Relationship between minimal residual disease measured by multiparametric flow cytometry prior to allogeneic hematopoietic stem cell transplantation and outcome in children with acute lymphoblastic leukemia

The evolution of minimal residual disease: key insights based on a bibliometric visualization analysis from 2002 to 2022

Background

The topic of minimal residual disease (MRD) has emerged as a crucial subject matter in the domain of oncology in recent years. The detection and monitoring of MRD have become essential for the diagnosis, treatment, and prognosis of various types of malignancy.

Aims

The purpose of this study is to explore the research trends, hotspots, and frontiers of MRD in the last two decades through bibliometric analysis.

Methods

We employed Web of Science databases to carry out a bibliometric visualization analysis of research on 8,913 academic papers about MRD research from 2002 to 2022. VOSviewer, CiteSpace, RStudio, and a bibliometric online analysis platform were mainly used to conduct co-occurrence analysis and cooperative relationship analysis of countries/regions, institutions, journals, and authors in the literature. Furthermore, co-occurrence, co-citation, and burst analyses of keyword and reference were also conducted to generate relevant knowledge maps.

Results

In the past 20 years, the number of MRD research papers has presented an overall rising trend, going through three stages: a plateau, development, and an explosion. The output of articles in the United States was notably superior and plays a dominant role in this field, and the Netherlands had the highest average citation per article. The most productive and influential institution was the University of Texas MD Anderson Cancer Center. Blood published the most papers and was the most cited journal. A collection of leading academics has come to the fore in the research field, the most prolific of which is Kantarjian HM. It was found that the application of MRD in "acute myeloid leukemia", "acute lymphoblastic leukemia", "multiple myeloma", as well as the detection technology of MRD, are the research hotspots and frontiers in this domain. Furthermore, we analyzed the co-citation network of references and found that the top 10 co-cited references were all associated with MRD in hematological malignancies.

Conclusion

This bibliometric visualization analysis conducted a thorough exploration into the research hotspots and trends in MRD from 2002 to 2022. Our findings can aid researchers in recognizing possible collaborations, guiding future research directions, and fostering the growth of MRD detection and monitoring technologies.

[Comparison of prognostic significance between multiparameter flow cytometry and real-time quantitative polymerase chain reaction in the detection of minimal residual disease of Philadelphia chromosome-positive acute B lymphocytic leukemia before allogeneic hematopoietic stem cell transplantation]

目的

探讨多参数流式细胞术（MFC）与实时定量聚合酶链反应技术（RQ-PCR）两种方法检测费城染色体阳性（Ph⁺）急性B淋巴细胞白血病（B-ALL）患者异基因造血干细胞移植（allo-HSCT）前微小残留病（MRD）的预后意义。

方法

回顾性分析2014年7月至2018年2月在北京大学血液病研究所接受allo-HSCT的280例Ph⁺ B-ALL患者，同时用MFC和RQ-PCR法（检测BCR-ABL融合基因表达）检测移植前MRD。

结果

RQ-PCR与MFC检测MRD具有相关性（rs＝0.435，P<0.001）。MFC、RQ-PCR法检测移植前MRD的阳性率分别为25.7％（72/280）、60.7％（170/280）。移植前MFC-MRD阳性组患者移植后白血病3年累积复发率（CIR）明显高于MFC-MRD阴性组（23.6％对8.6％，P<0.001）。RQ-PCR检测BCR/ABL融合基因阳性组（RQ-PCR MRD阳性组）的3年CIR、非复发死亡（NRM）、无白血病生存（LFS）、总生存（OS）与BCR/ABL融合基因阴性组（RQ-PCR MRD阴性组）相比差异均无统计学意义（P>0.05）。移植前RQ-PCR MRD≥1％组比<1％组具有更高的3年CIR（23.1％对11.4％，P＝0.032）、更低的LFS率（53.8％对74.4％，P＝0.015）与OS率（57.7％对79.1％，P＝0.009）。多因素分析显示，移植前MFC-MRD阳性是影响移植后CIR的危险因素（HR＝2.488，95％CI1.216～5.088，P＝0.013），移植前RQ-PCR MRD≥1％是影响LFS（HR＝2.272，95％CI 1.225～4.215，P<0.001）、OS（HR＝2.472，95％ CI 1.289～4.739，P＝0.006）的危险因素。MFC检测MRD预测复发的敏感性、特异性、阳性预测值（PPV）、阴性预测值（NPV）分别为48.50％、77.56％、23.62％、87.16％。以RQ-PCR MRD≥1％预测复发的敏感性、特异性、PPV、NPV分别为23.00％、88.59％、17.15％、91.84％。移植前MFC-MRD阳性或RQ-PCR MRD≥1％二者任一成立为指标预测移植后复发的敏感性、特异性、PPV、NPV分别为54.29％、73.88％、45.70％、91.87％。

结论

MFC和RQ-PCR法检测移植前MRD水平均可预测Ph⁺ B-ALL患者移植预后。移植前MFC-MRD阳性是移植后复发的危险因素。联合使用两种方法（移植前MFC-MRD阳性状态或RQ-PCR MRD≥1％成立）可提高预测移植后复发的敏感性、阳性预测值与阴性预测值，有助于更好筛选出高危患者。

A risk score system for stratifying the risk of relapse in B cell acute lymphocytic leukemia patients after allogenic stem cell transplantation

BACKGROUND

For patients with B cell acute lymphocytic leukemia (B-ALL) who underwent allogeneic stem cell transplantation (allo-SCT), many variables have been demonstrated to be associated with leukemia relapse. In this study, we attempted to establish a risk score system to predict transplant outcomes more precisely in patients with B-ALL after allo-SCT.

