急性髓细胞性白血病细胞表面CD分子表达及临床意义研究

目的 探讨急性髓细胞性白血病(AML)细胞表面CD分子的表达情况.方法 采用CD45分子作为靶目标抗原,应用多参数流式细胞术检测300例AML患者细胞表面的CD分子,分析患者的免疫表型.结果以表达百分比﹥20%作为阳性,300例AML患者的CD抗原表达均不相同,cyt-MPO、CD33、CD117和CD38表达最强,为强阳性(80%~100%).以CD抗原表达>60%为阳性,结果显示:CD33、CD117、CD13、cyt-MPO四种抗原阳性表达的患者,阳性细胞所占的比例高于其他抗原,差异有统计学意义(P﹤0.05).CD15/CD64、CD15/CD33和CD33/CD64抗原的阳性表达比较,差异均有统计学意义(P﹤0.05);CD33/cyt-MPO抗原的阳性表达比较,差异无统计学意义(P﹥0.05).结论 AML细胞表面的CD抗原表达具有差异性,CD13、cyt-MPO、CD33、CD117呈高表达.CD分子在AML细胞中阳性表达的差异性可为治疗提供有价值的线索.     

Detection of molecular targets on the surface of CD34+/CD38-- stem cells in various myeloid malignancies

Recent data suggest that myeloid neoplasms are organized hierarchically in terms of self-renewal and maturation of early progenitor cells, similar to normal myelopoiesis. In acute myeloid leukemia (AML), the NOD/SCID mouse-repopulating leukemic stem cells usually co-express CD123 with CD34, but lack CD38. So far, however, little is known about expression of other markers and targets on these progenitors. In the present study, expression of target antigens on CD34+/CD38- cells was analysed by multi-color flow cytometry in patients with AML (n = 18), myelodysplastic syndromes (MDS, n = 6), chronic myeloid leukemia (CML, n = 8) and systemic mastocytosis (SM, n = 9). The IL-3Ralpha chain (CD123) was found to be expressed on CD34+/CD38- cells in a majority of the patients in all disease categories. Independent of the type of disease, the vast majority of these stem cells co-expressed aminopeptidase-N (CD13) and CD44 in all patients. By contrast, the CD34+/CD38- progenitor cells expressed variable amounts of the target receptor CD33, c-kit (CD117) and AC133 (CD133). In conclusion, neoplastic stem cells in various myeloid neoplasms appear to express a similar phenotype including target antigens such as CD13, CD33 and CD44. Since many of these targets are not expressed on all stem cells in all patients, the elimination of the entire clone may require combinations of targeted antibodies or use of additional drugs.     

CD117在急性白血病中的表达及其临床意义

 目的 探讨细胞表面抗原CD117在各型急性白血病（AL）中的表达规律及其临床意义。方法 采用流式细胞术（FCM）检测139例AL患者骨髓或外周血中CD117的表达情况,并进行分析和比较。结果 急性淋巴细胞白血病（ALL）患者CD117阳性细胞表达水平与正常对照组相比差异无统计学意义（P＞0.05）;急性髓细胞白血病（AML）患者CD117阳性患者比例及阳性细胞表达水平较正常对照组和ALL组均升高,差异有统计学意义（均P＜0.05）。在AML各亚型中,CD117阳性患者比例及阳性细胞表达水平以M0／M1最高,M5b最低;在5种髓系膜抗原标志中,虽然CD117检测AML的灵敏度低于CD13和CD33,但特异性都较高;CD117与CD34及HLA-DR在AML中的表达呈显著正相关,但在M3中,CD117表达明显高于CD34和HLA-DR。结论 CD117可作为AL患者MIC诊断分型的重要髓系免疫表型指征,在AML的诊断分型以及AML和ALL的鉴别诊断中具有重要意义。     

Immunological classification of acute myeloblastic leukemias: relevance to patient outcome.

