Improved flow cytometric detection of minimal residual disease in childhood acute lymphoblastic leukemia

Next-Generation Sequencing in Adult B Cell Acute Lymphoblastic Leukemia Patients

We used next-generation sequencing (NGS) of the immunoglobulin genes to evaluate residual disease in 153 specimens from 32 patients with adult B cell acute lymphoblastic leukemia enrolled in a single multicenter study. The sequencing results were compared with multiparameter flow cytometry (MFC) data in 66 specimens (25 patients) analyzed by both methods. There was a strong concordance (82%) between the methods in the qualitative determination of the presence of disease. However, in 17% of cases, leukemia was detected by sequencing but not by MFC. In 54 bone marrow (BM) and peripheral blood (PB) paired specimens, the burden of leukemia detected by NGS was lower in PB than in BM, although it was still detectable in 68% of the 28 paired specimens with positive BM. Lastly, patients without disease detected by NGS or MFC had a 5-year relapse free survival of > 80%. The results suggest that residual disease detection by immunoglobulin gene sequencing is an extremely sensitive technique and may identify patients that might benefit from transplantation. Moreover, the increased sensitivity of the method may allow frequent peripheral blood testing to supplement marrow sampling to measure disease response.

Standardized flow cytometry for highly sensitive MRD measurements in B-cell acute lymphoblastic leukemia

A fully-standardized EuroFlow 8-color antibody panel and laboratory procedure was stepwise designed to measure minimal residual disease (MRD) in B-cell precursor (BCP) acute lymphoblastic leukemia (ALL) patients with a sensitivity of ≤10^-5, comparable to real-time quantitative polymerase chain reaction (RQ-PCR)-based MRD detection via antigen-receptor rearrangements. Leukocyte markers and the corresponding antibodies and fluorochromes were selected based on their contribution in separating BCP-ALL cells from normal/regenerating BCP cells in multidimensional principal component analyses. After 5 multicenter design-test-evaluate-redesign phases with a total of 319 BCP-ALL patients at diagnosis, two 8-color antibody tubes were selected, which allowed separation between normal and malignant BCP cells in 99% of studied patients. These 2 tubes were tested with a new erythrocyte bulk-lysis protocol allowing acquisition of high cell numbers in 377 bone marrow follow-up samples of 178 BCP-ALL patients. Comparison with RQ-PCR-based MRD data showed a clear positive relation between the percentage concordant cases and the number of cells acquired. For those samples with >4 million cells acquired, concordant results were obtained in 93% of samples. Most discordances were clarified upon high-throughput sequencing of antigen-receptor rearrangements and blind multicenter reanalysis of flow cytometric data, resulting in an unprecedented concordance of 98% (97% for samples with MRD < 0.01%). In conclusion, the fully standardized EuroFlow BCP-ALL MRD strategy is applicable in >98% of patients with sensitivities at least similar to RQ-PCR (≤10^-5), if sufficient cells (>4 × 10⁶, preferably more) are evaluated.

Investigating CD99 Expression in Leukemia Propagating Cells in Childhood T Cell Acute Lymphoblastic Leukemia

A significant number of children with T-lineage acute lymphoblastic leukemia (T-ALL) fail to respond to therapy and experience early relapse. CD99 has been shown to be overexpressed on T-ALL cells and is considered to be a reliable detector of the disease. However, the relevance of CD99 overexpression in ALL has not been investigated in a functional context. The aim of this study was to investigate the functional capacity of CD99⁺ cells in childhood ALL and determine the suitability of CD99 as a therapeutic target. Flow cytometric analyses confirmed higher expression of CD99 in ALL blasts (81.5±22.7%) compared to normal hemopoietic stem cells (27.5±21.9%) and T cells (3.1±5.2%, P≤0.004). When ALL cells were sorted and assessed in functional assays, all 4 subpopulations (CD34⁺/CD99⁺, CD34⁺/CD99^-, CD34^-/CD99⁺ and CD34^-/CD99^-) could proliferate in vitro and establish leukemia in NSG mice. Leukemia propagating cell frequencies ranged from 1 in 300 to 1 in 7.4x10⁴ but were highest in the CD34⁺/CD99^- subpopulation. In addition, all four subpopulations had self-renewal ability in secondary NSG mice. Cells in each subpopulation contained patient specific TCR rearrangements and karyotypic changes that were preserved with passage through serial NSG transplants. Despite high levels of CD99 antigen on the majority of blast cells, leukemia initiating capacity in vivo was not restricted to cells that express this protein. Consequently, targeting CD99 alone would not eliminate all T-ALL cells with the ability to maintain the disease. The challenge remains to develop therapeutic strategies that can eliminate all leukemia cells with self-renewal capacity in vivo.

