Site-specific deletions involving the tal-1 and sil genes are restricted to cells of the T cell receptor alpha/beta lineage: T cell receptor delta gene deletion mechanism affects multiple genes.

Site-specific deletions in the tal-1 gene are reported to occur in 12-26% of T cell acute lymphoblastic leukemias (T-ALL). So far two main types of tal-1 deletions have been described. Upon analysis of 134 T-ALL we have found two new types of tal-1 deletions. These four types of deletions juxtapose the 5' part of the tal-1 gene to the sil gene promoter, thereby deleting all coding sil exons but leaving the coding tal-1 exons undamaged. The recombination signal sequences (RSS) and fusion regions of the tal-1 deletion breakpoints strongly resemble the RSS and junctional regions of immunoglobulin/T cell receptor (TCR) gene rearrangements, which implies that they are probably caused by the same V(D)J recombinase complex. Analysis of the 134 T-ALL suggested that the occurrence of tal-1 deletions is associated with the CD3 phenotype, because no tal-1 deletions were found in 25 TCR-gamma/delta + T-ALL, whereas 8 of the 69 CD3- T-ALL and 11 of the 40 TCR-alpha/beta + T-ALL contained such a deletion. Careful examination of all TCR genes revealed that tal-1 deletions exclusively occurred in CD3- or CD3+ T-ALL of the alpha/beta lineage with a frequency of 18% in T-ALL with one deleted TCR-delta allele, and a frequency of 34% in T-ALL with TCR-delta gene deletions on both alleles. Therefore, we conclude that alpha/beta lineage commitment of the T-ALL and especially the extent of TCR-delta gene deletions determines the chance of a tal-1 deletion. This suggests that tal-1 deletions are mediated via the same deletion mechanism as TCR-delta gene deletions.

Differential expression of p73 isoforms in relation to drug resistance in childhood T-lineage acute lymphoblastic leukaemia.

The T-lineage phenotype of childhood acute lymphoblastic leukaemia (ALL) is associated with an increased relapse-risk and in vitro resistance to drugs as compared to a precursor B phenotype. Antiapoptotic isoforms of p73 that lack part of the transactivation (TA) domain (DeltaTA-p73, i.e. p73Deltaex2, p73Deltaex3, p73Deltaex2/3 and DeltaN-p73) may cause resistance to anticancer agents through inhibition of p53 and/or proapoptotic p73 family members (TA-p73). We demonstrate in our study that the expression of total p73 mRNA was higher in childhood T-ALL compared to controls (P=0.004). In T-ALL, the relative contribution of antiapoptotic DeltaTA-p73 (88%) was larger than of proapoptotic TA-p73 (12%). Leukaemic cells of T-ALL patients expressing higher levels of antiapoptotic p73 were more resistant to the DNA-damaging drug daunorubicin compared to cells of patients with low or negative expression or these isoforms (P(trend)=0.045). Interestingly, p73Deltaex2 was the most abundantly expressed antiapoptotic isoform in daunorubicin-resistant patient cells (44% of total p73). No association was found between high expression of proapoptotic TA-p73 or antiapoptotic DeltaTA-p73 and relapse-risk. Our results suggest that childhood T-ALL is associated with a high expression of DeltaTA-p73. These isoforms may play a role in cellular resistance to DNA-damaging drugs in children at initial diagnosis of T-ALL.

A new recurrent 9q34 duplication in pediatric T-cell acute lymphoblastic leukemia.

Over the last decade, genetic characterization of T-cell acute lymphoblastic leukemia (T-ALL) has led to the identification of a variety of chromosomal abnormalities. In this study, we used array-comparative genome hybridization (array-CGH) and identified a novel recurrent 9q34 amplification in 33% (12/36) of pediatric T-ALL samples, which is therefore one of the most frequent cytogenetic abnormalities observed in T-ALL thus far. The exact size of the amplified region differed among patients, but the critical region encloses approximately 4 Mb and includes NOTCH1. The 9q34 amplification may lead to elevated expression of various genes, and MRLP41, SSNA1 and PHPT1 were found significantly expressed at higher levels. Fluorescence in situ hybridization (FISH) analysis revealed that this 9q34 amplification was in fact a 9q34 duplication on one chromosome and could be identified in 17-39 percent of leukemic cells at diagnosis. Although this leukemic subclone did not predict for poor outcome, leukemic cells carrying this duplication were still present at relapse, indicating that these cells survived chemotherapeutic treatment. Episomal NUP214-ABL1 amplification and activating mutations in NOTCH1, two other recently identified 9q34 abnormalities in T-ALL, were also detected in our patient cohort. We showed that both of these genetic abnormalities occur independently from this newly identified 9q34 duplication.

