A multiplex PCR for improved detection of typical and atypical BCR-ABL fusion transcripts

Application of droplet digital PCR in minimal residual disease monitoring of rare fusion transcripts and mutations in haematological malignancies

Leukaemia of various subtypes are driven by distinct chromosomal rearrangement or genetic abnormalities. The leukaemogenic fusion transcripts or genetic mutations serve as molecular markers for minimal residual disease (MRD) monitoring. The current study evaluated the applicability of several droplet digital PCR assays for the detection of these targets at RNA and DNA levels (atypical BCR::ABL1 e19a2, e23a2ins52, e13a2ins74, rare types of CBFB::MYH11 (G and I), PCM1::JAK2, KMT2A::ELL2, PICALM::MLLT10 fusion transcripts and CEBPA frame-shift and insertion/duplication mutations) with high sensitivity. The analytical performances were assessed by the limit of blanks, limit of detection, limit of quantification and linear regression. Our data demonstrated serial MRD monitoring for patients at molecular level could become "digitalized", which was deemed important to guide clinicians in treatment decision for better patient care.

A review on characterization of BCR - ABL transcript variants for molecular monitoring of chronic myeloid leukemia phenotypes

Chronic myeloid leukemia (CML) is a clonal myeloproliferative growth of human pluripotent stem cells which is estimated to occur at a rate of 1/100000 populations every year worldwide. A characteristic feature of this disease is the presence of the Philadelphia chromosome genotype, which results from the reciprocal translocation between human chromosomes 9 and 22. Two types of major genotypes are involved, which consequently result in two major types of expressed fusion mRNA transcripts: b3a2 and b2a2, i.e. major breakpoint segments (happening after exon 13 & after exon 14) of the BCR gene on chromosome 22 fuze with the ABL1 gene breakpoint (happening after exon 2) on chromosome 9, forming two genotypes coding for two transcripts: b3a2 (e14a2) and b2a2 (e13a2). The protein 'p210 BCR-ABL1', a protein which characteristically exhibits a high tyrosine kinase activity which is followed by the activation of various cellular processes that lead to increased cellular proliferation and cancer, is coded by both major BCR - ABL1 mRNA transcripts. Recent developments in the treatment of CML through molecular monitoring of the disease have managed to reduce patient morbidity and mortality. Advanced molecular techniques are aimed at detecting BCR-ABL1 transcript levels to monitor treatment response. Transcript typing is necessary to detect minimal residual disease and to achieve molecular response by helping to provide selective therapy based on the type of transcript identified, as transcript type is correlated with the disease course.The purpose of this review is to discuss: the role of the BCR-ABL1 fusion gene in the pathogenesis of CML; the role of BCR-ABL1 transcript characterization in the molecular monitoring of CML therapy; the association of BCR - ABL1 transcript types with different CML phenotypes, molecular responses, and treatment responses; and the laboratory techniques employed to detect and characterize BCR - ABL1 transcripts.

FISH-negative BCR::ABL1-positive e19a2 chronic myeloid leukaemia: the most cryptic of insertions

BACKGROUND

Chronic myeloid leukaemia (CML) is one of the most well characterised human malignancies. Most patients have a cytogenetically visible translocation between chromosomes 9 and 22 which generates the pathognomonic BCR::ABL1 fusion gene. The derivative chromosome 22 ('Philadelphia' or Ph chromosome) usually harbours the fusion gene encoding a constitutively active ABL1 kinase domain. A small subset of patients have no visible translocation. Historically, these 'Philadelphia chromosome negative' patients caused diagnostic confusion between CML and other myeloproliferative neoplasms; it is now well established that the BCR::ABL1 fusion gene can be generated via submicroscopic intrachromosomal insertion of ABL1 sequence into BCR, or, more rarely, of BCR into ABL1. The fusion genes arising from cryptic insertions are not detectable via G-banded chromosome analysis [karyotype] but can nevertheless always be detected using fluorescence in situ hybridisation (FISH) and/or qualitative reverse transcriptase PCR.

CASE PRESENTATION

A 43-year-old female presented with suspected CML in 2007; however, contemporaneous gold standard laboratory investigations, G-banded chromosome analysis and FISH, were both negative. The reverse transcriptase quantitative PCR (RT-qPCR) assay available at the time, which was capable of detecting the common BCR::ABL1 transcripts (e13a2/e14a2), was also negative. Upon review in 2009, the newly recommended reverse transcriptase multiplex PCR (capable of detecting all BCR::ABL1 transcripts including the atypical ones) subsequently detected an e19a2 fusion. The patient then responded to tyrosine kinase inhibitor therapy. In contrast, FISH studies of both samples with three commercially available probes remained consistently negative. Retrospective whole genome sequencing, undertaken as part of the 100,000 Genomes Project, has now revealed that the patient's BCR::ABL1 fusion gene arose via a uniquely small insertion of 122 kb ABL1 sequences into BCR.

CONCLUSIONS

We present a patient with suspected chronic myeloid leukaemia whose genetic investigations were originally negative at the time of diagnosis despite the use of contemporaneous gold standard methods. This is the first report of a FISH-negative, BCR::ABL1 positive CML which demonstrates that, even after sixty years of research into one of the most well understood human malignancies, whole genome sequencing can yield novel diagnostic findings in CML.

