Minimal Residual Disease In ALL Research Articles

Retrospective Analysis of Minimal Residual Disease Testing By High Throughput Immunosequencing Versus High Sensitivity Flow Cytometry and qPCR in B-Lymphoblastic Leukemia

Introduction: Detection of minimal residual disease (MRD) is one of the most powerful predictors of prognosis in patients with B-Lymphoblastic Leukemia (ALL). Standard methods to detect MRD in ALL include high-resolution flow cytometry (FC) (sensitivity 10 -4 to 10 -5) and qPCR for Ph+ ALL (sensitivity 10 -5 to -6). More recently, high-throughput sequencing (NGS) has been leveraged to detect MRD (sensitivity 10 -6). Retrospective, non-clinical trial based real-world data comparing between these methodologies in the literature is limited to absent. We report our experience at a high-volume cancer center comparing NGS, qPCR, and FC.Methods: All cases of ALL with NGS MRD data at the Moffitt Cancer Center were identified. Corresponding FC, qPCR (p190 and p210) and clinical data were collected electronically and via chart review.10-color flow cytometry was performed on a Gallios System and analyzed on Kaluza (Beckman Coulter, IN). 750,000 events were collected on all cells. Validated lower limit of detection was at least 0.01%. Antibodies included CD15, CD130, CD10, CD58, CD22, CD33, CD13, CD123, CD19, CD20, CD45, CD38, CD34, CD81, CD200 (BD, Biolegend, Beckman Coulter).Quantidex™ BCR-ABL IS Kit (RT qPCR) was used to quantify BCR-ABL (p190 and p210) and ABL transcripts in total RNA in patients with ALL on Applied Biosystems 7500 Fast Dx Real-Time PCR instrument. The results were expressed by normalized BCR-ABL to ABL (control) ratio.clonoSEQ ® (Adaptive Biotechnologies, Seattle, WA) testing was performed which uses multiplex polymerase chain reaction (PCR) and NGS to identify, characterize, and monitor clonotypes of immunoglobulin (Ig) IgH (V-J), IgH (D-J), IgK, and IgL receptor gene sequences, and translocated BCL1/IgH (J) and BCL2/IgH (J) sequences.Statistical analysis was performed by Spearman correlation coefficient and Kaplan-Meier analysis.Results: 95 samples from 54 unique patients were identified that had both NGS and FC data. A subset of patients had qPCR data (n=31 samples). FC+ values ranged from 0.00004 to 0.75. NGS+ values ranged from 8.25E-08 to 0.49. Spearman correlation coefficient showed moderate concordance between NGS and FC at r=0.62 (p<0.001). Spearman correlation coefficient for qPCR vs Flow was r= 0.08 (p=0.68). Three samples were positive by FC (mean tumor burden (MTB= 0.002) but missed by NGS; whereas 31 samples were detected by NGS (MTB= 0.0016) that were missed by flow cytometry. By FC, 9 samples were equivocal of which 7 were definitively designated as MRD+ by NGS. There were 7 qPCR+/NGS- samples (MTB= 2.5 x 10 -5) and 6 qPCR-/NGS+ cases (MTB= 0.012). Overall survival was worse for MRD+ (by NGS, qPCR, or FC) vs MRD(-) (Figure 1).Conclusion:Our study confirms the importance of MRD detection in ALL and shows the robust utility of NGS for MRD detection in routine hematopathology practice. While qPCR, FC and NGS are complementary given that each can potentially detect MRD missed by another method, the data supports the increased sensitivity of NGS over FC. [Display omitted] DisclosuresShah: Servier Genetics: Other; Jazz Pharmaceuticals: Research Funding; Incyte: Research Funding; BeiGene: Consultancy, Honoraria; Acrotech/Spectrum: Honoraria; Pharmacyclics/Janssen: Honoraria, Other: Expenses; Kite, a Gilead Company: Consultancy, Honoraria, Other: Expenses, Research Funding; Precision Biosciences: Consultancy; Amgen: Consultancy; Pfizer: Consultancy, Other: Expenses; Novartis: Consultancy, Other: Expenses; Bristol-Myers Squibb/Celgene: Consultancy, Other: Expenses; Adaptive Biotechnologies: Consultancy. Hussaini: Stemeline Therapeutics: Honoraria.