Development-associated immunophenotypes reveal the heterogeneous and individualized early responses of adult B-acute lymphoblastic leukemia

B cell acute lymphoblastic leukemia (B-ALL) exhibits phenotypes reminiscent of normal stages of B-cell development. As demonstrated by flow cytometry, the immunophenotypes are able to determine the stages of B cell development. Multicolor flow cytometry (MFC) is more accurate at identifying cell populations. In this study, 9-color panels, including CD10, CD19, CD20, CD22, CD34, CD79a, CD179a, and IgM, which are sequentially expressed during B cell development, were designed to detect the leukemia cell subpopulations in adult B-ALL patients. In 23 patients at diagnosis, 192 heterogeneous subpopulations of leukemia cells were detected. Compared with their counterparts at diagnosis and after the 1st course of induction therapy, the responses of the subpopulations were also heterogeneous. In the CD10 population, the residual B cell subpopulations in the BCR/ABL patients were obviously reduced compared to those in the BCR/ABL patients. New subpopulations were detected in 22 of 23 patients and were primarily located in the CD34CD10 populations. Subpopulations of clonal evolution were heterogeneous after induction therapy. Our results suggest that the subpopulations in B-ALL patients should be dynamically monitored by development-associated immunophenotyping before, during, and after induction therapy and to predict the prognosis of the disease.

Excellent outcome of minimal residual disease-defined low-risk patients is sustained with more than 10 years follow-up: results of UK paediatric acute lymphoblastic leukaemia trials 1997-2003

BACKGROUND

Minimal residual disease (MRD) is defined as the presence of sub-microscopic levels of leukaemia. Measurement of MRD from bone marrow at the end of induction chemotherapy (day 28) for childhood acute lymphoblastic leukaemia (ALL) can highlight a large group of patients (>40%) with an excellent (>90%) short-term event-free survival (EFS). However, follow-up in recent published trials is relatively short, raising concerns about using this result to infer the safety of further therapy reduction in the future.

METHODS

We examined MRD data on 225 patients treated on one of three UKALL trials between 1997 and 2003 to assess the long-term (>10 years follow-up) outcome of those patients who had low-risk MRD (<0.01%) at day 28.

RESULTS

Our pilot data define a cohort of 53% of children with MRD <0.01% at day 28 who have an EFS of 91% and long-term overall survival of 97%. Of 120 patients with day-28 MRD <0.01% and extended follow-up, there was one death due to treatment-related toxicity, one infectious death while in complete remission, and four relapse deaths.

CONCLUSIONS

The excellent outcome for childhood ALL in patients with MRD <0.01% after induction chemotherapy is sustained for more than 10 years from diagnosis. This supports the potential exploration of further reduction of therapy in this group, in an attempt to reduce treatment-related mortality and late effects.

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.

A novel and easy FxCycle™ violet based flow cytometric method for simultaneous assessment of DNA ploidy and six-color immunophenotyping

Abnormal DNA ploidy is a valuable prognostic factor in many neoplasms, especially in hematological neoplasms like B-cell acute lymphoblastic leukemia (B-ALL) and multiple myeloma (MM). Current methods of flow-cytometric (FC) DNA-ploidy evaluation are either technically difficult or limited to three- to four-color immunophenotyping and hence, challenging to evaluate DNA-ploidy in minute tumor population with background rich of its normal counterpart cells and other hematopoietic cells. We standardized a novel sensitive and easy method of simultaneous evaluation of six- to seven-color immunophenotyping and DNA-ploidy using a dye-FxCycle Violet (FCV). Linearity, resolution, and coefficient of variation (CV) for FCV were studied using chicken erythrocyte nuclei. Ploidy results of FCV were compared with Propidium iodide (PI) in 20 samples and intra-assay variation for FCV was studied. Using this six-color immunophenotyping & FCV-protocol DNA-ploidy was determined in bone-marrow samples from 124 B-ALL & 50 MM patients. Dilution experiment was also conducted to determine the sensitivity in detection of aneuploidy in minute tumor population. FCV revealed high linearity and resolution in 450/50 channel. On comparison with PI, CV of Go/G1-peak with FCV (mean-CV 4.1%) was slightly higher than PI (mean-CV 2.9%) but had complete agreement in ploidy results. Dilution experiment showed that aneuploidy could be accurately detected up to the limit of 0.01% tumor cells. Intra-assay variation was very low with CV of 0.005%. In B-ALL, hypodiploidy was noted in 4%, hyperdiploidy in 24%, near-hyperdiploidy in 13% and remaining 59% were diploid. In MM, hypodiploidy was in 2%, hyperdiploidy in 58%, near-hyperdiploidy in 8% and remaining 30% were diploid. FCV-based DNA-ploidy method is a sensitive and easy method for simultaneous evaluation of six-color immunophenotyping and DNA analysis. It is useful in DNA-ploidy evaluation of minute tumor population in cases like minimal residual disease and MM precursor conditions.