Prognosis in Chronic Myeloid Leukemia: Baseline Factors, Dynamic Risk Assessment and Novel Insights

The introduction of tyrosine kinase inhibitors (TKIs) has changed the treatment paradigm of chronic myeloid leukemia (CML), leading to a dramatic improvement of the outcome of CML patients, who now have a nearly normal life expectancy and, in some selected cases, the possibility of aiming for the more ambitious goal of treatment-free remission (TFR). However, the minority of patients who fail treatment and progress from chronic phase (CP) to accelerated phase (AP) and blast phase (BP) still have a relatively poor prognosis. The identification of predictive elements enabling a prompt recognition of patients at higher risk of progression still remains among the priorities in the field of CML management. Currently, the baseline risk is assessed using simple clinical and hematologic parameters, other than evaluating the presence of additional chromosomal abnormalities (ACAs), especially those at "high-risk". Beyond the onset, a re-evaluation of the risk status is mandatory, monitoring the response to TKI treatment. Moreover, novel critical insights are emerging into the role of genomic factors, present at diagnosis or evolving on therapy. This review presents the current knowledge regarding prognostic factors in CML and their potential role for an improved risk classification and a subsequent enhancement of therapeutic decisions and disease management.

Estimating prognostic relevant cutoff values for a multiplex PCR detecting BCR::ABL1 in chronic myeloid leukemia patients on tyrosine kinase inhibitor therapy in resource-limited settings

The prognosis of chronic myeloid leukemia (CML) on tyrosine kinase inhibitor (TKI) treatment is based on the quantification of BCR::ABL1 fusion gene transcript copy number, harmonized by an international scale (IS) based on TaqMan-based real-time quantitative PCR (qRT-PCR). In Ethiopia, as in most low- and middle-income countries (LMICs), access to standard diagnostic, follow-up, and prognostic tools is very limited, and it has been challenging to strictly follow international guidelines. This seriously compromises clinical outcome, despite the availability of TKIs through the Glivec International Patient Assistance Program (GIPAP). Multiplex PCR (mpx-PCR), conventionally regarded as a "screening tool," offers a potential solution to this problem. A total of 219 samples from confirmed CML patients were assayed. In reference to qRT-PCR, the AUC of ROC curve for mpx-PCR was 0.983 (95% CI: 0.957 to 0.997). At the optimum cut-off value, equivalent to BCR::ABL1 (IS) transcript copy number of 0.6%, the specificity and sensitivity were 93% and 95%, respectively, with 94% accuracy. Albeit the sensitivity and accuracy of mpx-PCR decrease below the optimum cutoff of 0.6% (IS), the specificity at 0.1% (IS) was 100%, making it an attractive means to rule-out relapse and drug non-adherence at later stages of treatment, which is particularly an issue in a low income setting. We conclude that the relative simplicity and low cost of mpx-PCR and prognostic relevant cutoff values (0.1-0.6% IS) should allow its use in peripheral clinics and thus maximize the positive impact of TKIs made available through GIPAP in most LMICs.

The Recurrent Atypical e8a2 BCR::ABL1 Transcript with Insertion of an Inverted 55 Base Pair ABL1 Intron 1b Sequence: A Detailed Molecular Analysis

Atypical BCR::ABL1 transcripts are found in approximately 2% of cases of chronic myeloid leukemia. It is important to detect them since affected patients also benefit from tyrosine kinase inhibitor therapy. In the rare e8a2 atypical BCR::ABL1 transcript, two out-of-frame exons are fused, thus, interposed nucleotides are usually found at the fusion site to restore the reading frame. In approximately half of previously reported e8a2 BCR::ABL1 cases, an inserted 55 bp sequence homologous to an inverted sequence from ABL1 intron 1b was detected. The generation of this recurrent transcript variant is not obvious. This work describes the molecular analysis of such an e8a2 BCR::ABL1 translocation from a CML patient. The genomic chromosomal breakpoint is identified, and the formation of this transcript is theoretically explained. The clinical course of the patient is reported, and recommendations are provided for the molecular analysis of future e8a2 BCR::ABL1 cases.

Chronic myeloid leukemia: cytogenetics and molecular biology’s part in the comprehension and management of the pathology and treatment evolution

Background

Chronic myelogenous leukemia (CML) is a type of blood cancer that affects hematopoietic stem cells and is often characterized by the presence of the Philadelphia chromosome. The Philadelphia chromosome encodes for a protein with high tyrosine kinase activity which acts as a tumorigenic factor.

Main body

This review article reports an update on the pathophysiology of CML and highlights the role of cytogenetic and molecular biology in screening, diagnosis, therapeutic monitoring as well as evaluating patients’ response to treatment. Additionally, these genetic tests allow identifying additional chromosomal abnormalities (ACA) and BCR-ABL tyrosine kinase domain mutations in intolerant or resistant patients. Thus, therapeutic advances have enabled this pathology to become manageable and almost curable in its clinical course. The scientific literature search used in the synthesis of this paper was carried out in the PubMed database, and the figures were generated using online software named BioRender.

Conclusion

The role of cytogenetic and molecular biology is crucial for the diagnosis and medical monitoring of patients. In-depth knowledge of molecular mechanisms of the BCR-ABL kinase facilitated the development of new targeted therapies that have improved the vital prognosis in patients. However, the emergence of ACA and new mutations resistant to tyrosine kinase inhibitors constitutes a real challenge in the quest for adequate therapy.

