Molecular detection of minimal residual disease in adult and childhood acute lymphoblastic leukaemia reveals differences in treatment response.

Immunoglobulin heavy chain gene (IgH gene) rearrangements are found in the majority of patients with B lineage acute lymphoblastic leukaemia (ALL). Two hundred and three bone marrow samples from 54 patients (33 adults and 21 children) were analysed by PCR within specific time-points after diagnosis (ie 1, 2-3, 4-6 and 7-12 months) using FR1 and JH primers (fingerprinting with a sensitivity > or =1:5 x 10[3]). CDR3-derived allele specific oligoprimers (ASO to achieve a sensitivity between 1:10[4] and 1:10[5]) were applied to 12 children and 18 adults, while size of CDR3 region, oligoclonality and background problems prevented their application to the remaining patients. All patients were followed clinically for > or =24 months. Thirty adults and 16 children presented as newly diagnosed ALL, while the remaining eight patients were analysed in first or subsequent relapse. Patients destined to relapse showed a higher proportion of positive tests (> or =50%), particularly after 1 month, than in the remission group, irrespective of age. Among patients staying in remission, a decrease in MRD-positive tests occurred during the first 12 months in both age groups. However, the proportion of positive tests dropped below 15% at a later stage in adults (4-6 months) than in children (2-3 months). Among children, only patients destined to relapse were MRD positive beyond 1 month, with the exception of only one patient, still positive at 2-3 months in the remission group. The difference in MRD positivity between relapse and remission patients was statistically significant in children (P < 0.03) at any time of testing, but only at 4-6 months in adults (P < 0.01). These data suggest that resolution of MRD in ALL occurs more rapidly in children compared to adults, particularly within the first 6 months. Children and adults, studied in first or subsequent relapse, showed a higher proportion of positive tests during reinduction compared to newly diagnosed patients.

Clustering of missense mutations in the ataxia-telangiectasia gene in a sporadic T-cell leukaemia.

Ataxia-telangiectasia (A-T) is a recessive multi-system disorder caused by mutations in the ATM gene at 11q22-q23 (ref. 3). The risk of cancer, especially lymphoid neoplasias, is substantially elevated in A-T patients and has long been associated with chromosomal instability. By analysing tumour DNA from patients with sporadic T-cell prolymphocytic leukaemia (T-PLL), a rare clonal malignancy with similarities to a mature T-cell leukaemia seen in A-T, we demonstrate a high frequency of ATM mutations in T-PLL. In marked contrast to the ATM mutation pattern in A-T, the most frequent nucleotide changes in this leukaemia were missense mutations. These clustered in the region corresponding to the kinase domain, which is highly conserved in ATM-related proteins in mouse, yeast and Drosophila. The resulting amino-acid substitutions are predicted to interfere with ATP binding or substrate recognition. Two of seventeen mutated T-PLL samples had a previously reported A-T allele. In contrast, no mutations were detected in the p53 gene, suggesting that this tumour suppressor is not frequently altered in this leukaemia. Occasional missense mutations in ATM were also found in tumour DNA from patients with B-cell non-Hodgkin's lymphomas (B-NHL) and a B-NHL cell line. The evidence of a significant proportion of loss-of-function mutations and a complete absence of the normal copy of ATM in the majority of mutated tumours establishes somatic inactivation of this gene in the pathogenesis of sporadic T-PLL and suggests that ATM acts as a tumour suppressor. As constitutional DNA was not available, a putative hereditary predisposition to T-PLL will require further investigation.

Molecular analysis of the leukaemic B cell in adult and childhood acute lymphoblastic leukaemia.

