Accelerated leukemogenesis by truncated CBF beta-SMMHC defective in high-affinity binding with RUNX1

Dominant RUNX1 inhibition has been proposed as a common pathway for CBF leukemia. CBF beta-SMMHC, a fusion protein in human acute myeloid leukemia (AML), dominantly inhibits RUNX1 largely through its RUNX1 high-affinity binding domain (HABD). However, the type I CBF beta-SMMHC fusion in AML patients lacks HABD. Here, we report that the type I CBF beta-SMMHC protein binds RUNX1 inefficiently. Knockin mice expressing CBF beta-SMMHC with a HABD deletion developed leukemia quickly, even though hematopoietic defects associated with Runx1-inhibition were partially rescued. A larger pool of leukemia-initiating cells, increased MN1 expression, and retention of RUNX1 phosphorylation are potential mechanisms for accelerated leukemia development in these mice. Our data suggest that RUNX1 dominant inhibition may not be a critical step for leukemogenesis by CBF beta-SMMHC.

The effects of benzene and other leukaemogenic agents on haematopoietic stem and progenitor cell differentiation

A characteristic shared by a diverse group of myelotoxic compounds and leukaemogens is the ability to act synergistically with granulocyte-macrophage colony stimulating factor (GM-CSF) in increasing clonogenic response. Pretreatment of murine or human bone marrow cells with the benzene metabolite, hydroquinone, but not phenol, catechol or trans, trans-muconaldehyde, results in a selective enhancement of GM-CSF but not an interleukin-3 (IL-3)-mediated clonogenic response. Clonal enhancement is preserved and magnified in enriched populations of CD34+ cells (> 95% purity), suggesting an intrinsic effect on haematopoietic progenitor cell (HPC) recruitment rather than a secondary effect involving accessory cytokines. Clonogenic enhancement of murine HPCs is not accompanied by alterations in GM-CSF receptor expression or ligand affinity and appears to be mediated via a p53-independent mechanism. These observations suggest that hydroquinone treatment alters recruitment and differentiation in a primitive subpopulation of CD34+ cells and are consistent with a role for altered stem cell differentiation in the development of chemically induced myelodysplasias.

[Characteristics of the morphofunctional condition of cell populations by the modal cell class in response to transplantation of lymphocytic leukemia p-388]

On the model of transplanted leukemia p-388, cytophotometry has shown that tumors' impact on the body includes two stages: direct affection of the target organ, indirect affection through changes in functional relations with cell populations of other organs due to the impact of transformed cells of the damaged target organ. Moreover, the progress of tumor growth alters functional relations between the organs.

Astrocytes survive chronic infection and cytopathic effects of the ts1 mutant of the retrovirus Moloney murine leukemia virus by upregulation of antioxidant defenses

The ts1 mutant of Moloney murine leukemia virus (MoMuLV) induces a neurodegenerative disease in mice, in which glial cells are infected by the retrovirus but neurons are not. ts1 infection of primary astrocytes, or of the immortalized astrocytic cell line C1, results in accumulation of the ts1 gPr80(env) envelope protein in the endoplasmic reticulum (ER), with ER and oxidative stress. Notably, only about half of the infected astrocytes die in these cultures, while the other half survive, continue to proliferate, and continue to produce virus. To determine how these astrocytes survive ts1 infection in culture, we established a chronically infected subline of the living cells remaining after the death of all acutely infected cells in an infected C1 cell culture (C1-ts1-S). We report here that C1-ts1-S cells proliferate more slowly, produce less virus, show reduced H2O2 levels, increase their uptake of cystine, and maintain higher levels of intracellular GSH and cysteine compared to acutely infected or uninfected C1 cells. C1-ts1-S cells also upregulate their thiol antioxidant defenses by activation of the transcription factor NF-E2-related factor 2 (Nrf2) and its target genes. Interestingly, despite maintenance of higher levels of intracellular reduced thiols, C1-ts1-S cells are more sensitive to cystine deprivation than uninfected C1 cells. We conclude that some ts1-infected astrocytes survive and adapt to virus-induced oxidative stress by successfully mobilizing their thiol redox defenses.

Graft-vs-leukemia activity and graft-vs-host disease induced by allogeneic Th1- and Th2-type CD4+ T cells in mice

INTRODUCTION

The transfer of allogeneic lymphocytes contained in a hematopoietic stem cell graft confers an immune-mediated antileukemic effect, termed the graft-vs-leukemia (GVL) effect. Graft-vs-host disease (GVHD), the most detrimental complication of allogeneic BMT, largely resides within the same lymphocyte population. Therefore, separation of GVL- and GVH-reactions is a long-standing goal of experimental studies dealing with allogeneic transplantation of hematopoietic stem cells.

MATERIALS AND METHODS

The objective of the current study was to assess the potential of Th1- and Th2-type CD4+ T cells in mediating GVHD and GVL effects in a fully allogeneic murine transplant model. BALB/c (H-2d) mice were given a dose of A20 (H-2d, B-cell leukemia) cells two days prior to lethal total body irradiation (TBI) and transplantation of fully mismatched (C57BL/6, H-2b) T-cell depleted (anti-Thy1.2, CD90) bone marrow (TCD-BM) cells. Graded numbers of either unmanipulated, Th1- or Th2-polarized highly enriched CD4+ donor type T cells (10(6) or 10(7)) were administered 2 h posttransplant. Infusion of 10(6) of unmanipulated, Th1-, or Th2-primed CD4+ T cells resulted in moderate GVHD-related mortality (40%, 50%, 10%) and significantly improved long-term survival (50%, 45%, 46% surviving the observation period of 120 days) as compared to animals receiving TCD-BM alone (18%).

RESULTS

The administration of 10(7) unmanipulated or Th1-type CD4+ T cells given shortly after transplantation led to death of all mice within 50 days due to fatal acute GVHD. In contrast, the adoptive transfer of 10(7) Th2-primed CD4+ T cells resulted in significant improvement of long-term survival (80%) compared to the TCD-BM group. This powerful GVL effect was associated with a substantially lower incidence of lethal acute GVHD (10%) if compared to the results of transplantation of Th1-type CD4+ T cells.

CONCLUSION

These results demonstrate that allogeneic Th2-type CD4+ T cells given post BMT can induce GVL effects in a cell-dose-dependent manner without increasing the risk of severe acute GVHD.