METHODS

A total of 477 patients with B-ALL who underwent allo-SCT at Peking University People's Hospital from December 2010 to December 2015 were enrolled in this retrospective study. We aimed to evaluate the factors associated with transplant outcomes after allo-SCT, and establish a risk score to identify patients with different probabilities of relapse. The univariate and multivariate analyses were performed with the Cox proportional hazards model with time-dependent variables.

RESULTS

All patients achieved neutrophil engraftment, and 95.4% of patients achieved platelet engraftment. The 5-year cumulative incidence of relapse (CIR), overall survival (OS), leukemia-free survival (LFS), and non-relapse mortality were 20.7%, 70.4%, 65.6%, and 13.9%, respectively. Multivariate analysis showed that patients with positive post-transplantation minimal residual disease (MRD), transplanted beyond the first complete remission (≥CR2), and without chronic graft-versus-host disease (cGVHD) had higher CIR (P  < 0.001, P = 0.004, and P  < 0.001, respectively) and worse LFS (P  < 0.001, P = 0.017, and P  < 0.001, respectively), and OS (P  < 0.001, P = 0.009, and P  < 0.001, respectively) than patients without MRD after transplantation, transplanted in CR1, and with cGVHD. A risk score for predicting relapse was formulated with the three above variables. The 5-year relapse rates were 6.3%, 16.6%, 55.9%, and 81.8% for patients with scores of 0, 1, 2, and 3 (P  < 0.001), respectively, while the 5-year LFS and OS values decreased with increasing risk score.

CONCLUSION

This new risk score system might stratify patients with different risks of relapse, which could guide treatment.

National Institutes of Health Consensus Development Project on Criteria for Clinical Trials in Chronic Graft-versus-Host Disease: I. The 2020 Etiology and Prevention Working Group Report

Preventing chronic graft-versus-host disease (GVHD) remains challenging because the unique cellular and molecular pathways that incite chronic GVHD are poorly understood. One major point of intervention for potential prevention of chronic GVHD occurs at the time of transplantation when acute donor anti-recipient immune responses first set the events in motion that result in chronic GVHD. After transplantation, additional insults causing tissue injury can incite aberrant immune responses and loss of tolerance, further contributing to chronic GVHD. Points of intervention are actively being identified so that chronic GVHD initiation pathways can be targeted without affecting immune function. The major objective in the field is to continue basic studies and to translate what is learned about etiopathology to develop targeted prevention strategies that decrease the risk of morbid chronic GVHD without increasing the risks of cancer relapse or infection. Development of strategies to predict the risk of developing debilitating or deadly chronic GVHD is a high research priority. This working group recommends further interrogation into the mechanisms underpinning chronic GVHD development, and we highlight considerations for future trial design in prevention trials.

Novel Biomarkers for Outcome After Allogeneic Hematopoietic Stem Cell Transplantation

Allogeneic hematopoietic stem cell transplantation (allo-HSCT) is a well-established curative treatment for various malignant hematological diseases. However, its clinical success is substantially limited by major complications including graft-vs.-host disease (GVHD) and relapse of the underlying disease. Although these complications are known to lead to significant morbidity and mortality, standardized pathways for risk stratification of patients undergoing allo-HSCT are lacking. Recent advances in the development of diagnostic and prognostic tools have allowed the identification of biomarkers in order to predict outcome after allo-HSCT. This review will provide a summary of clinically relevant biomarkers that have been studied to predict the development of acute GVHD, the responsiveness of affected patients to immunosuppressive treatment and the risk of non-relapse mortality. Furthermore, biomarkers associated with increased risk of relapse and subsequent mortality will be discussed.

Different Effects of Pre-transplantation Measurable Residual Disease on Outcomes According to Transplant Modality in Patients With Philadelphia Chromosome Positive ALL

Background: This study compared the effects of pre-transplantation measurable residual disease (pre-MRD) on outcomes in Philadelphia chromosome (Ph)-positive ALL patients who underwent human leukocyte antigen-matched sibling donor transplantation (MSDT) or who received unmanipulated haploidentical SCT (haplo-SCT). Methods: A retrospective study (n = 202) was performed. MRD was detected by RT-PCR and multiparameter flow cytometry. Results: In the total patient group, patients with positive pre-MRD had a higher 4-year cumulative incidence of relapse (CIR) than that in patients with negative pre-MRD (26.1% vs. 12.1%, P = 0.009); however, the cumulative incidence of non-relapse mortality (NRM) (7.4% vs. 15.9%, P = 0.148), probability of leukemia-free survival (LFS) (66.3% vs. 71.4%, P = 0.480), and overall survival (OS) (68.8% vs. 76.5%, P = 0.322) were comparable. In the MSDT group, patients with positive pre-MRD had increased 4-year CIR (56.4% vs. 13.8%, P < 0.001) and decreased 4-year LFS (35.9% vs. 71.0%, P = 0.024) and OS (35.9% vs. 77.6%, P = 0.011) compared with those with negative pre-MRD. In haplo-SCT settings, the 4-year CIR (14.8% vs. 10.7%, P = 0.297), NRM (7.3% vs. 16.3%, P = 0.187) and the 4-year probability of OS (77.7% vs. 72.3%, P = 0.804) and LFS (80.5% vs. 75.7%, P = 0.660) were comparable between pre-MRD positive and negative groups. In subgroup patients with positive pre-MRD, haplo-SCT had a lower 4-year CIR (14.8% vs. 56.4%, P = 0.021) and a higher 4-year LFS (77.7% vs. 35.9%, P = 0.036) and OS (80.5% vs. 35.9%, P = 0.027) than those of MSDT. Multivariate analysis showed that haplo-SCT was associated with lower CIR (HR, 0.288; P = 0.031), superior LFS (HR, 0.283; P = 0.019) and OS (HR, 0.252; P = 0.013) in cases with a positive pre-MRD subgroup. Conclusions: Our results indicate that the effects of positive pre-MRD on the outcomes of patients with Ph-positive ALL are different according to transplant modality. For Ph-positive cases with positive pre-MRD, haplo-SCT might have strong graft-vs.-leukemia (GVL) effects.