Incidence of additional genetic changes in the TEL and AML1 genes in DCOG and COALL-treated t(12;21)-positive pediatric ALL, and their relation with drug sensitivity and clinical outcome.

Clinical heterogeneity within t(12;21) or TEL/AML1-positive ALL (25% of childhood common/preB ALL) indicates that additional genetic changes might contribute to outcome. We studied the relation between additional genetic changes in TEL(ETV6) and AML1(RUNX1) (FISH), drug sensitivity (MTT assay) and clinical outcome in 143 DCOG and COALL-treated t(12;21)-positive ALL patients. Additional genetic changes in TEL and AML1 were present in 83% of the patients, and consisted of (partial) deletion of the second TEL gene (70%), an extra AML1 gene (23%) or an extra der(21)t(12;21) (10%). More than one additional change was observed in 20%. Disease-free survival (pDFS) of DCOG patients without additional genetic changes (4 years pDFS +/- s.e. 53 +/- 17%) and of those with an extra der(21)t(12;21) (60 +/- 22%) is poorer than that of compared to patients with other additional genetic changes in TEL or AML1 (79 +/- 6%; P-trend = 0.02). This was mainly due to the occurrence of early relapses within 2.5 years after the first diagnosis. Similar observations were found in the COALL cohort, albeit not significant owing to limited follow-up. Multivariate analysis including age, WBC and genetic abnormalities in TEL and/or AML1 showed that especially, in vitro resistance to prednisolone (hazard ratio 5.78, 95% CI 1.45-23.0; P=0.01) is an independent prognostic factor in DCOG- and COALL-treated t(12;21)-positive ALL.

Relation between genetic variants of the ataxia telangiectasia-mutated (ATM) gene, drug resistance, clinical outcome and predisposition to childhood T-lineage acute lymphoblastic leukaemia.

The T-lineage phenotype in children with acute lymphoblastic leukaemia (ALL) is associated with in vitro drug resistance and a higher relapse-risk compared to a precursor B phenotype. Our study was aimed to investigate whether mutations in the ATM gene occur in childhood T-lineage acute lymphoblastic leukaemia (T-ALL) that are linked to drug resistance and clinical outcome. In all, 20 different single nucleotide substitutions were found in 16 exons of ATM in 62/103 (60%) T-ALL children and 51/99 (52%, P = 0.21) controls. Besides the well-known polymorphism D1853N, five other alterations (S707P, F858L, P1054R, L1472W, Y1475C) in the coding part of ATM were found. These five coding alterations seem to occur more frequently in T-ALL (13%) than controls (5%, P = 0.06), but did not associate with altered expression levels of ATM or in vitro resistance to daunorubicin. However, T-ALL patients carrying these five coding alterations presented with a higher white blood cell count at diagnosis (P = 0.05) and show an increased relapse-risk (5-year probability of disease-free survival (pDFS) = 48%) compared to patients with other alterations or wild-type ATM (5-year pDFS = 76%, P = 0.05). The association between five coding ATM alterations in T-ALL, their germline presence, white blood cell count and unfavourable outcome may point to a role for ATM in the development of T-ALL in these children.

Treatment strategy and results in children treated on three Dutch Childhood Oncology Group acute myeloid leukemia trials.

This report describes the long-term follow-up data of three consecutive Dutch Childhood Oncology Group acute myeloid leukemia (AML) protocols. A total of 303 children were diagnosed with AML, of whom 209 were eligible for this report. The first study was the AML-82 protocol. Results were inferior (5-year probability of overall survival (pOS) 31%) to other available regimes. Study AML-87 was based on the BFM-87 protocol, with prophylactic cranial irradiation in high-risk patients only, and without maintenance therapy. This led to a higher cumulative incidence of relapse than that reported by the Berlin-Frankfurt-Münster (BFM), but survival was similar (5-year pOS 47%), suggesting successful retrieval at relapse. The subsequent study AML-92/94 consisted of a modified BFM-93 protocol, that is, without maintenance therapy and prophylactic cranial irradiation. However, all patients were to be transplanted (auto- or allogeneic), although compliance was poor. Antileukemic efficacy was offset by an increase in the cumulative incidence of nonrelapse mortality, especially in remission patients, and survival did not improve (5-year pOS 44%). Our results demonstrate that outcome in childhood AML is still unsatisfactory, and that further intensification of therapy carries the risk of enhanced toxicity. Our patients are currently included in the MRC AML studies, based on the results of their AML 10 trial.