Transfection techniques affecting Stat3 activity levels

Transfection techniques, such as calcium-phosphate or liposome-mediated gene transfer, are commonly used for the examination of the effect of a gene upon cellular phenotype and biochemical properties. We previously demonstrated that cell to cell adhesion causes a dramatic increase in Stat3 activity. Given that the opportunities for cell to cell adhesion could be altered due to the presence of the DNA-containing complexes, we examined the effect of the calcium-phosphate transfection procedure upon Stat3 activity levels. The results revealed a dramatic increase in Stat3 phosphorylation at the critical tyr705 site and Stat3 activity following calcium-phosphate transfection. This increase was noted even in the absence of DNA and was not due to the mere presence of calcium ions. In contrast, DNA introduction through electroporation or infection with a retroviral vector did not affect Stat3 activity, while cationic lipids such as lipofectamine or Fugene6 had a less pronounced effect than calcium-phosphate transfection. These results indicate that caution is required in the interpretation of results with regard to activity of Stat3 following certain commonly used transient transfection regimens.

Transplantation of spermatogonial stem cells isolated from leukemic mice restores fertility without inducing leukemia

More than 70% of patients survive childhood leukemia, but chemotherapy and radiation therapy cause irreversible impairment of spermatogenesis. Although autotransplantation of germ cells holds promise for restoring fertility, contamination by leukemic cells may induce relapse. In this study, we isolated germ cells from leukemic mice by FACS sorting. The cell population in the high forward-scatter and low side-scatter regions of dissociated testicular cells from leukemic mice were analyzed by staining for MHC class I heavy chain (H-2K/H-2D) and for CD45. Cells that did not stain positively for H-2K/H-2D and CD45 were sorted as the germ cell-enriched fraction. The sorted germ cell-enriched fractions were transplanted into the testes of recipient mice exposed to alkylating agents. Transplanted germ cells colonized, and recipient mice survived. Normal progeny were produced by intracytoplasmic injection of sperm obtained from recipient testes. When unsorted germ cells from leukemic mice were transplanted into recipient testes, all recipient mice developed leukemia. The successful birth of offspring from recipient mice without transmission of leukemia to the recipients indicates the potential of autotransplantation of germ cells sorted by FACS to treat infertility secondary to anticancer treatment for childhood leukemia.

Large-scale identification of disease genes involved in acute myeloid leukemia

Acute myeloid leukemia (AML) is a heterogeneous group of diseases in which chromosomal aberrations, small insertions or deletions, or point mutations in certain genes have profound consequences for prognosis. However, the majority of AML patients present without currently known genetic defects. Retroviral insertion mutagenesis in mice has become a powerful tool for identifying new disease genes involved in the pathogenesis of leukemia and lymphoma. Here we have used the Graffi-1.4 strain of murine leukemia virus, which causes predominantly AML, in a screen to identify novel genes involved in the pathogenesis of this disease. We report 79 candidate disease genes in common integration sites (CISs) and 15 genes whose family members previously were found to be affected in other studies. The majority of the identified sequences (60%) were not found in lymphomas and monocytic leukemias in previous screens, suggesting a specific involvement in AML. Although most of the virus integrations occurred in or near the 5' or 3' ends of the genes, suggesting deregulation of gene expression as a consequence of virus integration, 18 CISs were located exclusively within the genes, conceivably causing gene disruption.

The roles of FLT3 in hematopoiesis and leukemia

FLT3 is a receptor tyrosine kinase expressed by immature hematopoietic cells and is important for the normal development of stem cells and the immune system. The ligand for FLT3 is expressed by marrow stromal cells and other cells and synergizes with other growth factors to stimulate proliferation of stem cells, progenitor cells, dendritic cells, and natural killer cells. Mutations of FLT3 have been detected in about 30% of patients with acute myelogenous leukemia and a small number of patients with acute lymphocytic leukemia or myelodysplastic syndrome. Patients with FLT3 mutations tend to have a poor prognosis. The mutations most often involve small tandem duplications of amino acids within the juxtamembrane domain of the receptor and result in constitutive tyrosine kinase activity. Expression of a mutant FLT3 receptor in murine marrow cells results in a lethal myeloproliferative syndrome and preliminary studies suggest that mutant FLT3 cooperates with other leukemia oncogenes to confer a more aggressive phenotype. Taken together, these results suggest that FLT3 is an attractive therapeutic target for kinase inhibitors or other approaches for patients with mutations of this gene.

Induced leukemia and antineoplastic agent carmustine cause permanent changes in craniofacial growth of immature rats

OBJECTIVES

The purpose of the present study was to investigate the possible effects of untreated terminal leukemia on craniofacial growth (Study I), and also the effects of the antineoplastic agent carmustine on craniofacial growth in both leukemic and healthy rats (Study II).

MATERIAL

A total of 367 inbred Piebald variegated rats was used.

METHOD

Transmission of leukemic cells was carried out intraperitoneally at 30 days of age, and without treatment (Study I), the rats reached the terminal phase within 17 +/- 1 days. Rats with induced leukemia was cured with 10 mg/kg carmustine (BCNU) given on days 6 and 13 following cell transmission (Study II), the rats remaining in remission until they were killed at 100 days of age. Final weight was recorded and 12 craniofacial dimensions and tibial length were measured with a digital sliding caliper.

RESULTS

The results showed that the effect of untreated terminal rat leukemia (Study I) on craniofacial growth differed between the genders. Male rats showed clearly reduced dimensions of facial structures and also retarded general body growth, whereas females showed differences mainly in general body growth. The effect of cured leukemia (Study II) as such was minor, while BCNU had a strong and permanent reducing effect on both craniofacial and general body growth in both genders.

CONCLUSION

We suggest that the results in Study I came both from a direct effect of leukemia and an indirect effect of untreated terminal leukemia through malnutrition. The alkylating agent BCNU seemed to be the main cause of permanent craniofacial and general growth retardation in Study II.

Effects of chronic methamphetamine exposure on heart function in uninfected and retrovirus-infected mice

Methamphetamine (MA) increases catecholamine levels, which have detrimental effects on heart function through vasoconstriction, myocardial hypertrophy, and fibrosis. Murine retrovirus infection induces dilated cardiomyopathy (DCM). The present study investigated the cardiovascular effects of chronic MA treatment on uninfected and retrovirus-infected mice. C57BL/6 mice were studied after 12 weeks treatment. The four study groups were (group I) uninfected, MA placebo; (group II) infected, MA placebo; (group III) uninfected, MA treatment; and (group IV) infected and MA treatment. MA injections were given i.p. once a day for 5 days/week with a increasing dose from 15 mg/kg to 40 mg/kg. Left ventricular mechanics were measured in situ a using Millar conductance catheter system for pressure-volume loop analysis. Cardiac pathology was determined with histological analysis. In the uninfected mice, the load independent contractile parameters, pre-load recruitable stroke work (PRSW) and dP/dt(max) vs. Ved, significantly decreased by 32% and 35% in MA treated mice when compared to the saline injected mice. In retrovirus-infected mice, although there were no significant difference in Ees, PRSW, and dP/dt(max) vs. Ved due to MA treatment, they were increased 45%, 15% and 42% respectively when compared to saline treated mice. No further lowered heart function during murine AIDS may be due to the counteraction of the retroviral DCM and the MA induced myocardial fibrosis and hypertrophy (thickening of the ventricular walls). This is supported by increases in the End-diastolic volume (Ved, 38%) and End-systolic volume (Ves, 84%) in the retrovirus-infected saline injected mice, the decreases of 33% and 17% in the uninfected MA-treated mice, but no significant changes in the retrovirus-infected MA treated mice when compared to uninfected saline injected mice. These data suggest that MA induced myocardial cellular changes compensate for retrovirus induced DCM.