Allogeneic stem cell transplantation in the era of novel therapies for acute lymphoblastic leukaemia

Immunotherapy is changing the treatment of acute lymphoblastic leukaemia (ALL) in adults and children. However, regardless of these new therapies, allogeneic hematopoietic cell transplantation (allo-HCT) still play a key role in the treatment of ALL, although it is uncertain how these new therapies will impact on the transplant procedure and indications. This article reviews the indications of allo-HCT for children and adults diagnosed with ALL, the different sources and conditioning regimens for transplantation as well as the role of measurable residual diseases pre- and post-HCT in the era of the new therapies for ALL.

Minimal residual disease status determined by multiparametric flow cytometry pretransplantation predicts the outcome of patients with ALL receiving unmanipulated haploidentical allografts

This study evaluated the effects of pretransplantation minimal residual disease (pre-MRD) on outcomes of patients with acute lymphoblastic leukemia (ALL) who underwent unmanipulated haploidentical stem cell transplantation (haplo-SCT). A retrospective study including 543 patients with ALL was performed. MRD was determined using multiparametric flow cytometry. Both in the entire cohort of patients and in subgroup cases with T-ALL or B-ALL, patients with positive pre-MRD had a higher incidence of relapse (CIR) than those with negative pre-MRD in MSDT settings (P < 0.01 for all). Landmark analysis at 6 months showed that MRD positivity was significantly and independently associated with inferior rates of relapse (HR, 1.908; P = 0.007), leukemia-free survival (LFS) (HR, 1.559; P = 0.038), and OS (HR, 1.545; P = 0.049). The levels of pre-MRD according to a logarithmic scale were also associated with leukemia relapse, LFS, and OS, except that cases with MRD <0.01% experienced comparable CIR and LFS to those with negative pre-MRD. A risk score for CIR was developed using the variables pre-MRD, disease status, and immunophenotype of ALL. The CIR was 14%, 26%, and 59% for subjects with scores of 0, 1, and 2-3, respectively (P < 0.001). Three-year LFS was 75%, 64%, and 42%, respectively (P < 0.001). Multivariate analysis confirmed the association of the risk score with CIR and LFS. The results indicate that positive pre-MRD, except for low level one (MRD < 0.01%), is associated with poor outcomes in patients with ALL who underwent unmanipulated haplo-SCT.

Recommendations for the assessment and management of measurable residual disease in adults with acute lymphoblastic leukemia: A consensus of North American experts

Measurable residual disease (MRD) that persists after initial therapy is a powerful predictor of relapse and survival in acute lymphoblastic leukemia (ALL). However, the optimal use of this information to influence therapeutic decisions is controversial. Herein, we comprehensively review the role of MRD assessment in adults with ALL, including methods to quantify residual leukemia cells during remission, prognostic impact of MRD across ALL subtypes, and available therapeutic approaches to eradicate MRD. This review presents consensus statements and provides an evidence-based framework for practicing hematologists and oncologists to use MRD information to make rational treatment decisions in adult patients with ALL.

Influence of pre-transplant minimal residual disease on prognosis after Allo-SCT for patients with acute lymphoblastic leukemia: systematic review and meta-analysis

BACKGROUND

This meta-analysis was performed to explore the impact of minimal residual disease (MRD) prior to transplantation on the prognosis for patients with acute lymphoblastic leukemia (ALL).

METHODS

A systematic search of PubMed, Embase, and the Cochrane Library was conducted for relevant studies from database inception to March 2016. A total of 21 studies were included.

RESULTS

Patients with positive MRD prior to allogeneic stem cell transplantation (allo-SCT) had a significantly higher rate of relapse compared with those with negative MRD (HR = 3.26; P <  0.05). Pre-transplantation positive MRD was a significant negative predictor of relapse-free survival (RFS) (HR = 2.53; P <  0.05), event-free survival (EFS) (HR = 4.77; P < 0.05), and overall survival (OS) (HR = 1.98; P < 0.05). However, positive MRD prior to transplantation was not associated with a higher rate of nonrelapse mortality.

CONCLUSIONS

Positive MRD before allo-SCT was a predictor of poor prognosis after transplantation in ALL.

TRIAL REGISTRATION

Not applicable.

Idarubicin-Intensified Hematopoietic Cell Transplantation Improves Relapse and Survival of High-Risk Acute Leukemia Patients with Minimal Residual Disease

The optimal conditioning regimen of allogeneic hematopoietic stem cell transplantation (allo-HSCT) for high-risk patients with minimal residual disease (MRD) remains controversial. We studied the results in 98 high-risk acute leukemia patients transplanted with idarubicin (IDA)-intensified conditioning regimens between 2012 January and 2017 January. Among these patients, 31 (31.6%) had more than 5% marrow blasts at time of transplantation and 67 patients were in morphologic remission: MRD negative status at time of conditioning was achieved in 39 patients (39.8%), whereas 28 (28.6%) remained carriers of any other positive MRD level in the bone marrow. Three-year relapse estimates of patients with MRD-positive remission was 22.0%, which was remarkably lower than patients with active disease (45.4%, P = .027) but approximate to that of patients in MRD-negative remission (15.5%, P = .522). There were no significant differences in terms of 3-year estimated overall survival (OS) and disease-free survival (DFS) between MRD-positive remission and MRD-negative remission groups (71.4% versus 79.1% [P = .562] and 67.9% versus 76.9% [P = .634], respectively). Moreover, the estimated rates of 3-year OS and DFS of patients in MRD-positive remission were significantly better than those in patients with active disease (71.4% versus 41.9% [P = .033] and 67.9% versus 38.7% [P = .037], respectively). These data indicate that IDA-intensified conditioning allo-HSCT could overcome the negative prognostic impact of MRD.

