Infectious triggers and novel therapeutic opportunities in childhood B cell leukaemia.

B cell acute lymphoblastic leukaemia (B-ALL) is the most common form of childhood cancer. Although treatment has advanced remarkably in the past 50 years, it still fails in ~20% of patients. Recent studies revealed that more than 5% of healthy newborns carry preleukaemic clones that originate in utero, but only a small percentage of these carriers will progress to overt B-ALL. The drivers of progression are unclear, but B-ALL incidence seems to be increasing in parallel with the adoption of modern lifestyles. Emerging evidence shows that a major driver for the conversion from the preleukaemic state to the B-ALL state is exposure to immune stressors, such as infection. Here, we discuss our current understanding of the environmental triggers and genetic predispositions that may lead to B-ALL, highlighting lessons from epidemiology, the clinic and animal models, and identifying priority areas for future research.

Commentary: Comparison of current flow cytometry methods for monoclonal B cell lymphocytosis detection.

Monoclonal B cell lymphocytosis (MBL) is now recognized as the B-lymphocyte analogue of a monoclonal gammopathy of unknown significance. MBL can be the precursor of chronic lymphocytic leukemia or associated with non-Hodgkin's lymphoma. It may be associated with an autoimmune abnormality or be related to aging (immunosenescence). The combination of available new fluorochrome-conjugated monoclonal antibody reagents, multilaser instrumentation, and improved software tools have led to a new level of multicolor analysis of MBL. Presently, several centers, including the University of Salamanca (Spain), Duke University (Durham, NC), Mayo Clinic (Rochester, MN), and the National Cancer Institute (Bethesda, MD) in conjunction with the Genetics and Epidemiology of Familial chronic lymphocytic leukemia Consortium, the Food and Drug Administration (Bethesda, MD), and the Centers for Disease Control and Prevention/Agency for Toxic Substances and Disease Registry (Atlanta, GA) in collaboration with Saint Luke's Hospital (Kansas City, MO), the Università Vita-Salute San Raffaele in Milan (Italy), and Leeds Teaching Hospital (UK) are all actively conducting studies on MBL. This commentary is an updated summary of the current methods used in these centers. It is important to note the diversity of use in reagents, instruments, and methods of analysis. Despite this diversity, there is a consensus in what constitutes the diagnosis of MBL and its subtypes. There is also an emerging consensus on what the next investigative steps should be.

Discordance of MLL-rearranged (MLL-R) infant acute lymphoblastic leukemia in monozygotic twins with spontaneous clearance of preleukemic clone in unaffected twin.

Concordance of MLL-rearranged acute leukemia in infant monozygotic twins is thought to be 100% with a very short latency period, suggesting that either the MLL fusion itself is sufficient to cause leukemia or that it promotes the rapid acquisition of additional oncogenic events that result in overt disease. We report the first case of discordance in an infant monozygotic twin pair. Twin A presented at age 9 months with MLL-ENL(+) acute lymphoblastic leukemia and twin B remains healthy 3 years later. The presence and eventual clearance of a clonal population of MLL-ENL(+) cells was shown in the bone marrow and peripheral blood of twin B. Clearance of this clone was temporally associated with viral-induced cytopenias, suggesting an immune-mediated clearance of the clone before the development of leukemia. Thus, concordance of MLL-rearranged acute leukemia in infant monozygotic twins is not universal. The implications of this case for MLL-rearranged leukemogenesis are discussed.

The immunoglobulin gene repertoire of low-count chronic lymphocytic leukemia (CLL)-like monoclonal B lymphocytosis is different from CLL: diagnostic implications for clinical monitoring.

In the revised National Cancer Institute Working Group (NCI-WG)/International Workshop on Chronic Lymphocytic Leukemia (IWCLL) guidelines for CLL, CLL-like monoclonal B lymphocytosis (MBL) is defined as the presence of less than 5 x 10(9)/L B lymphocytes in the peripheral blood. However, the concentration of MBL in the blood is extremely variable. MBL in subjects with lymphocytosis require treatment at a rate of 1.1% per year and present immunoglobulin (IG) gene features and similar to good prognosis CLL. Little is known about low-count MBL cases, accidentally found in the general population. We analyzed IGHV-D-J rearrangements in 51 CLL-like MBL cases from healthy individuals, characterized by few clonal B cells. Seventy percent of the IGHV genes were mutated. The most frequent IGHV gene was IGHV4-59/61, rarely used in CLL, whereas the IGHV1-69 gene was lacking and the IGHV4-34 gene was infrequent. Only 2 of 51 (3.9%) MBL cases expressed a CLL-specific stereotyped HCDR3. Therefore, the IG gene repertoire in low-count MBL differs from both mutated and unmutated CLL, suggesting that the detection of MBL in an otherwise healthy subject is not always equivalent to a preleukemic state. Detailed IG analysis of individual MBL may help to identify cases that necessitate continuous clinical monitoring to anticipate disease progression.

