An in vivo and in vitro comparison of the effects of b2-a2 and b3-a2 p210BCR-ABL splice variants on murine 32D cells

The Philadelphia (Ph) chromosome, a characteristic cytogenetic marker of chronic myeloid leukaemia (CML), is caused by a reciprocal translocation juxtaposing the 3' region of the ABL gene onto the 5' region of the BCR gene. Due to conservation of the reading frame, but depending on the site of the breakpoint in the BCR gene, two alternatively spliced variants of the p210BCR-ABL mRNA (known as b2-a2 and b3-a2) are produced. To investigate whether there are any biological differences between these splice variants we have transfected the b3-a2 or b2-a2 cDNA into a murine myeloid cell line, 32D. We have also included the previously prepared 32Dp210 cell line (which expresses the b3-a2 transcript) in all of our comparisons. RT-PCR analysis indicated that transcription levels were comparable between the variants. Morphological examination of the cells expressing either of the BCR-ABL transcripts indicated that these cells were more mature with increased cytoplasm:nuclear ratios compared to the 32D parental and 32Dneo vector control cells. However, the 32Dp210 cells had a very different appearance from the other panel members and flow karyotyping indicated a clonal evolution and cytogenetic instability in these cells alone. At 10(6) and 10(7) cell doses all 32D cells expressing BCR-ABL caused ill health and tissue infiltration in SCID mice with such rapidity that statistical analysis was not informative. However, at the 10(5) and 10(4) dosage levels there were similar survival rates between mice injected with 32Db2-a2 or 32Db3-a2 while mice injected with 32Dp210 had a significantly shorter survival time. The study of this 32D cell line panel indicated that there were no overt differences in the biological properties conferred by the b3-a2 or b2-a2 transcripts to the 32D cells although these transcripts were able to confer in vitro and in vivo biological effects. This panel of BCR-ABL expressing 32D cells provides a useful model for CML disease progression studies.

High FUS/TLS expression in acute myeloid leukaemia samples

Retinoic acid has the ability to induce differentiation in some myeloid leukaemia cell lines and has been used to induce remission in acute promyelocytic leukaemia patients. We have analysed changes in gene expression, by differential display, in HL60 cells exposed to all-trans retinoic acid (ATRA) for only 1 h. Only about 0.4% of the genes examined by this technique showed changes in expression level, and all four of the gene fragments identified were downregulated during the short 1 h exposure. Two of the fragments were novel, a third was MYC and the fourth was the FUS proto-oncogene. Northern analysis showed that FUS was downregulated within 1 h only during induced neutrophil differentiation but not at all during induced monocyte differentiation. Unlike the sensitive cell lines, ATRA-resistant cell lines did not show a downregulation of FUS over a 24 h period of exposure to ATRA. Using a semiquantitative PCR analysis, no difference in FUS levels was observed between ATRA-sensitive and -resistant cell lines. A similar analysis was carried out on primary acute myeloid leukaemia (AML), peripheral stem cell harvests (PBSC) and cord blood samples. The PBSC and cord blood samples had FUS levels that were similar or generally less than the cell lines. However, much higher levels were seen in 63% of the AML samples examined. The data presented are consistent with previous reports for a role for FUS in the promotion and maintenance of cellular proliferation.

Inhibition of mitochondrial function in HL60 cells is associated with an increased apoptosis and expression of CD14

The myelomonocytic cell line HL60 can be induced by a variety of chemical agents to differentiation to either neutrophils or monocytes. Examination of gene expression, by differential display, in cells induced to monocytes with 1alpha,25-dihydroxyvitamin D(3) or neutrophils with all-trans retinoic acid (ATRA) identified a number of clones with altered patterns of expression over the period of differentiation. One of these clones was the mitochondrial gene NADH dehydrogenase subunit 4 (ND4) which showed a differential pattern of expression between the neutrophil and monocyte lineages. The potential of mitochondrial inhibitors to induce differentiation was investigated by treating the HL60 cells with either the NADH dehydrogenase inhibitor, Rotenone, the complex III inhibitor, Antimycin A, or the highly specific mitochondrial ATP-synthase inhibitor, Oligomycin. Although functional assays of differentiation did not produce any positive results, all the inhibitors resulted in a dramatic increase in CD14 expression at day 1, with CD38 markers not observed until day 3. The increased expression of CD14 was accompanied by a decrease in viability and all CD14 positive cells were also positive for Annexin V, a marker of apoptosis. These results suggest that inhibition of the components of the mitochondrial pathways may lead to the marking of some cells, via CD14, for cell death, whilst allowing commitment to differentiation to occur in the surviving population.

