Minimal residual disease in BCR::ABL1-positive acute lymphoblastic leukemia: different significance in typical ALL and in CML-like disease

Recently, we defined "CML-like" subtype of BCR::ABL1-positive acute lymphoblastic leukemia (ALL), resembling lymphoid blast crisis of chronic myeloid leukemia (CML). Here we retrospectively analyzed prognostic relevance of minimal residual disease (MRD) and other features in 147 children with BCR::ABL1-positive ALL (diagnosed I/2000-IV/2021, treated according to EsPhALL (n = 133) or other (n = 14) protocols), using DNA-based monitoring of BCR::ABL1 genomic breakpoint and clonal immunoglobulin/T-cell receptor gene rearrangements. Although overall prognosis of CML-like (n = 48) and typical ALL (n = 99) was similar (5-year-EFS 60% and 49%, respectively; 5-year-OS 75% and 73%, respectively), typical ALL presented more relapses while CML-like patients more often died in the first remission. Prognostic role of MRD was significant in the typical ALL (p = 0.0005 in multivariate analysis for EFS). In contrast, in CML-like patients MRD was not significant (p values > 0.2) and inapplicable for therapy adjustment. Moreover, in the typical ALL, risk-prediction could be further improved by considering initial hyperleukocytosis. Early distinguishing typical BCR::ABL1-positive ALL and CML-like patients is essential to enable optimal treatment approach in upcoming protocols. For the typical ALL, tyrosine-kinase inhibitors and concurrent chemotherapy with risk-directed intensity should be recommended; in the CML-like disease, no relevant prognostic feature applicable for therapy tailoring was found so far.

Impact of BCR::ABL1 transcript type on RT-qPCR amplification performance and molecular response to therapy

Several studies have reported that chronic myeloid leukaemia (CML) patients expressing e14a2 BCR::ABL1 have a faster molecular response to therapy compared to patients expressing e13a2. To explore the reason for this difference we undertook a detailed technical comparison of the commonly used Europe Against Cancer (EAC) BCR::ABL1 reverse transcriptase quantitative polymerase chain reaction (RT-qPCR) assay in European Treatment and Outcome Study (EUTOS) reference laboratories (n = 10). We found the amplification ratio of the e13a2 amplicon was 38% greater than e14a2 (p = 0.015), and the amplification efficiency was 2% greater (P = 0.17). This subtle difference led to measurable transcript-type dependent variation in estimates of residual disease which could be corrected by (i) taking the qPCR amplification efficiency into account, (ii) using alternative RT-qPCR approaches or (iii) droplet digital PCR (ddPCR), a technique which is relatively insensitive to differences in amplification kinetics. In CML patients, higher levels of BCR::ABL1/GUSB were identified at diagnosis for patients expressing e13a2 (n = 67) compared to e14a2 (n = 78) when analysed by RT-qPCR (P = 0.0005) but not ddPCR (P = 0.5). These data indicate that widely used RT-qPCR assays result in subtly different estimates of disease depending on BCR::ABL1 transcript type; these differences are small but may need to be considered for optimal patient management.

Analysis of chronic myeloid leukaemia during deep molecular response by genomic PCR: a traffic light stratification model with impact on treatment-free remission

This work investigated patient-specific genomic BCR-ABL1 fusions as markers of measurable residual disease (MRD) in chronic myeloid leukaemia, with a focus on relevance to treatment-free remission (TFR) after achievement of deep molecular response (DMR) on tyrosine kinase inhibitor (TKI) therapy. DNA and mRNA BCR-ABL1 measurements by qPCR were compared in 2189 samples (129 patients) and by digital PCR in 1279 sample (62 patients). A high correlation was found at levels of disease above MR4, but there was a poor correlation for samples during DMR. A combination of DNA and RNA MRD measurements resulted in a better prediction of molecular relapse-free survival (MRFS) after TKI stop (n = 17) or scheduled interruption (n = 25). At 18 months after treatment cessation, patients with stopped or interrupted TKI therapy who were DNA negative/RNA negative during DMR maintenance (green group) had an MRFS of 80% and 100%, respectively, compared with those who were DNA positive/RNA negative (MRFS = 57% and 67%, respectively; yellow group) or DNA positive/RNA positive (MRFS = 20% for both cohorts; red group). Thus, we propose a "traffic light" stratification as a TFR predictor based on DNA and mRNA BCR-ABL1 measurements during DMR maintenance before TKI cessation.