Immunophenotyping is a major tool to assign acute leukemia blast cells to the myeloid lineage. However, because of the large heterogeneity of myeloid-related lineages, no clinically relevant immunological classification of acute myeloblastic leukemia (AML) has been devised so far. To attempt at formulating such a classification, we analyzed the pattern of expression of selected antigens, on blast cells collected at AML diagnosis. Patients were eligible if they had a first diagnosis of de novo AML and a sufficient number of blast cells for proper immunophenotyping. The relative expression of CD7, CD13, CD14, CD15, CD33, CD34, CD35, CD36, CD65, CD117, and HLA-DR were analyzed by cytometry in a test series of 176 consecutive AML cases. Statistical tools of clusterization allowed to remove antigens with overlapping distribution, leading us to propose an AML classification that was validated in a second AML cohort of 733 patients. We identified five AML subsets (MA to ME) based on the expression of seven antigens within four groups (CD13/CD33/CD117, CD7, CD35/CD36, CD15).-MA and MB-AML have exclusively myeloid features with seldom extramedullary disease and rare expression of lymphoid antigens. No cases of acute promyelocytic leukemia (APL) were observed within MB AML. MC AML have either myeloid or erythroblastic features. MD AML have more frequently high WBC counts than other subsets, which were related to the expression of CD35/CD36 and CD14 and to monoblastic differentiation. ME AML lack CD13, CD33, and CD117 but display signs of terminal myeloid differentiation. Specific independent prognostic factors were related to poor overall survival in each immunological subset: CD34+ (P<3 x 10(-4)) in MA AML, CD7+ in MB AML, non-APL cases (P<0.03) in MC AML, CD34+ (P<0.002) and CD14+ (P<0.03) in MD AML, CD14+ in ME AML (P<0.01). The inclusion of seven key markers in the immunophenotyping of AML allows a stratification into clinically relevant subsets with individual prognostic factors, which should be considered to define high-risk AML populations.     

Enhanced myeloid specificity of CD117 compared with CD13 and CD33

The c-kit proto-oncogene encodes a 145 kd tyrosine kinase transmembrane receptor, which plays a key role in haemopoiesis. The c-kit has been classified as CD117 and is especially useful in the differential diagnosis of acute myelogenous leukemia (AML) and acute lymphoblastic leukemia (ALL). We analysed 104 consecutive cases (55 AML, 23 B-cell lineage ALL, three T-cell ALL, 11 blast crisis of chronic myeloproliferative disorders and 12 cases of myelodysplastic syndromes with more than 10% of blasts) referred to our Hospital for immunophenotypic diagnosis and compared the expression pattern of CD13, CD33 and CD117 using the same fluorochrome (phycoerythrin-PE). The recommendations of the EGIL group were followed in order to establish lineage involvement of the blastic population. The threshold used to assign positivity for CD117 was 10%. Bcr/abl, TEL/AML-1 and MLL rearrangements were assessed by molecular methods. CD117 expression was detected in 91% of AML and MDS. All the negative cases corresponded to acute monocytic leukemias. The calculated specificity for myeloid involvement was 0.86 for CD117, 0.36 for CD13 and 0.44 for CD33 (P < 0.005). CD117 was also positive in four cases of ALL. None of these cases showed bcr/abl or MLL rearrangements. In the light of these findings, CD117 expression should yield a higher score, at least one point, in the system currently applied for the diagnosis of biphenotypic acute leukemias (BAL) as its myeloid specificity is greater than that of CD13 and CD33. Moreover, its absence in AML could identify two subgroups of M5b cases. The coexpression of CD117 with cytoplasmic CD79a is often associated with CD7 reactivity, suggesting a stem cell disorder. CD117 should be included on a routine basis for the immunophenotypic diagnosis of acute leukemias.     

