Aberrant marker expression patterns on the CD34+CD38- stem cell compartment in acute myeloid leukemia allows to distinguish the malignant from the normal stem cell compartment both at diagnosis and in remission.

Acute myeloid leukemia (AML) is generally regarded as a stem cell disease. In CD34-positive AML, the leukemic stem cell has been recognized as CD38 negative. This CD34+CD38- population survives chemotherapy and is most probable the cause of minimal residual disease (MRD). The outgrowth of MRD causes relapse and MRD can therefore serve as a prognostic marker. The key role of leukemogenic CD34+CD38- cells led us to investigate whether they can be detected under MRD conditions. Various markers were identified to be aberrantly expressed on the CD34+CD38- population in AML and high-risk MDS samples at diagnosis, including C-type lectin-like molecule-1 and several lineage markers/marker-combinations. Fluorescent in situ hybridization analysis revealed that marker-positive cells were indeed of malignant origin. The markers were neither expressed on normal CD34+CD38- cells in steady-state bone marrow (BM) nor in BM after chemotherapy. We found that these markers were indeed expressed in part of the patients on malignant CD34+CD38- cells in complete remission, indicating the presence of malignant CD34+CD38- cells. Thus, by identifying residual malignant CD34+CD38- cells after chemotherapy, MRD detection at the stem cell level turned out to be possible. This might facilitate characterization of these chemotherapy-resistant leukemogenic cells, thereby being of help to identify new targets for therapy.     

Resistance of leukemic stem-like cells in AML cell line KG1a to natural killer cell-mediated cytotoxicity

Leukemic stem cells (LSCs) play the central role in the relapse and refractory of acute myeloid leukemia (AML) and highlight the critical need for the new therapeutic strategies to directly target the LSC population. However, relatively little is known about the unique molecular mechanisms of drug and natural killer cells (NK)-killing resistance of LSCs because of very small number of LSCs in bone marrow. In this study, we investigated whether established leukemia cell line contains LSCs. We showed that KG1a leukemia cell line contained leukemic stem-like cells, which have been phenotypically restricted within the CD34(+)CD38(-) fractions. CD34(+)CD38(-) cells could generate CD34(+)CD38(+) cells in culture medium and had renewal function. Moreover, CD34(+)CD38(-) cells had self-renewal potential. We found that leukemic stem-like cells from KG1a cells were resistant to chemotherapy and NK-mediated cytotoxicity. NKG2D ligands involve in protecting LSCs from NK-mediated attack. Taken together, our studies provide a novel cell model for leukemic stem cells research. Our data also shed light on mechanism of double resistant to chemotherapy and NK cell immunotherapy, which was helpful for developing novel effective strategies for LSCs.     

CD34+/CD38- Stem Cell Burden Could Predict Chronic Myeloid Leukemia Patients’ Outcome

Background: The current predictor of the Chronic myeloid leukemia (CML)  patients’ outcome is the degree of response to targeted therapy; here we search for a biomarker predicting CML outcome before start of therapy. This study aimed to assess the impact of the  CD34+/CD38- stem cells (SCs) burden in chronic myeloid leukemia (CML) on  treatment response and patients’ outcomes. Methods: Our study included 65 CML patients in the chronic phase. The patients’  CD34+/CD38- stem cells were quantified  using flowcytometry before and after treatment by frontline imatinib (IM) therapy. The median follow-up for all patients was 18 months. Results: CD34+/CD38- stem cells frequency at diagnosis and after therapies are correlated to known prognostic markers (blast cells count, spleen size, total White cell count, and clinical scores). After therapy, the leukemic stem cells count dropped rapidly. The pretreatment CD34+/CD38- stem cells burden predicts response to frontline therapy. In addition, high SCs frequency at diagnosis predicts poor molecular response, transformation to AML, and poor patients’ outcomes. Conclusion: The percentage of CD34+/CD38- SCs burden at diagnosis reflects the CML disease behavior and is considered a biomarker for predicting CML patients’ response to first-line Tyrosine kinase inhibitors (TKI) therapy.     

