Insights into the manifestations, outcomes, and mechanisms of leukemogenesis in Down syndrome

Children with Down syndrome (DS) show a spectrum of clinical anomalies, including cognitive impairment, cardiac malformations, and craniofacial dysmorphy. Moreover, hematologists have also noted that these children commonly show macrocytosis, abnormal platelet counts, and an increased incidence of transient myeloproliferative disease (TMD), acute megakaryocytic leukemia (AMKL), and acute lymphoid leukemia (ALL). In this review, we summarize the clinical manifestations and characteristics of these leukemias, provide an update on therapeutic strategies and patient outcomes, and discuss the most recent advances in DS-leukemia research. With the increased knowledge of the way in which trisomy 21 affects hematopoiesis and the specific genetic mutations that are found in DS-associated leukemias, we are well on our way toward designing improved strategies for treating both myeloid and lymphoid malignancies in this high-risk population.

TEL-AML1 preleukemic activity requires the DNA binding domain of AML1 and the dimerization and corepressor binding domains of TEL

The t(12;21)(p13;q22) translocation generates the TEL-AML1 (TEL, translocation-Ets-leukemia; AML1, acute myeloid leukemia-1) (ETV6-RUNX1) fusion product and is the most common chromosomal abnormality in pediatric leukemia. Our previous studies using a murine fetal liver transplantation model demonstrated that TEL-AML1 promotes the self-renewal of B-cell precursors in vitro and enhances the expansion of hematopoietic stem cells (HSCs) in vivo. This is consistent with the hypothesis that TEL-AML1 induces expansion of a preleukemic clone. Several studies have described domains within TEL-AML1 involved in the transcriptional regulation of specific target genes. However, it is unclear which of these domains is important for the activity of TEL-AML1 in preleukemic hematopoiesis. In order to examine this, we have generated a panel of deletion mutants and expressed them in HSCs. These experiments demonstrate that TEL-AML1 requires multiple domains from both TEL and AML1 to alter hematopoiesis. Furthermore, mutation of a single amino-acid residue within the runt homology domain of AML1, required for DNA binding, was sufficient to abrogate TEL-AML1 activity. These data suggest that TEL-AML1 acts as an aberrant transcription factor to perturb multiple pathways during hematopoiesis.

TEL-AML1 promotes development of specific hematopoietic lineages consistent with preleukemic activity

The t(12;21)(p13;q22) translocation is the most common chromosomal abnormality yet identified in any pediatric leukemia and gives rise to the TEL-AML1 fusion product. To investigate the effects of TEL-AML1 on hematopoiesis, fetal liver hematopoietic progenitor cells (HPCs) were transduced with retroviral vectors expressing this fusion protein. We show that TEL-AML1 dramatically alters differentiation of HPCs in vitro, preferentially promoting B-lymphocyte development, enhancing self-renewal of B-cell precursors, and leading to the establishment of long-term growth factor-dependent pre-B-cell lines. However, it had no effect on myeloid development in vitro. Further experiments were performed to determine whether TEL-AML1 also demonstrates lineage-specific activity in vivo. TEL-AML1-expressing HPCs displayed a competitive advantage in reconstituting both B-cell and myeloid lineages in vivo but had no effect on reconstitution of the T-cell lineage. Despite promoting these alterations in hematopoiesis, TEL-AML1 did not induce leukemia in transplanted mice. Our study provides a unique insight into the role of TEL-AML1 in leukemia predisposition and a potential model to study the mechanism of leukemogenesis associated with this fusion.

Lack of circulating megakaryoblasts in newborn peripheral blood: development and validation of a sensitive flow cytometric detection method

It is currently thought that approximately 1% of children with Down syndrome will develop a "premalignant" syndrome known as transient myeloproliferative disorder (TMD). Prospective, population-based studies of the incidence of TMD in Down syndrome infants is lacking. Although most cases of TMD resolve by 1 year of age, data suggest that 10% to 20% of Down syndrome patients with TMD develop AML-M7 (megakaryoblastic leukemia). To identify the true incidence of TMD in the Down syndrome population, a sensitive, rapid, and cost-effective method of quantifying circulating megakaryoblasts in large numbers of patients was needed. In this pilot study, the authors tested the hypothesis that there are fewer than 1% megakaryoblasts of nucleated cells circulating in the blood of normosomic infants. Four-antigen flow cytometry was used to establish the percentage of megakaryoblasts present in each of 100 cord blood samples collected blindly from "normosomic" live births. There was a mean percentage of 0.017% megakaryoblasts in 100 cord blood samples from normosomic infants. Flow cytometry proved to be a sensitive, rapid, and reproducible method for the quantification of megakaryoblasts. Less than 1% of circulating nucleated cells in the blood of newborn infants are megakaryoblasts, providing a comparison population for the authors' larger proposed incidence study.

