Early assessment of minimal residual disease in AML by flow cytometry during aplasia identifies patients at increased risk of relapse

Novel Tools for Diagnosis and Monitoring of AML

In recent years, major advances in the understanding of acute myeloid leukemia (AML) pathogenesis, together with technological progress, have led us into a new era in the diagnosis and follow-up of patients with AML. A combination of immunophenotyping, cytogenetic and molecular studies are required for AML diagnosis, including the use of next-generation sequencing (NGS) gene panels to screen all genetic alterations with diagnostic, prognostic and/or therapeutic value. Regarding AML monitoring, multiparametric flow cytometry and quantitative PCR/RT-PCR are currently the most implemented methodologies for measurable residual disease (MRD) evaluation. Given the limitations of these techniques, there is an urgent need to incorporate new tools for MRD monitoring, such as NGS and digital PCR. This review aims to provide an overview of the different technologies used for AML diagnosis and MRD monitoring and to highlight the limitations and challenges of current versus emerging tools.

Flow cytometric measurable residual disease in adult acute myeloid leukemia: a preliminary report from Eastern India

Presence of measurable residual disease (MRD) in acute myeloid leukemia (AML) is considered to be an independent predictor of relapse and poorer survival outcomes. MRD can be measured by flow cytometric, quantitative PCR, and NGS-based assays at varying sensitivities. There is scant Indian data on different aspects of MFC-MRD in AML including analysis strategies as well as molecular spectrum, clinical correlation, etc. This retrospective observational study included all newly diagnosed patients of acute myeloid leukemia in whom complete baseline diagnostic workup was available including flow cytometry and cytogenetic and molecular studies. Among patients with cytogenetic abnormalities (n = 25), no statistically significant correlation was observed between flow cytometric MRD positivity and presence of ≥ 3 mutations as well as relapsed disease. However, in AML patients with normal karyotype (n = 32), MRD positivity correlated strongly with relapsed status (p = 0.02), although no significant correlation was found with respect to FLT3 mutation, IDH mutation, NPM1 mutation, or complex genotype. Interestingly, 90.5% of MRD-positive patients belonged to ELN (2017) intermediate to high-risk category unlike only 9.5% in the good risk category (p = 0.0002). Median relapse-free survival was 8.5 months with a follow-up range of 3-24 months. On the basis of the observations of the present study, it can be clearly inferred that MRD status affects relapse status in the normal karyotype subgroup and can delineate patients who require stem cell transplantation in addition to molecular signatures.

Prognostic Impact of Unsupervised Early Assessment of Bulk and Leukemic Stem Cell Measurable Residual Disease in Acute Myeloid Leukemia

PURPOSE

Acute myeloid leukemias (AML) are clonal diseases that develop from leukemic stem cells (LSC) that carry an independent prognostic impact on the initial response to induction chemotherapy, demonstrating the clinical relevance of LSC abundance in AML. In 2018, the European LeukemiaNet published recommendations for the detection of measurable residual disease (Bulk MRD) and suggested the exploration of LSC MRD and the use of multiparametric displays.

EXPERIMENTAL DESIGN

We evaluated the performance of unsupervised clustering for the post-induction assessment of bulk and LSC MRD in 155 patients with AML who received intensive conventional chemotherapy treatment.

RESULTS

The median overall survival (OS) for Bulk+ MRD patients was 16.7 months and was not reached for negative patients (HR, 3.82; P < 0.0001). The median OS of LSC+ MRD patients was 25.0 months and not reached for negative patients (HR, 2.84; P = 0.001). Interestingly, 1-year (y) and 3-y OS were 60% and 39% in Bulk+, 91% and 52% in Bulk-LSC+ and 92% and 88% in Bulk-LSC-.

CONCLUSIONS

In this study, we confirm the prognostic impact of post-induction multiparametric flow cytometry Bulk MRD in patients with AML. Focusing on LSCs, we identified a group of patients with negative Bulk MRD but positive LSC MRD (25.8% of our cohort) with an intermediate prognosis, demonstrating the interest of MRD analysis focusing on leukemic chemoresistant subpopulations.

Association of hematologic response and assay sensitivity on the prognostic impact of measurable residual disease in acute myeloid leukemia: a systematic review and meta-analysis

Measurable residual disease (MRD) is associated with relapse and survival in acute myeloid leukemia (AML). We aimed to quantify the impact of MRD on outcomes across clinical contexts, including its association with hematologic response and MRD assay sensitivity. We performed systematic literature review and meta-analysis of 48 studies that reported the association between MRD and overall survival (OS) or disease-free survival (DFS) in AML and provided information on the MRD threshold used and the hematologic response of the study population. Among studies limited to patients in complete remission (CR), the estimated 5-year OS for the MRD-negative and MRD-positive groups was 67% (95% Bayesian credible interval [CrI], 53-77%) and 31% (95% CrI, 18-44%), respectively. Achievement of an MRD-negative response was associated with superior DFS and OS, regardless of MRD threshold or analytic sensitivity. Among patients in CR, the benefit of MRD negativity was highest in studies using an MRD cutoff less than 0.1%. The beneficial impact of MRD negativity was observed across MRD assays and timing of MRD assessment. In patients with AML in morphological remission, achievement of MRD negativity is associated with superior DFS and OS, irrespective of hematologic response or the MRD threshold used.

Reproducible measurable residual disease detection by multiparametric flow cytometry in acute myeloid leukemia

Measurable residual disease (MRD) detected by multiparametric flow cytometry (MFC) is associated with unfavorable outcome in patients with AML. A simple, broadly applicable eight-color panel was implemented and analyzed utilizing a hierarchical gating strategy with fixed gates to develop a clear-cut LAIP-based DfN approach. In total, 32 subpopulations with aberrant phenotypes with/without expression of markers of immaturity were monitored in 246 AML patients after completion of induction chemotherapy. Reference values were established utilizing 90 leukemia-free controls. Overall, 73% of patients achieved a response by cytomorphology. In responders, the overall survival was shorter for MRDpos patients (HR 3.8, p = 0.006). Overall survival of MRDneg non-responders was comparable to MRDneg responders. The inter-rater-reliability for MRD detection was high with a Krippendorffs α of 0.860. The mean time requirement for MRD analyses at follow-up was very short with 04:31 minutes. The proposed one-tube MFC approach for detection of MRD allows a high level of standardization leading to a promising inter-observer-reliability with a fast turnover. MRD defined by this strategy provides relevant prognostic information and establishes aberrancies outside of cell populations with markers of immaturity as an independent risk feature. Our results imply that this strategy may provide the base for multicentric immunophenotypic MRD assessment.