A case report of pediatric acute lymphoblastic leukemia with e8a2 BCR/ABL1 fusion transcript

Background

Acute lymphoblastic leukemia is the most common type of cancer in children. Most often it affects the age group between 2 and 5 years of age. Studies have shown an improvement in general survivability, more than 90% 5-year overall survival (OS). Current treatment protocols for acute lymphoblastic leukemia require verification of the presence of favorable and unfavorable genetic abnormalities, which help qualify patients to the appropriate risk group and select a more suitable treatment. The presence of the BCR/ABL1 fusion gene stratifies the patient into a high-risk group and requires special treatment with tyrosine kinase inhibitors (TKI). The three dominant mRNA transcripts are e1a2, e13a2, and e14a2. Nevertheless, cases of atypical BCR/ABL1 transcripts have also been reported.

Case presentation

This paper presents the case of a pediatric patient with Ph + B-cell precursor acute lymphoblastic leukemia with rare atypical e8a2 BCR/ABL1 fusion transcript. Our patient achieved complete remission after 33 days of treatment. Molecular and cytogenetic studies in TP1 did not reveal the presence of the BCR/ABL1 transcript. The PCR-MRD test in TP1b was negative, the patient did not require hematopoietic stem cell transplantation.

Conclusion

Genetic evaluation of the bone marrow sample is crucial in the initial stage of the diagnosis. Fluorescent in situ hybridization and reverse transcriptase polymerase chain reaction with Sanger sequencing are the appropriate methods used in the detection of rare variants of BCR/ABL1 transcripts.

Genetic Landscape of Myeloproliferative Neoplasms with an Emphasis on Molecular Diagnostic Laboratory Testing

Chronic myeloproliferative neoplasms (MPNs) are hematopoietic stem cell neoplasms with driver events including the BCR-ABL1 translocation leading to a diagnosis of chronic myeloid leukemia (CML), or somatic mutations in JAK2, CALR, or MPL resulting in Philadelphia-chromosome-negative MPNs with constitutive activation of the JAK-STAT signaling pathway. In the Philadelphia-chromosome-negative MPNs, modern sequencing panels have identified a vast molecular landscape including additional mutations in genes involved in splicing, signal transduction, DNA methylation, and chromatin modification such as ASXL1, SF3B1, SRSF2, and U2AF1. These additional mutations often influence prognosis in MPNs and therefore are increasingly important for risk stratification. This review focuses on the molecular alterations within the WHO classification of MPNs and laboratory testing used for diagnosis.

Impact of the Breakpoint Region on the Leukemogenic Potential and the TKI Responsiveness of Atypical BCR-ABL1 Transcripts

Chronic Myeloid Leukemia (CML) is a hematological disorder characterized by the clonal expansion of a hematopoietic stem cell carrying the Philadelphia chromosome that juxtaposes the BCR and ABL1 genes. The ensuing BCR-ABL1 chimeric oncogene is characterized by a breakpoint region that generally involves exons 1, 13 or 14 in BCR and exon 2 in ABL1. Additional breakpoint regions, generating uncommon BCR-ABL1 fusion transcripts, have been detected in various CML patients. However, to date, the impact of these infrequent transcripts on BCR-ABL1-dependent leukemogenesis and sensitivity to tyrosine kinase inhibitors (TKIs) remain unclear. We analyzed the transforming potential and TKIs responsiveness of three atypical BCR-ABL1 fusions identified in CML patients, and of two additional BCR-ABL1 constructs with lab-engineered breakpoints. We observed that modifications in the DC2 domain of BCR and SH3 region of ABL1 affect BCR-ABL1 catalytic efficiency and leukemogenic ability. Moreover, employing immortalized cell lines and primary CD34-positive progenitors, we demonstrate that these modifications lead to reduced BCR-ABL1 sensitivity to imatinib, dasatinib and ponatinib but not nilotinib. We conclude that BCR-ABL1 oncoproteins displaying uncommon breakpoints involving the DC2 and SH3 domains are successfully inhibited by nilotinib treatment.

Characteristics of BCR-ABL gene variants in patients of chronic myeloid leukemia

Background

Depending on breakpoints of rearrangement different types of BCR–ABL fusion protein can be generated in patients of chronic myeloid leukemia (CML). The aim of this study is to observe frequencies of major transcripts in CML patients by reverse transcriptase polymerase chain reaction (RT-PCR) and their hematological features at the time of presentation.

Materials and methods

This cross sectional study was performed at Molecular Lab of Riphah International University, Islamabad from January to June 2019. Consecutive peripheral blood samples of 70 newly diagnosed CML patients in chronic phase were analyzed by RT-PCR to detect different BCR–ABL transcripts. Routine blood cell counts were assessed by an automated hematology analyzer.

Results

All samples expressed typical BCR–ABL rearrangement. Expression of either e14a2 or e13a2 transcript was detected in 38 (54%) and 30 (43%) patients, respectively. Coexpression of e13a2 + e14a2 was found in 2 (3%) patients. The mean total leukocyte count was higher in group expressing e13a2 (P = 0.01). Higher mean platelet count was noted in patients with e14a2 transcript, but this difference was statistically insignificant (P = 0.1). The association of male gender was observed with the group exhibiting e14a2 (P = 0.01). There was no statistically significant association between transcript type and different ranges of age, hemoglobin levels, and platelet and total leukocyte counts (P > 0.05).

Conclusion

e14a2 transcript was most common transcript in CML patients. Patients exhibiting e13a2 subgroup presented with significantly higher mean white blood cell count at the time of presentation. Significantly higher proportion of male patients was found to express e14a2 transcript over e13a2.