Metabolic profile of leukemia cells influences treatment efficacy of L-asparaginase

BACKGROUND

Effectiveness of L-asparaginase administration in acute lymphoblastic leukemia treatment is mirrored in the overall outcome of patients. Generally, leukemia patients differ in their sensitivity to L-asparaginase; however, the mechanism underlying their inter-individual differences is still not fully understood. We have previously shown that L-asparaginase rewires the biosynthetic and bioenergetic pathways of leukemia cells to activate both anti-leukemic and pro-survival processes. Herein, we investigated the relationship between the metabolic profile of leukemia cells and their sensitivity to currently used cytostatic drugs.

METHODS

Altogether, 19 leukemia cell lines, primary leukemia cells from 26 patients and 2 healthy controls were used. Glycolytic function and mitochondrial respiration were measured using Seahorse Bioanalyzer. Sensitivity to cytostatics was measured using MTS assay and/or absolute count and flow cytometry. Mitochondrial membrane potential was determined as TMRE fluorescence.

RESULTS

Using cell lines and primary patient samples we characterized the basal metabolic state of cells derived from different leukemia subtypes and assessed their sensitivity to cytostatic drugs. We found that leukemia cells cluster into distinct groups according to their metabolic profile. Lymphoid leukemia cell lines and patients sensitive to L-asparaginase clustered into the low glycolytic cluster. While lymphoid leukemia cells with lower sensitivity to L-asparaginase together with resistant normal mononuclear blood cells gathered into the high glycolytic cluster. Furthermore, we observed a correlation of specific metabolic parameters with the sensitivity to L-asparaginase. Greater ATP-linked respiration and lower basal mitochondrial membrane potential in cells significantly correlated with higher sensitivity to L-asparaginase. No such correlation was found in the other cytostatic drugs tested by us.

CONCLUSIONS

These data support that cell metabolism plays a prominent role in the treatment effect of L-asparaginase. Based on these findings, leukemia patients with lower sensitivity to L-asparaginase with no specific genetic characterization could be identified by their metabolic profile.

ERG deletions in childhood acute lymphoblastic leukemia with DUX4 rearrangements are mostly polyclonal, prognostically relevant and their detection rate strongly depends on screening method sensitivity

ERG-deletions occur recurrently in acute lymphoblastic leukemia, especially in the DUX4-rearranged subtype. The ERG-deletion was shown to positively impact prognosis of patients with IKZF1-deletion and its presence precludes assignment into IKZF1^plus group, a novel high-risk category on AIEOP-BFM ALL trials. We analyzed the impact of different methods on ERG-deletion detection rate, evaluated ERG-deletion as a potential marker for DUX4-rearranged leukemia, studied its associations with molecular and clinical characteristics within this leukemia subtype, and analyzed its clonality. Using single-nucleotide-polymorphism array, genomic polymerase chain reaction (PCR) and amplicon-sequencing we found ERG-deletion in 34% (16 of 47), 66% (33 of 50) and 78% (39 of 50) of DUX4-rearranged leukemia, respectively. False negativity of ERG-deletion by single-nucleotide-polymorphism array caused IKZF1^plus misclassification in 5 patients. No ERG-deletion was found outside the DUX4-rearranged cases. Within DUX4-rearranged leukemia, the ERG-deletion was associated with higher total number of copy-number aberrations, and, importantly, the ERG-deletion positivity by PCR was associated with better outcome [5-year event-free survival (EFS), ERG-deletion-positive 93% vs. ERG-deletion-negative 68%, P=0.022; 5-year overall survival (OS), ERG-deletion-positive 97% vs. ERG-deletion-negative 75%, P=0.029]. Ultra-deep amplicon-sequencing revealed distinct co-existing ERG-deletions in 22 of 24 patients. In conclusion, our data demonstrate inadequate sensitivity of single-nucleotide-polymorphism array for ERG-deletion detection, unacceptable for proper IKZF1^plus classification. Even using more sensitive methods (PCR/amplicon-sequencing) for its detection, ERG-deletion is absent in 22-34% of DUX4-rearranged leukemia and does not represent an adequately sensitive marker of this leukemia subtype. Importantly, the ERG-deletion potentially stratifies the DUX4-rearranged leukemia into biologically/clinically distinct subsets. Frequent polyclonal pattern of ERG-deletions shows that late origin of this lesion is more common than has been previously described.

