Does the type of BCR/ABL junction predict the survival of patients with Ph1-positive chronic myeloid leukemia?

The prognostic value of the site of DNA rearrangement within the M-BCR on chromosome 22 or of the type of transcript has been debated in the last years. The majority of the studies do not support the hypothesis of a predictive value of such molecular parameters. Results coming from a multicentric, prospective trial, based on alpha-IFN therapy, seem to indicate a better karyotypic response in 3' rearranged patients. The possibility of evoking a cytotoxic immune response directed towards peptides originating from each of the different BCR/ABL junctions constitute an important challenge for the future.

Ph positive acute lymphoblastic leukemia in adults: molecular and clinical studies

Fifty-six patients with ALL were investigated for bcr involvement by PCR. Breakpoints were found in 15 patients (26.8%). There were no differences in clinical and hematologic features or the percentages of complete response (CR) between the Ph+ and Ph- cases. The duration of CR was 6 and 8 months, respectively. In 7/9 Ph1 relapsed ALL we observed increased expression of myeloid markers and 2/9 showed a switch of cytotype (Ly-->My). In none of the 13 Ph- relapsed ALL patients did we observe these findings. 7/15 of Ph+ cases expressed P190 and mRNA ela2 and 8/15 patients showed P210, with mRNA b3a2 in 5 and b2a2 in 3, respectively. The percentage of CR was 57% in the P190+ and 87% in the P210+ group. Investigation of more Ph1+ ALL cases treated with a uniform protocol should be performed in the future in order to determine whether any such biological and clinical differences exist.

Expression of GATA-1 mRNA in human myeloid leukemic cells

Expression of the transcription factor GATA-1, which regulates several erythroid specific genes and possibly also some megakaryocytic genes, has been previously detected in normal erythroblasts, megakaryocytes, and basophils, and in some myeloid cell lines. It has been suggested that GATA-1 may be first expressed in a common progenitor and then further activated during erythroid-megakaryocytic and basophilic differentiation and repressed during myeloid maturation. We investigated GATA-1 mRNA expression in highly purified leukemic blasts representing different lineages and stages of myeloid differentiation and in a recently established leukemic cell line, GF-D8, which exhibits morphological, cytochemical and immunophenotypic characteristics of early myeloid progenitor cells. We found GATA-1 expression in five of five myeloid and in one megakaryocytic blast crisis of CML, in four of six cases of myelomonocytic leukemias (M4 according to FAB classification), in one case of erythroleukemia (M6), whereas lymphoid blast crisis of CML and all other FAB groups were completely negative. In addition, a low level of GATA-1 mRNA was also expressed by the GF-D8 cell line. These data further support the hypothesis that GATA-1 expression may occur not only in erythroid and megakaryocytic progenitors, but also in early myeloid progenitors, and then be further regulated during lineage-specific maturation.

Analysis of the p53 gene in myeloid malignancies associated with chromosomal abnormalities involving the short arm of chromosome 17

p53 protein is encoded by a tumor-suppressor gene located on the short arm of chromosome 17. We looked for mutations or rearrangements of the p53 gene in five patients with acute transformation of a chronic myeloproliferative disorder and cytogenetic anomalies involving the short arm of chromosome 17. Two patients had a isochromosome i(17q); three more patients showed the presence of unbalanced translocations involving chromosome 17. One of these patients had a single base pair deletion, causing a frameshift mutation, in the exon 5 of the p53 gene. The karyotype of this patient showed a translocation t(5;17)(q11;p11), with loss of a normal homologue of both chromosomes 5 and 17. In all other cases the configuration of the p53 gene, as tested by PCR-SSCP analysis of exons 5 to 9 and Southern blot, was normal. Our data suggest that mutations of the p53 gene occur in a minority of hemopoietic malignancies characterized by monosomy for the short arm of chromosome 17. However, the unbalanced translocation t(5q;17p) could be a chromosomal abnormality specifically associated with loss of function of the p53 gene.

