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

Pre-Emptive Immunotherapy for Clearance of Molecular Disease in Childhood Acute Lymphoblastic Leukemia after Transplantation

Monitoring of minimal residual disease (MRD) or chimerism may help guide pre-emptive immunotherapy (IT) with a view to preventing relapse in childhood acute lymphoblastic leukemia (ALL) after transplantation. Patients with ALL who consecutively underwent transplantation in Frankfurt/Main, Germany between January 1, 2005 and July 1, 2014 were included in this retrospective study. Chimerism monitoring was performed in all, and MRD assessment was performed in 58 of 89 patients. IT was guided in 19 of 24 patients with mixed chimerism (MC) and MRD and by MRD only in another 4 patients with complete chimerism (CC). The 3-year probabilities of event-free survival (EFS) were .69 ± .06 for the cohort without IT and .69 ± .10 for IT patients. Incidences of relapse (CIR) and treatment-related mortality (CITRM) were equally distributed between both cohorts (without IT: 3-year CIR, .21 ± .05, 3-year CITRM, .10 ± .04; IT patients: 3-year CIR, .18 ± .09, 3-year CITRM .13 ± .07). Accordingly, 3-year EFS and 3-year CIR were similar in CC and MC patients with IT, whereas MC patients without IT experienced relapse. IT was neither associated with an enhanced immune recovery nor an increased risk for acute graft-versus-host disease. Relapse prevention by IT in patients at risk may lead to the same favorable outcome as found in CC and MRD-negative-patients. This underlines the importance of excellent MRD and chimerism monitoring after transplantation as the basis for IT to improve survival in childhood ALL.

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.

Pre- and post-transplant quantification of measurable ('minimal') residual disease via multiparameter flow cytometry in adult acute myeloid leukemia

Measurable (“minimal”) residual disease (MRD) before or after hematopoietic cell transplantation (HCT) identifies adults with AML at risk of poor outcomes. Here, we studied whether peri-transplant MRD dynamics can refine risk assessment. We analyzed 279 adults receiving myeloablative allogeneic HCT in first or second remission who survived at least 35 days and underwent 10-color multiparametric flow cytometry (MFC) analyses of marrow aspirates before and 28±7 days after transplantation. MFC-detectable MRD before (n=63) or after (n=16) transplantation identified patients with high relapse risk and poor survival. Forty-nine patients cleared MRD with HCT conditioning, whereas 2 patients developed new evidence of disease. The 214 MRD^neg/MRD^neg patients had excellent outcomes, whereas both MRD^neg/MRD^pos patients died within 100 days following transplantation. For patients with pre-HCT MRD, outcomes were poor regardless of post-HCT MRD status, although survival beyond 3 years was observed among the 58 patients with decreasing but not the 7 patients with increasing peri-HCT MRD levels. In multivariable models, pre-HCT but not post-HCT MRD was independently associated with OS and RR. These data indicate that MRD^pos patients before transplantation have a high relapse risk regardless of whether or not they clear MFC-detectable disease with conditioning and should be considered for pre-emptive therapeutic strategies.

Minimal Residual Disease Monitoring in Adult ALL to Determine Therapy

Almost 90 % of children and 50 % of adults with acute lymphoblastic leukemia (ALL) are cured by modern treatment regimens, with significant variations due to several disease- and host-related characteristics. The attainment of an early remission and the avoidance of relapse and treatment-related mortality are the fundamental therapeutic steps. In remission patients, the assessment of the disease response to early intensive therapy through the detection and monitoring of minimal residual disease (MRD) can accurately refine the individual prognosis and is increasingly used to support a risk-oriented treatment strategy. In this way, only the patients with an unfavorable MRD response are preferably selected for allogeneic stem cell transplantation, irrespective of their clinical risk class. This choice spares transplant-related toxicities to MRD responsive cases. Further advancement is expected by integrating the MRD analysis with improved pediatric-type regimens and novel targeting agents for ALL subsets at higher risk of relapse.