Intragenic ERG Deletions Do Not Explain the Biology of ERG-Related Acute Lymphoblastic Leukemia

Intragenic ERG deletions occur in 3-5% of B-cell precursor acute lymphoblastic leukemia, specifically in B-other subtype lacking the classifying genetic lesions. They represent the only genetic lesion described so far present in the majority of cases clustering into a subgroup of B-other subtype characterized by a unique gene expression profile, probably sharing a common, however, not yet fully described, biological background. We aimed to elucidate whether ERG deletions could drive the specific biology of this ERG-related leukemia subgroup through expression of aberrant or decreased expression of wild type ERG isoforms. We showed that leukemic cells with endogenous ERG deletion express an aberrant transcript translated into two proteins in transfected cell lines and that one of these proteins colocalizes with wild type ERG. However, we did not confirm expression of the proteins in acute lymphoblastic leukemia cases with endogenous ERG deletion. ERG deletions resulted in significantly lower expression of wild type ERG transcripts compared to B-other cases without ERG deletion. However, cases with subclonal ERG deletion, clustering to the same ERG deletion associated subgroup, presented similar levels of wild type ERG as cases without ERG deletion. In conclusion, our data suggest that neither the expression of aberrant proteins from internally deleted allele nor the reduced expression of wild type ERG seem to provide a plausible explanation of the specific biology of ERG -related leukemia subgroup.

Slower early response to treatment and distinct expression profile of childhood high hyperdiploid acute lymphoblastic leukaemia with DNA index < 1.16

Acute lymphoblastic leukaemias (ALL) with 51-67 chromosomes are defined as high hyperdiploid (HHD) and are generally associated with good prognosis. However, several studies show heterogeneity in HHD ALL and suggest that the favourable prognosis is associated rather with higher ploidy defined by DNA index (DNAi) ≥ 1.16 or with a presence of specific single or combined trisomies. HHD ALL with DNAi < 1.16 are only rarely studied separately. Using single nucleotide polymorphism array, we analysed 89 childhood HHD ALL patients divided into groups with lower (<1.16; n = 34) and higher (≥1.16; n = 55) DNAi. We assessed treatment response, presence of secondary aberrations, mutations in RAS pathway genes and CREBBP and also gene expression profile (GEP) to reveal differences between the two subgroups. Cases with 51-54 chromosomes had DNAi 1.1-1.16 and cases with 55-67 chromosomes had DNAi ≥ 1.16. The groups with lower and higher DNAi had distinct response to early treatment and distinct GEP. The better response of the group with higher DNAi was associated with specific trisomies (trisomy of chromosome 10 or combined with trisomies 4 and/or 17). Our results suggest that cytogenetically defined HHD ALL can in fact be divided into two biologically distinguishable subgroups and that DNAi 1.16 is a relevant value to separate between the two. © 2016 Wiley Periodicals, Inc.

Characterization of 46 patient-specific BCR-ABL1 fusions and detection of SNPs upstream and downstream the breakpoints in chronic myeloid leukemia using next generation sequencing

In chronic myeloid leukemia, the identification of individual BCR-ABL1 fusions is required for the development of personalized medicine approach for minimal residual disease monitoring at the DNA level. Next generation sequencing (NGS) of amplicons larger than 1000 bp simplified and accelerated a process of characterization of patient-specific BCR-ABL1 genomic fusions. NGS of large regions upstream and downstream the individual breakpoints in BCR and ABL1 genes, respectively, also provided information about the sequence variants such are single nucleotide polymorphisms.

An unusual case of high hyperdiploid childhood ALL with cryptic BCR/ABL1 rearrangement

Background

Both high hyperdiploidy (HeH) and the translocation t(9;22)(q34;q11) are recurrent abnormalities in childhood B-cell acute lymphoblastic leukemia (ALL) and both are used in current classification to define different genetic and prognostic subtypes of the disease. The coexistence of these two primary genetic aberrations within the same clone is very rare in children with ALL. Here we report a new case of a 17-year-old girl with newly diagnosed ALL and uncommon cytogenetic and clinical finding combining high hyperdiploidy and a cryptic BCR/ABL1 fusion and an inherited Charcot-Marie-Tooth neuropathy detected during the induction treatment.

Results

High hyperdiploid karyotype 51,XX,+X,+4,+14,+17,+21 without apparent structural aberrations was detected by conventional cytogenetic analysis and multicolor FISH. A cryptic BCR/ABL1 fusion, which was caused by the insertion of part of the ABL1 gene into the 22q11 region, was proved in HeH clone by FISH, RT-PCR and CGH-SNP array. In addition, an abnormal FISH pattern previously described as the deletion of the 3′BCR region in some BCR/ABL1 positive cases was not proved in our patient.

Conclusion

A novel case of extremely rare childhood ALL, characterized by HeH and a cryptic BCR/ABL1 fusion, is presented and to the best of our knowledge described for the first time. The insertion of ABL1 into the BCR region in malignant cells is supposed. Clearly, further studies are needed to determine the genetic consequences and prognostic implications of these unusual cases.