Quantitation of minimal residual disease in acute myelogenous leukemia and myelodysplastic syndromes in complete remission by molecular cytogenetics of progenitor cells

Prognostic value of combined WT1 and multiparameter flow cytometry assessment for measurable residual disease after induction in non-APL acute myeloid leukemia

The objective of this study was to investigate the expression pattern of Wilms tumor 1 (WT1) gene at diagnosis, complete remission (CR) and relapse status in non-acute promyelocytic leukemia (non-APL) acute myeloid leukemia (AML) patients, and further explore the prognostic value of measurable residual disease (MRD) assessment by WT1 gene and multiparameter flow cytometry (MFC). Our results showed that the average expression level of WT1 was 4026 ± 616.1 copies/104 ABL at diagnosis, 155.3 ± 36.03 copies/104 ABL at CR, and 1766 ± 238.8 copies/104 ABL at relapse, with statistically significant differences (p = .000). ROC analysis showed that WT1 expression levels were 118.1 copies/104 ABL and MFC-MRD was 0.155%, which had good predictive efficacy for relapse of patients during consolidation therapy. Both WT1-MRD and MFC-MRD had a significant impact on relapse-free survival (RFS) and overall survival (OS). Patients with WT1-MRD positive or MFC-MRD positive were associated with worse RFS (HR 3.840, 95% CI 1.582-9.320, p = .003), (HR 4.464, 95% CI 1.841-10.984, p = .001) and worse OS (HR 2.963, 95% CI 1.058-8.295, p = .039), (HR 3.590, 95% CI 1.254-10.280, p = .017). Besides, compared with patients who were negative for both WT1-MRD and MFC-MRD, patients who were positive both WT1-MRD and MFC-MRD were associated with worse RFS (HR 6.200, 95% CI 2.206-17.430, p = .001) and worse OS (HR 4.886, 95% CI 1.388-17.197, p = .013). This study demonstrates that combined assessment of MRD by WT1 and MFC improves relapse and prognosis prediction in non-APL AML patients, and may help guide interventions for disease relapse.

Acute Myeloid Leukemia Stem Cells in Minimal/Measurable Residual Disease Detection

Acute myeloid leukemia (AML) is a hematological malignancy characterized by an abundance of incompletely matured or immature clonally derived hematopoietic precursors called leukemic blasts. Rare leukemia stem cells (LSCs) that can self-renew as well as give rise to leukemic progenitors comprising the bulk of leukemic blasts are considered the cellular reservoir of disease initiation and maintenance. LSCs are widely thought to be relatively resistant as well as adaptive to chemotherapy and can cause disease relapse. Therefore, it is imperative to understand the molecular bases of LSC forms and functions during different stages of disease progression, so we can more accurately identify these cells and design therapies to target them. Irrespective of the morphological, cytogenetic, and cellular heterogeneity of AML, the uniform, singularly important and independently significant prognosticator of disease response to therapy and patient outcome is measurable or minimal residual disease (MRD) detection, defined by residual disease detection below the morphology-based 5% blast threshold. The importance of LSC identification and frequency estimation during MRD detection, in order to make MRD more effective in predicting disease relapse and modifying therapeutic regimen is becoming increasingly apparent. This review focuses on summarizing functional and cellular composition-based LSC identification and linking those studies to current techniques of MRD detection to suggest LSC-inclusive MRD detection as well as outline outstanding questions that need to be addressed to improve the future of AML clinical management and treatment outcomes.

Phase 1 study of combinatorial sorafenib, G-CSF, and plerixafor treatment in relapsed/refractory, FLT3-ITD-mutated acute myelogenous leukemia patients