The assessment and appraisal of regenerative medicines and cell therapy products: an exploration of methods for review, economic evaluation and appraisal

BACKGROUND

The National Institute for Health and Care Excellence (NICE) commissioned a 'mock technology appraisal' to assess whether changes to its methods and processes are needed. This report presents the findings of independent research commissioned to inform this appraisal and the deliberations of a panel convened by NICE to evaluate the mock appraisal.

METHODS

Our research included reviews to identify issues, analysis methods and conceptual differences and the relevance of alternative decision frameworks, alongside the development of an exemplar case study of chimeric antigen receptor (CAR) T-cell therapy for treating acute lymphoblastic leukaemia.

RESULTS

An assessment of previous evaluations of regenerative medicines found that, although there were a number of evidential challenges, none was unique to regenerative medicines or was beyond the scope of existing methods used to conceptualise decision uncertainty. Regarding the clinical evidence for regenerative medicines, the issues were those associated with a limited evidence base but were not unique to regenerative medicines: small non-randomised studies, high variation in response and the intervention subject to continuing development. The relative treatment effects generated from single-arm trials are likely to be optimistic unless it is certain that the historical data have accurately estimated the efficacy of the control agent. Pivotal trials may use surrogate end points, which, on average, overestimate treatment effects. To reduce overall uncertainty, multivariate meta-analysis of all available data should be considered. Incorporating indirectly relevant but more reliable (more mature) data into the analysis can also be considered; such data may become available as a result of the evolving regulatory pathways being developed by the European Medicines Agency. For the exemplar case of CAR T-cell therapy, target product profiles (TPPs) were developed, which considered the 'curative' and 'bridging to stem-cell transplantation' treatment approaches separately. Within each TPP, three 'hypothetical' evidence sets (minimum, intermediate and mature) were generated to simulate the impact of alternative levels of precision and maturity in the clinical evidence. Subsequent assessments of cost-effectiveness were undertaken, employing the existing NICE reference case alongside additional analyses suggested within alternative frameworks. The additional exploratory analyses were undertaken to demonstrate how assessments of cost-effectiveness and uncertainty could be impacted by alternative managed entry agreements (MEAs), including price discounts, performance-related schemes and technology leasing. The panel deliberated on the range of TPPs, evidence sets and MEAs, commenting on the likely recommendations for each scenario. The panel discussed the challenges associated with the exemplar and regenerative medicines more broadly, focusing on the need for a robust quantification of the level of uncertainty in the cost-effective estimates and the potential value of MEAs in limiting the exposure of the NHS to high upfront costs and loss associated with a wrong decision.

CONCLUSIONS

It is to be expected that there will be a significant level of uncertainty in determining the clinical effectiveness of regenerative medicines and their long-term costs and benefits, but the existing methods available to estimate the implications of this uncertainty are sufficient. The use of risk sharing and MEAs between the NHS and manufacturers of regenerative medicines should be investigated further.

FUNDING

The National Institute for Health Research Health Technology Assessment programme.

When Less Is Good, Is None Better? The Prognostic and Therapeutic Significance of Peri-Transplant Minimal Residual Disease Assessment in Pediatric Acute Lymphoblastic Leukemia

The measurement of minimal residual disease (MRD) in pediatric acute lymphoblastic leukemia (ALL) has become the most important prognostic tool of, and the backbone to, upfront risk stratification. While MRD assessment is the standard of care for assessing response and predicting outcomes for pediatric patients with ALL receiving chemotherapy, its use in allogeneic hematopoietic stem cell transplant (HSCT) has been less clearly defined. Herein, we discuss the importance of MRD assessment during the peri-HSCT period and its role in prognostication and management.

Evaluation of new markers for minimal residual disease monitoring in B-cell precursor acute lymphoblastic leukemia: CD73 and CD86 are the most relevant new markers to increase the efficacy of MRD 2016; 00B: 000-000

BACKGROUND

Multiparametric flow cytometry (MFC) is a popular technique for minimal residual disease (MRD) analysis. However, its applicability is still limited to 90% of B-cell precursor acute lymphoblastic leukemia (BCPALL) due to two major issues, i.e. a proportion of cases do not express adequate leukemia associated immunophenotype (LAIPs) with currently used markers and drug-induced antigen modulation. Hence, the incorporation of additional reliable markers is required for the further improvement of MFC-based MRD evaluation. We studied the utility of new markers in improvising MFC-based MRD detection in BCPALL.

METHODS

Expression-patterns of six new markers, i.e. CD24, CD44, CD72, CD73, CD86, and CD200 were studied in leukemic-blasts from ninety childhood BCPALL patients and in hematogones from 20 uninvolved staging bone marrow (BM) and ten postinduction non-BCPALL BM samples using eight-color MFC. The utility of these new markers in the day 35 postinduction MRD evaluation was determined.