Definition, Epidemiology, Pathophysiology, and Essential Criteria for Diagnosis of Pediatric Chronic Myeloid Leukemia

Simple Summary

The low incidence (1:1,000,000) of chronic myeloid leukemia (CML) in the first two decades of life presents an obstacle to accumulation of pediatric experience and knowledge on this leukemia. Biological features of CML are shared but also differing between adult and pediatric patients. This review aims; (i) to define the disease based on an unified terminology, (ii) to list the diseases to be considered as a differential diagnosis in children, (iii) to outlines the morphological, histopathological and immuno-phenotypical findings of pediatric CML, (iv) to illustrate rare but classical complications resulting from high white cell and platelet counts at diagnosis, and (v) to recommend a uniform approach for the diagnostic procedures to be applied. Evidently, only a clear detailed picture of all relevant features can lay the basis for standardized treatment approaches.

Abstract

Depending on the analytical tool applied, the hallmarks of chronic myeloid leukemia (CML) are the Philadelphia Chromosome and the resulting mRNA fusion transcript BCR-ABL1. With an incidence of 1 per 1 million of children this malignancy is very rare in the first 20 years of life. This article aims to; (i) define the disease based on the WHO nomenclature, the appropriate ICD 11 code and to unify the terminology, (ii) delineate features of epidemiology, etiology, and pathophysiology that are shared, but also differing between adult and pediatric patients with CML, (iii) give a short summary on the diseases to be considered as a differential diagnosis of pediatric CML, (iv) to describe the morphological, histopathological and immunophenotypical findings of CML in pediatric patients, (v) illustrate rare but classical complications resulting from rheological problems observed at diagnosis, (vi) list essential and desirable diagnostic criteria, which hopefully in the future will help to unify the attempts when approaching this rare pediatric malignancy.

Targeting BCL-2 as a Therapeutic Strategy for Primary p210BCR-ABL1-positive B-ALL Cells

BACKGROUND/AIM

Philadelphia-positive acute lymphoblastic leukemia (Ph⁺ B-ALL) is caused by the malignant transformation of lymphoid cells induced by BCR-ABL1 constitutive catalytic activity. BCR-ABL1 tyrosine kinase inhibitors (TKIs) are effective against chronic myeloid leukemia (CML) cells, inducing durable hematological, cytogenetic and molecular responses. However, in Ph⁺ B-ALL - as in CML progressing to blast crisis - TKIs fail to maintain disease remission. We, therefore, wanted to investigate if dual targeting of BCL-2 and BCR-ABL1 would be more effective in killing Ph⁺ B-ALL cells.

MATERIALS AND METHODS

p210-B-ALL CD34-positive cells were used to evaluate the BCR-ABL expression and pharmacological targeting of BCL-2, by venetoclax, alone or in combination with BCR-ABL1 inhibition.

RESULTS

We demonstrated the cytotoxic effect of BCL-2 inhibition and that dual targeting of BCL-2 and BCR-ABL1 with venetoclax and nilotinib further increases this cytotoxicity.

CONCLUSION

BCL-2 is a key survival factor for primary Ph⁺ B-ALL cells and its inhibition - alone or in combination with a BCR-ABL1 TKI - should be further investigated as a potential therapeutic strategy for these patients.

Chronic Myeloid Leukemia, Version 2.2021, NCCN Clinical Practice Guidelines in Oncology

Chronic myeloid leukemia (CML) is defined by the presence of Philadelphia chromosome (Ph) which results from a reciprocal translocation between chromosomes 9 and 22 [t(9;22] that gives rise to a BCR-ABL1 fusion gene. CML occurs in 3 different phases (chronic, accelerated, and blast phase) and is usually diagnosed in the chronic phase. Tyrosine kinase inhibitor therapy is a highly effective first-line treatment option for all patients with newly diagnosed chronic phase CML. This manuscript discusses the recommendations outlined in the NCCN Guidelines for the diagnosis and management of patients with chronic phase CML.

Impact of the major BCR-ABL1 transcript type on clinical and biological parameters and molecular response in patients with chronic myeloid leukemia

AIM

In chronic myeloid leukemia (CML), the impact of MBCR-ABL1 major transcript type on disease phenotype and response to treatment still controversial to date. This work aims to study the influence of Mb3a2 and Mb2a2 transcripts on clinico-biological parameters and the molecular response in patients with chronic phase chronic myeloid leukemia (CP-CML) treated with Imatinib as frontline therapy.

METHODS

This is six years prospective study started in March 1 st, 2013. 67 patients with newly CP-CML were treated by Imatinib as frontline therapy. Clinical and biological characteristics disease were collected for all patients. Molecular typing was performed by multiplex RT-PCR and quantification of transcripts by real-time quantitative PCR (qRT-PCR). The cumulative incidence of deep molecular response (DMR) was estimated by the Kaplan-Meier method. The comparison was made using the parametric Log-Rank test. A value of P ≤ 0.05 is considered significant.

RESULTS

61% of patients expressed b3a2, 35.82% b2a2 and 2.98% expressed a rare transcript of type e19a2. At diagnosis, the b2a2 type had a higher level of expression than that of b3a2 (67.92 vs 53.79%; P = 0.03). This insignificant difference between the two transcript subgroups was also observed for rates below 1% at 6 months (54 vs 39; P = 0.26) and below 0.1% (54 vs 44 %; P = 0.50), (77 vs 50%; P = 0.09) and (81 vs 78 %; P = 0.52) at 12, 18 and 24 months respectively. The two types of transcript had almost the same kinetics. Nevertheless, the absolute value of the BCR-ABL1/ABL ratio decrease was faster in the group of patients expressing b3a2, than in those expressing b2a2. At 18 months post IM therapy, patients with a b3a2 transcript have a trend of better MMR that those with b2a2 (77 vs 50%; P = 0.09). The DMR was not significantly different between two groups at 24 months (50 vs 32%; P = 0.20) and 36 months (75 vs 70%; P = 0.54) respectively. The cumulative probability of achieving MRD at 5 years was higher in patients with b3a2 type but not statistically significant; (85 vs. 68%; P = 0.17).

