B precursor acute lymphoblastic leukemia third complementarity-determining regions predominantly represent an unbiased recombination repertoire: leukemic transformation frequently occurs in fetal life

Comparison of secular trends of leukemia in China and the United States from 1990 to 2021 and their projections for the next 15 years

Background

Leukemia imposes a large healthcare burden both in China and the United States (US). The disease burden differs greatly between the two countries, but related research is limited. We explored the differences in leukemia incidence and mortality between China and the US.

Methods

Data on leukemia in China and the US from 1990 to 2021 were collected from the Global Burden of Disease 2021 database. Incidence and mortality were used to estimate the disease burden, and joinpoint regression was performed to compare their secular trends. We used an age-period-cohort model to analyze the effects of age, period, and birth cohort and project future trends in the next 15 years.

Results

In 2021, the age-standardized incidence rate (ASIR) and the age-standardized death rate (ASDR) of leukemia were lower in China than in the US. However, the incidence and mortality of acute lymphoblastic leukemia (ALL) was considerably higher in China. In the past decades, the ASIR showed decreased tendency in the US, while ASIR showed stable in China. The ASDR tended to decrease in both countries from 1990 to 2021. Males have higher rates of incidence and mortality than females in two countries. The age effects showed that children and older individuals have higher RRs for incidence and mortality in China, while the RRs for incidence and mortality in the US particularly increased in the older population. The disease burden of leukemia in children is obviously greater in China. The ASIRs and ASDRs of leukemia will continue to decline in the next 15 years in China and the US, with the US experiencing a more obvious downtrend.

Conclusions

Over the past decades, the ASDRs in two countries both tended to decrease. And compared to the US, China had lower leukemia incidence and mortality, However, the ASIRs in China tended toward stable, which it was showed downtrend in the US. Children have obviously greater RRs for incidence and mortality in China. The incidence and mortality will decrease continuously in two countries. Effective intervention measures are needed to reduce the burden of leukemia.

Presence of leukemic clone-specific immunoglobulin heavy chain rearrangements in neonatal blood spots of children with B-cell precursor acute lymphoblastic leukemia

INTRODUCTION

Childhood B-cell precursor acute lymphoblastic leukemia (BCP-ALL) can be traced back to birth using leukemic clone-specific immunoglobulin heavy chain (IGH) rearrangements, implying prenatal origin of this disease.

METHODS

We retrospectively analyzed neonatal blood spots (Guthrie cards) of 24 patients with childhood BCP-ALL aged 1-9.6 years (median 3.1 years) for the presence of clonotypic IGH rearrangements identified in diagnostic bone marrow samples. Based on the sequences of IGH rearrangements, 2 patient-specific primers were designed for each patient and used in semi-nested polymerase chain reaction for the detection of preleukemic clones at birth.

RESULTS

Clonotypic IGH rearrangements were detected in neonatal blood spots of 54.2% of patients (13/24). In two cases with double IGH rearrangements detected at diagnosis, only one rearrangement was present at birth, while in the third case both leukemic rearrangements were detected in neonatal blood. Guthrie card-positive findings were significantly more frequent in children ≤5 years of age than in older children (p = 0.011). Regarding patients' characteristics at birth and at diagnosis, Guthrie card-positivity was not associated with sex, birth weight and mother's age, as well as with white blood cell count, percentage of bone marrow blasts, immunophenotype and the presence of ETV6/RUNX1 and TCF3/PBX1 fusion genes at diagnosis.

CONCLUSION

Our study confirms that a large proportion of childhood BCP-ALL originates in utero, regardless of the molecular subtype defined by chromosomal aberrations. The observed trend toward younger age at diagnosis in Guthrie card-positive versus Guthrie card-negative patients implies that the age at diagnosis depends on the presence of preleukemic clone at birth, as well as on the timing of postnatal transforming genetic events.

Secular trend in disease burden of leukemia and its subtypes in China from 1990 to 2019 and its projection in 25 years

Leukemia and its subtypes impose a major public health challenge in China. Identifying the secular trend of leukemia burden is critical to facilitate optimal healthcare planning and improve the management of leukemia. The incidence rates of leukemia from 1990 to 2019 were collected from the Global Burden of Disease Study 2019 database according to the following: subtype (acute lymphocytic leukemia [ALL], acute myeloid leukemia [AML], chronic lymphocytic leukemia [CLL], chronic myelogenous leukemia [CML], and other leukemia subtypes), sex, and age group. The average annual percentage changes and relative risks were calculated using joinpoint regression and the age-period-cohort model, respectively. The Bayesian age-period-cohort model was also applied to predict the future trend of the incidence of leukemia and its subtypes in the next 25 years. From 1990 to 2019, the age-standardized incidence rates (ASIRs) of leukemia slightly declined in males and females, which is similar to the trend of other leukemia subtypes. However, the four major leukemia subtypes, namely, ALL, AML, CLL, and CML, have been on the rise over the past three decades. The incidence rates of leukemia in children and the elderly were considerably higher than those in other age groups in males and females. Age effects were the most influential risk factor for leukemia incidence. Period effects showed that the risks of leukemia and its subtypes incidence increased with time. For cohort effects, the risks of leukemia and its subtypes were higher among the early-born cohorts compared with the late-born cohorts. The ASIRs of leukemia and its subtypes will continue to increase in the next 25 years. The burden of leukemia and its subtypes is expected to continue to increase in the next 25 years in males and females. A comprehensive understanding of the risk characteristics and disease pattern of leukemia and its subtypes is needed to formulate timely and effective intervention measures to reduce the leukemia burden in China.

Clinical observations on chemotherapy curable malignancies: unique genetic events, frozen development and enduring apoptotic potential

BACKGROUND

A select number of relatively rare metastatic malignancies comprising trophoblast tumours, the rare childhood cancers, germ cells tumours, leukemias and lymphomas have been routinely curable with chemotherapy for more than 30 years. However for the more common metastatic malignancies chemotherapy treatment frequently brings clinical benefits but cure is not expected. Clinically this clear divide in outcome between the tumour types can appear at odds with the classical theories of chemotherapy sensitivity and resistance that include rates of proliferation, genetic development of drug resistance and drug efflux pumps. We have looked at the clinical characteristics of the chemotherapy curable malignancies to see if they have any common factors that could explain this extreme differential sensitivity to chemotherapy.

DISCUSSION

It has previously been noted how the onset of malignancy can leave malignant cells fixed with some key cellular functions remaining frozen at the point in development at which malignant transformation occurred. In the chemotherapy curable malignancies the onset of malignancy is in each case closely linked to one of the unique genetic events of; nuclear fusion for molar pregnancies, choriocarcinoma and placental site trophoblast tumours, gastrulation for the childhood cancers, meiosis for testicular cancer and ovarian germ cell tumours and VDJ rearrangement and somatic hypermutation for acute leukemia and lymphoma. These processes are all linked to natural periods of supra-physiological apoptotic potential and it appears that the malignant cells arising from them usually retain this heightened sensitivity to DNA damage. To investigate this hypothesis we have examined the natural history of the healthy cells during these processes and the chemotherapy sensitivity of malignancies arising before, during and after the events. To add to the debate on chemotherapy resistance and sensitivity, we would argue that malignancies can be functionally divided into 2 groups. Firstly those that arise in cells with naturally heightened apoptotic potential as a result of their proximity to the unique genetic events, where the malignancies are generally chemotherapy curable and then the more common malignancies that arise in cells of standard apoptotic potential that are not curable with classical cytotoxic drugs.