Comparable outcomes between autologous and allogeneic transplant for adult acute myeloid leukemia in first CR

Although allogeneic hematopoietic stem cell transplantation from an HLA-matched sibling donor (MSD) is a potentially curative post-remission treatment for adults with acute myeloid leukemia (AML) in their first CR, transplant-related morbidity and mortality remains a major drawback. We retrospectively compared the outcomes of patients who underwent autologous peripheral blood stem cell transplantation (auto-PBSCT; n=375) with those who underwent allogeneic bone marrow transplantation (allo-BMT; n=521) and allo-PBSCT (n=380) from MSDs for adults with AML/CR1, in which propensity score models were used to adjust selection biases among patients, primary physicians and institutions to overcome ambiguity in the patients' background information. Both the multivariate analysis and propensity score models indicated that the leukemia-free survival rate of auto-PBSCT was not significantly different from that of allo-BMT (hazard ratio (HR), 1.23; 95% confidence interval (CI), 0.92 to 1.66; P=0.16) and allo-PBSCT (HR, 1.13; 95% CI, 0.85-1.51; P=0.40). The current results suggest that auto-PBSCT remains a promising alternative treatment for patients with AML/CR1 in the absence of an available MSD.

Should acute myeloid leukemia patients with actionable targets be offered investigational treatment after failing one cycle of standard induction therapy?

PURPOSE OF REVIEW

Therapeutic failure in acute myeloid leukemia remains common. It may be advantageous to identify patients with suboptimal treatment responses early as they may benefit from timely care strategy changes. Here, responses portending failure of standard induction therapy are reviewed and therapeutic options examined, including use of investigational, targeted agents for suitable patients.

RECENT FINDINGS

Patients entering complete remission without minimal residual disease early, that is, with one cycle of standard induction chemotherapy, have a lower relapse risk and live longer than other similarly-treated patients, supporting the proposition of early complete remission without minimal residual disease as a criterion for induction therapy success. Investigational small molecule drugs are appealing for patients who fail standard therapies, but complete remission rates as a single agent are typically modest.

SUMMARY

The relative value of different treatment strategies if a first standard induction therapy cycle fails to produce complete remission is unknown. However, retreatment with the same therapy often leads to complete remission and provides a benchmark against which other approaches should be compared. Addition of investigational small molecule drugs to standard reinduction therapy in patients with actionable targets could offer an attractive therapeutic strategy in this situation that might improve outcomes and facilitate clinical drug testing.

Allogeneic Hematopoietic Cell Transplantation for Acute Myeloid Leukemia: Time to Move Toward a Minimal Residual Disease-Based Definition of Complete Remission?

PURPOSE

Patients with acute myeloid leukemia (AML) who are in morphologic complete remission are typically considered separately from patients with active disease (ie, ≥ 5% marrow blasts by morphology) in treatment algorithms for allogeneic hematopoietic cell transplantation (HCT), which implies distinct outcomes for these two groups. It is well recognized that the presence of minimal residual disease (MRD) at the time of transplantation is associated with adverse post-HCT outcome for those patients in morphologic remission. This effect of pre-HCT MRD prompted us to compare outcomes in consecutive patients in MRD-positive remission with patients with active AML who underwent myeloablative allogeneic HCT at our institution.

PATIENTS AND METHODS

We retrospectively studied 359 consecutive adults with AML who underwent myeloablative allogeneic HCT from a peripheral blood or bone marrow donor between 2006 and 2014. Pre-HCT disease staging included 10-color multiparametric flow cytometry on bone marrow aspirates in all patients. Any level of residual disease was considered to be MRD positive.

RESULTS

Three-year relapse estimates were 67% in 76 patients in MRD-positive morphologic remission and 65% in 48 patients with active AML compared with 22% in 235 patients in MRD-negative remission. Three-year overall survival estimates were 26%, 23%, and 73% in these three groups, respectively. After multivariable adjustment, MRD-negative remission status remained statistically significantly associated with longer overall and progression-free survival as well as lower risk of relapse compared with MRD-positive morphologic remission status or having active disease, with similar outcomes between the latter two groups.

CONCLUSION

The similarities in outcomes between patients in MRD-positive morphologic remission and those with active disease at the time of HCT support the use of treatment algorithms that use MRD- rather than morphology-based disease assessments.

Autologous stem cell transplantation for adult acute leukemia in 2015: time to rethink? Present status and future prospects

The use of autologous stem cell transplantation (ASCT) as consolidation therapy for adult patients with acute leukemia has declined over time. However, multiple randomized studies in the past have reported lower relapse rates after autologous transplantation compared with chemotherapy and lower non-relapse mortality rates compared with allogeneic transplantation. In addition, quality of life of long-term survivors is better after autologous transplantation than after allogeneic transplantation. Further, recent developments may improve outcomes of autograft recipients. These include the use of IV busulfan and the busulfan+melphalan combination, better detection of minimal residual disease (MRD) with molecular biology techniques, the introduction of targeted therapies and post-transplant maintenance therapy. Therefore, ASCT may nowadays be reconsidered for consolidation in the following patients if and when they reach a MRD-negative status: good- and at least intermediate-1 risk acute myelocytic leukemia in first CR, acute promyelocytic leukemia in second CR, Ph-positive acute lymphocytic leukemia. Conversely, patients with MRD-positive status or high-risk leukemia should not be considered for consolidation with ASCT.

