Immunoglobulin heavy-chain gene rearrangement in adult acute lymphoblastic leukemia reveals preferential usage of J(H)-proximal variable gene segments

Comparison of Two Quantitative PCR-Based Assays for Detection of Minimal Residual Disease in B-Precursor Acute Lymphoblastic Leukemia Harboring Three Major Fusion Transcripts

Two quantitative PCR (qPCR)-based methods, for clonal Ig or T-cell receptor gene (Ig/TCR) rearrangements and for fusion transcripts, are widely used for the measurement of minimal residual disease (MRD) in patients with B-precursor acute lymphoblastic leukemia (ALL). MRD of bone marrow samples from 165 patients carrying the three major fusion transcripts, including 74 BCR-ABL1, 54 ETV6-RUNX1, and 37 TCF3-PBX1, was analyzed by using the two qPCR-based methods. The coefficient correlation of both methods was good for TCF3-PBX1 (R² = 0.8088) and BCR-ABL1 (R² = 0.8094) ALL and moderate for ETV6-RUNX1 (R² = 0.5972). The concordance was perfect for TCF3-PBX1 ALL (97.2%), substantially concordant for ETV6-RUNX1 ALL (87.1%), and only moderate for BCR-ABL1 ALL (70.6%). The discordant MRD, positive for only one method with a difference greater than one log, was found in 4 of 93 samples (4.3%) with ETV6-RUNX1, 31 of 245 samples (12.7%) with BCR-ABL1, and 0 of TCF3-PBX1 ALL. None of the eight nontransplanted patients with BCR-ABL1-MRD (+)/Ig/TCR-MRD (-) with a median follow-up time of 73.5 months had hematologic relapses. Our study showed an excellent MRD concordance between the two qPCR-based methods in TCF3-PBX1 ALL, whereas qPCR for Ig/TCR is more reliable in BCR-ABL1 ALL.

Determination of VH Family Usage in B-Cell Malignancies via the BIOMED-2 IGH PCR Clonality Assay

OBJECTIVES

To determine whether V H family usage in B-cell lymphoproliferative disorders can be deduced from polymerase chain reaction (PCR) product-length information obtained through the BIOMED-2 (Invivoscribe, San Diego, CA) clonality assay.

METHODS

We develop an algorithm that uses the sizing information of the BIOMED-2 immunoglobulin heavy chain (IGH) clonality assay to deduce V H family usage. PCR with family-specific primers on 51 clinical samples containing 54 rearranged alleles were used to validate the algorithm.

RESULTS

The clonal PCR products in different framework reactions contain the same NDN segment (because they are from the same allele). Subtracting the size of the framework III product from the size of the framework I and II products yields the relative position of the framework primer binding sites for the V H segment used. The V H family can be assigned with these relative positions because they are V H family specific in the BIOMED-2 assay. The V H family assigned by the algorithm was concordant with family-specific PCR results for 49 (96%) of the 51 specimens.

CONCLUSIONS

We have developed an algorithm that can correctly assign V H family usage when all three BIOMED-2 framework reactions produced clonal products. Given the wide adoption of BIOMED-2 assay, the algorithm can facilitate collection of IGH V H usage data without additional cost to the laboratories.

Minimal residual disease detection in Tunisian B-acute lymphoblastic leukemia based on immunoglobulin gene rearrangements

IGH gene rearrangement and IGK-Kde gene deletion can be used as molecular markers for the assessment of B lineage acute lymphoblastic leukemia (B-ALL). Minimal residual disease detected based on those markers is currently the most reliable prognosis factor in B-ALL. The aim of this study was to use clonal IGH/IGK-Kde gene rearrangements to confirm B-ALL diagnosis and to evaluate the treatment outcome of Tunisian leukemic patients by monitoring the minimal residual disease (MRD) after induction chemotherapy. Seventeen consecutive newly diagnosed B-ALL patients were investigated by multiplex PCR assay and real time quantitative PCR according to BIOMED 2 conditions. The vast majority of clonal VH-JH rearrangements included VH3 gene. For IGK deletion, clonal VK1f/6-Kde recombinations were mainly identified. These rearrangements were quantified to follow-up seven B-ALL after induction using patient-specific ASO. Four patients had an undetectable level of MRD with a sensitivity of up to 10-5. This molecular approach allowed identification of prognosis risk group and adequate therapeutic decision. The IGK-Kde and IGH gene rearrangements might be used for diagnosis and MRD monitoring of B-ALL, introduced for the first time in Tunisian laboratories.