Expression of c-kit Receptor (CD 117) and CD34 in Leukemic Cells

The expression of c-kit receptor (c-kit R; CD117) and CD34 was examined in acute myeloid leukemia (AML), acute lymphoid leukemia (ALL), chronic myeloid leukemia (CML) in blastic transformation (BT), and myelofibrosis (MF) in myeloid BT. In myeloid leukemia including AML, CML-myeloid BT and MF-myeloid BT, both c-kit R and CD34 were expressed synchronously, while in lymphoid leukemia including ALL and CML-lymphoid BT, only CD34 was highly expressed. A close correlation between c-kit R and CD33 expression and an inverse correlation between c-kit R and CD 19 expression were observed when all of the myeloid plus lymphoid leukemia cells were analysed. There was a close correlation between c-kit R and CD34 expression in the myeloid leukemia cells, c-kit R expression may be associated with myeloid phenotypes of leukemic cells and may be useful for the diagnosis of myeloid leukemia. The literature of c-kit R expression in leukemic cells is reviewed here and the comparison of c-kit R and CD34 expression in normal hematopoietic progenitor cells with those on the leukemic counterparts was discussed.     

CD34/CD117 positivity in assessment of prognosis in children with myelodysplastic syndrome

Myelodysplastic syndromes (MDS) are a heterogeneous group of clonal stem cell disorders that are characterized by morphology identifying dysplastic changes in one or more cell lineages, peripheral blood cytopenias and a propensity to evolve into secondary acute myeloid leukemia (AML). CD34 is commonly expressed in all types of childhood leukemias, whereas CD117 is a reliable and specific marker to detect leukemia cells committed to myeloid lineage. Co-expression of CD34/CD117 may strongly suggest the diagnosis of AML (Rytting ME. Pediatric myelodysplastic syndromes. Curr hematol Rep 2004;3(3):173-7. May; U?kan D, Hi?s?nmez G, Yetgin S, Gürgey A, Cetin M, Karaa?ao?lu E, et al. CD34/CD117 co-expression in childhood acute leukemia. Leukemia Res 2000;24:201-6.). We describe the case of a 22 month-old-girl with MDS and Down syndrome who was presented with severe anemia and thrombocytosis at diagnosis, transformed into AML-M7. In our patient, CD34 and CD117 markers were positive on the blast cells of the BM 6 months before the chemotherapy decision. As the disease progressed, CD34/117 co-existence was increased and MDS transformed into AML. As a result, an increase in CD34 and CD117 positivity of the BM blast cells may be associated with a higher risk of leukemic transformation.     

CD34/CD117 co-expression in childhood acute leukemia

CD117 protein is expressed by the primitive CD34 positive haemopoietic stem cells and also demonstrated on the blasts of 30-100% of AML cases, but rarely on lymphoblasts. Therefore several investigators have used CD117 expression to exclude lymphoblastic origin of blasts. However, conflicting results exist in the literature. We investigated CD34 and CD117 status at initial presentation of 232 children with acute leukemia. CD34 was commonly expressed in all types of acute leukemias, whereas CD117 molecule seemed to be a more specific marker for leukemia of myeloid origin being demonstrated on > 5% of blasts in 60 out of 73 cases of AML patients, but rarely detected in ALL (9/140 patients). Moreover, co-expression of CD34/CD117 was extremely rare on lymphoblasts with only 3/140 ALL patients demonstrating > 5% co-expression of CD34 and CD117, and therefore we suggest that it should be used in the exclusion of ALL.     

Expression of Bcl-2-related genes in normal and AML progenitors: changes induced by chemotherapy and retinoic acid.

