Impact of two independent bone marrow samples on minimal residual disease monitoring in childhood acute lymphoblastic leukaemia

Minimal residual disease (MRD) diagnostics are used for risk group stratification in several acute lymphoblastic leukaemia (ALL) treatment protocols. It is, however, unclear whether MRD is homogeneously distributed within the bone marrow (BM) and whether this affects MRD diagnostics. We, therefore, analysed MRD levels in 141 paired BM samples (two independent punctures at different locations) from 26 ALL patients by real-time quantitative polymerase chain reaction (PCR) analysis of immunoglobulin and T-cell receptor gene rearrangements. MRD levels were comparable in 112 paired samples (79%), whereas two samples (both taken at day 15) had MRD levels that differed more than threefold. In the remaining 27 paired samples, MRD could be quantified or detected in one sample only. In four patients, MRD-based risk group classification was dependent on the site of BM puncture. Repetition of MRD analyses using 10-fold replicates instead of triplicates resolved most differences. In conclusion, MRD levels in paired BM samples were highly comparable, indicating that it is sufficient to analyse MRD in a single sample only. Nevertheless, MRD-based risk group classification can differ between paired BM samples, mainly because of variation below the quantitative range of the PCR assay rather than to a different distribution of leukaemic cells within the BM.     

Donor lymphocyte infusion for childhood acute lymphoblastic leukaemia relapsing after bone marrow transplantation

Four children with acute lymphoblastic leukaemia (ALL) who relapsed after allogeneic bone marrow transplantation (BMT) were treated with donor lymphocyte infusion (DLI) without prior conditioning. Three patients had previously received a non-T-cell-depleted matched sibling BMT and the fourth had a T-cell-depleted matched unrelated BMT. Two patients developed grade III–IV acute graft-versus-host-disease (GVHD) of the skin, which required intervention. Both are alive in complete haematological remission 7 and 10 months from DLI with chronic GVHD of the skin requiring immunosuppressive therapy. A third patient went into haematological remission 6 weeks after DLI, but with no clinical evidence of GVHD. His bone marrow remained in remission 11 months post-DLI despite the disease (ALL) relapsing in extramedullary sites. The fourth patient showed no clinical or haematological response to three consecutive doses of DLI given at 4-weekly intervals and died from progressive disease 11 months after relapse. These preliminary observations indicate that in constrast to experience in adult ALL, DLI may be effective in inducing sustained remission in children with ALL relapsing after BMT, and a response may occur even in the absence of clinical evidence of GVHD.     

Residual leukaemia after bone marrow transplant in children with acute lymphoblastic leukaemia after first haematological relapse or with poor initial presenting features

Relapse is the major obstacle to cure for children with acute lymphoblastic leukaemia (ALL) after allogeneic bone marrow transplant (BMT). Development of salvage therapy for post-transplant relapse could be expedited by understanding the post-transplant behaviour of microscopically undetectable leukaemia and the ability to predict impending relapse. We have used a quantitative polymerase chain reaction method (sensitivity of 5.0 x 10-6) to measure residual leukaemia before the conditioning regimen, and at five time-points after transplantation. In total, 18 patients with ALL transplanted in first or second remission were studied for 1 year: For the first year post BMT, 12 remained in remission, four had haematological relapses, one had a cutaneous relapse, and one died of severe graft-versus-host disease. The post-engraftment levels of the leukaemia-specific immunoglobulin heavy (IgH) chain gene rearrangement for patients with haematological relapses were significantly different from those who remained in remission. The levels for the patients who remained in remission decreased with time, although there were occasional increases consistent with the known standard deviation of the measurement assay. In contrast, all clinical relapses were preceded by a rapid increase in levels. Both the rate of this increase and its timing were variable. These results suggest that residual leukaemia measurements can be used to direct post-transplant interventions and measure their effects.     

