Assessment of the morphology and significance of the lymph nodal and hepatic lesions produced in rats by the feeding of certain mineral oils and waxes. Proceedings of a pathology workshop held at the Fraunhofer Institute of Toxicology and Aerosol Research Hannover, Germany, May 7-9, 2001

A Panel of medical and veterinary pathologists reviewed published and unpublished reports dealing with studies of various white mineral oils and waxes in F344 and Sprague-Dawley rats. They also had available and studied histologic slides from both subchronic and chronic studies of certain mineral hydrocarbons (90-day oral study of low melting point wax (LMPW) in female Fischer 344 and Sprague-Dawley rats; 90-day studies of P15H* and P70H white oil and high melting point wax (HMPW) in male and female F344 rats and 24 month study of P70H white oil in male and female F344 rats. The Panel also reviewed mineral oil-induced alterations in tissues of human patients (liver, hepatic lymph node and spleen). The Panel agreed that certain of the mineral hydrocarbons produced lesions in the mesenteric lymph nodes and liver of the F344 rat and these lesions were best described as microgranulomas/granulomas. The lesions were fundamentally similar in both organs, although varying in severity with dose and type of mineral hydrocarbons. The Panel agreed that hepatic lesions with inflammatory cell infiltration, necrosis, and fibrosis were produced only by feeding of LMPW and the lesions were confined to F344 rats and not found in Sprague-Dawley rats. The most severe granulomatous lesions in the mesenteric lymph nodes were found in high dose LMPW-fed F344 rats. The microgranulomas were similar in subchronic and chronic studies. Also, little difference existed between controls and treated F344 rats in the incidence and severity of the lesions after 2 years of feeding P70H white oil. The Panel agreed that some slight reversibility existed for these lesions, but also agreed that complete resolution was unlikely as regression of the lesions in the rat would likely be slow. The Panel agreed that a minimal severity infiltrate of mononuclear inflammatory cells occurred in the base of the mitral valve in a slightly increased incidence in F344 rats fed LMPW. The Panel concluded that these mitral valve alterations had little if any toxicologic significance as the focal infiltrate was minimal in severity, occurred in controls, occurred in association with murine cardiomyopathy, and were unlike the responses in the liver and mesenteric lymph nodes. The Panel agreed that the lesions observed in the liver and mesenteric lymph nodes of F344 rats exposed to MHCs, especially the LMPW, were different morphologically from changes observed in lymph node, liver, and spleen of humans that were mineral oil-users. These changes in humans are usually found incidentally in tissues taken at biopsy or autopsy. The MHC-induced lesions can be considered incidental and inconsequential in humans.

The Bcr N-terminal oligomerization domain contributes to the full oncogenicity of P190 Bcr/Abl in transgenic mice

The Bcr/Abl P190 oncoprotein is responsible for the development of Philadelphia-chromosome positive acute lymphoblastic leukemia (ALL). The Bcr moiety in Bcr/Abl activates the Abl tyrosine kinase, an ingredient essential for the transforming capability of Bcr/Abl. Residues 1-63 of Bcr form an N-terminal oligomerization domain and are key to Abl activation in vitro. Mice transgenic for P190 BCR/ABL reproducibly develop an aggressive B-lineage lymphoblastic leukemia/lymphoma. Here we test the hypothesis that residues 1-63 of Bcr have a major in vivo contribution to the oncogenicity of Bcr/Abl P190 by the generation of mice transgenic for an N-terminal deleted form of P190. We find that although the transgene is expressed in the bone marrow of mice at an early age, the incidence of leukemogenesis is greatly diminished as compared to mice transgenic for non-mutated P190 Bcr/Abl. Sporadic hematological malignancies which did develop showed decreased levels of phosphotyrosine as compared to those of wild-type P190 transgenics, although Ras was activated. These results demonstrate that the Bcr oligomerization domain contributes to the oncogenicity of Bcr/Abl in vivo.

Crkl enhances leukemogenesis in BCR/ABL P190 transgenic mice

The adapter protein Crkl has been implicated in the abnormal signal transduction pathways activated by the Bcr/Abl oncoprotein, which causes Philadelphia-positive leukemias in humans. To investigate the role of Crkl in tumorigenesis, we have generated transgenic mice that express human Crkl from the CRKL promoter. Western blot analysis showed a 4-6-fold overexpression of transgenic Crkl above endogenous crkl in two lines and increased constitutive complex formation between Crkl and C3G, an exchange factor for the small GTPase Rap1. This was associated with a significant increase in integrin-based motility of transgenic macrophages. Overexpression of Crkl was associated with increased incidence of tumor formation, and Rap1 was activated in a metastatic mammary carcinoma. The coexpression of Crkl and Bcr/Abl in mice transgenic for P190 BCR/ABL and CRKL markedly increased the rapidity of development of leukemia/lymphoma, decreasing the average survival by 3.8 months. These results provide direct evidence that Crkl plays a role in tumor development and is important in the leukemogenesis caused by Bcr/Abl.

Biological characterization of uncleavable plasma membrane-anchored human macrophage colony-stimulating factor

The cell-surface form of human macrophage colony-stimulating factor (CSF-1(256), M-CSFalpha) is a plasma membrane-anchored transmembrane protein from which the soluble CSF-1 is released by ectodomain proteolytic cleavage. We have previously generated two forms of cell surface CSF-1 which failed to undergo the cleavage by deleting residues 161-165 or residues 159-165 in the extracellular juxtamembrane region (1). To determine the biologic significance of the ectodomain cleavage, we compared the biosynthesis and biologic activities of uncleavable mutant CSF-1 forms with those of the cleavable wild-type (WT) CSF-1. We found that the uncleavable CSF-1 forms were able to accumulate on cell surface at about threefold higher level than the cleavable WT CSF-1 did. We further demonstrated that the uncleavable plasma membrane-anchored forms of CSF-1 were biologically active in mediating the proliferation of CSF-1-dependent cells as well as the intercellular adhesion between CSF-1 receptor-bearing cells and CSF-1 expressing cells. Furthermore, the adhesive activity of uncleavable CSF-1 forms was about twofold stronger than that of WT CSF-1, which indicated that the ectodomain cleavage system plays an important role in regulating the biologic activities of membrane-anchored CSF-1.

Reduced oncogenicity of p190 Bcr/Abl F-actin-binding domain mutants

The deregulated Bcr/Abl tyrosine kinase is responsible for the development of Philadelphia (Ph)-positive leukemia in humans. To investigate the significance of the C-terminal Abl actin-binding domain within Bcr/Abl p190 in the development of leukemia/lymphoma in vivo, mutant p190 DNA constructs were used to generate transgenic mice. Eight founder and progeny mice of 5 different lines were monitored for leukemogenesis. Latency was markedly increased and occurrence decreased in the p190 del C lines as compared with nonmutated p190 BCR/ABL transgenics. Western blot analysis of involved hematologic tissues of the p190 del C transgenics with end-stage disease showed high-level expression of the transgene and tyrosine phosphorylation of Cbl and Hef1/Cas, proteins previously shown to be affected by Bcr/Abl. These results show that the actin-binding domain of Abl enhances leukemia development but does not appear to be an absolute requirement for leukemogenesis.

Combination of CD80 and granulocyte-macrophage colony-stimulating factor coexpression by a leukemia cell vaccine: preclinical studies in a murine model recapitulating Philadelphia chromosome-positive acute lymphoblastic leukemia

Philadelphia chromosome-positive acute lymphoblastic leukemia (Ph+ ALL) is a highly aggressive malignancy caused by the bcr-abl translocation oncogene. To explore alternative treatments for Ph+ ALL we tested gene-modified cell vaccines in the BALB/c-derived BM185 leukemia model. We compared the efficacy of BM185 cell vaccine expressing CD80 alone or in combination with IL-2 or GM-CSF. Mice injected with viable BM185 leukemia cells modified to express CD80 and GM-CSF (BM185/CD80+GM-CSF) showed the highest leukemia rejection rates. Cell vaccines consisting of irradiated BM185/CD80+GM-CSF cells administered subcutaneously stimulated a potent cytotoxic T lymphocyte (CTL) response against parental BM185. Histological examination of the vaccination site showed a large concentration of immune cells. Administration of the BM185/CD80+GM-CSF cell vaccine before intravenous challenge with parental cells caused strong inhibition of leukemia development. Vaccination after subcutaneous challenge with BM185 cells caused efficient elimination of leukemia promoting 40-60% long-term survival rates. The immunization efficacy of the BM185/CD80+ GM-CSF cell vaccine was directly correlated with the percentage of cells expressing the transgenes. In all, this preclinical study shows that leukemia cell vaccines coexpressing CD80 and GM-CSF can potentially be explored for immunotherapy in Ph+ ALL patients.

