Transformation of mononuclear phagocytes in vivo and malignant histiocytosis caused by a novel murine spleen focus-forming virus

Dendritic Cells Cause Bone Lesions in a New Mouse Model of Histiocytosis

Langerhans cell histiocytosis (LCH) is a rare disease caused by the clonal accumulation of dendritic Langerhans cells, which is often accompanied by osteolytic lesions. It has been reported that osteoclast-like cells play a major role in the pathogenic bone destruction seen in patients with LCH and these cells are postulated to originate from the fusion of DCs. However, due to the lack of reliable animal models the pathogenesis of LCH is still poorly understood. In this study, we have established a mouse model of histiocytosis- recapitulating human disease for osteolytic lesions seen in LCH patients. At 12 weeks after birth, severe bone lesions were observed in our multisystem histiocytosis (Mushi) model, when CD8α conventional dendritic cells (DCs) are transformed (MuTuDC) and accumulate. Most importantly, our study demonstrates that bone loss in LCH can be accounted for the transdifferentiation of MuTuDCs into functional osteoclasts both in vivo and in vitro. Moreover, we have shown that injected MuTuDCs reverse the osteopetrotic phenotype of oc/oc mice in vivo. In conclusion, our results support a crucial role of DCs in bone lesions in histiocytosis patients. Furthermore, our new model of LCH based on adoptive transfer of MuTuDC lines, leading to bone lesions within 1–2 weeks, will be an important tool for investigating the pathophysiology of this disease and ultimately for evaluating the potential of anti-resorptive drugs for the treatment of bone lesions.

The histopathologic and molecular basis for the diagnosis of histiocytic sarcoma and histiocyte-associated lymphoma of mice

Histiocytic sarcoma (HS) and histiocyte-associated lymphoma (HAL) of mice are difficult to distinguish histologically. Studies of multiple cases initially diagnosed as HS or HAL allowed us to define HS as round, fusiform, or mixed cell types that were F4/80+, Mac-2+, and PAX5-; that lacked markers for other sarcomas; and that had immune receptor genes in germline configuration. Two other subsets had clonal populations of lymphocytes. The first, HAL, featured malignant lymphocytes admixed with large populations of normal-appearing histiocytes. The second appeared to be composites of lymphoma and HS. Several cases suggestive of B myeloid-lineage plasticity were also observed.

CY15, a malignant histiocytic tumor that is phenotypically similar to immature dendritic cells

The origin and pathogenesis of histiocytic malignancies and the biology of the tumor cells are poorly understood. We have isolated a murine histiocytic tumor cell line (CY15) from a BALB/c IFNgamma(-/-) mouse and characterized it in terms of phenotype and function. The morphology, as judged by electron microscopy, and the surface marker phenotype suggests that CY15 cells are similar to immature dendritic cells (CD11c (low), MHC II (low), CD11b(+), B7.1(+), B7.2(+), and CD40(+)). The cells form tumors in BALB/c mice and metastasize to spleen, liver, lung, kidney, and to a lesser extend to lymph nodes and bone marrow, as judged by the growth of green fluorescent protein transfected tumor cells in mice. CY15 cells are capable of actively taking up antigen (FITC-ovalbumin) and can stimulate T lymphocytes in an allogenic mixed lymphocyte reaction but less effectively than their normal counterparts (immature dendritic cells). They respond to interleukin 4 (IL-4) with up-regulation of CD11c. If stimulated with IFNgamma the cells up-regulate MHC II, CD40 B7.1, and B7.2. Lipopolysaccharide induces the cells to up-regulate B7.1 and B7.2 and to secrete tumor necrosis factor alpha and IL-12. Based on these data, CY15 is a dendritic cell-like tumor cell line and may serve as a transplantable tumor model for histiocytosis in humans.

Aberrant expression of pRb and p16(INK4), alone or in combination, indicates poor outcome after resection in patients with colorectal carcinoma

This study aimed to identify potential abnormalities of retinoblastoma protein (pRb) and p16(INK4a) (p16) expression in resectable colorectal carcinomas (CRCs) and to assess the prognostic significance of pRb and p16 levels in patients with CRC. From July 1990 through December 1993, 117 consecutive patients with CRC underwent curative resection with radical lymphadenectomy. The resected specimens were examined immunohistochemically using monoclonal antibodies to identify abnormalities of pRb and p16 expression. The association of pRb and p16 expression status with clinicopathologic features was analyzed retrospectively. The Cox proportional hazards model was used to identify factors independently affecting survival after resection. The median follow-up period was 62 months. Aberrant expression of pRb and p16 was identified in 82 (70%) and 87 (74%) patients, respectively. Coincident abnormalities of these proteins occurred in 61 (52%) patients. Loss of pRb expression correlated with tumor site (P = 0.0119), whereas p16 overexpression correlated with tumor size (P = 0.0034). Coincident abnormalities of pRb and p16 were associated with TNM tumor stage (P = 0.011). The outcome after resection was worse in patients with aberrant expression of pRb and/or p16 than in patients with normally expressed pRb and p16 (for pRb, P = 0.0151; for p16, P = 0.0247). Coincident abnormalities of pRb and p16 indicated the worst patient survival (P = 0.0310). Aberrant expression of pRb and p16 independently affected postresection survival (relative risk = 6.312, P <0.0001; relative risk = 5.994, P <0.0001, respectively). Most CRCs demonstrate aberrant expression of pRb and/or p16 at resectable stages. Aberrant expression of pRb and p16, alone and in combination, heralds poor prognosis in patients with CRC.