Immunoglobulin heavy chain gene (IgH gene) rearrangements are found in the majority of cases of B-lineage acute lymphoblastic leukaemia (ALL). We have examined bone marrow samples taken at presentation or relapse from 109 patients (79 adults and 30 children) and have performed sequence analysis of the complementarity determining region 3 (CDR3) on 65 alleles from 54 patients. We aimed to define immunoglobulin heavy chain (IgH) variable segment family use and investigate biological and structural features of the B cell in adult and childhood ALL. Using the FR1 fingerprinting method, a rearranged band was identified in 70 (89%) of 79 adult ALL and in 29 (97%) of 30 childhood ALL. This study found no preferential use or selection of IgH VH genes and no statistically significant structural differences between normal and leukaemic B cells in either adult and childhood ALL. An equal proportion of amplifiable cases of adult and childhood ALL uses more than one VH family gene (24/70, 34%, and 8/29, 27.5%, respectively). There were no significant differences in the structure or size of the CDR3 region and the variable (V) or joining (J) segment use in ALL patients compared to normal B cells. We observed that the N2 region was shorter than N1 in children whereas the opposite was observed in adults (not statistically significant). The J4 segment was a more common rearrangement in children than in adults, and in both groups J4 was more frequently associated with multiple D segment VDJ rearrangements. An increase in VH6 use in leukaemic alleles compared to normal B lymphocytes (2%) was observed but it was not statistically significant in our group of patients. Amongst children and adults, in-frame CDR3 junctions occurred in 78% and 64% of rearranged alleles, respectively, compared to 75% of in-frame sequences reported by others to occur among normal B cells.

The use of IgH fingerprinting and ASO-dependent PCR for the investigation of residual disease (MRD) in ALL.

In acute lymphoblastic leukaemia (ALL), investigation of minimal residual disease by conventional morphology and immunology fails to detect levels of residual disease of < 1 leukaemic in 10-100 normal cells. The use of polymerase chain reaction (PCR) to exploit the diversity of the complementarity determining region (CDR) and immunoglobulin variable heavy chain (VH) family specific usage has greatly improved the sensitivity up to one leukaemic cell in 10(5)-10(6) normal bone marrow cells. Here we report on a prospective study of 14 patients with ALL of B-cell lineage by using a combined PCR approach which estimates levels of disease between 1:10(3) and 1:10(5). The sequential use of allele-specific oligoprimer (ASO) independent tests (using framework 1. FR1 and 3, FR3 primers with a JH consensus primer, sensitivity up to 1:5 x 10(3)) and ASO-dependent PCR (sensitivity up to 1:10(5)) assays were applied to 64 bone marrow (BM) follow-up samples in a sequential array of tests. Results presented in this study indicate high concordance of MRD among different tests for samples with level of residual disease > 1:5 x 10(3). Consequently, samples positive by the FR1 and FR3 fingerprinting tests were confirmed by the more sensitive ASO-dependent tests, as expected. However, the ASO-dependent assays revealed levels of disease undetected by the FR1 and FR3 test. Although a higher level of sensitivity is provided by the ASO-dependent tests, the FR1 and FR3 fingerprinting tests allow MRD investigation in patients with oligoclonal B cell proliferations, CDR3 region of size < 15 bp or with ASO primers unsuitable for PCR investigation on technical grounds (i.e. background signal). If a sequential order of investigation from less (e.g. FR1 and FR3 fingerprinting) to more sensitive tests (ASO-dependent) is applied, an indirect estimate of MRD is obtained for patients with level of disease < 1:10(3).

Evidence for protein kinase C--independent pathways mediating phorbol ester induced plasmacytoid differentiation of B chronic lymphocytic leukemia cells.

The effects of phorbol esters on many cell types are known to be mediated through activation of the protein kinase C (PKC) signal transduction pathway. By using the specific inhibitor of this enzyme 1-(5-isoquinolinylsulfonyl)-2-methyl-piperazine dihydrochloride (H7) we have assessed the role of PKC activation in phorbol ester (phorbol 12-myristate 13-acetate, PMA)-induced plasmacytoid differentiation of B chronic lymphocytic leukemia cells (B-CLL) as a model of terminal differentiation of human B lymphocytes. H7 affected a dose-dependent inhibition of PMA-induced thymidine and uridine uptake with ID50 values of 41 microM and 32 microM, respectively. A comparable ID50 value (34 microM) was obtained for H7 inhibition of B-CLL PKC activity in a cell-free system. PMA-induced changes in cell morphology, expression of CD20, CD37 and FMC7 surface antigens together with increased secretion of immunoglobulin were variably abrogated by H7 suggesting that PKC activation is more important in B cell activation/DNA synthesis than in the differentiative response. Consistent with this, expression of a sizable proportion of PMA-inducible genes was not significantly affected by H7. These data are consistent with the existence of a PMA-activated, PKC-independent signal transduction pathway which may be important, though by itself apparently insufficient, for eliciting full terminal differentiation in B lymphocytes.

Activation of Harvey ras oncogene by mutation at codon 12 is very rare in hemopoietic malignancies.