The human major histocompatibility complex and childhood leukemia: an etiological hypothesis based on molecular mimicry.

The extended human major histocompatibility complex (MHC) is a gene-rich region of about 7.6 Mb on chromosome 6, and includes a high proportion of genes involved in the immune response. Among these are the two Human Leukocyte Antigen (HLA) gene clusters, class I and class II, which encode highly polymorphic classical HLA-A, B, C and HLA-DR, DQ and DP genes, respectively. The protein products of the classical HLA genes are heterodimeric cell surface molecules that bind short peptides derived from non-self and self proteins, including infections and auto-antigens. The presentation of these HLA-anchored peptides to T lymphocytes triggers a cascade of responses in immune-associated genes that leads to adaptive immunity. Associations between HLA class II alleles and childhood leukemia have been reported in a number of studies. This could be due to the role of HLA allele-restricted peptide binding and T cell activation, or linkage disequilibrium to an MHC-linked "leukemia gene" in the pathogenesis of childhood leukemia. Efforts are currently in progress to resolve these questions, using large leukemia case-control sample series such as the UK Childhood Cancer Study (UKCCS) and the Northern California Childhood Leukemia Study (NCCLS). Here we review the background to these studies, and present a novel hypothesis based on the paradigm of HLA-associated auto-immune disease that might explain an infection-based etiology of childhood leukemia.

Structurally distinct ligand-binding or ligand-independent Notch1 mutants are leukemogenic but affect thymocyte development, apoptosis, and metastasis differently.

We previously found that provirus insertion in T cell tumors of mouse mammary tumor virus/c-myc transgenic (Tg) mice induced two forms of Notch1 mutations. Type I mutations generated two truncated molecules, one intracellular (IC) (Notch1(IC)) and one extracellular (Notch1(EC)), while in type II mutations Notch1 was deleted of its C terminus (Notch1(DeltaCT)). We expressed these mutants in Tg mice using the CD4 promoter. Both Notch1(IC) and Notch1(DeltaCT), but not Notch1(EC), Tg mice developed double-positive (DP) thymomas. These disseminated more frequently in Notch1(DeltaCT) Tg mice. Double (Notch1(IC) x myc) or (Notch1(DeltaCT) x myc) Tg mice developed thymoma with a much shorter latency than single Tg mice, providing genetic evidence of a collaboration between these two oncogenes. FACS analysis of preleukemic thymocytes did not reveal major T cell differentiation anomalies, except for a higher number of DP cells and an accumulation of TCR(high)CD2(high)CD25(high) DP cells in Notch1(IC), and less so in Notch1(DeltaCT) Tg mice. This was associated with enhanced in vivo thymocyte proliferation. However, Notch1(IC), but not Notch1(DeltaCT), DP thymocytes were protected against apoptosis induced in vivo by dexamethasone and anti-CD3 and in vitro by anti-CD3/CD28 Abs. This indicates that the C terminus of Notch1 and/or the conserved regulation by its ligands have a significant impact on the induced T cell phenotype. Therefore, Notch1(IC) and Notch1(DeltaCT) behave as oncogenes for T cells. Because these two Notch1 mutations are very similar to those described in some forms of human T cell leukemia, these Tg mice may represent relevant models of these human leukemias.

BASH-novel PKC-Raf-1 pathway of pre-BCR signaling induces kappa gene rearrangement.

The pre-B-cell receptor (pre-BCR) is thought to signal transcriptional activation of the immunoglobulin light (L) chain gene locus, proceeding to its V-J rearrangement. The pre-BCR signaling pathway for this process is largely unknown but may involve the adaptor protein BASH (BLNK/SLP-65). Here we report that the pre-B leukemia cell lines established from affected BASH-deficient mice rearrange kappaL-chain gene locus and down-regulate pre-BCR upon PMA treatment or BASH reconstitution. Analyses with specific inhibitors revealed that activation of novel PKC (nPKC) and MEK, but not Ras, is necessary for the rearrangement. Accordingly, retroviral transduction of active PKCeta, PKCepsilon, or Raf-1, but not Ras, induced the kappa gene rearrangement and expression in the pre-B-cell line. Tamoxifen-mediated BASH reconstitution resulted in the translocation of PKCeta to the plasma membrane and kappa chain expression. These data make evident that the Ras-independent BASH-nPKC-Raf-1 pathway of pre-BCR signaling induces the L-chain gene rearrangement and expression.