Natural killer cell therapy in children with relapsed leukemia

BACKGROUND

Novel therapies are needed for children with relapsed or refractory leukemia. We therefore tested the safety and feasibility of haploidentical natural killer cell therapy in this patient population.

PROCEDURE

Twenty-nine children who had relapsed or refractory leukemia were treated with chemotherapy followed by the infusion of haploidentical NK cells. Cohort 1 included 14 children who had not undergone prior allogeneic hematopoietic cell transplantation (HCT), whereas Cohort 2 included 15 children with leukemia that had relapsed after HCT.

RESULTS

Twenty-six (90%) NK donors were KIR mismatched (14 with one KIR and 12 with 2 KIRs). The peak NK chimerism levels were >10% donor in 87% of the evaluable recipients. In Cohort 1, 10 had responsive disease and 12 proceeded to HCT thereafter. Currently, 5 (36%) are alive without leukemia. In Cohort 2, 10 had responsive disease after NK therapy and successfully proceeded to second HCT. At present, 4 (27%) are alive and leukemia-free. The NK cell infusions and the IL-2 injections were well-tolerated.

CONCLUSIONS

NK cell therapy is safe, feasible, and should be further investigated in patients with chemotherapy-resistant leukemia.

Monitoring of Minimal Residual Disease After Allogeneic Stem-Cell Transplantation in Relapsed Childhood Acute Lymphoblastic Leukemia Allows for the Identification of Impending Relapse: Results of the ALL-BFM-SCT 2003 Trial

Purpose

To elucidate the impact of minimal residual disease (MRD) after allogeneic transplantation, the Acute Lymphoblastic Leukemia Berlin-Frankfurt-Münster Stem Cell Transplantation Group (ALL-BFM-SCT) conducted a prospective clinical trial.

Patients and Methods

In the ALL-BFM-SCT 2003 trial, MRD was assessed in the bone marrow at days +30, +60, +90, +180, and +365 after transplantation in 113 patients with relapsed disease. Standardized quantification of MRD was performed according to the guidelines of the Euro-MRD Group.

Results

All patients showed a 3-year probability of event-free survival (pEFS) of 55%. The cumulative incidence rates of relapse and treatment-related mortality were 32% and 12%, respectively. The pEFS was 60% for patients who received their transplantations in second complete remission, 50% for patients in ≥ third complete remission, and 0% for patients not in remission (P = .015). At all time points, the level of MRD was inversely correlated with event-free survival (EFS; P < .004) and positively correlated with the cumulative incidence of relapse (P < .01). A multivariable Cox model was fitted for each time point, which showed that MRD ≥ 10−4 leukemic cells was consistently correlated with inferior EFS (P < .003). The accuracy of MRD measurements in predicting relapse was investigated with time-dependent receiver operating curves at days +30, +60, +90, and +180. From day +60 onward, the discriminatory power of MRD detection to predict the probability of relapse after 1, 3, 6, and 9 months was more than 96%, more than 87%, more than 71%, and more than 61%, respectively.

Conclusion

MRD after transplantation was a reliable marker for predicting impending relapses and could thus serve as the basis for pre-emptive therapy.

Advancing the Minimal Residual Disease Concept in Acute Myeloid Leukemia

The criteria to evaluate response to treatment in acute myeloid leukemia (AML) have changed little in the past 60 years. It is now possible to use higher sensitivity tools to measure residual disease burden in AML. Such minimal or measurable residual disease (MRD) measurements provide a deeper understanding of current patient status and allow stratification for risk of subsequent clinical relapse. Despite these obvious advantages, and after over a decade of laboratory investigation and preclinical validation, MRD measurements are not currently routinely used for clinical decision-making or drug development in non-acute promyelocytic leukemia (non-APL) AML. We review here some potential constraints that may have delayed adoption, including a natural hesitancy of end users, economic impact concerns, misperceptions regarding the meaning of and need for assay sensitivity, the lack of one single MRD solution for all AML patients, and finally the need to involve patients in decision-making based on such correlates. It is our opinion that none of these issues represent insurmountable barriers and our hope is that by providing potential solutions we can help map a path forward to a future where our patients will be offered personalized treatment plans based on the amount of AML they have left remaining to treat.