Protein kinase C mediates mutant N-Ras-induced developmental abnormalities in normal human erythroid cells

RAS mutations are one of the most frequent molecular abnormalities associated with myeloid leukemia and preleukemia, yet there is a poor understanding of how they contribute to the pathogenesis of these conditions. Here, we describe the consequences of ectopic mutant N-Ras (N-Ras*) expression on normal human erythropoiesis. We show that during early (erythropoietin [EPO]-independent) erythropoiesis, N-Ras* promoted the amplification of a phenotypically primitive but functionally defective subpopulation of CD34(+) erythroblasts. N-Ras* also up-regulated the expression of megakaryocyte antigens on human erythroblasts. Although early erythroblasts expressing N-Ras* were able to respond to erythropoietin and generate mature progeny, this occurred with greatly reduced efficiency, probably explaining the poor colony growth characteristics of these cells. We further report that this oncogene promoted the expression and activation of protein kinase C (PKC) and that the effects of N-Ras* on erythropoiesis could be abrogated or attenuated by inhibition of PKC. Similarly, the effects of this oncogene could be partially mimicked by treatment with PKC agonist. Together, these data suggest that expression of N-Ras* is able to subvert the normal developmental cues that regulate erythropoiesis by activating PKC. This gives rise to phenotypic and functional abnormalities commonly observed in preleukemia, suggesting a direct link between RAS mutations and the pathogenesis of preleukemia.

[Preleukemic states: an experimental murine model for myelodysplastic human syndromes]

Using a model of experimental leukemia in mice, we have demonstrated that tumor development depends upon interactions between preleukemic cells and their microenvironment whose functions are altered. Cytokine injections inhibit tumor development by inducing a functional restoration of this environment. Human myelodysplastic syndromes (MDS) are marrow pathologies considered as preleukemic stages. As in murine leukemias, it is possible that marrow environment could play a key role in their evolution. We currently establish a model of human hematopoiesis in NOD/SCID mice grafted with human bone fragments. We hope that this model would allow to analyse the role of the marrow stromal cells in MDS and to establish treatments restoring their functions.

[Leukemia and pre-leukemic conditions occurring after treatment of breast cancer]

OBJECTIVE

The purpose of this study was to determine the clinical and prognostic features of leukemias and preleukemic states, whatever the mode of development, observed in patients after treatment of breast cancer.

PATIENTS AND METHODS

A retrospective multicentric analysis was made of 121 patients treated for breast cancer and who later developed leukemia or a preleukemic state. Initially, 44 patients had undergone mastectomy, 72 had conservative surgery and 119 had locoregional irradiation. At least one chemotherapy session was performed in 90 patients and 48 had received tamoxifen. The risk of relapse of breast cancer was high, moderate or low for 44, 46 and 24 patients respectively (data not available for 7 patients).

RESULTS

By class, the hematology diseases found were: myelodysplasia (n = 9), refractory anemia with blast excess (n = 7), acute lymphoblastic leukemia (n = 6), acute myoblastic leukemia (n = 93 including a majority of type 2 and type 4). For acute myeloblastic leukemia, mean delay to onset was 65 and 37 months respectively without and after chemotherapy. The prognosis of these cases of leukemia and preleukemic states was poor with an overall death rate of 86%.

CONCLUSION

In light of the recent development of indications for adjuvant chemotherapy even for subgroups of patients at moderate risk, it is important to more precisely assess the absolute benefit in terms of survival compared with the risk of severe complications, particular secondary leukemia. In the future, a systematic registry and a case-control study are required.