New CFSE-based assay to determine susceptibility to lysis by cytotoxic T cells of leukemic precursor cells within a heterogeneous target cell population.

For the clinical evaluation of the efficacy of cellular immunotherapy it is necessary to analyze the effector functions of T cells against primary leukemic target cell populations which are usually considerably heterogeneous caused by differential maturation stages of the leukemic cells. An appropriate assay should not only allow the quantitative analysis of rapid cell death induction as measured by the conventional 51Cr release assay but also of the more slowly executing pathways of T-cell-induced apoptosis occurring within days instead of hours which cannot be measured using this method. Furthermore, it should dissect the differential susceptibility to T-cell-induced cell death of various target cell subpopulations and characterize the malignant precursor cells capable of producing malignant progeny. To fulfill these requirements we developed a new assay based on carboxyfluorescein diacetate succinimidyl ester (CFSE) labeling of the target cell population combined with antibody staining of specific cell populations and addition of fluorescent microbeads to quantitatively monitor target cell death occurring within a longer time frame up to at least 5 days. This new assay facilitates the analysis of differential recognition of distinct cell types within a heterogeneous target cell population and allows simultaneously evaluation of the proliferative status of surviving target cells in response to relevant cytokines.

B cell chronic lymphocytic leukemia: lessons learned from studies of the B cell antigen receptor.

B cell chronic lymphocytic leukemia (B-CLL) is an accumulative disease of slowly proliferating CD5(+) B lymphocytes that develops in the aging population. Whereas some patients with B-CLL have an indolent course and die after many years from unrelated causes, others progress very rapidly and succumb within a few years from this currently incurable leukemia. Over the past decade studies of the structure and function of the B cell antigen receptor (BCR) used by these leukemic cells have helped redefine the nature of this disease. In this review we summarize and reinterpret several aspects of these BCR-related studies and how they might relate to the disease. In particular, we address the ability of antigens to select out and drive B cell clones from the normal state to overt leukemic cells by binding to BCRs that are relatively unique and characteristic of B-CLL cells. The differential capacity of some B-CLL cases to continue to transduce signals through the BCR during the leukemic phase and the consequences for the in vivo biology of the leukemic clone is also considered. Finally, we discuss current and emerging views of the cellular origin of B-CLL cells and the differentiation pathways down which we believe these cells progress.

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 with MLL 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 V(D)2-D(D)3 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.

Immunotoxins against CD19 and CD22 are effective in killing precursor-B acute lymphoblastic leukemia cells in vitro.

Monoclonal antibodies (Mabs) conjugated to toxins or their subunits (immunotoxins or ITs) are undergoing clinical testing in adults with a variety of malignancies. The potential impact of this form of therapy in pediatric precursor B-lineage acute lymphoblastic leukemia (pre-B ALL) has yet to be determined. Mabs directed against the cell surface antigens, CD19 and CD22 conjugated to deglycosylated ricin A chain (dgRTA) have been tested in patients with non-Hodgkin's lymphoma (NHL), but not in patients with pre-B ALL. Because of the encouraging performance of these ITs in phase I trials, we evaluated the specific cytotoxicity of anti-CD19 (HD37-dgRTA) and anti-CD22 (RFB4-dgRTA) ITs or their combination (Combotox) on patient-derived pre-B ALL cells maintained in vitro on a stromal feeder layer. After 48 h in culture, cytotoxicity to tumor cells was determined by flow cytometry using propidium iodide (PI) and fluorescein isothiocyanate (FITC)-conjugated anti-CD10, 19, and 22. Both RFB4-dgRTA and HD37-dgRTA induced a statistically significant reduction in the number of viable leukemic cells, and Combotox was even more effective. Our results demonstrate that these ITs are specifically cytotoxic to primary pre-B ALL cells and that they should be further evaluated for the therapy of B-lineage ALL.

CD3xCD19 bispecific antibodies and CD28 bivalent antibodies enhance T-cell reactivity against autologous leukemic cells in pediatric B-ALL bone marrow.