Molecular mechanisms of tumor progression in chronic myeloproliferative disorders

We have investigated the involvement of tumor suppressor genes (p53 and RB1) and dominantly acting oncogenes (Ras family genes) in BCR/ABL positive and negative chronic myeloproliferative disorders (CMPD) at different stages of the disease, including 26 cases of BCR/ABL+ chronic myeloid leukemia (CML) blast crisis, 9 myelosclerosis with myeloid metaplasia, 4 polycythemia vera, 10 essential thrombocythemia, 1 juvenile CML, and 8 BCR/ABL- CML. The presence of mutations in p53 exons 5 through 9, as well as in RB1 exons 10-27 and in N-, K-, H-Ras exons 1 and 2 was tested by the PCR-Single Strand Conformation Polymorphism technique and by PCR-Direct Sequencing. In addition, Southern blot analysis was used to investigate the occurrence of gross rearrangements in the p53 gene as well as loss of heterozygosity at 17p13, the site of p53. Acute phase BCR/ABL-CMPD cases displayed a high frequency of p53 (2/7) and Ras (3/7) lesions, whereas BCR/ABL- CMPD in chronic phase displayed only germline p53 and Ras sequences. Conversely, p53 inactivation was restricted to only 1/26 cases of BCR/ABL+ CML blast crisis. No alterations in the RB1 gene were detected in any of the cases analyzed. These data indicate that p53 inactivation and/or Ras activation might play a role in acute transformation of BCR/ABL- CMPD and that the molecular mechanisms of tumor progression may be different in BCR/ABL+ versus BCR/ABL-CMPD.

Clinical and haematological improvement induced by etidronate in a patient with idiopathic myelofibrosis and osteosclerosis

We report a patient with agnogenic myeloid metaplasia associated with debilitating bone pain due to increased bone turnover and osteosclerosis. Treatment with etidronate at a dose of 6 mg/kg per day on alternate months resulted in a complete recovery of bone symptoms and normalization of metabolic parameters of bone turnover; unexpectedly, a sustained haematological improvement was also observed after several months of therapy, suggesting that bone marrow microenvironment improvement was able to restore a nearly normal haemopoiesis. We suggest that diphosphonate therapy may be of value in patients with AMM and increased bone turnover.

Genetic analysis of p53 and RB1 tumor-suppressor genes in blast crisis of chronic myeloid leukemia

We have investigated the involvement of the p53 and RB1 tumor-suppressor genes in 26 cases of chronic myeloid leukemia (CML) blast crisis, including 17 myeloid, eight lymphoid, and one megakaryoblastic crisis. The presence of p53 mutations in exons 5 through 9 was tested by the PCR-single-strand conformation polymorphism (SSCP) assay, followed by PCR-direct sequencing; in addition, loss of heterozygosity (LOH) at 17p13, the site of the p53 gene, was assayed by Southern blot. Given the variability of the mechanisms of inactivation of the RB1 gene in human tumors, a combination of Southern blot and mutational analysis by PCR-SSCP was used. p53 mutations were restricted to one case of myeloid blast crisis, showing a CGC-->TGC (Arg-->Cys) mutation at codon 283; two additional cases displayed LOH at 17p13 in the absence of p53 mutations. No molecular lesions of the RB1 gene were detected in any of the cases analyzed. These data indicate that inactivation of p53 and RB1 is a rare event in the molecular pathogenesis of CML acute transformation.

Preferential clustering of chromosomal breakpoints in Burkitt's lymphomas and L3 type acute lymphoblastic leukemias with a t(8;14) translocation

We have analyzed the type of MYC/IG heavy-chain locus (IGH) rearrangement present in 15 patients affected by t(8;14)-positive primary Burkitt's lymphoma or acute lymphoblastic leukemia of the L3 type in an attempt to map in detail the locations of the chromosome 8 and chromosome 14 breakpoints. The almost constant position of the chromosome 8 breakpoint (within or immediately 5' of the MYC gene) together with two distinct clusters of breakpoints on chromosome 14 resulted in two main types of MYC/IGH (present in 12 of 15 cases). In the first type (six cases), the MYC gene or at least its coding portion was joined with the JH region on chromosome 14, whereas in the second, present in another six cases, the MYC gene and the C alpha I region were juxtaposed. Physical linkage between the translocated MYC and a known enhancer element of the IGH locus is the common feature in the two types of rearrangement, suggesting that a high-level constitutive expression plays a prominent role in MYC activation. Interestingly, the chromosome 14 break site within the switch alpha 1 region, which has been only occasionally described in other cases, is present in 40% of our patients, suggesting the existence of preferential breakpoint cluster regions in cases of similar geographic origin.