Occurrence of ²¹⁰Po and biological effects of low-level exposure: the need for research

BACKGROUND

Polonium-210 (²¹⁰Po) concentrations that exceed 1 Bq/L in drinking-water supplies have been reported from four widely separated U.S. states where exposure to it went unnoticed for decades. The radionuclide grandparents of ²¹⁰Po are common in sediments, and segments of the public may be chronically exposed to low levels of ²¹⁰Po in drinking water or in food products from animals raised in contaminated areas.

OBJECTIVES

We summarized information on the environmental behavior, biokinetics, and toxicology of ²¹⁰Po and identified the need for future research.

METHODS

Potential linkages between environmental exposure to ²¹⁰Po and human health effects were identified in a literature review.

DISCUSSION

²¹⁰Po accumulates in the ovaries where it kills primary oocytes at low doses. Because of its radiosensitivity and tendency to concentrate ²¹⁰Po, the ovary may be the critical organ in determining the lowest injurious dose for ²¹⁰Po. ²¹⁰Po also accumulates in the yolk sac of the embryo and in the fetal and placental tissues. Low-level exposure to ²¹⁰Po may have subtle, long-term biological effects because of its tropism towards reproductive and embryonic and fetal tissues where exposure to a single alpha particle may kill or damage critical cells. ²¹⁰Po is present in cigarettes and maternal smoking has several effects that appear consistent with the toxicology of ²¹⁰Po.

CONCLUSIONS

Much of the important biological and toxicological research on ²¹⁰Po is more than four decades old. New research is needed to evaluate environmental exposure to ²¹⁰Po and the biological effects of low-dose exposure to it so that public health officials can develop appropriate mitigation measures where necessary.

Perspectives on the causes of childhood leukemia

Acute leukemia is the most common cancer in children but the causes of the disease in the majority of cases are not known. About 80% are precursor-B cell in origin (CD19+, CD10+), and this immunophenotype has increased in incidence over the past several decades in the Western world. Part of this increase may be due to the introduction of new chemical exposures into the child's environment including parental smoking, pesticides, traffic fumes, paint and household chemicals. However, much of the increase in leukemia rates is likely linked to altered patterns of infection during early childhood development, mirroring causal pathways responsible for a similarly increased incidence of other childhood-diagnosed immune-related illnesses including allergy, asthma, and type 1 diabetes. Factors linked to childhood leukemia that are likely surrogates for immune stimulation include exposure to childcare settings, parity status and birth order, vaccination history, and population mixing. In case-control studies, acute lymphoblastic leukemia (ALL) is consistently inversely associated with greater exposure to infections, via daycare and later birth order. New evidence suggests also that children who contract leukemia may harbor a congenital defect in immune responder status, as indicated by lower levels of the immunosuppressive cytokine IL-10 at birth in children who grow up to contract leukemia, as well as higher need for clinical care for infections within the first year of life despite having lower levels of exposure to infections. One manifestation of this phenomenon may be leukemia clusters which tend to appear as a leukemia "outbreak" among populations with low herd immunity to a new infection. Critical answers to the etiology of childhood leukemia will require incorporating new tools into traditional epidemiologic approaches - including the classification of leukemia at a molecular scale, better exposure assessments at all points in a child's life, a comprehensive understanding of genetic risk factors, and an appraisal of the interplay between infectious exposures and the status of immune response in individuals.

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.

Acute lymphoblastic leukemia with t(4;11) in children 1 year and older: The ‘big sister’ of the infant disease?

The t(4;11)-positive acute lymphoblastic leukemia (ALL) is a rare disease in children above the age of 1 year. We studied the clinical and biological characteristics in 32 consecutively diagnosed childhood cases (median age 10.0 years, range 1.0-17.1 years). Immunophenotyping revealed a pro-B and a pre-B stage in 24 and eight cases, respectively. IGH genes were rearranged in 84% of leukemias with a predominance of incomplete DJ(H) joints. Whereas IGK-Kde and TCRD rearrangements were rare, TCRG rearrangements were present in 50% of cases and involved mainly Vgamma11 or Vgamma9 together with a Jgamma1.3./2.3 gene segment, an unusual combination among t(4;11)-negative B-cell precursor ALL. Oligoclonality was found in about 30% as assessed by heterogeneous IGH and TCRG rearrangements. Our data are in line with transformation of a precursor cell at an early stage of B-cell development but retaining the potential to differentiate to the pre-B cell stage in vivo. Although a distinct difference between infant and older childhood cases with t(4;11) became evident, no age-related biological features were found within the childhood age group. In contrast to infants with t(4;11)-positive ALL, childhood cases had a relatively low cumulative incidence of relapse of 25% at 3.5 years with BFM-based high-risk protocols.

Immunogenotype changes prevail in relapses of young children with TEL-AML1-positive acute lymphoblastic leukemia and derive mainly from clonal selection

PURPOSE

Variations of the immunogenotype and TEL deletions in children with TEL-AML1+ acute lymphoblastic leukemia support the hypothesis that relapses derive from a persistent TEL-AML1+ preleukemic/leukemic clone rather than a resistant leukemia. We aimed at elucidating the relationship between the immunogenotype patterns at diagnosis and relapse as well as their clinical and biological relevance.

PATIENTS AND METHODS

Immunoglobulin and T-cell receptor gene rearrangements were analyzed in 41 children with a TEL-AML1+ acute lymphoblastic leukemia and an early (up to 30 months after diagnosis; n = 12) or late (at 30 months or later; n = 29) disease recurrence by a standardized PCR approach.

RESULTS

In 68% of the patients (group I), we identified differences in the immunogenotype patterns, whereas no changes were observed in the remaining 32% (group II). The divergence resulted more often from clonal selection than clonal evolution and consisted predominantly of losses (0-6, median 5) and/or gains (0-4, median 1) of rearrangements. The frequency and number of clonal immunoglobulin/T-cell receptor rearrangements in group I was higher at diagnosis (2-13, median 5) than at relapse (2-7, median 4), whereas it was the lowest in group II (1-5, median 3). Although group I children were younger at diagnosis, there was no correlation between particular immunogenotype patterns and remission duration.

CONCLUSION

These findings imply that the clonal heterogeneity in younger children most likely reflects an ongoing high recombinatorial activity in the preleukemic/leukemic cells, whereas the more uniform repertoire observed in older children mirrors end-stage rearrangement patterns of selected cell clones that evolved during the prolonged latency period.

Distinctive IGH gene segment usage and minimal residual disease detection in infant acute lymphoblastic leukaemias

Infant acute lymphoblastic leukaemia (ALL) represents a rare but unique subset with poor prognosis. We analysed mixed-lineage leukaemia (MLL) gene rearrangements and the sequences of complete and incomplete immunoglobulin heavy chain gene rearrangements (IGH) in 14 infants (age < or = 12 months at diagnosis) enrolled on Dana-Farber Cancer Institute ALL Consortium Protocol 95-01. The dynamics of the leukaemic clone were followed during the course of the disease by quantitative real-time polymerase chain reaction of IGH rearrangements. Sixteen sequences were obtained from 13 (93%) of these infants. There was marked over usage of the V(H)6.1 gene segment (64%) in infants compared with older children with ALL (8%), (P < 0.001) and overusage of D(H)6 (P = 0.004) and J(H)1 (P = 0.004). Poor outcome was associated with MLL gene rearrangements rather than any specific V(H)D(H)J(H) gene usage patterns. Levels of minimal residual disease (MRD) at the end of induction appeared to be high in infants with ALL compared with older children, and although the number of infant cases studied was small, there were no differences in MRD levels after induction therapy in infant ALL with or without MLL gene rearrangements (P = 0.41) and quantitative MRD assessment at the early time points may not be predictive of outcome. Novel treatment strategies are required to improve the outcome in this poor prognosis subset of children with ALL.