Bispecific CD3xCD19 antibodies and CD28 co-stimulating antibodies were used to activate T cells in bone marrow aspirates (n = 8) of children with B cell-derived acute lymphoblastic leukemia. Bone marrow specimens were incubated for 10 days with CD3xCD19 bispecific and CD28 antibodies. Changes in the numbers of T lymphocytes and tumoral B cells as well as surface expression of T cell-activation markers were determined by flow cytometry, and cytokines (human IFN-gamma, IL-2, IL-4 and IL-12) were measured in the cell culture supernatant. In 7 of 8 bone marrow samples, an increase in the number of CD4- and CD8-positive T lymphocytes was found, which correlated with an up-regulation of T cell-activation markers. Additionally, we demonstrated a decrease of tumoral B cells in 3 samples and enhanced cytotoxic T-cell activity against autologous malignant B cells. ELISpot analyses in an autologous Epstein-Barr virus model showed that bispecific antibodies (CD3xCD19+CD28) were more potent at generating T-cell responses against autologous and allogeneic tumoral targets than a combination of monospecific antibodies (CD3+CD28). Thus, T-cell targeting by CD3xCD19 bispecific and CD28 antibodies may be used to eliminate leukemic B cells ex vivo and reconstitute immunological control of residual malignant disease by the induction of anti-tumoral T-cell responses.

[Myelodysplastic syndromes: preleukemic syndromes]. / Les syndromes myélodysplasiques: syndromes préleucémiques.

The myelodysplastic syndromes (MDS) are a heterogeneous group of disorders characterized by peripheral blood cytopenias with a hypercellular bone marrow exhibiting dyspoiesis. The predominant in elderly patients are associated with a high risk of progression to acute myelogenous leukemia. The etiology of MDS is unknown in most cases. About 10% of MDSs are secondary. MDS are classified by the French American British (FAB) classification into five subgroups. The incidence of the disorders is difficult to estimate but it seems to be increasing. Clonal cytogenetic aberrations are found in 30 to 50% of de novo MDS. The only currative treatment for MDS is allogeneic bone marrow transplantation.

Ex vivo generation of human anti-pre-B leukemia-specific autologous cytolytic T cells.

In contrast to other neoplasms, antigen-specific autologous cytolytic T cells have not been detected in patients with human pre-B-cell leukemias. The absence of efficient B7 family (B7-1/CD80; B7-2/CD86) -mediated costimulation has been shown to be a major defect in tumor cells' capacity to function as antigen-presenting cells. We show here the generation of autologous anti-pre-B-cell leukemia-specific cytolytic T-cell lines from the marrows of 10 of 15 patients with pre-B-cell malignancies. T-cell costimulation via CD28 is an absolute requirement for the generation of these autologous cytolytic T cells (CTL). Although costimulation could be delivered by either bystander B7 transfectants or professional antigen-presenting cells (indirect costimulation), optimal priming and CTL expansion required that the costimulatory signal was expressed by the tumor cell (direct costimulation). These anti-pre-B-cell leukemia-specific CTL lysed both unstimulated and CD40-stimulated tumor cells from each patient studied but did not lyse either K562 or CD40-stimulated allogeneic B cells. Cytolysis was mediated by the induction of tumor cell apoptosis by CD8+ T cells via the perforin-granzyme pathway. Although we were able to generate anti-leukemia-specific CTL from the bone marrow, we were unable to generate such CTL from the peripheral blood of these patients. These studies show that antigen-specific CTL can be generated from the bone marrow of patients with pre-B-cell leukemias and these findings should facilitate the design of adoptive T-cell-mediated immunotherapy trials for the treatment of patients with B-cell precursor malignancies.

Disruption of T-cell differentiation precedes T-cell tumor formation in LMO-2 (rhombotin-2) transgenic mice.

Transgenic mice expressing LMO-2 (rhombotin-2) were constructed by placing the LMO-2 gene under control of the metallothionein promoter. Thymic tumors developed in approximately 15% of the transgenic mice between 37 and 71 weeks. Only T-cell tumors were found in the transgenic mice despite high expression of LMO-2 in all tissues. The thymic tumors were aggressive and were invariably associated with metastasis to non-lymphoid organs. In approximately 50% of apparently healthy transgenic mice there was up to a 10-fold expansion of CD4-CD8- double negative (DN) cells. Expansion of the DN cells was accompanied by the compensatory decrease in CD4+CD8+ double positive (DP) cells, indicating that breach of homeostasis within the thymus had not occurred in these animals. The increase in DN cells was associated with a clonal expansion of thymocytes, and increased proliferation within the thymus. Our data indicate that the ectopic expression of LMO-2 in T-cells disrupts normal T-cell differentiation by selectively expanding the DN thymocyte population prior to breach of homeostasis and overt leukemia/lymphoma.

In vitro modulation of preleukemic AKR mouse macrophage function by bacterial immunomodulators.