[The characteristics of the pre- and leukemic stages of chronic myeloproliferative diseases in persons suffering as a result of the Chernobyl catastrophe]

Clinical, morphological and cytogenetic investigations were done in those patients with leukocytosis having become victims of the Chernobyl catastrophe. Of these (n = 10), six patients demonstrated chromosomal abnormalities. In the study made at a later date in six patients with cytogenetic abnormalities, five patients were found to have chronic myeloproliferative disorders, with four cases presenting with chronic myeloid leukemia and one patient having osteomyelofibrosis.

Possible retroviral origin of prion disease: could prion disease be reconsidered as a preleukemia syndrome?

A retroviral etiology might explain why amyloid plaque and/or spongiosis are or are not associated with neuronal death in prion diseases. While retroviral genes themselves may be responsible for neuronal death, a retrovirus may also cause mutations in cellular genes. Hence, the prion gene may be altered by a retrovirus in the same way as a cellular proto-oncogene is altered to produce an oncogene, either by transduction or by integration of the provirus in its vicinity. In both cases, the resulting abnormal prion protein, acting as a catalyst, may induce the formation of amyloid plaques. In addition, a wild type retrovirus may recombine to the vesicular stomatitis virus (VSV) to give rise to a pseudotyped retrovirus able to induce spongiosis. It is reported here that in scrapie, a blood monocytoid cell proliferates in vitro. If confirmed in other species, this raises the question of the potential link between prion disease and leukemia. Indeed neurovirulent strains of murine leukemia virus, a slow acting retrovirus, are known to induce spongiform encephalopathies. A preliminary attempt to purify reverse transcriptase by chromatography, using the classical protocol, failed because of the presence of a prion-like protein secreted by the blood mononuclear cells which stuck to the phosphocellulose column. Therefore, if a retrovirus is present in prion diseases, it would be evidenced only in animals developing the disease in the absence of prion protein. From this point of view, mice obtained in 1997 by the group of D. Dormont in France, offer a unique opportunity to test the retroviral hypothesis.

Pancytopenic prodrome (pre-ALL) of acute lymphoblastic leukemia in adults: possible pathogenesis

We report two cases of adult acute lymphoblastic leukemia presenting with preleukemic phase of pancytopenia with a few abnormal lymphoid cells in bone marrow aspirates. The initial diagnosis of each case was suspicious aplastic anemia and hypoplastic anemia. Both cases progressed to overt acute lymphoblastic leukemia within 1 year. We suggest that initial pancytopenic phase (pre-ALL) may precede the diagnosis of acute lymphoblastic leukemia in adults and differential diagnosis from myelodysplastic syndrome and primary aplastic anemia will be needed. We also suggest that primary bone marrow lymphoma and "primary unknown metastatic lymphoma of bone marrow" may be possible as the pathogenesis in a case like ours.

A fludarabine-based protocol for bone marrow transplantation in Fanconi's anemia

Allogeneic bone marrow transplantation (BMT) is an effective therapy for Fanconi's anemia (FA). However, mortality and transplant-related complications are usually high due to increased sensitivity to the alkylating agents and radiation commonly used for pre-transplant conditioning. Fludarabine monophosphate is a purine analogue that has been proven effective as a conditioning agent for chronic lymphocytic leukemia patients. We report a child with FA in leukemic transformation with thrombocytopenia and 20% myeloblasts who underwent successful BMT following conditioning with fludarabine/ATG/cyclophosphamide. The regimen was well tolerated, no transplant-related complications were observed, and engraftment was rapid. The child is currently 10 months post-BMT, in excellent clinical condition with a normal blood count, 100% chimerism and no sign of graft-versus-host disease (GVHD). We suggest that this fludarabine-based regimen may be effective in the conditioning of standard, as well as transforming, FA patients for BMT.