Clinical significance of minimal residual disease in patients with acute leukaemia undergoing haematopoietic stem cell transplantation

In patients with acute leukaemia, the relative risk of relapse influences the choice between chemotherapy and haematopoietic stem cell transplantation (HSCT). The demonstration that minimal residual disease (MRD) is the strongest overall prognostic indicator and can identify patients who are unlikely to be cured by standard chemotherapy has added a powerful new factor to consider when making this decision. There is substantial data indicating that the likelihood of relapse after transplant is directly correlated with levels of MRD before transplant. This knowledge can be used to adjust the timing of HSCT, and guide the selection of donor, conditioning regimen, and post‐HSCT strategies to maximize the graft‐versus‐leukaemia effect. Because MRD emerging post‐transplant carries a dire prognosis, its detection can trigger withdrawal of immunosuppression, additional cellular and molecular therapies, or preparations for a second HSCT. Although it is not yet clear whether any of these actions will significantly improve outcome, it is likely that they will be most effective for patients with a relatively low tumour burden, who can be identified only through MRD testing. In this article, we review the clinical significance of MRD in the context of autologous and allogeneic HSCT.     

Minimal residual disease detection after allogeneic stem cell transplantation is correlated to relapse in patients with acute lymphoblastic leukaemia

Minimal residual disease (MRD) assessments were performed retrospectively after allogeneic stem cell transplantation (SCT) in 32 patients (23 children and nine adults) with acute lymphoblastic leukaemia (ALL). Using immunoglobulin and T-cell receptor rearrangements as clonal markers, MRD was detected after SCT in nine patients, eight of whom have relapsed. The median time between first MRD detection and relapse was 5.5 (range 0.5-30) months. In 23 patients without MRD, six have relapsed to date: lower sensitivity, central nervous system relapse and clonal exchange of the leukaemic clone were factors that may explain the failure to detect MRD before relapse in these patients. In univariate analysis, factors associated with decreased risk of relapse were transplantation in first remission (P=0.02), the combination of acute and chronic graft-versus-host disease (P=0.03) and absence of MRD after SCT (P=0.005). In multivariate analysis, only MRD detection after SCT was significantly associated with increased risk of relapse (P=0.05). In conclusion, MRD detection after SCT is correlated with relapse and provides the opportunity for initiating immunotherapeutic intervention at an early stage when the tumour cell burden is still low.     

Defining the correct role of minimal residual disease tests in the management of acute lymphoblastic leukaemia

Minimal residual disease (MRD) has acquired a prominent role in the management of childhood and adult Acute Lymphoblastic Leukaemia (ALL) for its high prognostic value. Several studies have demonstrated the strong association between MRD and risk of relapse in childhood and adult ALL, irrespective of the methodology used. MRD is now used in clinical trials for risk assignment and to guide clinical management. Negativity at early time points may be considered to decrease treatment burden in patients who are likely to be cured with reduced intensity regimens. On the other hand, high MRD levels at late time points (end of consolidation) define ALL subgroups which deserve investigation of more effective treatments. The predictivity of MRD as a measurement of drug response in vivo opened new perspectives for its use in clinical decision, to deliver risk-based treatments, and possibly as a surrogate for efficacy in the evaluation of novel therapeutic approaches.     

Low burden of minimal residual disease prior to transplantation in children with very high risk acute lymphoblastic leukaemia: The NOPHO ALL2008 experience

