Immunophenotypical detection of minimal residual disease in acute leukemia

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.

Quality control of flow cytometry data analysis for evaluation of minimal residual disease in bone marrow from acute leukemia patients during treatment

Low levels of leukemia cells in the bone marrow, minimal residual disease (MRD), are considered to be a powerful indicator of treatment response in acute lymphatic leukemia (ALL). A Nordic quality assurance program, aimed on standardization of the flow cytometry MRD analysis, has been established before implementation of MRD at cutoff level 10 as one of stratifying parameters in next Nordic Society of Pediatric Hematology and Oncology (NOPHO) treatment program for ALL. In 4 quality control (QC) rounds 15 laboratories determined the MRD levels in 48 follow-up samples from 12 ALL patients treated according to NOPHO 2000. Analysis procedures were standardized. For each QC round a compact disc containing data in list-mode files was sent out and results were submitted to a central laboratory. At cutoff level 10, which will be applied for clinical decisions, laboratories obtained a high concordance (91.6%). If cutoff level 10 was applied, the concordance would be lower (85.3%). The continuing standardization resulted in better concordance in QC3 and QC4 compared with QC1 and QC2. The concordance was higher in precursor B as compared with T-cell ALL. We conclude that after standardization, flow cytometry MRD detection can be reliably applied in international, multicenter treatment protocols.

Minimal residual disease monitoring after allogeneic transplantation may help to individualize post-transplant therapeutic strategies in acute myeloid malignancies

This study evaluates the prognostic value of minimal residual disease (MRD) monitoring by multiparametric flow cytometry in 41 patients with acute myeloid leukemia or myelodysplastic syndrome undergoing allogeneic transplantation. MRD assessment after transplant (day +100) allowed to discriminate different risk populations, being the most significant cut-off value for outcome level of MRD < or > or = 10(-3). Outcome was significantly better among patients with low (<10(-3)) versus high (> or = 10(-3)) MRD at day +100 after transplant. Thus, overall survival was 73% versus 25% at 4 years among patients with low versus high MRD at day +100 after transplant (P = 0.002); 74% of patients with low MRD were event free at 4 years as compared to 17% among patients with high MRD (P = 0.01). In multivariate analysis, MRD value as well as chronic GVHD significantly influenced outcome. In conclusion, MRD monitoring early post-transplant is an important tool for outcome prediction and should be considered in decision making after allogeneic transplantation.

Quantitation of Minimal Residual Disease in Acute Myeloid Leukemia by Tryptase Monitoring Identifies a Group of Patients with a High Risk of Relapse

PURPOSE

Recent data suggest that tryptase is produced by blast cells in a group of patients with acute myeloid leukemia (AML). In these patients, serum tryptase levels are elevated at diagnosis and decrease to normal (<15 ng/mL) or near normal values in those achieving complete hematologic remission (CR) after chemotherapy.

PATIENTS

In this study, we examined the value of tryptase as a marker of minimal residual AML. In 61 patients with de novo AML exhibiting elevated serum tryptase (>15 ng/mL) at diagnosis, tryptase levels were measured serially during and after chemotherapy by a fluoroenzyme immunoassay.

RESULTS

Of the 61 patients, 42 (68.9%) entered hematologic CR in response to induction chemotherapy. Twenty-nine of these 42 patients also entered biochemical remission (BR) defined by a decrease of tryptase levels to normal (<15 ng/mL). The remaining 13 patients exhibited elevated enzyme levels despite of hematologic CR. As assessed by multivariate analysis, the elevated tryptase in CR was found to be an independent prognostic variable concerning disease-free survival. Thus, AML relapses occurred in 15 of 29 patients with CR + BR (52%) and in 12 of 13 patients with CR without BR (92%), resulting in a significantly reduced probability of continuous CR for patients with CR without BR (P < 0.05). In all patients with continuous hematologic CR, tryptase levels remained constantly normal, whereas a recurrent elevation of tryptase in CR was invariably followed by a hematologic relapse.

CONCLUSION

A persistently elevated tryptase level in AML in CR is indicative of minimal residual AML and associated with a high risk of relapse.