Constitutive HOXA5 expression inhibits erythropoiesis and increases myelopoiesis from human hematopoietic progenitors

The role of the homeobox gene HOXA5 in normal human hematopoiesis was studied by constitutively expressing the HOXA5 cDNA in CD34(+) and CD34(+)CD38(-) cells from bone marrow and cord blood. By using retroviral vectors that contained both HOXA5 and a cell surface marker gene, pure populations of progenitors that expressed the transgene were obtained for analysis of differentiation patterns. Based on both immunophenotypic and morphological analysis of cultures from transduced CD34(+) cells, HOXA5 expression caused a significant shift toward myeloid differentiation and away from erythroid differentiation in comparison to CD34(+) cells transduced with Control vectors (P =.001, n = 15 for immunophenotypic analysis; and P <.0001, n = 19 for morphological analysis). Transduction of more primitive progenitors (CD34(+)CD38(-) cells) resulted in a significantly greater effect on differentiation than did transduction of the largely committed CD34(+) population (P =.006 for difference between HOXA5 effect on CD34(+) v CD34(+)CD38(-) cells). Erythroid progenitors (burst-forming unit-erythroid [BFU-E]) were significantly decreased in frequency among progenitors transduced with the HOXA5 vector (P =.016, n = 7), with no reduction in total CFU numbers. Clonal analysis of single cells transduced with HOXA5 or control vectors (cultured in erythroid culture conditions) showed that HOXA5 expression prevented erythroid differentiation and produced clones with a preponderance of undifferentiated blasts. These studies show that constitutive expression of HOXA5 inhibits human erythropoiesis and promotes myelopoiesis. The reciprocal inhibition of erythropoiesis and promotion of myelopoiesis in the absence of any demonstrable effect on proliferation suggests that HOXA5 diverts differentiation at a mulitpotent progenitor stage away from the erythroid toward the myeloid pathway.

Expression of the human immunodeficiency virus-Tat gene in lymphoid tissues of transgenic mice is associated with B-cell lymphoma

The human immunodeficiency virus type 1 (HIV-1) Tat gene, a potent transactivator of viral and cellular genes, has been proposed as a key agent in the pathogenesis of acquired immune deficiency syndrome related disorders, including non-Hodgkin's lymphoma. In cultured cells, the HIV-1 Tat protein can induce the expression of the cytokines interleukin-6 (IL-6) and IL-10, which are known to induce proliferation and differentiation of lymphoid cells. Such alterations in cytokine expression, together with a secondary genetic event, are thought to ultimately lead to oncogenic transformation. To address the influence of Tat on lymphoid development in the context of the whole organism, we produced several transgenic mouse lines that express the Tat gene under the control of an actin promoter. We show here that this promoter directs expression to a variety of sites, including spleen, bone marrow, and lymph nodes. Approximately 25% to 30% of the Tat-transgenic population developed enlarged spleens within 1 year after birth. On histological examination, a significant number of spleens from Tat-transgenic mice exhibited malignant lymphoma of B-cell origin. IgG heavy chain rearrangement confirmed the clonal B-cell nature of these lymphoproliferations. In contrast, T-cell receptor genes exhibited a germline (unrearranged) structure. Reverse transcription polymerase chain reaction analysis of transgenic spleens revealed that mRNA encoding cytokines IL-6 and IL-10 was upregulated, suggesting a possible mechanism for the B-cell expansion in vivo.

Multiple factors determine the selection of the ectodomain cleavage site of human cell surface macrophage colony-stimulating factor

Human cell surface macrophage colony-stimulating factor (CSF-1256, M-CSF alpha) is converted to a soluble growth factor by a regulated proteolytic cleavage process at amino acid residues 157-159. We have previously shown that multiple factors specified by the juxtamembrane region determine the cleavage efficiency [Deng, P., Rettenmier, C. W., and Pattengale, P. K. (1996) J. Biol. Chem. 271, 16338-16343]. In the present paper, we studied the effect of various deletion, insertion, and substitution mutations at or near the cleavage site on both the number and size of cleaved CSF-1(256) products to identify the mechanisms by which the cleavage sites are selected. Deletion of regions 161-162 or 163-165, C-terminal to the cleavage site, as well as deletion of region 150-156, N-terminal to the cleavage site, each yielded a single cleavage product that was smaller than that derived from the wild type (WT). In these experiments cleavage apparently occurred at a specific distance from the transmembrane domain. Insertion of three additional residues between the normal cleavage site and the transmembrane domain yielded one major product that was the same size as the processed form of WT CSF-1(256). In this case the selection of the cleavage site was apparently determined by the amino acid sequence of the juxtamembrane region rather than by the distance from the transmembrane domain. Other amino acid substitutions at the cleavage site caused changes in cleavage site selection, providing additional evidence for the role of amino acid sequence in cleavage site selection. Finally, a comparison of cleavage site selection in the presence and absence of tunicamycin treatment showed that N-glycosylation of certain mutant forms of CSF-1(256) sterically interfered with protease accessibility, which in turn had an effect on the selection of the site used for cleavage. Taken together, these results indicate that cleavage site selection is determined by the amino acid sequence of the juxtamembrane region, the distance of the site from the transmembrane domain, and steric accessibility of the protease.

Thymic lymphoproliferative disease after successful correction of CD40 ligand deficiency by gene transfer in mice

Inherited deficiency of the CD40 ligand (X-linked hyper-IgM syndrome) is characterized by failure of immunoglobulin isotype switching and severe defects of cell-mediated immunity. To test the potential for gene transfer therapy to correct this disorder, we transduced murine bone marrow or thymic cells with a retroviral vector containing the cDNA for the murine CD40 ligand (CD40L) and injected them into CD40L-/- mice. Even low-level, constitutive expression of the transgene stimulated humoral and cellular immune functions in these mice. With extended follow-up, however, 12 of 19 treated mice developed T-lymphoproliferative disorders, ranging from polyclonal increases of lymphoblasts to overt monoclonal T-lymphoblastic lymphomas that involved multiple organs. Our findings show that constitutive (rather than tightly regulated), low-level expression of CD40L can produce abnormal proliferative responses in developing T lymphocytes, apparently through aberrant interaction between CD40L+ and TCRalphabeta+CD40+ thymocytes. Current methods of gene therapy may prove inappropriate for disorders involving highly regulated genes in essential positions in proliferative cascades.

Immune response to Philadelphia chromosome-positive acute lymphoblastic leukemia induced by expression of CD80, interleukin 2, and granulocyte-macrophage colony-stimulating factor

We examined the potential of generating an immune response against Philadelphia chromosome-positive acute lymphoblastic leukemia. The immunostimulatory molecules chosen for this study were the cytokines IL-2 and GM-CSF and the costimulatory ligand CD80 (B7.1). We used a murine model based on a BALB/c pre-B cell line, BM185wt, in which leukemia is induced by the p185 BCR-ABL oncogenic product, which reproduces Philadelphia chromosome-positive ALL. BM185wt cells were transduced with retroviral vectors and the transduced clones expressing mIL-2, mGM-CSF, or mCD80 were used for challenge. Expression of the immunomodulators by BM185 cells was correlated with delay in leukemia development in immunocompetent mice, but not in immunodeficient mice, indicating an immune response against the modified leukemia cells. Expression of CD80 caused leukemia rejection in 50% of the cohort, which was associated with the CD4+ and CD8+ T cell-dependent development of anti-leukemia cytotoxic T lymphocytes. Furthermore, mice surviving the BM185/CD80 challenge or preimmunized with irradiated BM185/CD80 cells developed an immune response against subsequent challenge with the parental leukemia. These studies provide evidence that immunotherapeutic approaches can be developed for the treatment of ALL.

Retrovirus-mediated gene transfer of NPM-ALK causes lymphoid malignancy in mice

Approximately 5% to 10% of all non-Hodgkin's lymphomas contain a t(2;5)(p23;q35) chromosomal rearrangement, which we have previously shown results in the generation of the fusion protein nucleophosmin-anaplastic lymphoma kinase (NPM-ALK). To assess the transforming potential of NPM-ALK in an animal model, we infected 5-fluorouracil-treated murine bone marrow using retroviral stocks and transplanted this infected marrow into lethally irradiated BALB/cByJ mice. Male mice were transplanted with bone marrow from female donors at 10 weeks of age, with 7 of the animals receiving marrow infected with a retroviral construct, pSR alphaMSVtkneo-NPM-ALK, that contains the human NPM-ALK cDNA, and 4 serving as a control group, receiving "empty" pSR alphaMSVtkneo-infected marrow. Whereas all mice in the control group were alive and well up to 11 months after transplantation, 4 of the 7 mice transplanted with marrow containing the NPM-ALK construct developed lymphoma within 4 to 6 months. Tumors arose in the mesenteric lymph nodes, with metastases to the lungs, kidneys, liver, spleen, and the paraspinal area. When cells from the tumors and bone marrow were transplanted into sublethally irradiated secondary recipients, 10 of these 13 mice developed tumors within 9 months. Immunoblot analysis of cell lysates using an ALK polyclonal antibody showed NPM-ALK expression in all tumors examined. Histologically, the tumors were composed of a uniform population of large immunoblastic cells with basophilic cytoplasm, centrally placed nuclei, and distinct nucleoli. Genotypic analysis showed that the tumors were B-lineage and clonal, with rearrangements of the Ig heavy- and kappa light-chain loci and no rearrangements of the T-cell receptor beta locus. Immunocytochemical studies confirmed the presence of IgM heavy chains and kappa light chains within the tumor cells. Thus, in this retroviral gene transfer model, NPM-ALK expression in mice causes B-lineage large-cell lymphoma, suggesting a direct causative role for this activated fusion tyrosine kinase in human lymphoma.