RESULTS

Frequencies of LAIPs of CD73, CD86, CD72, CD44, CD200, and CD24 in diagnostic samples were 76.7, 56.7, 55.6, 50, 28.9, and 20%, respectively. Differential expression of all new markers was highly significant (P < 0.01) between early (CD10+ CD19+ CD34+) hematogones, late (CD10+ CD19+ CD34-) hematogones and BCPALL blasts except between early hematogones and BCPALL blasts for CD200 (P = 0.1). In MRD-positive samples, CD73 showed the maximum (83%) frequency of LAIP and CD86 showed the highest (100%) stability of aberrant expression. Inclusion of CD73 and CD86 increased the applicability of MFC-MRD assay to 98.9% MRD samples.

CONCLUSION

CD73 and CD86 are the most relevant markers to incorporate in the routine MRD evaluation of BCPALL. © 2016 International Clinical Cytometry Society.

Current Strategies for the Detection of Minimal Residual Disease in Childhood Acute Lymphoblastic Leukemia

Acute lymphoblastic leukemia (ALL) is the most common cancer in children. Current treatment strategies for childhood ALL result in long-term remission for approximately 90% of patients. However, the therapeutic response is worse among those who relapse. Several risk stratification approaches based on clinical and biological aspects have been proposed to intensify treatment in patients with high risk of relapse and reduce toxicity on those with a greater probability of cure.

The detection of residual leukemic cells (minimal residual disease, MRD) is the most important prognostic factor to identify high-risk patients, allowing redefinition of chemotherapy. In the last decades, several standardized research protocols evaluated MRD using immunophenotyping by flow cytometry and/or real-time quantitative polymerase chain reaction at different time points during treatment. Both methods are highly sensitive (10⁻³ a 10⁻⁵), but expensive, complex, and, because of that, require qualified staff and frequently are restricted to reference centers.

The aim of this article was to review technical aspects of immunophenotyping by flow cytometry and real-time quantitative polymerase chain reaction to evaluate MRD in ALL.

Refractory acute lymphoblastic leukemia in Chinese children: bridging to stem cell transplantation with clofarabine, cyclophosphamide and etoposide

Refractory or relapsed acute lymphoblastic leukemia (r/r ALL) represents the leading cause of cancer mortality in children. Clofarabine is effective in inducing remission thus enabling bridging to hematopoietic stem cell transplantation (HSCT). We report the results in treating Hong Kong Chinese pediatric patients with r/rALL by clofarabine/cyclophosphamide/etoposide (CLO-218) combination therapy. A retrospective review of patients treated between January 2009 and December 2014 in the two tertiary referral pediatric oncology units in Hong Kong. Thirteen patients were identified. All were Chinese and seven were male. Median age at clofarabine treatment was 8 years and the median duration of follow-up was 10 months. Nine patients had B-ALL and four had T-ALL. All were refractory to the preceding regimen(s). The median number of prior treatment regimens was 2; two patients had previous HSCT. Complete remission (CR) was achieved in five patients, Complete remission with incomplete counts (CRi) in two, PR in two, and non-remission (NR) in two. All four patients with T-ALL responded with three patients achieving CR. Eight out of nine patients who responded could be bridged to HSCT. Among those who were transplanted, four remained alive and in remission, three relapsed post-HSCT, and one died from transplant-related mortality. Treatment toxicities were common including febrile neutropenia in all subjects and culture-proven bacteremia in five patients. Hepatotoxicity was mild and reversible with no case of veno-occlusive disease. The clofarabine-based regimen is a promising strategy to induce disease remission in r/rALL and bridge to HSCT. Septic complications are, however, frequent necessitating prompt management with adequate supportive care in specialized centers.

New frontiers in pediatric Allo-SCT: novel approaches for children and adolescents with ALL

Although most children with ALL can be cured by chemotherapy approaches, allogeneic hematopoietic cell transplant (HCT) therapy offers a better chance of cure to selected high-risk patients in first remission and most children who relapse. Although transplant-related mortality has decreased significantly in the past decade, relapse remains high after HCT for ALL; developing strategies to decrease relapse and improve survival are vital. Recent studies have shown that relapse risk can be accurately defined using measurements of minimal residual disease (MRD) both pre- and post-HCT and by knowing whether patients get GVHD in the first 2 months after transplant. With these risk definitions in hand, investigators are now applying novel agents and immunotherapeutic methods in attempt to lower MRD before transplant and modulate the GVL effect after transplant. With powerful new immunological approaches coming on line, the transplant process itself will likely expand to include pre and/or post-HCT interventions aimed at reducing relapse.

The addition of sirolimus to tacrolimus/methotrexate GVHD prophylaxis in children with ALL: a phase 3 Children's Oncology Group/Pediatric Blood and Marrow Transplant Consortium trial

Sirolimus has activity against acute lymphoblastic leukemia (ALL) in xenograft models and efficacy in preventing acute graft-versus-host disease (aGVHD). We tested whether addition of sirolimus to GVHD prophylaxis of children with ALL would decrease aGVHD and relapse. Patients were randomized to tacrolimus/methotrexate (standard) or tacrolimus/methotrexate/sirolimus (experimental). The study met futility rules for survival after enrolling 146 of 259 patients. Rate of Grade 2-4 aGVHD was 31% vs 18% (standard vs experimental, P = .04), however, grade 3-4 aGVHD was not different (13% vs 10%, P = .28). Rates of veno-occlusive disease (VOD) and thrombotic microangiopathy (TMA) were lower in the nonsirolimus arm (9% vs 21% VOD, P = .05; 1% vs 10% TMA, P = .06). At 2 years, event free survival (EFS) and overall survival (OS) were 56% vs 46%, and 65% vs 55% (standard vs experimental), respectively (P = .28 and .23). Multivariate analysis showed increased relapse risk in children with ≥0.1% minimal residual disease (MRD) pretransplant, and decreased risk in patients with grades 1-3 aGVHD (P = .04). Grades 1-3 aGVHD were associated with improved EFS (P = .02), whereas grade 4 aGVHD and extramedullary disease at diagnosis led to inferior OS. Although addition of sirolimus decreased aGVHD, survival was not improved. This study is registered with ClinicalTrials.gov as #NCT00382109.