Myeloid antigens in childhood lymphoblastic leukemia: clinical data point to regulation of CD66c distinct from other myeloid antigens

Background

Aberrant expression of myeloid antigens (MyAgs) on acute lymphoblastic leukemia (ALL) cells is a well-documented phenomenon, although its regulating mechanisms are unclear. MyAgs in ALL are interpreted e.g. as hallmarks of early differentiation stage and/or lineage indecisiveness. Granulocytic marker CD66c – Carcinoembryonic antigen-related cell adhesion molecule 6 (CEACAM6) is aberrantly expressed on ALL with strong correlation to genotype (negative in TEL/AML1 and MLL/AF4, positive in BCR/ABL and hyperdiploid cases).

Methods

In a cohort of 365 consecutively diagnosed Czech B-precursor ALL patients, we analyze distribution of MyAg+ cases and mutual relationship among CD13, CD15, CD33, CD65 and CD66c. The most frequent MyAg (CD66c) is studied further regarding its stability from diagnosis to relapse, prognostic significance and regulation of surface expression. For the latter, flow cytometry, Western blot and quantitative RT-PCR on sorted cells is used.

Results

We show CD66c is expressed in 43% patients, which is more frequent than other MyAgs studied. In addition, CD66c expression negatively correlates with CD13 (p < 0.0001), CD33 (p = 0.002) and/or CD65 (p = 0.029). Our data show that different myeloid antigens often differ in biological importance, which may be obscured by combining them into "MyAg positive ALL". We show that unlike other MyAgs, CD66c expression is not shifted from the onset of ALL to relapse (n = 39, time to relapse 0.3–5.3 years). Although opposite has previously been suggested, we show that CEACAM6 transcription is invariably followed by surface expression (by quantitative RT-PCR on sorted cells) and that malignant cells containing CD66c in cytoplasm without surface expression are not found by flow cytometry nor by Western blot in vivo. We report no prognostic significance of CD66c, globally or separately in genotype subsets of B-precursor ALL, nor an association with known risk factors (n = 254).

Conclusion

In contrast to general notion we show that different MyAgs in lymphoblastic leukemia represent different biological circumstances. We chose the most frequent and tightly genotype-associated MyAg CD66c to show its stabile expression in patients from diagnosis to relapse, which differs from what is known on the other MyAgs. Surface expression of CD66c is regulated at the gene transcription level, in contrast to previous reports.

Drug-induced immunophenotypic modulation in childhood ALL: implications for minimal residual disease detection

Assessment of minimal residual disease (MRD) by flow cytometry is considered to be based on the reproducibility of the leukemic immunophenotype detected at diagnosis. However, we previously noticed modulation of surface antigen expression in acute lymphoblastic leukemia (ALL) during the early treatment. Hence, we investigated this in 30 children with B-cell precursor ALL consecutively enrolled in the AIEOP-BFM ALL 2000 protocol. Quantitative expression of seven antigens useful in MRD monitoring was studied at diagnosis and compared to that measured at different time points of remission induction therapy. Downmodulation in the expression of CD10 and CD34 occurred at follow-up. By contrast, upmodulation of CD19, CD20, CD45RA, and CD11a was observed, while the expression of CD58 remained stable. Despite this, we could unambiguously discriminate leukemic cells from normal residual B cells. This holds true when bone marrow (BM) samples from similarly treated T-ALL patients, but not from healthy donors, were used as reference. Our results indicate that immunophenotypic modulation occurs in ALL during the early phases of BFM-type protocols. However, the accuracy of MRD detection by flow cytometry seems not negatively affected if adequate analysis protocols are employed. Investigators should take this phenomenon into account in order to avoid pitfalls in flow cytometric MRD studies.

Gene expression profiling of minimal residual disease in acute myeloid leukaemia by novel multiplex-PCR-based method

In acute myeloid leukaemia (AML), alterations in apoptotic pathways are crucial for treatment outcome, resulting either in refractoriness or in minimal residual disease (MRD). The apoptosis characteristics of MRD cells may differ from those at diagnosis and thereby determine the adequacy of further treatment. Such characteristics are largely unknown, since studies hereto are hampered by minimal cell availability. This study explores the applicability of the recently described RT-Multiplex Ligation-dependent Probe Amplification (RT-MLPA) for gene expression analysis of small amounts of RNA obtained from MRD cells. Reproducibility and dilution experiments showed that the relative expression of 37 apoptosis-related genes starting with only 1000 cells could be measured with 12% variation; for 100 cells, 31/37 genes could still be quantified, though expression variation increased. In practice 100-1000 leukemic cells can be obtained from bone marrow samples with clinically relevant MRD percentages of 0.01-0.1. Procedures often necessary to obtain AML blasts, that is, FACS-sorting, freeze-thawing or combinations are possible, provided that selected viable nonapoptotic cells are used. Concluding, RT-MLPA allows accurate gene expression profiling of MRD cells. This method will help to gain insight into the processes of MRD emergence and persistence in AML, which may ultimately guide new therapeutic strategies in AML.