Disruption of hematopoiesis and thymopoiesis in the early premalignant stages of infection with SL3-3 murine leukemia virus

A time course analysis of SL3-3 murine leukemia virus (SL3) infection in thymus and bone marrow of NIH/Swiss mice was performed to assess changes that occur during the early stages of progression to lymphoma. Virus was detectable in thymocytes, bone marrow, and spleen as early as 1 to 2 weeks postinoculation (p.i.). In bone marrow, virus infection was detected predominantly in immature myeloid or granulocytic cells. Flow cytometry revealed significant reductions of the Ter-119(+) and Mac-1(+) populations, and significant expansions of the Gr-1(+) and CD34(+) populations, between 2 and 4 weeks p.i. Analysis of colony-forming potential confirmed these findings. In the thymus, SL3 replication was associated with significant disruption in thymocyte subpopulation distribution between 4 and 7 weeks p.i. A significant thymic regression was observed just prior to the clonal outgrowth of tumor cells. Proviral long terminal repeats (LTRs) with increasing numbers of enhancer repeats were observed to accumulate exclusively in the thymus during the first 8 weeks p.i. Observations were compared to the early stages of infection with a virtually nonpathogenic SL3 mutant, termed SL3DeltaMyb5, which was shown by real-time PCR to be replication competent. Comparison of SL3 with SL3DeltaMyb5 implicated certain premalignant changes in tumorigenesis, including (i) increased proportions of Gr-1(+) and CD34(+) bone marrow progenitors, (ii) a significant increase in the proportion of CD4(-) CD8(-) thymocytes, (iii) thymic regression prior to tumor outgrowth, and (iv) accumulation of LTR enhancer variants. A model in which disrupted bone marrow hematopoiesis and thymopoiesis contribute to the development of lymphoma in the SL3-infected animal is discussed.

Temporal effects of gamma interferon deficiency on the course of Friend retrovirus infection in mice

The current studies demonstrate complex and seemingly contradictory effects by gamma interferon (IFN-gamma) on Friend virus (FV) infection. Both temporal and tissue-specific effects were observed. During the first week of infection, IFN-gamma-deficiency caused increased levels of FV infection in multiple tissues. Surprisingly, however, by 2 weeks postinfection, IFN-gamma-deficient mice had significantly lower levels of infection in both the spleen and bone marrow compared to wild-type mice. The rapid reduction of virus in the IFN-gamma-deficient mice correlated with a more rapid virus-neutralizing antibody response than was observed in the wild-type mice. Furthermore, the virus-neutralizing antibody response in wild-type mice could be accelerated by ablation of their IFN-gamma response. Although the IFN-gamma-deficient mice developed an accelerated virus-neutralizing antibody response, they did not class-switch to immunoglobulin G class immunoglobulins nor could they maintain long-term virus-neutralizing antibody titers. Eventually, all of the IFN-gamma-deficient mice failed to keep persistent virus in check and developed fatal FV-induced erythroleukemia.

Determination of a humane endpoint in the L1210 model of murine leukemia

The purpose of our study was to derive an alternate end-point to death or moribund appearance for the frequently used L1210 model of murine leukemia. In reviewing the published literature, we were unable to identify a suitable intermediate marker of substantive disease that predicted outcome in the BDF1 recipient of the L1210 leukemia. In an attempt to refine the use of animals in our laboratory, we developed a scoring sheet for behavioral and physical changes that followed intravenous injection of L1210 lymphocytic leukemia cells into BDF1 recipients. At 12-h intervals for the first 2 days after tumor-cell injection and at 6-h intervals thereafter, animals were observed and scored for each parameter. When death was imminent, animals were euthanized by inhalation of methoxyflurane followed by decapitation. Changes in physical and behavioral characteristics then were correlated with the end-point of death. Changes occurred in the mice approximately 7 days after tumor cell inoculation and 24 h before death. The earliest of these signs was hunched posture, followed by one or more other characteristics including decreased activity, increased facial swelling, ears in backward position, abdominal swelling, squinting eyes, and labored breathing. From these data, we were able to develop criteria for early euthanasia. Use of these intermediate end-points likely will substantially reduce the stress on the animals without compromising scientific outcomes in experiments using this or related preclinical models of cancer.

cis-Active elements of Friend spleen focus-forming virus: from disease induction to disease prevention

The polycythemic strain of the Friend spleen focus-forming virus (SFFVp) is a replication-defective, acutely transforming retrovirus inducing a bistage erythroleukemia in susceptible mice. The first stage of the disease is an acute polyclonal erythroblastosis induced by the proliferation-promoting effect of gp55. gp55 is expressed from a spliced subgenomic message of SFFVp and stimulates the cellular receptor for erythropoietin. Using a selectable SFFVp that otherwise mimics the specificity of the disease, we demonstrate that the kinetics of the polyclonal expansion depends on the transcriptional strength of the retroviral cis-active elements. By exchanging gp55 for apathogenic genes, we show that SFFVp enhancer and splice signals can be successfully utilized for the development of retroviral vectors mediating very efficient transgene expression in hematopoietic cells. Apathogenic selectable SFFVp-based vectors carrying distinct enhancer alterations are a valuable tool to analyze transcriptional control of leukemia viruses in the absence of oncogenic proteins. Moreover they might have therapeutic potential.