Combined IKZF1 and IG markers as new tools for diagnosis and minimal residual disease assessment in Tunisian B-ALL

INTRODUCTION

The monitoring of minimal residual disease (MRD) approach in patients diagnosed with B-acute lymphoblastic leukemia (B-ALL) allows an early detection of residual clones inducing relapses and therefore appropriate therapy strategy. The molecular markers may identify and quantify the residual blasts in B-ALL with normal cytology. In this study, we aimed to use combined IKZF1, IGH and IGK immunoglobulin genes for diagnosis and MRD monitoring in B-ALL sample using MLPA, multiplex PCR and real-time quantitative PCR.

MATERIAL

We showed that multiplex PCR and MLPA are necessary and complementary to detect IKZF1 deletions.

RESULTS

We have identified at the diagnosis clonal IGH rearrangement (VH3-JH5) and IKZF1 deletion (Δ4-7), which we have used it for MRD evaluation after induction chemotherapy. Despite the absence of chromosome abnormality, the patient may be classified in high-risk group with a relapse rate of residual blasts>10^-4 and sensitivity up to 10^-5. This molecular approach enabled the patient's stratification, which was overlooked by classical methods.

CONCLUSION

The combined IKZF1 and immunoglobulin genes will be used as appropriate molecular tools for diagnosis and MRD assessment of B-lineage leukemias and introduced as a routine tests in Tunisian clinical laboratories. They will be useful to stratify patients into risk groups leading to better treatment strategy.

Clinical drug resistance linked to interconvertible phenotypic and functional states of tumor-propagating cells in multiple myeloma

The phenotype and function of cells enriched in tumor-propagating activity and their relationship to the phenotypic architecture in multiple myeloma (MM) are controversial. Here, in a cohort of 30 patients, we show that MM composes 4 hierarchically organized, clonally related subpopulations, which, although phenotypically distinct, share the same oncogenic chromosomal abnormalities as well as immunoglobulin heavy chain complementarity region 3 area sequence. Assessed in xenograft assays, myeloma-propagating activity is the exclusive property of a population characterized by its ability for bidirectional transition between the dominant CD19(-)CD138(+) plasma cell (PC) and a low frequency CD19(-)CD138(-) subpopulation (termed Pre-PC); in addition, Pre-PCs are more quiescent and unlike PCs, are primarily localized at extramedullary sites. As shown by gene expression profiling, compared with PCs, Pre-PCs are enriched in epigenetic regulators, suggesting that epigenetic plasticity underpins the phenotypic diversification of myeloma-propagating cells. Prospective assessment in paired, pretreatment, and posttreatment bone marrow samples shows that Pre-PCs are up to 300-fold more drug-resistant than PCs. Thus, clinical drug resistance in MM is linked to reversible, bidirectional phenotypic transition of myeloma-propagating cells. These novel biologic insights have important clinical implications in relation to assessment of minimal residual disease and development of alternative therapeutic strategies in MM.

Multiplex PCR and Genescan analysis to detect immunoglobulin heavy chain gene rearrangement in feline B-cell neoplasms

