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PubMed1988

Characterization of a promonocyte clone chronically infected with HIV and inducible by 13-phorbol-12-myristate acetate.

The present study has investigated the effect of PMA, an inducer of monocyte differentiation, on HIV expression in a chronically infected promonocyte clone. After acute HIV infection of U937 cells, clones that constitutively expressed varying levels of HIV were isolated by limiting dilution. One clone (U1) produced low levels of HIV but was found to increase its production 20-fold after PMA induction, as detected by reverse transcriptase or A capture. Further characterization of U1 indicated that PMA could induce cellular differentiation and maturation in the clone similar to that in uninfected U937 cells. In addition, functional studies revealed that superoxide anion production from the U1 clone was not different from that of uninfected U937 cells. Electron microscopic studies of U1 indicated that PMA induced endocytotic vesicles containing many HIV particles. These studies provide a model at the clonal level to 1) examine latency or chronicity of HIV infection in monocytes and 2) delineate the signals required for conversion to high level viral expression.

Cell Differentiation↗
PubMed1995

Evidence for a mechanism that can provide both short-term and long-term haemopoietic repopulation by a seemingly uniform population of primitive human haemopoietic precursor cells.

One of the controversies surrounding the repopulating capacities of haemopoietic stem cells is whether or not the same or different populations are responsible for short-term and long-term repopulation after transplantation. To address this question, we analysed results obtained from an in vitro model for the clonal production of granulocyte-macrophage colony-forming cells (CFU-GM) by individual primitive multilineage precursors in adult human bone marrow. The primitive precursors adhere to plastic and produce CFU-GM in a 1-week long 'delta' type culture. The clones that form are classified as having short maturation pathways (clones containing predominantly day 7 CFU-GM) or long maturation pathways (clones containing predominantly day 21 CFU-GM). The results indicate that individual primitive (P delta) cells produce clones that reach full maturity after different periods of time so that cells corresponding to a range of maturational stages can become available simultaneously. Consequently, transplanted stem cells may be able to provide both rapid and long-term mature cell recovery whilst at the same time reconstituting the stem cell pool. These results suggest that it might be possible to use highly purified stem cell populations, devoid of committed progenitors, for clinical transplantation.

Bone Marrow Cells↗
PubMed1998

Genetic alterations in primary bladder cancers and their metastases.

Bladder cancer progression is thought to be associated with sequential genetic events. To search for the specific genetic changes associated with the metastatic process, comparative genomic hybridization was performed on 22 primary tumors and 24 metastases (10 distant and 14 nodal metastases) from 17 patients with stage pT2-4 bladder cancer. There was a striking similarity between the genetic alterations present in the primary and metastatic tumor samples from the same patient. The mean number of genetic changes/tumor was 12.2 for primary tumors and 11.7 for metastases. There was a strong concordance in the specific aberrations present in each patient's primary and metastatic lesions (mean, 75%). Concordance was also high among multiple sites from an individual primary tumor (mean, 96%) and multiple metastases from the same patient (mean, 75%). There were no specific genetic changes overrepresented in the metastases compared with their primary tumors. Genetic alterations present in more than 40% of tumors included gains on 6p, 8q, 10q, and 17q and losses involving 8p, 10q, and Y. Two regions of high-level amplification were common: (a) 10q22.1-q23.1 (32.6%); and (b) 17q11-21.3 (23.9%; the locus of erbB-2). A summary statistic was developed to quantitate the degree of clonal relationships between biopsies from the same patient. These data support a model in which minimal clonal evolution occurs in the metastatic tumor cell population after the metastatic event. When comparing primary cancers from patients with and without metastases, however, several unique genetic changes were identified in those cancers with metastases, suggesting that these loci may harbor genes important to the metastatic process.

Aged↗
PubMed1999

12-O-tetradecanoylphorbol-13-acetate induces clonal expansion of potentially malignant keratinocytes in a tissue model of early neoplastic progression.