Minimal residual disease monitoring by flow cytometry

In patients with acute leukaemia, studies of minimal residual disease (MRD) provide powerful and independent prognostic information. Multiparameter flow cytometry is a widely applicable and reliable approach for monitoring MRD. Using triple or quadruple marker combinations, aberrant or uncommon phenotypic profiles can be identified in about 80% of patients with acute myeloid leukaemia (AML) and 95% of patients with acute lymphoblastic leukaemia (ALL). These profiles can reveal leukaemic cells even when these are not evident by morphological analysis. Thus, one leukaemic cell among 1000-10000 normal bone marrow or peripheral blood cells can be routinely detected. In this chapter we discuss technical aspects of MRD detection by flow cytometry and summarize results of correlative studies between MRD, clinical and biological features of leukaemia and treatment outcome. Current knowledge indicates that MRD studies using well-tested methodologies are clinically useful and should be incorporated into the clinical management of patients with acute leukaemia.

Detection of minimal residual disease in acute myelogenous leukemia

Acute myelogenous leukemia (AML) is considered to be in complete remission when fewer than 5% of the cells in bone marrow are blasts. Nevertheless, approximately two thirds of patients relapse due to persisting leukemic blasts. The persistence of these cells, below the threshold of morphological detection, is termed minimal residual disease (MRD) and various methods are used for its detection. These methods include classical cytogenetics, fluorescence in situ hybridization, qualitative and quantitative RT-PCR and multiparametric flow cytometry. Currently, less than half of the AML patients have a specific marker detectable by RT-PCR techniques. The major specific molecular markers are involvement of the MLL gene with up to 50 different partners and partial tandem duplications, the core binding factor leukemias with AML1/ETO and CBFbeta/MYH11 rearrangements, PML/RARalpha in acute promyelocytic leukemia, internal tandem duplications and mutations of FLT3 and some other rare translocations. In addition, several other genes show abnormal expression levels in AML, including the Wilms tumor gene, the PRAME gene and Ig/TCR rearrangements. Most of these genetic abnormalities can be detected by qualitative but more importantly by quantitative RT-PCR. The kinetics of disappearance of molecular markers in AML differs between the various types of leukemias, although at least a 2 log reduction of transcript after induction chemotherapy is necessary for long-term remission in all types. Conversely, the change of PCR from negativity to positivity is highly predictive of relapse. Whereas in acute lymphoblastic leukemia, multiparametric flow cytometry is an established method for MRD detection, this is less so in AML. The reason is the absence of well-characterized leukemia-specific antigens and the existence of phenotypic changes at relapse. On the other hand, this method is convenient due to its simplicity and universal applicability. In conclusion, several methods can be used for MRD detection in AML patients; each has its pros and cons. Several issues still remain to be settled including the choice of the best method and the timing for MRD monitoring and above all the practical clinical implications of MRD in the various types of AML.

Flow cytometric detection of minimal residual disease in acute lymphoblastic leukemia

Assessment of minimal residual disease (MRD) during the first months of therapy gives information on the timely response to treatment, and proves to be a powerful and independent indicator of treatment outcome in patients with acute lymphoblastic leukemia (ALL). Immunological evaluation by flow cytometry (FCM) is one of the most attractive approaches to this. The present review summarizes the historical development of this approach over the last 20 years, and shows that current methodology is based on the existence of leukemia-associated patterns of derangement in antigen expression with respect to normal differentiation or location of occurrence. Recent clinical studies are summarized which proved that FCM is applicable to more than 90% of patients with ALL and gives prognostic information comparable to polymerase chain-reaction (PCR)-based technology. Ongoing efforts based on parallel application of both technologies are explained which are designed to clarify which approach bears the best cost-relevance ratio in order to be broadly used in the future for risk assessment and tailoring of treatment modalities. Concluding perspectives relate to further technical developments like usage of peripheral blood (PB) instead of bone marrow (BM), absolute quantification, or strategic placement of investigative time-points, which may allow to simplify the MRD approach and thus augment it's economic efficiency.