Mutations in the P53 and RAS family genes are associated with tumor progression of BCR/ABL negative chronic myeloproliferative disorders

We have investigated the involvement of the p53 tumor suppressor gene and RAS family proto-oncogenes in BCR/ABL-negative chronic myeloproliferative disorders (CMPD), including nine cases of myelosclerosis with myeloid metaplasia, four polycythemia vera, 10 essential thrombocythemia, one juvenile chronic myeloid leukemia, and eight BCR/ABL-negative chronic myeloid leukemia. Twenty-five samples were studied in the chronic phase, while seven samples were analyzed in the acute accelerated or blastic phase. The presence of mutations in p53 exons 5-9, as well as in N-, K-, H-Ras exons 1 and 2 (containing codons 12, 13, and 61) was tested by the polymerase chain reaction (PCR) single strand conformation polymorphism technique and by PCR direct sequencing. In addition, restriction analysis was performed to screen for gross rearrangements within the p53 locus. Alterations of the p53 tumor suppressor gene and Ras family proto-oncogenes were detected in 2/7 and 3/7 cases of acute phase BCR/ABL-negative CMPD, respectively, while consistently negative in all the chronic phase samples analyzed. These results suggest that p53 inactivation and/or Ras activation might play a role in acute transformation of BCR/ABL-negative CMPD.

Molecular defects associated with the acute phase CML

Parts of the Bcr/Abl hybrid transcript supposed to be important for its transforming ability were sequenced in a series of CML blast crises, in order to evaluate the possible presence of alterations responsible for the disease transition from the chronic to the acute phase. In addition, the N- and Ki-ras as well as the p53 involvement was investigated by exploring their structure and expression in the same patients. We used traditional types of molecular analysis including Southern and Northern blot, together with methods that allow a rapid detection of point mutations and microdeletions, such as SSCP, single strand conformation polymorphism and direct sequencing. The results obtained may be summarized as follows: no alterations were found in the parts of the Bcr/Abl transcripts investigated in the present study (SH2, SH3 and the region surrounding codon 832); p53 alterations were observed in 5% and N- and Ki-RAS mutations in 5% of the cases examined. These molecular defects are therefore responsible for the clinical progression of the Ph1-positive CML only in a minority of cases.

Transient cytogenetic relapse in a Ph1-positive chronic myelogenous leukemia patient previously treated with alpha-interferon

Therapy with alpha-interferon (IFN alpha) can suppress the Ph1-positive hemopoiesis in a percentage of patients with chronic myelogenous leukemia (CML). We used IFN alpha to treat a 30-year-old CML patient, characterized by favourable prognostic signs (such as low leukocytosis, absence of splenomegaly and no increase in bone marrow blasts) at diagnosis, and obtained a complete remission, as evaluated by Southern blot and cytogenetic analysis, after one year of treatment. However, the polymerase chain reaction (PCR) revealed the persistence of a minimal residual disease. The IFN alpha therapy was stopped and the hematological status remained stable until eighteen months later, when a cytogenetic analysis revealed the appearance of a clone characterized by t(9;22) and trisomy 8, accounting for 30% of bone marrow metaphases. This cell population spontaneously regressed in the following months, before any cytotoxic treatment. However, as leukemic cells, detected by PCR, were still present, the patient received a high dose chemotherapy, which induced the complete eradication of the Ph1-positive clone, as demonstrated by the absence of bcr-abl transcript at the PCR reaction. Molecular and cytogenetic remission persist one year later, without any further therapy.