The role of individual cysteine residues in the processing, structure, and function of human macrophage colony-stimulating factor

The shortest form of human macrophage colony-stimulating factor (M-CSF alpha, CSF-1(256) is expressed on the cell surface as a homodimeric type I transmembrane glycoprotein. The seven cysteine residues in CSF-1(256) form three intrachain disulfide bonds (Cys7-Cys90, Cys48-Cys139, and Cys 102-Cys146), and one interchain disulfide bond (Cys31-Cys31). To examine the role of the seven cysteine residues in CSF-1(256), we replaced each half-cystine by a serine using site-directed mutagenesis, and stably expressed the mutated genes in mouse NIH 3T3 cells. We showed that each of the seven cysteines of CSF-1(256) is essential for its biological activity. Our data further show that substitution of Cys48 or Cys139 totally blocked dimer formation and cell surface expression of CSF-1(256), and that substitution of Cys102 and Cys146 severely impaired CSF-1 dimer formation and cell surface expression. In contrast, substitution of Cys7 or Cys90 affected CSF-1 dimer formation to a lesser degree but did not significantly affect cell surface expression of CSF-1. Furthermore, disruption of the interchain disulfide bond led to efficient cell surface expression of monomeric CSF-1. All of the cell surface expressed mutant CSF-1 proteins, either dimeric or monomeric, still underwent efficient ectodomain cleavage. The electrophoretic mobilities of the cleaved dimeric ectodomains of these mutant CSF-1 proteins on SDS-PAGE exhibited distinctly different patterns as compared with the wild type. Substitution of either Cys7 or Cys90 produced the same shift, while substitution of either Cys102 or Cys146 resulted in a shift distinct from that caused by substitution of Cys7 or Cys90. These data suggest that replacement of either of a pair of intrachain half-cystine residues results in similar conformational changes, and may provide a novel method for mapping intrachain disulfide bonds in dimeric proteins.

Structural requirements for the ectodomain cleavage of human cell surface macrophage colony-stimulating factor

One form of human macrophage colony-stimulating factor (CSF-1(256), M-CSFalpha) is a member of a restricted set of cell surface transmembrane proteins, which is selected to undergo proteolytic ectodomain cleavage. To determine the substrate requirements for this cleavage, we have constructed a series of mutations in the cytoplasmic tail, transmembrane domain, and juxtamembrane region of CSF-1(256) and stably expressed the mutated genes in NIH 3T3 cells. Our results demonstrate that membrane association of the CSF-1 precursor is required for cleavage of its growth factor ectodomain and furthermore that the juxtamembrane region Pro161-Gln162-Leu163-Gln164-Glu165 (PQLQE) (residues 161-165 of the ectodomain) is an essential determinant of cell surface CSF-1(256) cleavage and that the cleavage site is partially sequence-specific. Furthermore, a mechanism of steric hindrance, which likely involves interference with protease accessibility, is postulated to explain the observed decreases in the cleavage efficiency in certain CSF-1 mutants. Finally, our results strongly suggest that the CSF-1 ectodomain is cleaved at or very near the cell surface by a membrane-associated proteolytic system.

BCR/ABL P210 and P190 cause distinct leukemia in transgenic mice

DNA constructs encoding BCR/ABL P210 have been introduced into the mouse germ line using microinjection of one-cell fertilized eggs. Kinetics of BCR/ABL P210 expression in transgenic mice were very similar to those of BCR/ABL P190 constructs in transgenic mice. mRNA transcripts were detectable early in embryonic development and also in hematopoietic tissue of adult animals. Expression of BCR/ABL in peripheral blood preceded development of overt disease. P210 founder and progeny transgenic animals, when becoming ill, developed leukemia of B, T-lymphoid, or myeloid origin after a relatively long latency period. In contrast, P190-transgenic mice exclusively developed leukemia of B-cell origin, with a relatively short period of latency. The observed dissimilarities are most likely due to intrinsically different properties of the P190 and P210 oncoproteins and may also involve sequences that control transgene expression. The delayed progression of BCR/ABL P210-associated disease in the transgenic mice is consistent with the apparent indolence of human chronic myeloid leukemia during the chronic phase. We conclude that, in transgenic models, comparable expression of BCR/ABL P210 and BCR/ABL P190 results in clinically distinct conditions.

Biological characterization and molecular cloning of murine C-type retroviruses derived from the TSZ complex from mainland China

Characterization of the SRS murine retrovirus complex, derived from the TSZ system of murine leukemia developed in China, was carried out. The initial stock contained XC+, NB-tropic virus (and possibly other viruses), and induced several neoplastic diseases in neonatally inoculated NIH Swiss mice: erythroid leukemia, myeloid leukemia (acute myeloblastic leukemia), and lymphoblastic lymphoma (both B- and T-lymphoid). In addition, approximately 30% of inoculated animals developed central nervous system disease--hindlimb paralysis or semilateral paralysis. Rescue of virus from the spleen of an animal with combined erythroid/myeloid leukemia, followed by endpoint dilution gave two stocks: 19-6 (XC+, NB-tropic) and 19-7 (XC-, NB-tropic). Both stocks induced erythroid and myeloid leukemia, and 19-6 induced CNS symptoms as well. Southern blot analysis indicated that the predominant viruses from the 19-6 and the 19-7 cultures were related, but different in the env region. An infectious virus molecular clone of provirus from 19-6 cells was obtained. The resulting cloned virus [SRS 19-6 murine leukemia virus (MuLV)] induced four kinds of leukemia: erythroid, myeloid, B-lymphoma, and T-lymphoma; in many cases, more than one tumor type was identified in the same animal. Such a broad spectrum of leukemias induced by a cloned MuLV is unusual. Flaccid hindlimb paralysis induced by SRS 19-6 MuLV could be attributed to meningeal B-lymphoma. Immunofluorescent staining with a panel of env-specific monoclonal antibodies confirmed that the 19-6 and 19-7 viral stocks contained different viruses, which differed from previously characterized MuLVs. The viruses of the SRS complex may provide interesting reagents for investigations of MuLV-induced disease.

Leukaemogenesis by the delta Mo + SV Moloney murine leukaemia virus (M-MuLV) variant in E mu pim-1 transgenic mice: high frequency of recombination with a solo endogenous M-MuLV LTR in vivo

We previously described an enhancer variant of Moloney murine leukaemia virus (M-MuLV), delta Mo + SV M-MuLV, in which the enhancers of MuLV have been deleted and replaced with the enhancers of the simian virus 40 (SV40). When this virus is injected into neonatal NIH Swiss mice, pre-B and B-lymphoblastic lymphomas develop with a latency of 17 months. Van Lohuizen et al. (1989) described a line of transgenic mice that carry an activated pim-1 proto-oncogene transgene (E mu pim-1). They also reported that E mu pim-1 transgenic mice show greatly accelerated lymphoma development when infected with wild-type M-MuLV at birth. In these experiments, neonatal E mu pim-1 transgenic mice were infected intraperitoneally with delta Mo + SV M-MuLV. Marked acceleration of T-lymphoid leukaemia was seen. However, 10 of the 11 tumours analysed were found to be negative for the SV40 enhancers, but they still contained M-MuLV DNA as measured by Southern blot analysis. The LTRs on viruses cloned from two such tumours (as well as on virus recovered by infection onto NIH 3T3 cells) were characterized by PCR amplification, molecular cloning and sequence analysis. The LTR's from the two tumours were identical to each other and were distinct from both the delta Mo + SV M-MuLV and wild-type M-MuLV LTRs. However, they were identical to a rearranged solo M-MuLV LTR present in the E mu pim-1 transgene. These results indicate that the recombination in vivo between delta Mo + SV M-MuLV and the E mu pim-1 transgene yielded a replication-competent and pathogenic virus at high efficiency. This is the first report of in vivo recombination between an exogenous MuLV and a solo endogenous LTR.