Immunologic monitoring in adults with acute lymphoblastic leukemia

Investigation of minimal residual disease (MRD) by immunophenotyping and molecular techniques has proven to be a powerful approach for disease monitoring in patients with acute leukemia. Multiparameter flow cytometry, through the use of triple or quadruple marker combinations, identifies aberrant or uncommon phenotypic profiles in more than 90% of adult patients with acute lymphoblastic leukemia (ALL) at diagnosis. These profiles allow identification of residual leukemic cells in bone marrow or peripheral blood once morphologic complete remission is achieved. Until now, most immunophenotypic MRD studies in ALL have focused on children. In contrast, information on the value of MRD in adults with ALL is scanty and usually restricted to polymerase chain reaction studies. In this review, we focus on technical aspects of MRD detection by flow cytometry and on the clinical data concerning the value of immunologic MRD studies as a tool for relapse prediction in adult ALL. Although prospective studies are needed, we assert that immunophenotypic MRD studies are clinically useful. Such studies should be incorporated into the routine management of adult ALL patients for identification of those at high risk of relapse, who could benefit from new alternative therapeutic approaches, and to distinguish these patients from others who could be cured with more conventional approaches.

Minimal residual disease detection in childhood precursor-B-cell acute lymphoblastic leukemia: relation to other risk factors. A Children's Oncology Group study

Minimal residual disease (MRD) can be detected in the marrows of children undergoing chemotherapy either by flow cytometry or polymerase chain reaction. In this study, we used four-color flow cytometry to detect MRD in 1016 children undergoing therapy on Children's Oncology Group therapeutic protocols for precursor-B-cell ALL. Compliance was excellent, with follow-up samples received at the end of induction on nearly 95% of cases; sensitivity of detection at this time point was at least 1/10,000 in more than 90% of cases. Overall, 28.6% of patients had detectable MRD at the end of induction. Patients with M3 marrows at day 8 were much more likely to be MRD positive (MRD+) than those with M2 or M1 marrows. Different genetically defined groups of patients varied in their prevalence of MRD. Specifically, almost all patients with BCR-ABL had high levels of end-of-induction MRD. Only 8.4% of patients with TEL-AML1 were MRD+>0.01% compared with 20.3% of patients with trisomies of chromosomes 4 and 10. Our results show that MRD correlates with conventional measures of slow early response. However, the high frequency of MRD positivity in favorable trisomy patients suggests that the clinical significance of MRD positivity at the end of induction may not be the same in all patient groups.

A flow cytometric method to detect apoptosis-related protein expression in minimal residual disease in acute myeloid leukemia

Minimal residual disease (MRD) cells are thought to be responsible for the persistence and relapse of acute myeloid leukemia (AML). Flow cytometric MRD detection by the establishment of a leukemia-associated phenotype (LAP) at diagnosis can be used in 80% of AML patients, allowing detection and functional characterization of MRD in follow-up bone marrow. One of the mechanisms contributing to inefficient chemotherapy is apoptosis resistance. Measuring apoptosis parameters in MRD cells will help to unravel the importance of apoptosis resistance in AML. We therefore developed a four-color flow cytometry method that enables establishment of apoptosis-related protein expression such as Bcl-2, Bcl-x(L), Mcl-1 and Bax at diagnosis and in MRD. Firstly, validation of this assay using Western blot analysis in five leukemia cell lines showed a significant correlation (R=0.70: P<0.0001). Secondly, the influence of the permeabilization procedure on LAP expression was investigated in 38 AML samples at diagnosis and in 42 MRD samples. Quantification of the frequency of LAP+ cells with and without permeabilization showed no significant differences (diagnosis: P= 0.57, follow-up: P= 0.43). The flow cytometric protocol thus enables analysis of apoptosis-related proteins at different stages of the disease, which will lead to a better understanding of the role of apoptosis resistance in the emergence of MRD in AML.