Eradication of Measurable Residual Disease in AML: A Challenging Clinical Goal

In non-promyelocytic (non-M3) AML measurable residual disease (MRD) detected by multi-parameter flow cytometry and molecular technologies, which are guided by Consensus-based guidelines and discover very low leukemic cell numbers far below the 5% threshold of morphological assessment, has emerged as the most relevant predictor of clinical outcome. Currently, it is well-established that MRD positivity after standard induction and consolidation chemotherapy, as well as during the period preceding an allogeneic hematopoietic stem cell transplant (allo-HSCT), portends to a significantly inferior relapse-free survival (RFS) and overall survival (OS). In addition, it has become absolutely clear that conversion from an MRD-positive to an MRD-negative state provides a favorable clinical outcome similar to that associated with early MRD negativity. Thus, the complete eradication of MRD, i.e., the clearance of the few leukemic stem cells-which, due to their chemo-radiotherapy resistance, might eventually be responsible of disease recurrence-has become an un-met clinical need in AML. Nowadays, this goal might potentially be achieved thanks to the development of novel innovative treatment strategies, including those targeting driver mutations, apoptosis, methylation patterns and leukemic proteins. The aim of this review is to analyze these strategies and to suggest any potential combination able to induce MRD negativity in the pre- and post-HSCT period.

Association of Measurable Residual Disease With Survival Outcomes in Patients With Acute Myeloid Leukemia: A Systematic Review and Meta-analysis

Importance

Measurable residual disease (MRD) refers to neoplastic cells that cannot be detected by standard cytomorphologic analysis. In patients with acute myeloid leukemia (AML), determining the association of MRD with survival may improve prognostication and inform selection of efficient clinical trial end points.

Objective

To examine the association between MRD status and disease-free survival (DFS) and overall survival (OS) in patients with AML using scientific literature.

Data Sources

Clinical studies on AML published between January 1, 2000, and October 1, 2018, were identified via searches of PubMed, Embase, and MEDLINE.

Study Selection

Literature search and study screening were performed according to the Preferred Reporting Items for Systematic Reviews and Meta-analyses guidelines. Studies that assessed DFS or OS by MRD status in patients with AML were included. Reviews, non-English-language articles, and studies reporting only outcomes after hematopoietic cell transplantation or those with insufficient description of MRD information were excluded.

Data Extraction and Synthesis

Study sample size, median patient age, median follow-up time, MRD detection method, MRD assessment time points, AML subtype, specimen source, and survival outcomes were extracted. Meta-analyses were performed separately for DFS and OS using bayesian hierarchical modeling.

Main Outcomes and Measures

Meta-analyses of survival probabilities and hazard ratios (HRs) were conducted for OS and DFS according to MRD status.

Results

Eighty-one publications reporting on 11 151 patients were included. The average HR for achieving MRD negativity was 0.36 (95% bayesian credible interval [CrI], 0.33-0.39) for OS and 0.37 (95% CrI, 0.34-0.40) for DFS. The estimated 5-year DFS was 64% for patients without MRD and 25% for those with MRD, and the estimated OS was 68% for patients without MRD and 34% for those with MRD. The association of MRD negativity with DFS and OS was significant for all subgroups, with the exception of MRD assessed by cytogenetics or fluorescent in situ hybridization.

Conclusions and Relevance

The findings of this meta-analysis suggest that achievement of MRD negativity is associated with superior DFS and OS in patients with AML. The value of MRD negativity appears to be consistent across age groups, AML subtypes, time of MRD assessment, specimen source, and MRD detection methods. These results support MRD status as an end point that may allow for accelerated evaluation of novel therapies in AML.

Measurable Residual Disease in Acute Myeloid Leukemia Using Flow Cytometry: A Review of Where We Are and Where We Are Going

The detection of measurable residual disease (MRD) has become a key investigation that plays a role in the prognostication and management of several hematologic malignancies. Acute myeloid leukemia (AML) is the most common acute leukemia in adults and the role of MRD in AML is still emerging. Prognostic markers are complex, largely based upon genetic and cytogenetic aberrations. MRD is now being incorporated into prognostic models and is a powerful predictor of relapse. While PCR-based MRD methods are sensitive and specific, many patients do not have an identifiable molecular marker. Immunophenotypic MRD methods using multiparametric flow cytometry (MFC) are widely applicable, and are based on the identification of surface marker combinations that are present on leukemic cells but not normal hematopoietic cells. Current techniques include a "different from normal" and/or a "leukemia-associated immunophenotype" approach. Limitations of MFC-based MRD analyses include the lack of standardization, the reliance on a high-quality marrow aspirate, and variable sensitivity. Emerging techniques that look to improve the detection of leukemic cells use dimensional reduction analysis, incorporating more leukemia specific markers and identifying leukemic stem cells. This review will discuss current methods together with new and emerging techniques to determine the role of MFC MRD analysis.

Clinical Challenges and Consequences of Measurable Residual Disease in Non-APL Acute Myeloid Leukemia

The ability to detect residual levels of leukemic blasts (measurable residual disease, MRD) has already been integrated in the daily routine for treatment of patients with chronic myeloid and acute lymphoblastic leukemia. In acute myeloid leukemia (AML), a variety of mostly retrospective studies have shown that individuals in AML remission who tested positive for MRD at specific time-points or had increasing MRD levels are at significantly higher risk of relapse and death compared to MRD-negative patients. However, these studies differ with respect to the "MRD-target", time-point of MRD determination, material analyzed, and method applied. How this probably very valuable MRD information in individual patients may be adapted in the daily clinical routine, e.g., to separate patients who need more aggressive therapies from those who may be spared additional-potentially toxic-therapies is still a work-in-progress. With the exception of MRD assessment in acute promyelocytic leukemia (APL), the lack of randomized, prospective trials renders MRD-based decisions and clinical implications in AML a difficult task. As of today, we still do not have proof that early intervention in MRD-positive AML patients would improve outcomes, although this is very likely. In this article, we review the current knowledge on non-APL AML MRD assessment and possible clinical consequences.

Impact of Time Between Induction Chemotherapy and Complete Remission on Survival Outcomes in Patients With Acute Myeloid Leukemia

BACKGROUND

The majority of patients with acute myeloid leukemia (AML) receive intensive induction chemotherapy for obtaining a complete remission (CR). Despite consolidation chemotherapy and advances in allogeneic hematopoietic stem cell transplantation, most of these patients finally relapse and die from AML. The aim of this study is to determine the impact of duration of remission achievement on survival of patients with newly diagnosed AML who achieve CR after induction chemotherapy.

MATERIALS AND METHODS

We retrospectively analyzed patients with AML who received first induction chemotherapy between 2001 and 2018.

RESULTS

The 5-year overall survival for patients who had early remission after induction chemotherapy and patients who had delayed remission after induction chemotherapy were 83% (95% confidence interval [CI], 0.79-0.87) and 35% (95% CI, 0.31-0.39), respectively (P < .001). The 5-year disease-free survival for patients who had early remission after induction chemotherapy and patients who had delayed remission after induction chemotherapy were 81% (95% CI, 0.75-0.87) and 28% (95% CI, 0.21-0.35), respectively (P < .001).