Interim Results of a Multicenter, Single-Arm Study to Assess Blinatumomab in Adult Patients (pts) with Minimal Residual Disease (MRD) of B-Precursor (BCP) Acute Lymphoblastic Leukemia (GMALL-MOLACT1-BLINA)

Interim Results of a Multicenter, Single-Arm Study to Assess Blinatumomab in Adult Patients (pts) with Minimal Residual Disease (MRD) of B-Precursor (BCP) Acute Lymphoblastic Leukemia (GMALL-MOLACT1-BLINA)

Error-corrected sequencing strategies enable comprehensive detection of leukemic mutations relevant for diagnosis and minimal residual disease monitoring

BackgroundPediatric leukemias have a diverse genomic landscape associated with complex structural variants, including gene fusions, insertions and deletions, and single nucleotide variants. Routine karyotype and fluorescence in situ hybridization (FISH) techniques lack sensitivity for smaller genomic alternations. Next-generation sequencing (NGS) assays are being increasingly utilized for assessment of these various lesions. However, standard NGS lacks quantitative sensitivity for minimal residual disease (MRD) surveillance due to an inherently high error rate.MethodsPrimary bone marrow samples from pediatric leukemia (n = 32) and adult leukemia subjects (n = 5), cell line MV4–11, and an umbilical cord sample were utilized for this study. Samples were sequenced using molecular barcoding with targeted DNA and RNA library enrichment techniques based on anchored multiplexed PCR (AMP®) technology, amplicon based error-corrected sequencing (ECS) or a human cancer transcriptome assay. Computational analyses were performed to quantitatively assess limit of detection (LOD) for various DNA and RNA lesions, which could be systematically used for MRD assays.ResultsMatched leukemia patient samples were analyzed at three time points; diagnosis, end of induction (EOI), and relapse. Similar to flow cytometry for ALL MRD, the LOD for point mutations by these sequencing strategies was ≥0.001. For DNA structural variants, FLT3 internal tandem duplication (ITD) positive cell line and patient samples showed a LOD of ≥0.001 in addition to previously unknown copy number losses in leukemia genes. ECS in RNA identified multiple novel gene fusions, including a SPANT-ABL gene fusion in an ALL patient, which could have been used to alter therapy. Collectively, ECS for RNA demonstrated a quantitative and complex landscape of RNA molecules with 12% of the molecules representing gene fusions, 12% exon duplications, 8% exon deletions, and 68% with retained introns. Droplet digital PCR validation of ECS-RNA confirmed results to single mRNA molecule quantities.ConclusionsCollectively, these assays enable a highly sensitive, comprehensive, and simultaneous analysis of various clonal leukemic mutations, which can be tracked across disease states (diagnosis, EOI, and relapse) with a high degree of sensitivity. The approaches and results presented here highlight the ability to use NGS for MRD tracking.

Comparison between Hypercvad and CALLG2008 Protocol in Adult Patients with Newly Diagnosed Acute Lymphoblastic Leukemia:a Single Center Study