Lymphoid neoplasms are usually diagnosed on the basis of cytological and histopathological findings. However, in some cases, discrimination of lymphoid neoplasms from reactive lymphoid proliferation is difficult. PCR amplification of complementarity-determining region 3 (CDR3) of the immunoglobulin heavy-chain variable region (IGHV) gene can be used to assess clonality of B-cell populations as a supportive diagnostic tool for B-cell neoplasms. Because of the sequence variation and possible somatic hypermutation of the IGHV gene, sensitivity of the PCR-based assay to detect clonal IGHV gene rearrangement largely depends on the sequences and numbers of primer sets. Prior to the development of an efficient assay, we cloned and sequenced 97 IGHV complementary DNAs (48 IGHV-1 and 49 IGHV-3 clones) from normal cat spleens. On the basis of these sequences, we designed 6 forward primers at the variable region and 5 reverse primers at the joining region. Using each of 6 forward primers and a mixture of 5 reverse primers, we amplified CDR3 of IGHV genes and analyzed the PCR products by conventional PAGE and Genescan analyses using fluorescence-labeled primers. Twenty-six feline B-cell neoplasms diagnosed by histopathological and immunohistochemical examinations were subjected to the newly developed analysis of IGHV gene rearrangement. Clonal IGHV gene rearrangement was detected in 22 of 26 (84%) samples by both PAGE and Genescan analyses. To reduce the number of PCR reactions, we constructed a multiplex PCR analysis system using a mixture of IGHV-1- and IGHV-3-specific primers as forward primers and a mixture of 5 joining region reverse primers. Results of the multiplex PCR were 100% concordant with those obtained by each of the singleplex PCRs. The multiplex PCR-based assay and Genescan analysis developed in the present study would be useful and practical tools to detect clonal IGHV gene rearrangement in feline B-cell neoplasms.

Clinical significance of productive immunoglobulin heavy chain gene rearrangements in childhood acute lymphoblastic leukemia

We analyzed the CDR3 region of 80 children with B-cell acute lymphoblastic leukemia (B-ALL) using the ImMunoGeneTics Information System and JOINSOLVER. In total, 108 IGH@ rearrangements were analyzed. Most of them (75.3%) were non-productive. IGHV@ segments proximal to IGHD-IGHJ@ were preferentially rearranged (45.3%). Increased utilization of IGHV3 segments IGHV3-13 (11.3%) and IGHV3-15 (9.3%), IGHD3 (30.5%), and IGHJ4 (34%) was noted. In pro-B ALL more frequent were IGHV3-11 (33.3%) and IGHV6-1 (33.3%), IGHD2-21 (50%), IGHJ4 (50%), and IGHJ6 (50%) segments. Shorter CDR3 length was observed in IGHV@6, IGHD7, and IGHJ1 segments, whereas increased CDR3 length was related to IGHV3, IGHD2, and IGHJ4 segments. Increased risk of relapse was found in patients with productive sequences. Specifically, the relapse-free survival rate at 5 years in patients with productive sequences at diagnosis was 75% (standard error [SE] ±9%), whereas in patients with non-productive sequences it was 97% (SE ±1.92%) (p-value =0.0264). Monoclonality and oligoclonality were identified in 81.2% and 18.75% cases at diagnosis, respectively. Sequence analysis revealed IGHV@ to IGHDJ joining only in 6.6% cases with oligoclonality. The majority (75%) of relapsed patients had monoclonal IGH@ rearrangements. The preferential utilization of IGHV@ segments proximal to IGHDJ depended on their location on the IGHV@ locus. Molecular mechanisms occurring during IGH@ rearrangement might play an essential role in childhood ALL prognosis. In our study, the productivity of the rearranged sequences at diagnosis proved to be a significant prognostic factor.

PAX5 mutations occur frequently in adult B-cell progenitor acute lymphoblastic leukemia and PAX5 haploinsufficiency is associated with BCR-ABL1 and TCF3-PBX1 fusion genes: a GRAALL study

Adult and child B-cell progenitor acute lymphoblastic leukemia (BCP-ALL) differ in terms of incidence and prognosis. These disparities are mainly due to the molecular abnormalities associated with these two clinical entities. A genome-wide analysis using oligo SNP arrays recently demonstrated that PAX5 (paired-box domain 5) is the main target of somatic mutations in childhood BCP-ALL being altered in 38.9% of the cases. We report here the most extensive analysis of alterations of PAX5 coding sequence in 117 adult BCP-ALL patients in the unique clinical protocol GRAALL-2003/GRAAPH-2003. Our study demonstrates that PAX5 is mutated in 34% of adult BCP-ALL, mutations being partial or complete deletion, partial or complete amplification, point mutation or fusion gene. PAX5 alterations are heterogeneous consisting in complete loss in 17%, focal deletions in 10%, point mutations in 7% and translocations in 1% of the cases. PAX5 complete loss and PAX5 point mutations differ. PAX5 complete loss seems to be a secondary event and is significantly associated with BCR-ABL1 or TCF3-PBX1 fusion genes and a lower white blood cell count.