Effects of plant-derived anti-leukemic drugs on individualized leukemic cell population profiles in Egyptian patients

Leukemias are a group of cancer types that originate from blood-forming tissues. In this disease, an abnormally large number of immature white blood cells is produced by the bone marrow. The relationship between treatments with plant-derived drugs and leukemia-associated immunophenotypes (LAIPs) of clinically isolated leukemia cells has yet to be established. The aim of the present study was to develop a preliminary clinical prognostic map for commonly expressed LAIPs in patients clinically diagnosed with leukemia, as well as to assess the potential involvement of LAIPs in the response rate to 10 natural products of plant origin. An increased expression of LAIPs, including CD4, CD14, CD33 and CD34, was considered a surrogate marker of the desired response of leukemia cells to treatment with plant-derived drugs. By contrast, the increased expression of the LAIPs, MPO and DR, was associated with poor prognostic outcomes following treatment with the plant-derived drugs. The results showed that 5 of the 10 plant-derived drugs tested induced the expression of several desirable LAIPs biomarkers. These findings clearly highlight the potential treatment efficacy of certain plant-derived drugs against leukemic cell types.

Minimal residual disease analysis by eight-color flow cytometry in relapsed childhood acute lymphoblastic leukemia

Multiparametric flow cytometry is an alternative approach to the polymerase chain reaction method for evaluating minimal residual disease in treatment protocols for primary acute lymphoblastic leukemia. Given considerable differences between primary and relapsed acute lymphoblastic leukemia treatment regimens, flow cytometric assessment of minimal residual disease in relapsed leukemia requires an independent comprehensive investigation. In the present study we addressed evaluation of minimal residual disease by flow cytometry in the clinical trial for childhood relapsed acute lymphoblastic leukemia using eight-color flow cytometry. The major challenge of the study was to reliably identify low amounts of residual leukemic cells against the complex background of regeneration, characteristic of follow-up samples during relapse treatment. In a prospective study of 263 follow-up bone marrow samples from 122 patients with B-cell precursor acute lymphoblastic leukemia, we tested various B-cell markers, adapted the antibody panel to the treatment protocol, and evaluated its performance by a blinded parallel comparison with the polymerase chain reaction data. The resulting eight-color single-tube panel showed a consistently high overall concordance (P<0.001) and, under optimal conditions, sensitivity similar to that of the reference polymerase chain reaction method. Overall, evaluation of minimal residual disease by flow cytometry can be successfully integrated into the clinical management of relapsed childhood acute lymphoblastic leukemia either as complementary to the polymerase chain reaction or as an independent risk stratification tool. ALL-REZ BFM 2002 clinical trial information: NCT00114348.

Minimal residual disease diagnostics in acute lymphoblastic leukemia: need for sensitive, fast, and standardized technologies

Monitoring of minimal residual disease (MRD) has become routine clinical practice in frontline treatment of virtually all childhood acute lymphoblastic leukemia (ALL) and in many adult ALL patients. MRD diagnostics has proven to be the strongest prognostic factor, allowing for risk group assignment into different treatment arms, ranging from significant treatment reduction to mild or strong intensification. Also in relapsed ALL patients and patients undergoing stem cell transplantation, MRD diagnostics is guiding treatment decisions. This is also why the efficacy of innovative drugs, such as antibodies and small molecules, are currently being evaluated with MRD diagnostics within clinical trials. In fact, MRD measurements might well be used as a surrogate end point, thereby significantly shortening the follow-up. The MRD techniques need to be sensitive (≤10(-4)), broadly applicable, accurate, reliable, fast, and affordable. Thus far, flow cytometry and polymerase chain reaction (PCR) analysis of rearranged immunoglobulin and T-cell receptor genes (allele-specific oligonucleotide [ASO]-PCR) are claimed to meet these criteria, but classical flow cytometry does not reach a solid 10(-4), whereas classical ASO-PCR is time-consuming and labor intensive. Therefore, 2 high-throughput technologies are being explored, ie, high-throughput sequencing and next-generation (multidimensional) flow cytometry, both evaluating millions of sequences or cells, respectively. Each of them has specific advantages and disadvantages.