CD34+/CD38- Stem Cell Burden Could Predict Chronic Myeloid Leukemia Patients’ Outcome

Background:The current predictor of the Chronic myeloid leukemia (CML) patients’ outcome is the degree of response to targeted therapy; here we search for a biomarker predicting CML outcome before start of therapy. This study aimed to assess the impact of the CD34+/CD38- stem cells (SCs) burden in chronic myeloid leukemia (CML) on treatment response and patients’ outcomes. Methods:Our study included 65 CML patients in the chronic phase. The patients’ CD34+/CD38- stem cells were quantified using flowcytometry before and after treatment by frontline imatinib (IM) therapy. The median follow-up for all patients was 18 months. Results:CD34+/CD38- stem cells frequency at diagnosis and after therapies are correlated to known prognostic markers (blast cells count, spleen size, total White cell count, and clinical scores). After therapy, the leukemic stem cells count dropped rapidly. The pretreatment CD34+/CD38- stem cells burden predicts response to frontline therapy. In addition, high SCs frequency at diagnosis predicts poor molecular response, transformation to AML, and poor patients’ outcomes. Conclusion:The percentage of CD34+/CD38- SCs burden at diagnosis reflects the CML disease behavior and is considered a biomarker for predicting CML patients’ response to first-line Tyrosine kinase inhibitors (TKI) therapy.Key Words: CML, CD34+/CD38, stem cells, outcome     

Clonal chromosomal abnormalities in the stem cell compartment of patients with acute myeloid leukemia in morphological complete remission.

Acute myeloid leukemia arises from the clonal expansion of a malignant transformed progenitor cell. Despite intensive chemotherapy, final disease eradication is achieved by a small proportion of cases only and 50-70% of adults with AML will ultimately relapse and die from their disease. Hence residual disease below the level of morphological detectability must be assumed in clinical and morphological complete remission. CD34+/CD38- and CD34+/CD38+ subpopulations of seven patients in morphological complete remission were isolated by FACS (purity >98%) and were analyzed by conventional cytogenetics or FISH for chromosomal aberrations. In five of seven patients, clonal chromosomal abnormalities were detected in the CD34+/CD38+ subpopulation and in one patient with AML M2 (add (2)(q37)) in the most immature CD34+/CD38- stem cell compartment. One patient with AML M4Eo (inv(16),+8), showed a normal karyotype by conventional cytogenetic analysis, whereas four of 15 metaphases of the sorted CD34+/CD38+ subpopulation revealed the inversion 16. These observations underline that leukemic cells can survive intensive chemotherapy in the niche of the stem cell compartment. In some patients the sensitivity for the detection of persistent leukemic cells seems to be higher in FACS-sorted subpopulations than conventional cytogenetic analysis of the unseparated bone marrow. Immunophenotyping revealed minimal residual disease in four of the patients. Functional analysis has to be performed to investigate the leukemogenic potential of these residual cells.     

Functional alterations of Lin-CD34+CD38+ cells in chronic myelomonocytic leukemia and on progression to acute leukemia

The functional behavior of hematopoietic stem cell (HSC) and progenitors in chronic myelomonocytic leukemia (CMML) and on disease progression is little known. We performed cell proliferation, apoptosis, hematopoietic colony forming/replating and differentiation potential studies in the purified subpopulations of Lin(-)CD34(+)CD38(-) and Lin(-)CD34(+)CD38(+) cells from 16 CMML with 6 cases after acute myeloid leukemia transformation (AML-t). We observed an expansion of the hematopoietic progenitor pool (Lin(-)CD34(+) cells) in AML-t comprising mainly Lin(-)CD34(+)CD38(+) cells. The Lin(-)CD34(+)CD38(+) cells in AML-t displayed high proliferative activity, resistance to apoptosis, enhanced myeloid colony formation/replating ability and a complete dendritic cell (DC) differentiation block. Our findings suggest Lin(-)CD34(+)CD38(+) cells instead of Lin(-)CD34(+)CD38(-) cells could be the target(s) of secondary genetic lesions underpinning progression from CMML to AML, which have implications for the further study of the biology of leukemic transformation and the design of new strategies for the effective treatment of CMML.     

Coculture and transplant of purified CD34(+)Lin(-) and CD34(-)Lin(-) cells reveals functional interaction between repopulating hematopoietic stem cells.