MgcRacGAP is involved in the control of growth and differentiation of hematopoietic cells

In a search for key molecules that prevent murine M1 leukemia cells from undergoing interleukin (IL)-6-induced differentiation into macrophages, we isolated an antisense complementary DNA (cDNA) that encodes full-length mouse MgcRac-GTPase-activating protein (GAP) through functional cloning. Forced expression of this antisense cDNA profoundly inhibited IL-6-induced differentiation of M1 cells into macrophage lineages. We also isolated a full-length human MgcRacGAP cDNA, which encodes an additional N-terminal polypeptide of 105 amino acid residues compared with the previously published human MgcRacGAP. In human HL-60 leukemic cells, overexpression of the full-length form of human MgcRacGAP alone induced growth suppression and macrophage differentiation associated with hypervacuolization and de novo expression of the myelomonocytic marker CD14. Analyses using a GAP-inactive mutant and 2 deletion mutants of MgcRacGAP indicated that the GAP activity was dispensable, but the myosin-like domain and the cysteine-rich domain were indispensable for growth suppression and macrophage differentiation. The present results indicated that MgcRacGAP plays key roles in controlling growth and differentiation of hematopoietic cells through mechanisms other than regulating Rac GTPase activity.

Increased blood-brain barrier permeability in LP-BM5 infected mice is mediated by neuroexcitatory mechanisms

Serum protein levels in LP-BM5 infected mouse brains were investigated to gain insight into the contribution of blood-brain barrier (BBB) patency to the pathogenesis of retroviral encephalopathy. Evans blue uptake by the forebrain and cerebellum was significantly increased between 8-12 weeks post inoculation. Immunohistochemistry revealed foci of albumin, transferrin, alpha(2)-macroglobulin and IgG transudation around blood vessels particularly in the cerebral cortex and cerebellar vermis. These leaks were often associated with astrocytosis and apoptotic cells. Unlike the other serum proteins, IgG immunoreactivity extended from the circumventricular organs and disseminated throughout the brain parenchyma, accumulating on the plasma membranes of hippocampal and cortical neurons. Consistent with the chronic elevation of free glutamate levels in LP-BM5 infected mice, the increase in Evans blue uptake into the forebrain was completely reversed following dizocilpine administration. Thus, the chronic increase in free glutamate levels in LP-BM5 infected mouse brain contributes to BBB disruption. Furthermore, the CNS accumulation of serum proteins, particularly IgG, observed in these mice may increase osmotic load, impair neuronal function, and cause white matter pallor. Administration of NMDA receptor antagonists may prove useful in managing BBB permeability in those neuropathologies, such as HIV-associated dementia/cognitive/motor complex, having a glutamatergic component.

The SCID-hu xenogeneic transplantation model: complex but telling

Animal models based on knock-out or transgenic technology are widely used in basic and applied biomedical research. An alternative to these approaches is the generation of xenogeneic transplantation models allowing the in-vivo investigation of cell types and organs. In the field of dermatology transplantation of human skin onto mice lacking functional B and T cells (SCID mice) and subsequent manipulation of these grafts yielded new insights in many different aspects of skin biology. This review highlights some of the applications of this versatile model focussing on phenomena relevant for the subject of dermatology.

Cycling, stressed-out and nervous: cellular functions of c-Abl

c-Abl, the product of the cellular homologue of the transforming gene of Abelson murine leukaemia virus, has been a protein in search of a purpose for over two decades. Because c-Abl is implicated in the pathogenesis of several human leukaemias, understanding the functions of Abl is an important goal. Recently, biochemical and genetic approaches have converged to shed new light on the mechanism of regulation of c-Abl kinase activity and the multiple roles of c-Abl in cellular physiology. This review summarizes our current understanding of the many facets of c-Abl biology, emphasizing recent studies on Drosophila and mammalian Abl.

Are selectins involved in metastasis?

The selectins are a family of intercellular adhesion molecules that mediate the attachment of leukocytes to the endothelial lining of blood vessels. Another biological process that may involve selectins is the adhesion of circulating tumour cells to endothelium in cancer metastasis. This review discusses the evidence for the involvement of E-, P- and L-selectin in the metastasis of different tumour types. It is concluded that, with certain reservations and qualifications, selectins can play a role in metastasis. For example, the evidence for the involvement of E-selectin in breast and colon cancer metastasis is very strong. For the other selectins and tumour types the evidence is less convincing and further investigations are required to clarify the situation. Certainly, selectins are not the only mechanism available for tumours to metastasise. In the future, measurement of selectins could be useful prognostically and manipulation of their levels could lead to new cancer therapies.

Core-binding factor: a central player in hematopoiesis and leukemia

Consistent chromosomal rearrangements are found in a large number of hematopoietic tumors. In many cases, these rearrangements disrupt genes whose normal function is required for the proper development of blood cells. Excellent examples are the chromosomal rearrangements t(8;21)(q22;q22), t(12;21)(p13;q22), and inv(16)(p13q22) that disrupt two of the genes encoding a small family of heterodimeric transcription factors, core-binding factors (CBFs). CBFs consist of a DNA-binding CBFalpha subunit and a non-DNA-binding CBFbeta subunit. The t(8;21), associated with de novo acute myeloid leukemias, disrupts the CBFA2 (AML1) gene, which encodes a DNA-binding CBFalpha subunit. The t(12;21), the most common translocation in pediatric acute lymphocytic leukemias, also disrupts CBFA2. The CBFB gene, which encodes the non-DNA-binding subunit of the CBFs, is disrupted by the inv(16) in de novo acute myeloid leukemias. All chromosomal rearrangements involving the CBFA2 and CBFB genes create chimeric proteins, two of which have been unequivocally demonstrated to function as transdominant negative inhibitors of CBF function. Both the Cbfa2 and Cbfb genes are essential for normal hematopoiesis in mice, because homozygous disruption of either gene blocks definitive hematopoiesis. Recent data suggest that Cbfa2 and Cbfb are required for the emergence of definitive hematopoietic stem cells in the embryo from a putative definitive hemangioblast precursor. The transdominant negative inhibitor of CBF created by the inv(16), when present from the beginning of embryogenesis, also blocks the emergence of definitive hematopoietic cells in the embryo. On the other hand, chromosomal translocations involving the CBFA2 and CBFB genes in leukemias block hematopoiesis at later steps. This may reflect a difference in the timing at which translocations are acquired in the leukemias, which presumably is subsequent to emergence of the definitive hematopoietic stem cell. The cumulative data suggest that although the earliest requirement for Cbfa2 and Cbfb is for emergence of definitive hematopoietic stem cells, both genes are also required at later stages in the differentiation of some hematopoietic lineages.