Minimal residual disease status in transplanted chronic myelogenous leukemia patients: low incidence of polymerase chain reaction positive cases among 48 long disease-free subjects who received unmanipulated allogeneic bone marrow transplants

Forty-eight long-term disease-free chronic myelogenous leukemia (CML) patients, who had received unmanipulated allogeneic bone marrow transplants (BMT) for eradication of the Philadelphia (Ph1)-positive clone were studied by polymerase chain reaction (PCR), using a very sensitive PCR procedure and very stringent criteria for preventing and revealing contamination. Nine patients (18%) were positive at the first PCR examination, but only one patient remained PCR positive four years after. However, a second PCR analysis performed on new bone marrow samples obtained at a median interval of 14 months (range 6-16) after the first specimen collection from six of nine originally positive cases, and from 16 of 39 originally negative cases, showed that only one of the six positive cases remained positive, whereas negativity was confirmed in all the originally negative patients. These data are evidence that the Ph1-positive clone is apparently completely eradicated in the majority of CML patients who survive disease-free long-term after an unmanipulated allogeneic BMT and that only sporadic cases remain PCR-positive four years post-BMT. The data also show that at least two sequential bone marrow samples for each patient must be analyzed before drawing conclusions regarding the stable persistence of BCR/ABL transcripts and the minimal residual disease status.

Tumorigenic activity of a rearranged c-myc gene from a human T-cell leukemia line

The T-lymphoma cell line Hut78 contains a rearranged c-myc oncogene derived from a translocation between the long arms of chromosomes 8 and 2; the event deletes the 3' end of the gene, causing the loss of the transcribed AT-rich sequence. It has recently been shown that the mutant c-myc mRNA is several-fold more stable than normal c-myc mRNA. We have assessed the tumorigenicity of the mutant c-myc allele by transfecting this gene and its normal counterpart into NIH3T3 cells, together with a neomycin resistance gene. Following selection for G-418 resistance, the cells were injected into nude mice. Tumors containing integrated c-myc arose in animals injected with cells transfected by the mutated, but not by the normal, allele. The results suggest that this rearranged c-myc bears a tumorigenic activity not observed in other naturally occurring mutated c-myc alleles and may have directly contributed to the tumorigenic event in the Hut78 cell line.

M-BCR breakpoint location does not predict survival in Philadelphia chromosome-positive chronic myeloid leukemia

BACKGROUND

Some reports in the recent literature have shown that the site of molecular rearrangement within the M-BCR area may have a prognostic value in Ph1 + CML patients. A number of studies have, however, failed to demonstrate this finding. Here we report the molecular rearrangements of 107 patients and their clinical follow-up.

METHODS

Localization of the breakpoints was determined according to conventional criteria, after digestion with 2 to 4 restriction endonucleases and hybridization with 1 or 2 molecular probes.

RESULTS

Sixty two patients were rearranged in the 5' area and 45 in the 3' area: there was no difference between the survival curves of the two groups, at least not after 3 years of follow-up.

CONCLUSIONS

The site of the breakpoint within the M-BCR has no prognostic significance in our series.

Therapy of acute phase chronic myelogenous leukemia with intensive chemotherapy, blood cell autotransplant and cyclosporine A