The human hematopoietic stem cell compartment is comprised of repopulating CD34(+) and CD34(-) cells. The interaction between these subsets with respect to their reconstitution capacity in vivo remains to be characterized. Here, lineage-depleted (Lin(-)) human CD34(+) and CD34(-) hematopoietic cells were isolated from human male and female umbilical cord blood (CB) and transplanted into immune-deficient NOD/SCID EMV(null) mice, thereby allowing the use of human and Y-chromosome-specific DNA sequences to discriminate human reconstitution contributed by CD34(+) vs CD34(-) repopulating stem cells. Although cultured human CB CD34(-)Lin(-) cells transplanted alone possessed only minimal repopulating capacity, with 15% of mice achieving low levels of engraftment, transplantation of cocultured male CD34(-)Lin(-) cells with female CD34(+)Lin(-) cells demonstrated human repopulation with a contribution from CD34(-)Lin(-)-derived progeny in 80% of the recipients. After coculture and transplantation, male CD34(-)Lin(-) cells gave rise to primitive CD34(+)CD38(-) cells isolated in vivo, which demonstrated clonogenic progenitor function into multiple lineages. Taken together, our study indicates that the presence of CD34(+)Lin(-) cells in coculture enhanced the low repopulating function of human CD34(-)Lin(-) cells in vivo. We propose that CD34(+)Lin and CD34(-)Lin cells represent phenotypically distinct, but related cell types that exhibit unique and previously unappreciated functional interaction.     

Gene expression profiles of AML derived stem cells; similarity to hematopoietic stem cells.

Tumors contain a fraction of cancer stem cells that maintain the propagation of the disease. The CD34(+)CD38(-) cells, isolated from acute myeloid leukemia (AML), were shown to be enriched leukemic stem cells (LSC). We isolated the CD34(+)CD38(-) cell fraction from AML and compared their gene expression profiles to the CD34(+)CD38(+) cell fraction, using microarrays. We found 409 genes that were at least twofold over- or underexpressed between the two cell populations. These include underexpression of DNA repair, signal transduction and cell cycle genes, consistent with the relative quiescence of stem cells, and chromosomal aberrations and mutations of leukemic cells. Comparison of the LSC expression data to that of normal hematopoietic stem cells (HSC) revealed that 34% of the modulated genes are shared by both LSC and HSC, supporting the suggestion that the LSC originated within the HSC progenitors. We focused on the Notch pathway since Jagged-2, a Notch ligand was found to be overexpressed in the LSC samples. We show that DAPT, an inhibitor of gamma-secretase, a protease that is involved in Jagged and Notch signaling, inhibits LSC growth in colony formation assays. Identification of additional genes that regulate LSC self-renewal may provide new targets for therapy.     

Induction of apoptosis by cladribine (2-CdA), gemcitabine and other chemotherapeutic drugs on CD34+/CD38+ and CD34+/CD38- hematopoietic progenitor cells: selective effects of doxorubicin and 2-CdA with protection of immature cells

Due to the emerging role of high dose chemotherapy with stem cell rescue and ex vivo purging in hematological diseases, we examined the effect of chemotherapeutic drugs on the rate of apoptosis in more mature CD34+/CD38+ and less differentiated CD34+/CD38- stem cells. CD34+ cells were obtained by cell apheresis from healthy donors (n = 25) or patients (n = 25) prepared for high dose chemotherapy and stem cell transplantation. Cells were incubated with different concentrations of doxorubicin, mitoxantrone, mafosphamide, cladribine or gemcitabine. Apoptosis was determined after 24 and 48 h. Generally, the percentage of apoptotic cells was higher in the more mature CD34+/CD38+ progenitor population than in the less differentiated CD34+/CD38- cells. By analysis of variance (ANOVA) significantly (p < 0.05) more apoptotic cells within the CD34+/CD38+ progenitors were calculated after incubation with mafosphamide, doxorubicine and cladribine. Mafosphamide induced the highest rate of apoptosis on CD34+/CD38- cells, whereas doxorubicine had nearly no effect on this immature population. Dose effect plots for mafosphamide and doxorubicin were steep, suggesting a large therapeutic index. The dose response of cladribine showed a flat course. Furthermore we found a selective induction of apoptosis by doxorubicin and cladribine on more mature CD34+/CD38+ progenitors in contrast to simultaneous protection of CD34+/CD38- progenitors. From these findings, in particular the demonstrated low stem cell toxicity, we conclude that doxorubicin and cladribine might be efficient alternatives in ex vivo purging of autologous grafts, as well as safe components in primary treatment schedules of lymphomas or prior to stem cell harvest with respect to stem cell toxicity.     

Apoptosis induction in peripheral leukemia cells by remission induction treatment in vivo: selective depletion and apoptosis in a CD34+ subpopulation of leukemia cells.