Treatment of Adult Acute Lymphoblastic Leukemia

In the early 1980s, adult acute lymphoblastic leukemia (ALL) was a rarely curable disease with overall survival < 10%. After adapting combinations employed by pediatric groups, the outcome improved to 30–40%. A period of stagnation followed with improvement only in distinct subgroups. In the past 5 years, however, striking new developments have been noticeable. Progress has been made in molecular diagnostics of ALL. Improvements to standard therapy including stem cell transplantation (SCT) have occurred and a variety of new drugs for ALL are under evaluation. Rapid diagnosis and classification of ALL is increasingly important to identify prognostic factors and molecular genetic subsets that will be the focus of “targeted” therapies as we enter the era of subset specific treatment. In the following review we will discuss treatment of adult ALL (excluding elderly patients,1 adolescents2 and patients with Ph/BCR-ABL positive ALL3).

Differential expression of CD180 and IgM by B-cell chronic lymphocytic leukaemia cells using mutated and unmutated immunoglobulin VH genes

We have studied the surface expression of the Toll-like receptor family member CD 180 on cells from 78 patients with B-chronic lymphocytic leukaemia (B-CLL). B-CLL cells had variable levels of CD 180 expression, but this was always less than that expressed by normal blood B cells and was stable for 24 months. Significantly higher levels of CD 180 were expressed by B-CLL cells with mutated IGVH genes compared with those using unmutated IGVH genes. This was in contrast to the higher levels of expression of surface immunoglobulin M by B-CLL cells using unmutated, rather than mutated IGVH genes. CD 180 was functional on B-CLL cells from some of the patients, as shown by the increased expression of CD 86 following incubation in vitro with anti-CD 180. The differential expression of CD 180 amongst B-CLL patients is one more marker that may define more precisely the different biological properties of this heterogeneous disease.

Immunoglobulin gene segment usage, location and immunogenicity in mutated and unmutated chronic lymphocytic leukaemia

The mutational status of the variable region of the immunoglobulin heavy chain gene (IgV(H)) is an important prognostic marker in B-cell chronic lymphocytic leukaemia (B-CLL), with mutated patients having improved outcome. To examine the impact of mutational status on V(H), D(H), and J(H) gene segment location and immunogenicity, we analysed 375 IgH sequences from 356 patients with B-CLL. Although V(H) and D(H) gene usage was different in mutated compared to unmutated patients, there was no impact of gene location on frequency of use or clinical outcome. Surprisingly, somatic mutations did not increase the immunogenicity of the Ig, as assessed by predicted binding affinity of Ig-derived peptides to major histocompatibility Class I and Class II molecules. Even excluding patients using V(H)1-69, cases using the V(H)1 gene family had a poor outcome. Both mutated and unmutated CLL patients demonstrated evidence of antigen selection. The worst outcome was seen in the subset of 14 unmutated patients with similar HCDR3 amino acid sequence using V(H)1-69, D(H)3-3 and J(H)6, suggesting an antigen-driven process modulating the clinical course.

A fluorescence in situ hybridization map of 6q deletions in acute lymphocytic leukemia: identification and analysis of a candidate tumor suppressor gene