The expression of Bcl-2 family members was examined in normal and leukemic hematopoietic cells. Immature hematopoietic progenitor cells (CD34+/33-/13-) did not express Bcl-2 but Bcl-XL, the majority of CD34 cells expressed Bcl-2, Bcl-XL and BAD, and normal promyelocytes (CD34-/33+) lacked expression of both Bcl-2 and Bcl-XL, while leukemic CD34+progenitors and promyelocytes expressed these anti-apoptotic proteins. In AML, Bcl-2 expression was higher on CD34+ than on all AML cells, however, expression of Bcl-2 or Bcl-XL did not predict achievement of complete remission. Surprisingly, low Bcl-2 content was associated with poor survival in a group of patients with poor prognosis cytogenetics. The anti-apoptotic BAD protein was found to be expressed in AML, but was phosphorylated in 41/42 samples. Phosphorylation was found at both sites, Ser 112 and Ser 136. During induction chemotherapy, Bcl-2 levels of CD34 cells increased significantly. In the context of evidence for small numbers of leukemic CD34+ cells expressing very high levels of Bcl-2 prior to therapy, this finding is interpreted as a survival advantage of Bcl-2 overexpressing progenitors and rapid elimination of cells with low Bcl-2. Bcl-2 and Bcl-XL were both expressed in minimal residual disease cells. Downregulation of Bcl-2 mRNA and protein was observed by ATRA and the combination of Ara-C, followed by ATRA, resulted in markedly increased cytotoxicity in HL-60 cells, as compared to Ara-C alone or ATRA followed by Ara-C. Implications of these findings for the development of new therapeutic strategies for AML are discussed.     

急性髓系及混合型白血病流式细胞术免疫分型检测结果

 目的　研究流式细胞术（FCM）检测在急性髓系白血病（AML）及混合型白血病（MAL）诊断中的意义。方法　采用四色FCM对52例AML和7例MAL患者进行免疫表型检测。结果　52 例AML患者以系列专一表达为主,主要表达 CD13（94.2 %）,CD117（90.4 %）,cMPO（90.4 %）CD33（86.5 %）,CD34（57.7 %）,HLA-DR（53.8 %）。7例MAL中髓系／B系（M／B）混合3例,均表达CD13,CD34,CD117,CD10,CD19,cMPO,cCD79a;髓系／T系（M／T）混合2例,均表达CD13,CD117,CD33,CD34,CD5,CD7,cMPO;B系／T系（B／T）混合2例,均表达CD5,CD7,CD10,CD19,CD20,CD34。且与形态学和组织化学诊断具有高符合率。结论　FCM能够提高AML和MAL的确诊率,对该类白血病的明确诊断及分型具有重要的临床指导意义。     

双克隆型多发性骨髓瘤五例

 目的　研究双克隆型多发性骨髓瘤（MM）患者的临床特点及治疗。方法　分析该科自1996年1月至2010年6月收治的5例双克隆型MM患者,男性2例,女性3例,年龄59～76岁,中位年龄72岁。其中IgG+IgA型3例,IgM+IgG／A型2例。结果　本组患者中诊断时均为DS分期Ⅲ期,治疗效果为2／4达到部分缓解（PR）,1／4为稳定（SD）,1／4为进展（PD）,无达到完全缓解（CR）的病例。结论　双克隆型MM较为罕见,目前对此型MM的诊断和治疗尚缺乏更深刻的认识,需要更多病例的分析。     

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.     

Phenotypic Characterization of Normal and CML CD34-Positive Cells: Only the Most Primitive CML Progenitors Include Ph-neg Cells

We studied the sequence of acquisition of CD33, CD38 and HLA-DR antigens on CD34+ cells from marrow and blood of Ph-chromosome positive CML patients and normal marrow. We examined the Ph status of the various CML cell populations. The mean proportions of normal and CML CD34+ cells expressing CD33 and CD38 were not significantly different. However, a significantly greater proportion of CML CD34+ cells expressed HLA-DR antigens compared with normal CD34+ cells and the level of HLA-DR expression per CML cell was abnormally high. When the sequence of acquisition of these antigens on normal and CML CD34+ cells was evaluated using 3-colour fluorescence analysis, the results suggested that HLA-DR was expressed earlier than CD38 or CD33 and these findings were confirmed by following the acquisition of CD38 and CD34t/DR + /CD38-subpopulation during liquid culture. We performed cytogenetic studies on CD34+ subpopulations in 6 cases. In 4 cases there were some Ph-negative metaphases detectable in the CD34+/DR-subpopulation (range 12.5 to 60%). In the CD34+/DR+ fractions, however, all 6 patients had only Ph-positive metaphases and only 1/5 patients had detectable Ph-negative metaphases in the CD34+/CD38-subpopulation. We conclude that expression of HLA-DR antigens may precede the expression of CD38 on CD34+ cells during normal stem cell differentiation. In CML DR may be expressed aberrantly and Ph-negative cells are found predominantly in the DR negative sub-population.     