The population-based Nordic/Baltic acute lymphoblastic leukaemia (ALL) Nordic Society for Paediatric Haematology and Oncology (NOPHO) ALL2008 protocol combined minimal residual disease (MRD)-driven treatment stratification with very intense first line chemotherapy for patients with high risk ALL. Patients with MRD ≥5% at end of induction or ≥10⁻³ at end of consolidation or following two high risk blocks were eligible for haematopoietic cell transplantation (HCT) in first remission. After at least three high risk blocks a total of 71 children received HCT, of which 46 had MRD ≥5% at end of induction. Ten patients stratified to HCT were not transplanted; 12 received HCT without protocol indication. Among 69 patients with evaluable pre-HCT MRD results, 22 were MRD-positive, one with MRD ≥10⁻³. After a median follow-up of 5·5 years, the cumulative incidence of relapse was 23·5% (95% confidence interval [CI]: 10·5–47·7) for MRD-positive versus 5·1% (95% CI: 1·3–19·2), P = 0·02) for MRD-negative patients. MRD was the only variable significantly associated with relapse (hazard ratio 9·1, 95% CI: 1·6–51·0, P = 0·012). Non-relapse mortality did not differ between the two groups, resulting in disease-free survival of 85·6% (95% CI: 75·4–97·2) and 67·4% (95% CI: 50·2–90·5), respectively. In conclusion, NOPHO block treatment efficiently reduced residual leukaemia which, combined with modern transplant procedures, provided high survival rates, also among pre-HCT MRD-positive patients.     

Clinical value of immunological monitoring of minimal residual disease in acute lymphoblastic leukaemia after allogeneic transplantation

In this study, we used multiparameter flow cytometry to quantify minimal residual disease (MRD) in 165 serial bone marrow samples from 40 patients diagnosed with acute lymphoblastic leukaemia (ALL) who underwent allogeneic stem cell transplantation (allo-SCT) from siblings (n = 34) or unrelated donors (n = 6). Samples were prospectively taken from 24 patients before starting the conditioning regimen, at days +30, +60 and +90 and subsequently every 2-3 months. Samples from 16 patients in complete remission (CR) after allo-SCT were taken at least twice. Six of 24 patients harboured MRD (0.2-10% of mononuclear cells) at transplant and 18 were negative. Estimated disease-free survival for the MRD+ and MRD- groups at transplant was 33.3% and 73.5% respectively (P = 0.03). During follow-up, increasing MRD levels were detected in nine patients, a finding that preceded marrow relapse by 1-6 months. Two patients with stable low MRD levels remained in CR. When we used flow cytometry to test the effect of donor leucocyte infusions (DLI) in six patients, we observed that the only sustained remission was achieved when DLI was applied prior to overt relapse. We conclude that MRD by flow cytometry can rapidly assess tumoral burden before transplant to predict outcome, and can be clinically useful for the timing of DLI for increasing levels of leukaemia after transplant.     

Pre‐ and post‐transplant minimal residual disease predicts relapse occurrence in children with acute lymphoblastic leukaemia

Relapse remains the leading cause of treatment failure in children with acute lymphoblastic leukaemia (ALL) undergoing allogeneic haematopoietic stem cell transplantation (HSCT). We retrospectively investigated the prognostic role of minimal residual disease (MRD) before and after HSCT in 119 children transplanted in complete remission (CR). MRD was measured by polymerase chain reaction in bone marrow samples collected pre‐HSCT and during the first and third trimesters after HSCT (post‐HSCT1 and post‐HSCT3). The overall event‐free survival (EFS) was 50%. The cumulative incidence of relapse and non‐relapse mortality was 41% and 9%. Any degree of detectable pre‐HSCT MRD was associated with poor outcome: EFS was 39% and 18% in patients with MRD positivity <1 × 10⁻³ and ≥1 × 10⁻³, respectively, versus 73% in MRD‐negative patients (P < 0·001). This effect was maintained in different disease remissions, but low‐level MRD had a very strong negative impact only in patients transplanted in second or further CR. Also, MRD after HSCT enabled patients to be stratified, with increasing MRD between post‐HSCT1 and post‐HSCT3 clearly defining cohorts with a different outcome. MRD is an important prognostic factor both before and after transplantation. Given that MRD persistence after HSCT is associated with dismal outcome, these patients could benefit from early discontinuation of immunosuppression, or pre‐emptive immuno‐therapy.     