Physical inactivity of murine retrovirus infected C57BL/6 mice is prevented by melatonin and dehydroepiandrosterone

LP-BM5 retrovirus infection and hormone synthesis modulate many physiological systems that could affect physical activity. Infection induced oxidative damage and immunodeficiency of female mice which hormone supplement prevented. Therefore, the effects of retrovirus infection and hormone supplementation were assessed on physical activity using a computerized video system. Retroviral infection increased activity when stationary while lowering average speed and resting time. Hormone supplementation partially modified changes due to murine AIDS. Dehydroepiandrosterone (DHEA) or melatonin (MLT) supplementation restored the average speed; ambulatory time and distance traveled of retrovirus infected mice. MLT as well as the combination of DHEA + MLT increased body movement, but decreased average speed and distance traveled. Thus, retrovirus infection had significant effects on physical activity. Further studies into the relationship between the DHEA and/or MLT and physical activity will assert the contribution of these hormones to the treatment of murine AIDS.

A role for growth hormone and prolactin in leukaemia and lymphoma?

Growth hormone (GH) and prolactin (PRL) quality as lymphohaemopoietic growth and differentiation factors, and so does insulin-like growth factor (IGF)-I, which mediates many of GH activities. Although there is only limited evidence that endocrine, paracrine or autocrine GH or PRL play a role in human leukaemia and lymphoma, the expression of these factors or their receptors may have diagnostic or therapeutic implications. Indeed, the participation of GH, PRL or IGF-I in the development or progression of certain haematological malignancies or to the antitumour immune response has been documented. Examples discussed in this review include a rat lymphoma in which the PRL receptor acts as an oncogene; the rat Nb2 lymphoma, which is dependent on PRL for growth; and experiments showing that PRL stimulates natural killer cell activity and the development of lymphokine-activated killer cells.

Differential behavior of the Mo + PyF101 enhancer variant of Moloney murine leukemia virus in rats and mice

The Mo + PyF101 enhancer variant of Moloney murine leukemia virus (M-MuLV) has been very useful in investigating M-MuLV leukemogenesis. When inoculated subcutaneously (s.c.) into neonatal mice, Mo + PyF101 M-MuLV is attenuated for development of disease. Previous studies in mice infected with wild-type M-MuLV have revealed several important preleukemic events, including development of splenic hyperplasia, defects in bone marrow hematopoiesis, and in vivo generation of MCF viruses that arise by recombination in the uninfected mouse. Mo + PyF101 M-MuLV is defective in inducing these effects after s.c. inoculation. In the experiments reported here, a study of Mo + PyF101 M-MuLV infection in rats was carried out. Wild-type M-MuLV is leukemogenic in rats, but infected rats do not form MCF recombinants since they lack the necessary endogenous polytropic envelope sequences. Since Mo + PyF101 M-MuLV's leukemogenic defect is correlated with a failure to generate MCF recombinants, it seemed possible that wild-type M-MuLV might not have a leukemogenic advantage over Mo + PyF101 M-MuLV in rats, where MCF recombinants cannot form. Neonatal Fisher F344 rats were inoculated s.c. or intraperitoneally by wild-type and Mo + PyF101 M-MuLVs. Surprisingly, Mo + PyF101 M-MuLV was completely deficient in leukemogenesis in rats when inoculated by either route while wild-type M-MuLV induced lymphoma with the predicted time course. The leukemogenic defect for Mo + PyF101 M-MuLV resulted from a pronounced defect for establishing infection in rats. Further studies of wild-type M-MuLV in rats indicated that infection was confined almost exclusively to the thymus at early times. In mice wild-type M-MuLV establishes substantial infection in other hematopoietic organs such as spleen and bone marrow as well. Thymic infection was also correlated with a decrease in thymic cellularity at early times.

Folate deficiency delays the onset but increases the incidence of leukemia in Friend virus-infected mice

Clinical studies have indicated that folate deficiency may enhance the development of various malignancies. In animal studies that examined the effect of folate deficiency on malignancies, conflicting results have been reported. In some studies, folate deficiency increased the development and growth of malignant tumors; in others, it decreased the development and growth of malignancies. We examined the effect of transient folate deficiency on the development of leukemia in mice infected with the anemia-inducing strain of Friend leukemia virus. Friend virus disease can be considered as a model for human acute leukemias that are preceded by a preleukemic period. These include leukemias that develop in patients who received previous chemotherapy and/or radiation therapy, as well as patients with chronic granulocytic leukemia or myelodysplasia. Folate deficiency around the time of Friend virus-infection delayed the onset but increased the incidence of leukemia. The rates of rearrangement of the Spi-1 (PU.1 ) oncogene by provirus integration and alteration of the p53 tumor-suppressor gene were the same in leukemia cell lines derived from folate-deficient mice as they were in cell lines from control mice. These results indicate that folate deficiency did not exert its enhancement of leukemogenesis through changes in either Spi-1 or p53, even though these two genes have been found to be the most frequently altered ones in Friend virus-induced leukemias. Our results suggest that folate deficiency may enhance the development of acute leukemia in patients who are at high risk for this disease.

Differentiation commitment in normal hemopoiesis and leukemic transformation

Differentiation commitment events are essential for the initiation of hemopoiesis and, in one form or another, occur continuously during adult hemopoiesis. The most studied type of differentiation commitment decision a hemopoietic cell can make involves the alternative choice of self-renewal versus the formation of progeny destined for maturation. Aberration in this commitment choice is a key abnormality necessary for the formation of a leukemic population.

Factors affecting induction of neurological disorder in mice by PVC viruses and the sequence of env-LTR region of PVC441

PVC111, PVC211, PVC321 and PVC441 cause neurological disorders associated with tremor and paralysis in rats. We tested the pathogenicity of these viruses in mice. Although histopathological studies revealed spongiform degeneration in the spinal cords of NFS mice infected with each PVC virus, only PVC441 caused a high incidence of tremor and paralysis. Further studies with PVC441 revealed dose and age dependence for tremor induction. In contrast to NFS mice, BALB/c, DBA/2 and C57BL/6 mice infected with PVC441 virus showed no neurological symptoms, although the virus replicated in each strain to titers within 5-fold of the titer in NFS mice. Despite absence of neurological symptoms, high degree of neuronal degeneration in the lumbar spinal cord was found in PVC441-infected BALB/c mice. Low degree of neuronal degeneration was found in PVC441-infected DBA/2 or C57BL/6 mice. Genetic crosses of these resistant mice with susceptible NFS mice indicated that resistance to PVC441-induced tremor induction was dominant in all strains and suggested that various host genes may control the susceptibility of mice to tremor induction by PVC441 virus. Sequencing of env-LTR region of PVC441 revealed an intermediate character between PVC211 and F-MuLV.