High cure rate with a moderately intensive treatment regimen in non-high-risk childhood acute lymphoblastic leukemia. Results of protocol ALL VI from the Dutch Childhood Leukemia Study Group.

PURPOSE: Here we report the results of a nationwide cooperative study in the Netherlands on acute lymphoblastic leukemia (ALL) in children. The aim of the study was to improve the cure rate and to minimize side effects in a group of non-high-risk ALL patients, especially with regard to the CNS. A second aim was to study potential prognostic factors. METHODS: Children (age 0 to 15 years) with non-high-risk ALL (WBC count < 50 x 10(9)/L, no mediastinal mass, no B-cell phenotype, and no CNS involvement) were treated with a uniform protocol, ALL VI. The treatment protocol used 6-week induction regimen with three drugs (vincristine, dexamethasone, and asparaginase), three weekly doses of intravenous (IV) medium high-dose methotrexate (2 g/m2), and 2-year maintenance therapy that consisted of alternating 5-week periods of methotrexate and mercaptopurine and 2-week periods of vincristine and dexamethasone. In the first year of maintenance, triple intrathecal therapy was administered every 7 weeks. RESULTS: From December 1, 1984 until July 1, 1988, 291 children with ALL were diagnosed; 206 were categorized as non-high-risk (71%), and 190 were treated according to protocol ALL VI. At 8 years, the event-free survival (EFS) rate was 81% (SE = 3%) and survival rate 85% (SE = 2.9%); the median follow-up time was 7.3 years (range, 36 to 117 months). The CNS relapse rate was 1.1% (two of 184 patients who achieved a complete remission [CR]). The only factor found to be of negative prognostic importance in terms of EFS (P = .05) was a positive acid phosphatase reaction. CONCLUSION: For children with non-high-risk ALL, the combination of IV medium high-dose methotrexate (2 g/m2 times three), triple intrathecal therapy in the first year of maintenance treatment, and the use of dexamethasone for induction and pulses during maintenance treatment has proved to be highly effective, especially in the prevention of CNS relapse. A high cure rate was achieved without the use of anthracyclines, alkylating agents, and cranial irradiation.

Patient stratification based on prednisolone-vincristine-asparaginase resistance profiles in children with acute lymphoblastic leukemia.

PURPOSE: To confirm the prognostic value of a drug resistance profile combining prednisolone, vincristine, and l-asparaginase (PVA) cytotoxicity in an independent group of children with acute lymphoblastic leukemia (ALL) treated with a different protocol and analyzed at longer follow-up compared with our previous study of patients treated according to the Dutch Childhood Leukemia Study Group (DCLSG) ALL VII/VIII protocol. PATIENTS AND METHODS: Drug resistance profiles were determined in 202 children (aged 1 to 18 years) with newly diagnosed ALL who were treated according to the German Cooperative Study Group for Childhood Acute Lymphoblastic Leukemia (COALL)-92 protocol. RESULTS: At a median follow-up of 6.2 years (range, 4.1 to 9.3 years), the 5-year disease-free survival probability (pDFS) rate +/- SE was 69% +/- 7.0%, 83% +/- 4.4%, and 84% +/- 6.8% for patients with resistant (PVA score 7 to 9), intermediate-sensitive (PVA score 5 to 6), and sensitive (SPVA score 3 to 4) profiles, respectively (sensitive and intermediate-sensitive v resistant, P

Differences in immunoglobulin heavy chain gene rearrangmeent patterns between bone marrow and blood samples in childhood precursor B-acute lymphoblastic leaukemia at diagnosis.