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.

High incidence and unique features of antigen receptor gene rearrangements in TEL-AML1-positive leukemias

The t(12;21) translocation resulting in the TEL-AML1 gene fusion is found in 25% of childhood B-cell precursor (BCP) acute lymphoblastic leukemias (ALL). Since TEL-AML1 has been reported to induce cell cycle retardation and thus may influence somatic recombination, we analyzed 214 TEL-AML1-positive ALL by PCR for rearrangements of the immunoglobulin (Ig) and T-cell receptor (TCR) genes. As a control group, 174 childhood BCP ALL without a TEL-AML1 were used. The majority of TEL-AML1-positive leukemias had a higher number of Ig/TCR rearrangements than control ALL. They also had a more mature immunogenotype characterized by their high frequency of complete IGH, IGK-Kde, and TCRG rearrangements. While IGK-Kde and TCRG were more frequently rearranged on both alleles at higher age, IGH and TCRD rearrangements decreased in their incidence along with a decrease in biallelic IGH rearrangements. This suggests that the recombination process continues in these leukemias leading to ongoing rearrangements and possibly also deletions of antigen receptor genes. We here provide first evidence that somatic recombination of antigen receptor genes is affected by the TEL-AML1 fusion, and that further age-related differences are probably caused by the longer latency period of the prenatally initiated TEL-AML1-positive leukemias in older children.

Detection of minimal residual disease in hematologic malignancies by real-time quantitative PCR: principles, approaches, and laboratory aspects

Detection of minimal residual disease (MRD) has prognostic value in many hematologic malignancies, including acute lymphoblastic leukemia, acute myeloid leukemia, chronic myeloid leukemia, non-Hodgkin's lymphoma, and multiple myeloma. Quantitative MRD data can be obtained with real-time quantitative PCR (RQ-PCR) analysis of immunoglobulin and T-cell receptor gene rearrangements, breakpoint fusion regions of chromosome aberrations, fusion-gene transcripts, aberrant genes, or aberrantly expressed genes, their application being dependent on the type of disease. RQ-PCR analysis can be performed with SYBR Green I, hydrolysis (TaqMan) probes, or hybridization (LightCycler) probes, as detection system in several RQ-PCR instruments. Dependent on the type of MRD-PCR target, different types of oligonucleotides can be used for specific detection, such as an allele-specific oligonucleotide (ASO) probe, an ASO forward primer, an ASO reverse primer, or germline probe and primers. To assess the quantity and quality of the RNA/DNA, one or more control genes must be included. Finally, the interpretation of RQ-PCR MRD data needs standardized criteria and reporting of MRD data needs international uniformity. Several European networks have now been established and common guidelines for data analysis and for reporting of MRD data are being developed. These networks also include standardization of technology as well as regular quality control rounds, both being essential for the introduction of RQ-PCR-based MRD detection in multicenter clinical treatment protocols.

Late relapses evolve from slow-responding subclones in t(12;21)-positive acute lymphoblastic leukemia: evidence for the persistence of a preleukemic clone

TEL/AML1-positive childhood acute lymphoblastic leukemias (ALLs) generally have low-risk features, but still about 20% of patients relapse. Our initial molecular genetic analyses in 2 off-treatment relapses suggested that the initial and relapse clones represent different subclones that evolved from a common TEL/AML1-positive, treatment-resistant precursor. In order to further elaborate on this hypothesis, we studied 2 patients with late systemic relapses of their TEL/AML1-positive ALL (41 months and 49 months after initial diagnosis, respectively) who had distinct clonal antigen receptor gene rearrangements at diagnosis and relapse. These clone-specific markers enabled us to determine the responsiveness of the individual clones to treatment. The matching genomic TEL/AML1 breakpoints of the initial and the relapse clones in these patients confirmed their origin from a common progenitor cell. This proof was especially important in one of these 2 leukemias without a common antigen receptor gene rearrangement. Our retrospective analysis revealed that in both cases the relapse clone was already present at diagnosis. Despite their small sizes (5 x 10(-3) and 1 x 10(-4), respectively), we were able to detect their much slower responses to therapy compared with the dominant leukemic clone. Moreover, in all instances, these initially slow-responding clones, after they had developed into the relapse leukemia, were rapidly eradicated by the relapse treatment, underlining their different biology at the 2 time points of leukemia manifestation. We thus hypothesize that the minor clone was not fully malignant at initial diagnosis but acquired further mutations that may be necessary for the manifestation of relapse.

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.

Site-specific translocation and evidence of postnatal origin of the t(1;19) E2A-PBX1 fusion in childhood acute lymphoblastic leukemia

The t(1;19) translocation yields a fusion between E2A and PBX1 genes and occurs in 5% of acute lymphoblastic leukemia in children and adults. We used chromosomal translocations and Ig heavy chain (IGH)/T cell antigen receptor (TCR) rearrangements to develop an understanding of the etiology and natural history of this subtype of leukemia. We sequenced the genomic fusion between E2A and PBX1 in 22 preB acute lymphoblastic leukemias and two cell lines. The prenatal origin of the leukemia was assessed in 15 pediatric patients by screening for the clonotypic E2A-PBX1 translocation in neonatal blood spots, or Guthrie cards, obtained from the children at the time of birth. Two patients were determined to be weakly positive for the fusion at the time of birth, in contrast to previously studied childhood leukemia fusions, t(12;21), t(8;21), and t(4;11), which were predominantly prenatal. The presence of extensive N-nucleotides at the point of fusion in the E2A-PBX1 translocation as well as specific characteristics of the IGH/TCR rearrangements provided additional evidence for a postnatal, preB cell origin. Intriguingly, 16 of 24 breakpoints on the 3.2-kb E2A intron 14 were located within 5 bp, providing evidence for a site-specific recombination mechanism. Breakpoints on the 232-kb PBX1 intron 1 were more dispersed but highly clustered proximal to exon 2. In sum, the translocation breakpoints displayed evidence of unique temporal, ontological, and mechanistic formation than the previously analyzed pediatric leukemia translocation breakpoints and emphasize the need to differentiate cytogenetic and molecular subgroups for studies of leukemia causality.

Low frequency of clonotypic Ig and T-cell receptor gene rearrangements in t(4;11) infant acute lymphoblastic leukaemia and its implication for the detection of minimal residual disease

Infant t(4;11) acute lymphoblastic leukaemia (ALL) is a rare but cytogenetically well defined subgroup of immature B-cell precursor (BCP) ALL. To date, the configuration of their antigen receptor genes has not been studied in a large group of patients so far. In this study on 27 t(4;11) infant ALL, we have used standardized primer sets for the detection of all incomplete and complete immunoglobulin (Ig) heavy chain (IGH) rearrangements, as well as for the Ig light chain kappa (IGK), T-cell receptor delta (TCRD) and gamma (TCRG) rearrangements that are most common in childhood BCP ALL. Only 52% of cases displayed clonotypic antigen receptor gene rearrangements (IGH in 48%, IGK, TCRD and TCRG in 12%, 41% and 6% respectively). This low frequency suggests, together with the findings of predominantly incomplete DJh joins and monoallelic IGH rearrangements, that they are derived from an immature progenitor cell. As 48% of the t(4;11) infant ALL cases had no detectable antigen receptor gene rearrangements that could be used for minimal residual disease (MRD) analysis, we established an expression-independent, leukaemia-specific polymerase chain reaction (PCR) using the genomic sequence of the MLL-AF4 fusion genes. This method had high sensitivity and specificity and resulted in identical estimations of tumour loads when compared with IGH targets. Thus, genomic MLL-AF4 fusion genes are a good alternative target for the analysis of MRD in patients with t(4;11) leukaemias.