Unravelling an HLA-DR association in childhood acute lymphoblastic leukemia

Genetic and environmental factors play an interactive role in the development of childhood acute lymphoblastic leukemia (ALL). Since the demonstration of a major histocompatibility complex (MHC) influence on mouse leukemia in 1964, an HLA association has been considered as a possible genetic risk factor. Despite extensive efforts, however, no strong evidence comparable to the H-2(k) influence on mouse leukemia has been shown. The number of negative serological studies resulted in a loss of interest and consequently, no molecular HLA-DR association study has been published to date. We reconsidered the HLA-DR association in childhood ALL in 114 patients from a single center and 325 local newborn controls by polymerase chain reaction (PCR) analysis of the HLA-DRB1/3/4/5 loci. With conventional analysis, there was a moderate allelic association with the most common allele in the HLA-DR53 group, HLA-DRB1*04, in the whole group that was stronger in males (P =.0005, odds ratio = 2.9). When the other expressed HLA-DRB loci were examined, homozygosity for HLA-DRB4*01, encoding the HLA-DR53 specificity, was increased in patients (21.1% v 8.3%; odds ratio = 2.9, P =.0005). Consideration of gender showed that all of these associations were reflections of a male-specific increase in homozygosity for HLA-DRB4*01 (32.8% v 4. 0%; odds ratio = 11.7, 95% confidence interval [CI] = 4.9 to 28.0; P = 3 x 10(-8)). This highly significant result provided the long-suspected evidence for the HLA-DR influence on the development of childhood ALL while confirming the recessive nature of the MHC influence on human leukemogenesis as in experimental models. The cross-reactivity between HLA-DR53 and H-2Ek, extensive mimicry of the immunodominant epitope of HLA-DR53 by several carcinogenic viruses, and the extra amount of DNA in the vicinity of the HLA-DRB4 gene argue for the case that HLA-DRB4*01 may be one of the genetic risk factors for childhood ALL.

Identification of a retinoic acid responsive aldoketoreductase expressed in HL60 leukaemic cells

Neutrophil and monocyte differentiation can be induced in HL60 leukaemia cells by all-trans-retinoic acid (ATRA) and 1alpha,25-dihydroxyvitamin D3 (D3), respectively, whose differentiating effects can be enhanced by exposure to 'anti-inflammatory agents' and steroids. We have provided evidence that this potentiation is via inhibition of the activity of an enzyme of the aldoketoreductase (AKR) family, but had failed to identify expression of known AKRs in HL60 cells. In this study, we have identified a previously unclassified aldoketoreductase family member (termed HAKR e) that is expressed in HL60 cells. HAKR e is dramatically and transiently up-regulated in HL60 cells within 24 h of exposure to ATRA, further supporting the proposition that a member(s) of this family of enzymes play(s) a role in controlling cell growth and/or differentiation.

Identification of transcription factors expressed during ATRA-induced neutrophil differentiation of HL60 cells

A recent clinical therapeutic initiative has been the use of chemical agents which induce the leukaemic cells to overcome their block in differentiation. In order to understand this block the cascade of molecular events needs to be characterized. Haemopoietic differentiation is ultimately controlled at the level of gene transcription which is mediated by an array of transcription factors. Many transcription factors contain similar structural protein sequences, and we have used an RT-PCR-based approach to isolate sequences, from transcription factor gene families which share similar domains. Degenerate primers corresponding to the TFIIIA zinc-finger consensus amino acid sequences and to the POU-homeodomain and POU-specific domain were used to amplify genes on the basis that they contained similarities in structural motifs shared within these families of transcription factors. A serum-independent HL60 cell line was induced towards the neutrophil lineage by treatment with all-trans retinoic acid (ATRA) for 24 h. CD38+ cells committed towards this lineage were enriched and a population of these cells treated with dihydroxyvitamin D3 to induce neutrophil maturation. RNA extracted from uninduced, ATRA-induced CD38+ cells, and vitamin D3 treated maturing cell cultures were amplified using the degenerate primers. PCR fragments were cloned, sequenced, clustered into homologous groups, and the group sequences searched on the GenBank database. The Oct 1 transcription factor, and a very close homologue, KIAA0144, was identified using the POU family primers. The zinc-finger primers identified three zinc-finger genes. The pattern of gene expression was suggested from the number of clones in each group at neutrophil commitment and maturation. The differential expression of the genes in the zinc finger and POU families will lead to a better understanding of the cascade of gene expression which occurs following ATRA-induced differentiation.