Outcome prediction by immunophenotypic minimal residual disease detection in adult T-cell acute lymphoblastic leukaemia

Flow-cytometric detection of minimal residual disease (MRD) identifies patients with high relapse risk in childhood acute lymphoblastic leukaemia (ALL). We studied the efficacy of this method in adult T-ALL treated with the Italian co-operative GIMEMA (Gruppo Italiano Malattie Ematologiche dell'Adulto) LAL0496 protocol. Bone marrow samples from 53 patients were taken at fixed treatment time points and MRD was analysed using a leukaemia-specific immunophenotype (cytoplasmic-CD3/nuclear-terminal desoxynucleotidyl transferase). The median follow-up was 17 months (range 3-61) and a median of 4.5 analyses/patient was performed (range 3-12). Six out of 53 (11.3%) patients were refractory to treatment, 30/53 (56.6%) relapsed and 17/53 (32.1%) remain in continuous complete remission. The probability of relapse at 2 years for MRD-positive patients at preconsolidation was 81.5%vs 38.9% for MRD-negative patients (P = 0.00078). This risk was still 54.5% for MRD-positive vs 15.8% for MRD-negative patients pre-third reinduction (P = 0.0098) and 50.0% for MRD-positive vs 16.4% for MRD-negative patients pre-sixth reinduction (P = 0.032). The relapse-predicting value of MRD did not depend on features at diagnosis such as age, sex and leucocyte count. Our data suggest that immunophenotypic MRD monitoring in the first year of treatment is a useful outcome predictor for adult T-ALL patients.

Flow cytometric follow-up of minimal residual disease in bone marrow gives prognostic information in children with acute lymphoblastic leukemia

Using flow cytometry (FC) and live gate (LG) analysis we have followed levels of minimal residual disease (MRD) in the bone marrow (BM) of 70 consecutive patients with childhood acute lymphoblastic leukemia (59 B precursor ALL and 11 T-ALL) treated according to the Nordic (NOPHO-92) protocols. Thorough studies of B and T cell antigen expression patterns in normal BM performed during BIOMED 1 Concerted Action on MRD, made it possible to tailor individual protocols of marker combinations for follow-up in 97% of patients. In 12% of LG analyses, the numbers of cells exceeded 10(6) and in 82% exceeded 10(5), giving the sensitivity level of MRD detection 10(-5) and 10(-4), respectively. The median follow-up time was 53 months. Patients with MRD levels > or = 0.01% at follow-up time-points during and after first induction, and at the end of treatment had significantly lower disease-free survival by comparison to patients with MRD values <0.01%. Seven of nine patient with recurrence in the BM showed under treatment persisting MRD levels > or = 0.01% of BM cells. This was also observed in another two patients with infant leukemia who relapsed. In conclusion, the investigation of levels and the dynamics of MRD by sensitive and quantitative FC can provide a basis for further clinical studies for at least upgrading of therapy.

Chimerism and minimal residual disease monitoring after reduced intensity conditioning (RIC) allogeneic transplantation