Tumor promoters stimulate the selective expansion of initiated mouse keratinocytes in the two-stage model of skin carcinogenesis. However, it is not clear whether these promoters directly modulate the growth of initiated cells or rather permit clonal expansion of initiated cells by modifying the environment of adjacent normal cells. The goal of this study was to further understand the mechanism of action of tumor promotion during early neoplastic progression of human stratified epithelium. To accomplish this, we have established an organotypic culture model that mimics a preneoplastic tissue and contains mixtures of genetically marked (beta-galactosidase), low-grade malignant keratinocytes (HaCaT-ras II-4) and normal human keratinocytes (NHKs) to monitor the fate and phenotype of these cells after treatment with 12-O-tetradecanoylphorbol-13-acetate (TPA). In submerged culture, concentrations of 0.001-1 microg/ml TPA were shown to limit the growth of NHKs yet had no effect on growth of II-4 cells. TPA (0.001 microg/ml) was then added to organotypic cultures containing mixtures of NHK:II-4 cells at varying ratios to determine whether this agent could selectively stimulate clonal expansion of II-4 cells in a normal epidermal background. Immunofluorescence for beta-galactosidase demonstrated that TPA caused a significant increase in the percentage of beta-galactosidase-positive areas in 12:1 and 4:1 mixtures. This TPA-induced expansion of II-4 cells was associated with a marked decrease in proliferation of NHKs, suggesting that II-4 could selectively expand because of its growth advantage relative to NHKs. Clonal expansion of tumor cells was temporally linked to the decreased expression of filaggrin and keratin 1 expression in adjacent NHKs. These findings indicate that TPA may enable expansion of potentially malignant cells through the epigenetic modification of proliferation in NHKs and differentiation of NHK and II-4 cells.

Animals↗
PubMed1992

Sensitivity analysis of a new model of carcinogenesis.

A new simulation model of carcinogenesis is described which, in addition to the features of a standard clonal two-stage model (loss of both copies of a tumor suppressor gene by point mutations, cell division and cell death), includes a quantitative description of mitotic recombination, DNA repair, and cell to cell interactions in all stages. The model is implemented as a discrete event process. The results of a sensitivity analysis of the model are presented. The most sensitive parameters were found to be: the number of normal cells at risk, and the division rate, death rate and DNA repair efficiency for the intermediate stage cells. Accurate information about these parameters is important for a quantitative understanding of carcinogenesis. The sensitivity of the model to the number of normal cells indicates the importance of understanding the nature of the cells at risk, for example, stem cells vs. differentiated cells. The model can be used to assess the importance of chromosomal damage such as mitotic recombination and epigenetic mechanisms such as hyperplasia and cytotoxicity in the onset of malignant tumors.

Cell Death↗
PubMed1987

Pretransplant cytotoxic conditioning produces effects consistent with clonal deletion mechanisms.

A rat cardiac allograft model (ACl to Lewis) was used to investigate the clonal deletion theory. Twelve groups of Lewis recipients received various combinations of donor-specific blood transfusions (DSTs), immediate post-DST immunosuppression with azathioprine/prednisone, and low-dose cyclosporine (1 mg/kg/day) posttransplant. DSTs and cyclosporine together gave modest prolongation of graft survival (from 6.0 to 17 days). DSTs plus immediate post-DST immunosuppression followed by low-dose cyclosporine prolonged graft survival to an average of 45 days. Third-party transfusions alone and in combination with immunosuppression did not significantly prolong allograft survival. Postoperative cyclosporine was required for the expression of this effect suggesting that clonal depression rather than clonal deletion had occurred. Combining DSTs with brief but intense preoperative immunosuppression may be a more effective method of pretransplant conditioning than DSTs alone.

Animals↗
PubMed1985

Growth characteristics of clonal cell populations constituting a B16 melanoma metastasis model system.

Three distinct dissemination-related phenotypes have been distinguished among cell subpopulations of the mouse B16 melanoma: tumorigenicity, spontaneous metastasis from subcutaneous tumors, and organ colonization following intravenous injection of cells. From a progenitor clone (G3) of tumorigenic but nonmetastatic and noncolonizing (null) cells that underwent phenotypic diversification in vitro and in vivo, 4 subclones were obtained: G3.5 (culture-generated metastatic), G3.12 (tumor-generated metastatic), G3.15 (culture-generated null), and G3.26 (tumor-generated colonizing). The growth potentials of the parent clone and derived subclones were investigated comparatively in in vivo assays (tumorigenicity, tumor growth rate, and lung colonization potential), monolayer culture assays (generation time, saturation density, clonogenicity, and rate of detachment by trypsin), and in soft agar. In overall growth potential, G3.26 greater than G3.12 greater than G3, G3.5 greater than G3.15. These results indicate that metastatic populations of the B16 melanoma are not the most rapidly and effectively growing cells obtainable from that tumor.