Treatment of Philadelphia-positive acute lymphoid leukemia

SUMMARY Philadelphia-positive (Ph+) acute lymphoblastic leukemia (ALL) represents approximately 15–30% of ALL in adults and is characterized by the expression of the fusion protein BCR–ABL with oncogenic activity. Remission and survival rates were lower whereas relapse risk was increased in Ph+ compared with Philadelphia-negative ALL, until remarkable improvements in the management of Ph+ ALL were achieved through the introduction of tyrosine kinase inhibitors that reduce the activity of the BCR–ABL protein. However, in patients achieving complete remission, allogeneic hematopoietic stem cell transplantation is in most cases a mandatory therapeutic step because rate of relapses are still high. This review will illustrate the current therapeutic options for the management of Ph+ ALL and indicate how better curative options may stem from appropriate implementation of tyrosine kinase inhibitors and novel antitumoral agents.

A clofarabine-based bridging regimen in patients with relapsed ALL and persistent minimal residual disease (MRD)

In patients with relapsed ALL, minimal residual disease (MRD) identified prior to allogeneic hematopoietic cell transplantation (HCT) is a strong predictor of relapse. We report our experience using a combination of reduced-dosing clofarabine, CY and etoposide as a 'bridge' to HCT in eight patients with high risk or relapsed ALL and pre-HCT MRD. All patients had detectable MRD (>0.01%, flow cytometry) at the start of therapy with all eight achieving MRD reduction following one cycle. The regimen was well tolerated with seven grade 3/4 toxicities occurring among four of the eight patients. Five patients (62.5%) are alive, one died from relapse (12.5%) and two from transplant-related mortality (25%). The combination of reduced-dose clofarabine, CY and etoposide as bridging therapy appears to be well tolerated in patients with relapsed ALL and is effective in reducing pre-HCT MRD.

Host lymphocyte depletion as a strategy to facilitate early full donor chimerism after reduced-intensity allogeneic stem cell transplantation

Reduced-intensity conditioning (RIC) allogeneic hematopoietic stem cell transplantation (RIC-alloHSCT) is associated with lower toxicity but higher rates of prolonged mixed chimerism than myeloablative conditioning. Decreased pretransplantation host T cell numbers are associated with less graft rejection and early full donor chimerism. To compensate for variability in pretransplantation host lymphocyte numbers and facilitate the achievement of rapid full donor chimerism, we tested a strategy of targeted lymphocyte depletion (TLD) using chemotherapy at conventional doses to provide cytoreduction and lymphocyte depletion before RIC-alloHSCT. In our study, 111 patients with advanced hematologic malignancies received 1 to 3 cycles of conventional-dose chemotherapy to reduce circulating lymphocytes to a predetermined level. Patients then underwent RIC-alloHSCT from HLA-matched siblings. Patients received a median of 2 cycles of TLD chemotherapy, resulting in a median 71% decline in CD4(+) count. All patients engrafted; there were no late graft failures. By day +14, median CD3(+) chimerism was 99% donor and was significantly associated with lower post-TLD CD4(+) counts (P = .012). One- and 5-year treatment-related mortality were 15% and 21%, respectively. At 1-year follow-up, 66% of patients had achieved complete remission (CR) of which 92% were not in CR at the time of transplantation. Overall survival at 1 and 5 years post transplantation were 66% and 47%, respectively.

Significance of persistent cytogenetic abnormalities on myeloablative allogeneic stem cell transplantation in first complete remission

Risk stratification is important to identify patients with acute myelogenous leukemia (AML) who might benefit from allogeneic hematopoietic stem cell transplantation (allo-HSCT) in first complete remission. We retrospectively studied 150 patients with AML and diagnostic cytogenetic abnormalities who underwent myeloablative allo-HSCT while in first complete remission to evaluate the prognostic impact of persistent cytogenetic abnormalities at allo-HSCT. Three risk groups were identified. Patients with favorable/intermediate cytogenetics at diagnosis (n = 49) and patients with unfavorable cytogenetics at diagnosis but without a persistent abnormal clone at allo-HSCT (n = 83) had a similar 3-year leukemia-free survival of 58%-60% despite the higher 3-year relapse incidence (RI) in the latter group (32.3%, versus 16.8% in the former group). A third group of patients with unfavorable cytogenetics at diagnosis and a persistent abnormal clone at allo-HSCT (n = 15) had the worst prognosis, with a 3-year RI of 57.5% and 3-year leukemia-free survival of only 29.2%. These data suggest that patients with AML and unfavorable cytogenetics at diagnosis and a persistent abnormal clone at allo-HSCT are at high risk for relapse after allo-HSCT. These patients should be considered for clinical trials designed to optimize conditioning regimens and/or to use preemptive strategies in the posttransplantion setting aimed at decreasing RI.