B-cell precursors differentiated from cord blood CD34+ cells are more immature than those derived from granulocyte colony-stimulating factor-mobilized peripheral blood CD34+ cells

Umbilical cord blood (CB) has been widely used instead of bone marrow (BM) and peripheral blood (PB) for stem cell transplantation (SCT). However, problems of sustained immunodeficiency after CB transplantation remain to be resolved. To elucidate the mechanism of immunodeficiency, we compared the characteristics of B cells differentiated in vitro from CD34+ cells of CB with those of PB. Purified CD34+ cells from CB and PB were cultured on murine stroma cell-line MS-5 with stem cell factor and granulocyte colony-stimulating factor for 6 weeks. The B-cell precursors (pre-B cells) that differentiated in this culture system, were analysed as to their immunoglobulin heavy chain (IgH) variable region gene repertoire and the expression of B-cell differentiation-related genes. CD10+ CD19+ pre-B cells were differentiated from both PB and CB. Although the usages of IgH gene segments in pre-B cells differentiated from CB and PB were similar, the N region was significantly shorter in CB-derived than PB-derived cells. Productive rearrangements were significantly fewer in cells of CB than PB in the third week. Among a number of B-cell differentiation-related genes, the terminal deoxynucleotidyl transferase (TdT) gene was not expressed in CB-derived cells during the culture. These results indicated that immature features of pre-B cells from CB, such as lack of TdT expression, and a short N region and few productive rearrangements in the IgH gene, might cause the delay in mature B-cell production.

Presence of N regions in the clonotypic DJ rearrangements of the immunoglobulin heavy-chain genes indicates an exquisitely short latency in t(4;11)-positive infant acute lymphoblastic leukemia

Childhood acute lymphoblastic leukemia (ALL) is frequently initiated in utero at a time of developmentally regulated insertion of N regions into the DJ(H) rearrangements of immunoglobulin heavy-chain (Ig(H)) genes. Here it is shown that N regions are present in the clonotypic DJ(H) rearrangements in 11 of 12 infant ALLs with t(4;11). These data are compared with the 122 previously published DJ(H) sequences and were found to have a pattern similar to that of ALL in children older than 3 years at diagnosis but were unlike that in children younger than 3 years who predominantly lack N regions. These findings, therefore, indicate that t(4;11)-positive infant ALL is initiated later in fetal development than most B-cell precursor ALL from children younger than 3 years and that they have a shorter latency period already in utero.

Immunoglobulin variable region structure and B-cell malignancies

The enormous diversity of immunoglobulin (Ig) variable (V) gene sequences encoding the antibody repertoire are formed by the somatic recombination of relatively few genetic elements. In B-lineage malignancies, Ig gene rearrangements have been widely used for determining clonality and cell origin. The recent development of rapid cloning and sequencing techniques has resulted in a substantial accumulation of IgV region sequences at various stages of B-cell development and has revealed stage-specific trends in the use of V, diversity, joining genes, the degree of noncoding nucleotide addition, and the rate of somatic mutations. Furthermore, sequences from B-lineage malignant cells nearly reflect the characteristics of the normal counterpart at each respective stage of development. Alternatively, from the IgV region structure of the malignant cells, it is possible to speculate at which stage of B-cell development the cells were transformed. As the complete nucleotide sequences of the human Ig heavy and Ig light V region loci have now been determined, the study of Ig genetics has entered into the super-information era.

Precursor-B-ALL with D(H)-J(H) gene rearrangements have an immature immunogenotype with a high frequency of oligoclonality and hyperdiploidy of chromosome 14

The IGH gene configuration was investigated in 97 childhood precursor-B-ALL patients at initial diagnosis. Rearrangements were found by Southern blotting in all but three patients (97%) and in 30 cases (31%) we observed oligoclonal IGH gene rearrangements. Heteroduplex PCR analysis revealed at least one clonal PCR product in all Southern blot-positive cases. In 89 patients (92%) complete V(D)J rearrangements were found, while incomplete D(H)-J(H) rearrangements occurred in only 21 patients (22%). In 5% of cases the D(H)-J(H) rearrangements were the sole IGH gene rearrangements. Sequence analysis of the 31 identified incomplete rearrangements revealed preferential usage of segments from the D(H)2, D(H)3 and D(H)7 families (78%). While D(H)2 and D(H)3 gene rearrangements occur frequently in normal B cells and B cell precursors, the relatively frequent usage of D(H)7-27 (19%) in precursor-B-ALL patients is suggestive of leukemic transformation during prenatal lymphopoiesis. Among J(H) gene segments in the incomplete D(H)-J(H) rearrangements, the J(H)6 segment was significantly overrepresented (61%). This observation together with the predominant usage of the most upstream D(H) genes indicates that many of the identified clonal D(H)-J(H) gene rearrangements in precursor-B-ALL probably represent secondary recombinations, having deleted pre-existing D(H)-J(H) joinings. The patients with incomplete D(H)-J(H) gene rearrangements were frequently characterized by hyperdiploid karyotype with additional copies of chromosome 14 and/or by IGH oligoclonality. The presence of incomplete D(H)-J(H) joinings was also significantly associated with a less mature immunogenotype: overrepresentation of V(H)6-1 gene segment usage, absence of biallelic TCRD deletions, and low frequency of TCRG gene rearrangements. This immature immunogenotype of precursor-B-ALL with incomplete IGH gene rearrangements was not associated with more aggressive disease.

An in situ study of CD34(+) cells in human fetal bone marrow

The purpose of this study was to characterize the spatial distribution, number and size of CD34(+) cells in fetal bone marrow. Thin sections of normal fetal bone marrow from lumbar vertebrae were stained using CD34 antibody QBend/10. Sections were used under light microscopy with various eyepiece graticules to make measurements of CD34(+) cells in situ. Results showed that at mid- and late gestation, approximately 2% and 0.5% of fetal bone marrow cells were CD34(+) respectively. The mean distance of CD34(+) cells from the nearest trabecular bone surface was 61 +/- 4 and 46 +/- 4 microm, respectively, for mid- and late gestation. The mean distance to the nearest neighbour was 46 +/- 5 and 105 +/- 15 microm, and the mean distance to the nearest blood vessel was 13 +/- 1 and 17 +/- 2 microm respectively. The concentration of CD34(+) cells in the peripheral region was 6.5 times greater than that at the centre of the sections. Overall, the percentage number of CD34(+) cells decreased with gestational age. The cellular and nuclear diameters of CD34(+) cells remained unchanged throughout mid- and late gestation at 5.4 +/- 0.1 and 3.8 +/- 0.1 microm respectively. This information will be used to calculate the natural background alpha-radiation dose to haemopoietic stem cells.