Agar↗
PubMed1993

Botulinum toxin A inhibits acetylcholine release from cultured neurons in vitro.

Clostridium botulinum type toxin A (BoTx) blocks stimulus-induced acetylcholine (ACh) release from presynaptic nerve terminals at peripheral neuromuscular junctions. However, the detailed mechanism of this effect remains elusive. One obstacle in solving this problem is the lack of a suitable in vitro homogenous cholinergic neuronal model system. We studied the clonal pheochromocytoma PC12 cell line to establish such a model. PC12 cells were differentiated in culture by treatment with 50 ng/ml nerve growth factor (NGF) for 4 days to enhance cellular ACh synthesis and release properties. Stimulation of these cells with high K+ (80 mM) in the perfusion medium markedly increased calcium-dependent [3H]ACh release compared to undifferentiated cells. Stimulated [3H]ACh release was totally inhibited by pretreatment of cells with 2 nM BoTx for 2 h. BoTx inhibition of [3H]ACh release was time- and concentration-dependent. A 50% inhibition was obtained after 2 h incubation with a low (0.02 nM) toxin concentration. The time required for 2 nM BoTx to cause a measurable inhibition (18%) of stimulated [3H]ACh release was 30 min. Botulinum toxin inhibition of stimulated ACh release was prevented by toxin antiserum and heat treatment, suggesting the specificity of the toxin effect. Our results show that by differentiation with NGF, PC12 cells can be shifted from an insensitive to a sensitive state with respect to BoTx inhibition of stimulated ACh release. This cell line, therefore, may serve as a valuable in vitro cholinergic model system to study the mechanism of action of BoTx.

Acetylcholine↗
PubMed2006

Stochastic modeling of oligodendrocyte generation in cell culture: model validation with time-lapse data.

BACKGROUND: The purpose of this paper is two-fold. The first objective is to validate the assumptions behind a stochastic model developed earlier by these authors to describe oligodendrocyte generation in cell culture. The second is to generate time-lapse data that may help biomathematicians to build stochastic models of cell proliferation and differentiation under other experimental scenarios. RESULTS: Using time-lapse video recording it is possible to follow the individual evolutions of different cells within each clone. This experimental technique is very laborious and cannot replace model-based quantitative inference from clonal data. However, it is unrivalled in validating the structure of a stochastic model intended to describe cell proliferation and differentiation at the clonal level. In this paper, such data are reported and analyzed for oligodendrocyte precursor cells cultured in vitro. CONCLUSION: The results strongly support the validity of the most basic assumptions underpinning the previously proposed model of oligodendrocyte development in cell culture. However, there are some discrepancies; the most important is that the contribution of progenitor cell death to cell kinetics in this experimental system has been underestimated.

Algorithms↗
PubMed1982

[Clonal multiplication and mitotic capacity].

On a theoretical model of cellular genome we demonstrate that the clonal multiplication induces an ineluctable decline of the "mitotic capacity". A cellular population is formed, the genomes of which include no more than one of each fundamental genetic element.

Cell Division↗
PubMed1987

Clonal analysis of autoreactive B cells in a murine model of autoimmune hemolytic anemia.

Hybridoma technology was used to examine the repertoire of autoantibody producing B cells in mice with autoimmune hemolytic anemia induced by injection of rat red blood cells (RBC). The results point to the importance of suppressor T cells (Ts) in both the induction as well as the maintenance of the self-specific B-cell repertoire at the clonal level. Thus when normal BALB/c mice were immunized to provoke a high autoantibody response, the hybrids generated were mainly (97%) cross-reactive with mouse RBC, whereas after immunization to elicit Ts and a low autoantibody response, hybrids were mainly (87%) rat RBC specific. In addition, when hybrids were generated from rat RBC immunized (CBA X B10A)F1 mice, in which Ts levels had been depleted during ontogeny, hybrids with "forbidden" purely anti-self (mouse RBC) specificity were detected.

Anemia, Hemolytic↗
PubMedDate not supplied

Autoimmune chronic liver disease as a model of human autoimmunity.