CONCLUSION

In conclusion, time to entering CR is a predictor factor of overall survival and disease-free survival for patients with newly diagnosed AML who achieve CR after first induction chemotherapy. Patients achieving CR only after a lengthy time (eg, more than 29 days) should be considered to have high relapse rate and should undergo allogeneic hematopoietic stem cell transplantation.

Colonic Wall Thickening as the First Indicator of Relapse of Acute Lymphoblastic Leukemia

The gastrointestinal (GI) tract is a rarely reported site of extramedullary relapse of acute lymphoblastic leukemia (ALL). We report a patient being effectively treated with immunotherapy for relapsed ALL who was incidentally noted to have colonic wall thickening on imaging that was subsequently pathologically confirmed to be the result of disease infiltration of colonic tissue. Primary ALL involvement of the GI tract should be considered in the evaluation of GI complaints in patients with ALL, particularly those with relapsed disease otherwise effectively treated with immunotherapy.

Optimal Measurable Residual Disease Testing for Acute Myeloid Leukemia

Increasing evidence supports the prognostic significance of measurable residual disease (MRD) in acute myeloid leukemia (AML). Dynamic MRD assessment for patients with AML complements baseline patient risk assessment factors in determining patient prognosis. MRD status may also be helpful in informing therapeutic decisions. The European Leukemia Net MRD working party recently issued consensus recommendations for the use of MRD in AML. The Food and Drug Administration also issued advice for using MRD in trials of hematologic malignancies. This article discusses MRD testing, highlights the challenges in adopting MRD testing in clinical practice, and provides insights into the future of the field.

In-silico comparison of two induction regimens (7 + 3 vs 7 + 3 plus additional bone marrow evaluation) in acute myeloid leukemia treatment

BACKGROUND

Clinical integration of systems biology approaches is gaining in importance in the course of digital revolution in modern medicine. We present our results of the analysis of an extended mathematical model describing abnormal human hematopoiesis. The model is able to describe the course of an acute myeloid leukemia including its treatment. In first-line treatment of acute myeloid leukemia, the induction chemotherapy aims for a rapid leukemic cell reduction. We consider combinations of cytarabine and anthracycline-like chemotherapy. Both substances are widely used as standard treatment to achieve first remission. In particular, we compare two scenarios: a single-induction course with 7 days cytarabine and 3 day of anthracycline-like treatment (7 + 3) with a 7 + 3 course and a bone marrow evaluation that leads, in case of insufficient leukemic cell reduction, to the provision of a second chemotherapy course. Three scenarios, based on the leukemias growth kinetics (slow, intermediate, fast), were analyzed. We simulated different intensity combinations for both therapy schemata (7 + 3 and 7 + 3 + evaluation).

RESULTS

Our model shows that within the 7 + 3 regimen a wider range of intensity combinations result in a complete remission (CR), compared to 7 + 3 + evaluation (fast: 64.3% vs 46.4%; intermediate: 63.7% vs 46.7%; slow: 0% vs 0%). Additionally, the number of simulations resulting in a prolonged CR was higher within the standard regimen (fast: 59.8% vs 40.1%; intermediate: 48.6% vs 31.0%; slow: 0% vs 0%). On the contrary, the 7 + 3 + evaluation regimen allows CR and prolonged CR by lower chemotherapy intensities compared to 7 + 3. Leukemic pace has a strong impact on treatment response and especially on specific effective doses. As a result, faster leukemias are characterized by superior treatment outcomes and can be treated effectively with lower treatment intensities.

CONCLUSIONS

We could show that 7 + 3 treatment has considerable more chemotherapy combinations leading to a first CR. However, the 7 + 3 + evaluation regimen leads to CR for lower therapy intensity and presumably less side effects. An additional evaluation can be considered beneficial to control therapy success, especially in low dose settings. The treatment success is dependent on leukemia growth dynamics. The determination of leukemic pace should be a relevant part of a personalized medicine.

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.

Methods of Detection of Measurable Residual Disease in AML

The presence of measurable ("minimal") residual disease (MRD) after induction and/or consolidation chemotherapy is a significant risk factor for relapse in patients with acute myeloid leukemia (AML). In recognition of the clinical significance of AML MRD, the European LeukemiaNet (ELN) recently recommended the establishment of CR-MRD^Negative as a separate category of treatment response. This recommendation represents a major milestone in the integration of AML MRD testing in standard clinical practice. This review article summarizes the methodologies employed in AML MRD detection and their application in clinical studies that provide evidence supporting the clinical utility of AML MRD testing. Future MRD evaluations in AML likely will require an integrated approach combining multi-parameter flow cytometry and high-sensitivity molecular techniques applied to time points during and after completion of therapy in order to provide the most accurate and comprehensive assessment of treatment response.

Persistence of pre-leukemic clones during first remission and risk of relapse in acute myeloid leukemia

Some patients with acute myeloid leukemia (AML) who are in complete remission after induction chemotherapy harbor persisting pre-leukemic clones, carrying a subset of leukemia-associated somatic mutations. There is conflicting evidence on the prognostic relevance of these clones for AML relapse. Here, we characterized paired pre-treatment and remission samples from 126 AML patients for mutations in 68 leukemia-associated genes. Fifty patients (40%) retained ≥1 mutation during remission at a VAF of ≥2%. Mutation persistence was most frequent in DNMT3A (65% of patients with mutations at diagnosis), SRSF2 (64%), TET2 (55%), and ASXL1 (46%), and significantly associated with older age (p < 0.0001) and, in multivariate analyses adjusting for age, genetic risk, and allogeneic transplantation, with inferior relapse-free survival (hazard ratio (HR), 2.34; p = 0.0039) and overall survival (HR, 2.14; p = 0.036). Patients with persisting mutations had a higher cumulative incidence of relapse before, but not after allogeneic stem cell transplantation. Our work underlines the relevance of mutation persistence during first remission as a novel risk factor in AML. Persistence of pre-leukemic clones may contribute to the inferior outcome of elderly AML patients. Allogeneic transplantation abrogated the increased relapse risk associated with persisting pre-leukemic clones, suggesting that mutation persistence may guide post-remission treatment.

CD7 is expressed on a subset of normal CD34-positive myeloid precursors

OBJECTIVE

To improve monitoring of myeloid neoplasms by flow cytometry-based minimal residual disease (MRD) analysis, we analyzed the significance of leukemia-associated immunophenotype (LAIP) markers in 44 patients.

METHODS

In a pilot study cohort, peripheral blood or bone marrow samples from 13 patients with myeloid neoplasms and one case of B lymphoblastic leukemia in complete hematologic remission after allogeneic bone marrow or stem cell transplantation were subjected to selection for leukemia-specific phenotypes by fluorescence-activated cell sorting using individual marker combinations, followed by PCR-based chimerism analysis.