BACKGROUD: HyperCVAD is one of the most frequent used protocols in adult ALL in routine practice. On the other hand, the CALLG2008 protocol was a published protocol designed by the Chinese Acute Lymphoblastic Leukemia Cooperative Group for adult ALL. In this retrospective study, we analyzed 70 Chinese patients with adult ALL to compare the efficacy, safety and costs of HyperCVAD regimen in comparison to CALLG2008. METHODS: Pts ≥ 15 years old with previously untreated newly-diagnosed ALL were eligible. All pts provided IRB-approved informed consent before chemotherapy. HyperCVAD and CALLG2008 were given as initially described. Imatinib (400 mg daily) was administered concurrently in patients with Ph-positive ALL. Prophylactic antibiotics, antifungals, and antiviral agents were provided according to the institutional guidelines. Red blood cells and platelet transfusions were given for hemoglobin&lt;60 g/L and platelets≤10×109/L or if with hemorrhage. Granulocyte colony-stimulating factor was given routinely. Bone marrow aspiration was performed after the completion of the first course of induction chemotherapy to assess their response to treatment. All patients were evaluated for minimal residual disease (MRD) in bone marrow at the end of the first course of induction by 6-color multi-parametric flow cytometry analysis and reverse-transcription quantitative polymerase chain reaction (RT-qPCR). Primary endpoint of the study was CR rate after the first course of induction therapy. Complete remission (CR) was defined as having &lt;5% marrow blasts, a normalization of peripheral counts (neutrophil count ≥1 × 109/L, platelet count ≥100 × 109/L, and no abnormal peripheral blasts), and absence of extramedullary disease. The criteria for the positive and negative MRD are based on the experience of the European ALL MRD Detection Research Collaborative Group. Adverse events occurring during the first 8 weeks after the first course of induction therapy are reported. Other treatment outcomes including blood transfusion requirement, recovery day of neutrophil count were collected, as well as detailed data regarding hospitalization time, complications and costs. RESULTS: Thirty patients were treated with HyperCVAD, and 40 with CALLG2008. Pre-treatment characteristics are shown in the Table 1. After the first course of induction chemotherapy, complete remission was obtained in 83% and 78% of patients, respectively. The CR rate did not vary significantly by different regimens, gender, age, immunophenotype. However, 96% of those with cytogenetic or molecular evidence of the Philadelphia (Ph) chromosome and 76% of those without such evidence achieved a CR (P=0.045). In Ph-negative group, MRD-negative rates were found to be significantly higher with HyperCVAD (58% vs 27%, P=0.036). The median durations of neutrophil recovery of CALLG2008 group was 4 days longer than HyperCVAD group (P=0.038). Moreover, grade 3-4 thrombocytopenic (&lt;500/μl) was more frequent on CALLG2008 regimens compared with the HyperCVAD regimens (90% vs 63%; P=0.007). Accordingly, a lower platelet transfusion rate was observed in favor of the HyperCVAD group (47% vs 73%, P=0.007). The CALLG2008 regimen had more all-grade hepatic toxicity than HyperCVAD regimen (53% vs 27%; P=0.03). Grade 3-4 hypofibrinogenemia was more frequent on CALLG2008 regimen compared with hyper-CVAD regimen (33% vs 7%; P=0.009). The average time to stay of the first course of chemotherapy were 19.4±3.5 and 24.2±8.6 days in HyperCVAD and CALLG2008 groups, respectively (P=0.002). The average drug-related costs for patients treated with HyperCVAD were significantly lower compared with that for those treated with CALLG2008 (30981.7 vs 59422.9 yuan, P=0.010). CONCLUSION: Although HyperCVAD and CALLG2008 regimens showed relatively similar early CR rate, the former yields deep remissions more powerfully in Ph-negative ALL. Additionally, HyperCVAD was more favorable in hematopoietic recovery than CALLG2008. Differences were also observed in terms of less complications, shorter hospitalization and lower drug-related expenditure in favor of HyperCVAD group. Disclosures No relevant conflicts of interest to declare.