Minimal residual disease testing in hematologic malignancies and solid cancer

Minimal residual disease (MRD) assays are of a great value to assess treatment efficacy and may provide prognostic information. This is particularly relevant in the era of targeted therapy where the introduction of MRD monitoring has fundamentally transformed the way in which cancer patients are managed. While MRD guidelines are well-established for chronic myeloid leukemia, acute promyelocytic leukemia and acute lymphoblastic leukemia, areas for continuing development are available. High level of standardization and regular external quality control rounds and recommendations for data interpretation remain essential to improve MRD monitoring. In this review, we describe the different applications of MRD assays in most frequent hematologic malignancies and solid cancer and provide an overview of the strengths and potential weaknesses of each method.

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%.

Methodological aspects of minimal residual disease assessment by flow cytometry in acute lymphoblastic leukemia: A French multicenter study

BACKGROUND

Minimal residual disease (MRD) assessment provides a powerful prognostic factor for therapeutic stratification in acute lymphoblastic leukemia (ALL). Multiparameter flow cytometry (MFC) has the potential for a rapid and sensitive identification of high risk patients. Our group has previously published that MRD levels analyzed by clone specific Ig/TcR-QPCR and MFC were concordant at a sensitivity of 10(-4) . Here we report the MFC methodological aspects from this multi-center experience.

METHODS

MRD was assessed by MFC in 1030 follow-up samples from 265 pediatric and adult patients with de novo ALL treated in the FRALLE, EORTC, or GRALL clinical trials. MRD assessment as applied by the eight participating MFC laboratories is described in detail regarding cell preparation, leukemia-associated immunophenotype (LAIP) markers and data analysis. Samples were obtained from bone marrow (BM) and peripheral blood (PB). Immunostaining was performed after erythrocyte lysis or Ficoll enrichment.

RESULTS

This study confirms the applicability of MFC-based MRD assessment in 97% of patients with ALL at the 10(-4) cut-off. MRD values after Ficoll enrichment and erythrocyte lysis were found comparable. Higher MRD values were obtained in BM than in PB, especially for B-lineage ALL.

CONCLUSIONS

Measurement of MRD by MFC at the 10(-4) cut-off is applicable within a few hours for almost all patients and using a comparable analytical strategy allows for multicenter collaborative studies. The method can be introduced in a strategy aimed at defining the risk of failure of patients with childhood or adult ALL.

Postinduction minimal residual disease monitoring by polymerase chain reaction in children with acute lymphoblastic leukemia

PURPOSE

Acute lymphoblastic leukemia (ALL) is the most common pediatric cancer. Monitoring minimal residual disease (MRD) by using real-time quantitative polymerase chain reaction (RQ-PCR) provides information for patient stratification and individual risk-directed treatment. Cooperative studies have documented that measurement of blast clearance from the bone marrow during and after induction therapy identifies patient populations with different risk of relapse. We explored the possible contribution of measurements of MRD during the course of treatment.

PATIENTS AND METHODS

We used RQ-PCR to detect MRD in 110 unselected patients treated in Italy in the International Collaborative Treatment Protocol for Children and Adolescents With Acute Lymphoblastic Leukemia (AIEOP-BFM ALL 2000). The trial took place in AIEOP centers during postinduction chemotherapy. Results were categorized as negative, low positive (below the quantitative range [< 5 × 10(-4)]), or high positive (≥ 5 × 10(-4)). Patients with at least one low-positive or high-positive result were assigned to the corresponding subgroup.

RESULTS

Patients who tested high positive, low positive, or negative had significantly different cumulative incidences of leukemia relapse: 83.3%, 34.8%, and 8.6%, respectively (P < .001). Two thirds of positive cases were identified within 4 months after induction-consolidation therapy, suggesting that this time frame may be most suitable for cost-effective MRD monitoring, particularly in patients who did not clear their disease at the end of consolidation.