Mutant N-RAS induces erythroid lineage dysplasia in human CD34+ cells

RAS mutations arise at high frequency (20-40%) in both acute myeloid leukemia and myelodysplastic syndrome (which is considered to be a manifestation of preleukemic disease). In each case, mutations arise predominantly at the N-RAS locus. These observations suggest a fundamental role for this oncogene in leukemogenesis. However, despite its obvious significance, little is known of how this key oncogene may subvert the process of hematopoiesis in human cells. Using CD34+ progenitor cells, we have modeled the preleukemic state by infecting these cells with amphotropic retrovirus expressing mutant N-RAS together with the selectable marker gene lacZ. Expression of the lacZ gene product, beta-galactosidase, allows direct identification and study of N-RAS-expressing cells by incubating infected cultures with a fluorogenic substrate for beta-galactosidase, which gives rise to a fluorescent signal within the infected cells. By using multiparameter flow cytometry, we have studied the ability of CD34+ cells expressing mutant N-RAS to undergo erythroid differentiation induced by erythropoietin. By this means, we have found that erythroid progenitor cells expressing mutant N-RAS exhibit a proliferative defect resulting in an increased cell doubling time and a decrease in the proportion of cells in S + G2M phase of the cell cycle. This is linked to a slowing in the rate of differentiation as determined by comparative cell-surface marker analysis and ultimate failure of the differentiation program at the late-erythroblast stage of development. The dyserythropoiesis was also linked to an increased tendency of the RAS-expressing cells to undergo programmed cell death during their differentiation program. This erythroid lineage dysplasia recapitulates one of the most common features of myelodysplastic syndrome, and for the first time provides a causative link between mutational activation of N-RAS and the pathogenesis of preleukemia.

Leukemogenesis by Moloney murine leukemia virus: a multistep process

Moloney murine leukemia virus is a prototypical simple retrovirus that has been an extremely useful model for leukemogenesis. Important steps in leukemogenesis include proviral activation of cellular proto-oncogenes, generation of mink cell focus-inducing recombinants, and early (preleukemic) virus-induced changes in hematopoiesis.

A new immunobiological view of radiation-promoted lymphomagenesis

Whole-body irradiation produces T-cell leukaemias/ lymphomas (TCL) in some strains of inbred mice in an X-ray dose-related manner. Radiation biologists have related the rapid "initiation' and early appearance of preleukaemic cells in these mice to unrepaired DNA damage inflicted by radiation. Following initiation, radiation-altered thymic differentiation fosters multi-step transformation changes in proto-oncogenes and suppressor gene expression in individual clones of non-invasive preleukaemia cells as they progress to malignancy. The malignant clones arising from small numbers of initiated preleukaemia thymocytes become fully transformed only after several more months to a year after irradiation in those strains of mice which develop T-cell lymphomas. When the RFM mouse was subjected to sublethal whole-body X-ray, only 50% of the mice developed TCL by 6 months, yet nearly all developed preleukaemia thymocytes. The T-cell-mediated immune response of the irradiated host has never been substantiated to contribute to malignant TCL development. Until recently, X-ray-induced TCL were not known to carry common tumour rejection antigens TATA. However, several studies have revealed that both preleukaemia cells and fully malignant TCL express an immunogenic, common oncofoetal glycoprotein, termed 44kD OFA. OFA-activated memory CD4 Tm and CD8 Ten. T-effector cells in irradiated mice expressing OFA. As most irradiated RFM mice exhibit preleukaemia thymocytes yet only half develop tumours, this finding implicates active host T-cell effector responses in X-ray-initiated tumorigenesis. Further, the recent discovery of OFA-specific CD8 Ts clones in irradiated mice, which inhibited cytotoxicity of CD8 clones to OFA or TSTA, may explain which mice develop T-cell lymphomas.

The process of leukemogenesis

Leukemias are monoclonal diseases that arise from cells in the hematopoietic stem and progenitor cell compartment. Consistent with emerging models of carcinogenesis, leukemogenesis is an evolutionary process that involves multiple independent genetic and epigenetic events. Over the last half-century a predominant paradigm has emerged to describe leukemia developing secondary to alkylating drug therapy or exposure to benzene in which progressive dysplastic changes, accompanied by a distinct pattern of clonal cytogenetic abnormalities, give rise to acute myelogenous leukemia. Characterization of these clonal chromosomal aberrations, together with observed alterations in other growth-promoting genes, provides a useful framework for studying chemical leukemogenesis and for use in understanding the origins and development of leukemia in general.