Point mutations within codon 12 of the Harvey (H-) ras proto-oncogene have recently been implicated in the progression of hemopoietic malignancy, particularly chronic myeloid leukemia. We have analyzed DNA from 170 cases of acute and chronic leukemia by using a restriction fragment length polymorphism. No evidence for clonal allelic H-ras codon 12 activation was found among these cases, which included 23 cases of chronic myeloid leukemia, 12 of which were in accelerated phase or blastic transformation. These data suggest that H-ras codon 12 mutations occur infrequently in hemopoietic neoplasms generally and may be less important in disease progression than has been previously suggested.

Correlation of immunophenotype with rearrangement of T cell antigen receptor beta and gamma genes in acute lymphoblastic leukemia of adults.

The structure of immunoglobulin heavy chain (IgH) and T cell antigen receptor (TCR) beta and gamma chain genes was studied in 38 cases of adult and two cases of childhood acute lymphoblastic leukemia (ALL). Seven cases of T-ALL all showed clonally rearranged TCR beta and gamma genes; only one of these also contained rearranged IgH genes. All precursor B cell ALLs and one case of unusual B cell ALL/lymphoma had clonally rearranged IgH genes, but a high proportion (22 of 32, 69%) of precursor B cell ALLs also had rearrangement of TCR beta and/or gamma genes. TCR beta gene rearrangement was less common in more mature precursor B cell ALL, expressing cytoplasmic IgM (pre-B-ALL) (0 of 5) than in other precursor B cell ALL cases (15 of 27). In the precursor B cell ALLs overall, 10 (32%) had rearrangement of both beta and gamma genes, while 7 (22%) had rearrangement of TCR gamma genes only. A further 5 (16%), all expressing one or more unusual immunophenotype markers, had TCR beta gene rearrangement without detectable gamma gene rearrangement. These observations, together with certain characteristics of constant-joining region usage of both TCR genes (a preference for rearrangement into the C beta 2 and C gamma 1 genes), distinguishes these "inappropriate" rearrangements from those found in T-ALL and suggests that they have arisen through a differentiation arrest which is not part of a normal T cell developmental program.

Rearrangement and expression of T cell antigen receptor genes in B cell chronic lymphocytic leukemia.

Fifty-nine patients with B cell chronic lymphocytic leukemia (B-CLL) were screened for clonal rearrangement of T cell receptor (TCR) beta and gamma chain genes. Four were found with rearranged TCR beta genes, but none had detectable rearrangement of TCR gamma genes. One typical patient with B-CLL had a TCR beta gene structure consistent with a variable-diversity-joining rearrangement into the C beta 2 gene on one allele. An apparently identical rearrangement pattern was seen in a second patient, which suggested that there may be a restriction on the repertoire of possible TCR beta gene recombinations in mature B cells. Two further patients had a simple deletion of sequences, consistent with a diversity-joining rearrangement into C beta 2 on one allele. All four patients had rearrangements of immunoglobulin heavy- and light-chain genes typical of mature B cell malignancies. However, on review of clinical, morphological, and immunophenotype data, two had features consistent with B cell prolymphocytic leukemia or B lymphoma, and a third had progressed to a prolymphocytic transformation. Low-level expression of a predominantly 1.0- to 1.2-kilobase germ line TCR beta gene transcript was detected in several B-CLLs and at a comparable level in the four with rearranged TCR beta genes. This, together with the low frequency of TCR gene rearrangement, suggests that most B-CLL cases arise at a developmental stage when factors required for TCR gene activity are not operative.

Rearrangement of immunoglobulin and T cell antigen receptor genes in acute myeloid leukemia with lymphoid-associated markers.

Ten cases of adult acute myeloid leukemia (AML) displaying lymphoid-associated markers CD7 and/or terminal deoxynucleotidyl transferase (TdT) have been investigated for rearrangement of immunoglobulin and T cell antigen receptor beta and gamma genes. Two of six TdT+ cases had clonally rearranged Ig genes, whereas six of eight CD7+ AMLs, including three that were TdT+, had a germ line configuration of both immunoglobulin and T cell receptor beta and gamma genes. A single case of CD7+ TdT- AML had clonal rearrangement of all three genes. These results indicate that expression of TdT and/or CD7 is not accompanied by gene rearrangement in most cases of adult AML. A minority of cases, displaying lymphoid-associated phenotypic markers and accompanying gene rearrangement, may represent a distinct subgroup of AML that arises from a rare, primitive stem cell, possessing extensive multilineage potential.