CONCLUSION

These findings provide further insights into the dynamic of MRD and the ongoing effort to define molecular relapse in childhood ALL.

Prognostic significance and treatment implications of minimal residual disease studies in Philadelphia-negative adult acute lymphoblastic leukemia

Acute lymphoblastic leukemia (ALL) is curable in about 40-50% of adult patients, however this is subject to ample variations owing to several host- and disease-related prognostic characteristics. Currently, the study of minimal residual disease (MRD) following induction and early consolidation therapy stands out as the most sensitive individual prognostic marker to define the risk of relapse following the achievement of remission, and ultimately that of treatment failure or success. Because substantial therapeutic advancement is now being achieved using intensified pediatric-type regimens, MRD analysis is especially useful to orientate stem cell transplantation choices. These strategic innovations are progressively leading to greater than 50% cure rates.

Optimization of rhabdomyosarcoma disseminated disease assessment by flow cytometry

Rhabdomyosarcoma (RMS) is the most common type of soft tissue sarcoma in children. Circulating tumor cells in peripheral blood or disseminated to bone marrow, a concept commonly referred to as minimal residual disease (MRD), are thought to be key to the prediction of metastasis and treatment efficacy. To date, two MRD markers, MYOD and MYOGENIN, have been tested; however, MRD detection continues to be challenging mainly owing to the closeness of the detection limit and the discordance of both markers in some samples. Therefore, the addition of a third marker could be useful for more accurate MRD assessment. The PAX3 gene is expressed during embryo development in all myogenic precursor cells in the dermomyotome. As RMS cells are thought to originate from these muscle precursor cells, they are expected to be positive for PAX3. In this study, PAX3 expression was characterized in cancer cell lines and tumors, showing wide expression in RMS. Detection sensitivities by quantitative polymerase chain reaction (qPCR) of the previously proposed markers, MYOD and MYOGENIN, were similar to that of PAX3, thereby indicating the feasibility of its detection. Interestingly, the flow cytometry experiments supported the usefulness of this technique in the quantification of MRD in RMS using PAX3 as a marker. These results indicate that flow cytometry, albeit in some cases slightly less sensitive, can be considered a good approach for MRD assessment in RMS and more consistent than qPCR, especially owing to its greater specificity. Furthermore, fluorescence-activated cell sorting permits the recovery of cells, thereby providing material for further characterization of circulating or disseminated cancer cells.

Treatment of High-Risk Philadelphia Chromosome–Negative Acute Lymphoblastic Leukemia in Adolescents and Adults According to Early Cytologic Response and Minimal Residual Disease After Consolidation Assessed by Flow Cytometry: Final Results of the PETHEMA ALL-AR-03 Trial

Purpose

Minimal residual disease (MRD) is an important prognostic factor in adults with acute lymphoblastic leukemia (ALL) and may be used for treatment decisions. The Programa Español de Tratamientos en Hematología (PETHEMA) ALL-AR-03 trial (Treatment of High Risk Adult Acute Lymphoblastic Leukemia [LAL-AR/2003]) assigned adolescent and adult patients (age 15 to 60 years) with high-risk ALL (HR-ALL) without the Philadelphia (Ph) chromosome to chemotherapy or to allogeneic hematopoietic stem-cell transplantation (allo-HSCT) according to early cytologic response (day 14) and flow-MRD level after consolidation.

Patients and Methods

Patients with good early cytologic response (< 10% blasts in bone marrow at day 14 of induction) and a flow-MRD level less than 5 × 10−4 at the end of consolidation were assigned to delayed consolidation and maintenance therapy, and allo-HSCT was scheduled in patients with poor early cytologic response or flow-MRD level ≥ 5 × 10−4.

Results

Complete remission was attained in 282 (87%) of 326 patients, and 179 (76%) of 236 patients who completed early consolidation were assigned by intention-to treat to receive allo-HSCT (71) or chemotherapy (108). Five-year disease-free survival (DFS) and overall survival (OS) probabilities were 37% and 35% for the whole series, 32% and 37% for patients assigned to allo-HSCT, and 55% and 59% for those assigned to chemotherapy. Multivariable analysis showed poor MRD clearance (≥ 1 × 10−3 after induction and ≥ 5 × 10−4 after early consolidation) as the only prognostic factor for DFS and OS.