Quantification of minimal residual disease levels by flow cytometry at time of transplant predicts outcome after myeloablative allogeneic transplantation in ALL

The potential impact on patient outcome of different Minimal residual disease (MRD) levels at time of transplant in patients with lymphoblastic leukemia undergoing allogeneic hematopoietic SCT (HSCT) remains uncertain. In this study, we quantified MRD levels at time of transplant using multiparameter flow cytometry (MFC). Mononuclear cells from marrow aspirates were obtained from 102 adult and child patients before their conditioning regimen. Quantification of MRD levels was carried out by detecting patient-specific leukemia-associated immunophenotypes using four-color MFC. Thirty patients exhibited measurable levels of MRD at the time of transplant, with low levels (0.01 to 0.1%) in 12 cases, intermediate levels (>0.1 to 1%) in 8 cases and high levels (>1%) in 10 cases. The leukemia-free survival (LFS) rates were 65.9±7.0%, 42.9±15.7% and 0% for negative, low levels 0.1% and intermediate-high levels >0.1%, respectively (P<0.001, log-rank test). Overall survival (OS) was 52.3±7.6%, 28.6±13.8% and 0% for MRD-negative, low levels 0.1% and intermediate-high levels >0.1%, respectively (P<0.001, log-rank test). Multivariate Cox analysis confirmed that detection of leukemia cells by flow cytometry at transplant was the most significantly adverse factor for OS, LFS and EFS after transplant.

Prognostic and therapeutic implications of minimal residual disease at the time of transplantation in acute leukemia

Relapse remains the major cause of treatment failure after hematopoietic cell transplantation (HCT) in acute leukemia, even in patients transplanted in morphologic CR. Various techniques now enable the sensitive quantification of 'minimal' amounts of residual disease (MRD) in patients with acute leukemia in remission. Numerous studies convincingly demonstrate that MRD at the time of transplantation is a powerful, independent predictor of subsequent relapse, with current detection levels of one leukemic cell in 10(5)-10(6) normal cells being prognostically relevant. This recognition provides the rationale to assign patients with detectable MRD (that is, 'MRD(+)' patients) to intensified therapies before, during, or after transplantation, although data supporting these strategies are still sparse. Limited evidence from observational studies suggests that outcomes with autologous HCT are so poor that MRD(+) patients should preferentially be assigned to allogeneic HCT, which can cure a subgroup of these patients, particularly if unmanipulated (T-cell replete) grafts and/or minimized immunosuppression are used to optimize the graft-vs-leukemia effect. Emerging data suggest that additional therapy with non-cross-resistant agents to decrease residual tumor burden before transplantation in MRD(+) patients might be beneficial. Further, other studies hint at immunotherapy (for example, rapid withdrawal of immunosuppression and/or donor lymphocyte infusions) as a means to prevent overt relapse if patients remain, or become, MRD(+) after HCT. Ultimately, controlled clinical studies are needed to define the value of MRD-directed therapies, and patients should be encouraged to enter such trials.

Treatment of relapsed acute lymphoblastic leukemia: approaches used by pediatric oncologists and bone marrow transplant physicians

BACKGROUND

Management of relapsed B-precursor acute lymphoblastic leukemia (ALL) is challenging and varied. We hypothesized that treatment approaches differ between pediatric oncologists and bone marrow transplant (BMT) physicians.

PROCEDURE

A survey addressing management of relapsed ALL was sent to pediatric oncologists (n = 883) and BMT (n = 86) physicians across North America.

RESULTS

A number of similarities in treatment approaches were identified including: choice of chemotherapy for re-induction/consolidation, preference for unrelated donors (URDs) in very early marrow relapse and the choice to not use URD donors in late marrow relapse. However, differences between the two disciplines were noted. For patients who relapsed 18-36 months from diagnosis, the majority of oncologists (53.7%) would retreat with chemotherapy while a majority BMT physicians (70.3%) recommended URD transplant (P < 0.001). Oncologists were also less likely to use minimal residual disease (MRD) in relapse assessment compared to BMT physicians (52% vs. 67.2%; P = 0.028) and more oncologists believed MRD testing was experimental and/or not proven in relapsed ALL (27.1% vs. 12.3%; P = 0.011).

CONCLUSIONS

This study highlights management differences in children with ALL between pediatric oncologists and BMT physicians, identifying opportunities for collaborative clinical trials.

Detectable minimal residual disease before hematopoietic cell transplantation is prognostic but does not preclude cure for children with very-high-risk leukemia

In patients with acute leukemia, detection of minimal residual disease (MRD) before allogeneic hematopoietic cell transplantation (HCT) correlates with risk of relapse. However, the level of MRD that is most likely to preclude cure by HCT is unclear, and the benefit of further chemotherapy to reduce MRD before HCT is unknown. In 122 children with very-high-risk acute lymphoblastic leukemia (ALL; n = 64) or acute myeloid leukemia (AML, n = 58), higher MRD levels at the time of HCT predicted a poorer survival after HCT (P = .0019); MRD was an independent prognostic factor in a multivariate analysis (P = .0035). However, the increase in risk of death associated with a similar increment of MRD was greater in ALL than in AML, suggesting that a pretransplantation reduction of leukemia burden would have a higher impact in ALL. At any given MRD level, survival rates were higher for patients treated in recent protocols: the 5-year overall survival for patients with ALL was 49% if MRD was detectable and 88% if it was not and the corresponding rates for patients with AML were 67% and 80%, respectively. Although MRD before HCT is a strong prognostic factor, its impact has diminished and should not be regarded as a contraindication for HCT.

Allogeneic hematopoietic cell transplantation for acute lymphoblastic leukemia in adults

PURPOSE OF REVIEW

Acute lymphoblastic leukemia (ALL) is a heterogeneous disease, for which treatment guidelines are still evolving. Allogeneic hematopoietic cell transplantation (allo-HCT) is a potentially curative therapeutic modality for ALL, and this review describes the recent studies and current practice patterns concerning the who, when, and how of allo-HCT in the management of ALL.