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

The aim of this study was to characterize individual-segment and overall patterns of V(H) gene usage in adult B-lineage acute lymphoblastic leukemia (ALL). Theoretical values of V(H) segment usage were calculated with the assumption that all V(H) segments capable of undergoing rearrangement have an equal probability of selection for recombination. Leukemic clones from 127 patients with adult B-lineage acute leukemias were studied by fingerprinting by means of primers for the framework 1 and joining segments. Clones from early preimmune B cells (245 alleles identified) show a predominance of V(H)6 family rearrangements and, consequently, do not conform to this hypothesis. However, profiles of V(H) gene family usage in mature B cells, as investigated in peripheral blood (6 samples), B-cell lymphomas (36 clones) and chronic lymphocytic leukemia (56 clones), are in agreement with this theoretical profile. Sequence analyses of 64 V(H) clones in adult ALL revealed that the rate of V(H) usage is proportional to the proximity of the V(H) gene to the J(H) locus and that the relationship can be mathematically defined. Except for V(H)6, no other V(H) gene is excessively used in adult ALL. V(H) pseudogenes are rarely used (n = 2), which implies the existence of early mechanisms in the pathway to B-cell maturation to reduce wasteful V(H)-(D(H))-J(H) recombination. Finally, similar to early immunoglobulin-H rearrangement patterns in the mouse, B cells of ALL derive from a pool of cells more immature than the cells in chronic lymphoid B-cell malignancies.

Application of germline IGH probes in real-time quantitative PCR for the detection of minimal residual disease in acute lymphoblastic leukemia

Large-scale clinical studies on detection of minimal residual disease (MRD) in acute lymphoblastic leukemia (ALL) have shown that quantification of MRD levels is needed for reliable MRD-based risk group classification. Recently, we have shown that 'real-time' quantitative PCR (RQ-PCR) can be applied for this purpose using patient-specific immunoglobulin (Ig) and T cell receptor (TCR) gene rearrangements as PCR targets with TaqMan probes at the position of the junctional region and two germline primers. Now, we tested an alternative approach on 35 immunoglobulin heavy chain (IGH) gene rearrangements, by designing three germline JH TaqMan probes to be used in combination with one of six corresponding germline JH primers and one allele specific oligonucleotide (ASO) primer complementary to the junctional region. In nine cases in which both approaches were compared, at least similar (n = 4) or slightly higher (n= 5) maximal sensitivities were obtained using an ASO primer. The ASO primer approach reached maximal sensitivities of at least 10(-4) in 33 out of 35 IGH rearrangements. The reproducible range for accurate quantification spanned four to five orders of magnitude in 31 out of 35 cases. In 13 out of 35 rearrangements the stringency of PCR conditions had to be increased to remove or diminish background signals; this only concerned the frequently occurring JH4, JH5 and JH6 gene rearrangements. After optimization of the conditions (mainly by increasing the annealing temperature), only occasional aspecific amplification signals were observed at high threshold cycle (CT) values above 42 cycles and at least six cycles above the CT value of the detection limit. Hence, these rare aspecific signals could be easily discriminated from specific signals. We conclude that the here presented set of three germline JH Taq-Man probes and six corresponding germline JH primers can be used to develop patient-specific RQ-PCR assays, which allow accurate and sensitive MRD analysis in almost all IGH gene rearrangements. These results will facilitate standardized RQ-PCR analysis for MRD detection in large clinical studies.

Detection of clonotypic IGH and TCR rearrangements in the neonatal blood spots of infants and children with B-cell precursor acute lymphoblastic leukemia

An attractive hypothesis is that in utero exposure of hematopoietic cells to oncogenic agents can induce molecular changes leading to overt acute lymphoblastic leukemia (ALL) in infants and perhaps older children as well. Although supported by studies of identical infant twins with concordant leukemia, and of nontwined patients withMLL gene rearrangements, this concept has not been extended to the larger population of B-lineage ALL patients who lack unique nonconstitutive mutations or abnormally rearranged genes. We therefore sought to demonstrate a prenatal origin for 7 cases of B-cell precursor ALL (either CD10+ or CD10−) that had been diagnosed in infants and children 14 days to 9 years of age. Using a polymerase chain reaction–based assay, we identified the same clonotypic immunoglobulin heavy-chain complementarity determining region or T-cell receptor VD2-DD3 sequences in the neonatal blood spots (Guthrie card) and leukemic cell DNAs of 2 infants with CD10− ALL and 2 of the 5 older patients with CD10+ ALL. Nucleotide sequencing showed a paucity of N or P regions and shortened D germ line and conserved J sequences, indicative of cells arising from fetal hematopoiesis. Our findings strongly suggest a prenatal origin for some cases of B-cell precursor ALL lacking specific clonotypic abnormalities.

Detection of clonotypic IGH and TCR rearrangements in the neonatal blood spots of infants and children with B-cell precursor acute lymphoblastic leukemia

An attractive hypothesis is that in utero exposure of hematopoietic cells to oncogenic agents can induce molecular changes leading to overt acute lymphoblastic leukemia (ALL) in infants and perhaps older children as well. Although supported by studies of identical infant twins with concordant leukemia, and of nontwined patients withMLL gene rearrangements, this concept has not been extended to the larger population of B-lineage ALL patients who lack unique nonconstitutive mutations or abnormally rearranged genes. We therefore sought to demonstrate a prenatal origin for 7 cases of B-cell precursor ALL (either CD10+ or CD10−) that had been diagnosed in infants and children 14 days to 9 years of age. Using a polymerase chain reaction–based assay, we identified the same clonotypic immunoglobulin heavy-chain complementarity determining region or T-cell receptor VD2-DD3 sequences in the neonatal blood spots (Guthrie card) and leukemic cell DNAs of 2 infants with CD10− ALL and 2 of the 5 older patients with CD10+ ALL. Nucleotide sequencing showed a paucity of N or P regions and shortened D germ line and conserved J sequences, indicative of cells arising from fetal hematopoiesis. Our findings strongly suggest a prenatal origin for some cases of B-cell precursor ALL lacking specific clonotypic abnormalities.

Presence of clone-specific antigen receptor gene rearrangements at birth indicates an in utero origin of diverse types of early childhood acute lymphoblastic leukemia

There is strong evidence that infant leukemias with a t(4;11) translocation originate in utero. To test whether other subtypes of childhood leukemias are also initiated during fetal life, we used clone-specific genetic markers for the analysis of neonatal blood spots from 5 children aged 6 months to 4 years 8 months at diagnosis of pro-B, common acute lymphoblastic leukemia (ALL), and T-ALL. In all children, the clonotypic antigen receptor gene rearrangements were already present at birth. The estimated amount of clonotypic cells was in the range of 10 to 100 cells per blood spot. In 2 infants with a t(4;11) positive ALL, we detected similar amounts of the fusion gene sequences compared with the clonal antigen receptor gene rearrangements, suggesting the presence of both markers in the same cells. Our data indicate that the first leukemogenic event of diverse types of childhood ALL may already occur in utero.

Presence of clone-specific antigen receptor gene rearrangements at birth indicates an in utero origin of diverse types of early childhood acute lymphoblastic leukemia

There is strong evidence that infant leukemias with a t(4;11) translocation originate in utero. To test whether other subtypes of childhood leukemias are also initiated during fetal life, we used clone-specific genetic markers for the analysis of neonatal blood spots from 5 children aged 6 months to 4 years 8 months at diagnosis of pro-B, common acute lymphoblastic leukemia (ALL), and T-ALL. In all children, the clonotypic antigen receptor gene rearrangements were already present at birth. The estimated amount of clonotypic cells was in the range of 10 to 100 cells per blood spot. In 2 infants with a t(4;11) positive ALL, we detected similar amounts of the fusion gene sequences compared with the clonal antigen receptor gene rearrangements, suggesting the presence of both markers in the same cells. Our data indicate that the first leukemogenic event of diverse types of childhood ALL may already occur in utero.