Spleen macrophages from 1- and 4-month-old preleukemic AKR mice were stimulated in vitro with the bacterial immunomodulators lipopolysaccharide (LPS), peptidoglycan monomer (PGM) and muramyl dipeptide (MDP), in order to study their migration ability and mitochondrial enzyme activity. Macrophages from 1-month-old AKR mice, characterized by higher functional activity, failed to demonstrate any changes in the parameters studied after in vitro stimulation with the employed compounds. Conversely, the depressed macrophage function, spontaneously developed in 4-month-old AKR mice, most probably related to the preleukemic state, improved significantly and to about the same extent with all three immunomodulators.

Poor prognosis of prethymic phenotype acute lymphoblastic leukemia (pre-T-ALL).

Pre-T-ALL is an important subgroup of ALL with clinical features different from adult T-ALL. Expression of intracytoplasmic CD3 represents the earliest marker for the prethymic phenotype. We studied four consecutive adult patients with this phenotype. Three of the four patients did not respond to the induction chemotherapy with vincristine, daunorubicin, prednisone and asparaginase. They reached a delayed remission only after chemotherapy with cyclophosphamide and cytosine arabinoside. All four patients relapsed 3, 9, 10 and 13 months after diagnosis. One patient died 2 months after relapse, another one 2 months after allogeneic BMT performed in second relapse. We conclude that patients with early T-cell precursor leukemia do not respond adequately to conventional chemotherapy and should be considered as a high-risk subgroup within the T-lineage ALL.

Clinical course of human T-lymphotropic virus type I carriers with molecularly detectable monoclonal proliferation of T lymphocytes: defining a low- and high-risk population.

To characterize the prodromal phase of adult T-cell leukemia (ATL), a prospective follow-up study was conducted on 50 carriers in a putative pre-ATL state. This state was defined by the presence of molecularly-detectable monoclonal proliferation of human T-lymphotropic virus type I (HTLV-I)-infected T lymphocytes, and the absence of clinical symptoms of leukemia. The median observation time was 50 months. The pre-ATL subjects were divided into two groups according to initial white blood cell (WBC) counts: group A, those with a normal WBC count (9,000/microL) (n = 30), and group B, those with an increased WBC count (9,000 to 15,000) (n = 20). Comparisons were made between the two groups and with a group of 25 patients with chronic ATL (group C) who had WBC counts of more than 15,000. Significant differences in survival rate were found between groups A and B (10-year survival 65.7%) and group C (32.8%) (P < .01), and between group A (10-year survival 90.0%) and group B (52.1%) (P < .05). The incidence of transformation to overt ATL was 10% (3 of 30) in group A and 50% (10 of 20) in group B (P < .01). In six transformed cases (one in A and five in B) we found exactly the same integration sites in pre-ATL and overt ATL phases, confirming the multistep leukemogenesis hypothesized for this disease. However, the pre-ATL subjects could be divided into two distinct prognostic groups based on the initial WBC count; those with good and those with poor prognosis. Although the 10% transformation rate (2.5% annually) in group A seemed to be extremely high compared with that in the general population of HTLV-I carriers (around 0.06% to 0.4% annually), the majority of group A subjects and some in group B showed stable clinical courses without transformation. Further, development of ATL was not observed in four group A subjects with HTLV-I-associated myelopathy (HAM), which is rarely associated with ATL. We propose to call this group of rather benign HTLV-I carriers "HTLV-I carriers with monoclonal proliferation of T lymphocytes (HCMPT)." Thus far we have been unable to identify reliable parameters other than WBC counts that prospectively distinguish HCMPT from the true pre-ATL state, in which there is a high probability of developing ATL. Further clinical and biologic approaches should elucidate the natural history of the HTLV-I carrier state and early events in ATL leukemogenesis.

Childhood acute lymphocytic leukemia with a preleukemic phase: report of an associated translocation and review of the literature.

A fourteen month old boy presented with hepatosplenomegaly and pancytopenia. An extensive evaluation, including bone marrow aspiration and biopsies of both liver and lymph nodes, revealed a polyclonal B cell proliferation consistent with a reactive process, with no evidence of leukemia. After receiving transfusions of red cells and platelets, his blood counts recovered. Five weeks later, he returned with an elevated white blood count and bone marrow findings diagnostic of acute lymphocytic leukemia. The leukemic blasts contained a novel chromosomal translocation, t(5;14) (q34;q12). We describe the clinical, immunophenotypic and cytogenetic features of this case, review the literature of acute lymphocytic leukemia associated with a preleukemic phase, and discuss the relationship of this clinical entity to the 5q-abnormality associated with myelodysplasia.