Charlotte Friend Memorial Lecture: murine leukemia virus (MuLV) tumorigenesis

Recent analysis of over 500 lymphomas occurring in NFS.V mice, congenic for Akv-type ecotropic MuLV structural genes, has revealed that about 90% are of B cell lineage as determined by demonstration of clonal rearrangements of Ig heavy chain genes, phenotyping by immunocytochemistry or cytofluorometric analysis, and by site and morphology of tumor. At least 40% of the B cell lymphomas were found to have their origin in the splenic marginal zone, a site only once before described for mouse lymphomas. Clonal somatic integrations of ecotropic MuLV occurred in 85% of tumors.

Histone H1 suppresses tumor growth of leukemia cells in vitro, ex vivo and in an animal model suggesting extracellular functions of histones

Purified histone H1 exerts growth inhibition of leukemia cells independent of lineage, stage, and maturation. At 200 micrograms/ml, H1 proved cytotoxic in 19 of 21 of the tested leukemia-derived cell lines and for 11 of 16 of the fresh tumor samples from leukemia patients. In all cases, normal peripheral blood mononuclear cells and bone marrow cells remained unaffected. Multicellular spheroids from the Burkitt's lymphoma cell line IM-9 were growth arrested at 500 micrograms H1/ml. The clonogenic growth of the Burkitt's lymphoma cell line Daudi was arrested at 160 micrograms H1/ml. Synthetic H1-peptides as well as peptides and proteins with biochemical properties similar to H1 had no inhibitory growth effect at equimolar concentrations. Furthermore, 250 micrograms H1 injected into a Burkitt's lymphoma (Daudi), xenotransplanted into nude mice, arrested tumor growth. As shown by electron microscopy and flow cytometry, incubation of leukemia cells with H1 resulted in severe plasma membrane damage and ultimately cytolysis. This report characterizes a 33-kd protein that binds H1 and is responsible for the cell death via destruction of the cell membrane integrity. New extranuclear functions of histones are presented.

Effects of excess GM-CSF levels on hematopoiesis and leukemia development in GM-CSF/max 41 double transgenic mice

Double transgenic mice were produced by mating granulocyte-macrophage colony-stimulation factor (GM-CSF) transgenic mice with max 41 transgenic mice that exhibit excess granulopoiesis and a predisposition to thymic lymphoma development. Although only two-thirds of the double transgenic mice had elevated circulating GM-CSF levels, double transgenic mice maintained significantly higher blood granulocytes and monocytes and more extreme granulopoietic hypercellularity in the marrow and spleen than max 41 transgenic mice. In double transgenic mice, early death occurred from the GM-CSF transgenic syndrome. Because of these early deaths, the incidence of thymic and generalized lymphomas was artificially lower than in max 41 mice but those lymphomas that did develop occurred earlier than in max 41 mice. While the excess GM-CSF levels in double transgenic mice stimulated increased granulocyte and monocyte formation and peritoneal dendritic cells were excessive, this failed to prevent the spontaneous development of T lymphomas, suggesting that dendritic cell-initiated suppression of tumor development may not be effective with this type of tumor.

Role of interleukin-1 beta converting enzyme (ICE) in leukemia

Interleukin (IL)-1 is a proinflammatory cytokine that plays a pivotal role in driving the in vitro proliferation of leukemic cells through autocrine or paracrine pathways. Both IL-1 genes, IL-1 alpha and the prominent IL-1 beta, produce 31 kDa proteins. Whereas the precursor (pro) 31 kDa form of IL-1 alpha is biologically active, pro-IL-1 beta is inactive unless cleaved to its mature form by a cytoplasmic cysteine protease termed IL-1 beta converting enzyme (ICE). Although ICE was first thought to be a unique enzyme with a single biologic activity, several investigators have demonstrated that ICE shares sequence homology with the protein product of ced-3, the gene for cell death of the nematode Caenorhabditis elegans, and can induce apoptosis in different cellular systems. However, recent data indicate that ICE is a member of an increasingly recognized family of ICE-related molecules whose other members, such as CPP32, do not cleave pro-IL-1 beta but rather are effective inducers of apoptotic cell death. We recently investigated the effect of ICE inhibition on acute myelogenous leukemia (AML) colony growth. We found that inhibition of ICE reduced the production of mature IL-1 beta and suppressed the proliferation of AML colony-forming units, confirming the central role of IL-1 beta in AML progenitor proliferation. These data suggest that the primary role of ICE in AML cells is cleavage of pro-IL-1 beta rather than induction of apoptosis and that the antileukemic activity of specific ICE inhibitors warrants further exploitation.

Paradoxical stimulation of normal and leukemic rat hematopoiesis by monoclonal antibody to CSF-1 receptor

We have recently developed a rat monoclonal antibody directed against the murine M-CSF receptor (c-fms). This reagent also inhibits in vitro colony formation by leukemic and normal rat splenocytes in response to M-CSF. At high antibody concentrations, the antibody augments, rather than inhibits, colony formation by rat cells in the presence of M-CSF, an effect that is not seen when murine cells are used as responders. The costimulatory and inhibitory activities of the monoclonal antibody preparations copurify in a number of purification methods, indicating that the costimulatory activity is intrinsic to the antireceptor antibody. Conversion of the antibody into monovalent Fab fragments by papain digestion destroys costimulatory activity. This finding raises a cautionary note for the in vivo use of intact monoclonal antibodies directed against growth factor receptors for the treatment of hematologic malignancies.

Both the changes of six amino acids and the C-terminal truncation caused by a one-base insertion in the defective env gene of Friend spleen focus-forming virus significantly affect the pathogenic activity of the encoded leukemogenic membrane glycoprotein (gp55)

Friend spleen focus-forming virus (F-SFFV) causes acute erythroleukemia in mice and encodes in its defective env gene an Env-like membrane glycoprotein (gp55). The F-SFFV env gene has three characteristic structures compared with that of ecotropic murine leukemia viruses (MuLVs): substitution by the polytropic MuLV env sequence, a 585-bp deletion, and a 1-bp insertion. All of these characteristic structures are essential for the leukemogenic potential of gp55 of polycythemia-inducing isolates of F-SFFV (F-SFFVp). The 1-bp insertion causes changes of six amino acids and truncation by 34 amino acids at the C terminus. In this study, we constructed 12 mutant F-SFFV genomes starting from the wild-type F-SFFVp and examined the effect of the C-terminal truncation and the six altered amino acids on the pathogenic activity of gp55. The results indicated that at least 18 to 24 amino acids must be deleted from the C terminus for the env product to be pathogenically active. We also found that the six altered amino acids contributed significantly to the pathogenic activity of gp55. Analyses of the cellular processing of these mutant gp55s supported a correlation between the pathogenic activity of gp55 and its efficiency in overall cellular processing.