Bone marrow (BM) and corresponding peripheral blood (PB) samples from 30 patients with precursor B-acute lymphoblastic leukemia (precursor B-ALL) were analyzed for the configuration of their immunoglobulin (Ig) heavy chain (IgH) and Ig kappa chain (Ig kappa) genes. Rearrangements and/or delections of the IgH and Ig kappa genes were detected in 100 and 47% of patients in this series of precursor B-ALL, respectively. Multiple rearranged IgH gene bands, generally differing in density, were found in 10 precursor B-ALL samples. This multi-band pattern is most probably caused by subclone formation due to continuing rearrangement processes. In five of the 10 bi/oligoclonal cases (50%) differences in IgH gene rearrangement patterns between BM and PB samples were observed, which could be interpreted as the presence of an edeletections of the IgH and Ig kappa genestra subclone in two cases and differences in the size of the subclones in three cases. In the 20 monoclonal precursor B-ALL, no dissimilarities in IgH gene rearrangement patterns between BM and the corresponding PB samples were found. Differences in Ig kappa gene rearrangement patterns between BM and PB were not observed in this series of precursor B-ALL, which is in line with the finding that no multiple Ig kappa gene rearrangements were detectable. In all five cases, the edelections of the IgH and Ig kappa genestra subclones or the relatively larger sized subclones were found in the BM samples, suggesting that subclone formation in precursor B-ALL occurs in the tissue compartment from which the precursor B-ALL cells are thought to originate. This phenomenon will lead to underestimation of subclone formation, if only IgH gene analysis of PB samples is performed. In addition, it will hamper the detection of minimal residual disease by the polymerase chain reaction mediated amplification of 'leukemia-specific' IgH gene junctional regions, because it is unpredictable which subclone will cause minimal residual disease and/or relapse.

Long-term follow-up of Dutch Childhood Leukemia Study Group (DCLSG) protocols for children with acute lymphoblastic leukemia, 1984-1991.

Here we report the long-term results of the DCLSG protocols ALL-6 and -7 with special emphasis on the incidence of CNS relapse after treatment without cranial irradiation. In DCLSG protocol ALL-6 (1984-1988), designed for patients with ALL non-high risk (ALL-NHR) (WBC <50 x 10(9)/l, no mediastinal mass, no B cell phenotype and no CNS involvement at diagnosis, comprising 71% of all ALL patients), CNS prophylaxis consisted of a combination of three methods of chemotherapeutic CNS prophylaxis (the use of dexamethasone during induction and maintenance therapy, i.v. medium dose methotrexate and prolonged administration of intrathecal triple therapy). Total duration of treatment: 116 weeks. 190 patients were enrolled in the study. At 10 years, the EFS rate for all patients is 81.5 +/- 2.8%, the survival rate 84.8 +/- 2.7%, and the cumulative incidence of isolated CNS relapse 1.1 +/- 0.8%. The 10-year survival rate for the 139/190 (73.1%) patients with standard risk non-T lineage ALL according to the NCI risk criteria is 80.5 +/- 3.4%. DCLSG protocol-7 was identical to the intensive ALL-BFM-86 protocol, but cranial irradiation was restricted to patients with initial CNS involvement. Patients were stratified into three risk groups (SRG, RG and EG). Treatment duration was 18 months. 218 patients were enrolled in the study. At 10 years, the EFS rate for all patients is 63.4 +/- 3.3%, the survival rate 76.4 +/- 3.0%, the 5-year cumulative incidence of isolated CNS relapse 5.7 +/- 1.8%. The EFS rate at 10 years of the 127/218 (58.3%) patients with standard risk non-T-lineage ALL according to the NCI risk criteria was 67.9 +/- 4.3%, which is not significantly different from the results achieved in this category of patients with the moderately intensive treatment according to protocol ALL-6 (logrank P = 0.17). These DCLSG studies indicate that omission of cranial irradiation does not jeopardize the overall good results.

In vitro cytotoxicity of mitoxantrone, daunorubicin and doxorubicin in untreated childhood acute leukemia.

Mitoxantrone (MIT) has not been studied as a single agent in children with untreated leukemia. The antileukemic activity of MIT in these patients and its activity in relation to clinical and cell biological features is unknown. We studied the in vitro cytotoxicity of MIT, daunorubicin (DNR) and doxorubicin (DOX) in untreated childhood acute lymphoblastic leukemia (ALL, n = 131) and acute nonlymphoblastic leukemia (ANLL, n = 20) samples, using the MTT assay. There were marked interindividual differences in resistance to all three drugs. A strong, significant cross-resistance was found in ALL between MIT, DNR and DOX. All samples of the T-lineage, a prognostically unfavorable immunophenotype, however, were significantly more resistant to DNR and DOX, but not to MIT, than common or pre-B ALL samples. ALL cells from children with a prognostically unfavorable age at diagnosis, especially those < 2 years, showed a relative resistance to all three drugs compared to the intermediate age-group. This was found within all patients, but also within the common or pre-B ALL cases only. Sex, white blood cell count, or FAB type was not related to in vitro drug resistance. None of the three drugs showed an overall preferential activity in ALL or ANLL. We conclude that the in vitro antileukemic activity of MIT, DNR and DOX is related to certain clinical and cell biological features. There were no major differences between the three drugs in antileukemic activity, except that T-ALL samples were more resistant than common or pre-B ALL samples to DNR and DOX, while MIT was equally active in these two immunophenotypes.