The characteristics of macrophage-like cell lines derived from normal sheep spleens

Macrophage-like cell lines were derived from sheep spleens using conditioned medium from L-929 mouse cells as a source of colony stimulating factor. In seven out of ten attempts colonies of macrophage-like cells appeared after 2-3 weeks of culture. The cells were established in culture as cell lines, and survived 120 passages. They were strongly (+ +) positive for non-specific esterase but negative for peroxidase and produced detectable but small amounts of lysozyme (0.21-1.76 micrograms/10(6) cells). Latex particles were actively phagocytosed. Bacteria (Staphylococcus albus, Staphylococcus aureus) attached to the cell surface and were internalized in the presence of specific antibody. Expression of receptors for immunoglobulin and complement varied somewhat between the different cell lines: the proportion of receptor-bearing cells ranged between 9 and 26% FC-receptors, and 10 and 38% for C-receptors. The cell lines displayed a peculiar karyotype as well as protein profile that were different from normal sheep but similar between the different cell lines. Culture supernatants of the cell lines contained a colony stimulating activity which was used to establish further cell lines. They also spontaneously produced an interleukin-1-like activity that had no effect on baseline proliferation of sheep lymphocytes but enhanced their response to PHA (1.7-fold) particularly in conjunction with sheep IL-2 (4-fold). Prostaglandin E2 was produced in a growth-cycle dependent manner: the peak production occurred on the second day (77-140 pg/ml) at 2 x 10(5) cells and declined to 33-50 pg/ml on the eighth day when cell numbers had increased to 2-3 x 10(6). These easily cultured cell lines derived from normal tissue without the introduction of viral DNA should provide a useful source of material for studies of macrophage function in sheep.

Tumoricidal alveolar macrophage and tumor infiltrating macrophage cell lines

Continuous alveolar macrophage (AM) and tumor-infiltrated (TIM) cell lines have been generated from C57B16J mice by in vitro infection with the J2 retrovirus carrying the v-raf and v-myc oncogens. Four cloned AM cell lines (AMJ2-C8, AMJ2-C10, AMJ2-C11, AMJ2-C20) and 3 cloned TIM cell lines (TIMJ2-C4, TIMJ2-C7 and TIMJ2-C15) were expanded for further characterization. Flow cytometry detected the product of the raf gene in the cytoplasm of all these cell lines. Studies on the tumoricidal properties of these AM and TIM cell lines demonstrated differences in their response to a panel of known macrophage activators. Four of these cell lines (AMJ2-C8, AMJ2-C10, TIMJ2-C7 and TIMJ2-C15) were activated following exposure to recombinant murine interferon gamma (rMuIFN-gamma) but not lipopolysaccharide (LPS) or muramyl dipeptide (MDP). AMJ2-C20 was only activated by incubation with rMuIFN-gamma plus LPS. AMJ2-C11 and TIMJ2-C4 are the cell lines that most closely resembled the response pattern of the parental AM and TIM, since they could be activated by either the combination of rMuIFN-gamma plus LPS or rMuIFN-gamma plus MDP. Constitutive expression of MHC-class-II antigens was low on AMJ2-C11 or TIMJ2-C4 but was increased following exposure to rMuIFN-gamma. Neither cell line secreted substantial amounts of IL-1 or TNF but both secreted large amounts of IL-6. Thus these cell lines could be powerful tools to study AM and TIM activation and cytotoxicity.