Stroma-leukemia interactions mediated by CXCR4, CD44, VLA4, and their respective ligands contribute to therapy resistance in FLT3-ITD-mutated acute myelogenous leukemia (AML). We conducted a phase 1 study with the combination of sorafenib (a FLT3-ITD inhibitor), plerixafor (a SDF-1/CXCR4 inhibitor), and G-CSF (that cleaves SDF-1, CD44, and VLA4). Twenty-eight patients with relapsed/refractory FLT3-ITD-mutated AML were enrolled from December 2010 to December 2013 at three dose levels of sorafenib (400, 600, and 800 mg twice daily) and G-CSF and plerixafor were administered every other day for seven doses starting on day one. Sorafenib 800 mg twice daily was selected for the expansion phase. While no dose-limiting toxicities (DLT) were encountered in the four-week DLT window, hand-foot syndrome and rash were seen beyond the DLT window, which required dose reductions in most patients. The response rate was 36% (complete response (CR) = 4, complete remission with incomplete platelet recovery (CRp) = 4, complete remission with incomplete hematologic recovery (CRi) = 1, and partial response (PR) = 1) for the intention to treat population. Treatment resulted in 58.4 and 47 mean fold mobilization of blasts and CD34 /38- stem/progenitor cells, respectively, to the circulation. Expression of the adhesion molecules CXCR4, CD44, and VLA4 on circulating leukemia cells correlated negatively with the mobilization of CD34+/38-, CD34+/38-/123+ "progenitor" cells (all P ≤ .002). Mass cytometry analysis of sequential samples from two patients demonstrated resistance emerging early on from sub-clones with persistent Akt and/or ERK signaling. In conclusion, the strategy of combined inhibition of FLT3 kinase and stromal adhesive interactions has promising activity in relapsed/refractory, FLT3-ITD-mutated AML, which warrants further evaluation in the front-line setting.

Achieving stringent CR is essential before reduced-intensity conditioning allogeneic hematopoietic cell transplantation in AML

Reduced-intensity conditioning (RIC) allogeneic hematopoietic cell transplantation (allo-HCT) can cure patients with AML in CR. However, relapse after RIC allo-HCT may indicate heterogeneity in the stringency of CR. Strict definition of CR requires no evidence of leukemia by both morphologic and flow cytometric criteria. We re-evaluated 85 AML patients receiving RIC allo-HCT in CR to test if a strict definition of CR had direct implications for the outcome. These patients had leukemia immunophenotype documented at diagnosis and analyzed at allo-HCT. Eight (9.4%) had persistent leukemia by flow cytometric criteria at allo-HCT. The patients with immunophenotypic persistent leukemia had a significantly increased relapse (hazard ratio (HR): 3.7; 95% confidence interval (CI): 1.3-10.3, P=0.01) and decreased survival (HR: 2.9; 95% CI: 1.3-6.4, P<0.01) versus 77 patients in CR by both morphology and flow cytometry. However, the pre-allo-HCT bone marrow (BM) blast count (that is, 0-4%) was not significantly associated with risks of relapse or survival. These data indicate the presence of leukemic cells, but not the BM blast count affects survival. A strict morphologic and clinical lab flow cytometric definition of CR predicts outcomes after RIC allo-HCT, and therefore is critical to achieve at transplantation.

Fluorescent in situ hybridization of DNA probes in the interphase and metaphase stages of the cell cycle

In the past decade, fluorescent in situ hybridization (FISH) has been used routinely in detecting molecular abnormalities in the interphase and metaphase stages of the cell cycle. Many of the molecular anomalies which are detected in this manner are diagnostic of a prenatal, postnatal, or neoplastic genetic disorder. With the continuous isolation of commercially available DNA probes specific to a particular chromosome region, FISH analysis has become standardized in its ability to detect characteristic chromosomal anomalies in association with genetic and neoplastic diseases. In recent years, FISH has also become automated to accommodate the increased volume of slide preparations necessary for the number of DNA probes needed to detect characteristic molecular anomalies in cancer tissues and bone marrow samples. FISH technology provides essential information to the physician regarding the diagnosis, response to treatment, and ultimately the prognosis of their patients' disorder. It has become an important source of information routinely used in conjunction with chromosome analyses, and presently to confirm molecular alterations detected by array comparative genomic hybridization (aCGH) analyses. In this chapter we describe the methods for performing FISH analyses in order to determine the presence or the absence of genetic abnormalities which define whether the patient has either a genetic syndrome or malignant disease.