Characterization of a new myeloid leukemia cell line with normal cytogenetics (CG-SH)

A new myeloid leukemia cell line (CG-SH) with normal cytogenetics was established from a patient with acute myelogenous leukemia (AML) following myelodysplastic syndrome (MDS). The cells of CG-SH are immature blasts and have an immature myeloid phenotype (positive for myeloperoxidase, CD7, CD34, CD38, CD117, HLA-DR, negative for CD10, CD19, CD20, CD41, CD42). A partial expression of CD13, CD15, CD65 and a weak expression of CD33 and CD133 was noted. The cells are negative for EBER. By molecular analysis, a mutation of NRAS and heterozygous mutations of RUNX1 were detected. No mutations were detected in FLT3-ITD, MLL-PTD or NPM1. By real-time PCR, a series of 19 microRNAs was identified which are strongly expressed in CG-SH. In conclusion, a new cell line was established which will be useful for the study of AML with normal cytogenetics and mutations in NRAS and/or RUNX1.     

Diagnostic value of CD117 in differential diagnosis of acute leukemias

C-kit receptor (CD117) and its ligand, stem cell factor, play a key role in normal hematopoiesis. It has been demonstrated that its expression extremely increases in leukemias with myeloid commitment. We analyzed findings on CD117 expression together with other myeloid related markers in 203 de novo acute leukemias, referred to Iranian immunophenotyping centers: Iranian Blood Transfusion Organization (IBTO) and Baghiatallah Hospital (BH). All cases were characterized based on the French American British cooperative group (FAB) and European Group for Immunological Classification of Leukemias (EGIL). The cases comprised of 111 acute myeloblastic leukemia (AML), 86 acute lymphoblastic leukemia (ALL), and 6 acute undifferentiated leukemia (AUL). CD117 was positive in 75 % of AML and 50 % of AUL, whereas none of the ALL cases was positive for this marker. Although CD117 was positive in 100 % of M5a cases, no M5b positive was found (p?=?0.036). The calculated specificity for myeloid involvement was 100 % for CD117 and CD33, and 98 % for CD13 and CD15 (p?<?0.001). The calculated sensitivity for myeloid involvement was 83, 76, 64, and 41 % for CD13, CD117, CD33, and CD15, respectively (p?<?0.001). We concluded that CD117 expression is a specific and rather sensitive marker for differential diagnosis between AML and ALL, and except for M5 subtypes, it fails to determine FAB subtypes; lack of expression in M5 can identify M5b. Therefore, it should be included in the routine primary panel for diagnosis of acute leukemias.     

儿童急性髓系白血病免疫表型特点分析

目的:分析儿童急性髓系白血病(AML)免疫表型特征,探讨其临床意义.方法:采用四色流式细胞术CD45/SSC双参数散点图设门方法,对127例儿童AML患者幼稚细胞进行免疫表型检测,对抗原表达情况进行分析.结果:在127例儿童急性髓系白血病患者中,髓系特异性抗原CD33、CD13和CD117的表达最常见,分别达95.3%、90.6%、90.6%.造血干/祖细胞抗原CD34、HLA-DR、CD38阳性率分别达53.5%、71.6%和97.6%.有65.4%的病例伴有淋系抗原的表达,其中以CD56的表达最常见占38.6%,其次为CD7占21.3%.有淋系抗原表达(LymAg+)患者早期抗原CD34和HLA-DR抗原表达阳性率明显高于无淋系抗原表达(LymAg-)患者(P<0.05).结论:免疫分型对儿童AML的诊断和不同亚型鉴别具有重要意义.     