Experience with MRD Testing in B- ALL By Flow Cytometry Does Not Prevent Interpretative Discordance

Background: Minimal residual disease (MRD) in B lymphoblastic leukemia (B-ALL) as measured by flow cytometry is well-established as an important prognostic factor; Its presence is used to adjust treatment in most therapeutic protocols in children , while the lack of a standardized assay has hampered the introduction of flow cytometric MRD in adult ALL trials. On the other hand, measuring MRD has become part of the standard of care even for patients not on clinical trials. Although flow cytometric analysis of MRD in B-ALL has been well standardized in clinical trials of the Children's Oncology Group (COG) in North America (Borowitz et al Blood 2015;126:964), there are no data on performance characteristics of this assay within routine clinical labs.Methods: As part of an ongoing effort to standardize and decentralize ALL MRD measurement, list-mode data from post-induction marrows were distributed from one COG reference lab to 7 different clinical flow cytometry labs self-identified as having experience with ALL MRD. All labs were provided with the COG protocol used for MRD analysis along with a template illustrating recommended gating strategies, and formulas for calculating MRD burden. List-mode files of pre-treatment B-ALL samples analyzed with the standard COG B-ALL MRD antibody panel were distributed for comparison. In the first rounds, list-mode files from 15 samples were distributed to the 7 labs. Samples included those with and without MRD as assayed in the reference lab. Samples were selected to include normal B-cell precursors (hematogones) or MRD that had undergone phenotypic change with therapy. Some samples had artifacts that could potentially mimic small MRD populations. To improve performance, educational sessions were implemented, and 10 more list-mode file samples were distributed in a second round of challenges.Results: There was considerable dispersion of MRD results among the 7 labs that analyzed the list-mode files (Fig 1A). Although high levels of MRD were uniformly recognized, several labs misclassified normal B-cell precursors and/or mischaracterized small artifacts as MRD. Moreover, among samples correctly identified as positive, quantitative differences in MRD levels from those reported by the reference lab were seen. Among 95 total challenges, the overall discordance rate was 24%. This included 11 false positives, 7 false negatives, and an additional 5 quantitatively discordant cases among positives (defined as outside +/- 0.5 log of the reference lab value). In the second round, positive and negative samples, as well as those with normal precursors were included, though these samples contained fewer artifacts than those of the first round. Performance improved considerably (Fig 1B); out of 70 challenges, there were 5 false positives and 1 false negative (8.6% discordance), and no cases were quantitatively discordant. Four of the 6 deviations occurred in a single lab. Three samples with hematogones were still misclassified as MRD.Conclusions: Despite the provision of a standardized analysis protocol, even experienced laboratories have difficulty with B-ALL MRD analysis by flow cytometry. Some of these difficulties can be overcome with education, but even with education recognition of hematogones still remains a challenge for some labs. Extrapolating these results to other laboratories with less experience indicates the need for caution in migrating MRD testing from centralized reference laboratories, and suggests that implementation of MRD testing as part of routine clinical management of B-ALL patients in a manner similar to that of routine flow cytometric classification of leukemia may require additional training and resources. [Display omitted] DisclosuresWood:Pfizer: Honoraria, Other: Laboratory Services Agreement; Juno: Other: Laboratory Services Agreement; Amgen: Honoraria, Other: Laboratory Services Agreement; Seattle Genetics: Honoraria, Other: Laboratory Services Agreement. Lozanski:Stemline Therapeutics Inc.: Research Funding; Beckman Coulter: Research Funding; Boehringer Ingelheim: Research Funding; Genentech: Research Funding. Mukundan:CCS Associates: Employment. Higley:CCS Associates: Employment. Sigman:CCS Associates: Equity Ownership. Borowitz:BD Biosciences: Research Funding; Medimmune: Research Funding; Bristol Myers Squibb: Research Funding; HTG Molecular: Consultancy.

Apparent CD19 expression by natural killer cells: a potential confounder for minimal residual disease detection by flow cytometry in B lymphoblastic leukemia.

Detection of minimal residual disease (MRD) by flow cytometry (FCM) in B lymphoblastic leukemia (B ALL) is important for guiding patient-specific clinical management. We describe apparent expression of CD19 by natural killer cells as a potential confounder in the detection of B ALL MRD by FCM. This finding was noted in seven different patient samples analyzed on different days as part of routine clinical care in our laboratory, with analysis of different anti-CD19 antibody clones and fluorochrome conjugates in five of the seven samples. Although the etiology of this finding is not clear, possibilities include true low level expression and trogocytosis. We highlight this finding to avoid potential misinterpretation when evaluating samples for MRD in patients with B lineage neoplasms, particularly in B ALL.