Image cytometry-based detection of aneuploidy by fluorescence in situ hybridization in suspension

Cytogenetic abnormalities are important diagnostic and prognostic criteria for hematologic malignancies. Karyotyping and fluorescence in situ hybridization (FISH) are the conventional methods by which these abnormalities are detected. The sensitivity of these microscopy-based methods is limited by the abundance of the abnormal cells in the samples and therefore these analyses are commonly not applicable to minimal residual disease (MRD) stages. A flow cytometry-based imaging approach was developed to detect chromosomal abnormalities following FISH in suspension (FISH-IS), which enables the automated analysis of several log-magnitude higher number of cells compared with the microscopy-based approaches. This study demonstrates the applicability of FISH-IS for detecting numerical chromosome aberrations, establishes accuracy, and sensitivity of detection compared with conventional FISH, and feasibility to study procured clinical samples of acute myeloid leukemia (AML). Male and female healthy donor peripheral blood mononuclear cells hybridized with combinations of chromosome enumeration probes (CEP) 8, X, and Y served as models for disomy, monosomy, and trisomy. The sensitivity of detection of monosomies and trisomies amongst 20,000 analyzed cells was determined to be 1% with a high level of precision. A high correlation (R(2) = 0.99) with conventional FISH analysis was found based on the parallel analysis of diagnostic samples procured from 10 AML patients with trisomy 8 (+8). Additionally, FISH-IS analysis of samples procured at the time of clinical remission demonstrated the presence of residual +8 cells indicating that this approach may be used to detect MRD and associated chromosomal defects.

Argininosuccinate lyase deficiency. Genet Med. 2012;14:501-507. [PMID: 22241104 DOI: 10.1038/gim.2011.1]

The urea cycle consists of six consecutive enzymatic reactions that convert waste nitrogen into urea. Deficiencies of any of these enzymes of the cycle result in urea cycle disorders (UCDs), a group of inborn errors of hepatic metabolism that often result in life-threatening hyperammonemia. Argininosuccinate lyase (ASL) catalyzes the fourth reaction in this cycle, resulting in the breakdown of argininosuccinic acid to arginine and fumarate. ASL deficiency (ASLD) is the second most common UCD, with a prevalence of ~1 in 70,000 live births. ASLD can manifest as either a severe neonatal-onset form with hyperammonemia within the first few days after birth or as a late-onset form with episodic hyperammonemia and/or long-term complications that include liver dysfunction, neurocognitive deficits, and hypertension. These long-term complications can occur in the absence of hyperammonemic episodes, implying that ASL has functions outside of its role in ureagenesis and the tissue-specific lack of ASL may be responsible for these manifestations. The biochemical diagnosis of ASLD is typically established with elevation of plasma citrulline together with elevated argininosuccinic acid in the plasma or urine. Molecular genetic testing of ASL and assay of ASL enzyme activity are helpful when the biochemical findings are equivocal. However, there is no correlation between the genotype or enzyme activity and clinical outcome. Treatment of acute metabolic decompensations with hyperammonemia involves discontinuing oral protein intake, supplementing oral intake with intravenous lipids and/or glucose, and use of intravenous arginine and nitrogen-scavenging therapy. Dietary restriction of protein and dietary supplementation with arginine are the mainstays in long-term management. Orthotopic liver transplantation (OLT) is best considered only in patients with recurrent hyperammonemia or metabolic decompensations resistant to conventional medical therapy.

Evaluation of ex vivo expanded human NK cells on antileukemia activity in SCID-beige mice

The possibility of using natural killer (NK) cells in treatment of human hematological malignancies has increased in recent years. One factor contributing to this is the introduction of new methods for ex vivo generation of enriched populations of clinical grade NK cells. The objective of the present study was to evaluate the safety and efficacy of human ex vivo expanded clinical grade NK cells against K562 leukemia cells in severe combined immunodeficiency disease (SCID)-beige mice. Irradiated SCID-beige mice were injected intravenously (i.v.) with K562 leukemia cells. Following leukemia cell injection, mice were injected with ex vivo expanded human NK cells. NK cells were followed in vivo and mice monitored for survival from leukemia. Administration of these ex vivo expanded clinical grade NK cells was safe and prevented leukemia development. In conclusion, these results imply possibilities for the use of this NK cell preparation in treatment trials of human hematological malignancies and possibly other forms of cancer.