Establishment and characterization of a human mixed-lineage, T-lymphoid/myeloid cell line (USP-91)

We report the establishment of a novel cell line from a pediatric patient with recurrent non-Hodgkin's lymphoma. This cell line, termed USP-91, showed both T-lymphoid cell as well as myeloid (ie, nonlymphoid) cell characteristics using a comprehensive multiparameter approach. The initial growth of this cell line was dependent on the presence of the murine stromal cell line, 14F1.1. Subsequently, a phenotypically stable, stroma-independent cell line was established. Although the recurrent biopsy material and the derivative cell line, USP-91, were clonally-derived from T-lineage lymphoid cells, as evidenced by the same rearrangement of the T-cell receptor-beta locus, USP-91 coexpressed both the T-cell antigens CD7, CD3, and CD4, and the myeloid antigens CD13, CD33, CD11b, and CD34. The myeloid features of USP-91 were most consistent with monocytic differentiation as these cells expressed alpha-napthol acetate esterase, lysozyme, alpha-1-antitrypsin, alpha-1-antichymotrypsin, as well as the cell surface receptor for macrophage colony-stimulating factor. In addition, incubation in the presence of phorbol esters induced USP-91 to exhibit morphologic and functional properties of mature mononuclear phagocytes. The expression of this bilineage phenotype suggests that USP-91 represents the malignant transformation of a progenitor cell capable of either myelomonocytic or T-lymphoid differentiation.

Specificity of disease induced by M-MuLV chimeric retroviruses containing v-myc or v-src is not determined by the LTR

The long terminal repeats (LTRs) of defective Moloney Murine Leukemia Virus (M-MuLV) containing the avian v-myc and v-src oncogenes were exchanged for LTRs from murine retroviruses inducing myeloid and erythroid disease, in an attempt to retarget disease specificity. Chimeric MuLVs containing either the Myeloproliferative sarcoma virus or the Rauscher mink cell focus-inducing virus LTRs induced the same disease as the parental viruses, suggesting that for these viruses the v-myc and v-src oncogenes are the major determinants in the disease specificity. However, substitution of the LTRs did affect the efficiency of tumorigenesis.

Quantitative and functional studies of impaired natural killer (NK) cells in patients with myelofibrosis, essential thrombocythemia, and polycythemia vera. I. A potential role for platelet-derived growth factor in defective NK cytotoxicity

In view of the possibility that immunological dysfunctions may be involved in initiating or contributing to the pathogenesis of myeloproliferative disease, we investigated quantitative and functional activity of natural killer (NK) cells in patients with polycythemia vera, essential thrombocythemia and myelofibrosis, and have demonstrated, especially in myelofibrosis, a measurable cytotoxic defect in the ability of their peripheral blood mononuclear cells to efficiently kill the standard NK target, K-562. Furthermore, highly purified, FACS-sorted CD16+ lymphoid cells from patients with myelofibrosis were consistently defective in their ability to lyse K-562 targets, and could not be augmented substantially with recombinant interleukin (IL)-2. Only patients with myelofibrosis had significantly lower percentages and absolute numbers of CD16+ cells as compared to patients with essential thrombocythemia and polycythemia vera. Further experiments demonstrated that patients with myelofibrosis, although having fewer CD16+ NK cells, had a significantly increased proportion of CD16+ cells with detectable platelet-derived growth factor (PDGF) on their surface. In contrast, surface PDGF was barely detectable on CD16+ cells from patients with polycythemia vera and essential thrombocythemia, as well as from normal controls. Having previously reported that physiologic quantities of PDGF significantly inhibit human NK cell cytotoxicity, and that patients with myelofibrosis and essential thrombocythemia have significantly elevated circulating levels of plasma PDGF, we now have demonstrated that pretreatment of normal NK cells with concentrated, PDGF-containing, platelet-poor plasma from patients with these diseases significantly inhibits NK cytotoxicity. This inhibitory effect was reversed by neutralization of plasma PDGF with anti-PDGF (coupled to Sepharose resin). Both the NK defects demonstrated in this study, and the abnormal plasma PDGF results reported earlier, are most striking in myelofibrosis and least abnormal in polycythemia vera, with an intermediate degree of abnormality in essential thrombocythemia. Our new findings suggest a causal correlation between abnormal platelet release, plasma accumulation of PDGF, and the observed NK immunodeficiency in these myeloproliferative patients.

Multiple tumor types appear in a transgenic mouse with the ras oncogene

A transgenic mouse strain with the zeta-globin promoter and the vHa-ras oncogene develops an array of mesenchymal and epithelial neoplasms described here. The predominate mesenchymal tumors were dermal spindle cell tumors, which resembled malignant fibrous histiocytomas found in humans. They were associated with hepatosplenomegaly and developed beneath squamous papillomas. The hepatosplenomegaly was associated with infiltrates of cells that tended toward myelocytic or monocytic differentiation. Other epithelial tumors included keratoacanthomas and squamous cell carcinomas. Squamous cysts, some with squamous cell carcinomas, of the salivary glands and mammary carcinomas were also found. Odontogenic tumors, which sometimes differentiated into ameloblastomas, were one of the more unusual tumor types observed. Other, less frequent tumors were also noted. The tumors described here are a potentially valuable experimental resource that may lead to an understanding of malignant fibrous histiocytoma-like lesions, odontogenic tumors, and tumor progression.

Restricted oncogenicity of BCR/ABL p190 in transgenic mice

A chimeric BCR/ABL oncogene encoding the p190 protein has been introduced into the mouse germline using microinjection of one-cell fertilized eggs. Founder and progeny transgenic animals, when becoming ill, were found to develop lymphoblastic leukemia/lymphoma which was transplantable to compatible recipients. Lymphoblasts were arrested at the pre-B stage of development. Expression of BCR/ABL was not detected in peripheral blood during the early stages of leukemia but became evident as the disease progressed. However, the transgene was expressed early in development in bone marrow and was also transcribed in nonhematopoietic tissues although this did not result in tumorigenesis. These results strongly suggest that the oncogenicity of BCR/ABL is limited to hematopoietic cells, including pre-B cells or their progenitors.

Human bcr-abl gene has a lethal effect on embryogenesis

The chimaeric bcr-abl oncogene is thought to have a crucial role in the development or maintenance of chronic myelogenous leukaemia. To study this oncogene in a more direct way, the bcr-abl gene encoding the P210 protein under control of the bcr gene promoter was introduced into fertilized one-cell embryos, which were then re-implanted into foster mothers. Our data, obtained after several experiments, demonstrate that no live transgenic progeny could be obtained using this bcr-abl construct. The bcr gene is expressed in the course of embryogenesis and the bcr-abl gene product appears to have a pleiotropic lethal effect during this period of development. In concordance, several gross abnormalities were observed while no evidence of neoplastic formation was found. These results suggest that the bcr-abl encoded protein severely affects the process of normal embryogenesis.

Deletion of a GC-rich region flanking the enhancer element within the long terminal repeat sequences alters the disease specificity of Moloney murine leukemia virus

Moloney murine leukemia virus (M-MuLV) is a replication-competent retrovirus which induces T-lymphoblastic lymphoma 2 to 4 months after inoculation. Enhancer sequences in the U3 region of the M-MuLV long terminal repeat, primarily the 75-bp tandem repeats, strongly influence the disease specificity and latency of M-MuLV. We investigated the role of GC-rich sequences downstream of the tandem repeats in the disease specificity of M-MuLV. A recombinant M-MuLV lacking 23 bases of a GC-rich sequence (-174 to -151), Delta 27A M-MuLV, was tested for pathogenesis in neonatal NIH Swiss mice. Delta 27A M-MuLV induced disease with a longer latency than did M-MuLV (7 versus 3 months) in greater than 85% of inoculated mice. More interestingly, this virus showed an expanded repertoire of hematopoietic diseases. Molecular analyses and histopathologic examinations indicated that while 39% of mice inoculated with Delta 27A M-MuLV developed T-cell lymphoblastic lymphoma typical of wild-type M-MuLV, the majority developed acute myeloid leukemia, erythroleukemia, or B-cell lymphoma. Viral DNA corresponding to Delta 27A M-MuLV was detectable in most of the tumors analyzed. These findings indicate that the GC-rich region significantly influences the disease specificity and latency of M-MuLV.

Inhibition of human natural killer cell activity by platelet-derived growth factor (PDGF). III. Membrane binding studies and differential biological effect of recombinant PDGF isoforms

We have previously reported that platelet-derived growth factor (PDGF) substantially inhibits human natural killer (NK) cell cytotoxicity, and that NK cells possess high-affinity surface binding sites for the PDGF-AB isoform. In this communication, we present direct evidence for the presence of A-type (alpha) PDGF receptors on human NK cells by demonstrating that human NK cells have approximately 150,000 high-affinity, surface binding sites for recombinant (r)PDGF-AA and approximately 300,000 high-affinity, surface binding sites for rPDGF-BB. This was determined by the competitive binding of 125I-labelled rPDGF-AA or 125I-labelled rPDGF-BB and homologous unlabelled rPDGF-AA or rPDGF-BB to FACS-sorted, CD16+ lymphoid (NK) cells, and Scatchard analysis of these data. In addition, we also demonstrate that the various isoforms of PDGF have differential effects on NK-cell cytotoxicity. Physiological quantities (100 ng/ml) of rPDGF-BB homodimers, highly purified PDGF-AB heterodimers from outdated platelets, and rPDGF-AB heterodimers substantially inhibited NK-cell cytotoxicity in both a dose- and time-dependent manner. In contrast, pretreatment of NK cells with equivalent nanogram amounts of rPDGF-AA homodimers resulted in a significantly weaker inhibitory effect on NK-cell cytotoxicity as compared with the PDGF-BB and PDGF-AB isoforms. The implications of these findings are discussed.