Apparent CD19 expression by natural killer cells: A potential confounder for minimal residual disease detection by flow cytometry in B lymphoblastic leukemia.

Detection of minimal residual disease (MRD) by flow cytometry (FCM) in B lymphoblastic leukemia (B ALL) is important for guiding patient specific clinical management. We describe apparent expression of CD19 by natural killer (NK) cells as a potential confounder in the detection of B ALL MRD by FCM. This finding was noted in seven different patient samples analyzed on different days as part of routine clinical care in our laboratory, with analysis of different anti-CD19 antibody clones and fluorochrome conjugates in five of the seven samples. Although the etiology of this finding is not clear, possibilities include true low level expression and trogocytosis. We highlight this finding to avoid potential misinterpretation when evaluating samples for MRD in patients with B lineage neoplasms, particularly in B ALL. © 2014 Clinical Cytometry Society.

Acting on minimal residual disease in ALL

Acting on minimal residual disease in ALL

A Novel Model of Immune-Mediated Disease Equilibrium in Acute Lymphoblastic Leukemia

AbstractAbstract 3540Acute lymphoblastic leukemia (ALL) is a challenging target for immunotherapy due to its poor antigen presentation, lack of costimulatory molecule expression, and resistance to cytotoxic killing by immune effector cells. In order to develop new strategies to generate autologous immune-mediated protection against ALL progression, we sought to understand more about the immune requirements that must be met in order to achieve disease control. To do this, we have transfected B cell precursor ALL cell lines derived from leukemic Eμ-ret transgenic BALB/c mice with a lentiviral construct encoding green fluorescent protein (GFP) and firefly luciferase (luc) in tandem. The luciferase protein serves a dual purpose as a potent neoantigen capable of stimulating leukemia-specific immune responses and as a bioluminescent reporter for highly sensitive detection of minimal residual disease (MRD).Intravenous injection of 106 non-transfected Eμ-ret-derived leukemia cells is consistently lethal in wild type BALB/c mice within 3–5 weeks. However, adoptive transfer of 106 GFP/luc-expressing leukemia cells into wild type BALB/c mice does not lead to morbidity or mortality (p=0.025, logrank for survival). These mice show detectable disease in bone marrow by bioluminescent imaging below the limit of detection by peripheral blood flow cytometry that increases until day 7–10, followed by a spontaneous decrease in leukemia burden to undetectable levels by imaging. BALB/c mice lacking B and T cells (RAG1−/−) or B, T and NK cells (gamma common−/−) injected with GFP/luc ALL cells develop leukemia that is lethal by day 25 (p=0.037, logrank). Early T cell-depletion in wild type BALB/c mice on days 0, 3, 6, and 9 with CD4- and/or CD8-depleting antibodies also results in complete breakthrough of disease, while NK cell-depletion with asialo-GM1 on the same days does not significantly alter the timeframe of leukemia clearance (p<0.0001, 2-way ANOVA; Figure 1). These results demonstrate that the presence of a neoantigen is sufficiently immunogenic to generate effective T cell-mediated control of the disease.We have followed immunocompetent mice that received GFP/luc ALL for up to 12 months. While most mice have long-term remissions both by imaging and peripheral blood sampling, a subset have evidence of persistent MRD by bioluminescent imaging that waxes and wanes in luminosity but may not break through to a fulminant relapse. Relapses in these mice have occurred up to 11 months from injection. Late T cell-depletion with CD4 and CD8 antibodies (weekly x12, beginning at day 28) leads to an increased rate of leukemia breakthroughs and occurs more frequently in mice who had cleared their leukemia in the setting of early NK cell depletion (p<0.001, 2-way ANOVA), suggesting early crosstalk between NK and T cells to develop a sustained immune response. In addition, many mice relapse with GFP/luc-expressing leukemia, while a proportion of mice have late relapses with GFP/luc-negative leukemia, suggesting antigen loss is one of several potential mechanisms of immune evasion in ALL.Finally, BALB/c mice transgenic for GFP and luciferase do not generate T cell protection against outgrowth of injected GFP/luc ALL cells and succumb to disease by day 20 (p = 0.027 versus wild type mice, logrank). This result suggests that tolerance mechanisms, rather than antigen presentation deficiencies, may undermine host immune responses against ALL.We present a novel model of immune equilibrium in ALL, made evaluable by exquisitely sensitive bioluminescent imaging. Importantly, despite its well-documented lack of immunogenicity, we have shown ALL can be a sensitive target for long-term leukemia-specific T cell-mediated immune control. We are currently investigating additional cellular mechanisms of immune protection, the role of antigen spreading in control of ALL, and the mechanisms allowing leukemia to escape from immune control. Our approach will enable the development of strategies to break immune tolerance towards leukemia antigens and generate control of MRD in ALL. [Display omitted] Disclosures:No relevant conflicts of interest to declare.