RESULTS

The feasibility of this method could be demonstrated, with selection being successful in 12 cases, including two cases where mixed chimerism was found exclusively in sorted cells. Interestingly, four specimens displayed full donor chimerism in cells expressing the presumably aberrant combination CD34⁺ /CD7⁺ . Further analyses, including assessment of an independent cohort of 25 patients not affected by neoplastic bone marrow infiltration, revealed that normal myeloid precursors usually include a population coexpressing CD34, CD13, CD33, and CD7.

CONCLUSION

We conclude that the combination CD34⁺ /CD7⁺ might not be suitable as an LAIP for MRD diagnostics and that a subset of normal myeloid precursors in the bone marrow expresses CD7.

Impact of FLT3 Receptor (CD135) Detection by Flow Cytometry on Clinical Outcome of Adult Acute Myeloid Leukemia Patients

BACKGROUND

The significance of FMS-like tyrosine kinase 3 (FLT3)-ITD mutation in acute myeloid leukemia (AML) prognosis has been well established. The aims of this study were to investigate the prognostic impact of the FLT3 protein (CD135) expression and its association with FLT3-ITD mutation, and to identify its role in minimal residual disease.

PATIENTS AND METHODS

CD135 was measured by flow cytometry on leukemic blasts of 257 adults with de novo AML. High expression of CD135 ≥ 20% was correlated with clinical, laboratory, and other prognostic factors that influenced treatment outcome. FLT3-ITD mutation was tested by PCR.

RESULTS

The frequency of CD135 expression was 138 (53.7%) of 257. FLT3-ITD was detected in (21.4%). Positive CD135 expression was associated with high total leukocyte count (P = .006), platelet count (P = .003), monocytic leukemia (P < .001), and CD34 (P = .008) and CD117 (P = .006) expression. CD135 expression ≥ 25% was a predictor of FLT3-ITD mutation (P = .03). CD135 overexpression was a negative predictor of complete remission and of postinduction minimal residual disease at days 14 and 28 (P < .001). CD135 had an adverse impact on overall and disease-free survival (68.5% vs. 15%, P = .002). Multivariate analysis indicated CD135 was the sole independent prognostic factor for overall survival (hazard ratio = 2.49; 95% confidence interval, 1.855-3.345; P < .001).

CONCLUSION

CD135 is emerging as a prognostic factor, a new marker for minimal residual disease, and a potential novel therapeutic target of AML.

Role of minimal residual disease in the management of acute myeloid leukemia-a case-based discussion

AML is stratified into risk-categories based on cytogenetic and molecular features that prognosticate survival and facilitate treatment algorithms, though there is still significant heterogeneity within risk groupings with regard to risk of relapse and prognosis. The ambiguity regarding prognosis is due in large part to the relatively outdated criteria used to determine response to therapy. Whereas risk assessment has evolved to adopt cytogenetic and molecular profiling, response criteria are still largely determined by bone marrow morphologic assessment and peripheral cell count recovery. Minimal residual disease refers to the detection of a persistent population of leukemic cells below the threshold for morphologic CR determination. MRD assessment represents standard of care for ALL and PML, but concerns over prognostic capability and standardization have limited its use in AML. However, recent advancements in MRD assessment and research supporting the use of MRD assessment in AML require the reconsideration and review of this clinical tool in this disease entity. This review article will first compare and contrast the major modalities used to assess MRD in AML, such as RQ-PCR and flow cytometry, as well as touching upon newer technologies such as next-generation sequencing and digital droplet PCR. The majority of the article will discuss the evidence supporting the use of MRD assessment to prognosticate disease at various time points during treatment, and review the limited number of studies that have incorporated MRD assessment into novel treatment algorithms for AML. The article concludes by discussing the current major limitations to the implementation of MRD assessment in this disease. The manuscript is bookended by a clinical vignette that highlights the need for further research and refinement of this clinical tool.

Monitoring of fusion gene transcripts to predict relapse in pediatric acute myeloid leukemia

BACKGROUND

In acute myeloid leukemia (AML), accurate detection of minimal residual disease (MRD) enables better risk-stratified therapy. There are few studies, however, on the monitoring of multiple fusion transcripts and evaluation of their accuracy as indicators of MRD at multiple time points.

METHODS

We retrospectively examined RNA obtained from 82 pediatric AML patients enrolled in the Japanese Pediatric Leukemia/Lymphoma Study Group (JPLSG) AML-05 study. The expression of six important fusion transcripts (AML1(RUNX1)-ETO, CBFB-MYH11, MLL(KMT2A)-AF9, MLL-ELL, MLL-AF6, and FUS-ERG) was analyzed at five time points 30-40 days apart following diagnosis.

RESULTS

In patients with AML1-ETO (n = 36 at time point 5), all six patients with >3,000 copies and four of 30 patients with ≤3,000 copies relapsed. AML1-ETO transcripts persisted during treatment even in patients without relapse, as well as CBFB-MYH11 transcripts. In contrast, in patients with MLL-AF9 (n = 9 at time point 5), two patients were positive for MLL-AF9 expression (>50 copies) and both relapsed. Only one of seven MLL-AF9-negative patients relapsed. In the AML1-ETO group, MRD-positive patients (>3,000 copies at time point 5) had significantly lower relapse-free survival (RFS; P < 0.0001) and overall survival (OS; P = 0.009) than MRD-negative patients. Similarly, in the MLL-AF9 group, MRD-positive patients (>50 copies at time point 5) had significantly lower RFS (P = 0.002) and OS (P = 0.002) than MRD-negative patients.

CONCLUSIONS

Detection of MLL-AF9 transcripts on real-time quantitative polymerase chain reaction is a promising marker of relapse in pediatric AML. In contrast, the clinical utility of detecting AML1-ETO and CBFB-MYH11 expression is limited, although higher AML1-ETO expression can be a potential predictor of relapse when assessed according to an optimal threshold.

Acute Myeloid Leukemia: How Do We Measure Success?

The development and approval of novel, effective therapies for acute myeloid leukemia (AML) has lagged behind other malignancies. Judging success of therapy with meaningful endpoints is critical to development of new treatments. Overall survival (OS) has typically been the parameter necessary for regulatory approval of experimental therapy in AML. Herein, we discuss different strategies to define outcomes for patients with AML and their relative challenges.