Clonal rearrangements in childhood and adult precursor B acute lymphoblastic leukemia: a comparative polymerase chain reaction study using multiple sets of primers

Ig heavy chain (IgH) and T-cell receptor (TCR) gene rearrangements were investigated by polymerase chain reaction (PCR) amplification of diagnostic tumour samples from 91 patients (57 children and 34 adults, with cut-off at age 16) with precursor B acute lymphoblastic leukemia (ALL). Using primers directed to the framework regions (FR) 1, 2 and 3 of the IgH gene, clonal IgH rearrangements were observed in 82, 58 and 58%, respectively, whereas clonality was presented in 45 and 27% using primers hybridising to the TCR delta and gamma genes. A combination of all five primer sets used resulted in 96% positive cases (children 100%, adults 88%). The frequency of clonal IgH rearrangements correlated to patient age with a significantly lower fraction of positive cases in the adult group. The concomitant usage of more than one V(H) family gene was similar for childhood and adult ALL, and an over-representation of V(H)6 rearrangements was found in childhood ALL. Twenty-five out of 91 cases (27%) displayed an oligoclonal pattern for either IgH or TCR gene rearrangements (children 37%, adults 12%). A comparative analysis of samples from different compartments was performed in 23 patients, and differences between two or three compartments were observed in seven cases. Unexpectedly large, clonally appearing PCR products of 540-715 bp were found in three leukemias and sequence analysis verified their clonal nature. In summary, using multiple sets of primers clonal rearrangements of IgH and TCR genes can be detected in a very high frequency, including previously neglected large size PCR products. A common heterogeneity was demonstrated in different compartments reflecting ongoing clonal evolution, which can make detection of minimal residual disease (MRD) in ALL troublesome. Therefore, we suggest that a minimum of three targets should be used to minimise false-negative results.

Protracted and Variable Latency of Acute Lymphoblastic Leukemia AfterTEL-AML1 Gene Fusion In Utero

We report a pair of identical twins with concordant acute lymphoblastic leukemia (ALL). Unusually, their diagnoses were spaced 9 years apart at ages 5 and 14. Leukemic cells in both twins had aTEL-AML1 rearrangement, which was characterized at the DNA level by an adaptation of a long distance polymerase chain reaction (PCR) method. The genomic fusion sequence was identical in the two leukemias, indicative of a single cell origin in one fetus, in utero. At the time twin 1 was diagnosed (aged 5 years), the bone marrow of twin 2 was hematologically normal. However, retrospective scrutiny of the DNA from an archived slide with clonotypic TEL-AML1 primers showed that the presumptive preleukemic clone was present and disseminated 9 years before a clinical diagnosis. These data provide novel insight into the natural history of childhood leukemia and suggest that consequent to a prenatal initiation of a leukemic clone, most probably by TEL-AML fusion itself, the latency of ALL can be both extremely variable and protracted. This, in turn, is likely to reflect the timing of critical secondary events.

CDR3 sequences of MALT lymphoma show homology with those of autoreactive B-cell lines

We have examined the CDR3 sequence and adjacent regions of immunoglobulin genes from B-cell lymphoma of mucosa-associated lymphoid tissue (MALT). Twenty-nine sequences (15 sequences from 13 low-grade MALT lymphomas, marginal zone B-cell lymphomas; 7 sequences from 6 high-grade MALT lymphomas; 7 sequences from 7 diffuse large cell lymphomas) were obtained after cloning of the polymerase chain reaction-amplified segments. In the low-grade MALT, high-grade MALT and diffuse large cell lymphomas, the mean length of the CDR3 region was 47.6+/-10.31 (range 21 to 60), 38.71+/-10.37 (range 27 to 57) and 40.86+/-3.34 (range 39 to 48) nucleotides, respectively. The length of the CDR3 region was significantly greater in the low-grade MALT lymphoma group than in the other two groups. CDR3 sequences in lymphoma cell clones of 14 cases showed 60 to 81% homology with autoantibody-associated lymphocyte clones including rheumatoid factor. The incidences of these autoantibody-associated lymphocyte clones were higher in the high-grade MALT (4/6) and diffuse large lymphomas (5/7) than in the low-grade MALT lymphoma (5/13). Cases with more than 70% homology at the nucleotide level were found to have 71 to 82% homology with autoantibodies at the protein level in the low-grade MALT lymphomas (2/13), and 67% homology in the high-grade MALT lymphomas (2/7). These results indicate that MALT lymphomas may be derived from the malignant transformation of autoreactive B-cells.

Unusual immunoglobulin and T-cell receptor gene rearrangement patterns in acute lymphoblastic leukemias

Immunoglobulin (Ig) and T-cell receptor (TCR) genes are rearranged in virtually all acute lymphoblastic leukemia (ALL) cases. However, the recombination patterns display several unusual features as compared to normal lymphoid counterparts. Cross-lineage gene rearrangements occur in more than 90% of precursor-B-ALL and in approximately 20% of T-ALL, whereas they are rare in normal lymphocytes. Approximately 25-30% of the Ig and TCR gene rearrangements at diagnosis are oligoclonal, and can undergo continuing or secondary recombination events during the disease course. Based on our extensive molecular studies we hypothesize that the unusual Ig and TCR gene rearrangements in ALL occur as an early postoncogenic event resulting from the continuing V(D)J recombinase activity on accessible gene loci. This hypothesis is on the one hand supported by the virtual absence of cross-lineage gene rearrangements in normal lymphocytes and mature lymphoid malignancies and on the other hand by the presence of oligoclonality and secondary Ig and TCR gene rearrangements in ALL.

Clonal analysis of B-cell leukemias and lymphomas using the polymerase chain reaction for the third complementarity determining region of the IgH gene: a study of 75 cases from Nagasaki Japan

Using semi-nested polymerase chain reaction (PCR), we examined 75 Japanese cases of hematologic malignancies with B-cell antigens including 25 common acute lymphoblastic leukemia (ALL), 13 chronic lymphocytic leukemia (CLL), 28 B-cell malignant lymphoma (B-ML), 2 hairy cell leukemia (HCL), 7 acute myelogenous leukemia with B-cell antigens (AML-B), and 23 controls. When amplified products were analysed by a standard polyacrylamide gel electrophoresis, the sensitivity for detection of clonal IgH rearrangements in each group of ALL, CLL, B-ML, HCL, and AML-B was 88%, 92.3%, 71.4%, 100%, and 57.1%, respectively, with an overall sensitivity of 80.0%. There were no false positive results in any of the control samples. Single strand conformation polymorphism (SSCP) analysis of the amplified products gave rise to a much greater sensitivity, up to 84% overall. The false negative samples were mainly encountered in B-ML with SmIgG and non-Ig, suggesting miss-annealing between the primers used and the template DNA because of somatic hypermutation of IgH genes in such clones. This indicates that PCR analysis is very useful in detecting the clonal IgH rearrangements in B-cell malignancies, especially in ALL and CLL, but not in B-ML corresponding to neoplasms originating from pre-germinal center naive B-cells.