Minimal residual disease in ALL

Minimal residual disease in ALL

Incorporation of Alemtuzumab into Front-Line Therapy of Adult Acute Lymphoblastic Leukemia (ALL) Is Feasible: A Phase I/II Study from the Cancer and Leukemia Group B (CALGB 10102).

Eradication of minimal residual disease (MRD) during the first months of treatment for patients (pts) with ALL is associated with improved disease-free survival (DFS). We hypothesized that Alemtuzumab, a humanized monoclonal antibody directed against CD52, might be an effective, novel agent for eradication of MRD in ALL based on data demonstrating strong CD52 expression in other lymphoid malignancies and in several ALL cell lines, and from case reports of clinical activity in advanced ALL. In CALGB 10102, to define the percentage of CD52+ cases and to demonstrate feasibility, we tested dose escalation of Alemtuzumab in sequential cohorts to a target dose of 30 mg administered sc 3X/week for 4 weeks (12 doses) during post-remission therapy. Pts are eligible to receive Alemtuzumab if lymphoblast CD52 expression at diagnosis is ≥ 10% as determined in a CALGB reference laboratory. The 10102 therapy is composed of monthly treatment modules outlined below:Treatment module sequence is: A,B,C, D, A, B, C followed by maintenance therapy for a total of 2 years. Antimicrobial prophylaxis for cytomegalovirus (CMV) (e.g. acyclovir 800 mg qid) and pneumocystis carinii is mandated. Weekly quantitative monitoring for CMV viremia is performed. 150 pts with untreated ALL have enrolled: Median age is 48 yrs. 124 (83%) pts have precursor-B; 19(13%) have precursor T-ALL and 7 (4%) have biphenotypic or bilineal ALL. Of 139 evaluable pts, 95 (68%) had CD52 ≥ 10%. By immunophenotype, 72% of precursor B and 61% of precursor T pts were eligible to receive Alemtuzumab. Phase I dose escalation was recently completed. Dose limiting toxicity (DLT) for Phase I was defined as the inability to proceed with protocol treatment within 6 weeks of the last dose of Alemtuzumab. Non-heme toxicities have been mild and sc Alemtuzumab administration was well tolerated. Hematologic and infectious toxicities are summarized below:Myelosuppression was transient and use of G-CSF was permitted during Module D. 2 pts were treated for CMV viremia due to rising CMV titers in 2 sequential assays. 6 other pts had transient CMV elevations during or immediately following completion of Alemtuzumab that did not require treatment. 22/24 phase I pts received all 12 doses of Alemtuzumab. There were 2 DLTs reported: 1 pt in cohort 2 due to CMV viremia requiring gancyclovir following completion of Alemtuzumab; and 1 pt in cohort 3 due to ANC < 1500 six weeks after Alemtuzumab (pt was not given G-CSF). Based on these Phase I data, the targeted dose of 30 mg Alemtuzumab was recommended for further study in the ongoing Phase II study. In summary, we report for the first time that CD52 is expressed in the majority of ALL cases and demonstrate the feasibility of employing Alemtuzumab in front-line therapy. Ongoing accrual to the phase II study will evaluate the efficacy of Alemtuzumab in eradication of MRD in adult ALL.Module AModule BModule CModule D (Alemtuzumab)MaintenanceCytoxanCytoxanMethotrexate (IV, PO, IT)10 mg* cohort 1VincristineDaunorubicinCytarabineVincristine20 mg* cohort 2DexamethasoneVincristineVincrisitne6-MP30 mg* cohort 36-MPDexamethasoneL-asparaginase*Phase I dose escalationMethotrexateL-asparaginaseIT-MethotrexateAlemtuzumab cohortsNMyelosuppression (grades 3 or 4)LymphopeniaCMV viremia10 mg621220 mg1011430 mg8102