[Prognostic significance of flow cytometric minimal residual disease in acute myeloid leukemia during aplasia]

Objective: To investigate the impact of minimal residual disease (MRD) by multiparameter flow cytometry (MPFC) during aplasia on efficacy and prognosis of de novo acute myeloid leukemia (AML) (non M(3)) patients. Methods: The MRD data by 8-color MPFC during aplasia (day 14-15 of induction therapy) in 85 de novo AML (non M(3)) patients and the MRD impact on efficacy and prognosis were retrospectively analyzed. Results: Data of 85 patients, including 42 males (49.4%) and 43 females (50.6%) , were collected, with a median age of 35 (15-54) years. The median MRD by MPFC during aplasia was 0.58% (0-81.11%) , and 70 (82.4%) patients achieved complete remission (CR) after first induction chemotherapy. The cutoff of MRD by receiver operating characteristic (ROC) analysis was 2.305% (Se= 0.867, Sp=0.800) . The CR rate after one course was significantly higher in patients with MRD<2.305% [96.6% (56/58) ]than in patients with MRD≥2.305%[51.9% (14/27) ] (χ(2)=22.348, P<0.001) ; no significant difference with respect to relapse-free survival rate (χ(2)=1.08, P=0.299) or overall survival rate (χ(2)=0.42, P=0.516) could be demonstrated for the comparison of the two groups. Multivariates analysis showed MRD divided by 2.305% was the only independent prognostic factor for CR after one course (OR= 21.560, 95% CI 4.129-112.579, P<0.001) . Conclusion: Flow cytometric MRD divided by 2.305% during aplasia could be a predictor of efficacy after first induction therapy in AML patients.

Haploidentical allograft is superior to matched sibling donor allograft in eradicating pre-transplantation minimal residual disease of AML patients as determined by multiparameter flow cytometry: a retrospective and prospective analysis

BACKGROUND

This study compared the effects of pre-transplantation minimal residual disease (pre-MRD) on outcomes in AML patients who underwent human leukocyte antigen-matched sibling donor transplantation (MSDT) or who received unmanipulated haploidentical allografts.

METHODS

A retrospective study (n = 339) and a prospective study (n = 340) were performed. MRD was determined using multiparameter flow cytometry.

RESULTS

Either after retrospective or prospective analysis, patients with negative pre-MRD (pre-MRDneg) had a lower incidence of relapse than those with positive pre-MRD (pre-MRDpos) in MSDT settings (P < 0.001 for all), but relapse was comparable in Haplo-SCT settings for patients with pre-MRDneg versus pre-MRDpos (P = 0.866 and 0.161, respectively). In either the retrospective (n = 65) or the prospective study (n = 76), pre-MRDpos subjects receiving Haplo-SCT experienced a lower incidence of relapse than those who underwent MSDT (P < 0.001 and p = 0.017, respectively). Of the patients with pre-MRDpos in either the total (n = 141) or the subgroup excluding cases which received donor lymphocyte infusion (DLI; n = 105), those who underwent MSDT had a higher incidence of relapse than those receiving haplo-SCT (P < 0.01 for all). Multivariate analysis showed that, for pre-MRDpos cases, haplo-SCT was associated with a low incidence of relapse and with better LFS and OS in either retrospective group, prospective group, combination groups, or subgroup not including cases which received DLI.

CONCLUSIONS

The results indicated that, for pre-MRD-positive AML patients, haplo-SCT was associated with lower incidence of relapse and better survival, suggesting a stronger anti-leukemia effect.

Immunotherapy in adult acute leukemia

The treatment of acute myeloid leukemia (AML) did not evolve profoundly in the last decades. Some improvement has been made for acute lymphoblastic leukemia (ALL). Emerging new treatment modalities, such as immunotherapy, are now beginning to be available for acute leukemia, mostly for patients suffering from ALL. This review aims to give an overview of these new therapeutic approaches, especially those already available. The focus is on cell-based immunotherapy, or molecules using preexisting host cells. Underlying mechanisms are explained and an overview of clinical experience with phase 1-3 studies is given. Immunotherapies discussed are antibody-drug conjugates, bispecific T-cell engagers (BiTEs), chimeric antigen receptor T cells (CARTs) and immune checkpoint inhibitors (ICPIs). Most of the clinical studies reviewed are in ALL patients, usually in the relapse setting, but where available, studies on AML patients were also considered. This new general treatment approach offers hope to patients with until now dismal clinical outcome. Hopes are high that future developments, and moving these therapies to an earlier treatment phase, will improve the prognosis of patients suffering from acute leukemia.

Minimal Residual Disease in Acute Myeloid Leukemia: Still a Work in Progress?

Minimal residual disease evaluation refers to a series of molecular and immunophenotypical techniques aimed at detecting submicroscopic disease after therapy. As such, its application in acute myeloid leukemia has greatly increased our ability to quantify treatment response, and to determine the chemosensitivity of the disease, as the final product of the drug schedule, dose intensity, biodistribution, and the pharmakogenetic profile of the patient. There is now consistent evidence for the prognostic power of minimal residual disease evaluation in acute myeloid leukemia, which is complementary to the baseline prognostic assessment of the disease. The focus for its use is therefore shifting to individualize treatment based on a deeper evaluation of chemosensitivity and residual tumor burden. In this review, we will summarize the results of the major clinical studies evaluating minimal residual disease in acute myeloid leukemia in adults in recent years and address the technical and practical issues still hampering the spread of these techniques outside controlled clinical trials. We will also briefly speculate on future developments and offer our point of view, and a word of caution, on the present use of minimal residual disease measurements in “real-life” practice. Still, as final standardization and diffusion of the methods are sorted out, we believe that minimal residual disease will soon become the new standard for evaluating response in the treatment of acute myeloid leukemia.

Enhancing acute myeloid leukemia therapy - monitoring response using residual disease testing as a guide to therapeutic decision-making

INTRODUCTION

Current standards for monitoring the response of acute myeloid leukemia (AML) are based on morphologic assessments of the bone marrow and recovery of peripheral blood counts. A growing experience is being developed to enhance the detection of small amounts of AML, or minimal residual disease (MRD). Areas covered: Available techniques include multi-color flow cytometry (MFC) of leukemia associated immunophenotypes (LAIP), quantitative reverse transcriptase polymerase chain reaction (QRT-PCR) for detecting fusion and mutated genes (RUNX1-RUNX1T1, CBFB-MYH11, and NPM1), overexpression of genes such as WT1, and next generation sequencing (NGS) for MRD. Expert commentary: While MRD monitoring is standard of care in some leukemia subsets such as acute promyelocytic leukemia, this approach for the broader AML population does not universally predict outcomes as some patients may experience relapse in the setting of undetectable leukemia while others show no obvious disease progression despite MRD positivity. However, there are instances where MRD can identify patients at increased risk for relapse that may change recommended therapy. Currently, prospective investigations to define clinically relevant MRD thresholds are ongoing. Risk-adapted trials are needed to best define the use of MRD in the follow up of AML patients after initial induction therapy.