CONCLUSION

Patients with b3a2 transcript may be associated with a better response to Imatinib therapy.

Prognostic Significance of Transcript-Type BCR - ABL1 in Chronic Myeloid Leukemia

Chronic myeloid leukemia (CML) is characterized by the presence of the BCR-ABL1 fusion gene. In more than 95% of CML patients, the typical BCR-ABL1 transcript subtypes are e13a2 (b2a2), e14a2 (b3a2), or the simultaneous expression of both. Other less frequent transcript subtypes, such as e1a2, e2a2, e6a2, e19a2, e1a3, e13a3, and e14a3, have been sporadically reported. The main purpose of this review is to assess the possible impact of different transcripts on the response rate to tyrosine kinase inhibitors (TKIs), the achievement of stable deep molecular responses (s-DMR), the potential maintenance of treatment-free remission (TFR), and long-term outcome of CML patients treated with TKIs. According to the majority of published studies, patients with e13a2 transcript treated with imatinib have lower and slower cytogenetic and molecular responses than those with e14a2 transcript. They should be considered a high-risk group that would most benefit from frontline treatment with second-generation TKIs (2GTIKIs). Although few studies have been published, similar significant differences in response rates to 2GTKIs have been not reported. The e14a2 transcript seems to be a favorable prognostic factor for obtaining s-DMR, irrespective of the TKI received, and is also associated with a very high rate of TFR maintenance. Indeed, patients with e13a2 transcript achieve a lower rate of s-DMR and experience a higher probability of TFR failure. According to most reported data in the literature, the type of transcript does not seem to affect long-term outcomes of CML patients treated with TKIs. In TFR, the e14a2 transcript appears to be related to favorable responses. 2GTKIs as frontline therapy might be a convenient approach in patients with e13a2 transcript to achieve optimal long-term outcomes.

Monitoring of Minimal Residual Disease (MRD) in Chronic Myeloid Leukemia: Recent Advances

Chronic myeloid leukemia (CML) is a myeloproliferative neoplasm caused by the BCR-ABL1 fusion gene generation as a consequence of the t(9;22)(q34;q11) rearrangement. The identification of the BCR-ABL1 transcript was of critical importance for both CML diagnosis and minimal residual disease (MRD) monitoring. In this review, we report the recent advances in the CML MRD monitoring based on RNA, DNA and protein analysis. The detection of the BCR-ABL1 transcript by the quantitative reverse-transcriptase polymerase chain reaction is the gold standard method, but other systems based on digital PCR or on GeneXpert technology have been developed. In the last years, DNA-based assays showed high sensitivity and specificity, and flow cytometric approaches for the detection of the BCR-ABL1 fusion protein have also been tested. Recently, new MRD monitoring systems based on the detection of molecular markers other than the BCR-ABL1 fusion were proposed. These approaches, such as the identification of CD26+ leukemic stem cells, microRNAs and mitochondrial DNA mutations, just remain preliminary and need to be implemented. In the precision medicine era, the constant improvement of the CML MRD monitoring practice could allow clinicians to choose the best therapeutic algorithm and a more accurate selection of CML patients eligible for the tyrosine kinase inhibitors discontinuation.

Real-time quantification of fusion transcripts with ligase chain reaction by direct ligation of adjacent DNA probes at fusion junction

Gene fusions, produced by aberrant juxtapositions of two or more genes even in different chromosomes, play important roles in the primary oncogenic mechanism and have been demonstrated to be typically associated with many cancers. So the fused genes or the transcripts can be specific predictive biomarkers for cancer diagnosis and therapy. Herein, we develop a direct ligation- and ligase chain reaction (LCR)-based method for a fusion transcript assay. In virtue of the high selectivity of ligase and the exponential amplification capacity of LCR, the proposed method can detect as low as 1 fM fusion transcripts with high specificity and has been successfully applied to real samples. With the real-time fluorescence measurements, the fusion transcripts can be assayed in a simple way. Therefore, the proposed method can provide a simple and cost-effective platform for fusion transcript detection in routine laboratories and clinical diagnosis.

Rapid decline of Philadelphia-positive metaphases after nilotinib treatment in a CML patient expressing a rare e14a3 BCR-ABL1 fusion transcript: A case report

We report a case of chronic myeloid leukemia in a 52-year-old male expressing a rare e14a3 BCR-ABL1 fusion transcript. Cytogenetic analysis showed the t(9;22) translocation and multiplex RT-PCR detected an atypical fragment of approximately 230 base pairs. Using two primers recognizing exon 10 of BCR and exon 4 of ABL1, a larger PCR product was identified, cloned, sequenced and defined as an e14a3 BCR-ABL1 rearrangement. The patient was treated with nilotinib and monitored measuring cytogenetic and hematological parameters, while BCR-ABL1 transcripts were surveyed by conventional and semi-nested PCR. The patient achieved a complete hematologic response after two months of treatment followed by a complete cytogenetic remission two months later. Furthermore, PCR and semi-nested PCR failed to detect the e14a3 BCR-ABL1 mRNA after 15 and 21 months of nilotinib, respectively.