Immunophenotypic changes between diagnosis and relapse in childhood acute lymphoblastic leukemia.

To get more insight into the phenotypic changes of childhood acute lymphoblastic leukemia (ALL) at relapse, a detailed morphological and immunophenotypic study in 40 childhood ALL cases (32 precursor B-ALL and 8 T-ALL) was performed. Expression patterns of non-lineage specific markers (terminal deoxynucleotidyl transferase (TdT), CD34, and HLA-DR), B-lineage markers (CD10, CD19, CD20, and CD22), T-lineage markers (CD1, CD2, CD3, CD4, CD5, CD7, and CD8), and cross-lineage myeloid markers (CD14, CD15, and CD33) were compared at diagnosis and relapse. In case of low blast counts (< or = 70%) at relapse, double labeling for membrane markers and TdT was used in order to define the precise immunophenotype of the TdT+ leukemic cells. An immunological marker-shift was defined as either a conversion from positive to negative and vice versa or a difference in positivity of > or = 50%. Morphological differences between diagnosis and relapse were detected in 34% of precursor B-ALL and 14% of T-ALL. Differences in immunological marker expression were found in 72% of precursor B-ALL and in 75% of T-ALL, and generally concerned minor shifts with loss or acquisition of a few markers. The morphological shifts and immunophenotypic shifts were not correlated. Immunophenotypic shifts were found for all markers tested in precursor B-ALL, except for HLA-DR. Shifts in CD10 expression (16% of cases) were only observed in relapses occurring 30 months or more after diagnosis. In four precursor B-ALL an intra-lineage shift was found at relapse (one common ALL to null ALL and three pre-B-ALL to common ALL or null ALL) and two precursor B-ALL cases were diagnosed as acute non-lymphocytic leukemia at relapse based on morphology and immunophenotype. In T-ALL, neither intra-lineage nor inter-lineage shifts were observed, although shifts were detected in all T cell markers tested, except for the lineage specific CD3 and T cell receptor (TcR) markers. In conclusion, immunophenotypic shifts at relapse frequently occur in precursor B-ALL and T-ALL, in a small percentage leading to an intra-lineage shift (10%) or inter-lineage shift (5%). Therefore immunophenotypic monitoring of minimal residual disease in ALL patients should be based on multiple marker combinations, preferably together with polymerase chain reaction analysis of rearranged immunoglobulin and/or TcR genes or chromosome aberrations.

Relation between age, immunophenotype and in vitro drug resistance in 395 children with acute lymphoblastic leukemia--implications for treatment of infants.

The prognosis of infant ALL, characterized by a high incidence of the immature CD10 negative B-lineage ALL (proB ALL) is poor. This study aimed to determine the resistance profile of infant ALL cells. In vitro drug resistance was determined by the MTT assay of 395 children with ALL at initial diagnosis: there were 21 infants <1.5 years of which nine <1 year, 284 children aged 1.5-10 years (intermediate age group) and 90 children >10 years. Immunophenotyping resulted in 310 cALL/preB ALL, 69 T-ALL, 15 proB ALL and one unknown cases. The following drugs were tested: daunorubicin, doxorubicin, mitoxantrone, idarubicin (Ida), prednisolone (Pred), dexamethasone (DXM), vincristine (VCR), Asparaginase (Asp), 6-MP, 6-TG, AraC, VM26 and 4-HOO-ifosfamide (Ifos). Infants <1.5 years were significantly more resistant to Pred (>500-fold), Asp (11-fold) and VM26 (2.7-fold) but significantly more sensitive to Ara-C (2.3-fold) compared to the intermediate age group. When analyzing infants <1 year of age similar results were found. ProB ALL cells (seven infants <1.5 years; eight children >1.5 years) were significantly more resistant to glucocorticoids, Asp, thiopurines, anthracyclines and Ifos compared to cALL/preB ALL but more sensitive to Ara-C. Cells from children >10 years were significantly more resistant to Pred, DXM, Asp, Ida and 6-MP. T-ALL cells showed a strong resistance to Pred, Asp and VCR and a mild but significant resistance to all other drugs except thiopurines and VM26. We conclude that the poor prognosis of infant ALL is associated with a resistance to glucocorticoids and Asp. However, ALL cells from infants show a relatively high sensitivity to Ara-C which suggests that infants with ALL might benefit from treatment schedules that incorporate more Ara-C than the current treatment protocols.