Secondary leukaemias. Clinical and cytobiological aspects

Patients treated with radiation and cytotoxic agents for a variety of neoplastic conditions develop with increased frequency a secondary leukaemia, usually a form of acute myeloblastic leukaemia. The authors illustrate and discuss the various morphological and cytobiological which characterize the "preleukaemic phase", and which comprise myelodysplastic alterations, cytochemical abnormalities, concerning the presence of glycogen and free iron in the red cell series, as well as a number of changes in enzymatic activities in the myeloid series, cytokinetic changes, indicative of accumulation of cells in G0 and G1, cytogenetic non-random abnormalities, involving specific chromosomes, and finally in vitro cultures which show a reduction in colony formation. The authors underline the differences between primary and secondary preleukaemic myelodysplastic states, consisting in the presence in the latter of frequent hypocellularity, fibrosis and almost invariability a clear involvement of multiple cell lines.

A multistep process of leukemogenesis in Moloney murine leukemia virus-infected mice that is modulated by retroviral pseudotyping and interference

Mixed retroviral infections frequently exhibit pseudotyping, in which the genome of one virus is packaged in a virion containing SU proteins encoded by another virus. Infection of mice by Moloney murine leukemia virus (M-MuLV), which induces lymphocytic leukemia, results in a mixed viral infection composed of the inoculated ecotropic M-MuLV and polytropic MuLVs generated by recombination of M-MuLV with endogenous retroviral sequences. In this report, we describe pseudotyping which occurred among the polytropic and ecotropic MuLVs in M-MuLV-infected mice. Infectious center assays of polytropic MuLVs released from splenocytes or thymocytes of infected mice revealed that polytropic MuLVs were extensively pseudotyped within ecotropic virions. Late in the preleukemic stage, a dramatic change in the extent of pseudotyping occurred in thymuses. Starting at about 5 weeks, there was an abrupt increase in the number of thymocytes that released nonpseudotyped polytropic viruses. A parallel increase in thymocytes that released ecotropic M-MuLV packaged within polytropic virions was also observed. Analyses of the clonality of preleukemic thymuses and thymomas suggested that the change in pseudotyping characteristics was not the result of the emergence of tumor cells. Examination of mice infected with M-MuLV, Friend erythroleukemia virus, and a Friend erythroleukemia virus-M-MuLV chimeric virus suggested that the appearance of polytropic virions late in the preleukemic stage correlated with the induction of lymphocytic leukemia. We discuss different ways in which pseudotypic mixing may facilitate leukemogenesis, including a model in which the kinetics of thymic infection, modulated by pseudotyping and viral interference, facilitates a stepwise mechanism of leukemogenesis.

Leukemogenic risk of hydroxyurea therapy in polycythemia vera, essential thrombocythemia, and myeloid metaplasia with myelofibrosis

In polycythemia vera (PV), treatment with chlorambucil and radioactive phosphorus (p32) increases the risk of leukemic transformation from 1% to 13-14%. This risk has been estimated to be 1-5.9% with hydroxyurea (HU) therapy. When compared with historical controls, the risk with use of HU does not appear to be statistically significant. The leukemogenic risk of HU therapy in essential thrombocytosis (ET) and in myelofibrosis with myeloid metaplasia (MMM) is unknown. HU remains the main myelotoxic agent in the treatment of PV, ET, and MMM. We studied 64 patients with these three disorders, seen at our institution during 1993-1995. The patients were studied for their clinical characteristics at diagnosis, therapies received, and development of myelodysplasia or acute leukemia (MDS/AL). Forty-two had PV, 15 ET, and 6 MMM, and 1 had an unclassified myeloproliferative disorder. Of the 42 patients with PV, 18 were treated with phlebotomy alone, 16 with HU alone, 2 with p32, 2 with multiple myelotoxic agents, and 2 with interferon-alpha (IFN-alpha). Two patients from the phlebotomy-treated group, one from the HU-treated group, and 1 from the multiple myelotoxic agent-treated group developed MDS/AL. In the larger group, 11 received no treatment or aspirin alone, 18 were treated with phlebotomy alone, 25 with HU, 5 with multiple myelotoxic agents, 2 with p32, 2 with IFN-alpha, and 1 with melphalan. Study of the entire group of 64 patients showed that only one additional patient (total of 5 out of 64) developed MDS/AL. This patient had been treated with HU alone. Statistical analysis did not show any association between clinical characteristics at diagnosis, or HU therapy, and development of MDS/AL (P=0.5). Thus, our data provide no evidence suggestive of increased risk of transformation to MDS/AL with HU therapy in PV, ET, and MMM. Larger, prospective studies are needed to study this issue further.