The malignant histiocytosis sarcoma virus, a recombinant of Harvey murine sarcoma virus and Friend mink cell focus-forming virus, has acquired myeloid transformation specificity by alterations in the long terminal repeat

The malignant histiocytosis sarcoma virus (MHSV), in contrast to other viruses with the ras oncogene, induces acute histiocytosis in newborn and adult mice. Molecular structure and function studies were initiated to determine the basis of its unique macrophage-transforming potential. Characterization of the genomic structure showed that the virus evolved by recombination of the Harvey murine sarcoma virus (Ha-MuSV) and a virus of the Friend-mink cell focus-forming virus family. Structural analysis of MHSV showed two regions of the genome that are basically different from the Ha-MuSV: (i) the ras gene, which is altered by a point mutation in codon 181 leading to a Cys----Ser substitution of the p21 protein, and (ii) the U3 region of the long terminal repeat, which is largely derived from F-MCFV and contains a deletion of one direct repeat as well as a duplication of an altered enhancer-like region. Biological studies of Ha-MuSV, MHSV, and recombinants between the two viruses show that the U3 region of the MHSV long terminal repeat is essential for the malignancy and specificity of the disease. A contributing role of the ras point mutation in determining macrophage specificity, however, cannot be excluded.

Mouse lysozyme M gene: isolation, characterization, and expression studies

We have isolated and characterized both cDNA and genomic DNA of the mouse lysozyme M gene. Derivation of the amino acid sequence from the nucleotide sequences revealed six positions in the carboxyl terminus that differ from partial sequences previously published. The differential detection of specific mRNAs from the closely related lysozyme M and P genes has revealed different but overlapping tissue specificities of expression. The M gene is expressed weakly in myeloblasts, moderately in immature macrophages, and strongly in both mature macrophages and macrophage-rich tissues, while high levels of P transcripts are present only in small intestine. Sites of protein accumulation, rather than gene expression, have been identified by comparative quantitation of mRNA and enzyme levels.

Identification of genes involved in growth autonomy of hematopoietic cells by analysis of factor-independent mutants

The factor-dependent myeloid precursor cell line D35 mutates spontaneously at a frequency greater than 2.4 x 10(-7) to growth factor autonomy. This frequency could be increased at least 20-fold by retrovirus insertional mutagenesis. The isolation and characterization of factor-independent mutants allowed the identification of genes involved in growth autonomy. Mutants could be subdivided into two sets: those that secreted a stimulating factor (10/11) and those that did not (1/11). In one case, the factor released was distinct from previously characterized growth factors. In most mutants (6/9), the activation of a growth factor gene was associated with rearrangement that could be attributed to the insertion of a transposable-like element either 5' or 3' of the factor coding region in all cases examined, excluding oncogene involvement. All factor-independent mutants were tumorigenic, consistent with the hypothesis that growth-factor independence initiated by aberrant growth factor gene activation is an important and early step in tumorigenesis.

Transformation of single myeloid precursor cells by the malignant histiocytosis sarcoma virus (MHSV): generation of growth-factor-independent myeloid colonies and permanent cell lines

Direct single-cell assays for oncogenic transformation are available for fibroblasts but not for other cell types. Using malignant histiocytosis sarcoma virus (MHSV), a member of the ras family of retroviruses, in vivo-infected granulocyte/macrophage and macrophage precursor cells lost the requirement for externally added hematopoietic growth factors. Factor-independent growth was demonstrated by colony-transfer experiments. More than 25% of the independent colonies were established as permanent macrophage cell lines following a phase of adaptation to tissue culture conditions. Factor-independent colony growth was also obtained by in vitro infection of single cells. As many as 50% of all myeloid precursor cells were target cells for MHSV as measured by this assay. About 2 x 10(-3) of these colony-forming cells acquired growth factor independence and immortality after in vitro infection. Cell lines derived from these colonies did not require adaptation to tissue culture conditions.

Abnormal serum phenylalanine-tyrosine ratio and hyperferritinemia in malignant histiocytosis

Nine cases of childhood malignant histiocytosis (MH) showed an abnormally high serum phenylalanine (Phe)/tyrosine (Tyr) ratio (3.47 +/- 1.32) coincident with hyperferritinemia (50,800 +/- 33,600 ng/ml). Lactate dehydrogenase activity was also increased in these patients. These values were compared with data on sera from two groups of patients, acute leukemia cases (n = 14) and measles cases (n = 13), and with control values from normal healthy children (n = 38). The Phe/Tyr ratio was 1.57 +/- 0.54 for the acute leukemia (p less than 0.01) and 2.58 +/- 1.46 for the measles cases (NS), serum ferritin was 245 +/- 124 ng/ml for acute leukemia (p less than 0.01) and 167 +/- 117 ng/ml for measles (p less than 0.01). Accordingly, the concurrence of both abnormalities is considered to be characteristic for MH. It was also found that both serum Phe/Tyr ratio and ferritin levels reflect the disease activity, indicating that these two factors are useful prognostic indicators in the treatment of patients with MH.

A retrovirus carrying the polyomavirus middle T gene induces acute thrombocythemic myeloproliferative disease in mice

Mice inoculated with an artificially constructed retrovirus carrying the middle T gene of polyomavirus develop acute myeloproliferative disease with severe thrombotic and hemorrhagic disorder and impaired platelet function. The megakaryocytic lineage appears to be a target for polyoma-murine leukemia virus infection and middle T gene expression. This newly described disease represents a unique model system for studying disorders of the megakaryocytic lineage.