In vitro studies demonstrating the induction of programmed cell death by cytotoxic drugs used in anticancer chemotherapy suggested that antileukemic treatment eliminates leukemia cells by apoptosis. We therefore analyzed apoptosis induction and activation of apoptosis signaling molecules in patients receiving remission induction treatment for AML and ALL during the initial phase of leukemia cell reduction. A coexistence of distinct populations of CD34(+) and CD34(-) leukemia cells could be identified. During chemotherapy, CD34(+) leukemia cells were more rapidly depleted than CD34(-) cells. Furthermore, a significant increase in leukemia cell apoptosis ex vivo was detected in CD34(+) cells, while no such increase was observed in the CD34(-) subpopulation, suggesting that CD34(+) leukemia cells are the main targets for apoptosis induction through antileukemic treatment. No alterations in Bax and Bcl-2 expression were found during in vivo chemotherapy, and CD95 expression and sensitivity remained low, indicating the induction of apoptosis independent of the CD95 system or regulation of protein levels of Bax and Bcl-2. The data suggest that analysis of leukemia cell subpopulations is required for further identification of apoptosis signaling molecules relevant for response to treatment and assessment of drug efficacy in vivo and in vitro.     

Azacitidine for treatment of imminent relapse in MDS or AML patients after allogeneic HSCT: results of the RELAZA trial

This study evaluated azacitidine as treatment of minimal residual disease (MRD) determined by a sensitive donor chimerism analysis of CD34(+) blood cells to pre-empt relapse in patients with CD34(+) myelodysplastic syndromes (MDS) or acute myeloid leukemia (AML) after allogeneic hematopoietic stem cell transplantation (HSCT). At a median of 169 days after HSCT, 20/59 prospectively screened patients experienced a decrease of CD34(+) donor chimerism to <80% and received four azacitidine cycles (75?mg/m(2)/day for 7 days) while in complete hematologic remission. A total of 16 patients (80%) responded with either increasing CD34(+) donor chimerism to ≥80% (n=10; 50%) or stabilization (n=6; 30%) in the absence of relapse. Stabilized patients and those with a later drop of CD34(+) donor chimerism to <80% after initial response were eligible for subsequent azacitidine cycles. A total of 11 patients (55%) received a median of 4 (range, 1-11) additional cycles. Eventually, hematologic relapse occurred in 13 patients (65%), but was delayed until a median of 231 days (range, 56-558) after initial decrease of CD34(+) donor chimerism to <80%. In conclusion, pre-emptive azacitidine treatment has an acceptable safety profile and can substantially prevent or delay hematologic relapse in patients with MDS or AML and MRD after allogeneic HSCT.     

C-type lectin-like molecule-1: a novel myeloid cell surface marker associated with acute myeloid leukemia

Acute myeloid leukemia (AML) has a poor prognosis due to treatment-resistant relapses. A humanized anti-CD33 antibody (Mylotarg) showed a limited response rate in relapsed AML. To discover novel AML antibody targets, we selected a panel of single chain Fv fragments using phage display technology combined with flow cytometry on AML tumor samples. One selected single chain Fv fragment broadly reacted with AML samples and with myeloid cell lineages within peripheral blood. Expression cloning identified the antigen recognized as C-type lectin-like molecule-1 (CLL-1), a previously undescribed transmembrane glycoprotein. CLL-1 expression was analyzed with a human anti-CLL-1 antibody that was generated from the single chain Fv fragment. CLL-1 is restricted to the hematopoietic lineage, in particular to myeloid cells present in peripheral blood and bone marrow. CLL-1 is absent on uncommitted CD34(+)/CD38(-) or CD34(+)/CD33(-) stem cells and present on subsets of CD34(+)/CD38(+) or CD34(+)/CD33(+) progenitor cells. CLL-1 is not expressed in any other tissue. In contrast, analysis of primary AMLs demonstrated CLL-1 expression in 92% (68 of 74) of the samples. As an AML marker, CLL-1 was able to complement CD33, because 67% (8 of 12) of the CD33(-) AMLs expressed CLL-1. CLL-1 showed variable expression (10-60%) in CD34(+) cells in chronic myelogenous leukemia and myelodysplastic syndrome but was absent in 12 of 13 cases of acute lymphoblastic leukemia. The AML reactivity combined with the restricted expression on normal cells identifies CLL-1 as a novel potential target for AML treatment.     

Human cord blood long-term engrafting cells are CD34+ CD38-.