Ig Heavy Chain Gene Rearrangements in T-Cell Acute Lymphoblastic Leukemia Exhibit Predominant Dh6-19 and Dh7-27 Gene Usage, Can Result in Complete V-D-J Rearrangements, and Are Rare in T-Cell Receptor β Lineage

Rearranged IGH genes were detected by Southern blotting in 22% of 118 cases of T-cell acute lymphoblastic leukemia (ALL) and involved monoallelic and biallelic rearrangements in 69% (18/26) and 31% (8/26) of these cases, respectively. IGH gene rearrangements were found in 19% (13/69) of CD3− T-ALL and in 50% of TCRγδ+ T-ALL (12/24), whereas only a single TCRβ+ T-ALL (1/25) displayed a monoallelicIGH gene rearrangement. The association with the T-cell receptor (TCR) phenotype was further supported by the striking relationship between IGH and TCR delta (TCRD) gene rearrangements, ie, 32% of T-ALL (23/72) with monoallelic or biallelicTCRD gene rearrangements had IGH gene rearrangements, whereas only 1 of 26 T-ALL with biallelic TCRD gene deletions contained a monoallelic IGH gene rearrangement. Heteroduplex polymerase chain reaction (PCR) analysis with Vh and Dh family-specific primers in combination with a Jhconsensus primer showed a total of 39 clonal products, representing 7 (18%) Vh-(Dh-)Jh joinings and 32 (82%) Dh-Jh rearrangements. Whereas the usage of Vh gene segments was seemingly random, preferential usage of Dh6-19 (45%) and Dh7-27 (21%) gene segments was observed. Although the Jh4 and Jh6 gene segments were used most frequently (33% and 21%, respectively), a significant proportion of joinings (28%) used the most upstream Jh1 and Jh2 gene segments, which are rarely used in precursor-B-ALL and normal B cells (1% to 4%). In conclusion, the high frequency of incomplete Dh-Jh rearrangements, the frequent usage of the more downstream Dh6-19 and Dh7-27 gene segments, and the most upstream Jh1 and Jh2 gene segments suggests a predominance of immature IGH rearrangements in immature (non-TCRβ+) T-ALL as a result of continuing V(D)J recombinase activity. More mature β-lineage T-ALL with biallelic TCRD gene deletions apparently have switched off their recombination machinery and are less prone to cross-lineageIGH gene rearrangements. The combined results indicate thatIGH gene rearrangements in T-ALL are postoncogenic processes, which are absent in T-ALL with deleted TCRD genes and completed TCR alpha (TCRA) gene rearrangements.

Ig Heavy Chain Gene Rearrangements in T-Cell Acute Lymphoblastic Leukemia Exhibit Predominant Dh6-19 and Dh7-27 Gene Usage, Can Result in Complete V-D-J Rearrangements, and Are Rare in T-Cell Receptor β Lineage

Rearranged IGH genes were detected by Southern blotting in 22% of 118 cases of T-cell acute lymphoblastic leukemia (ALL) and involved monoallelic and biallelic rearrangements in 69% (18/26) and 31% (8/26) of these cases, respectively. IGH gene rearrangements were found in 19% (13/69) of CD3− T-ALL and in 50% of TCRγδ+ T-ALL (12/24), whereas only a single TCRβ+ T-ALL (1/25) displayed a monoallelicIGH gene rearrangement. The association with the T-cell receptor (TCR) phenotype was further supported by the striking relationship between IGH and TCR delta (TCRD) gene rearrangements, ie, 32% of T-ALL (23/72) with monoallelic or biallelicTCRD gene rearrangements had IGH gene rearrangements, whereas only 1 of 26 T-ALL with biallelic TCRD gene deletions contained a monoallelic IGH gene rearrangement. Heteroduplex polymerase chain reaction (PCR) analysis with Vh and Dh family-specific primers in combination with a Jhconsensus primer showed a total of 39 clonal products, representing 7 (18%) Vh-(Dh-)Jh joinings and 32 (82%) Dh-Jh rearrangements. Whereas the usage of Vh gene segments was seemingly random, preferential usage of Dh6-19 (45%) and Dh7-27 (21%) gene segments was observed. Although the Jh4 and Jh6 gene segments were used most frequently (33% and 21%, respectively), a significant proportion of joinings (28%) used the most upstream Jh1 and Jh2 gene segments, which are rarely used in precursor-B-ALL and normal B cells (1% to 4%). In conclusion, the high frequency of incomplete Dh-Jh rearrangements, the frequent usage of the more downstream Dh6-19 and Dh7-27 gene segments, and the most upstream Jh1 and Jh2 gene segments suggests a predominance of immature IGH rearrangements in immature (non-TCRβ+) T-ALL as a result of continuing V(D)J recombinase activity. More mature β-lineage T-ALL with biallelic TCRD gene deletions apparently have switched off their recombination machinery and are less prone to cross-lineageIGH gene rearrangements. The combined results indicate thatIGH gene rearrangements in T-ALL are postoncogenic processes, which are absent in T-ALL with deleted TCRD genes and completed TCR alpha (TCRA) gene rearrangements.

IgM Heavy Chain Complementarity-Determining Region 3 Diversity Is Constrained by Genetic and Somatic Mechanisms Until Two Months After Birth

Due to the greater range of lengths available to the third complementarity determining region of the heavy chain (HCDR3), the Ab repertoire of normal adults includes larger Ag binding site structures than those seen in first and second trimester fetal tissues. Transition to a steady state range of HCDR3 lengths is not complete until the infant reaches 2 mo of age. Fetal constraints on length begin with a genetic predilection for use of short DH (D7-27 or DQ52) gene segments and against use of long DH (e.g., D3 or DXP) and JH (JH6) gene segments in both fetal liver and fetal bone marrow. Further control of length is achieved through DH-specific limitations in N addition, with D7-27 DJ joins including extensive N addition and D3-containing DJ joins showing a paucity of N addition. DH-specific constraints on N addition are no longer apparent in adult bone marrow. Superimposed upon these genetic mechanisms to control length is a process of somatic selection that appears to ensure expression of a restricted range of HCDR3 lengths in both fetus and adult. B cells that express Abs of an “inappropriate” length appear to be eliminated when they first display IgM on their cell surface. Control of N addition appears aberrant in X-linked agammaglobulinemia, which may exacerbate the block in B cell development seen in this disease. Restriction of the fetal repertoire appears to be an active process, forcing limits on the diversity, and hence range of Ab specificities, available to the young.

The Fetal Origin of B-Precursor Leukemia in the Eμ-ret Mouse

Before the clinical onset of B-precursor lymphoblastic leukemia, Eμ-ret mice have an expansion of late pro-B cells (CD45R+CD43+CD24+BP-1+) within the bone marrow. To characterize the early effects of the transgene product on lymphopoiesis, we initially sequenced the Ig heavy chain (IgH) rearrangements within the late pro-B cells in 24-day-old Eμ-ret and transgene negative mice. In both mouse populations, the IgH rearrangements were polyclonal, predominately nonproductive, and exhibited similar V, D, and J gene usage. However, the frequency of N regions, a marker of postnatal lymphopoiesis, was notably different. At the VD junction, N regions were found in 25 of 25 (100.0%) rearrangements from transgene-negative mice compared with 12 of 36 (33.3%) rearrangements from Eμ-ret mice. At the DJ junction, N regions were found in 21 of 25 (84.0%) rearrangements from transgene negative mice compared with 4 of 36 (11.1%) rearrangements from Eμ-ret mice. Subsequently, we sequenced the clonal IgH rearrangements from 9 leukemias that developed in 10-to 38-week-old mice and found that 7 leukemias had a least 1 rearrangement that lacked N regions at the DJ junction. In addition, V replacement events were observed in the 1 leukemia studied in detail. Terminal deoxynucleotidyl transferase, the enzyme responsible for N region addition, was expressed at markedly lower levels in late pro-B cells from 7- to 10-day-old Eμ-ret mice compared with transgene-negative mice. Examination of fetal lymphopoiesis in Eμ-ret mice identified a relative increase in early (CD45R+CD43+CD24+BP-1−) and late pro-B cells and a decrease in more differentiated CD43− B-lineage cells. Fetal early pro-B cells from Eμ-ret mice proliferated threefold to fivefold greater but differentiated to a lesser extent than those from transgene negative mice when cultured in vitro with interleukin-7. These data suggest that the B precursor leukemias in adult Eμ-ret mice arise from the progeny of pro-B cells generated in utero.