Clinical characteristics and prognostic significance of chronic myeloid leukemia with rare BCR-ABL1 transcripts

The prognostic significance of rare BCR-ABL1 transcripts is uncertain in the tyrosine kinase inhibitor (TKI) era. In this retrospective study, 40 (1.7%) patients with rare BCR-ABL1 transcripts were identified from a cohort of 2331 chronic myeloid leukemia (CML) patients; 4 types of rare transcripts were identified, including e1a2 (0.9%), e19a2 (0.4%), e13a3 (0.1%), and e14a3 (0.3%). Compared to patients with the typical transcript, those with the e1a2 transcript had an inferior response to TKIs and a worse outcome. Patients with the e19a2 transcript had a high rate of early optimal response to TKIs, but most of them later lost the complete cytogenetic response (CCyR) due to BCR-ABL1 mutations, resulting in a poor prognosis. Patients with the e13a3/e14a3 transcript responded well to TKIs and had a good outcome. These findings indicate that the type of BCR-ABL1 transcript should be considered when determining the treatment for CML patients in the TKI era.

Association of BCR/ABL transcript variants with different blood parameters and demographic features in Iraqi chronic myeloid leukemia patients

Background

Chronic myeloid leukemia (CML) is a myeloproliferative neoplasm characterized by the presence of BCR‐ABL fusion gene (GenBank accession NC_000022.11). In the vast majority of CML patients, the typical subtype of BCR‐ABL transcript are b3a2, b2a2 or both. The aim of this study was to determine the different subtypes of BCR‐ABL transcript and their impact on the demographic and hematological parameters in Iraqi patients with CML.

Methods

One hundred patients with chronic phase CML (11 newly diagnosed and 89 imatinib‐resistant) were enrolled in this study. Ribonucleic acid (RNA) was extracted from leukocytes, and complementary DNA was created using reverse transcriptase polymerase chain reaction technique. A multiplex polymerase chain reaction with four specific primers was used to determine the BCR‐ABL fusion subtypes in each patient.

Results

Male to female ratio was 1.38:1. Fifty‐nine patients expressed b3a2 transcript, whereas 39 of the remaining cases were positive for b2a2 variant. One case expressed b2a3 transcript, while the last case coexpressed the two subtypes of mRNA b3a2/b2a2. Male and female were significantly associated with b3a2 and b2a2 subtypes, respectively. The b3a2 subtype showed higher total leukocyte count than b2a2 subgroup, while b2a2 variant demonstrated significantly elevated platelet counts compared to those with b3a2 transcript. A significantly higher plateletcrit percentage (PCT%) was found in patients with b2a2 transcript whereas.

Conclusions

The testified Iraqi group expressed M‐BCR‐ABL type with preponderance of b3a2 over b2a2 subtype. There was a gender‐skewed distribution in BCR‐ABL transcript types with b3a2 transcript more prevalent in males. The type of BCR‐ABL transcript is reflected by different leukocyte and platelet counts at diagnosis, which might represent a distinct phenotype and disease biology.

Analytical Validation of a Highly Sensitive, Multiplexed Chronic Myeloid Leukemia Monitoring System Targeting BCR-ABL1 RNA

This study describes the analytical performance of the QuantideX qPCR BCR-ABL IS Kit, the first Food and Drug Administration–cleared assay designed to monitor breakpoint cluster region–Abelson tyrosine-protein kinase 1 (BCR-ABL1) fusion transcripts isolated from peripheral blood specimens from patients with chronic myeloid leukemia. This multiplex real-time quantitative RT-PCR assay amplifies both e13a2 and e14a2 Major BCR-ABL1 transcripts and the reference target ABL1. The test results are provided in international scale (IS) values by incorporating armored RNA-based calibrators that have defined IS values tied directly to the World Health Organization BCR-ABL1 Primary Reference Materials, without the necessity of determining and maintaining conversion factors. For each batch run, the integrated interpretive software evaluates run and specimen quality control metrics (including a sufficient amount of ABL1 control transcripts to ensure a minimal limit of detection) and calculates both molecular response (MR) and %IS values for each specimen. The test has a limit of detection of MR4.7 (0.002%IS) and a linear range from MR0.3 (50%IS) to MR4.7 (0.002%IS) for both Major transcripts. Single-site and multisite precision studies demonstrated a maximum SD of 0.13 MR (30% CV within the assay range between MR0.7 and MR3.7). The performance of this BCR-ABL1 monitoring test meets all of the clinical guideline recommendations for sensitivity and IS reporting for the management of chronic myeloid leukemia patients.

Feasibility of Qualitative Testing of BCR-ABL and JAK2 V617F in Suspected Myeloproliperative Neoplasm (MPN) Using RT-PCR Reversed Dot Blot Hybridization (RT-PCR RDB)

BACKGROUND

Defining the presence of BCR-ABL transcript in suspected myeloproliferative neoplasm is essential in establishing chronic myeloid leukemia. In the absence of BCR-ABL, the conventional diagnostic algorithm recommends JAK2 V617F mutation testing to support diagnosis of other MPN diseases such as polycythemia vera, essential thrombocythemia, and primary myelofibrosis. In certain cases of thrombocythemia, simultaneous upfront testing of both BCR-ABL and JAK2 may be desirable. We wanted to test the feasibility of multiplex detection of BCR-ABL transcript variants and JAK2 V617F mutation simultaneously using the reverse transcriptase polymerase chain reaction (RT-PCR)-based reverse dot-blot hybridization (RDB) method.