Antileukemia Efficacy and Mechanisms of Action of SL-101, a Novel Anti-CD123 Antibody Conjugate, in Acute Myeloid Leukemia

Purpose: The persistence of leukemia stem cells (LSC)-containing cells after induction therapy may contribute to minimal residual disease (MRD) and relapse in acute myeloid leukemia (AML). We investigated the clinical relevance of CD34⁺CD123⁺ LSC-containing cells and antileukemia potency of a novel antibody conjugate SL-101 in targeting CD123⁺ LSCs.Experimental Methods and Results: In a retrospective study on 86 newly diagnosed AML patients, we demonstrated that a higher proportion of CD34⁺CD123⁺ LSC-containing cells in remission was associated with persistent MRD and predicted shorter relapse-free survival in patients with poor-risk cytogenetics. Using flow cytometry, we explored the potential benefit of therapeutic targeting of CD34⁺CD38^-CD123⁺ cells by SL-101, a novel antibody conjugate comprising an anti-CD123 single-chain Fv fused to Pseudomonas exotoxin A The antileukemia potency of SL-101 was determined by the expression levels of CD123 antigen in a panel of AML cell lines. Colony-forming assay established that SL-101 strongly and selectively suppressed the function of leukemic progenitors while sparing normal counterparts. The internalization, protein synthesis inhibition, and flow cytometry assays revealed the mechanisms underlying the cytotoxic activities of SL-101 involved rapid and efficient internalization of antibody, sustained inhibition of protein synthesis, induction of apoptosis, and blockade of IL3-induced p-STAT5 and p-AKT signaling pathways. In a patient-derived xenograft model using NSG mice, the repopulating capacity of LSCs pretreated with SL-101 in vitro was significantly impaired.Conclusions: Our data define the mechanisms by which SL-101 targets AML and warrant further investigation of the clinical application of SL-101 and other CD123-targeting strategies in AML. Clin Cancer Res; 23(13); 3385-95. ©2017 AACR.

Prognostic Significance of Residual Acute Myeloid Leukemia in Bone Marrow Samples Taken Prior to Allogeneic Hematopoietic Cell Transplantation

OBJECTIVES

We sought to identify features in routine evaluation of pre-hematopoietic cell transplantation (HCT) bone marrow samples from patients with acute myeloid leukemia (AML) that influenced patient outcome.

METHODS

Of 140 patients, evidence of residual leukemia (RL) was identified in 38 (27%) of pre-HCT samples, as defined by 5% or more aspirate blasts, increased blood blasts, clustered or necrotic blasts on biopsy specimens, and/or leukemia-associated karyotypic abnormalities.

RESULTS

Morphologic or karyotypic evidence of RL was significantly associated with shorter leukemia-free survival (LFS) compared with cases without identifiable RL (median, 7.1 vs 28.3 months; P  < .0001). Upon multivariable analysis, RL, prior relapse, age, high-risk karyotype, and alternate donor source were each independently associated with shorter LFS. RL in pre-HCT samples was more strongly associated with shorter LFS in patients with intermediate or favorable-risk AML karyotype ( P  = .001) than secondary or adverse karyotype-risk AML ( P  = .04).

CONCLUSIONS

Rigorous morphologic and karyotypic evaluation of pretransplant marrows is practical and important for posttransplant prognosis.

New tools in cytometry

Cytometry aims to analyze cells, of any type, using dedicated instruments. The quantitative aspect makes flow cytometry (FCM) a good complementary tool for morphology. Most of the identification tools are based on immunostaining of cell structure details and more and more tools are available in terms of specificities and labels. FCM is under exponential development thanks to technical, immunological and data analysis progresses. Actual generations are now routinely using 6 to 10 simultaneous immuno-labeling on 20 to 100,000 cells, at high speed and short sample preparation and can easily detect rare events at frequency below 10^-4 cells. Data interpretation is complex and requires expertise. Mathematical tools are available to support analysis and classification of cells based. Cells from tissues can also be analyzed by FCM after mechanical and or enzymatic separation, but in situ cells can also be analyzed with the help of cytometry. Very new instruments bring spectral analysis, image in flow and mass spectrometry. Medical applications are very broad, notably in hemopathies, immunology, solid tumors, but also microbiology, toxicology, drug discovery, food and environmental industry. But, the limit of FCM is its dependence on operator from sample preparation, instrument settings up to data analysis and a strong effort is now under progress for standardization and constitution of international data bank for references and education.

Unfavorable-risk acute myeloid leukemia dissected

PURPOSE OF REVIEW

Acute myeloid leukemia (AML) is an immensely heterogeneous disease based on the presence of varying combinations of morphologic, immunophenotypic, genetic, and molecular characteristics identified among those diagnosed with this disease. Although current therapeutic strategies provide a reasonable likelihood of achieving a complete remission for the majority of patients, relapse rates and subsequent disease-related mortality remain unacceptably high. Improved methods of risk stratification are needed to better identify patients at considerable risk of relapse in hopes of allowing for early therapeutic intervention and/or intensification that may lead to a higher likelihood of cure. The current status of risk stratification of AML and emerging technologies with potential to improve prognostic classification and outcomes are summarized in this review.

RECENT FINDINGS

Refinement of our understanding of the impact of current pretreatment AML cytogenetic, immunophenotypic, and molecular aberrations to predict outcomes and guide therapeutic decision-making is ongoing. Emerging data suggest that incorporation of the degree of posttreatment response and/or the detection of minimal residual disease can improve the accuracy of risk stratification for individual patients.

SUMMARY

Although pretreatment disease characteristics remain the hallmark of prognostication for AML patients, posttreatment parameters such as minimal residual disease assessment and degree of response to therapy possess the ability to further refine our identification of patients with unfavorable disease and thereby influence decisions regarding therapeutic planning.

Minimal Residual Disease in Acute Myeloid Leukemia of Adults: Determination, Prognostic Impact and Clinical Applications

Pretreatment assessment of cytogenetic/genetic signature of acute myeloid leukemia (AML) has been consistently shown to play a major prognostic role but also to fail at predicting outcome on individual basis, even in low-risk AML. Therefore, we are in need of further accurate methods to refine the patients’ risk allocation process, distinguishing more adequately those who are likely to recur from those who are not. In this view, there is now evidence that the submicroscopic amounts of leukemic cells (called minimal residual disease, MRD), measured during the course of treatment, indicate the quality of response to therapy. Therefore, MRD might serve as an independent, additional biomarker to help to identify patients at higher risk of relapse. Detection of MRD requires the use of highly sensitive ancillary techniques, such as polymerase chain reaction (PCR) and multiparametric flow cytometry(MPFC). In the present manuscript, we will review the current approaches to investigate MRD and its clinical applications in AML management.