The expansion of the Philadelphia (Ph) chromosome positive clone in chronic myeloid leukemia (CML) may depend on its capacity to suppress the proliferation of Ph-negative stem cells, but this proliferative advantage might, in certain circumstances, be reversible. Various lines of evidence suggest that Ph-negative cells, albeit in a suppressed state, must still be present. As recently suggested, the expansion of 'putative' normal Ph-negative hemopoietic stem cells might have, in certain circumstances, a proliferative advantage over the Ph clone in CML. This suggests that the treatment of CML with intensive chemotherapy might allow the collection of Ph-negative hemopoietic cells in the early phase of recovery. Eight patients with acute phase chronic myelogenous leukemia (AP-CML) were treated with idarubicin, intermediate dose cytarabine and etoposide. During recovery from bone marrow aplasia, when the white blood cell count reached 0.3-1 x 10(-9), blood cells were collected with 2-5 (median 3) consecutive leukapheresis. In 5/8 patients, these peripheral cells were Ph-negative at the cytogenetic analysis. Moreover, in one case the polymerase chain reaction analysis performed to detect the presence of minimal residual disease in the cells collected by leukapheresis was negative, further confirming that this approach may induce a very high degree of suppression of the Ph-positive clones. After complete recovery, these five patients were subsequently treated with high-dose etoposide, cyclophosphamide and total body radiation (10 Gy, single dose) followed by reinfusion of Ph-negative peripheral blood stem cells. All these patients received cyclosporine A post-autotransplant in an attempt to induce acute graft-versus-host-disease. Three of 5 patients remain in clinical and cytogenetic remission 5-15 months post-transplant. It is concluded that Ph-negative peripheral blood stem cells can be recovered from patients with AP-CML and used successfully to restore Ph-negative hemopoiesis after high dose therapy.

Identical utilization of T-cell receptor gene regions in B-lymphoid blast crisis of chronic myeloid leukemia and B-precursor acute lymphoblastic leukemia

The configuration of the T-cell receptor (TCR) beta, gamma and delta chain genes was analyzed in 16 cases of B-lymphoid blastic crisis of chronic myeloid leukemia (BC-CML) for a better definition of the biological aspects of this cellular population, in comparison with the molecular features of B-precursor acute lymphoblastic leukemia (ALL). All cases displayed B-phenotypic features, were Ph'-positive and had a rearranged configuration of the breakpoint cluster region (bcr) and of the immunoglobulin heavy chain gene region (JH). The TCR beta chain gene was rearranged in four cases (25%), all of which displayed a monoallelic rearrangement involving the J beta 2 region. The TCR gamma chain gene was rearranged in 13 cases (81%); 13 rearranged alleles utilized the J1/2 regions, while the remaining five utilized JP1. The V regions of the group I were mostly involved. The TCR delta chain gene was rearranged or deleted in 15 cases (94%); the 10 rearranged chromosomes displayed exclusively two patterns referable to partial recombinations, a V2-(D)-D3 and a (D)-D3 type. These two configurations are predominant in B-precursor ALL (75% of rearranged chromosomes) and almost absent in T-ALL. Taken together, these results document the close similarities between the genotypic features of B-lymphoid BC-CML and B-precursor ALL, not only in terms of the incidence of rearrangement but more relevantly with regard to the choice of regions involved in the recombinations. This aspect is particularly evident at the TCR delta locus level.

Molecular diagnosis of Philadelphia chromosome-positive chronic myeloid leukemia

BACKGROUND

In virtually all Ph1 chromosome-positive CML patients, the breakpoint on chromosome 22 maps in a very restricted area of 5.8 Kb, which has been named "breakpoint cluster region" or "bcr". Several molecular probes of this region are presently available, and this makes the molecular diagnosis of CML a useful approach which can be particularly important in those cases in which cytogenetic analysis does not reveal the presence of a Ph1 chromosome. Here we report the problems and our experience during the molecular analysis of the 478 patients examined so far.

METHODS

Molecular analyses were performed after digestion of the DNA with 2 to 4 restriction enzymes and hybridization with different probes. Individual samples were subjected to PCR since no rearrangements had been obtained with Southern blotting.

RESULTS

Rearrangement bands were detected in all the samples examined. In 473 cases the breakpoint was located within the bcr. In one of these cases, it was detected only after PCR analysis, and in two cases only after the use of the PHL/BCR probe. In 5 cases the breakpoint was localized either 5' or 3' with respect to the bcr.

CONCLUSIONS

In this paper, the criteria for a correct molecular diagnosis of CML are presented. The "PHL/BCR" probe appeared to be very specific and time-saving, since it required only one digestion to evidence the rearrangement. Our results confirm the high specificity of the breakpoint on chromosome 22 in CML and the relatively rare incidence of molecular variants.