One- and two-step transformations of rat thyroid epithelial cells by retroviral oncogenes

A system of epithelial cells is described in which it is possible to study the number and the nature of genes capable of conferring the malignant phenotype. Two fully differentiated, hormone-responsive cell lines from rat thyroid glands are presented which are susceptible to one-step or two-step transformation upon infection with several murine acute retroviruses. After infection, both cell lines became independent from their thyrotropic hormone requirement for growth. However, complete transformation was achieved with one of the cell lines (FRTL-5 Cl 2), whereas the other cell line (PC Cl 3) failed to grow in agar and to give rise to tumors in vivo. The latter cell line was susceptible to complete transformation upon cooperation of the v-ras-Ha and the human c-myc oncogenes.

One- and two-step transformations of rat thyroid epithelial cells by retroviral oncogenes

A system of epithelial cells is described in which it is possible to study the number and the nature of genes capable of conferring the malignant phenotype. Two fully differentiated, hormone-responsive cell lines from rat thyroid glands are presented which are susceptible to one-step or two-step transformation upon infection with several murine acute retroviruses. After infection, both cell lines became independent from their thyrotropic hormone requirement for growth. However, complete transformation was achieved with one of the cell lines (FRTL-5 Cl 2), whereas the other cell line (PC Cl 3) failed to grow in agar and to give rise to tumors in vivo. The latter cell line was susceptible to complete transformation upon cooperation of the v-ras-Ha and the human c-myc oncogenes.

Macrophage cell lines transformed by the malignant histiocytosis sarcoma virus: increase of CSF receptors suggests a model for transformation

The malignant histiocytosis sarcoma virus (MHSV) contains Ha-v-ras-related oncogenic sequences and rapidly transforms myeloid cells in vivo and in vitro. Myeloid cell lines can be derived which do not require growth factor for continued proliferation. We initiated this work to define the process of transformation leading to autonomy of cell growth in transformed myeloid cells. Five established cell lines were examined. All express macrophage-specific cell-surface antigens and exhibit several other properties typical for mature macrophages. Growth properties, growth factor release, and growth factor receptor presentation were examined: Release of growth factors is not a consistent feature. All cell lines show cell-density-independent colony formation and do not release self-stimulating factors, thus excluding autocrine stimulation as a model leading to transformation. All cell lines express unusually high levels of granulocyte-macrophage (GM)- and multi-CSF receptors and, except for one, M-CSF receptors. The high increase in GM-CSF and other growth factor receptors may be causally related to the transformed state of the cells. MHSV can be used as a tool to easily derive cell lines of the macrophage pathway as a model to study myeloid transformation, differentiation, and macrophage function.

MPLV: a retrovirus complex inducing an acute myeloproliferative leukemic disorder in adult mice

A novel murine retrovirus complex was derived from the in vivo passage of a molecularly cloned Friend ecotropic helper virus. The virus isolate, myeloproliferative leukemia virus (MPLV), causes an acute (2-3 weeks) and generalized myeloproliferative disorder in adult mice. All strains of mice examined, including the C57BL/6J strain, developed the acute syndrome. This syndrome is characterized by a rapid hepatosplenomegaly, no thymus or lymph node involvement, granulocytosis, thrombocytosis, and erythroblastosis leading to polycythemia. The most prominent feature at the terminal phase of the disease is a granulocytic hyperplasia. The MPLV isolate replicates in vitro on NIH 3T3 fibroblasts but does not induce foci of transformed cells. Thus, MPLV exhibits unique biological properties that distinguish it either from the Friend virus complexes or from acutely transforming sarcomatogenic murine retrovirus which also induced a rapid splenomegaly.

Long terminal repeat sequences impart hematopoietic transformation properties to the myeloproliferative sarcoma virus

The myeloproliferative sarcoma virus not only transforms fibroblasts but also causes extensive expansion of the hematopoietic stem cell compartment on infection of adult mice. Similar to the Moloney sarcoma virus, it carries the mos oncogene. Moloney sarcoma virus, however, does not induce myeloproliferation and leukemia in adult mice. The difference between the two viruses was explored by using their molecularly cloned genomes and the cellular mos oncogene to construct recombinant genomes. It was shown that the U3 region of the viral long terminal repeat (LTR) has a decisive function in determining the target cell specificity of the myeloproliferative sarcoma virus. Any mos gene, whether of cellular or viral origin, is sufficient in conjunction with the proper LTR to induce myeloproliferation. Our results indicate that the pathogenicity of acutely transforming viruses is determined not only by the oncogene but also by sequences in the viral LTR.