Conclusion

Prognosis for Ph-negative HR-ALL in adolescents and adults with good early response to induction and low flow-MRD levels after consolidation is quite favorable when allo-HSCT is avoided. In this study, the pattern of MRD clearance was the only prognostic factor for DFS and OS.

Molecular diagnostics of T-cell lymphoproliferative disorders

T-cell neoplasms include both mature T-cell leukemias and lymphomas and immature proliferations of precursor T cells. Molecular laboratories routinely assay suspected T-cell proliferations for evidence of clonality. In addition, some T-cell neoplasms are characterized by recurrent structural abnormalities that can be readily identified by such techniques as fluorescence in situ hybridization. New massively parallel sequencing technologies have led to the identification of numerous recurrent gene mutations in T-cell neoplasms. These findings are reviewed. As new technologies become implemented in molecular diagnostic laboratories and as targeted therapies are developed, it is anticipated that more extensive genomic characterization of T-cell neoplasms will be routinely performed in the future.

Prognostic significance of monitoring leukemia-associated immunophenotypes by eight-color flow cytometry in adult B-acute lymphoblastic leukemia

Minimal residual disease (MRD) is of the most important factor for predicting prognosis and guiding treatment of acute lymphoblastic leukemia (ALL). In this study, we investigated the prognostic significance of leukemia-associated immunophenotypes (LAIPs) as assessment of index of MRD in 125 adult B-lineage ALL (B-ALL) patients by eight-color flow cytometry. The LAIPs could be identified in 96% and 81.6% of patients with the sensitivity of 10(-4) and 10(-5), respectively. MRD-negative status could clearly predict a favorable 2-year relapse-free survival (RFS) and overall survival (OS) at the end of induction of complete remission and one cycle of consolidation treatment. Moreover, we identified a group of cases with MRD of 0.001% to <0.01%, which showed significantly higher 2-year relapse rate than those with undetectable one. In multivariate analysis, MRD status was associated with RFS or OS independently. Furthermore, MRD assessed by LAIPs and RQ-PCR assay for patients with BCR-ABL fusion gene yielded concordant results in 89.7% of cases. In conclusion, MRD evaluated by eight-color flow cytometry could provide an important tool to assess treatment response and prognosis precisely in adult B-ALL.

Leukemia surfaceome analysis reveals new disease-associated features

A better description of the leukemia cell surface proteome (surfaceome) is a prerequisite for the development of diagnostic and therapeutic tools. Insights into the complexity of the surfaceome have been limited by the lack of suitable methodologies. We combined a leukemia xenograft model with the discovery-driven chemoproteomic Cell Surface Capture technology to explore the B-cell precursor acute lymphoblastic leukemia (BCP-ALL) surfaceome; 713 cell surface proteins, including 181 CD proteins, were detected through combined analysis of 19 BCP-ALL cases. Diagnostic immunophenotypes were recapitulated in each case, and subtype specific markers were detected. To identify new leukemia-associated markers, we filtered the surfaceome data set against gene expression information from sorted, normal hematopoietic cells. Nine candidate markers (CD18, CD63, CD31, CD97, CD102, CD157, CD217, CD305, and CD317) were validated by flow cytometry in patient samples at diagnosis and during chemotherapy. CD97, CD157, CD63, and CD305 accounted for the most informative differences between normal and malignant cells. The ALL surfaceome constitutes a valuable resource to assist the functional exploration of surface markers in normal and malignant lymphopoiesis. This unbiased approach will also contribute to the development of strategies that rely on complex information for multidimensional flow cytometry data analysis to improve its diagnostic applications.

Measurements of treatment response in childhood acute leukemia

Measuring response to chemotherapy is a backbone of the clinical management of patients with acute leukemia. This task has historically relied on the ability to identify leukemic cells among normal bone marrow cells by their morphology. However, more accurate ways to identify leukemic cells have been developed, which allow their detection even when they are present in small numbers that would be impossible to be recognized by microscopic inspection. The levels of such minimal residual disease (MRD) are now widely used as parameters for risk assignment in acute lymphoblastic leukemia (ALL) and increasingly so in acute myeloid leukemia (AML). However, different MRD monitoring methods may produce discrepant results. Moreover, results of morphologic examination may be in stark contradiction to MRD measurements, thus creating confusion and complicating treatment decisions. This review focusses on the relation between results of different approaches to measure response to treatment and define relapse in childhood acute leukemia.