Patterns of gene expression during plasmacytoid differentiation of chronic lymphocytic leukaemia cells.

Chronic lymphocytic leukaemia (CLL) cells may be induced to undergo plasmacytoid differentiation in vitro in response to 12-O-tetradecanoyl phorbol acetate (TPA). We show here that plasmacytoid differentiation and the accompanying accumulation of Cmu immunoglobulin mRNA are preceded by a rapid transient increase in the expression of the proto-oncogenes, c-myc and c-fos. In terminally differentiated cells the level of c-fos mRNA returned to the original basal level whilst c-myc expression remained appreciably higher than in undifferentiated CLL cells. These data support a possible role for c-fos and c-myc in the programmed chain of events that occur during terminal differentiation of B-lymphocytes.

Rapid down-regulation of protein kinase C and membrane association in phorbol ester-treated leukemia cells.

Peripheral blood lymphocytes from patients with chronic lymphocytic leukemia (CLL) acquire after several days of exposure to 12-O-tetradecanoylphorbol-13-acetate (TPA) several morphological, immunological and histochemical features of hairy cell leukemia. We have investigated the short term effects of TPA treatment on protein kinase C and its subcellular distribution. Within minutes of addition of TPA to CLL cells 20% of the cytosolic protein kinase C had associated with the particulate fraction. The remaining 80% of protein kinase C activity was down-regulated. The association with the membrane dramatically increased the resistance of the enzyme to inhibition by the non-ionic detergent, Triton X-100. These results suggest that activation of protein kinase C causes multiple biological changes in CLL cells.

Phytohemagglutinin-induced changes in tyrosine protein kinase and its endogenous substrates in human lymphocytes.

We have measured changes in tyrosine protein kinase activity in the particulate and soluble fractions of phytohemagglutinin (PHA)-stimulated human lymphocytes using a synthetic tyrosine-containing peptide as substrate. Following PHA stimulation, the activity of this enzyme remained stable for 24 h and then fell sharply in both fractions. Phosphorylation of endogenous substrates was also studied by gel electrophoresis of the same subcellular preparations which had been incubated with [gamma-32P]ATP. Gels were treated with alkali to hydrolyse phosphoserine, dried and autoradiographed. In the particulate fraction from resting lymphocytes, two prominent bands were labelled, one of 55-60 kD and another of 38 kD. Direct analysis showed that these proteins were labelled largely on tyrosine residues. The 38 kD band became less intensely labelled 24 h following PHA addition, and had disappeared by 72 h. Two new bands appeared at this time: a 42 kD band which was phosphorylated mostly on threonine and a 32 kD band phosphorylated on tyrosine. The 55-60 kD band remained unchanged up to 96 h following PHA addition. The final band pattern in stimulated lymphocytes resembled that of the malignant T lymphoblastic cell line JM1. Our data suggest that tyrosine protein kinases in resting lymphocytes are part of a mechanism which transduces external growth signals to the cell interior, and that this mechanism is inactivated once the signal has been transmitted. The pattern of endogenous substrates which are phosphorylated on tyrosine and threonine residues in the malignant T lymphoblastic cell lines JM1 is likely to be characteristic of proliferating T lymphoid cells rather than of the malignant state, since similar bands appear in normal lymphocytes upon PHA stimulation.

Tyrosine protein kinases and their substrates in human leukemia cells.

We have quantitated tyrosine protein kinase (TPK) activity in particulate and cytosolic fractions from human leukemic cells. Slowly proliferating cells from patients with chronic lymphocytic leukemia (CLL) had levels of TPK similar to those of quiescent normal lymphocytes. Cells from patients with acute lymphoblastic leukemia (ALL), acute myeloid leukemia (AML) and chronic granulocytic leukemia (CGL) contained markedly lower levels of TPK activity, similar to the levels in phytohaemagglutinin-stimulated (proliferating) normal lymphocytes and in bone marrow cells. This suggested that TPK is part of a mechanism for transducing growth signals and is down-regulated following signal transmission. We also identified endogenous substrates for TPK in leukemic cells. Particulate fractions from ALL, CLL and AML cells contained substrates identical to those previously detected in normal lymphocytes. In particular, a 38kD substrate thought to be involved in early stages of growth signal transduction in normal lymphocytes was found in all samples of these groups examined. Cytosolic fractions from these groups of leukemia cells contained higher molecular weight substrates not found in resting or proliferating normal lymphocytes or bone marrow cells. In contrast, TPK substrates in both particulate and cytosolic fractions from CGL cells resembled those of normal bone marrow cells in that only proteins with molecular weight below 40kD were labelled on tyrosine. We conclude that leukemic cells do not contain higher levels of TPK than do normal hemopoietic cells. Qualitative differences in TPK species or in their substrates may result in aberrant regulation of proliferation in leukemic cells. However, we cannot exclude the possibility that additional TPK substrates detected in leukemic cells were a feature of the normal equivalent hematopoietic cells from which the leukemia cells were derived.