The Fetal Origin of B-Precursor Leukemia in the Eμ-ret Mouse

Before the clinical onset of B-precursor lymphoblastic leukemia, Eμ-ret mice have an expansion of late pro-B cells (CD45R+CD43+CD24+BP-1+) within the bone marrow. To characterize the early effects of the transgene product on lymphopoiesis, we initially sequenced the Ig heavy chain (IgH) rearrangements within the late pro-B cells in 24-day-old Eμ-ret and transgene negative mice. In both mouse populations, the IgH rearrangements were polyclonal, predominately nonproductive, and exhibited similar V, D, and J gene usage. However, the frequency of N regions, a marker of postnatal lymphopoiesis, was notably different. At the VD junction, N regions were found in 25 of 25 (100.0%) rearrangements from transgene-negative mice compared with 12 of 36 (33.3%) rearrangements from Eμ-ret mice. At the DJ junction, N regions were found in 21 of 25 (84.0%) rearrangements from transgene negative mice compared with 4 of 36 (11.1%) rearrangements from Eμ-ret mice. Subsequently, we sequenced the clonal IgH rearrangements from 9 leukemias that developed in 10-to 38-week-old mice and found that 7 leukemias had a least 1 rearrangement that lacked N regions at the DJ junction. In addition, V replacement events were observed in the 1 leukemia studied in detail. Terminal deoxynucleotidyl transferase, the enzyme responsible for N region addition, was expressed at markedly lower levels in late pro-B cells from 7- to 10-day-old Eμ-ret mice compared with transgene-negative mice. Examination of fetal lymphopoiesis in Eμ-ret mice identified a relative increase in early (CD45R+CD43+CD24+BP-1−) and late pro-B cells and a decrease in more differentiated CD43− B-lineage cells. Fetal early pro-B cells from Eμ-ret mice proliferated threefold to fivefold greater but differentiated to a lesser extent than those from transgene negative mice when cultured in vitro with interleukin-7. These data suggest that the B precursor leukemias in adult Eμ-ret mice arise from the progeny of pro-B cells generated in utero.

Evaluating the relationships among maternal reproductive history, birth characteristics, and infant leukemia: a report from the Children's Cancer Group

PURPOSE

Specific events in the mother's reproductive history and certain birth characteristics have been associated with childhood leukemia. Few studies have explored these associations specifically in infants.

METHODS

The Children's Cancer Group (CCG) conducted three separate case-control studies of childhood leukemia that involved similar methodologies and data collection. Data from interviews of the mothers of a total of 303 children diagnosed with leukemia at 1 year of age or younger and their matched controls (n = 468) were available from the three studies. These data included maternal reproductive history (stillbirths, abortions, and miscarriages) and certain birth characteristics of the index child.

RESULTS

Compared with controls, cases were significantly more likely to be female (P < 0.01) and were more often heavier at birth (particularly cases diagnosed after 6 months of age (odds ratio, 4.18; 95% confidence interval, 1.75-10.02)). Overall, there were no statistically significant differences between cases and controls in regard to maternal report of any type of previous fetal loss. Finally, being a later-born child was associated with an increased risk of acute myeloid leukemia but not of acute lymphoblastic leukemia.

CONCLUSIONS

The relationships among birthweight, prior fetal loss, and risk of infant leukemia appear to be complex. Further studies of infant leukemia that incorporate molecular as well as epidemiologic data may help to elucidate these differences.

Monoclonal Origin of Concordant T-Cell Malignancy in Identical Twins

Acute leukemia has a high concordance rate in young identical twins and in infants this is known, from molecular analysis, to reflect an in utero origin in one twin followed by prenatal metastasis to the other twin via intraplacental anastomoses. The situation in older twins with leukemia has been less clear. We describe a pair of identical twins who were diagnosed with a T-cell malignancy at 9 and 11 years of age, one with T-cell non-Hodgkin's lymphoma and the other with T-cell acute lymphoblastic leukemia. Leukemic cells from the twins shared the same TCRβ gene rearrangement with an identical 11 bp N region. The most plausible interpretation of this result is that these malignancies were initiated in one twin fetus in utero, in a single T-lineage cell that had stable bi-allelic TCRβ rearrangements. Progeny of this cell then spread to the other twin before birth via shared placental vasculature. This was then followed by a 9- and 11-year preleukemic latent period before clinical disease manifestation as leukemia or lymphoma. This result has considerable implications for the etiology and natural history of pediatric leukemia.

Monoclonal Origin of Concordant T-Cell Malignancy in Identical Twins

Acute leukemia has a high concordance rate in young identical twins and in infants this is known, from molecular analysis, to reflect an in utero origin in one twin followed by prenatal metastasis to the other twin via intraplacental anastomoses. The situation in older twins with leukemia has been less clear. We describe a pair of identical twins who were diagnosed with a T-cell malignancy at 9 and 11 years of age, one with T-cell non-Hodgkin's lymphoma and the other with T-cell acute lymphoblastic leukemia. Leukemic cells from the twins shared the same TCRβ gene rearrangement with an identical 11 bp N region. The most plausible interpretation of this result is that these malignancies were initiated in one twin fetus in utero, in a single T-lineage cell that had stable bi-allelic TCRβ rearrangements. Progeny of this cell then spread to the other twin before birth via shared placental vasculature. This was then followed by a 9- and 11-year preleukemic latent period before clinical disease manifestation as leukemia or lymphoma. This result has considerable implications for the etiology and natural history of pediatric leukemia.

Big babies and infant leukemia: a role for insulin-like growth factor-1?

Several epidemiologic studies have demonstrated that high birthweight is associated with an increased risk of infant leukemia; however, the reason for this relationship is unclear. Biologic data demonstrate that birth weight is correlated positively with circulating levels of insulin-like growth factor-1 (IGF-1). IGF-1 is important in blood formation and regulation and has been shown to stimulate the growth of both myeloid and lymphoid cells in culture. Since infants who develop leukemia are likely to have had at least one transforming event occur in utero, we hypothesize that high levels of IGF-1 may both produce a larger baby and contribute to leukemogenesis.

Monoclonality of B-cell lineage in primary pulmonary lymphoma demonstrated by immunoglobulin heavy chain gene sequence analysis of histologically non-definitive transbronchial biopsy specimens

Immunoglobulin heavy chain (IgH) gene rearrangements were amplified in transbronchial lung biopsy (TBLB) specimens taken from five patients with primary lymphoma of the lung in whom the diagnosis was established by surgical specimens. By histopathological analysis of TBLB specimens, only two of the five cases were diagnosed as lymphoma, the other three cases being classified as equivocal due mainly to low levels of cellular atypia and to artefactual distortion. All five TBLB specimens, as well as the subsequent surgical specimens, showed a sharp monoclonal band of IgH gene rearrangement on electrophoresis of polymerase chain reaction (PCR) products. By contrast, three surgical biopsy specimens from cases of lymphoid interstitial pneumonia (LIP) showed smear polyclonal bands. No clonal rearrangements were detected in six non-neoplastic controls, including five cases of chronic bronchitis and one of sarcoidosis. The PCR products of three of the lymphoma cases were sequenced from both TBLB and surgical specimens. In all three cases, there was dominant expression of a particular rearrangement, assumed to be tumour-derived. In each case, the major clones derived from the TBLB and the surgical specimen were identical. In both lymphoma and LIP cases, more frequent usages of JH4 and JH6 were evident. The diagnosis of lymphoma can be confirmed on TBLB specimens by use of this technique.