Establishment and study of different real-time polymerase chain reaction assays for the quantification of cells with deletions of chromosome 7

The evaluation of residual disease, which has prognostic value in the treatment of hematological malignancies, is currently assessed by scoring a limited number of cells by karyotyping and molecular cytogenetics. Real-time polymerase chain reaction (PCR) is an easier and more sensitive technique, enables analysis of a larger number of cells, and decreases sampling error. However, real-time PCR has been applied only to target transcripts of fusion genes. Here, we considered two real-time PCR strategies to quantify a number of cells carrying a partial deletion of chromosome 7 mixed with normal disomic cells. The first strategy was based on the amplification of two sequences, one on chromosome 7 and the other on chromosome 14. In the second strategy residual disease was assessed by the ratio between the two alleles of a bi-allelic marker, mapped on chromosome 7, measured with allele-specific assays. Precision and accuracy of the two approaches were tested by reference samples with nominal values of residual disease ranging from 2 to 95%. As expected the second strategy resulted in more precise and accurate monitoring within the range from 5 to 95%. Furthermore, this method may be applied to assess the number of dysplastic or neoplastic clones carrying any unbalanced chromosome changes.

An in vivo propagated human acute myeloid leukemia expressing ABCA3

Analyzing the regenerative compartment in the blast cell population of patients with acute myeloid leukemia (AML) may yield important insights into the mechanisms of disease progression. Here we present findings with a human AML cell line (AML-SP1), initiated from leukemic precursor cells and consecutively propagated by serial xenotransplantation in vivo. AML-SP1 maintained the characteristics of a human AML, consistently exhibiting a small leukemic side population (SP) of blast cells with high Hoechst 33342 exclusion. In the AML-SP1 line, an increased expression of the ABC transporters MDR1, MRP, ABCG2 and ABCA3 was found in the SP cells. The detection of ABCA3 in leukemic progenitor cells merits further investigation with regard to intracellular drug transport in AML blast cells. In vivo propagation of leukemias, such as AML-SP1 is a model system of maintaining the populational heterogeneity of AML disease, especially the unique characteristics of leukemic SP cells.

Monitoring treatment efficiency in MDS at the molecular level; possibilities now and in the future

Myelodysplastic syndromes (MDS) are a heterogeneous group of bone marrow (BM) diseases. MDS patients suffer from bone marrow failure because of the expansion of a malignant clone, resulting in abnormal differentiation of blood cells and severe pancytopenias. MDS patients have a high propensity for the development of acute myeloid leukemia (AML). During the last few years it has become increasingly clear that MDS is a stem cell disease. Two methods have generally been used to study the clonal origin of MDS bone marrow cells. First, the combination of fluorescent in situ hybridization (FISH) in combination with cell sorting has been used to study MDS specific numerical chromosomal aberrations in various cell types. Secondly, the determination of the X-chromosome inactivation patterns (XCIP) in different cell types of female MDS patients has been used to study clonality irrespective of the presence of a disease-specific marker. Both techniques have also been used to monitor treatment efficiency. Both methods showed that a molecular remission occurred in approximately half of the patients who achieved complete clinical remission after intensive antileukemic treatment, depending on the study and the type of treatment. In case of cytogenetic analysis this proved to be of prognostic significance. This review discusses the advantages and disadvantages of both techniques for the determination of clonality at diagnosis as well as for the assessment of treatment efficiency in past and in ongoing clinical trials. Future directions and possibilities for further research are also discussed.

Determination of cutoff values to detect small aneuploid clones by interphase fluorescence in situ hybridization: the Poisson model is a more appropriate approach. Should single-cell trisomy 8 be considered a clonal defect?