Extensive junctional diversity of gamma delta T-cell receptors expressed by T-cell acute lymphoblastic leukemias: implications for the detection of minimal residual disease.

Rearrangements, junctional regions and expression of T-cell receptor (TcR)-gamma and TcR-delta genes were analyzed in thirteen TcR-gamma delta + T-cell acute lymphoblastic leukemias (T-ALL). All TcR-gamma genes were rearranged except for one deleted allele and one allele in germline configuration. The expressed TcR-gamma protein chains showed a preference for V gamma l (11/13), J gamma 2.3 (7/13) and C gamma 2 (8/13). Furthermore, the TcR-gamma combinatorial repertoire appears to be even more limited by the fact that particular V gamma genes are preferentially used in TcR-gamma 1 or TcR-gamma 2 derived receptors, i.e. in disulfide-linked or non-disulfide-linked TcR-gamma delta receptors. The combinatorial repertoire of the expressed TcR-delta genes was homogeneous, as all thirteen T-ALL expressed V delta 1-D delta-J delta 1-C delta protein chains. In contrast to the limited combinatorial repertoire of the TcR-gamma and TcR-delta genes, the junctional diversity of both TcR genes was extensive due to insertion of N-region, P-region, and D delta gene nucleotides in addition to deletion of nucleotides by trimming. Using polymerase chain reaction (PCR)-mediated amplification and subsequent direct sequencing, we determined the junctional region sequences of all TcR-gamma and TcR-delta rearrangements. Sequence analysis showed that in the TcR-gamma junctional regions insertion varied from 0 to 25 nucleotides (average 8.0) and deletion from 1 to 27 nucleotides (average 8.7). In TcR-delta junctional regions, nucleotide insertion varied from 5 to 47 nucleotides (average 25.5) and deletion from 0 to 29 nucleotides (average 6.2) per junctional region. In general, the N-region nucleotides were the most prominent element in the junctional regions, i.e. 97% of the TcR-gamma and 55% of the TcR-delta junctional regions. D delta genes contributed significantly (40%) to the TcR-delta junctional diversity, whereas P-regions were hardly found in both TcR genes. Altogether, the junctional regions of TcR-delta genes were far more diverse than the junctional regions of TcR-gamma genes. With respect to the new methods of detecting minimal residual disease (MRD) in lymphoid malignancies utilizing PCR-mediated amplification of the junctional regions of TcR genes, our data indicate that this MRD-PCR analysis will generally be more sensitive if TcR-delta instead of TcR-gamma junctional-region-specific probes are used.

Multiple rearranged immunoglobulin genes in childhood acute lymphoblastic leukemia of precursor B-cell origin.

Sixty precursor B-cell acute lymphoblastic leukemia (ALL) patients were analyzed for the configuration of their immunoglobulin (Ig) genes. Rearrangements and/or deletions of the Ig heavy chain (IgH), Ig kappa chain (Ig kappa), and Ig lambda chain (Ig lambda) genes were detected in 98, 48, and 23% of cases, respectively. Although these percentages suggest the presence of a hierarchical order in IgH and Ig light chain (IgL) gene rearrangements during B-cell differentiation, no correlation was found between the immunophenotype of the precursor B-ALL and the arrangement patterns of their IgH and IgL genes. Multiple rearranged IgH gene bands, generally differing in density, were found in 27 (45%) of the precursor B-ALL in various restriction enzyme digests. Cytogenetic data were used to determine whether the presence of more than two rearranged IgH gene bands was caused by hyperdiploidy of chromosome 14 or other chromosome 14 aberrations. The combined cytogenetic and IgH gene data allowed the precursor B-ALL to be divided into three groups: a monoclonal group (n = 36; 60%), a biclonal group (n = 16; 27%), and an oligoclonal group (n = 8; 13%). In five biclonal ALL biclonality at the Ig kappa gene level was also found. Such subclone formation was not detected at the Ig lambda gene level. As the detection limit of the Southern blot technique is 2-5%, it might well be that small subclones remained undetected, implying that the frequency of subclone formation at the IgH gene level in precursor B-ALL is probably higher than 40%. It has been suggested that precursor B-ALL with multiple IgH gene rearrangements have a higher tendency to relapse. Although higher relapse rates were found in the oligoclonal group (53%) and in the combined bi-oligoclonal group (33%) compared with the monoclonal group (20%), the log rank trend test showed no significance. The occurrence of multiple subclones in precursor B-ALL as found by IgH gene analyses will severely hamper the detection of minimal residual disease using the polymerase chain reaction (PCR) mediated amplification of 'tumor-specific' IgH gene junctional regions, because it cannot be predicted which detectable (or undetectable) subclone will cause minimal residual disease and/or relapse. Therefore it can be expected that the PCR technique will frequently produce false negative results during the follow-up of precursor B-ALL.