Detection of minimal residual disease in childhood acute lymphoblastic leukaemia using fluorescence in-situ hybridization

Summary. Using centromere-specific probes and a fluorescence in-situ hybridization (FISH) technique in cases of childhood hyperdiploid acute lymphoblastic leukaemia (ALL), cells with extra copies of chromosomes can be differentiated from normal cells by their extra signals in both metaphase and interphase nuclei. In this way the entire cell population, not only those cells in division, can be analysed, thereby providing a valuable technique not only for determining leukaemia cell karyotype at diagnosis but also for the detection of minimal residual disease (MRD). We have conducted 161 analyses of remission bone marrow aspirates (BMs) in 13 children with hyperdiploid ALL. Slides were analysed blind and in parallel to 35 control samples. Control BMs showed very low numbers of trisomic cells (mean ± 2 × SD = 013 ± 0.34%). MRD was detected in 5/13 cases of ALL investigated while on chemotherapy. One out of five newly diagnosed cases and all three relapse cases of ALL had significantly raised levels of hyperdiploid cells in day 28 BMs. The presence of detectable disease in day 28 BMs suggests the need for larger studies to find whether this data is of prognostic value.     

Monitoring minimal residual disease in peripheral blood in B-lineage acute lymphoblastic leukaemia

The use of peripheral blood rather than marrow has potential advantages for monitoring minimal residual disease during the treatment of leukaemia. To determine the feasibility of using blood, we used a sensitive polymerase chain reaction method to quantify leukaemia in the blood and marrow in 35 paired samples from 15 children during induction treatment. Leukaemic cells in the blood ranged from 1.1 × 10⁻² to < 9.4 × 10⁻⁷ leukaemic cells/total cells, corresponding to 1.3 × 10⁷ to < 2 × 10³ leukaemic cells/l. In 15 paired samples, leukaemia could be quantified in both tissues and in 20 paired samples, leukaemia was not detected in one or both tissues so that only upper level limits could be set. In the former 15 pairs, the level of leukaemia in peripheral blood was directly proportional to that in marrow but was a mean of 11.7-fold lower. Leukaemia in blood was detected in 10/12 pairs in which the level in marrow was > 10⁻⁴, but in only two of 13 pairs in which the level in marrow was < 10⁻⁵. Patients studied at multiple time-points showed parallel declines in the number of leukaemic cells in both tissues. The results showed that leukaemia could be monitored in peripheral blood during induction therapy, and quantitative considerations based on the results suggest that monitoring of blood during post-induction therapy may be of value in detecting molecular relapse.     

Preventing relapse after haematopoietic stem cell transplantation for acute leukaemia: the role of post‐transplantation minimal residual disease (MRD) monitoring and MRD‐directed intervention

Relapse is the main cause of treatment failure after allogeneic haematopoietic stem cell transplantation (allo‐HSCT) for acute leukaemia (AL). Post‐transplantation minimal residual disease (MRD) monitoring enables risk stratification and identifies AL patients at higher risk of relapse. MRD assessment primarily involves the determination of leukaemia‐associated immunophenotypic patterns using multiparameter flow cytometry, and the polymerase chain reaction (PCR)‐based evaluation of expression levels of leukaemia‐related genes (specific reciprocal gene rearrangements and other mutation types). In addition, next generation sequencing and digital PCR may further enrich current MRD detection. Several MRD‐directed interventions have demonstrated the ability to reduce the risk of relapse with acceptable treatment‐related toxicities. Donor lymphocyte infusion (DLI) is the most important intervention for MRD‐positive patients, while several modified strategies, such as granulocyte colony‐stimulating factor–mobilized peripheral blood cells followed by short term immune suppression and escalating dose regimen, further improve the safety and efficacy of DLI. Interferon therapy, targeted drugs, and hypomethylating agents have also been introduced for MRD‐directed interventions. Referring to the issues of whether and who would benefit from pre‐emptive intervention according to MRD, in this review, we summarized this rapidly evolving area of MRD monitoring and MRD‐directed interventions in AL patients after allo‐HSCT.     