c-myc locus amplification and the acquisition of trisomy 8 in the evolution of chronic myeloid leukaemia

The biological progression of chronic myeloid leukaemia is often associated with secondary cytogenetic abnormalities but the molecular mechanisms underlying this progression are poorly understood. This study explores the association of c-myc gene amplification with the progression of chronic myeloid leukaemia in fourteen individuals. Three of these cases showed amplification of c-myc during the course of their disease. Cytogenetic and molecular analysis of serial samples from some patients suggested the successive expansion of distinct clones of malignant cells. Our findings also suggest that trisomy 8 and locus amplification could represent alternative mechanisms for increasing c-myc gene dosage.

p53 mutations, methylation and genomic instability in the progression of chronic myeloid leukaemia

In chronic myeloid leukaemia (CML), as with other tumour types, mutations of the p53 gene are associated with disease progression. Changes in regional methylation of DNA with CML tumour development have also been demonstrated. Methylation is one mechanism by which gene expression is controlled and the CpG sites, which are the targets of DNA methylation, are also the sites of a number of the mutations found in the p53 gene. Cells harbouring mutant p53 have been shown to accumulate further genomic and genetic aberrations and methylation which alters the conformation of DNA is also believed to play a role in genomic stability. There appears to be an interplay between p53 deregulation and changing methylation patterns with the progression of CML. The cause and effect of changes in both of these critical gene regulating, DNA repair and genomic stability factors and their deviation during the progression of CML will be discussed.

DNA methylation: biology and significance

The modification of DNA by cytosine methylation is crucial for normal development. DNA methylation patterns are distinctive between tissues and are maintained with high fidelity during cell division. DNA methylation probably exerts its effects through alterations in chromatin structure, with a resultant effect on genetic transcription. 5-methylcytosine is also prone to spontaneous hydrolytic deamination to thymine. Whilst most G:T mismatches so produced are repaired, failure of mismatch repair leads to established mutation. Indeed, mutations that are the result of 5-methylcytosine transitions account for a disproportionate number of genetic mutations described in malignant and non-malignant disease. There is also evidence for substantial deregulation of DNA methylation in malignancy. Whether this deregulation is crucial for the transformation process, or simply an epiphenomenon associated with it, is still not established.

Amplification of mitochondrial DNA in acute myeloid leukaemia

There is a long-standing interest in the possible role of mitochondria in malignancy. We sought to discover whether amplification of mitochondrial DNA (mtDNA) occurred in leukaemia, and found it was often remarkably amplified in the blast cells of acute myeloid leukaemia (AML). We used gene dosage experiments to quantify the amount of mtDNA relative to nuclear DNA. DNA extracted from peripheral blood leucocytes or bone marrow of healthy individuals or patients was simultaneously hybridized with a probe for the mitochondrial genome and a control probe for the renin gene on human chromosome 1. Comparative densitometric ratios of approximately 1 were obtained between the two signals in 20 normal control peripheral blood samples. In contrast, comparative ratios in the range of 2-50 were observed in 25 AML samples and 13 of these showed 8-fold or greater amplification of mtDNA relative to normal peripheral blood controls. An additional four cases of AML were investigated at both presentation and remission and showed 3-10-fold amplification of mtDNA at presentation, but no amplification when in clinical remission. 18 cases of chronic granulocytic leukaemia (CGL) were also studied in chronic phase and showed mtDNA dosage levels equivalent to normal peripheral blood controls. However, 8/9 CGL patients showed mtDNA amplification during transformation from chronic phase. We conclude that amplification of mtDNA is an invariable feature of acute myeloid leukaemia and that it may be a useful marker for detecting transformation of CGL.