Acute leukaemia in bcr/abl transgenic mice

The Philadelphia chromosome, widely implicated in human leukaemia, is the result of a reciprocal translocation t(9;22) (q34;q11) in which the abl oncogene located at 9q34 is translocated to chromosome 22q11, where it is fused head-to-tail with 5' exons of the bcr gene. In acute lymphoblastic leukaemia, some patients have a breakpoint within the major breakpoint cluster region of the bcr gene, whereas others have the break within its first intron. This second type of translocation results in the transcription of a 7.0-kilobase chimaeric bcr/abl messenger RNA translated into a bcr/abl fusion protein, p190, which has an abnormal tyrosine kinase activity and is strongly autophosphorylated in vitro. We have generated mice transgenic for a bcr/abl p190 DNA construct and find that progeny are either moribund with, or die of acute leukaemia (myeloid or lymphoid) 10-58 days after birth. This finding is evidence for a causal relationship between the Philadelphia chromosome and human leukaemia.

Immunogenetic analysis of bone marrow aspirates in patients with non-Hodgkin lymphomas

The immunogenetic analysis (IGA) on the staging bone marrow aspirates in 15 patients with non-Hodgkin lymphoma (NHL) is reported. We found the sensitivity of IGA and morphologic examination in detecting bone marrow involvement by malignant lymphoma to be 91% and 82%, respectively. In 11 cases there was agreement between the morphologic findings and IGA. In 8 of these 11 cases, IGA confirmed the morphologic involvement of the bone marrow by demonstrating clonal rearrangement of either the immunoglobulin heavy- and/or light-chain or the T-cell receptor beta chain (TCR) genes. In 3 of these 11 cases, morphology showed no involvement and IGA showed germline configurations for both the immunoglobulin heavy- and light-chain or the TCR genes. In 2 additional cases the techniques proved to be complementary, as involvement was detected by only 1 of the 2 procedures. In 1 of these 2 cases, IGA showed gene rearrangement while morphologic examination was negative for involvement by NHL, while in the other case, morphologic examination showed involvement by NHL, but IGA did not show gene rearrangement. IGA was also useful in determining the clonality of solitary lymphoid nodules in the 2 remaining cases when morphologic interpretation was equivocal. In the 12 cases with bone marrow involvement, the immunophenotype and immunogenotype agreed in 11 cases. In the one case in which there was a discordance between the immunophenotype and immunogenotype, the immunophenotype was incorrectly interpreted as B-cell lineage, while the immunogenotype demonstrated a T-cell lineage. IGA also demonstrated a clonal population in 1 case of T-chronic lymphocytic leukemia where other techniques could not demonstrate the clonality of the pathologic process. IGA analysis may detect bone marrow involvement in NHL which may not be detected by morphologic examination because of patchy distribution.

Platelet-derived growth factor concentrations in platelet-poor plasma and urine from patients with myeloproliferative disorders

Our enzyme-linked immunosorbent assay (ELISA) for measuring human platelet-derived growth factor (PDGF) detects nanogram quantities (ranging from 0.007 to 16 ng/100 microL) in purified PDGF standards. This assay is sensitive enough for studying plasma and urine. The range in normal volunteers was 0.6 to 2.3 micrograms/L for platelet-poor plasma and 1.4 to 3.3 micrograms/L for urine. We determined PDGF levels in the circulation (outside platelets) in patients with myeloproliferative diseases. Platelet-poor plasma and urine PDGF were significantly elevated in patients with myelofibrosis (6.2 +/- 2.0 micrograms/L for plasma; 7.8 +/- 2.4 micrograms/L for urine) and essential thrombocythemia (5.5 +/- 1.5 micrograms/L for plasma; 11.4 +/- 2.2 micrograms/L for urine), but not in patients with chronic myelogenous leukemia (2.1 +/- 0.4 micrograms/L for plasma; 2.8 +/- 1.2 micrograms/L for urine). Polycythemia vera produced an intermediate pattern: although plasma PDGF was within the normal range (2.1 +/- 0.2 micrograms/L), urine levels were increased (3.7 +/- 0.6 micrograms/L). These results show that PDGF is increased in the circulation in some but not all myeloproliferative diseases, and suggest that this is due to abnormal in vivo release from either megakaryocytes in the bone marrow or circulating platelets.

Animal models of human disease. Pathology and molecular biology of spontaneous neoplasms occurring in transgenic mice carrying and expressing activated cellular oncogenes

This present review focuses on spontaneous neoplasms occurring in transgenic mice carrying and expressing activated cellular oncogenes. The historical development of transgenic mice as in vivo disease models is briefly traced, followed by a brief description of the actual technology in such systems. Additional emphasis is placed on the concept of targeting activated cellular oncogenes to specific tissues in transgenic mice. Cumulative experience with activated (Vmyc, ras, and neu (erb-B2] oncogenes in transgenic mice is considered in detail, with particular attention paid to the observed pathology, as well as to the kinetics of disease occurrence. It is concluded that transgenic mice offer the interested investigator(s) an excellent prospective, in vivo model of oncogenesis.

Murine interleukin-4 displays potent anti-tumor activity in vivo

We have devised a sensitive means to assess the anti-tumor effect of cytokines that act via the mobilization of host-mediated defenses. This assay involves transfecting malignant cells to produce a specific cytokine (in this case, IL-4) and measuring the ability of transfectants to form tumors alone and when mixed with a variety of nontransfected tumor cells. In this way, we have identified a potent, non-cell autonomous, anti-tumor effect of IL-4 which is effective against a wide range of tumor cell types in vivo. The effect is reversed by anti-IL-4 antibody, correlates closely with levels of IL-4 production, and is evident in nu/nu mice. The anti-tumor effect seems to be mediated by an inflammatory infiltrate composed of eosinophils and macrophages.

Differentiation in vitro of a leukemia virus-induced B-cell lymphoma into macrophages

Cells of the hemopoietic system arise by proliferation and differentiation of progenitor cells. This process begins with multipotential stem cells which can self-renew and also undergo progressive differentiation to progenitor cells committed to particular lineages, ultimately yielding mature blood cells (D. Metcalf and M. A. S. Moore, Haematopoietic Cells, 1971). Early commitment of lymphoid progenitors is generally believed to separate the lymphoid lineage from the myeloid and erythroid lineages, whose progenitors are separated late in differentiation (Metcalf and Moore, 1971). We recently developed a derivative of Moloney murine leukemia virus (M-MuLV) in which the enhancer sequences from simian virus 40 were substituted into the M-MuLV long terminal repeat. This recombinant virus (delta Mo + SV M-MuLV) induces pre-B and B lymphoid leukemia with long latency after inoculation of 2-day-old NIH Swiss mice (R. Hanecak, P. K. Pattengale, and H. Fan, J. Virol. 62:2427-2436, 1988). In this report, we describe the derivation of a permanent, virus-producing cell line with the phenotypic characteristics of mature macrophages from a B-cell-derived lymphoblastic lymphoma induced by delta Mo + SV M-MuLV. Comparison studies of immunoglobulin heavy-chain gene rearrangements and also delta Mo + SV M-MuLV proviral integration sites confirmed that the macrophage cell line was derived from the original B-lymphoblastic lymphoma. Moreover, inoculation of the macrophage cell line into animals resulted in histiocytic sarcomas of the macrophage type, thus reflecting stable conversion of B-lymphoid tumor cells to the macrophage phenotype. These results suggest a closer relationship between lymphoid and myeloid cells than previously believed.