Spontaneous and induced apoptosis after whole body radiation exposure: experimental approaches. Observations in radio-induced thymic lymphomagenesis

Radio-induced thymic lymphomagenesis is associated with alterations in the balance between thymocyte subsets and cytokinetic perturbations. The objectives of this work were to investigate whether these alterations are associated with alterations in the basic levels of thymocyte apoptosis. For this purpose, we tested DNA fragmentation by gel electrophoresis, analyzed DNA content by propidium iodide staining of ethanol fixed cells and looked for DNA strand breaks on tissue sections by in situ end labeling. We described an increase of the levels of apoptosis in cultured thymocytes during the preleukemic period, while the basic levels of apoptosis observed in situ are similar in normal and in preleukemic thymuses. We propose that after leukemogenic irradiations, there is an increase of cells wherein the cell suicide program is activated but that environmental thymic factors rescue them from apoptosis. Preleukemic cells could belong to this abnormally surviving population of cells "programmed to die," wherein additional genomic abnormalities would lead to fully neoplastic transformation.

The leukemogenic potential of an enhancer variant of Moloney murine leukemia virus varies with the route of inoculation

We previously showed that the Mo+PyF101 variant of Moloney murine leukemia virus (M-MuLV) is poorly leukemogenic when inoculated subcutaneously (s.c.) into neonatal mice. We recently found that intraperitoneal (i.p.) inoculation of neonatal mice with the same virus significantly enhanced its leukemogenicity. In this study, infections of neonatal mice by the two different routes of inoculation were compared. We studied replication of the virus in vivo to identify critical preleukemic events. These would be observed in mice inoculated i.p. by Mo+PyF101 M-MuLV but not when inoculation was s.c. Infectious center assays indicated that regardless of the route of inoculation, Mo+PyF101 M-MuLV showed delayed infection of the thymus compared with wild-type M-MuLV. On the other hand, i.p.-inoculated mice showed more rapid appearance of infectious centers in the bone marrow than did s.c.-inoculated animals. Thus, the enhanced leukemogenicity of i.p. inoculation correlated with efficient early infection of the bone marrow and not with early infection of the thymus. These results suggest a role for bone marrow infection for efficient leukemogenesis in Mo+PyF101 M-MuLV-infected mice. Consistent with this notion, if bone marrow infection was decreased by injecting 10- to 12-day-old animals i.p., leukemogenicity resembled that of s.c. inoculation. Thus, two cell types that are critical for the induction of efficient leukemia were implicated. One cell delivers virus from the site of s.c. inoculation (the skin) to the bone marrow and is apparently restricted for Mo+PyF101 M-MuLV replication. The second cell is in the bone marrow, and its early infection is required for efficient leukemogenesis.

Radiation leukemogenesis: quantitative relationship between pre-leukemic cells in the thymus and lymphoma induction

Fractionated irradiation of C57BL/6 mice induces a population of pre-leukemic (PL) cells that progress into mature thymic lymphomas after a latency of 4 to 6 months. Transfer of graded numbers of thymocytes from an irradiated mouse into recipient mice indicated that PL cells first appear in the thymus 6 weeks after irradiation. The initial proportion of the thymic PL cells is > or = 10(-5) and their frequency continuously increases with time, reaching > or = 10(-3) 10 weeks after irradiation. The PL cell population that emerges early during the pre-malignant latency consists of pleioclonal T lymphocytes. However, within 4 weeks a dominant PL clone can be detected which becomes the progenitor of a clonal lymphoma 9 to 15 weeks later. These results suggest that radiation leukemogenesis involves continuous accumulation of pleioclonal PL cells in the thymus, one of which is then selected for further maturation into frank lymphoma.