We applied a dual-color interphase in situ fluorescence hybridization (I-FISH) technique using centromeric probes specific to chromosomes 7 and 8 on 20 control samples in order to define the statistical model best suited to determine cutoff values for detection of small abnormal clones. We found that the Poisson model is a more appropriate approach than a Gaussian model. Then, based on the analysis of 91 samples from 80 patients with myelocytic malignant hemopathies and either clonal or nonclonal -7 or +8 as determined with conventional cytogenetics (CC), we compared the respective power of I-FISH and CC for detection of aneuploidy, with special emphasis on the potential contribution of I-FISH as a complement to CC in the case of small abnormal clones. The I-FISH results were positive in samples with clonal -7 or +8 according to CC analysis. Whereas I-FISH was negative in samples with nonclonal -7 according to CC, thus confirming the reliability of the criteria used to define the clonality of -7; the situation was different with nonclonal +8. I-FISH revealed the clonality of +8 in most samples with single-cell +8. In several cases, however, the unquestionable clonal nature of +8, as evidenced during follow-up, could not be established with either CC or I-FISH according to accepted criteria. Our data suggest that, in case of a single metaphase with +8, the general rule should be amended and the single-cell +8 should be considered and reported as potentially clonal.

Monitoring bcr-abl by polymerase chain reaction in the treatment of chronic myeloid leukemia

The elucidation of the molecular biology of chronic myeloid leukemia (CML) has provided a paradigm for understanding leukemogenesis, targeted drug development, and disease monitoring at the molecular level. Minimal residual disease (MRD) monitoring by fluorescence in situ hybridization and polymerase chain reaction (PCR) has become an important tool in predicting relapse after allogeneic transplant, allowing for early intervention strategies such as donor lymphocyte infusion. MRD monitoring is important for assessment of disease status in patients who obtain a complete cytogenetic remission, and this approach is likely to play an important role in following patients to determine who will relapse on imatinib mesylate therapy. This review focuses primarily on MRD monitoring by PCR.

Comparison of cytogenetics with FISH in 40 myelodysplastic syndrome patients

Karyotyping is important for diagnosis and prognosis of myelodysplastic syndrome (MDS). Using fluorescence in situ hybridization (FISH) either mitotic or interphase cells can be analyzed and a higher number of cells can be screened. This study evaluated the effectiveness of FISH in detecting the most common chromosomal abnormalities [-5/del 5q/-7/+8/del 11q23 and -Y] in 40 patients with MDS. Karyotype detected abnormalities in 35.2% of the patients and FISH in 35%, while some abnormalities remained undetected by each approach but the association of both methods increased the detection rate up to 40%.

Detection of minimal residual disease in peripheral blood stem cells from two acute myeloid leukemia patients with trisomy 8 predicts early relapse after autologous bone marrow transplantation

We report two cases of acute myeloid leukemia (AML) French-American-British M4 classification with trisomy 8 at diagnosis as the sole chromosome abnormality. Both patients were treated with the GIMEMA AML-10 protocol and underwent autologous bone marrow transplantation (ABMT) in hematologic remission. Peripheral blood stem cells (PBSC), and bone marrow in one patient, were collected after consolidation therapy and tested by fluorescence in situ hybridization (FISH) analysis with an alpha-satellite probe for chromosome 8. It revealed that all samples were positive for minimal residual disease (MRD) as the value of trisomic cells exceeded the mean +3 standard deviations of the controls. ABMT was done following a myeloablative regimen (busulphan/cyclophosphamide) and PBSC were reinfused. Both patients relapsed, 4 and 2 months, respectively, after autotransplant. Although more data are needed, these results suggest that the persistence of MRD, as detected by FISH, in stem cell collections, is associated with a poor outcome in AML patients with trisomy 8 undergoing ABMT.

Molecular cytogenetics

Refinements in cytogenetic techniques over the past 30 years have allowed the increasingly sensitive detection of chromosome abnormalities in haematological malignancies. In particular, the advent of fluorescence in situ hybridization techniques has provided significant advances in both diagnosis and research of leukaemias. The application of new multicolour karyotyping techniques has allowed the complete dissection of complex chromosome rearrangements and provides the prospect of identifying new recurrent chromosome rearrangements. Both comparative genomic hybridization and interphase fluorescence in situ hybridization avoid the use of metaphase chromosomes altogether and have allowed the genetic analysis of previously intractable targets. Recent developments in comparative genomic hybridization to DNA microarrays provide the promise of high resolution and automated screening for chromosomal imbalances. Rather than replacing conventional cytogenetics, however, these techniques have extended the range of cytogenetic analyses when applied in a complementary fashion.