Limited combinatorial repertoire of gamma delta T-cell receptors expressed by T-cell acute lymphoblastic leukemias.

Detailed analysis of the rearrangement and expression of T-cell receptor gamma (TcR-gamma) and TcR-delta genes was performed in ten TcR-gamma delta+ T-cell acute lymphoblastic leukemias (T-ALL). In nine T-ALL the TcR-gamma genes were rearranged on both alleles, whereas in the tenth leukemia one allele was rearranged and the other was in germline configuration. Twelve out of the 19 rearranged alleles contained rearrangements of the J gamma 2.3 gene segment, five of which were to the V gamma 8 gene segment and three to the V gamma 3 gene segment. This implies that the combinatorial repertoire of the rearranged TcR-gamma gene is restricted due to the preferential usage of several V gamma and J gamma gene segments. The TcR-delta genes were rearranged on both alleles in nine T-ALL, whereas in the tenth leukemia one allele was rearranged and the other deleted. The combinatorial repertoire of the TcR-delta genes was homogeneous, as in all ten T-ALL at least one allele contained a V delta 1-J delta 1 rearrangement. In at least nine of the ten T-ALL the V delta 1-J delta 1 allele coded for the expressed TcR-delta chain, as was supported by reactivity with the anti-V delta 1-J delta 1 (delta TCS1) antibody in all T-ALL tested. As the total repertoire of the TcR molecules is not only dependent on combinations of gene segments, but also on the size and diversity of the junctional regions, we studied the V delta 1-J delta 1 junctional regions using the polymerase chain reaction (PCR) technique. These PCR analyses showed that the size of the V delta 1-J delta 1 junctional regions differed markedly (up to approximately 30 bases or more) between the leukemias. Therefore we conclude that the combinatorial repertoire of TcR-delta S+ T-ALL is limited, especially due to the homogeneous TcR-gamma gene rearrangements, but that the junctional repertoire of the TcR-delta genes seems to be extensive.

Different cellular drug resistance profiles in childhood lymphoblastic and non-lymphoblastic leukemia: a preliminary report.

The better prognosis of acute lymphoblastic leukemia (ALL) than of acute non-lymphoblastic leukemia (ANLL) in children, and the often observed better prognosis of myeloid-antigen (MyAg) negative ALL than of MyAg-positive ALL, may be related to differences in cellular drug resistance. We therefore compared the resistance to 12 drugs of 125 ALL and 28 ANLL samples with the MTT assay. ALL samples were median > 75-fold more sensitive to the glucocorticoids prednisolone and dexamethasone (p < 0.00001), and 2-fold more sensitive to vincristine (p = 0.05) than ANLL samples. Differences for the other drugs were not significant. MyAg-negative ALL samples were more sensitive to glucocorticoids than MyAg-positive ALL-samples (p < or = 0.04). Prednisolone, and dexamethasone if tested, had a stimulatory effect on leukemic cell survival in 36% of ANLL, but in only 2% of ALL samples (p < 0.0001). Vincristine, and vindesine if tested, had a similar effect in 11% of ANLL, and in 4% of ALL samples (p = 0.11). We conclude that the more favorable response of ALL against ANLL to combination chemotherapy in children may be explained by the higher antileukemic activity of glucocorticoids and of vincristine in ALL, while none of the drugs was more active in ANLL. Similarly, the better prognosis of MyAg-negative ALL than of MyAg-positive ALL may be explained by a relative sensitivity to glucocorticoids. Glucocorticoids and vinca-alkaloids induced leukemia cell proliferation in part of the samples, most frequently in ANLL. The findings may be useful in the design of new chemotherapeutic regimens for ALL and ANLL.

Topoisomerase II alpha gene expression in childhood acute lymphoblastic leukemia.