Absolute number of circulating CD34+ cells is abnormally low in refractory anemias and extremely high in RAEB and RAEB-t; novel pathologic features of myelodysplastic syndromes identified by highly sensitive flow cytometry

We scored absolute numbers of circulating CD34+ cells by a highly sensitive triple-color flow cytometric analysis using CD45 monoclonal antibody, CD34 monoclonal antibody and propidium iodide. Forty-one patients with MDS (RA: 27, RARS: 1, RAEB: 6, RAEB-t: 3,CMML: 4), 12 patients with aplastic anemia (AA) and 36 age-adjusted normal subjects were studied. RA had significantly decreased numbers of cells expressing CD34 (0.21 +/- 0.29 x 10(6)/l) compared with normal subjects (0.81 +/- 0.36 x 10(6)/l)(P < 0.001). This low number of CD34+ cells in RA resembles the case of AA (0.39 +/- 0.73 x 10(6)/l). In light-scatter analysis, the CD34+ cells of RA patients were distributed mainly in low forward scatter (FSC) (lymphocyte region). In contrast, the CD34+ cell counts were extremely high in patients with RAEB (46.54 +/- 71.37 x 10(6)/l) and RAEB-t (57.00 +/- 52.36 x 10(6)/l) (P < 0.001) and the CD34+ cells were observed in high FSC (blast region).CMML patients showed moderately increased numbers of CD34+ cells (3.69 +/- 4.64 x 10(6)/l). Thus, there was a distinct difference in cell size and number of circulating CD34+ cells between RA and RAEB/RAEB-t. In univariate and multivariate analysis, a high CD34+ cell count (> or = 1.0 x 10(6)/l) was a poor prognostic factor. This method allows one to distinguish RA from other MDS subtypes more reliably than by morphology alone and provides early signs of progression to acute leukemia.     

急性髓细胞性白血病细胞培养上清对树突细胞分化、成熟、凋亡及功能的影响

背景与目的:树突细胞(dendritic cell,DC)存机体抗瘤免疫中起重要作用.研究已表明肿瘤患者和荷瘤动物体内DC功能受损并伴有DC数量的降低.最近的研究提示这种DC功能的受损可能是肿瘤细胞分泌的可溶性因子介导的免疫抑制所致.本研究拟观察急性髓系白血病(acute myeloid leukemia,AML)细胞分泌的可溶性因子对单核细胞来源DC的分化、成熟、凋亡及其功能的影响.方法:原代AML细胞培养24 h后收集上清.在含有或不含有AML细胞培养上清的培养液中,利用IL-4和GM-CSF刺激单核细胞分化成不成熟DC(immature DC,iDC),IL-1β、IL-6、TNF-α和PGE-2促进DC成熟.流式细胞仪检测DC表型和凋亡率的变化.计算前体细胞频率(precursorfrequency,PF),观察DC对异基因CD4 T细胞和CD8 T细胞的刺激功能.结果:AML细胞培养上清可显著抑制DC表面协同刺激分子CD80和CD86的表达,并可降低促成熟细胞因子对DC的促成熟作用.同时,与对照组相比,AML细胞培养上清可显著诱导DC的凋亡,凋亡率分别为(15.1±4.2)%和(29.4±9.5)%(P＜0.01).相对于正常成熟DC,AML细胞培养上清诱生的DC对异基因CD4 T细胞和CD8 T细胞的刺激功能显著降低(P＜0.01),其中CD4 T细胞的前体细胞频率分别为(5.2±1.6)%和(1.8±0.5)%,CD8 T细胞的前体细胞频率分别为(6.5±2.0)%和(2.1±0.6)%.结论:AML细胞分泌的可溶性因子可抑制DC的发育和功能.     

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.