Aberrant Immunophenotypes Detected by Flow Cytometry in Acute Lymphoblastic Leukemia

The present study was designed to analyse the proportion of ALL patients in which the phenotypic detection of minimal residual disease (MRD) is feasible, based on the presence of aberrant phenotypes: lineage infidelity, asynchronous expression, overexpression and ectopic phenotype. For this purpose we have prospectively investigated the phenotype of blast cells from 25 patients at diagnosis using a large panel of monoclonal antibodies by multiparametric flow cytometry. The mean age was 23.3 × 17.3 with 10 children and 15 adults. 14 patients were classified as L1, 9 L2 and 2 L3 according to the FAB classification. 17 cases were B-lineage ALL and 8 T-ALL. 23 out of 25 cases (92%) included in this study displayed phenotypic aberrations at diagnosis (15 out of 17 cases of B-lineage ALL and all T-ALL patients). 76% of patients displayed two or more than two aberrancies. The phenotypic aberrations were lineage infidelity, found in 12 patients, asynchronous antigen expression detected in 17 patients, antigen overexpression in 4 patients and ectopic phenotype in 7 patients.In summary our results show that when a large panel of MoAbs is used for the immunophenotypical characterization of ALL, most patients display aberrant phenotypes, the coexistence of more than two aberrant antigen expressions being frequently detected. These results suggest that the use of immunological methods for the detection of MRD in ALL based on the existence of aberrant phenotypes could be of great help for the follow-up of patients in complete remission.

Detection of minimal residual disease in ALL.

Complete remission (CR) of acute leukemia is defined in clinical practice as the presence in the bone marrow of less than 5% blast cells, a level determined by the limits of reliable detection by morphology. Mathematical models predict that the level of residual disease during clinical remission could vary from 1010 leukemic cells following early remission induction to perhaps none in some patients at later stages of treatment [1]. The practical relevance of minimal residual disease (MRD) is in the relationship between the level of the residual tumor burden and the risk of relapse. The ability to detect and quantitate MRD in hematological malignancies and to relate this to relapse risk could potentially provide a means of monitoring the effectiveness of treatment and the basis for design of more stratified treatment protocols. It is, however, worth emphasizing that the detection of residual disease by sensitive techniques does not necessarily predict relapse. There are instances in the literature both of ‘clonal’ remissions [2] and stable persistence of residual disease during remission [3]. The large body of work on the influence of immune effector mechanisms in the control or elimination of residual disease provides a potential basis for some of these observations (see [4]). Clearly, prediction of relapse cannot be determined solely by the presence of a given burden of residual disease; assessment of a variety of additional parameters, including the viability and clonal nature of residual cells, is also necessary.KeywordsAcute Lymphoblastic LeukemiaMinimal Residual DiseaseGene RearrangementAcute Lymphoblastic LeukaemiaVariable Number Tandem RepeatThese keywords were added by machine and not by the authors. This process is experimental and the keywords may be updated as the learning algorithm improves.