A leukemic stem cell with intrinsic drug efflux capacity in acute myeloid leukemia

The hematopoietic stem cell underlying acute myeloid leukemia (AML) is controversial. Flow cytometry and the DNA-binding dye Hoechst 33342 were previously used to identify a distinct subset of murine hematopoietic stem cells, termed the side population (SP), which rapidly expels Hoechst dye and can reconstitute the bone marrow of lethally irradiated mice. Here, the prevalence and pathogenic role of SP cells in human AML were investigated. Such cells were found in the bone marrow of more than 80% of 61 patients and had a predominant CD34(low/-) immunophenotype. Importantly, they carried cytogenetic markers of AML in all 11 cases of active disease examined and in 2 out of 5 cases in complete hematological remission. Comparison of daunorubicin and mitoxantrone fluorescence emission profiles revealed significantly higher drug efflux from leukemic SP cells than from non-SP cells. Three of 28 SP cell transplants generated overt AML-like disease in nonobese diabetic--severe combined immunodeficient mice. Low but persistent numbers of leukemic SP cells were detected by molecular and immunological assays in half of the remaining mice. Taken together, these findings indicate that SP cells are frequently involved in human AML and may be a target for leukemic transformation. They also suggest a mechanism by which SP cells could escape the effects of cytostatic drugs and might eventually contribute to leukemia relapse. (Blood. 2001;98:1166-1173)

Studies of minimal residual disease in acute lymphocytic leukemia

During the past 2 decades, there has been considerable progress made in the treatment of childhood and adult lymphocytic leukemia (ALL). Currently, 70% to 90% of adults achieve a complete remission, and 25% to 50% of these patients may experience prolonged disease-free survival and may be cured of their disease. Unfortunately, most adults with ALL will ultimately experience a recurrence and die of their leukemia. Although most children with ALL may now be cured with current therapeutic regimens, the ability to distinguish good-risk patients from those who are likely to relapse has important clinical implications. Relapse, in most pediatric and adult cases, is thought to result from residual leukemia cells that remain following achievement of "complete" remission but are below the limits of detection using conventional morphologic assessment of the bone marrow. Sensitive techniques are now available to detect subclinical levels of residual leukemia, termed minimal residual disease.

Myelodysplasia

The epidemiology of myelodysplasia, or myelodysplastic syndrome (MDS), is in evolution. As populations are aging and therapies for cancer are improving, the frequency of this disease is increasing. Recent population surveys and case-control studies are reviewed. Knowledge of the molecular pathogenesis and pathophysiology of MDS is advancing at a remarkable pace and new information on molecular events is presented. The treatment of MDS is complex and highly individualized. Although many patients are older and may have significant co-morbid disease or poor performance status, there are curative options with allogeneic transplantation for selected patients. The recent transplant publications are reviewed. Other investigative treatment approaches, including the use of new chemotherapy agents, growth factor combinations, and antithymocyte globulin appear promising and are reviewed.

Minimal residual disease

Monitoring of residual disease in patients with malignant hematologic disorders has been recognized as an important diagnostic tool for assessment of the response to treatment and the individual risk of relapse. In a number of malignancies, employment of sensitive techniques permitting the identification of tumor cells within a 10(4)-fold or greater excess of normal cells revealed that the presence and persistence of residual disease at this level does not necessarily imply inevitable relapse. Several studies demonstrated that surveillance of persisting neoplastic cells by quantitative techniques can provide prognostically relevant information on the sensitivity of the malignant population to the treatment applied and the biologic behavior of the residual tumor cell clone during and after therapy. It has been shown in different types of leukemia that investigation of the level or the dynamics of residual disease by sensitive and quantitative approaches can provide a basis for clinical decision making.