Pre-transplantation minimal residual disease with cytogenetic and molecular diagnostic features improves risk stratification in acute myeloid leukemia

Our aim was to improve outcome prediction after allogeneic hematopoietic stem cell transplantation in acute myeloid leukemia by combining cytogenetic and molecular data at diagnosis with minimal residual disease assessment by multicolor flow-cytometry at transplantation. Patients with acute myeloid leukemia in first complete remission in whom minimal residual disease was assessed at transplantation were included and categorized according to the European LeukemiaNet classification. The primary outcome was 1-year relapse incidence after transplantation. Of 152 patients eligible, 48 had minimal residual disease at the time of their transplant. Minimal residual disease-positive patients were older, required more therapy to achieve first remission, were more likely to have incomplete recovery of blood counts and had more adverse risk features by cytogenetics. Relapse incidence at 1 year was higher in patients with minimal residual disease (32.6% versus 14.4%, P=0.002). Leukemia-free survival (43.6% versus 64%, P=0.007) and overall survival (48.8% versus 66.9%, P=0.008) rates were also inferior in patients with minimal residual disease. In multivariable analysis, minimal residual disease status at transplantation independently predicted 1-year relapse incidence, identifying a subgroup of intermediate-risk patients, according to the European LeukemiaNet classification, with a particularly poor outcome. Assessment of minimal residual disease at transplantation in combination with cytogenetic and molecular findings provides powerful independent prognostic information in acute myeloid leukemia, lending support to the incorporation of minimal residual disease detection to refine risk stratification and develop a more individualized approach during hematopoietic stem cell transplantation.

The prognostic value of hematogones in patients with acute myeloid leukemia

In acute myeloid leukemia (AML), new prognostic tools are needed to assess the risk of relapse. Hematogones (HGs) are normal B-lymphocyte precursors that increase in hematological diseases and may influence remission duration in AML. HG detection was prospectively investigated in 262 AML patients to determine its prognostic value. Flow cytometric HG detection was performed in bone marrow aspiration after intensive chemotherapy at the time of hematological recovery. Patients with HGs in bone marrow samples had a significantly better relapse-free survival (RFS) and overall survival (OS) than patients without HGs (P = 0.0021, and P = 0.0016). Detectable HGs independently predicted RFS (HR = 0.61, 95%CI: 0.42 - 0.89, P = 0.012) and OS (HR = 0.59, 95%CI: 0.38 - 0.92, 0.019) controlling for age, ELN classification, the number of chemotherapy cycles to achieve CR, performance status, secondary AML and flow cytometric minimal residual disease (MRD). In intensively treated AML, individual determination of HGs could be useful to stratify the optimal risk-adapted therapeutic strategy after induction chemotherapy. Am. J. Hematol. 91:566-570, 2016. © 2016 Wiley Periodicals, Inc.

The Time to Clearance of Peripheral Blood Blasts Predicts Complete Remission and Survival in Chinese Adults with Acute Myeloid Leukemia

The value of clearance of peripheral blood blasts (PBB) as a predictor of outcomes in acute myeloid leukemia (AML) is controversial. To investigate the prognostic significance of the time to clearance of PBB after induction in Chinese patients with AML, a retrospective analysis of 146 patients with newly diagnosed AML at Shanghai Ruijin Hospital was performed. Patients were categorized into early blast clearance (EBC; ≤5 days) and delayed blast clearance (DBC; >5 days) groups based on a receiver operating characteristic analysis. Complete remission (CR) after induction chemotherapy was related to the time to clearance of PBB (p < 0.001). Relapse-free survival (RFS; p = 0.003) and overall survival (p < 0.001) were longer in the EBC group. Multivariate analysis demonstrated that the time to clearance of PBB and cytogenetic risk independently predicted CR and RFS. Early clearance of PBB after induction chemotherapy can be a significant predictor of survival outcomes in AML patients.

Is the D14 bone marrow in acute myeloid leukemia still the gold standard?

PURPOSE OF REVIEW

Early bone marrow evaluation on day 14 of induction is common practice assisting in decision making regarding reinduction need in acute myeloid leukemia (AML). Studies exploring day 14 bone marrow false positive and negative rates yielded diverse data, and a highly specific method for early bone marrow evaluation is warranted. Given the improved induction-associated death rate, the risk of redundant reinduction administered to patients anticipating remission with one induction cycle may be outweighed by the benefit from the potential reduction in the falsely interpreted nadir bone marrow. The purpose of this review is to analyze current evidence on ways to optimize early bone marrow evaluation during induction in AML.

RECENT FINDINGS

Day 14 bone marrow blast count is affected by patient's age, leukemic risk, and induction regimen, and its remission prediction power is enhanced if more stringent cutoffs are used to define significant residual blast numbers or if morphologic bone marrow evaluation is performed on day 5 of induction.

SUMMARY

Early bone marrow evaluation has a potential to personalize the induction regimen, but because of limitations of day 14 bone marrow results, earlier bone marrow evaluation or the use of flow cytometry to detect minor blast populations may improve remission prediction in AML.

Minimal residual disease evaluation by flow cytometry is a complementary tool to cytogenetics for treatment decisions in acute myeloid leukaemia

The clinical utility of minimal residual disease (MRD) analysis in acute myeloid leukaemia (AML) is not yet defined. We analysed the prognostic impact of MRD level at complete remision after induction therapy using multiparameter flow cytometry in 306 non-APL AML patients. First, we validated the prognostic value of MRD-thresholds we have previously proposed (≥ 0.1%; ≥ 0.01-0.1%; and <0.01), with a 5-year RFS of 38%, 50% and 71%, respectively (p=0.002). Cytogenetics is the most relevant prognosis factor in AML, however intermediate risk cytogenetics represent a grey zone that require other biomarkers for risk stratification, and we show that MRD evaluation discriminate three prognostic subgroups (p=0.03). Also, MRD assessments yielded relevant information on favourable and adverse cytogenetics, since patients with favourable cytogenetics and high MRD levels have poor prognosis and patients with adverse cytogenetics but undetectable MRD overcomes the adverse prognosis. Interestingly, in patients with intermediate or high MRD levels, intensification with transplant improved the outcome as compared with chemotherapy, while the type of intensification therapy did not influenced the outcome of patients with low MRD levels. Multivariate analysis revealed age, MRD and cytogenetics as independent variables. Moreover, a scoring system, easy in clinical practice, was generated based on MRD level and cytogenetics.

Major impact of an early bone marrow checkpoint (day 21) for minimal residual disease in flow cytometry in childhood acute lymphoblastic leukemia

The early persistence of minimal residual disease (MRD) is considered a poor prognostic factor indicative of chemoresistance in acute lymphoblastic leukemia. In French children, chemosensitivity is assessed at day 21 post-induction by cytomorphology. Here, it was investigated whether a more precise evaluation could be obtained at this time point with multiparameter flow cytometry (MFC). This study enrolled 123 children with de novo acute lymphoblastic leukemia. MRD0 was investigated at day 21 in MFC with a combination of antibodies based on the immunophenotype of diagnosis. It was also evaluated at day 35 by immunoglobulin/T-cell receptor quantitative real-time polymerase chain reaction (MRD1). Three risk groups could be delineated based on MRD0. Patients with MFC/MRD0 levels >10^-2 (n = 25) were considered high risk, those with levels between 10^-2 and 10^-4 (n = 46) intermediate risk, and those <10^-4 (n = 50) low risk. Overall survival (p = 0.048) and event-free survival (EFS, p = 0.00017) were significantly different between these three groups. EFS of the 14 corticoresistant patients strongly depended on their MRD0 level (p = 0.004). Similarly, both EFS (p = 0.0004) and overall survival (p = 0.02) were significantly different in the 109 chemosensitive patients, according to MRD0 levels. MRD0 and MRD1 levels, compared with 112 patients, were consistent (-/- or +/+) in 57.2% of the cases. Both MRD0+/MRD1+ and MRD0+/MRD1- patients had a significantly worse EFS (p = 0.0001) than those with undetectable MRD at both MRD0 and MRD1. This study confirms the usefulness and superiority of an early point of MRD detection by MFC. In addition, MRD0 in MFC identifies a subgroup of patients with poorer prognosis (MRD0+/MRD1-). Copyright © 2015 John Wiley & Sons, Ltd.