RECENT FINDINGS

Allogeneic stem cell transplantation is the treatment of choice for patients with ALL after first relapse and is also recommended for high-risk patients in first complete remission (CR1). Minimal residual disease evaluation and monitoring is developing as an important prognostic factor and could guide physicians in determining which patients, especially those with standard risk, might require transplant. Tyrosine kinase inhibitor (TKI) therapy allows a much higher proportion of Philadelphia-chromosome-positive ALL patients to attain remission and proceed to transplant with improved results; posttransplant TKI maintenance therapy may also provide survival benefit. Reduced-intensity conditioning regimens are a reasonable alternative for patients who would otherwise be ineligible for transplant because of age or comorbidity.

SUMMARY

For patients with high-risk features, there is general agreement that allo-HCT in CR1 is a potentially curative option; however, there is no consensus on early transplant for standard-risk patients.

Minimal residual disease markers before and after allogeneic hematopoietic stem cell transplantation in acute myeloid leukemia

PURPOSE OF REVIEW

This study will review the role of minimal residual disease (MRD) in predicting leukemia relapse following an allogeneic hematopoietic stem cell transplant (HSCT) for acute myeloid leukemia (AML).

RECENT FINDINGS

PCR and multiparameter flow cytometry (MFC) assays are the most important methods of identifying MRD. PCR technique allows to recognize early genetic abnormalities of residual leukemic cells with high specificity and sensitivity. MFC assay using six-color to 10-color technology is an alternative option for MRD monitoring in AML patients without gene markers to detect leukemia-associated immunophenotype antigens (LAIPs).

SUMMARY

Despite the evidence that early detection of MRD after allogeneic HSCT is associated with a high risk of hematological relapse, it is still unclear whether this information can be translated into clinical practice, in order to prevent hematological relapse.

Role of cytotoxic therapy with hematopoietic stem cell transplantation in the treatment of pediatric acute lymphoblastic leukemia: update of the 2005 evidence-based review

Clinical research published since the first evidence-based review on the role of hematopoietic stem cell transplantation (SCT) in the treatment of pediatric acute lymphoblastic leukemia (ALL) is presented and critically evaluated in this update. Treatment recommendations are provided by an expert panel. Allogeneic SCT is recommended for children who: are in second complete remission (CR2) after experiencing an early marrow relapse for precursor-B ALL; experienced primary induction failure, but subsequently achieved a CR1; have T-lineage ALL in CR2; or have ALL in third or greater remission. Although the 2005 pediatric ALL evidence-based review (EBR) recommended allogeneic SCT for children with Philadelphia chromosome positive (Ph+) ALL in CR1, preliminary tyrosine kinase inhibitor (TKI) data demonstrate that early outcomes are comparable for allogeneic SCT and chemotherapy + imatinib. Based on the evidence, autologous SCT is not recommended for ALL in CR1. Allogeneic SCT is not recommended for: T-lineage ALL in CR1; mixed-lineage leukemia (MLL)+ ALL when it is the sole adverse risk factor; isolated central nervous system (CNS) relapse in precursor-B ALL. Based on expert opinion, allogeneic SCT may be considered for hypodiploid ALL and persistent minimal residual disease [corrected] (MRD) positivity in ALL in CR1 or greater, although these are areas that need further study. Treatment recommendations pertaining to various transplantation techniques are also provided, as are areas of needed future research.

Application of flow cytometry in pediatric hematology-oncology

Applications of flow cytometry in pediatric cancers have expanded substantially in recent years. In acute leukemias, the commonest childhood cancer, flow cytometry can now define complex antigenic profiles that are associated with specific cytogenetic/molecular defects and can also directly identify BCR-ABL fusion protein. Flow cytometry based scoring system has been described for diagnosis of myelodysplastic syndromes. In solid tumors, flow cytometry was previously used mainly to determine DNA content for prognosis; however, recent studies in children with neuroblastoma and Ewing sarcoma have identified its diagnostic utility. In this review, we will discuss the current and future applications of flow cytometry in pediatric hematology-oncology.

Minimal residual disease following allogeneic hematopoietic stem cell transplantation

Minimal residual disease (MRD), both before and after transplantation, is a clinically important yet relatively poorly defined aspect of allogeneic hematopoietic stem cell transplantation (alloHSCT). The clinical relevance of MRD in the context of alloHSCT has been demonstrated by its association with the development of clinical relapse. However, with the possible exception of chronic myeloid leukemia (CML), the specific techniques, timing, frequency, and clinical utility, relative to improvement in patient outcomes, for monitoring MRD in the setting of alloHSCT has yet to be clearly defined. A concise overview of monitoring techniques for detecting MRD, as well as treatment strategies and biological and clinical research initiatives for MRD suggested by the National Cancer Institute First International Workshop on the Biology, Prevention, and Treatment of Relapse after Allogeneic Hematopoietic Stem Cell Transplantation, is covered in this article.

Immunologic minimal residual disease detection in acute lymphoblastic leukemia: a comparative approach to molecular testing

The generation of antisera directed against leukocyte differentiation antigens opened the possibility of studying minimal residual disease (MRD) in patients with acute lymphoblastic leukemia (ALL). During the three decades that followed the pioneering studies in this field, great progress has been made in the development of a wide array of monoclonal antibodies and of flow cytometric techniques for rare event detection. This advance was accompanied by an increasingly greater understanding of the immunophenotypic features of leukemic and normal lymphoid cells, and of the antigenic differences that make MRD studies possible. In parallel, molecular methods for MRD detection were established. The systematic application of immunologic and molecular techniques to study MRD in clinical samples has demonstrated the clinical significance of MRD in patients, leading to the use of MRD to regulate treatment intensity in many contemporary protocols. In this article, we discuss methodologic issues related to the immunologic monitoring of MRD and the evidence supporting its clinical significance, and compare the advantages and limitations of this approach to those of molecular monitoring of MRD.