In this study, we examined a large number of patients to clarify FLT3 gene has some structural similarities including the the distribution and frequency of a recently described FLT3 tannumber of exons, size of exons and exon/intron boundaries dem duplication among hematopoietic malignancies, including with genes RTKs, FMS, KIT, and platelet-derived growth-factor of 24 showed internal tandem duplication with or withoutWe recently demonstrated internal tandem duplication insertion of nucleotides. In one AML, insertion and deletion within JM/TK-I domains as a somatic mutation of FLT3 found without duplication was determined. All 24 lengthened in 17% of patients with acute myelogenous leukemia (AML). 14 sequences were in-frame. Duplication takes place in the Since this mutation was not found in any patients with acute sequence coding for the JM domain and leaves the TK domain lymphocytic leukemia, we described that this mutation could intact. In conclusion, we emphasize that the length mutation of FLT3 at JM/TK-I domains were restricted to AML and MDS.be specific in myeloid malignancies. To clarify the incidence Since all these mutations resulted in in-frame, this abnormality and distribution of the FLT3 mutation among hematological might function for the proliferation of leukemic cells.malignancies, we examined a large number of patients with

without detectable blast infiltration. At diagnosis of MDS, interface cytogenetic and RT-PCR analyses, respectively, showed trisomy 8 and absence of AF9-MLL rearrangement in Introduction the bone marrow (BM). On readmission with florid leukemia, his peripheral white blood cell count was 13 200/mm 3 , with A subtle, reciprocal translocation exchanging the terminal 56% leukemic blasts. His hemoglobin concentration was short and long arm segments of chromosomes 9 and 11, 15.0 g/dl, and his platelet count was 22 000/mm 3 . The bone respectively t(9;11)(p21-22;q23), is associated with acute marrow aspiration showed 92% leukemic blasts, and the mormyeloid leukemia (AML)-M5, 1 particularly the M5a subtype. 2 phological diagnosis was made as AML-M5a. Cytogenetic Ascertainment may be difficult in suboptimal preparations analysis was interpreted as: 47, XY, +8, t(9;11)(p22;q23). and, despite being regarded as the 'standard' cytogenetic Immunophenotyping analysis of fresh leukemia blasts change in acute monoblastic leukemia, its overall incidence revealed no significant expression of CD antigens associated and pattern of associations remain uncertain. 2 A recent study with the myelo-monocytic lineage. CD34 was 30% positive comparing AML-M1 and -M5 patients, analyzed simuland non-lineage-associated HLA-DR was found to be positive taneously by reverse transcriptase-polymerase chain reaction at 70%; whereas those indicative of lymphoid lineage includ-(RT-PCR), Southern blotting and fluorescence in situ hybridizing CD3, CD4, CD8, CD10, CD19 were absent or weakly ation (FISH) with an MLL-specific yeast artificial chromosome expressed. Myeloperoxidase activity was weakly detected on (YAC) probe, suggests the overall incidence of MLL rearrangethe fresh leukemic blasts. Despite receiving chemotherapy, he ment in AML-M5 may be as high as 60%. 3 It was apparent in succumbed to rapidly progressive leukemia on 15 August that study that approximately half the cases with MLL 1995. rearrangement went undetected by cytogenetic methods, including a cryptic t(6;11)(q27;q23) resulting from a cytogenetically invisible insertion juxtaposing AF6 and MLL.Materials and methods A case of AML-M5a with de novo MLL-AF9 fusion evolving from MDS with trisomy 8 present at all phases has recently Cell culture been described. 4 We describe a pair of cell lines, MOLM-13 During relapse, after chemotherapy, a heparinized peripheral blood specimen, obtained with informed consent, was proCorrespondence: Y Matsuo,

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Human leukemia-lymphoma (LL) cell lines represent an extremely important resource for research in a variety of fields and disciplines. As the cell lines are used as in vitro model systems in lieu of primary cell material, it is crucial that the cells in the culture flasks faithfully correspond to the purported objects of study. Obviously, proper authentication of cell line derivation and precise characterization are indispensable requirements to use as model systems. A number of studies has shown an unacceptable level of LL cell lines to be false. We present here the results of authenticating a comprehensively large sample (n = 550) of LL cell lines mainly by DNA fingerprinting and cytogenetic evaluation. Surprisingly, nearidentical incidences (ca 15%) of false cell lines were observed among cell lines obtained directly from original investigators (59/395: 14.9%) and from secondary sources (23/155: 14.8%) implying that most cross-contamination is perpetrated by originators, presumably during establishment. By comparing our data with those published, we were further able to subclassify the false cell lines as (1) virtual: cross-contaminated with and unretrievably overgrown by other cell lines during initiation, never enjoying independent existence; (2) misidentified: crosscontaminated subsequent to establishment so that an original prototype may still exist; or (3) misclassified: unwittingly established from an unintended (often normal) cell type. Prolific classic leukemia cell lines were found to account for the majority of cross-contaminations, eg CCRF-CEM, HL-60, JUR-KAT, K-562 and U-937. We discuss the impact of cross-contaminations on scientific research, the reluctance of scientists to address the problem, and consider possible solutions. These findings provide a rationale for mandating the procurement of reputably sourced LL cell lines and their regular authentication thereafter.