With the objective of identifying candidate tumor suppressor genes, we used fluorescence in situ hybridization to map leukemia-related deletions of the long arm of chromosome 6 (6q). Twenty of 24 deletions overlapped to define a 4.8-Mb region of minimal deletion between markers D6S1510 and D6S1692 within chromosome 6 band q16. Using reverse transcription-PCR, we found evidence of expression in hematopoietic cells for 3 of 15 genes in the region (GRIK2, C6orf111, and CCNC). Comparison between our own and published deletion data singled out GRIK2 as the gene most frequently affected by deletions of 6q in acute lymphocytic leukemia (ALL). Sequence analysis of GRIK2 in 14 ALL cases carrying heterozygous 6q deletions revealed a constitutional and paternally inherited C to G substitution in exon 6 encoding for an amino acid change in one patient. The substitution was absent among 232 normal alleles tested, leaving open the possibility that heterozygous carriers of such mutations may be susceptible to ALL. Although low in all normal hematopoietic tissues, quantitative reverse transcription-PCR showed higher baseline GRIK2 expression in thymus and T cells than other lineages. Among T-cell ALL patients, 6q deletion was associated with a statistically significant reduction in GRIK2 expression (P = 0.0001). By contrast, elevated GRIK2 expression was measured in the myelomonocytic line THP-1 and in one patient with common ALL. Finally, we detected significant levels of GRIK2 expression in prostate, kidney, trachea, and lung, raising the possibility that this gene may be protective against multiple tumor types.

Utilization of Ig heavy chain variable, diversity, and joining gene segments in children with B-lineage acute lymphoblastic leukemia: implications for the mechanisms of VDJ recombination and for pathogenesis

Sequence analysis of the immunoglobulin heavy chain genes (IgH) has demonstrated preferential usage of specific variable (V), diversity (D), and joining (J) genes at different stages of B-cell development and in B-cell malignancies, and this has provided insight into B-cell maturation and selection. Knowledge of the association between rearrangement patterns based on updated databases and clinical characteristics of pediatric acute lymphoblastic leukemia (ALL) is limited. We analyzed 381 IgH sequences identified at presentation in 317 children with B-lineage ALL and assessed the V(H)D(H)J(H) gene utilization profiles. The D(H)J(H)-proximal V(H) segments and the D(H)2 gene family were significantly overrepresented. Only 21% of V(H)-J(H) joinings were potentially productive, a finding associated with a trend toward an increased risk of relapse. These results suggest that physical location at the V(H) locus is involved in preferential usage of D(H)J(H)-proximal V(H) segments whereas D(H) and J(H) segment usage is governed by position-independent molecular mechanisms. Molecular pathophysiology appears relevant to clinical outcome in patients who have only productive rearrangements, and specific rearrangement patterns are associated with differences in the tumor biology of childhood ALL.

Design and standardization of PCR primers and protocols for detection of clonal immunoglobulin and T-cell receptor gene recombinations in suspect lymphoproliferations: report of the BIOMED-2 Concerted Action BMH4-CT98-3936

In a European BIOMED-2 collaborative study, multiplex PCR assays have successfully been developed and standardized for the detection of clonally rearranged immunoglobulin (Ig) and T-cell receptor (TCR) genes and the chromosome aberrations t(11;14) and t(14;18). This has resulted in 107 different primers in only 18 multiplex PCR tubes: three VH-JH, two DH-JH, two Ig kappa (IGK), one Ig lambda (IGL), three TCR beta (TCRB), two TCR gamma (TCRG), one TCR delta (TCRD), three BCL1-Ig heavy chain (IGH), and one BCL2-IGH. The PCR products of Ig/TCR genes can be analyzed for clonality assessment by heteroduplex analysis or GeneScanning. The detection rate of clonal rearrangements using the BIOMED-2 primer sets is unprecedentedly high. This is mainly based on the complementarity of the various BIOMED-2 tubes. In particular, combined application of IGH (VH-JH and DH-JH) and IGK tubes can detect virtually all clonal B-cell proliferations, even in B-cell malignancies with high levels of somatic mutations. The contribution of IGL gene rearrangements seems limited. Combined usage of the TCRB and TCRG tubes detects virtually all clonal T-cell populations, whereas the TCRD tube has added value in case of TCRgammadelta(+) T-cell proliferations. The BIOMED-2 multiplex tubes can now be used for diagnostic clonality studies as well as for the identification of PCR targets suitable for the detection of minimal residual disease.