Since graft-versus-leukemia (GVL) is the main weapon for disease eradication after reduced intensity conditioning (RIC) allogeneic SCT, the availability of sensitive and specific techniques to monitor changes in tumor load after transplant are especially helpful. These minimal residual disease techniques would allow an early intervention in the event of low tumor burden, for which immunotherapy is highly effective. Some authors have found an association between persistence of MRD, mixed chimerism and risk of relapse. Nevertheless, data from the literature remain contradictory and further correlations should be established, especially in RIC transplants. In this study we have analyzed the impact of MRD and chimerism monitoring on the outcome of 34 patients undergoing RIC allogeneic SCT who were considered poor candidates for conventional transplantation due to advanced age or other concurrent medical conditions. At day +100 25 (75%) patients reached complete remission (CR), there were five (15%) partial responses and three patients progressed. Incidence of grade 2-4 aGVHD and extensive cGVHD were 35% and 58%, respectively. Sixteen percent of patients developing aGVHD relapsed as compared to 47% in those without aGVHD (P = 0.03) and also 10% of patients developing cGVHD relapsed as compared to 50% relapses in those without cGHVD (P = 0.03). Four patients (12%) died due to early (n = 1) and late (n = 3) transplant-related mortality. After a median follow-up of 15 months, 24 out of the 34 patients remain alive. Projected overall survival and disease-free survival at 3 years are 68% and 63%, respectively. Early chimerism analysis showed 67% of patients with complete chimerism (CC) in bone marrow (BM), 86% in peripheral blood (PB), 89% in granulocytes and 68% in T lymphocytes. On day +100, these figures were 68%, 79%, 90% and 73%, respectively, and on day +180 there were 83% patients with CC in BM, 100% in PB, 100% in granulocytes and 100% in T lymphocytes. We observed a trend to a higher incidence of relapse in patients with mixed chimerism (MC) as compared to patients with CC. MRD monitoring by flow cytometry and/or RT-PCR analysis was performed in 23 patients. MRD assessment on days +21 to +56 after transplant allowed identification of patients at risk of relapse. In this sense, seven out of 12 patients (58.3%) who had positive MRD on days +21 to +56 relapsed as compared to none out of 11 patients who had negative MRD (P = 0.002). Of the seven patients with criteria to monitor MRD who relapsed after transplant, all but one remained MRD positive until relapse. By contrast, 10 patients remained MRD negative and all of them are in continuous CR. In nine additional patients, persistence of MRD or mixed chimerism was observed after transplant and withdrawal of cyclosporin with or without DLI was performed. Only two out of these nine patients relapsed. MRD clearance was preceded by CC and GVHD. In conclusion, in our study we found that RIC allogeneic transplantation can be used in patients considered poor candidates for conventional transplantation due to advanced age or other concurrent medical conditions with both low toxicity and low transplant-related mortality. Simultaneous studies of both chimerism and MRD are a useful tool in order to predict risk of relapse in patients undergoing RIC transplants and so can be helpful for individualizing treatment strategies after transplant.

Incidence of phenotypic aberrations in a series of 467 patients with B chronic lymphoproliferative disorders: basis for the design of specific four-color stainings to be used for minimal residual disease investigation

Multiparameter immunophenotypic analysis of neoplastic cells has proven to be of great help for the investigation of minimal residual disease in acute leukemias; however, its utility has not been systematically explored in B cell chronic lymphoproliferative disorders. The aim of the present study was to investigate the incidence of phenotypic aberrations in a series of 467 consecutive leukemic B cell chronic lymphoproliferative disorders through the comparison of the phenotypic characteristics of tumor vs normal peripheral blood (n = 10) and bone marrow (n = 10) B cells, in order to explore the applicability of this strategy for minimal residual disease monitoring. An additional goal of our study was to evaluate the sensitivity of multiparameter flow cytometry for the detection of minimal residual disease in leukemic B cell chronic lymphoproliferative disorders through dilutional experiments (n = 19). From the patients analyzed 382 corresponded to B cell chronic lymphocytic leukemia/small lymphocytic lymphoma (353 typical and 29 atypical); five to prolymphocytic leukemia; 13 to hairy cell leukemias; 12 to lymphoplasmacytic lymphomas; 14 to splenic marginal zone lymphomas; 22 were follicular lymphomas; and 19 mantle cell lymphomas. The following triple stainings were systematically applied to both normal and leukemic samples: FMC7/CD5/CD19, CD22/CD23/CD19, CD103/CD25/CD19, CD10/CD11c/CD19 and sIg/sIg(lambda)/CD19. Overall, 98% of the leukemic B cell chronic lymphoproliferative disorders cases displayed aberrant phenotypes at diagnosis with no significant differences being found between cases analyzed in peripheral blood vs bone marrow samples. The most common types of aberrant criteria detected included asynchronous antigen expression (92%) and antigen over-expression (54%); abnormally light scatter characteristics were found in 17% of the cases. Most of the cases studied (90%) displayed four or more phenotypic aberrations. Once patients were divided according to the different diagnostic subgroups, the overall incidence of aberrant phenotypes ranged from 79 to 80% among atypical B cell chronic lymphocytic leukemia/small lymphocytic lymphoma and prolymphocytic leukemia to 97% of follicular lymphoma and 100% of typical B cell chronic lymphocytic leukemia/small lymphocytic lymphoma, hairy cell leukemia, lymphoplasmacytic lymphomas, splenic marginal zone lymphomas and mantle cell lymphomas. Based on the aberrant phenotypes detected unique four-color stainings could be built for the specific identification of aberrant phenotypes. These include CD22/CD23/CD19/CD5 and sIg(kappa)/sIg(lambda)/CD19/CD5 for lymphocytic leukemia/small lymphocytic lymphoma and prolymphocytic leukemia, CD103/CD25 or CD22/CD19/CD11c for hairy cell leukemia, FMC7/CD22/CD19/CD103 and sIg(kappa)/sIg(lambda)/CD22/CD19 for splenic marginal zone lymphomas, CD22/CD23/CD19/CD10 for follicular lymphomas and CD10/CD22/CD19/CD5 for mantle cell lymphomas. Serial dilutional experiments showed that the sensitivity level of immunophenotyping ranges between 10(-4) and 10(-5). In summary, the present study shows that immunophenotypic analysis allows the identification of aberrant phenotypes in 98% of leukemic B cell chronic lymphoproliferative disorders and these phenotypes can be used for minimal residual disease monitoring with a sensitivity limit of 10(-4)-10(-5).