Inhibition of human natural killer cell activity by platelet-derived growth factor. II. Membrane binding studies, effects of recombinant IFN-alpha and IL-2, and lack of effect on T cell and antibody-dependent cellular cytotoxicity

We have previously reported that a 2-h pre-treatment with physiologic (nanogram) quantities of the naturally occurring biologic substance, platelet-derived growth factor (PDGF), significantly inhibits human NK cell activity (cytotoxicity) in a dose-dependent manner as measured against the NK-sensitive target K-562, as well as the single-cell binding of human NK cells to K-562 targets (i.e., conjugate formation). In this study, we have completed a more detailed and longer time course evaluation of PDGF-mediated human NK cell inhibition, and demonstrate a more marked inhibition of human NK cells at 8 to 20 h as compared to 2 h. We also show that either rIFN-alpha or IL-2 reverses the PDGF-mediated NK cell inhibition; and furthermore, that PDGF does not inhibit the lymphokine augmented NK activity of recombinant alpha-IFN or IL-2-activated human NK cells. In addition, we have further demonstrated that PDGF does not inhibit cytotoxic T cell activity as generated in the MLR, nor does PDGF significantly inhibit antibody-dependent cellular cytotoxicity. Finally, we have demonstrated that human NK cells have roughly 12,000 high-affinity, surface binding sites for PDGF, as determined by the competitive binding of 125I-labeled purified PDGF and unlabeled PDGF to B73.1+ FACS-sorted lymphoid (NK) cells, and Scatchard analysis of these data. The implications of these findings are discussed.

Inhibition of human natural killer cell activity by platelet-derived growth factor. II. Membrane binding studies, effects of recombinant IFN-alpha and IL-2, and lack of effect on T cell and antibody-dependent cellular cytotoxicity

We have previously reported that a 2-h pre-treatment with physiologic (nanogram) quantities of the naturally occurring biologic substance, platelet-derived growth factor (PDGF), significantly inhibits human NK cell activity (cytotoxicity) in a dose-dependent manner as measured against the NK-sensitive target K-562, as well as the single-cell binding of human NK cells to K-562 targets (i.e., conjugate formation). In this study, we have completed a more detailed and longer time course evaluation of PDGF-mediated human NK cell inhibition, and demonstrate a more marked inhibition of human NK cells at 8 to 20 h as compared to 2 h. We also show that either rIFN-alpha or IL-2 reverses the PDGF-mediated NK cell inhibition; and furthermore, that PDGF does not inhibit the lymphokine augmented NK activity of recombinant alpha-IFN or IL-2-activated human NK cells. In addition, we have further demonstrated that PDGF does not inhibit cytotoxic T cell activity as generated in the MLR, nor does PDGF significantly inhibit antibody-dependent cellular cytotoxicity. Finally, we have demonstrated that human NK cells have roughly 12,000 high-affinity, surface binding sites for PDGF, as determined by the competitive binding of 125I-labeled purified PDGF and unlabeled PDGF to B73.1+ FACS-sorted lymphoid (NK) cells, and Scatchard analysis of these data. The implications of these findings are discussed.

A human immunoglobulin gene reduces the incidence of lymphomas in c-Myc-bearing transgenic mice

Transgenic mice carrying an immunoglobulin enhancer-driven c-myc oncogene develop rapid-onset pre-B cell lymphomas. The incidence of these malignancies is greatly reduced when an additional transgene encoding the membrane-bound form (but not the secreted form) of human Ig mu is bred into the susceptible strain. This suppressive effect correlates with a subtle alteration in B-cell development induced by the immunoglobulin transgene.

Characterization of lymphoid tumors induced by a recombinant murine retrovirus carrying the avian v-myc oncogene. Identification of novel (B-lymphoid) tumors in the thymus

Lymphoid tumors induced by a recombinant murine retrovirus carrying the v-myc oncogene of avian MC29 virus were characterized. The Moloney murine leukemia virus myc oncogene (M-MuLV (myc], carried by an amphotropic MuLV helper, induced tumors in NIH Swiss and NFS/N mice after a relatively long latency (8 to 24 wk). Tumor masses appeared in the thymus, spleen, and lymph nodes. Flow cytometry of the tumor cells indicated that approximately 50% were positive for Thy 1.2. Most of these tumors also expressed one or more other cell surface markers of thymocytes and mature T cells (CD4, CD8). Southern blot hybridization revealed genomic rearrangements for the TCR beta genes. The TCR beta analysis suggested that the M-MuLV(myc)-induced Thy 1.2+ tumors were derived from somewhat less mature cells than tumors induced by M-MuLV, which is a classical non-acute retrovirus lacking an oncogene. The remainder of the M-MuLV(myc)-induced tumors were Thy 1.2-, but they were positive for Ly-5 (B220) and also for MAC-2. The Thy 1.2- tumors were characteristically located in the thymus. However, they were negative for TCR beta gene rearrangements. Some, but not all, of the Thy 1.2- tumors contained rearrangements for Ig genes. Additionally, they typically expressed mRNA specific for B but not for T cells. Thus, these thymic tumors had characteristics of the B cell lineage. Tumor transplantation experiments demonstrated that the Thy 1.2- tumor cells could reestablish in the thymus and spleen of irradiated hosts, and low level expression of the Thy 1 molecule was observed in the thymus but not the spleen on the first passage. After serial passage, one Thy 1- tumor altered its cell surface phenotype to Thy 1low B220-.

Characterization of lymphoid tumors induced by a recombinant murine retrovirus carrying the avian v-myc oncogene. Identification of novel (B-lymphoid) tumors in the thymus

Lymphoid tumors induced by a recombinant murine retrovirus carrying the v-myc oncogene of avian MC29 virus were characterized. The Moloney murine leukemia virus myc oncogene (M-MuLV (myc], carried by an amphotropic MuLV helper, induced tumors in NIH Swiss and NFS/N mice after a relatively long latency (8 to 24 wk). Tumor masses appeared in the thymus, spleen, and lymph nodes. Flow cytometry of the tumor cells indicated that approximately 50% were positive for Thy 1.2. Most of these tumors also expressed one or more other cell surface markers of thymocytes and mature T cells (CD4, CD8). Southern blot hybridization revealed genomic rearrangements for the TCR beta genes. The TCR beta analysis suggested that the M-MuLV(myc)-induced Thy 1.2+ tumors were derived from somewhat less mature cells than tumors induced by M-MuLV, which is a classical non-acute retrovirus lacking an oncogene. The remainder of the M-MuLV(myc)-induced tumors were Thy 1.2-, but they were positive for Ly-5 (B220) and also for MAC-2. The Thy 1.2- tumors were characteristically located in the thymus. However, they were negative for TCR beta gene rearrangements. Some, but not all, of the Thy 1.2- tumors contained rearrangements for Ig genes. Additionally, they typically expressed mRNA specific for B but not for T cells. Thus, these thymic tumors had characteristics of the B cell lineage. Tumor transplantation experiments demonstrated that the Thy 1.2- tumor cells could reestablish in the thymus and spleen of irradiated hosts, and low level expression of the Thy 1 molecule was observed in the thymus but not the spleen on the first passage. After serial passage, one Thy 1- tumor altered its cell surface phenotype to Thy 1low B220-.

Leukemogenicity of Moloney murine leukemia viruses carrying polyoma enhancer sequences in the long terminal repeat is dependent on the nature of the inserted polyoma sequences

The leukomogenicity of Moloney murine leukemia virus (M-MuLV) variants with chimeric long terminal repeats (LTRs) containing sequences from polyomavirus was studied. We previously showed that insertion of the B enhancer element from the PyF101 variant into the M-MuLV LTR between the M-MuLV enhancers and promoter abolished leukemogenicity. PyF101 differs from wild-type polyoma in that it can productively infect undifferentiated F9 embryonal carcinoma cells; this is due to alterations in the B enhancer element. Two additional chimeric M-MuLVs were generated that contained the B enhancers from wild-type polyoma and also from a second host range variant (PyF441), which differs from wild-type polyoma by only a single base change. In contrast to Mo+PyF101 M-MuLV, both Mo+Pywt and Mo+-PyF441 M-MuLV induced T-lymphoid leukemia in neonatal NIH Swiss mice with the same time course as wild-type M-MuLV. Thus the lack of leukemogenicity of Mo+PyF101 M-MuLV was related to the exact nature of the PyF101 B enhancers. While both Mo+Pywt and Mo+PyF441 M-MuLVs induced leukemia, they showed differences when the resulting tumors were examined. First, approximately one-third of the tumors induced by Mo+Pywt M-MuLV contained proviruses which lacked polyoma sequences, while all of the tumors induced by Mo+PyF441 M-MuLV contained proviruses with the chimeric LTR. Second, a majority of tumors induced by Mo+Pywt M-MuLV (and also wild-type, M-MuLV) showed proviral integrations near one or more of the cellular c-myc, pim-1, or pvt-1 loci. In contrast, tumors induced by Mo+PyF441 M-MuLV showed infrequent integrations at these loci.

Transgenic mice bearing the human c-myc gene activated by an immunoglobulin enhancer: a pre-B-cell lymphoma model

Transgenic mice carrying a fusion gene in which the mouse immunoglobulin enhancer has been inserted into an otherwise normal human c-myc gene develop a narrow spectrum of pre-B-cell lymphomas. Tumor occurrence is correlated with expression of the transgene in organs in which large numbers of pre-B cells predominate. These tumors, which arise stochastically, are virtually all lymphoblastic lymphomas of the pre-B-cell type. Evidently the isolated enhancer targets oncogene expression and tumorigenesis to the early B-cell population in preference to more mature B-cell populations. The transgene also confers enhanced in vitro growth properties on nontransformed pre-B cells as observed in bone marrow cultures derived from transgenic animals. These cultured cells represent a population in which the activating function of c-myc can be uncoupled from secondary oncogenic events occurring in vivo.