MATERIAL AND METHODS

Separate biotinylated RT-PCR primers were designed to amplify specific BCR-ABL transcripts and JAK2 V617F mutant alleles. Specific hybridization of RT-PCR products with arrays of membrane-bound probes followed by colorimetric development would allow simultaneous visualization of BCR-ABL and/or JAK2 mutant transcripts in a given specimen. To validate the RDB method, we used cDNA specimens previously referred to our laboratory for routine clinical testing of BCR-ABL and/or JAK2.

RESULTS

The limit of detection or analytical sensitivity of the RDB method using cDNA specimens was 0.5% and 6.25% in detecting BCR-ABL and JAK2 mutant transcripts, respectively. The diagnostic specificity and sensitivity to detect BCR-ABL and JAK2 were 100% and 92.3% (N = 38); and 100% and 100% (N = 27), respectively. RDB also detected BCR-ABL transcripts in 22% of JAK2 V617F mutation-positive samples (N = 14).

CONCLUSIONS

RT-PCR RDB is a promising qualitative multiplex method to detect BCR-ABL and JAK2 mutant transcripts simultaneously.

Molecular monitoring in CML: how deep? How often? How should it influence therapy?

With the advent of tyrosine kinase inhibitors (TKIs), the goals of therapy in chronic myeloid leukemia (CML) are steadily shifting. Long-term disease control on TKI therapy has been the goal and expectation for most patients. More recently, treatment-free remission (TFR) has entered mainstream practice and is increasingly being adopted as the main goal of therapy. This therapeutic shift not only influences TKI selection but also, has necessitated the refinement and dissemination of highly sensitive and accurate molecular monitoring techniques. Measurement of BCR-ABL1 messenger RNA expression through reverse transcription quantitative polymerase chain reaction, reported according to the International Scale, has become the primary tool for response assessment in CML. Achieving specific time-dependent molecular milestones, as defined by global therapeutic guidelines, has been established as critical in maximizing optimal outcomes while identifying patients at risk of therapy failure. Depth and duration of a deep molecular response have become the new therapeutic targets in patients considered for TFR. Consequently, molecular monitoring in CML has become even more critical to ongoing response assessment, identifying patients with TKI resistance and poor drug adherence, and enabling TFR to be attempted safely and effectively.

Molecular monitoring in CML: how deep? How often? How should it influence therapy?

With the advent of tyrosine kinase inhibitors (TKIs), the goals of therapy in chronic myeloid leukemia (CML) are steadily shifting. Long-term disease control on TKI therapy has been the goal and expectation for most patients. More recently, treatment-free remission (TFR) has entered mainstream practice and is increasingly being adopted as the main goal of therapy. This therapeutic shift not only influences TKI selection but also, has necessitated the refinement and dissemination of highly sensitive and accurate molecular monitoring techniques. Measurement of BCR-ABL1 messenger RNA expression through reverse transcription quantitative polymerase chain reaction, reported according to the International Scale, has become the primary tool for response assessment in CML. Achieving specific time-dependent molecular milestones, as defined by global therapeutic guidelines, has been established as critical in maximizing optimal outcomes while identifying patients at risk of therapy failure. Depth and duration of a deep molecular response have become the new therapeutic targets in patients considered for TFR. Consequently, molecular monitoring in CML has become even more critical to ongoing response assessment, identifying patients with TKI resistance and poor drug adherence, and enabling TFR to be attempted safely and effectively.

New rapid method to detect BCR-ABL fusion genes with multiplex RT-qPCR in one-tube at a time

Fast identification of BCR-ABL fusion genes is critical for precise diagnosis, risk stratification and therapy scheme selection in leukemia. More convenient methods are needed for quickly detection of the BCR-ABL fusion genes. Multiplex fluorescent reverse transcription quantitative real-time PCR (Multiplex RT-qPCR) methods are developed for detection of the at least 14 subtypes of BCR-ABL fusion genes in one tube at a time by using patients' bone marrow samples. The new Multiplex RT-qPCR method could quickly detect BCR-ABL fusion genes with sensitivity up to 10-10⁶ copies. It can detect the fusion genes in patients' bone marrow samples containing any subtypes of the major bcr (M-bcr) e13a2, e14a2, e13a3 and e14a3, the minor bcr (m-bcr) e1a2 and e1a3, the micro bcr (μ-bcr) e19a2 and e19a3, and the nano bcr (n-bcr) e6a2 and e6a3. The specificity is comparable to the FISH methods. The cutoff for clinical diagnosis of BCR-ABL(+) is also determined by testing in clinical chronic myeloid leukemia samples. This is a new fast method with high sensitivity and specificity for clinical detection of BCR-ABL fusion genes. It will benefit the precise diagnosis, targeted therapy and minimal residual disease (MRD) monitoring in leukemia.

Characterization of a novel variant BCR-ABL1 fusion transcript in a patient with chronic myeloid leukemia: Implications for molecular monitoring

Molecular monitoring of BCR-ABL1 transcript levels using quantitative polymerase chain reaction is an essential part of the modern management of chronic myeloid leukemia patients treated with tyrosine kinase inhibitors. Establishing the diagnostic BCR-ABL1 fusion transcript is necessary in order to select appropriate primers and probes for such monitoring. A case is described in which quantitative polymerase chain reaction failed to detect the presence of BCR-ABL1 fusion transcript in a Philadelphia chromosome-positive chronic myeloid leukemia patient. Further investigation demonstrated a novel in-frame BCR-ABL1 fusion transcript with a breakpoint in BCR exon 13 and insertion of a sequence of ABL1 intron 1, therefore enabling subsequent molecular monitoring. This case highlights the requirement for characterization of the BCR-ABL1 transcript type at chronic myeloid leukemia diagnosis. Issues concerning standardized methodological approaches and interpretation of transcript levels in such rare cases are discussed.