V(D)J recombinatorial repertoire diversification during intraclonal pro-B to B-cell differentiation

The initial B-cell repertoire is generated by combinatorial immunoglobulin V(D)J gene segment rearrangements that occur in a preferential sequence. Because cellular proliferation occurs during the course of these rearrangement events, it has been proposed that intraclonal diversification occurs during this phase of B-cell development. An opportunity to examine this hypothesis directly was provided by the identification of a human acute lymphoblastic leukemic cell line that undergoes spontaneous differentiation from pro-B cell to the pre-B and B-cell stages with concomitant changes in the gene expression profile that normally occur during B-cell differentiation. After confirming the clonality of the progressively differentiating cells, an analysis of immunoglobulin genes and transcripts indicated that pro-B cell members marked by the same DJ rearrangement generated daughter B cells with multiple V(H) and V(L) gene segment rearrangements. These findings validate the principle of intraclonal V(D)J diversification during B-cell generation and define a manipulable model of human B-cell differentiation.

Polymerase chain reaction (PCR)- and reverse transcription PCR-based minimal residual disease detection in long-term follow-up of childhood acute lymphoblastic leukaemia

Minimal residual disease (MRD) was investigated in 52 children with acute lymphoblastic leukaemia (ALL), using antigen receptor gene rearrangements and reverse transcription polymerase chain reaction for fusion transcripts as molecular targets. Patients [treated according to the Medical Research Council United Kingdom ALL (MRC UKALL) XI protocol or Total XI and XIII protocols] were monitored for a median period of 45 months (range, 9-110 months). Among 17 patients who relapsed, MRD persisted for longer (66.7%, 47.1%, 53.8% and 41.7% at 0-2, 3-5, 6-9, 10-24 months respectively) than patients who remained in continuous clinical and immunological remission (n = 35) (27.3%, 11.1%, 4.3%, 8.0%). Association between MRD tests and outcome was assessed and found to be significant at all time-points. The difference in survival for MRD-positive and MRD-negative patients (using the log-rank test) was statistically significant at all time intervals, as was risk of relapse for MRD-positive patients (1.89, 2.20, 2.65 and 2.16) and MRD-negative patients (0.72, 0.82, 0.65 and 0.70). Sixteen of the 52 patients had an oligoclonal pattern at presentation but oligoclonality did not have an impact on outcome. Cox regression analysis revealed that MRD assessment is an independent and prognostically significant factor during treatment and should be used for patients' stratification in future studies.

Molecular analysis of minimal residual disease in adult acute lymphoblastic leukaemia

Despite intensive chemotherapy and stem cell transplantation (SCT) programmes, overall survival in adult acute lymphoblastic leukaemia (ALL) remains poor compared to that in childhood ALL. Despite clinical and morphological remission being achieved by over 80% of patients, 5-year survival is limited to 40% of patients, clearly indicating that morphology is insufficient in predicting future outcome. Molecular assessment of residual disease in bone marrow using immunoglobulin genes as markers of clonality has recently been evaluated in a large adult ALL study in our institution. Analysis of disease-free survival (DFS) rates for minimal residual disease-(MRD-) positive and -negative patients established that MRD positivity was associated with increased relapse rates at all times, being most significant at 3-5 months post-induction and beyond. Pre-autologous SCT tests are predictive of outcome, but for allogeneic SCT outcome is related to results of the tests after the procedure rather than before. The association of MRD test results and DFS was independent of, and greater than, other standard predictors of outcome and is therefore important in determining treatment for individual patients.

Minimal residual disease tests provide an independent predictor of clinical outcome in adult acute lymphoblastic leukemia

PURPOSE

Investigation of minimal residual disease (MRD) in childhood acute lymphoblastic leukemia (ALL) using molecular markers has proven superior to other standard criteria (age, sex, and WBC) in distinguishing patients at high, intermediate, and low risk of relapse. The aim of our study was to determine whether MRD investigation is valuable in predicting outcome in Philadelphia-negative adult patients with ALL.

PATIENTS AND METHODS

MRD was assessed in 85 adult patients with B-lineage ALL by semiquantitative immunoglobulin H gene analysis on bone marrow samples collected during four time bands in the first 24 months of treatment. Fifty patients received chemotherapy only and 35 patients received allogeneic (n = 19) or autologous (n = 16) bone marrow transplantation (BMT) in first clinical remission. The relationship between MRD status and clinical outcome was investigated and compared with age, sex, immunophenotype, and presenting WBC count.