Single-step induction of mammary adenocarcinoma in transgenic mice bearing the activated c-neu oncogene

We have used transgenic mice that carry an activated c-neu oncogene driven by a mouse mammary tumor virus (MMTV) promoter to assess the stepwise progression of carcinogenesis in mammary epithelium. Unlike the stochastic occurrence of solitary mammary tumors in transgenic mice bearing the MMTV/c-myc or the MMTV/v-Ha-ras oncogenes, transgenic mice uniformly expressing the MMTV/c-neu gene develop mammary adenocarcinomas that involve the entire epithelium in each gland. Because these tumors arise synchronously and are polyclonal in origin, expression of the activated c-neu oncogene appears to be sufficient to induce malignant transformation in this tissue in a single step. In contrast, expression of the c-neu transgene in the parotid gland or epididymis leads to benign, bilateral epithelial hypertrophy and hyperplasia which does not progress to full malignant transformation during the observation period. These results indicate that the combination of activated oncogene and tissue context are major determinants of malignant progression and that expression of the activated form of c-neu in the mammary epithelium has particularly deleterious consequences.

Addition of substitution of simian virus 40 enhancer sequences into the Moloney murine leukemia virus (M-MuLV) long terminal repeat yields infectious M-MuLV with altered biological properties

Moloney murine leukemia virus (M-MuLV) is a replication-competent retrovirus which induces T-cell lymphoma in mice. The enhancer sequences present within the M-MuLV long terminal repeat (LTR) region of the proviral genome have been shown to influence the disease specificity of the virus strongly. We examined the contribution of the M-MuLV enhancers to the transcriptional activity and pathogenesis of M-MuLV by constructing LTRs containing heterologous enhancer elements. The simian virus 40 enhancer region (72- and 21-base-pair repeats) was inserted into the U3 region (at -150 base pairs) of the M-MuLV LTR (Mo + SV) and also into a deleted form of the LTR which lacks the M-MuLV enhancer sequences (delta Mo + SV). These chimeric LTRs were used to generate infectious M-MuLVs by transfection of corresponding proviral plasmids into mouse fibroblasts. The relative infectivities of Mo + SV and delta Mo + SV recombinant viruses as determined by rat XC cell plaque assay and reverse transcriptase assay were 60 to 70% of wild-type M-MuLV levels. To study the pathogenicity of these two recombinant viruses, we inoculated newborn NIH Swiss mice with either Mo + SV or delta Mo + SV M-MuLV. Both viruses induced disease more slowly than M-MuLV, which induces disease 2 to 4 months postinoculation. Mo + SV M-MuLV-inoculated animals became moribund at 3 to 13 months postinoculation, whereas delta Mo + SV M-MuLV-inoculated animals became moribund at 6 to 24 months postinoculation. The tumors induced by the two viruses were characterized histologically and molecularly. Mo + SV M-MuLV-induced tumors were primarily T-cell-derived lymphoblastic lymphomas containing extensive rearrangements of the T-cell receptor beta gene. In contrast, delta Mo + SV M-MuLV induced pre-B- and B-cell lymphoblastic lymphomas, B-cell-derived follicular-center cell lymphomas, and acute myeloid leukemia. The delta Mo + SV tumor DNAs from B-lineage tumors were typically rearranged at the immunoglobulin gene loci and contained germ line configurations of the T-cell receptor beta gene. Southern blot hybridization confirmed that the tumor DNAs contained the predicted Mo + SV M-MuLV or delta Mo + SV M-MuLV provirus.

Comparison of three recombinant murine leukemia viruses carrying the v-src oncogene of avian sarcoma virus: differences in in vitro transformation and in vivo pathogenicity

We previously described a recombinant Moloney murine leukemia virus (Mo-MuLV) carrying the v-src oncogene, Mo-MuLV(src). Mo-MuLV(src) encodes a gag-src fusion protein, transforms cells in culture, and induces fibrosarcomas in vivo. To compare transforming properties of the gag-src fusion protein to pp60src encoded by Rous sarcoma virus, we constructed a new recombinant virus, Mo-MuLV(+ src). Mo-MuLV(+ src) encodes pp60src in the context of Mo-MuLV. Cells transformed by Mo-MuLV(+ src) were round and formed colonies in soft agar, whereas Mo-MuLV(src)-infected cells were fusiform and did not grow in suspension. Thus, the extent of transformation induced by Mo-MuLV(+ src) was greater than that induced by Mo-MuLV(src). Subcutaneous inoculation of either virus into neonatal NIH Swiss mice resulted in fibrosarcomas at the site of injection. Further studies indicated that tumors induced by Mo-MuLV(+ src) grew rapidly but rarely metastasized. In contrast, tumors induced by Mo-MuLV(src) grew somewhat more slowly but metastasized with a high frequency (60%). These viruses may provide a useful model system for tumor metastasis. Another src-containing virus was also studied, MRSV (constructed by Anderson and Scolnick). MRSV also encodes pp60src but in the context of amphotropic MuLV. When injected intravenously into six-week-old mice, MRSV induced splenomegaly and spleen foci but no solid tumors, as reported previously. In contrast, Mo-MuLV(src)-induced fibrosarcomas mostly in the spleen under the same inoculation protocol. These results suggest that the v-src oncogene was the major pathogenic determinant in neonatal mice for all three src-containing viruses; however, variations in the nature of the transforming protein modulated the behavior of the induced tumors. In adult mice, greater differences in pathogenicity were observed.

Natural killer (NK) cell immunodeficiency in patients with chronic myelogenous leukemia. II. Successful cloning and amplification of natural killer cells

Defective natural killer (NK) cell populations from patients with chronic myelogenous leukemia (CML), that reacted with both HNK-1+ and B73.1+ antibodies, were obtained by a fluorescence-activated cell sorter (FACS). These fractions, along with NK fractions from normal donors which reacted with both antibodies, were expanded as bulk cultures or clones by limiting dilution, for 4 weeks in the presence of 10% interleukin 2 (IL 2), human type AB plasma, and irradiated human allogeneic mononuclear cells. Successfully established clones from patients with CML, with lytic activity against autologous and more differentiated neoplastic granulocytes, were generated more efficiently from B73.1+ than from HNK-1+ subsets. However, there were no significant differences among the generations of B73.1+ and HNK-1+ clones for both patients and normal donors with lytic activity against NK susceptible K-562 targets. Fresh myeloblast preparations from a blast crisis were found to be more susceptible to lysis by IL 2-proliferative B73.1+ and HNK-1+ clones than were fresh myelocyte preparations from a chronic phase CML patient, which were lytically susceptible to only B73.1+ clones. B73.1+ and HNK-1+ subsets from CML patients demonstrated major histocompatibility complex nonrestricted killing, and showed the following predominant phenotypes: B73.1+T3+T8+ or B73.1+T3+T8- from B73.1+ subsets; and HNK-1-T3+T8+ (initially HNK-1+) from HNK-1+ subsets. In contrast, B73.1+ and HNK-1+ clones from normal donors showed the following predominant phenotypes: B73.1+T3-T8-; and HNK-1-T3-T8- or HNK-1-T3-T8+ (initially all HNK-1+). Short-term in vitro IL 2 or interferon treatment of fresh NK defective subsets from CML patients resulted in minimal cytotoxic augmentation. In contrast, defective NK cells from CML patients, whether HNK-1+ or B73.1+ subsets, proliferated with complete regeneration of cytolytic activity after a 3-4 week exposure to IL 2, but differed in phenotypic profiles as compared to those of normal donors. These observations imply that not only fresh defective NK cells but also the cytotoxically restored clones from CML patients are derived from different NK subsets and may represent undifferentiated forms of NK cells that may be arrested at an early stage of development by yet unknown mechanism(s). In vitro substantiation of autologous leukemia cell killing by IL 2-proliferative NK cell clones is encouraging and may allow for new in vivo immunotherapeutic modalities in CML patients.

Suppressor T lymphocytes from lepromatous leprosy skin lesions

The immune response in leprosy forms a spectrum with lepromatous leprosy patients exhibiting specific unresponsiveness to antigens of Mycobacterium leprae. This unresponsiveness is thought to be related to the prevalence of T8-positive lymphocyte in these lepromatous lesions. To analyze the immunoregulatory function of these T8 cells, we developed simple procedures to extract lymphocytes from skin biopsy specimens of patients with leprosy. These lymphocytes were sorted for T8 and T4 positive cells, and cell lines were established by expansion with interleukin 2 (IL 2) and irradiated feeder cells. All T8 positive lines tested were positive for IL 2 receptors and HLA-DR determinants. These lines were additionally assayed for lepromin-induced suppression of the normal peripheral blood lymphocyte Con A proliferative response. Thirteen of 32 lines from six lepromatous patients showed significant suppressor activity, whereas nine lines from six tuberculoid patients and one line from normal peripheral blood failed to show suppression (p less than 0.001). Taken together, the finding of M. leprae-triggered suppressor cells within lepromatous skin lesions may in part explain the M. leprae unresponsiveness of lepromatous leprosy patients.