Clinical significance of minimal residual disease at day 15 and at the end of therapy in childhood acute lymphoblastic leukaemia

Detection of minimal residual disease (MRD) after induction and consolidation therapy is highly predictive of outcome for childhood acute lymphoblastic leukaemia (ALL) and is used to identify patients at high risk of relapse in several current clinical trials. To evaluate the prognostic significance of MRD at other treatment phases, MRD was measured by real-time quantitative polymerase chain reaction on a selected group of 108 patients enrolled on the Australian and New Zealand Children's Cancer Study Group Study VII including 36 patients with a bone marrow or central nervous system relapse and 72 matched patients in first remission. MRD was prognostic of outcome at all five treatment phases tested: at day 15 (MRD ≥ 5 × 10⁻², log rank P  < 0·0001), day 35 (≥1 × 10⁻², P  = 0·0001), 4 months (≥5 × 10⁻⁴, P  < 0·0001), 12 months (MRD ≥ 1 × 10⁻⁴, P  = 0·006) and 24 months (MRD ≥ 1 × 10⁻⁴, P  < 0·0001). Day 15 was the best early MRD time-point to differentiate between patients with high, intermediate and low risk of relapse. MRD testing at 12 and particularly at 24 months, detected molecular relapses in some patients up to 6 months before clinical relapse. This raised the question of whether a strategy of late monitoring and salvage therapy will improve outcome.     

Epstein-Barr virus associated B-cell lymphoma after autologous bone marrow transplantation for T-cell acute lymphoblastic leukaemia

Epstein-Barr virus associated lymphoproliferative disease after autologous bone marrow transplantation (ABMT) has rarely been reported. We report a case of B-cell lymphoma following ABMT for T-acute lymphoblastic leukaemia; bone marrow was purged in vitro with monoclonal antibodies to remove T cells. Immunoglobulin and T-cell receptor gene rearrangement studies were used to demonstrate clonality and to show that this patient developed a second neoplasm after ABMT. EBV proteins and genome (type A) were present in post-transplantation lymphoma, suggesting a causative role in its development.     

Persistent MRD before and after allogeneic BMT predicts relapse in children with acute lymphoblastic leukaemia

Minimal residual disease (MRD) during early chemotherapy is a powerful predictor of relapse in acute lymphoblastic leukaemia (ALL) and is used in children to determine eligibility for allogeneic haematopoietic stem cell transplantation (HSCT) in first (CR1) or later complete remission (CR2/CR3). Variables affecting HSCT outcome were analysed in 81 children from the ANZCHOG ALL8 trial. The major cause of treatment failure was relapse, with a cumulative incidence of relapse at 5 years (CIR) of 32% and treatment‐related mortality of 8%. Leukaemia‐free survival (LFS) and overall survival (OS) were similar for HSCT in CR1 (LFS 62%, OS 83%, n = 41) or CR2/CR3 (LFS 60%, OS 72%, n = 40). Patients achieving bone marrow MRD negativity pre‐HSCT had better outcomes (LFS 83%, OS 92%) than those with persistent MRD pre‐HSCT (LFS 41%, OS 64%, P < 0·0001) or post‐HSCT (LFS 35%, OS 55%, P < 0·0001). Patients with B‐other ALL had more relapses (CIR 50%, LFS 41%) than T‐ALL and the main precursor‐B subtypes including BCR‐ABL1, KMT2A (MLL), ETV6‐RUNX1 (TEL‐AML1) and hyperdiploidy >50. A Cox multivariate regression model for LFS retained both B‐other ALL subtype (hazard ratio 4·1, P = 0·0062) and MRD persistence post‐HSCT (hazard ratio 3·9, P = 0·0070) as independent adverse prognostic variables. Persistent MRD could be used to direct post‐HSCT therapy.     