A role for mitochondrial DNA in the pathogenesis of radiation-induced myelodysplasia and secondary leukemia

The onset of acute myeloid leukemia following ionizing radiation or alkylating agent exposure is antedated months to years by the development of 'preleukemia', or secondary myelodysplastic syndrome (sMDS). Mitochondrial abnormalities induced by chloramphenicol and clonal deletions of mitochondrial DNA (mt DNA) in the bone marrow create hematological defects similar to sMDS, and abnormal dimers of mt DNA are observed in acute leukemia. This suggests a role for mt DNA in the pathogenesis of sMDS and secondary leukemia. We outline disparate experimental evidence to support this concept and suggest a role for select protease inhibitors in the clinical management of this disorder.

t(8;21) prior to acute leukemia

A t(8;21)(q22;q22) without blood and bone marrow invasion by immature myeloid precursor cells occurred in a patient previously treated for polycythemia vera. The presence of a molecular rearrangement confirmed that the chromosomal abnormality was identical to that observed in acute leukemia with t(8;21). This case shows that the translocation, t(8;21), may occur in myelodysplasia and suggests that it can precede the appearance of overt leukemia.

Second malignancies following treatment in non-Hodgkin's lymphoma

Second malignancies represent an important iatrogenic complication of the treatment of hematologic and other neoplasms. In this review we summarize the literature relating specifically to malignancies developing in the wake of treated non-Hodgkin's lymphoma (NHL). In these patients, the risk of myelodysplastic syndrome (MDS) and acute non lymphocytic leukemia (ANLL) is reported to be increased 10-105 fold over that of the general population. Factors in the development of MDS and ANLL include basic defects in cellular immunity in NHL patients as well as treatment with alkylating agents and low dose total body irradiation. Biologically these secondary MDS and ANLLs are characterized by specific cytogenetic abnormalities and results of treatment are poor. Currently bone marrow transplantation offers the only potential cure. There is no clear statistical evidence that solid tumors occur more frequently after NHL. However, bladder carcinoma, in cyclophosphamide treated patients, and lung cancer have been reported by some to occur with an increased incidence. Further investigation of the molecular events leading to the occurrence of second malignancies in NHL patients and the role played by oncogenes and tumor suppressor genes in this process is still needed.

Involvement of the spleen in preleukemic development of a murine retrovirus-induced promonocytic leukemia

An acute myeloid leukemia can result from the inoculation of Moloney murine leukemia virus into BALB/c mice undergoing a 2,6,10,14-tetramethylpentadecane-induced chronic inflammatory response in the peritoneal cavity. This leukemia is ultimately observed in the peritoneal cavity as an ascites with cells infiltrating the granulomatous tissue. It has been proposed, however, that hematopoietic organs such as the spleen and bone marrow are involved in preleukemic development of Moloney murine leukemia. Therefore, to determine if the spleen plays a role in this development, mice were splenectomized at various times relative to virus inoculation. When splenectomies were performed 3 days before and 2, 4, 6, and 8 weeks after virus inoculation there was, in all cases, a decreased death rate compared to sham-splenectomized controls. The greatest difference in death rate due to promonocytic leukemia was observed when mice were splenectomized at 4 weeks after virus inoculation. The decrease in disease incidence observed as a result of splenectomy was not caused by decreased virus spread in hematopoietic organs or an alteration in the profile of the cellular infiltrate in the granuloma. It was found, however, that the spleens of 2,6,10,14-tetramethylpentadecane-treated mice, relative to those of normal mice, have a significantly increased number of granulocyte-macrophage colony-forming cells and a slightly increased number of multipotential colony-forming cells. These observations suggest that a population of target cells for transformation, consisting of granulocyte-macrophage precursor cells, may reside in the spleen. Alternatively, partially transformed cells may reside temporarily in the spleen during the developmental stages of the disease process.

Transient myeloproliferative disorder in Down's syndrome: three cases with megakaryocytic markers

In this paper we describe three infants with Down's syndrome and transient myeloproliferative disorder. The blast cells of all three displayed positive megakaryocytic markers. One patient developed acute megakaryoblastic leukemia in his second year, with blasts identical to those of the initial episode. The other two cases remain well at 12 and 15 months of age.

