

P-glycoprotein in primary acute myeloid leukemia and treatment outcome of idarubicin/cytosine arabinoside-based induction therapy

The expression of the drug transport protein, P-glycoprotein (Pgp/MDR1) has been found to be of prognostic significance for the achievement of complete remission (CR) or the duration of survival after daunorubicin (DNR)-containing induction therapy in acute myeloid leukemia (AML). This would suggest that the expression of Pgp in AML is high enough to have significant impact on intracellular DNR concentrations and on clinical therapy failure in AML. Recently, DNR has been replaced in many centers by idarubicin (IDA) as the first choice anthracycline in AML treatment. We have, therefore, performed a study in a group of 98 primary AML patients, who all received IDA, but not DNR during induction therapy in order to determine if the response to IDA-containing induction therapy might be related to the biologic characteristic of Pgp expression in AML. The AML samples were studied for Pgp expression by MRK16 antibody staining and for Pgp activity measured as the modulation of rhodamine 123 uptake by 2 microM PSC 833. No correlation of Pgp with complete response rate, event-free survival or overall survival was found. In addition to Pgp, the expression of another protein that has been implicated by some studies in response failure to DNR-containing therapy, the major vault protein (Mvp/LRP), was studied. This marker did not correlate with CR or survival after IDA-containing therapy. The results of this patient study are consistent with model studies showing that the steady-state cellular accumulation of lipophilic anthracyclines such as IDA are little affected by Pgp. Therefore, putative beneficial effects of the inclusion of PSC 833 in IDA-containing therapy might rather be related to alternative mechanisms than to inhibition of Pgp-mediated IDA efflux.

Mobilisation of haemopoietic progenitors in CML: a second course of intensive chemotherapy does not improve Ph-negativity in stem cell harvests

We collected peripheral blood stem cells (PBSC) in 19 early chronic phase CML patients following each of two consecutive cycles of intensive chemotherapy (CT) to evaluate whether an additional cycle of CT would increase Philadelphia (Ph)-negativity of the PBSC harvest. Autologous SCT (autoSCT) was performed if a major cytogenetic response (MCR) of the PBSC harvest was obtained. CT consisted of cytarabine 200 mg/ m2/day (days 1-7)/idarubicin 12 mg/m2/day (days 1-2) (cycle one) and cytarabine 2000 mg/m2/day (days 1-6)/amsacrine 120 mg/m2/day (days 1-3) (cycle two). One patient died of fungal pneumonia after the first cycle. Stem cells were harvested in 18 patients after cycle one and in 16 patients after cycle two. After the first cycle, all patients showed a cytogenetic response of their graft (MCR in eight patients: three complete, five partial), after cycle two, seven patients obtained an MCR (one complete, six partial). Seven patients became eligible for autoSCT. All patients proceeded with IFNalpha maintenance. Currently, 16 patients are alive. At the latest cytogenetic examination of bone marrow, four patients showed an MCR and four a minor response. In conclusion, although a second cycle of CT may contribute to elimination of leukemia residing in the patient, it appeared to be ineffective in improving the Ph-negativity of the PBSC graft.

Regulation of megakaryocytopoiesis in an in vitro stroma model: preferential adhesion of megakaryocytic progenitors and subsequent inhibition of maturation

OBJECTIVE

Studies of megakaryocytic progenitor cell interactions have focused on single receptor-ligand interactions using isolated components of the extracellular matrix. To approach a physiologic condition, we studied megakaryocytic development of human progenitor cells cultured on two stromal cell lines and on human bone marrow stroma.

MATERIALS AND METHODS

Human CD34(+) cells were cocultured with stromal layers in the presence of thrombopoietin. Megakaryocytes were quantified by monoclonal antibodies against glycoprotein (GP) IIb/IIIa (CD41) and GPIX (CD42a). Megakaryocytic clonogenic capacity (burst-forming unit-megakaryocyte and colony-forming unit-megakaryocyte) was determined using fibrin clot assays.

RESULTS

After 6 days, a higher percentage of megakaryocytes and more megakaryocytic colonies were recovered from the adherent cell fraction compared to the nonadherent cell fraction. In contrast, significantly more granulocytic and erythroid colonies were recovered from the nonadherent cell fraction. Repeated replating of nonadherent cells onto fresh stroma showed a decline in megakaryocytic recovery of the remaining adherent cells, pointing toward selective adhesion of megakaryocytic progenitors. This was supported further by the finding that burst-forming unit and colony-forming unit megakaryocytes were preferentially recovered from the adherent cell fraction at 24 hours. No effect of blocking the beta(1) integrins VLA-4 and VLA-5 on human progenitor cells was observed. A higher expression of CD42a antigen and a higher percentage of morphologically recognizable polyploid megakaryocytes were found when cells were grown in noncontact cultures compared to when grown adhered to stroma.

CONCLUSION

In contrast to granulocytic and erythroid progenitors, both very early and more mature megakaryocytic progenitors are preferentially located in the adherent fraction in an in vitro stromal model, leading to inhibition of maturation of megakaryocytes. This suggests that the presence of stroma components in ex vivo expansion cultures, aimed at preservation and expansion of megakaryocytic progenitors, might be a prerequisite.