CD34 and CD117 are overexpressed in AML and may be valuable to detect minimal residual disease

We estimated by quantitative flow cytometry (FC) the expression of CD13, CD33, CD34 and CD117 antigens in cells from 64 patients with acute myeloid leukaemia (AML) and 22 normal bone marrows (BMs). The method converts fluorescence intensity into number of antigen molecules per cell, measured by antibody binding capacity (ABC). The number of molecules per cell in normal BM was 9.5+/-5.7 for CD13, 7+/-2.3 for CD33, 6+/-0.7 for CD34, and 6.3+/-1.5x10(3) for CD117. AML blasts expressed 11.4+/-12.4 molecules per cell for CD13, 9.5+/-9.7 for CD33, 74+/-2328.5 for CD34 and 12.5+/-33 x 10(3) for CD117. The number of CD34 and CD117 molecules were significantly higher in AML than in normals (P<0.0001 and P<0.05, respectively) while only in a few cases, CD13 and CD33 were abnormally expressed in myeloblasts. Our results indicate that quantitative analysis of CD34 and CD117 may be useful to detect minimal residual disease (MRD) and could be tested in a future to monitor therapy in AML.

Antigen expression patterns reflecting genotype of acute leukemias

Multi-parameter flow cytometry, molecular genetics, and cytogenetic studies have all contributed to new classification of leukemia. In this review we discuss immunophenotypic characteristics of major genotypic leukemia categories. We describe immunophenotype of: B-lineage ALL with MLL rearrangements, TEL/AML1, BCR/ABL, E2A/PBX1 translocations, hyperdiploidy, and myc fusion genes; T-ALL with SCL gene aberrations and t(5;14) translocation; and AML with AML1/ETO, PML/RARalpha, OTT/MAL and CBFbeta/MYH11 translocations, trisomies 8 or 11 and aberrations of chromosomes 7 and 5. Whereas some genotypes associate with certain immunophenotypic features, others can present with variable immunophenotype. Single molecules (as NG2, CBFbeta/SMMHC and PML/RARalpha proteins) associated with or derived from specific translocations have been described. More often, complex immunophenotype patterns have been related to the genotype categories. Most known associations between immunophenotype and genotype have been defined empirically. Therefore, these associations should be validated in independent patient cohorts before they can be widely used for prescreening of leukemia. Progress in our knowledge on leukemia will show how the molecular-genetic changes modulate the immunophenotype as well as how the expressed protein molecules further modulate cell behavior.

Flow cytometric analysis of cerebrospinal fluid samples and its usefulness in routine clinical practice

Low volume and few cells have hampered the use of flow cytometry for studying cerebrospinal fluid (CSF) in routine clinical practice, although information about the cellular phenotypes present in this type of sample is of great value in many diseases. We developed a novel flow cytometric strategy capable of identifying total CSF T lymphocytes and the CD4+ subset, even in CSF samples with as few as 1 leukocyte per 3 microL of sample. We also showed that identification of CD8+ T cells could be achieved in most samples, while B lymphocytes are detectable only in samples with more than 5 cells per microliter. These findings demonstrate the reliability of this method to improve the diagnostic accuracy of classic cytologic studies in many neurologic disorders.