There have been controversies about CD34 and CD38 expression by human cord blood (CB) stem cells. Using the newborn NOD/SCID/beta2-microglobulin-null mouse assay that we recently developed, we examined the in vivo engrafting capability of human CB cells. Almost all of the 4-5 months engrafting cells were found in CD34(+) population. The capability of secondary reconstitution was found only in the CD34(+) cells. When the CD34(+) CB cells were separated into CD38(-) and CD38(+) subpopulations and tested for engraftment, the majority of the engrafting cells were detected in the CD38(-) subpopulation. These findings are consistent with the results from studies of murine stem cells and strongly indicate that the phenotype of human CB stem cells is CD34(+) CD38(-).     

Homing, proliferation and survival sites of human leukemia cells in vivo in immunodeficient mice.

The cellular components of the hematopoietic stem cell niche have been gradually identified. However, the niche for malignant hematopoiesis remains to be elucidated. Here, using human leukemia cells, which could be transplanted to immunodeficient mice, we studied the in vivo homing, proliferation and survival sites by immunohistopathology, compared with the corresponding sites for cord blood CD34(+) (CBCD34(+)) cells. The human leukemia cells initially localized on the surface of osteoblasts in the epiphysial region, and expanded to the inner vascular and diaphysial regions within 4 weeks. The percentage of CD34(+) leukemia cells in the bone marrow was transiently increased up to 50%. In vivo 5-bromo-2'-deoxyuridine labeling revealed that the epiphysis was the most active site for leukemia cell proliferation. CBCD34(+) cells showed the similar pattern of homing and proliferation to leukemia cells. After high-dose administration of cytosine-1-beta-D-arabinofuranoside, residual leukemia cells were localized in the perivascular endothelium as well as in contact with the trabecular endosteum. These findings suggest that xenotransplantation into immunodeficient mice provides a useful model to study the leukemia niche.     

Enrichment of N-Cadherin and Tie2-bearing CD34/CD38/CD123 leukemic stem cells by chemotherapy-resistance

Acute myeloid leukemia (AML) arises from genetic changes at the level of stem cell, various mutations have been elucidated, including AML1–ETO fusion gene has been shown as the representative target of cellular transformation for LSCs originating from hematopoietic stem cells (HSCs) compartment. LSCs resemble HSCs with respect to self-renewal capacity and chemotherapy-resistance. However, LSCs possess specific cell-surface markers, they are proposed to reside within the CD34⁺/CD38⁻/CD123⁺ compartment. And the interaction mediated by adhesion molecules between LSCs and niche played a role in chemoresistance of LSCs. Therefore, study on the LSCs surface makers related to niche is helpful for the potential target therapy in the future. In this study, the proportions of CD34⁺/CD38⁻/CD123⁺ LSCs compartment co-expressing the three adhesion molecules, N-Cadherin, Tie2 and CD44, respectively, from AML patients before and after chemotherapy were analyzed. We demonstrated N-Cadherin and Tie2 positive CD34⁺/CD38⁻/CD123⁺ LSCs populations could be enriched by chemotherapy. Furthermore, AML1/ETO fusion signals and MDR1 expression were detected on the CD34⁺/CD38⁻/CD123⁺ LSCs populations expressing N-Cadherin and Tie2. Therefore, N-Cadherin and Tie2 are probably the potential markers for identification of LSCs.     

Detection of cytogenetic aberrations both in CD90 (Thy-1)-positive and (Thy-1)-negative stem cell (CD34) subfractions of patients with acute and chronic myeloid leukemias.

Acute myeloid leukemia (AML) and chronic myeloid leukemia (CML) are thought to arise from malignant hematopoietic progenitor cells representing early and undifferentiated stem cell clones. In CML there is evidence for a progenitor cell subset free of leukemic clones, depending on the course of the disease. Additionally, it has been suggested that in AML, the early stem cell compartment (CD34+/90+) does not harbor the malignant clone. We analyzed white blood cells from leukemia patients for the presence of aberrant cells in stem cell subfractions. Sixteen patients with CML, six patients with AML, two patients with acute lymphatic leukemia (ALL) and one with chronic myelomonocytic leukemia (CMMOL), all with known cytogenetic abnormalities, were evaluated according to their CD90 (Thy-1)-positive or -negative phenotype. Subsets were sorted on to slides and further characterized by FISH and/or standard cytogenetic testing. The bcr-abl translocation or gross chromosomal abnormalities could be detected in equally high amounts of 92.2% and 89.2% in both stem cell subsets. We conclude, that in progressed AML and CML cells characterized by specific genetic aberrations implicated in the malignant state can be found in the CD34+/CD90+ and CD90- population, thus making CD90 an inappropriate marker to distinguish benign from malignant cells in these leukemias.     