Higher tyrosine protein kinase activity in resting lymphocytes than in proliferating normal or leukaemic blood cells.

We have studied tyrosine phosphorylation in particulate fractions from 11 leukaemic cell lines by using as substrate either a synthetic tyrosine containing peptide or the endogenous proteins. The results were compared with those obtained using similar fractions from normal lymphocytes and bone marrow cells. Particulate fractions from all the leukaemic cell lines and normal bone marrow cells exhibited lower levels of tyrosine protein kinase activity compared to normal lymphocytes. When the phosphorylation of endogenous substrates was assayed, proteins were phosphorylated on tyrosine residues (rather than serine or threonine residues) to a larger extent in normal lymphocytes than in leukaemic cell lines. Separation of labelled endogenous substrates on sodium dodecyl sulfate-polyacrylamide gels showed a number of phosphorylated alkali-resistant bands in the range 14-175kd in the lymphoid cell lines; normal lymphocytes exhibited a smaller number of strongly phosphorylated bands. Normal lymphocytes from different individuals showed reproducible patterns of phosphorylated substrates. Normal bone marrow cells and myeloid leukaemia lines showed weak, if any, phosphorylation. Among the leukaemic cell lines no particular pattern of phosphorylated substrates common to cells of similar phenotype could be detected. We suggest that the level of overall tyrosine protein kinase activity in these fractions reflects their position in the cell cycle rather than their normal or malignant status.

Gel filtration of a complex of DNA polymerase and DNA precursor-synthesizing enzymes from a human lymphoblastoid cell line.

A multienzyme complex containing at least DNA polymerase (EC 2.7.7.7), thymidine kinase (EC 2.7.1.21), dTMP kinase (EC 2.7.4.9) nucleoside diphosphokinase (EC 2.7.4.6) and thymidylate synthetase was separated from the corresponding free enzymes of DNA precursor synthesis by gel filtration of a gently lysed preparation of HPB-ALL cells (a human lymphoblastoid cell line). The isolated incorporated the distal DNA precursors [3H]thymidine or [3H]dTMP into an added DNA template at rates comparable to those observed using the immediate precursor [3H]dTTP. Measurement of the apparent overall concentrations of [3H]dTTP produced during incorporation of [3H]thymidine and of [3H]dTMP were so low as to suggest that these precursors were channelled into DNA by the operation of a kinetically linked complex of precursor-synthesizing enzymes and of DNA polymerase. The DNA polymerase inhibitor 1-beta-D-arabinofuranosylcytosine triphosphate reduced incorporation of distal precursors into DNA. However [3H]dTTP did not accumulate in the reaction mixture. This suggested that the DNA polymerase regulated the flow of substrates through the complex. The results in this paper constitute direct evidence for the existence of multienzyme complexes of DNA synthesis in mammalian cells.

Solubilization and partial characterization of a multienzyme complex of DNA synthesis from human lymphoblastoid cells.

1. Gently lysed human lymphoblastoid cells (HPB-ALL) catalysed incorporation of the distal DNA precursors [3H]thymidine, [3H]dTMP, and [3H]dUMP into DNA. Measurement of the [3H]dTTP, produced during the incorporation reactions, provided kinetic evidence for the channelling of the distal precursors into DNA by a multienzyme complex consisting of precursor-synthesizing enzymes and of DNA polymerase. 2. In the presence of the DNA polymerase inhibitor, 1-beta-D-arabinofuranosylcytosine triphosphate, incorporation of [3H]dTMP into DNA was abolished. However, there was no accumulation of [3H]dTTP, suggesting that the flow of substrates through the complex was regulated by the activity of DNA polymerase. 3. Multienzyme complexes were detected by chromatography of a lysate on a column of Sepharose 6B. These complexes retained the ability to channel [3H]thymidine and [3H]dTMP into DNA.