Deep molecular response in chronic myeloid leukemia: the new goal of therapy?

Chronic myeloid leukemia (CML) is caused by formation of the BCR-ABL1 fusion protein. Tyrosine kinase inhibitors (TKI) that target BCR-ABL1 are now the standard of care for patients with CML. Molecular monitoring of residual BCR-ABL1 mRNA transcripts, typically performed using real-time quantitative PCR, has improved treatment management, particularly for patients with CML in chronic phase. Major molecular response (MMR; i.e., a ≥3-log reduction in BCR-ABL1 transcript levels) is used in current treatment guidelines to assess prognosis. Recent evidence suggests that deeper molecular responses (≥4-log reductions in BCR-ABL1 transcript levels), particularly when attained early during treatment, may have even better correlation with long-term outcomes, including survival and disease progression. Furthermore, achieving deep molecular response is a requirement for entering trials evaluating treatment-free remission (TFR). In this review, we discuss the evolving definition of minimal residual disease and the various levels of molecular response under evaluation in current clinical studies. In addition, the available clinical data on achieving MMR and deeper levels of molecular response with TKI therapy, the prognostic value of deep molecular response, and factors that may predict a patient's ability to achieve and sustain a deep molecular response on TKI therapy are also discussed. Available data from TFR studies are addressed. We discuss current knowledge of the ideal conditions for attempting treatment discontinuation, factors predictive of molecular relapse, when TKI therapy should be restarted, and which therapeutic strategies (when administered in the first-line setting and beyond) are expected to best enable successful TFR.

Genotyping of chimerical BCR-ABL1 RNA in chronic myeloid leukemia by integrated DNA chip

Chronic myelogenous leukemia (CML) and Philadelphia chromosome-positive (Ph(+)) acute lymphoblastic leukemia (ALL) are associated with fusion of the BCR and ABL1 genes by chromosome translocation. The chimerical BCR-ABL1 gene encodes different fusion proteins that vary in size, depending on the breakpoint in the BCR region. Different types of fusion genes in CML and Ph(+) ALL are thought to be related to the clinical course and outcome of each patient. Currently, the genotypes are determined by PCR, followed by gel electrophoresis or DNA sequencing (among other methodologies). Our major aim was to develop a diagnostic method for CML genotyping by means of an integrated process of DNA microarray. Here, we describe a method of integrated multiplex reverse transcription, asymmetric PCR, and hybridization, all in the same reaction mixture in a chamber assembled on the surface of capture oligonucleotide probes immobilized on a glass slide. The integrated system successfully identified the four predominant types of chimerical BCR-ABL1 RNA (b3a2, b2a2, e1a2, and c3a2), which together account for 98% of CML cases. The integrated multiplex system also had a high sensitivity of detection (as little as 200 molecules of target RNA molecules). The integrated process saves time and effort, and it also the advantage of minimizing the steps needed for automated detection of different types of chimerical CML RNA.

Guidelines for the measurement of BCR-ABL1 transcripts in chronic myeloid leukaemia

Molecular testing for the BCR-ABL1 fusion gene by real time quantitative polymerase chain reaction (RT-qPCR) is the most sensitive routine approach for monitoring the response to therapy of patients with chronic myeloid leukaemia. In the context of tyrosine kinase inhibitor (TKI) therapy, the technique is most appropriate for patients who have achieved complete cytogenetic remission and can be used to define specific therapeutic milestones. To achieve this effectively, standardization of the laboratory procedures and the interpretation of results are essential. We present here consensus best practice guidelines for RT-qPCR testing, data interpretation and reporting that have been drawn up and agreed by a consortium of 21 testing laboratories in the United Kingdom and Ireland in accordance with the procedures of the UK Clinical Molecular Genetics Society.

Technical aspects and clinical applications of measuring BCR-ABL1 transcripts number in chronic myeloid leukemia

Chronic myeloid leukemia (CML) is a myeloproliferative disorder characterized by a triphasic clinical course, the morphologic expansion of a terminally differentiated myeloid cell and the presence of the BCR-ABL1 fusion gene, the hallmark of CML. The fusion gene is usually, but not always, associated with a Philadelphia chromosome, the result of a reciprocal exchange of genetic material between chromosome 22 and chromosome 9, which leads to the production of the activated BCR-ABL1 gene and oncoprotein. The breakpoint in the BCR gene occurs commonly downstream of exons e13 or e14 (M-BCR) and less frequently downstream of exons e1 and e2 (m-BCR). Less than 1% of cases carry a breakpoint downstream of exon 6 or 8 ("variant fusion genes") or exon 19 (mu-BCR). Breakpoints in the ABL1 gene cluster upstream of exon a2 (or of exon a3 in less than 5% of patients with CML). Conventional cytogenetic, fluorescence in situ hybridization, and molecular testing for the BCR-ABL1 fusion gene are key investigations for the diagnosis and monitoring of CML. Treatment using tyrosine kinase inhibitors has revolutionized the management of CML with hematologic and cytogenetic response within 12-18 months observed in >85% of patients. Nevertheless, between 15 and 20% of patients may evolve to blastic phase. Measurement of low level or "minimal" residual disease using molecular tests is becoming the gold-standard approach to measure response to therapy due to its higher sensitivity compared to other routine techniques. The technical aspects and clinical applications of molecular monitoring will be the main focus of this article.