Preleukaemia and myelodysplastic syndromes today

The clinical picture of myelodysplastic syndromes (MDS) results from the expansion of an abnormal clone of haemopoietic stem cells that has undergone premalignant transformation. Different types of "oncogene" may be involved in this process, some of which code for growth factors and their receptors, some for membrane or cytoplasmic proteins and some for nuclear binding proteins. The insults causing gene mutations are not known, though chemical, viral or radiation damage could be important. The most striking feature of MDS is the inadequate production of dysplastic, poorly functional cells as a result of impaired differentiation and premature cell death in the bone marrow. Treatment is currently directed to supportive therapy with blood components and antibiotics, attempts to stimulate proliferation and differentiation with recombinant human growth factors, and, in a few cases, bone marrow transplantation. Chemotherapy alone has met with little success.

[Taxonomic analysis of the distribution of peripheral blood indicators in workers in chemical plants and automobile transport]

Certain occupational groups demonstrate some deviations in the peripheral blood parameters which can be regarded as a multi-component hematological trait for selection of the group to be placed under observation.

Myelodysplasia, chemical exposure, and other environmental factors

This paper describes a case-control study of the occupational and environmental exposures of patients with myelodysplasia. The methodology, first described in Canada for solid tumors, estimates lifetime exposures to a number of potential toxic hazards or carcinogens. This pilot study confirms that the methodology, with the use of questionnaires and interviews, can estimate exposures to specific chemicals and shows some significant associations with myelodysplasia, including exposure to petrol or diesel compounds.

Prevention of T-cell lymphoma in AKR/J mice

Injection of a dual tropic virus (DTV) isolated from a T cell lymphoma AKR/J mice into the thymus of 14 day old AKR/J puppies accelerates lymphoma development; 90-100% of the injected mice develop the disease within 120 days. In contrast a cell free centrifuge CFC-666 prepared B cell lymphoma of AKR/J origin injected into the thymus of 14 day old AKR/J mice failed to accelerate T cell lymphomagenesis and actually prevented the spontaneous T cell lymphoma development. However, 50% of the treated mice developed B cell lymphoma with a latency of 417 + 18 days. DTV injection induces amplification of thymic expression of MuLV related antigens, besides changes in thymus subpopulation. Such changes emerge spontaneously in 5-6 month preleukemic AKR/J mice (at the time of spontaneous DTV formation in the thymus). These changes in the thymus were not observed following CFC-666 injection. We assume therefore that CFC-666 interferes with spontaneous DTV formation that contributes to T cell lymphomagenesis.

Adult T cell leukemia-like disease experimentally induced in rabbits

An HTLV-I-transformed T cell line, obtained from the peripheral blood of a virus-infected (B/J X Chbb:HM) F1 rabbit, was able to kill syngeneic newborn rabbits within 7 days, when inoculated intraperitoneally at a dose of 1 X 10(8) cells. Inoculation of 1 X 10(7) cells killed or rendered moribund 50% of inoculated animals, while surviving animals exhibited cell-mediated cytotoxic activities against the transformed cells. The peripheral blood leukocyte counts increased in all surviving animals, in association with appearance of abnormal lymphocytes with convoluted or lobulated nuclei. Pathological examination of animals that died one week post-inoculation revealed no tumors in the abdominal cavity, but accumulation of ascites containing abnormal lymphocytes. Histological examination showed leukemic infiltration in the liver, lungs, spleen and mesenteric lymph nodes. The same cell line was also able to kill syngeneic adult rabbits in 8-10 days when inoculated intravenously, but not intraperitoneally, at a dose of 1 X 10(8) cells. Leukemic infiltration was observed in the major organs of these animals. Adult animals which were already virus carriers were resistant to this lethal inoculation. This rabbit ATL-like disease may prove to be useful as an experimental model for acute adult T cell leukemia.

Induction of preleukemic stage of adult T cell leukemia-like disease in rabbits

Two HTLV-I-carrying T cell lines were prepared from peripheral lymphocytes of a virus-infected (B/J X Chbb:HM) F1 rabbit, and these cells were inoculated intraperitoneally into 5 newborn F1 rabbits. These animals were killed 3-5 weeks later. Their leukocyte counts were higher than those in normal control animals, with abnormal lymphocytes amounting to 3-5% of total leukocytes. Histological examination showed leukemic infiltration in liver, spleen, lung and kidneys of all these animals. The peripheral lymphocytes at first lacked HTLV-I antigens, but became antigen-positive after in vitro culture. Southern blot analysis of these cells revealed HTLV-I integration patterns different from those of the inoculated cells.