Defining minimal residual disease in acute myeloid leukemia: which platforms are ready for “prime time”?

The past 40 years have witnessed major advances in defining the cytogenetic aberrations, mutational landscape, epigenetic profiles, and expression changes underlying hematological malignancies. Although it has become apparent that acute myeloid leukemia (AML) is highly heterogeneous at the molecular level, the standard framework for risk stratification guiding transplant practice in this disease remains largely based on pretreatment assessment of cytogenetics and a limited panel of molecular genetic markers, coupled with morphological assessment of bone marrow (BM) blast percentage after induction. However, application of more objective methodology such as multiparameter flow cytometry (MFC) has highlighted the limitations of morphology for reliable determination of remission status. Moreover, there is a growing body of evidence that detection of subclinical levels of leukemia (ie, minimal residual disease, MRD) using MFC or molecular-based approaches provides powerful independent prognostic information. Consequently, there is increasing interest in the use of MRD detection to provide early end points in clinical trials and to inform patient management. However, implementation of MRD assessment into clinical practice remains a major challenge, hampered by differences in the assays and preferred analytical methods employed between routine laboratories. Although this should be addressed through adoption of standardized assays with external quality control, it is clear that the molecular heterogeneity of AML coupled with increasing understanding of its clonal architecture dictates that a “one size fits all” approach to MRD detection in this disease is not feasible. However, with the range of platforms now available, there is considerable scope to realistically track treatment response in every patient.

Defining minimal residual disease in acute myeloid leukemia: which platforms are ready for "prime time"?

The past 40 years have witnessed major advances in defining the cytogenetic aberrations, mutational landscape, epigenetic profiles, and expression changes underlying hematological malignancies. Although it has become apparent that acute myeloid leukemia (AML) is highly heterogeneous at the molecular level, the standard framework for risk stratification guiding transplant practice in this disease remains largely based on pretreatment assessment of cytogenetics and a limited panel of molecular genetic markers, coupled with morphological assessment of bone marrow (BM) blast percentage after induction. However, application of more objective methodology such as multiparameter flow cytometry (MFC) has highlighted the limitations of morphology for reliable determination of remission status. Moreover, there is a growing body of evidence that detection of subclinical levels of leukemia (ie, minimal residual disease, MRD) using MFC or molecular-based approaches provides powerful independent prognostic information. Consequently, there is increasing interest in the use of MRD detection to provide early end points in clinical trials and to inform patient management. However, implementation of MRD assessment into clinical practice remains a major challenge, hampered by differences in the assays and preferred analytical methods employed between routine laboratories. Although this should be addressed through adoption of standardized assays with external quality control, it is clear that the molecular heterogeneity of AML coupled with increasing understanding of its clonal architecture dictates that a "one size fits all" approach to MRD detection in this disease is not feasible. However, with the range of platforms now available, there is considerable scope to realistically track treatment response in every patient.

Prognostic impact of minimal residual disease in adult acute lymphoblastic leukemia

SUMMARY 

While adult acute lymphoblastic leukemia (ALL) is curable in 40–50% of the patients, the individual prognosis is rather unpredictable due to associated biological and clinical risk factors. In both B- and T-precursor ALL, minimal residual disease (MRD) represents the most sensitive prognostic marker, useful to support critical treatment decisions, ranging from allogeneic stem cell transplantation in patients with inadequate MRD response to chemotherapy only in MRD responsive ones. This optimized risk-adapted strategy allows to spare transplant-associated morbidity and mortality in patients curable by chemotherapy. Further progress is expected from the integration of the MRD-based strategy with improved pediatric-type regimens and novel targeting agents for discrete ALL subsets. These changes are increasing the cure rate to above 50%.

Diagnosing and following adult patients with acute myeloid leukaemia in the genomic age

The diagnosis and follow-up process of adult patients with acute myeloid leukaemia (AML) is challenging to clinicians and laboratory staff alike. While several sets of recommendations have been published over the years, the development of high throughput screening and characterization for both genetic and epigenetic events have evolved with astonishing speed. Here we attempt to provide a practical guide to diagnose and follow adult AML patients with a focus on how to balance the wealth of information on the one hand, with the restriction put on these processes in terms of time, feasibility and economy when caring for these patients, on the other.

Defining minimal residual disease in acute myeloid leukemia: which platforms are ready for "prime time"?

