High resolution banding of chronic myeloid leukemia chromosomes

Characterization of two novel sublines established from a human megakaryoblastic leukemia cell line transfected with p210(BCR-ABL)

Disease progression in chronic myelogenous leukemia (CML) is usually accompanied by chromosomal abnormalities such as an additional Ph chromosome, trisomies of chromosome 8 or 19, or i(17) in addition to the standard translocation t(9;22) (q34;q11). However, detailed studies of the various steps involved during this evolution are difficult to perform, thereby making the study of cell lines that contain the transposed genes BCR-ABL, especially those of human origin, an important focus. In this analysis we investigated the human megakaryoblastic cell line MO7e and its subline transfected with BCR-ABL, MO7e/p210. Initial studies demonstrated that the phenotype of the MO7e line was consistent with a megakaryocytic lineage as originally described and was growth factor dependent in liquid culture. The MO7e/p210 subline, however, was growth factor independent and could be further separated into two distinct sublines based on expression of glycophorin A using the monoclonal antibody R10. The subline R10 negative (R10-) was similar to the parent line MO7e but R10 positive (R10+) cells had a distinct erythroid phenotype. In addition, the R10- and R10+ sublines demonstrated strikingly different colony morphology when cultured in semisolid medium. Furthermore, R10+ cells had additional chromosomal abnormalities not detected in the R10- population. These results demonstrate that the insertion of the BCR-ABL in this human leukemia cell line resulted in two distinct subpopulations of cells, each now growth factor independent, but one with a phenotype and karyotype identical to the parent cell line and the other with a different phenotype and additional chromosomal abnormalities. These two subpopulations derived from the MO7e/p210 transfected cell line may prove useful in further understanding the multistep events that occur in the progression of this disease.

BCR/ABL fusion located on chromosome 9 in chronic myeloid leukemia with a masked Ph chromosome

A reciprocal translocation, t(10;22)(q22;q11), resulting in a masked Ph chromosome was identified in a patient diagnosed with chronic myeloid leukemia (CML). Both homologs of chromosome 9 were of the normal pattern. Two signals for the ABL probe, both of them hybridized to chromosome 9, were demonstrated via fluorescence in situ hybridization (FISH). Furthermore, cohybridization with two differently labeled BCR/ABL translocation DNA probes indicated a BCR/ABL fusion apparently located on 9q34. Molecular studies revealed a rearrangement of the BCR region and expression of a chimeric BCR/ABL mRNA of CML configuration. These findings indicate that the BCR/ABL fusion resulted from an unusual relocation of the BCR gene from its normal position on 22q11 to 9q34 adjacent to the ABL gene.

Reverse transcription polymerase chain reaction for the rearranged retinoic acid receptor alpha clarifies diagnosis and detects minimal residual disease in acute promyelocytic leukemia

The characteristic t(15;17) of acute promyelocytic leukemia (APL) fuses the retinoic acid receptor alpha (RAR-alpha) gene on chromosome 17 to a gene on chromosome 15 called PML, a putative transcription factor. This distinct translocation results in a fusion mRNA detected by Northern analysis. Two cDNAs have been isolated that differ in the extent of 3' PML nucleic acid sequence contained. This study describes a reverse transcription polymerase chain reaction (RT-PCR) assay for the PML/RAR-alpha fusion transcript, which amplifies PML/RAR-alpha mRNA from APL cells with either reported breakpoint. DNA sequencing of the predominant RT-PCR products from 6 patients showed identical RAR-alpha exonic breakpoints and two PML breakpoints. This RT-PCR assay was positive in leukemic cells from 30/30 APL patients with the molecular rearrangement confirmed by cytogenetics or Northern analysis. In leukemic cells of patients with a morphologic diagnosis of APL lacking the t(15;17) by routine cytogenetics, a positive RT-PCR assay predicted clinical response to all-trans-retinoic acid (RA) therapy. Dilutional studies with leukemic cells that express (NB4) or do not express (HL-60) a PML/RAR-alpha fusion mRNA reveal that this RT-PCR assay detects the transcript from as little as 50 pg of total RNA. In APL cells from 5/6 patients treated with RA alone, a complete response by clinical and cytogenetic criteria accompanied a persistently positive RT-PCR assay. This preceded relapse by 1-6 months. RT-PCR for PML/RAR-alpha mRNA provides a more-sensitive test for the t(15;17) than routine cytogenetics or Northern analysis. This molecular rearrangement detected by RT-PCR best defines this RA-responsive malignancy. The RT-PCR assay for the PML/RAR-alpha transcript yields important diagnostic and prognostic information in the management of APL patients.