Outcome prediction by immunophenotypic minimal residual disease detection in adult T-cell acute lymphoblastic leukaemia

Flow-cytometric detection of minimal residual disease (MRD) identifies patients with high relapse risk in childhood acute lymphoblastic leukaemia (ALL). We studied the efficacy of this method in adult T-ALL treated with the Italian co-operative GIMEMA (Gruppo Italiano Malattie Ematologiche dell'Adulto) LAL0496 protocol. Bone marrow samples from 53 patients were taken at fixed treatment time points and MRD was analysed using a leukaemia-specific immunophenotype (cytoplasmic-CD3/nuclear-terminal desoxynucleotidyl transferase). The median follow-up was 17 months (range 3-61) and a median of 4.5 analyses/patient was performed (range 3-12). Six out of 53 (11.3%) patients were refractory to treatment, 30/53 (56.6%) relapsed and 17/53 (32.1%) remain in continuous complete remission. The probability of relapse at 2 years for MRD-positive patients at preconsolidation was 81.5%vs 38.9% for MRD-negative patients (P = 0.00078). This risk was still 54.5% for MRD-positive vs 15.8% for MRD-negative patients pre-third reinduction (P = 0.0098) and 50.0% for MRD-positive vs 16.4% for MRD-negative patients pre-sixth reinduction (P = 0.032). The relapse-predicting value of MRD did not depend on features at diagnosis such as age, sex and leucocyte count. Our data suggest that immunophenotypic MRD monitoring in the first year of treatment is a useful outcome predictor for adult T-ALL patients.     

Concurrent detection of minimal residual disease (MRD) in childhood acute lymphoblastic leukaemia by flow cytometry and real-time PCR

Minimal (i.e. submicroscopic) residual disease (MRD) predicts outcome in childhood acute lymphoblastic leukaemia (ALL). To be used clinically, MRD assays must be reliable and accurate. Two well-established techniques, flow cytometry (FC) and polymerase chain reaction (PCR), can detect leukaemic cells with a sensitivity of 0.01% (10(-4)). We analysed diagnostic samples of 45 ALL-patients (37 B-lineage ALL, eight T-lineage ALL) by four-colour FC and real-time PCR. Leukaemia-associated immunophenotypes, at a sensitivity of MRD detection by FC at the 0.01% level, were identified in 41 cases (91%); antigen-receptor gene rearrangements suitable for MRD detection with a sensitivity of 0.01% or better by PCR were identified in 38 cases (84%). The combined use of FC and PCR allowed MRD monitoring in all 45 patients. In 105 follow-up samples, MRD estimates by both methods were highly concordant, with a deviation factor of <5 by Bland-Altman analysis. Importantly, the concordance between FC and PCR was also observed in regenerating bone marrow samples containing high proportions of CD19(+) cells, and in samples studied 24 h after collection. We conclude that both MRD assays yield generally concordant results. Their combined use should enable MRD monitoring in virtually all patients and prevent false-negative results due to clonal evolution or phenotypic shifts.     

Implications of delayed bone marrow aspirations at the end of treatment induction for risk stratification and outcome in children with acute lymphoblastic leukaemia

Minimal residual disease (MRD) at the end of induction therapy is important for risk stratification of acute lymphoblastic leukaemia (ALL), but bone marrow (BM) aspiration is often postponed or must be repeated to fulfil qualitative and quantitative criteria for morphological assessment of haematological remission and/or MRD analysis. The impact of BM aspiration delay on measured MRD levels and resulting risk stratification is currently unknown. We analysed paired MRD data of 289 paediatric ALL patients requiring a repeat BM aspiration. MRD levels differed in 108 patients (37%) with a decrease in the majority (85/108). This would have resulted in different risk group allocation in 64 of 289 patients (23%) when applying the ALL‐Berlin‐Frankfurt‐Münster 2000 criteria. MRD change was associated with the duration of delay; 40% of patients with delay ≥7 days had a shift to lower MRD levels compared to only 18% after a shorter delay. Patients MRD‐positive at the original but MRD‐negative at the repeat BM aspiration (n = 50) had a worse 5‐year event‐free survival than those already negative at first aspiration (n = 115) (86 ± 5% vs. 94 ± 2%; P = 0·024). We conclude that BM aspirations should be pursued as scheduled in the protocol because delayed MRD sampling at end of induction may result in false‐low MRD load and distort MRD‐based risk assessment.