The past 40 years have witnessed major advances in defining the cytogenetic aberrations, mutational landscape, epigenetic profiles, and expression changes underlying hematological malignancies. Although it has become apparent that acute myeloid leukemia (AML) is highly heterogeneous at the molecular level, the standard framework for risk stratification guiding transplant practice in this disease remains largely based on pretreatment assessment of cytogenetics and a limited panel of molecular genetic markers, coupled with morphological assessment of bone marrow (BM) blast percentage after induction. However, application of more objective methodology such as multiparameter flow cytometry (MFC) has highlighted the limitations of morphology for reliable determination of remission status. Moreover, there is a growing body of evidence that detection of subclinical levels of leukemia (ie, minimal residual disease, MRD) using MFC or molecular-based approaches provides powerful independent prognostic information. Consequently, there is increasing interest in the use of MRD detection to provide early end points in clinical trials and to inform patient management. However, implementation of MRD assessment into clinical practice remains a major challenge, hampered by differences in the assays and preferred analytical methods employed between routine laboratories. Although this should be addressed through adoption of standardized assays with external quality control, it is clear that the molecular heterogeneity of AML coupled with increasing understanding of its clonal architecture dictates that a "one size fits all" approach to MRD detection in this disease is not feasible. However, with the range of platforms now available, there is considerable scope to realistically track treatment response in every patient.

Comparison of chimerism and minimal residual disease monitoring for relapse prediction after allogeneic stem cell transplantation for adult acute lymphoblastic leukemia

Little data are available on the relative merits of chimerism and minimal residual disease (MRD) monitoring for relapse prediction after allogeneic hematopoietic stem cell transplantation (HCT). We performed a retrospective analysis of serial chimerism assessments in 101 adult HCT recipients with acute lymphoblastic leukemia (ALL) and of serial MRD assessments in a subgroup of 22 patients. All patients had received myeloablative conditioning. The cumulative incidence of relapse was significantly higher in the patients with increasing mixed chimerism (in-MC) compared with those with complete chimerism, low-level MC, and decreasing MC, but the sensitivity of in-MC detection with regard to relapse prediction was only modest. In contrast, MRD assessment was highly sensitive and specific. Patients with MRD positivity after HCT had the highest incidence of relapse among all prognostic groups analyzed. The median time from MRD positivity to relapse was longer than the median time from detection of in-MC, but in some cases in-MC preceded MRD positivity. We conclude that MRD assessment is a powerful prognostic tool that should be included in the routine post-transplantation monitoring of patients with ALL, but chimerism analysis may provide additional information in some cases. Integration of these tools and clinical judgment should allow optimal decision making with regard to post-transplantation therapeutic interventions.

Minimal residual disease testing in acute leukemia

SUMMARY Predictive/prognostic factors in acute leukemia continue to be sought, in order to refine treatment strategies. Minimal residual disease (MRD) testing has been shown to be a statistically significant factor by multivariate analysis in both acute lymphoblastic leukemia (ALL) and acute myeloid leukemia. Its utility in guiding therapy has been more extensively studied in pediatric ALL, with some protocols having instituted MRD testing into therapeutic algorithms. The clinical impact of MRD testing in ALL and acute myeloid leukemia will be presented, including both molecular and flow cytometric methodologies, with a more focused discussion of the strategy, methodology and interpretation of MRD testing by multiparametric flow cytometry.

Gemtuzumab ozogamicin can reduce minimal residual disease in patients with childhood acute myeloid leukemia

BACKGROUND

Gemtuzumab ozogamicin (GO) is an active agent for the treatment of CD33-postive acute myeloid leukemia (AML) and may improve the outcome of specific patient subgroups when combined with conventional chemotherapy. However, to the best of the authors' knowledge, the effects of GO on levels of minimal residual disease (MRD) are unknown.

METHODS

Pediatric patients with AML who received GO, either alone or in combination with chemotherapy on the AML02 multicenter trial, were analyzed to determine the effects of GO on MRD and outcome.

RESULTS

Among 17 patients who received GO alone because of persistent leukemia, 14 had a reduction in their MRD level and 13 became MRD negative. Of the 29 who received chemotherapy in combination with GO after responding poorly to chemotherapy, 28 demonstrated reduced MRD and 13 became MRD negative. Treatment with GO effectively reduced MRD before hematopoietic stem cell transplantation and was not found to be associated with increased treatment-related mortality after transplantation.

CONCLUSIONS

GO is effective in reducing MRD levels in pediatric patients with AML and may improve the outcome of those patients at high risk of disease recurrence.