Prognostic Value of CD11b Expression Level for Acute Myeloid Leukemia Patients: A Meta-Analysis

BACKGROUND

Study results on the prognostic value of CD11b for acute myeloid leukemia (AML) patients are inconsistent. An up-to-date meta-analysis was conducted to assess the prognostic value of CD11b expression level for AML patients.

METHODS

Electronic databases including PubMed, Embase, Cochrane Library, Web of Science and Chinese BioMedical Literature Database (CBM) were searched to identify studies that investigated the association between CD11b expression level and prognosis of AML patients. Pooled hazard ratios (HRs) with 95% confidence intervals (CIs) for overall survival (OS) and disease-free survival (DFS) and pooled odds ratio (OR) with 95% CI for complete remission rate (CRR) were calculated using Revman 5.3 and Stata 11.0.

RESULTS

13 total studies with 2619 patients were included in this meta-analysis. Results of the meta-analysis showed that CD11b positivity was associated with lower CRR (OR = 0.44; 95% CI, 0.25-0.79; p = 0.006) and shorter OS (HR = 0.66; 95% CI, 0.55-0.80; p < 0.0001), but did not affect DFS (HR = 0.67; 95% CI, 0.31-1.48; p = 0.32). Subgroup analysis by ethnicity, cut-off value for CD11b positivity, treatment, subtype and sample preparation method showed no significant interaction between these factors with the prognostic value of CD11b expression level for AML patients. Sensitivity analysis yielded consistent results with the main meta-analysis.

CONCLUSION

CD11b positivity could predict a poor prognosis for AML patients. Thus, CD11b expression level might be considered a prognostic biomarker for AML patients.

Clinical significance of day 5 peripheral blast clearance rate in the evaluation of early treatment response and prognosis of patients with acute myeloid leukemia

BACKGROUND

Minimal residual disease detection in the bone marrow is usually performed in patients with acute myeloid leukemia undergoing one course of induction chemotherapy. To optimize the chemotherapy strategies, more practical and sensitive markers are needed to monitor the early treatment response during induction. For instance, peripheral blood (PB) blast clearance rate may be considered as such a monitoring marker.

METHODS

PB blasts were monitored through multiparameter flow cytometry (MFC). Absolute counts were determined before treatment (D0) and at specified time points of induction chemotherapy (D3, D5, D7, and D9). The cut-off value of D5 peripheral blast clearance rate (D5-PBCR) was defined through receiver operating characteristic (ROC) analysis. Prognostic effects were compared among different patient groups according to D5-PBCR cut-off value.

RESULTS

D5-PBCR cut-off value was determined as 99.55%. Prognostic analysis showed that patients with D5-PBCR ≥99.55% more likely achieved complete remission (94.6% vs. 56.1%, P < 0.001) and maintained a relapse-free status than other patients (80.56% vs. 57.14%, P = 0.027). Survival analysis revealed that relapse-free survival (RFS) and overall survival (OS) were longer in patients with D5-PBCR ≥99.55% than in other patients (two-year OS: 71.0% vs. 38.7%, P = 0.011; two-year RFS: 69.4% vs. 30.7%, P = 0.026). In cytogenetic-molecular intermediate-risk group, a subgroup with worse outcome could be distinguished on the basis of D5-PBCR (<99.55%; OS: P = 0.033, RFS: P = 0.086).

CONCLUSIONS

An effective evaluation method of early treatment response was established by monitoring PB blasts through MFC. D5-PBCR cut-off value (99.55%) can be a reliable reference to predict treatment response and outcome in early stages of chemotherapy. The proposed marker may be used in induction regimen modification and help optimize cytogenetic-molecular prognostic risk stratification.

Clinical overview of anti-CD19 BiTE(®) and ex vivo data from anti-CD33 BiTE(®) as examples for retargeting T cells in hematologic malignancies

Blinatumomab, a bispecific antibody construct targeting CD19, is the most advanced member of bispecific T-cell engager (BiTE(®)) molecules. The clinical development program includes B-precursor acute lymphoblastic leukemia (ALL) and B-cell non-Hodgkin lymphoma (NHL). Minimal residual disease (MRD) response in patients with MRD-positive B-precursor ALL has translated into long-term clinical benefits as demonstrated by an estimated relapse-free survival (RFS) of 60% with sustained MRD negativity at a follow-up of 31 months. Remissions induced in pediatric and adult patients with relapsed/refractory B-precursor ALL have allowed for successful allogeneic hematopoietic stem cell transplantation (HSCT) in this setting. Blinatumomab has also induced durable responses in low-grade B-cell NHL. Blinatumomab recently gained approval in the United States by the U.S. Food and Drug Administration for treatment of Philadelphia chromosome-negative B-precursor relapsed/refractory acute lymphoblastic leukemia. AMG 330 is an investigational anti-CD33 BiTE(®) antibody construct. Targeting CD33 ex vivo in primary samples from patients with acute myeloid leukemia (AML) has shown AMG 330-mediated T-cell expansion and T-cell cytotoxicity against AML cells.

New generation dendritic cell vaccine for immunotherapy of acute myeloid leukemia

Dendritic cell (DC)-based immunotherapy is a promising strategy for the elimination of minimal residual disease in patients with acute myeloid leukemia (AML). Particularly, patients with a high risk of relapse who are not eligible for hematopoietic stem cell transplantation could benefit from such a therapeutic approach. Here, we review our extensive studies on the development of a protocol for the generation of DCs with improved immunogenicity and optimized for the use in cell-based immunotherapy. This new generation DC vaccine combines the production of DCs in only 3 days with Toll-like receptor-signaling-induced cell maturation. These mature DCs are then loaded with RNA encoding the leukemia-associated antigens Wilm's tumor protein 1 and preferentially expressed antigen in melanoma in order to stimulate an AML-specific T-cell-based immune response. In vitro as well as in vivo studies demonstrated the enhanced capacity of these improved DCs for the induction of tumor-specific immune responses. Finally, a proof-of-concept Phase I/II clinical trial is discussed for post-remission AML patients with high risk for disease relapse.