The dielectrophoresis enrichment of CD34+ cells from peripheral blood stem cell harvests

There is considerable interest in isolating the CD34+ cell population from leukaemic patients undergoing peripheral blood stem cell harvests. The techniques currently available make use of antibodies specific to the CD34+ surface markers. However, all of these techniques involve disturbance of the cell surface, are time-consuming and relatively expensive. In this study, we have used dielectrophoresis, which does not rely on the presence of cell-specific markers, to separate CD34+ cells from peripheral blood stem cell harvest samples containing an untreated natural mixed cell population. The separation is achieved by exploiting differences in the inherent dielectric properties of the various cell types. Samples obtained from peripheral blood stem cell harvests were resuspended in medium with a conductivity of less than 50 microS/cm and introduced into the dielectrophoretic separation chamber. Alternating field frequencies, from 500 kHz to 5 kHz, were used to collect cell fractions which were analysed by FACS, using a CD34-specific antibody, to quantify the CD34+ population within the fractions. On average a nearly five-fold increase in the frequency of the CD34+ cell population was observed in the fractions collected within the 50-10 kHz range. For this dielectrophoretic separation technique to be suitable in harvesting CD34+ cells for transplantation, it is important to demonstrate that the cells remain viable after the separation process. Cells obtained from each fraction grew when plated in colony assay cultures, GM-CFU and BFU-E, demonstrating that the cells remain normal, viable and capable of colony formation when cultured for 2 weeks. The number of colonies formed correlated with the percentage of CD34+ cells in each fraction. The dielectrophoretic separation technique is simple to operate, the separation is fast, the procedure non-invasive and although not tested has the potential to be incorporated as a batch-wise online facility with the standard harvesting equipment to increase the yield and speed of CD34+ cells in the PBSC harvest.

Increasing methylation of the calcitonin gene during disease progression in sequential samples from CML patients

In chronic myeloid leukaemia (CML), disease progression from the initial chronic phase to the acute phase or blast crisis has previously been shown to be correlated with progressive increases in hyper-methylation of the calcitonin gene, located at chromosome 11p15. However, sequential studies of individual patients were not performed in these investigations. We have analysed 44 samples from nine patients with typical Philadelphia chromosome positive CML throughout their disease progression to determine the methylation state of the calcitonin gene at these time points. Densitometry was used to quantitate the ratio of the normal 2.0 kb Hpa II fragments, indicating normal methylation status of the gene, compared to the intensity of the abnormal, hyper-methylated, 2.6-3.1 kb Hpa II fragments. We found a gradual increase in the ratio of methylated:unmethylated calcitonin gene during chronic phase with a dramatic rise at blast crisis. Further, the ratio of the abnormal hypermethylated 3.1 kb fragments to the methylated 2.6 kb fragment resulted in the identification of a clonal expansion of abnormally methylated cells. This expansion of cells with hypermethylation of the calcitonin gene during chronic phase was shown to coincide with the presence of a mutation in the p53 gene. The data presented in this study would suggest that an increased methylation status of the calcitonin gene during disease progression may indicate the expansion of abnormal blast cell populations and subsequent progression to blast crisis.

Influence of the major histocompatibility complex on age at onset of chronic lymphoid leukaemia

The major histocompatibility complex is one of the interactive factors in the multifactorial model of carcinogenesis. Its main influence in experimental models is on the age at onset of malignancies. We have previously shown a similar effect of homozygosity for HLA-DR53 in CML. In the present study, we investigated 79 patients with CLL and 329 local controls from Germany. In addition to full serotyping, all patients and 116 of controls were also typed by HLA-DRB PCR analysis. The homozygosity rates for DR53 in patients under and over the median age (60 years) were 18.6% and 2.9%, respectively (p = 0.03). Eight of the 9 homozygous patients were under the median age. The sex ratio in the DR53 homozygous group was reversed in favour of females. The homozygosity rates for DR53 were different in the overall groups of patients and controls, yielding a relative risk (RR) of 2.4 (p = 0.03). This association was stronger in the early-onset group compared to age-matched controls (RR = 4.4; p = 0.008) and for females with an early onset compared to age- and sex-matched controls (RR = 17.9; p = 0.0008). The simultaneous occurrence of the alleles of the haplotype A2B62DR4 showed a strong association with CLL (RR = 4.1; p = 0.002). This was probably the reason behind the association with HLA-DRB1*0401 (RR = 2.4; p = 0.009). Compared to the accelerating effect of HLA-DR53, HLA-DR52 showed a significant delaying effect on the onset of CLL. These findings confirmed the influence of the HLA complex on the development of another leukaemia.