Immunological evaluation of minimal residual disease (MRD) in acute myeloid leukaemia (AML)

Immunophenotypic analysis of leukaemic cells using multiparametric flow cytometry has proved to be an attractive approach for MRD investigation in acute lymphoblastic leukaemia (ALL); by contrast, information on acute myeloid leukaemia (AML) is still scanty. Here, we first review the methodological strategies for these studies. Triple or quadruple antigenic combinations, analysed by multiparametric flow cytometry, have shown that in 80% of AML patients it is possible to identify aberrant or uncommon phenotypic profiles on blast cells, thereby allowing their distinction from normal cells and their use as leukaemia-associated phenotypes (LAP). We also focus on technical aspects that are important in the definition of LAP. We then review pitfalls that could potentially affect results using this approach. Finally, we review available information concerning the clinical value of these studies. Although reported data in the literature are still scanty, several authors have shown that this technique could be used for the prognostic evaluation of AML patients, when immunophenotypic evaluation is applied after induction therapy.

Fusion gene transcripts and Ig/TCR gene rearrangements are complementary but infrequent targets for PCR-based detection of minimal residual disease in acute myeloid leukemia

PCR-based monitoring of minimal residual disease (MRD) in acute leukemias can be achieved via detection of fusion gene transcripts of chromosome aberrations or detection of immunoglobulin (Ig) and T cell receptor (TCR) gene rearrangements. We wished to assess whether both PCR targets are complementary in acute myeloid leukemia (AML). We investigated 105 consecutive AML cases for the presence of fusion gene transcripts by reverse transcriptase polymerase chain reaction (RT-PCR): AML1-ETO associated with t(8;21), CBFB-MYH11 with inv(16), PML-RARA with t(15;17), BCR-ABL with t(9;22), and MLL-AF4 with t(4;11). In 17 out of 105 AML cases (16%), fusion gene transcripts were found. Ninety-five of these AML patients (13 with fusion gene transcripts) were also investigated for the presence of IGH, IGK, TCRG and TCRD rearrangements by Southern blot and/or PCR heteroduplex analysis and sequencing. In nine out of 95 patients (9.5%), such rearrangements were found. Combined data revealed that only one patient with a fusion gene transcript had a coexistent Ig/TCR rearrangement. The nine AML patients with Ig/TCR rearrangements, as well as five additional AML patients from a previous study were investigated in more detail, revealing that Ig/TCR rearrangements in AML are immature and unusual. The presence of Ig/TCR rearrangements in AML did not correlate with RAG gene expression levels as determined by real-time quantitative PCR. In conclusion, fusion gene transcripts and Ig/TCR rearrangements are infrequent, but complementary MRD-PCR targets in AML.

Early immunophenotypical evaluation of minimal residual disease in acute myeloid leukemia identifies different patient risk groups and may contribute to postinduction treatment stratification

Early response to therapy is one of the most important prognostic factors in acute leukemia. It is hypothesized that early immunophenotypical evaluation may help identify patients at high risk for relapse from those who may remain in complete remission (CR). Using multiparametric flow cytometry, the level of minimal residual disease (MRD) was evaluated in the first bone marrow (BM) in morphologic CR obtained after induction treatment from 126 patients with acute myeloid leukemia (AML) who displayed aberrant phenotypes at diagnosis. Based on MRD level, 4 different risk categories were identified: 8 patients were at very low risk (fewer than 10(-4) cells), and none have relapsed thus far; 37 were at low risk (10(-4) to 10(-3) cells); and 64 were at intermediate risk (fewer than 10(-3) to 10(-2) cells), with 3-year cumulative relapse rates of 14% and 50%, respectively. The remaining 17 patients were in the high-risk group (more than 10(-2) residual aberrant cells) and had a 3-year relapse rate of 84% (P =.0001). MRD level not only influences relapse-free survival but also overall survival (P =.003). The adverse prognostic impact was also observed when M3 and non-M3 patients with AML were separately analyzed, and was associated with adverse cytogenetic subtypes, 2 or more cycles to achieve CR, and high white blood cell counts. Multivariate analysis showed that MRD level was the most powerful independent prognostic factor, followed by cytogenetics and number of cycles to achieve CR. In conclusion, immunophenotypical investigation of MRD in the first BM in mCR obtained after AML induction therapy provides important information for risk assessment in patients with AML.