Previously, we showed that in vitro resistance to daunorubicin (DNR) at initial diagnosis was related to a poor long-term clinical outcome in childhood acute lymphoblastic leukemia (ALL), and that cells of relapsed ALL were in vitro more resistant to DNR than cells of untreated ALL. Topoisomerase II (Topo II) is an intracellular target for anthracyclines and epipodophyllotoxins. Decreased levels and/or activity of Topo II have been associated with multidrug resistance in cell lines. We investigated Topo II alpha gene expression in fresh leukemic samples from 19 children with untreated and 14 children with relapsed ALL using a sensitive RNase protection assay. The in vitro cytotoxicity of the Topo II inhibitors DNA and teniposide (VM26) was measured using the MTT assay, and the cell cycle distribution of leukemic samples was analyzed by DNA flow cytometry. Results showed that (1) relapsed ALL samples were more resistant to DNR, but not to VM26 compared to untreated samples; (2) large interpatient variations existed in both Topo II alpha gene expression and in vitro cytotoxicity results; (3) Topo II alpha gene expression was detectable in 29/33 childhood ALL samples with a median expression of 5% the level of a relatively chemosensitive human small cell lung cancer cell line; (4) Topo II alpha gene expression did not differ between untreated and relapsed ALL; (5) Topo II alpha gene expression was positively correlated with the percentage of ALL cells in S- and G2M-phase, but not with the in vitro cytotoxicity of the drugs tested. In conclusion, resistance to DNR in childhood ALL can not be explained by decreased levels of Topo II alpha gene expression, but additional Topo II activity studies in fresh leukemia samples may need further exploration.

T cell receptor gamma (TCRG) gene rearrangements in T cell acute lymphoblastic leukemia refelct 'end-stage' recombinations: implications for minimal residual disease monitoring.

The T cell receptor gamma (TCRG) gene configuration was established in a large series of 126 T cell acute lymphoblastic leukemia (T-ALL) patients using combined Southern blotting (SB) and heteroduplex PCR analyses. The vast majority of TALL (96%) displayed clonal TCRG gene rearrangements, with biallelic recombination in 91% of patients. A small immature subgroup of CD3- T-ALL (n = 5) had both TCRG genes in germline configuration, three of them having also germline TCRD genes. In five patients (4%) combined SB and PCR results indicated oligoclonality. In five rearrangements detected by SB, the Vgamma gene segment could not be identified suggesting illegitimate recombination. Altogether, 83% of TCRG gene rearrangements involved either the most upstream Vgamma2 gene (including four cases with interstitial deletion of 170 bp in Vgamma2) and/or the most downstream Jgamma2.3 segment, which can be perceived as 'end-stage' recombinations. Comparative analysis of the TCRG gene configuration in the major immunophenotypic subgroups indicated that TCRgammadelta+ T-ALL display a less mature immunogenotype as compared to TCRalphabeta+ and most CD3- cases. This was reflected by a significantly increased usage of the more downstream Vgamma genes and the upstream Jgamma1 segments. Comparison between adult and pediatric T-ALL patients did not show any obvious differences in TCRG gene configuration. The high frequency, easy detectability, rare oligoclonality, and frequent 'end-stage' recombinations make TCRG gene rearrangements principal targets for PCR-based detection of minimal residual disease (MRD) in T-ALL. We propose a simple heteroduplex PCR strategy, applying five primer combinations, which results in the detection of approximately 95% of all clonal TCRG gene rearrangements in T-ALL. This approach enables identification of at least one TCRG target for MRD monitoring in 95% of patients, and even two targets in 84% of T-ALL.

Extramedullary infiltrates at diagnosis have no prognostic significance in children with acute myeloid leukaemia.

This retrospective study was designed to review the relative frequency and prognostic significance of extramedullary infiltrates in children with acute myeloid leukaemia (AML). The registration data and initial discharge summaries were reviewed for all children diagnosed with AML, and registered by the Dutch Childhood Leukaemia Study Group (DCLSG). Between 1972 and 1998, 477 children were diagnosed with AML. Of these patients, 120 (25.1%) had extramedullary leukaemia (EML) at diagnosis. Four categories of EML were found: skin, soft tissue or bone, gingival infiltration and central nervous system (CNS) involvement. Patients who presented with gingival infiltrates, were older than those without EML or those in the other EML subgroups, had a high initial WBC count and a high proportion of M4/M5 morphological variants. This type of presentation could indicate a special biological entity. Univariate analysis of prognostic factors in patients treated after 1985 with intensive protocols showed that initial WBC count and the presence of favourable cytogenetic findings were significant. The presence of EML at diagnosis had no significant effect on event-free survival. In a stepwise multiple regression analysis only favourable cytogenetic findings remained significant.