Nature of HLA-associated predisposition to childhood acute lymphoblastic leukemia

A molecular analysis was carried out in 63 sequentially diagnosed childhood acute lymphoblastic leukemia (ALL) patients and 1011 controls to investigate the homozygosity rate for HLA-DR53. HLA-DR53 is associated with acute myeloblastic leukemia at the protein level, and our previous study has shown its association with early-onset chronic myeloid leukemia only in homozygous form at the DNA level. In the present study, the homozygosity rates for DR53 were 17.5 and 13.6% in patients and controls, respectively. Ten of the 11 homozygous patients were boys. In the common ALL group (n = 40), all seven DR53 homozygous patients were boys, and among 19 girls this genotype was not observed (P = 0.006). For males, homozygosity for DR53 revealed a relative risk (RR) of 3.29 (P = 0.008) for common ALL. Five of the 11 relapsed patients were homozygous for DR53. Heterozygous frequencies for HLA-DR53 were not different between patients and controls. Homozygosity for DR53 was associated with a very high relapse rate (45.5 vs 7.7%, P = 0.002, RR = 9.1). These results extended our findings in chronic myeloid leukemia and showed the recessive nature and the male predominance of the interactive HLA influence on the development of childhood leukemia. Molecular mimicry of an HLA-DR53 epitope by oncogenic (retro)viruses or putative susceptibility genes in linkage disequilibrium with HLA-DR53 may be responsible for this association.

Dielectrophoretic separation and enrichment of CD34+ cell subpopulation from bone marrow and peripheral blood stem cells

Dielectrophoresis has been used to enrich selected cell subpopulations in a mixed cell population by exploiting differential dielectric properties. Six-fold enrichment of stem cells expressing the CD34+ antigen has been achieved for bone marrow samples and peripheral blood, without the requirement for initial chemical treatment associated with immunoadsorption techniques.

No evidence for microsatellite instability or consistent loss of heterozygosity at selected loci in chronic myeloid leukaemia blast crisis

The aim of the present study was to investigate loss of heterozygosity (LOH) or microsatellite instability in chronic myeloid leukaemia (CML) blast crisis at genomic locations which are known or postulated to harbour tumour suppressor genes. We studied 48 patients in blast crisis of myeloid (n = 31), lymphoid (n = 15), megakaryocytic (n = 1), or mixed lineage (n = 1) phenotype by comparing constitutional DNA extracted from buccal epithelial cells or chronic phase leucocytes with DNA obtained from blast crisis leucocytes. Twelve variable number tandem repeat loci from six different chromosomes were amplified by polymerase chain reaction using labelled primers, and fractionated on polyacrylamide gels. After autoradiography, length as well as intensity of the amplified products were compared between constitutional and blast crisis samples. LOH was scored as complete, partial or none in informative patients. Complete LOH was found in one patient at 8p22 and another at 13q14; partial LOH was detected in three patients at 11p13 and/or 11p15. No LOH was found at 6q27, 8p21, 18q21, 22q11-12 and 22q13 in any patient. Furthermore, no consistent difference in allelic length was observed in 517 paired amplifications indicating no microsatellite instability. We conclude that the Rb gene at 13q14, the Wilms tumour gene at 11p13, the DCC gene at 18q21, the neurofibromatosis 2 gene at 22q11-13 and uncloned tumour suppressor genes at 6q27, 8p21-22 and 11p15, as well as genes responsible for microsatellite instability, are unlikely to be involved in the progression of CML to blast crisis in the majority of patients.

Long-term culture and molecular biological studies highlight differences in relative BCR-ABL expression levels in the peripheral blood and bone marrow of a patient with chronic granulocytic leukaemia

A patient with accelerating Ph+ve chronic granulocytic leukaemia (CGL) was considered for autologous BMT using marrow 'purged' by 4 weeks long-term culture (LTC). Efficacy of purging was determined using reverse transcriptase PCR for BCR-ABL mRNA transcripts b2a2 and b3a2. Peripheral blood and bone marrow were compared. Three observations emerged: (i) the initial b2a2:b3a2 ratios for unmanipulated blood and marrow were different with values of 9:1 and 2:1 respectively; (ii) both transcripts were successfully 'purged' with LTC of blood but not marrow; and (iii) LTC of marrow caused a transient increase in relative levels of b3a2 mRNA and a corresponding reduction in the b2a2 signal. This is the first case where such differences have been demonstrated in association with LTC.