Differentiation therapy of acute promyelocytic leukemia with tretinoin (all-trans-retinoic acid)

BACKGROUND AND METHODS

Patients with acute promyelocytic leukemia have a characteristic (15;17) translocation, with a breakpoint on chromosome 17 in the region of the retinoic acid receptor-alpha (RAR-alpha). Since this receptor has been shown to be involved with growth and differentiation of myeloid cells in vitro, and since recent clinical studies have reported that tretinoin (all-trans-retinoic acid) induces complete remission in patients with acute promyelocytic leukemia we studied the effects of tretinoin on cellular maturation and molecular abnormalities in patients undergoing the induction of remission with this agent.

RESULTS

Eleven patients with acute promyelocytic leukemia were treated with tretinoin administered orally at a dose of 45 mg per square meter of body-surface area per day. Nine of the 11 patients entered complete remission. In two patients, complete remission was preceded by striking leukocytosis that then resolved despite continued drug treatment. Serial studies of cellular morphologic features, cell-surface immunophenotypic analysis, and fluorescence in situ hybridization with a chromosome 17 probe revealed that clinical response was associated with maturation of the leukemic clone. All patients who responded to treatment who were tested by Northern blot analysis had expression of aberrant RAR-alpha. As patients entered complete remission, the expression of the abnormal RAR-alpha message decreased markedly; however, it was still detectable in several patients after complete morphologic and cytogenetic remission had been achieved.

CONCLUSIONS

Tretinoin is a safe and highly effective agent for inducing complete remission in patients with acute promyelocytic leukemia. Clinical response to this agent is associated with leukemic-cell differentiation and is linked to the expression of an aberrant RAR-alpha nuclear receptor. Molecular detection of the aberrant receptor may serve as a useful marker for residual leukemia in patients with this disease.

Detection of posttransplant minimal disease chronic myelogenous leukemia by bcr rearrangement analysis

Until recently, cytogenetic detection of the Philadelphia chromosome (Ph) was the only reliable test to diagnose chronic myelogenous leukemia (CML) and detect minimal disease or early relapse following treatment. However, the recently developed ability to detect the Ph chromosome as a rearrangement in the bcr gene of chromosome 22 permits identification of the leukemic clone comprising as little as 5% of the cell population. We present results of simultaneous cytogenetic and DNA rearrangement studies in 28 CML patients considered for or treated with bone marrow transplantation. Our results show that the molecular method is significantly more sensitive than the cytogenetic method in the detection of minimal disease Ph-positive clones.

A t (11;21) (13;q22) in Ph-positive chronic myelogenous leukemia

Reciprocal translocations, in addition to that of the Ph chromosome, though rare, have been reported in chronic myelogenous leukemia (CML). We describe here a case of Ph-positive CML with a new translocation, t (11;21) (q13;q22), and missing Y, which were present both during transformation to the blastic crisis and in the subsequent reversion to the chronic phase. The possible significance of this abnormality is discussed.

Human chromosome 22

The acrocentric chromosome 22, one of the shortest human chromosomes, carries about 52 000 kb of DNA. The short arm is made up essentially of heterochromatin and, as in other acrocentric chromosomes, it contains ribosomal RNA genes. Ten identified genes have been assigned to the long arm, of which four have already been cloned and documented (the cluster of lambda immunoglobulin genes, myoglobin, the proto-oncogene c-sis, bcr). In addition, about 10 anonymous DNA segments have been cloned from chromosome 22 specific DNA libraries. About a dozen diseases, including at least four different malignancies, are related to an inherited or acquired pathology of chromosome 22. They have been characterised at the phenotypic or chromosome level or both. In chronic myelogenous leukaemia, with the Ph1 chromosome, and Burkitt's lymphoma, with the t(8;22) variant translocation, the molecular pathology is being studied at the DNA level, bridging for the first time the gap between cytogenetics and molecular genetics.

Genomic diversity of Philadelphia-positive chronic myelogenous leukemia

The incidence of breakpoints in CML patients with variant translocations was investigated. There was no relationship between the length of various chromosomes with breakpoint frequency. However, a significantly higher (p less than 0.05) incidence of breaks were seen on the long arms as compared to the short arms due mainly to the involvement of 9q and 22q in these translocations. Chromosome 17 showed a significantly (p less than 0.005) higher involvement in these translocations, however only when 9q34-qter was not cytogenetically involved. A total of 683 breaks were found in 225 cases. 362 of these were located at c-abl and c-sis, while 110 were at other oncogenetic sites. The prognostic and hematologic features of patients with variant translocations are not significantly different from those of CML cases with the typical 9q;22q translocation. Some of these complex translocation, where the breakpoints are correlated with oncogenetic sites, are further discussed in molecular terms.