Different suppression of Ph1 positive hemopoiesis induced by intensive chemotherapy in lymphoid and myeloid blast crisis of CML

BACKGROUND

The suppression of Ph1-positive hemopoiesis is a major goal in the treatment of CML; in this context the CML patients in blast crisis obtaining a complete clinical remission represent a useful model to investigate the behavior of the Ph1-positive and negative clones during bone marrow repopulation after ablative therapy.

METHODS

Seven CML patients in blast crisis (four lymphoid and three myeloid) who obtained a complete clinical remission after an intensive polychemotherapy treatment were evaluated by cytogenetic and molecular analysis both in blast and remission phases. Standard cytogenetic and Southern techniques were employed; in addition, minimal residual disease status (MRD) was ascertained by amplification (PCR) of the specific bcr-abl chimeric transcripts.

RESULTS

After a single cycle of induction, all lymphoid cases displayed a complete restoration of Ph1-negative hemopoiesis; by contrast, one myeloid blast crisis showed a partial suppression of Ph1-positive hemopoiesis only after two cycles of chemotherapy, and in the remaining two cases the hematological remission was indeed a reversion to the chronic phase.

CONCLUSIONS

Ph1-positive chronic clones present in lymphoid blast crisis showed a higher degree of sensitivity to intensive chemotherapy than those present in the myeloid cases. This observation further suggests that the growth properties of the Ph1-positive clones are highly variable from case to case and probably tend to progress during the time-course of the disease.

New type of Bcr/Abl junction in Philadelphia chromosome-positive chronic myelogenous leukemia

A new and rare type of Bcr/Abl junction between exon C3 of the 3' portion of the Bcr gene and Abl exon 2 has been identified in the leukemic cells of two Ph1-positive chronic myelogenous leukemia patients in chronic phase. This is the fourth type of Bcr/Abl junction so far identified in Ph1-positive hematologic malignancies and is a consequence of an unusual breakpoint position on chromosome 22 that falls approximately 20 kb downstream of the major breakpoint cluster region (bcr) of the Bcr gene. The new hybrid mRNA is 540 base pairs (bp) longer than that expressed by the K562 cell line and could codify for a Bcr/Abl protein carrying 180 additional aminoacids with respect to the larger P210 protein so far identified. The hematologic phenotype expressed by the two patients carrying this unusual type of Bcr/Abl rearrangement does not significantly differ from that commonly seen in chronic myelogenous leukemia.

Therapy-induced Ph1 suppression in chronic myeloid leukemia: molecular and cytogenetic studies in patients treated with alpha-2b IFN, high-dose chemotherapy and autologous stem cell infusion

In this study, cytogenetic and molecular analyses were employed to assess the response to therapy in 29 chronic myeloid leukemia patients undergoing high dose chemotherapy followed by autologous stem cell infusion. Of these, 11 had previously achieved hematologic remission and cytogenetic improvement after alpha-2b interferon (IFN) treatment, whereas 18 underwent autografting in an early phase of the disease. In each case bone marrow samples were examined pre-treatment and at +2, +6 and +12 months in order to verify the degree of Ph1 suppression. In addition, the position of the breakpoint within the BCR region was mapped with multiple restriction enzymes. In 17 cases (59%) a significant Ph1 reduction was observed at +60 days (0-57% residual Ph1+ cells). In three of these cases, a complete cytogenetic response was confirmed at the DNA level by Southern blotting, but specific amplification of the BCR/ABL junction by the polymerase chain reaction (PCR), performed in two cases, still showed residual disease. The remaining 12 patients (41%) revealed a substantial persistence of Ph1+ metaphases (90-100%). Nine of 17 responding patients (53%) showed an increase of Ph1+ cells at 6 months, and five of 20 evaluated had a further increase at 12 months. With the exception of the results seen by PCR, comparison of molecular and cytogenetic techniques did not show significant differences. The variable degrees of Ph1 suppression observed did not appear to be associated with the position of BCR breakpoints. The factors predicting cytogenetic response to IFN and stem cell autograft and long-term durability of cytoconversion should be elucidated in further studies and with longer follow-up.