MRx102, a triptolide derivative, has potent antileukemic activity in vitro and in a murine model of AML

Triptolide, isolated from the herb Tripterygium wilfordii, has been shown to potently induce apoptosis in various malignant cells by inhibiting RNA synthesis and nuclear factor-κB activity. Previously, we showed that triptolide promotes apoptosis in acute myeloid leukemia (AML) cells via the mitochondria-mediated pathway, in part, by decreasing levels of the anti-apoptotic proteins XIAP and Mcl-1. MRx102 is a triptolide derivative, currently in preclinical development. Here we show that MRx102 potently promoted apoptosis in AML cell lines, with EC(50) values of 14.5±0.6?nM and 37.0±0.9?nM at 48?h for OCI-AML3 and MV4-11 cells, respectively. MRx102, at low nanomolar concentrations, also induced apoptosis in bulk, CD34(+) progenitor, and more importantly, CD34(+)CD38(-) stem/progenitor cells from AML patients, even when they were protected by coculture with bone marrow derived mesenchymal stromal cells. MRx102 decreased XIAP and Mcl-1 protein levels and inhibited RNA synthesis in OCI-AML3 cells. In vivo, MRx102 greatly decreased leukemia burden and increased survival time in non-obese diabetic/severe combined immunodeficiency mice harboring Ba/F3-ITD cells. Collectively, we demonstrated that MRx102 has potent antileukemic activity both in vitro and in vivo, has the potential to eliminate AML stem/progenitor cells and overcome microenvironmental protection of leukemic cells, and warrants clinical investigation.     

Migratory behavior of leukemic cells from acute myeloid leukemia patients.

The chemokine stromal cell-derived factor-1 (SDF-1) and its receptor CXCR-4 contribute to stem cell homing and may play a role in the trafficking of leukemic cells. Therefore, we analyzed migration across Transwell filters of cells derived from bone marrow (BM) or peripheral blood (PB) from 26 acute myeloid leukemia (AML) patients. The presence of the extracellular matrix protein fibronectin (FN) strongly enhanced the spontaneous and SDF-1-induced migration of leukemic PB and BM cells. No differences in spontaneous, SDF-1-induced migration or CXCR-4 expression were observed between the different AML subtypes. Subsequently, it was determined whether SDF-1 preferentially promoted migration of subsets of leukemic cells. Leukemic cells expressing CD34, CD38 and HLA-DR were preferentially migrating, whereas cells expressing CD14 and CD36 showed diminished migration. Analysis of paired PB and BM samples indicated that significantly higher SDF-1-induced migration was observed in AML for CD34(+) BM-derived cells compared to CD34(+) PB-derived cells, suggesting a role for SDF-1 in the anchoring of leukemic cells in the BM or other organs. The lower percentage of circulating leukemic blasts in patients with a relatively high level of SDF-1-induced migration also supports this hypothesis. In conclusion, we have shown that primary AML cells are migrating towards SDF-1 independent of the AML subtypes.     

Efficacy of first-line bleomycin, etoposide, and cisplatin chemotherapy for peripheral blood stem cell mobilization in patients with germ cell cancer

Background We assessed the efficacy of first-line bleomycin, etoposide, and cisplatin (BEP) chemotherapy for the mobilization of peripheral blood stem cells (PBSC) in patients with testicular cancer, and analyzed the predictive factors indicating the optimal time of PBSC harvest. Patients and Methods A total of 29 aphereses, performed during first-line BEP chemotherapy between 1994 and 1996 for 10 patients with metastatic germ cell cancer were analyzed. The predictive value for the optimal time of PBSC harvest was determined by analysis of the correlation between the rate of each cellular component in peripheral blood, and the number of CD34-positive cells harvested. Results The median number of CD34-positive cells obtained at a single apheresis was 11.2×10⁶/kg (range, 0.14 to 47.9×10⁶/kg), and the median cumulative number of CD34-positive cells collected during first-line BEP chemotherapy per patient was 31.9×10⁶/kg (range, 9.7 to 75.5×10⁶/kg). The percentage of immature leukocytes (myelocytes plus metamyelocytes) was significantly correlated with the number of harvested CD34-positive cells. Conclusion Adequate amounts of CD34-positive cells can be harvested during first-line BEP chemotherapy for patients with germ cell cancer. The monitoring of the percentage of immature leukocytes might be useful in ascertaining the optimal time of apheresis.