Suppressor T lymphocytes from lepromatous leprosy skin lesions

The immune response in leprosy forms a spectrum with lepromatous leprosy patients exhibiting specific unresponsiveness to antigens of Mycobacterium leprae. This unresponsiveness is thought to be related to the prevalence of T8-positive lymphocyte in these lepromatous lesions. To analyze the immunoregulatory function of these T8 cells, we developed simple procedures to extract lymphocytes from skin biopsy specimens of patients with leprosy. These lymphocytes were sorted for T8 and T4 positive cells, and cell lines were established by expansion with interleukin 2 (IL 2) and irradiated feeder cells. All T8 positive lines tested were positive for IL 2 receptors and HLA-DR determinants. These lines were additionally assayed for lepromin-induced suppression of the normal peripheral blood lymphocyte Con A proliferative response. Thirteen of 32 lines from six lepromatous patients showed significant suppressor activity, whereas nine lines from six tuberculoid patients and one line from normal peripheral blood failed to show suppression (p less than 0.001). Taken together, the finding of M. leprae-triggered suppressor cells within lepromatous skin lesions may in part explain the M. leprae unresponsiveness of lepromatous leprosy patients.

Rearrangements and insertions in the Moloney murine leukemia virus long terminal repeat alter biological properties in vivo and in vitro

The effects of rearrangement and insertion of sequences in the Moloney murine leukemia virus (M-MuLV) long terminal repeat (LTR) were investigated. The alterations were made by recombinant DNA manipulations on a plasmid subclone containing an M-MuLV LTR. Promoter activity of altered LTRs was measured by fusion to the bacterial chloramphenicol acetyltransferase gene, followed by transient expression assay in NIH 3T3 cells. M-MuLV proviral organizations containing the altered LTRs were also generated, and infectious virus was recovered by transfection. Infectivity of the resulting virus was quantified by XC plaque assay, and pathogenicity was determined by inoculating neonatal NIH Swiss mice. Inversion of sequences in the U3 region containing the tandemly repeated enhancer sequences (-150 to -353 base pairs [bp]) reduced promoter activity approximately fivefold in the transient-expression assays. Infectious virus containing the inverted sequences (Mo- M-MuLV) showed a 20-fold reduction in relative infectivity compared with wild-type M-MuLV, but the virus still induced thymus-derived lymphoblastic lymphoma or leukemia in mice, with essentially the same kinetics as for wild-type M-MuLV. We previously derived an M-MuLV which carried inserted enhancer sequences from the F101 strain of polyomavirus (Mo + PyF101 M-MuLV) and showed that this virus is nonleukemogenic. In Mo + PyF101 M-MuLV, the PyF101 sequences were inserted between the M-MuLV promoter and the M-MuLV enhancers (at -150 bp). A new LTR was generated in which the PyF101 sequences were inserted to the 5' side of the M-MuLV enhancers (at -353 bp, PyF101 + Mo M-MuLV). The PyF101 + Mo LTR exhibited promoter activity similar (40 to 50%) to that of wild-type M-MuLV, and infectious PyF101 + Mo M-MuLV had high infectivity on NIH 3T3 cells (50% of wild type). In contrast to the nonleukemogenic Mo + PyF101 M-MuLV, PyF101 + Mo M-MuLV induced leukemia with kinetics similar to that of wild-type M-MuLV. Thus, the position of the PyF101 sequences relative to the M-MuLV LTR affected the biological behavior of the molecular construct. Furthermore, PyF101 + Mo M-MuLV induced a different spectrum of neoplastic disease. In comparison with wild-type M-MuLV, which induces a characteristic thymus-derived lymphoblastic lymphoma with extremely high frequency, PyF101 + Mo M-MuLV was capable of inducing both acute myeloid leukemia or thymus-derived lymphoblastic lymphoma, or both. Tumor DNA from both the PyF101 + Mo- and Mo- M-MuLV-inoculated animals contained recombinant proviruses with LTRs that differed from the initially inoculated virus.

Generation and characterization of a recombinant Moloney murine leukemia virus containing the v-myc oncogene of avian MC29 virus: in vitro transformation and in vivo pathogenesis

A new retrovirus consisting of the v-myc oncogene sequences of avian MC29 virus inserted into the genome of Moloney murine leukemia virus (M-MuLV) was generated. This was accomplished by constructing a recombinant DNA clone containing the desired organization, introducing the recombinant DNA into mouse NIH 3T3 cells, and superinfecting the cells with replication-competent M-MuLV. The construction was designed so that an M-MuLV gag-myc fusion protein would be produced. The resulting virus, M-MuLV(myc), morphologically transformed uninfected NIH 3T3 cells. Stocks of M-MuLV(myc)-M-MuLV were infected into secondary mouse embryo cultures. M-MuLV(myc) induced striking growth and proliferation of hematopoietic cells. These cells were of the myeloid lineage by morphology, phagocytic properties, and surface staining with Mac-1 and Mac-2 monoclonal antibodies. They resembled mature macrophages, although they displayed minor properties of immaturity. The myeloid cells were transformed in comparison with uninfected myeloid cells since they were less adherent and had unlimited proliferative capacity and reduced growth factor requirements. The transformed myeloid cells with proliferative potential were actually myeloid progenitors which apparently underwent terminal differentiation to macrophages. It was possible to derive a permanent line of factor-independent macrophages from M-MuLV(myc)-transformed myeloid cells. M-MuLV(myc) also immortalized and morphologically transformed mouse embryo fibroblasts. These in vitro properties closely resembled the biological activity of MC29 virus in avian cells and suggested that the nature of the v-myc oncogene was an important determinant in transformation specificity. Neonatal NIH Swiss mice inoculated intraperitoneally with M-MuLV(myc)-M-MuLV only developed lymphoblastic lymphoma characteristic of the M-MuLV helper alone, and no acute fibrosarcomas or myeloid tumors resulted. In light of the strong myeloid transformation observed in vitro, the absence of acute in vivo myeloid disease was noteworthy. Interestingly, when a derivative of M-MuLV(myc) carried by a nonpathogenic amphotropic MuLV helper was inoculated, T lymphomas developed with long latency. Molecular hybridization confirmed that these tumors contained M-MuLV(myc).

Genetically restricted suppressor T-cell clones derived from lepromatous leprosy lesions

Leprosy is a spectral disease in which immune responses to Mycobacterium leprae correlate with the clinical, bacteriological and histopathological manifestations of disease, so study of its pathology provides insights into immunoregulatory mechanisms in man. At the tuberculoid pole, patients have few lesions in the skin which contain rare organisms and are able to mount strong cell-mediated immune responses to M. leprae antigens. In contrast, at the lepromatous pole, patients have disseminated skin lesions containing large numbers of acid-fast bacilli and are selectively unresponsive to antigens of M. leprae. M. leprae-induced suppressor cells derived from peripheral blood have been reported to be active in vitro, yet their in vivo significance has remained unclear. Because the focal point of the immune response to M. leprae is the skin lesion consisting of lymphocytes and macrophages, we have recently developed methods for isolating lymphocytes from skin biopsies of leprosy patients. We report here that two T8 clones derived from lepromatous leprosy skin biopsies, in the presence of lepromin, suppress concanavalin A (Con-A) responses both of peripheral blood mononuclear cells and of T4 clones in an HLA-D (HLA, histocompatibility locus antigen)-restricted manner. Moreover, these T8 clones suppressed responses of HLA-D-matched, but not HLA-D-mismatched antigen-responsive T4 clones to M. leprae antigens, indicating that T-cell suppression is major histocompatibility complex (MHC)-restricted at some level in man.

Consequences of widespread deregulation of the c-myc gene in transgenic mice: multiple neoplasms and normal development

We have constructed a transgenic mouse strain in which a mammary tumor virus LTR/c-myc fusion gene is anomalously expressed in a wide variety of tissues. The deregulated c-myc transgene, now glucocorticoid inducible, contributes to an increased incidence of a variety of tumors, including those of testicular, breast, lymphocytic (B cell and T cell), and mast cell origin. The deregulated gene does not, however, otherwise disturb cell proliferation, nor does it interfere with normal development in these animals. Moreover, since not all tissues that express the transgene develop neoplasms, these results begin to define the transforming spectrum of the c-myc oncogene. They also extend to several organ systems the notion that elements in addition to an activated c-myc gene are required to induce malignancy in the living organism.