Environmental lighting alters the infection process in an animal model of AIDS

In this study, we examined the effects of altered environmental lighting on the infection process of a murine leukemia virus, E-55(+), which induces a thymic lymphoma/leukemia in 100% of BALB.K mice inoculated as adults. One to two weeks after inoculation, high levels of proviral DNA are usually found. This is followed by an asymptomatic period of many weeks during which proviral DNA becomes essentially undetectable. Leukemia develops approximately 28 weeks postinoculation. In this experiment, one group of mice was exposed a consistent 10L: 14D cycle while a second was maintained in constant light (LL). A third group was exposed to a rotating cycle characterized by phase shifting a 10L: 14D cycle every three 24-h days (rLD). All cycles began 2 weeks prior to inoculation and were maintained thereafter. Animals were sacrificed at 1, 5, 10, and 15 weeks, and hematopoietic tissue was examined for proviral DNA content. At 1 week, LL- and rLD-exposed animals showed considerably less proviral DNA in bone marrow and spleen compared with controls. At 15 weeks, thymuses from controls were showing signs of infection whereas tissue from LL and rLD mice remained at background levels. We conclude that environmental lighting does alter the infective pattern displayed by this retrovirus, although whether this effect is mediated by changes in the target stem cells or through immunoenhancement has not yet been determined.

Preclinical investigations of drug resistance

The effectiveness of antileukemic therapy is limited by intrinsic and acquired cellular resistance. Preclinical investigations support a complex and redundant network of cytoprotective mechanisms resulting from decreased drug accumulation, intracellular drug detoxification, alterations in nuclear targets of the antineoplastic agent, impaired transduction of growth arrest signals, and inherent cytokinetic resistance to S-phase active agents. Some, but not all, of these mechanisms are coordinately regulated, and correlative studies suggest that some may indeed contribute to clinical chemotherapy resistance.

Susceptibility and resistance to Moloney murine leukemia virus-induced promonocytic leukemia

Moloney murine leukemia virus (M-MuLV) induces promonocytic leukemias, called MML, in pristane-treated adult mice. These tumors invariably express fused gag-myb mRNA as a consequence of virus integration and activation of the c-myb locus. In the present study it was determined that while BALB/c and DBA/2N mice are highly susceptible, C57BL/6, C3H/He, STS/A, NFS, NIH/Swiss, SJL/J, and NZB mice are strongly resistant to tumor induction. Although C57BL/6 mice were resistant because they were unable to support early virus replication in hematopoietic tissue, NFS and C3H/He mice supported replication and were shown, using RT-PCR, to have cells in the bone marrow and spleen that expressed the aberrant, leukemia-related gag-myb mRNA. This provided evidence that early stages of leukemia were permitted to develop in these mice, but preneoplastic cells were unable to progress to the acute phase. Experiments in which MML was induced by M-MuLV plus pristane treatment in immunodeficient C3H/He nu/nu and sublethally irradiated C3H/He mice suggested that the immune response may play a role in eliminating preleukemic cells in immunocompetent C3H/He. Tumors from these mice had rearrangements at the c-myb locus and expressed gag-myb RNA. It was concluded that, at least in the case of C3H/He mice, resistance is not due to an inability of virus to activate c-myb or to a lack of other tumor promoting events. Rather, leukemia development appears to be restricted by an immune response, presumably T-cell mediated. Evidence is provided that non-H-2 MHC genes are required for resistance in both C57BL/6 and C3H/He mice and that resistance is dominant. This provides an animal model for the study of tumor progression as it relates to the immune response.

Increase in the chemically-induced differentiation of human leukemia cell lines by tubulin disruptors

The effect of various structural/functional tubulin disruptors (including colchicine-type disruptors, vinblastine, rhizoxin, maytansine, peptide-type disruptors, and taxol) on the chemically induced differentiation of human leukemia cell lines (HL-60 and K562) was examined. As differentiation-inducing agents, 12-O-tetradecanoylphorbol-13-acetate (TPA) was used for the differentiation of both HL-60 and K562 to monocyte/macrophages, retinoids were used for the differentiation of HL-60 to mature granulocytes, and hemin was used for the erythroid differentiation of K562. All the tubulin disruptors investigated increased the chemically-induced differentiation of HL-60 and K562 cell lines to the cognate mature cell types, regardless of the nature of the differentiation.

Secondary combined resistance to the multidrug-resistance-reversing activity of cyclosporin A in the cell line F4-6RADR-CsA

Multidrug-resistant tumor cells can be resensitized by combined application of the selecting cytostatic drug and a chemosensitizer, such as cyclosporin A (CsA) or a calcium channel blocker. Since clinical trials on the circumvention of multidrug resistance (MDR) with chemosensitizers report disparate results, we investigated whether tumor cells of the MDR phenotype can develop additional resistance to the cytostatic chemosensitizer combination. Thus, the Adriamycin(ADR)-selected, P-glycoprotein-positive MDR Friend leukemia cell line F4-6RADR was exposed to stepwise increased concentrations of CsA at a constant level of 0.05 microgram/ml ADR. The initial CsA concentration (plus 0.05 microgram/ml ADR) to inhibit cell growth of F4-6RADR cells by 50% (IC50) was 0.04 microgram/ml. By continuous incubation for more than 6 months, the IC50 for CsA (at constant ADR) was elevated to 3.6 micrograms/ml (90-fold), thus generating the variant F4-6RADR-CsA. The F4-6RADR-CsA cells were cross-resistant for cyclosporin H (CsH), a non-immunosuppressive derivative of CsA. As shown by immunocytochemistry as well as by the polymerase chain reaction and by Western blotting including densitometry, P-glycoprotein was preserved in the F4-6RADR-CsA variant and was expressed at a 4-fold higher level than in F4-6RADR cells. Sodium dodecyl sulfate/polyacrylamide gel electrophoresis analysis could detect no new proteins in F4-6RADR-CsA as compared to F4-6RADR. Interestingly, resistance of F4-6RADR-CsA cells remained reversible for the calcium antagonists verapamil and dihydropyridine B859-35 (dexniguldipine-HCl), indicating that CsA and these compounds interfere with the P glycoprotein function by different pharmacodynamic mechanisms. Transport studies with [14C]ADR, performed in the presence and absence of chemosensitizers, confirmed the good correlation of P-glycoprotein function with the pattern of resistance found in proliferation assays. Cellular accumulation of [3H]cyclosporin was reduced to 71% of that of the F4-6 controls in F4-6RADR-CsA cells, but remained at the level of controls in F4-6RADR cells. Results indicate that increased amounts of the P-glycoprotein--besides other, perhaps more important mechanisms that are as yet unknown--partially mediate CsA resistance in F4-6RADR-CsA cells. We have designated this new form of resistance "secondary combined resistance" (SCR). The results suggest that at least some clinical cases of insensitivity to chemosensitizers or of relapse after reversing therapy could be explained by SCR, and that resensitizing treatment of tumor patients should be based on the consideration of several chemosensitizers of different pharmacodynamics.