Homozygous MHC genotypes and longevity

To investigate the relevance of the major histocompatibility complex (MHC) in longevity, we carried out a molecular analysis of the MHC in 432 unrelated healthy individuals. The comparison of individuals < or = 25 years and > 25 years showed that the 5.8-kb DQA1 allele, which corresponds to HLA-DR53, was negatively associated with longevity (p = 0.0035) resulting mainly from decreased homozygosity with age for that allele (p = 0.008), and restricted to males (p = 0.008). The difference was more striking for the 5.8 kb DQA1: 9.0 kb HSP70 haplotype again only in males (26.3 vs. 6.2%; p = 0.017, OR = 5.4, 95% CI = 1.5 - 19.5). The oldest male subject homozygous for this DQA1: HSP70 haplotype was 54 years (p = 0.005). Comparing leukemic patients and healthy individuals with the same ethnic and geographical origin, homozygosity for these genotypes was more frequent in the young leukemic group. The results suggested the existence of recessive deleterious genes in a segment of HLA-DR53 haplotypes.

Human major histocompatibility complex contains several leukemia susceptibility genes

In mice, homozygosity for the Mhc haplotype H-2k is associated with increased susceptibility to spontaneous and virus-induced leukemia, lymphoma and other neoplasms in the predisposed host. The influence of the Mhc on malignant development in these models is to shorten the latency after virus inoculation. Here, we present evidence that a similar phenomenon results in early-onset of human leukemia. A molecular analysis of the MHC in 112 CML patients showed that those who developed the disease when aged less than 35 years (early-onset group) had higher homozygosity rates for the DOA1, HSP70 and C4 alleles of the DR53 group of ancestral haplotypes, for a subtype of HLA-A3, and a higher allele frequency of BfFb compared to the late-onset group. The oldest patient (n = 13) homozygous for DR53 was 52-years-old (p = 0.004), and all HLA-A3 homozygous patients (n = 4) were in the early-onset group (p = 0.01). The relative risk for early-onset CML yielded by HLA-A3 homozygosity was 17.6. The well-known serological HLA-Cw4 association was not confirmed at the DNA level and thought to be due to linkage disequilibrium with BfFb. The factor B association was sex-limited. The DR52 group haplotypes appeared to be protective. The HLA-identical sibling frequency was increased only in the early-onset group (p < 0.01). Our findings agree with the concept of an MHC influence on the development of malignancies. The similarity in the location of the susceptibility loci and the serological cross-reaction between H-2Ek and DR53 raise the possibility that the mouse and human MHC share the same leukemia susceptibility genes.

Methylation of the major breakpoint cluster region (M-bcr) in Philadelphia-positive CML

It has previously been shown that a cluster of HpaII sites with the potential to be methylated exist around exon b3 of the M-bcr region involved in the formation of the Philadelphia chromosome in chronic myeloid leukemia (CML). The degree of hypermethylation of these sites can be directly correlated with the percentage of immature cells, whilst progressive hypomethylation occurs during the maturation of the granulocyte lineage. We have examined samples obtained from CML patients at diagnosis, during chronic phase, and blast crisis to examine the degree of methylation of this region in the non-rearranged BCR gene and the rearranged BCR-ABL gene. A low degree of methylation of the non-rearranged gene, similar to that observed in normal individuals, was observed in diagnosis and chronic phase samples. Increased methylation was observed during blast crisis indicative of the presence of immature cells in the samples. In contrast, a significantly lower degree of methylation was observed in the rearranged BCR-ABL gene at the onset of blast crisis. Division of the samples into those patients who had lost exon b3 during the formation of the BCR/ABL gene and those that had retained exon b3 produced differing patterns of methylation during disease progression. The former group, who also expressed a b2-a2 mRNA, showed an increase in methylation of the non-rearranged BCR gene prior to and during blast crisis, with a inverse decrease in the methylation of the BCR/ABL gene. Those patients who had retained exon b3, and expressed a b3-a2 mRNA, showed no change in the extent of methylation of the BCR/ABL gene but did exhibit an increase in methylation of the BCR gene during blast crisis. The consequence of the differing degree of methylation during disease progression could affect, to some extent, the specificity of protein binding or RNA expression.