RESULTS

Fisher's exact test established a statistically significant concordance between MRD results and clinical outcome at all times. Disease-free survival (DFS) rates for MRD-positive and -negative patients and log-rank testing established that MRD positivity was associated with increased relapse rates at all times (P <.05) but was most significant at 3 to 5 months after induction and beyond. MRD status after allogeneic BMT rather than before was found to be an important predictor of outcome in 19 adult patients with ALL tested. In patients receiving autologous BMT (n = 16), the MRD status before BMT was more significant (P =.005).

CONCLUSION

The association of MRD test results and DFS was independent of and greater than other standard predictors of outcome and is therefore important in determining treatment for individual patients.

Pro-B-cell to pre-B-cell development in B-lineage acute lymphoblastic leukemia expressing the MLL/AF4 fusion protein

The most common chromosomal abnormality of infant acute lymphoblastic leukemia (ALL) is the t(4;11)(q21;q23) that gives rise to the MLL/AF4 fusion gene. Leukemic blasts expressing MLL/AF4 are arrested at an early progenitor stage with lymphoid or monocytoid characteristics. A novel B-lineage ALL cell line termed B-lineage-3 (BLIN-3) requiring human bone marrow (BM) stromal cell contact and interleukin-7 (IL-7) for optimal proliferation has been established. BLIN-3 cells have a CD19(+)/CD10(-) phenotype typical of infant ALL, and they harbor the t(4;11)(q21;q23) chromosomal translocation. Reverse transcription-polymerase chain reaction and Western blot analysis confirmed the presence of the MLL/AF4 fusion mRNA and protein in BLIN-3. Initial BLIN-3 cultures had a pro-B cell phenotype and did not express cytoplasmic or surface mu heavy chain. After approximately 5 months in culture on BM stromal cells plus IL-7, BLIN-3 sublines emerged expressing mu heavy chain and VpreB on the cell surfaces (ie, pre-B-cell receptor [BCR](+)). BLIN-3 cells expressing pre-BCR had the t(4;11)(q21;q23) translocation and expressed the MLL/AF4 fusion protein. Cross-linking the BLIN-3 pre-BCR led to enhanced cell proliferation, demonstrating that BLIN-3 expressed a functional pre-BCR. Increased acquisition of surface pre-BCR in BLIN-3 sublines was associated with loss of DJ rearrangements and the appearance of VDJ rearrangements. These results indicate that expression of the MLL/AF4 fusion protein is compatible with BM stromal cell and cytokine dependency, functional immunoglobulin gene segment rearrangement, and subsequent expression of a potentially diverse antigen receptor repertoire. Thus, the expression of MLL/AF4 is compatible with the normal developmental program of human B-lineage cells.

Heterogeneity of VH-JH gene rearrangement patterns: an insight into the biology of B cell precursor ALL

Oligoclonal B cell proliferation, as defined by the presence of more than one leukemic clone, has been detected in approximately 20% to 30% of patients with acute lymphoblastic leukemia (ALL) using PCR or Southern blotting. An accurate assessment of these populations is required to avoid false negative measurements of minimal residual disease (MRD) in follow-up bone marrow (BM) samples of ALL patients. In this study, we analysed 29 ALL patients with two or more immunoglobulin heavy (IGH) chain gene rearrangements in the presentation samples using IGH fingerprinting PCR and sequence analysis. Thirty-nine (51%) of 76 sequences (from 15 patients), shared no VNDNJ homology (ie different CDR3 regions). In the remaining 14 patients, at least two related VH sequences were identified in each patient (identical DNJ sequences). Numerical abnormalities of chromosome 14 was detected in 10 patients. Eight patients were analysed at presentation and relapse. In four of them, expansion of a minor presentation-clone was detected at relapse while the major presentation clone disappeared, confirming 'subclonal evolution'. Finally, in our cohort of patients, the presence of related or unrelated IGH clones did not influence overall survival.