[Reverse correlation between natural resistance of mice to transplanted leukemia EL-4 and rectal temperature]

Mice F1 (CBA x C57Bl) life span after transplantation of standard number of leukemia EL-4 cells at different clock hours was evaluated. At the same time, as injection was done, rectal temperature of mouse was measured. Both parameters showed circadian trend. Mice life span was in negative correlation with rectal temperature. So it is possible to consider temperature rhythm as marker rhythm of natural antitumor resistance.

Effect of Calphostin C (PKC inhibitor) on daunorubicin resistance in P388/ADR and HL60/AR cells: reversal of drug resistance possibly via P-glycoprotein

Calphostin C is a potent and specific inhibitor of protein kinase C (PKC). In this investigation we examined the effect of Calphostin C (without prior exposure to light) on daunorubicin (DNR) accumulation and sensitivity to DNR in multidrug-resistant (MDR) murine leukemia P388/ADR and human myeloid leukemia HL60/AR cells. P388/ADR cells overexpress P-glycoprotein, whereas HL60/AR cells lack any expression of P-glycoprotein (both at mRNA and protein levels). Calphostin C, in a concentration-dependent manner, increased the accumulation of DNR in P388/ADR cells and partially reversed (threefold) the DNR resistance in P388/ADR cells but had no effect on either of the parameters in HL60/AR cells. Calphostin C-induced increased accumulation of DNR in P388/ADR cells was due to increased uptake and decreased efflux of DNR. Furthermore, Calphostin C increased the uptake and decreased the efflux of rhodamine 123 (a substrate for P-gp) in P388/ADR cells but had no such effect in P388 cells. In addition, Calphostin C without exposure to light did not inhibit PKC activity in any of the cell lines studied. Taken together, these data suggest that Calphostin C may reverse drug resistance via P-glycoprotein independently of its effect on PKC activity. Therefore, any data regarding the effect of Calphostin C on the reversal of MDR should be interpreted in the light of these findings.

[Effects of light deprivation on carcinogenesis induced by N-nitrosomethylurea in female rats]

One month-old female rats were blinded by surgery and received single intravenous injections of 50 mg/kg body weight of N-nitrosomethylurea (NMU) two weeks later. Simultaneously, normal animals were injected an identical dose of NMU. The frequency of NMU-induced neoplasms in blind rats was 33% vs. 75% in control (P < 0.05), with neoplastic development latency being longer as compared with controls. The frequency of mammary gland adenocarcinoma, leukemia and adenoma of the pituitary and thyroid gland in blind rats was significantly lower while mammary gland fibroadenoma was more frequent than in intact animals. Carcinogen-treated blind animals survived much longer (448 +/- 21 days) than normal controls (284 +/- 22 days) (P < 0.001). The frequency of spontaneous neoplasms in blind and normal rats was identical. The inhibitory effect on carcinogenesis seems to be due to enhanced functional activity of the pineal gland in blind animals.

Both megakaryocytopoiesis and erythropoiesis are induced in mice infected with a retrovirus expressing an oncogenic erythropoietin receptor

Increasing direct and indirect evidence suggests that erythropoietin (Epo) promotes both erythropoiesis and megakaryocytopoiesis. Here we report that, in mice infected with a recombinant spleen focus-forming retrovirus (SFFV) expressing an oncogenic erythropoietin receptor (EpoR), there was an increase in platelet count preceding the ensuing erythrocytosis. Concurrently, there was a substantial increase in splenic megakaryocytes. Culture of the bone marrow and spleen cells from infected mice showed enhanced numbers of multipotent megakaryocytic progenitors. DNA polymerase chain reaction analysis of individual megakaryocyte-containing colonies showed recombinant SFFV (SFFVcEpoR) proviral integration. Immunofluorescence of spleen sections showed overexpression of EpoR protein in the megakaryocytes. Mice infected with a strain of SFFV also developed splenic megakaryocytosis without activating overexpression of the EpoR in megakaryocytes. This in vivo system shows that a relationship between erythropoiesis and thrombopoiesis can exist at the level of the Epo-EpoR signaling pathway. Also, SFFV-based vectors may be excellent vehicles for the introduction of genes into multipotent, hematopoietic progenitors, in vitro.

Decreased blood flow to rat bone marrow, bone, spleen, and liver in acute leukemia

An acute promyelocytic leukemia in the rat (BNML) has been used in model studies on pathogenesis and therapy of human acute myeloid leukemia. The blood supply to bone marrow during BNML development has hitherto not been examined, even though in general, blood flow to hematopoietic tissues might affect drug treatment and marrow transplantation regimes. We measured the perfusion of various organs during the course of the disease in untreated rats and in rats given one injection of cyclophosphamide treatment. Organ perfusion was measured with radioactive microspheres. Blood flow per gram tissue to the bone marrow, bone, spleen, and liver declined gradually during the leukemic progression, thus paralleling the growth of leukemic deposits. Cyclophosphamide treatment retarded, but did not reverse, the decreasing perfusion of these tissues.

Graffi murine leukemia virus: molecular cloning and characterization of the myeloid leukemia-inducing agent

The Graffi murine leukemia virus (MuLV) is a retroviral mixture that induces predominantly myeloid leukemia in several inbred strains of mice. To analyze the viral component responsible for the myeloid leukemogenesis, we cloned several proviruses from a Graffi MuLV-infected cell line. Several infectious molecular clones were obtained that could be classified into two distinct groups of infectious MuLV. Both types of MuLV were nondefective, ecotropic, and NB tropic and induced granulocytic leukemia in BALB/c and NFS mice. Restriction enzyme analysis and molecular hybridization with several MuLV probes on one molecular clone from each group revealed that both groups are closely related to each other but are clearly distinct from all known retroviruses. One component of MuLV, however, induced leukemia with a shorter latency period and harbored a lengthier long terminal repeat. The long terminal repeat of the more leukemogenic component of MuLV had acquired a 60-bp perfect duplication in the U3 region. Analysis of the tumor DNAs with probes for the mouse T-cell receptor and immunoglobulin heavy chain genes revealed frequent rearrangements with one or both probes. This concomitant expression by leukemic cells of markers of different lineages, observed in human leukemias, has been termed "lineage infidelity" and confirms that the latter rearrangements are not restricted to hematopoietic precursors committed to lymphoid differentiation.