Although clonal deletion and clonal energy have been demonstrated in transgenic mice, the findings that autoreactive B or T cells are present in healthy subjects suggest that they are not the sole mechanisms of tolerance. As regards helper T lymphocytes, tolerance to self-antigens can arise by preventing class II MHC expression on non-lymphoid cells and autoantigen presentation to helper T cells initiating the autoimmune response. Autoimmune chronic active hepatitis (CAH) seems to be a good model of self-tolerance bypass. Hepatocytes are able to express class II molecules and can perform accessory cell functions with respect to T cell clones generated from lymphocytes infiltrating the liver in autoimmune CAH patients. The class II antigen expression on hepatocytes may be modulated by IFN-gamma released by infiltrating T lymphocytes; thus, the activated liver cells can present autoantigens to autoreactive T cell clones. On the other hand, these findings may occur only when the upregulation of IFN-gamma or other lymphokines permits the expression of rare class II antigens on hepatocytes capable of binding particular residues of a liver-autoantigen which are recognized by specific autoreactive T cell clones binding different residues on the same epitope.

Autoimmune Diseases↗
PubMed2006

Hepatitis C virus protease gene diversity in patients coinfected with human immunodeficiency virus.

The clonal variability of the hepatitis C virus (HCV) protease gene in 24 individuals with HCV genotypes 1a, 1b, 2b, and 3a who were coinfected with the human immunodeficiency virus was evaluated. Within-genotype variability at the nucleotide and amino acid levels ranged from 6.5 to 8.6% and 2.2 to 3.8%, respectively. After adjustments were made for correlation of intrapatient clonal variation, mixed-model analysis indicated that nucleotide and amino acid variability among patients with different genotypes did not differ significantly. However, within individual patients, clonal variability differed by up to 5.3% and 5.8% at the nucleotide and amino acid levels, respectively, and genotype 1a had significantly greater nucleotide variability than other genotypes (P = 0.01). Significant variability exists within HCV protease gene variants at the patient level and could affect the effectiveness of HCV protease inhibitors.

Adult↗
PubMed1986

Radiation survival of human mammary carcinoma cells: criteria for an agar-based clonogenic assay.

A human in vivo-in vitro model for breast cancer has been developed based on culture methods that were systematically optimized for solid breast carcinomas. A V-79 cell clonal agar-based model was used to define the analysis problem encountered with agar based clonogenic survival assays. Based on this, we established methods for the generation and analysis of the survival of primary and recurrent breast carcinomas following irradiation. Four out of five primary breast carcinomas studied had similar radiation-cell survival curves. The fifth tumor was more radioresistant. Interestingly, a recurrent breast carcinoma arising in a heavily irradiated chest wall was no more radioresistant than our series of unirradiated primary carcinomas. These methods may be useful both for the study of the radiobiology of human neoplasms and for customizing the treatments and prognosis of individual patients.

Breast Neoplasms↗
PubMed1974

Clonal selection, attenuation and differentiation in an in vitro model of hyperplasia.

Observations of the growth kinetics and morphologies of clones and subclones of diploid human skin fibroblast cultures lead to the working hypothesis that these cells, presumably like their counterparts in healing wounds, constitute a differentiating system. There is attenuation of the growth of serial clones, with continual selection for more vigorous stem cells. The latter segregate daughter cells of varying growth potential, including a class of cells which may be regarded as terminally differentiating; we propose that such cells may be histiocytes or macrophages. These studies a) demonstrate extensive epigenetic heterogeneity in fibroblast cultures, b) suggest that hyperplastic foci may be monoclonal or oligoclonal, c) rule out a simple biologic clock mechanism as an explanation of clonal senescence, d) suggest a new approach to the analysis of various inborn errors of metabolism, such as Werner's Syndrome.

Cell Differentiation↗
PubMed1997

Evidence for clonal deletion and clonal anergy after intrathymic antigen injection in a transplantation model.

Intrathymic (IT) antigen injection has been shown to induce antigen-specific systemic tolerance in the rodent. To delineate the mechanisms responsible for the induction of tolerance, we used the 2C line of T cell receptor transgenic mice. The majority of T cells in 2C mice express an antigen receptor specific for the major histocompatibility complex class I alloantigen Ld and can be identified with the clonotypic monoclonal antibody 1B2. IT injection of lymphoid cells expressing Ld was found to induce a significant prolongation in BALB/c skin allograft survival. The allograft prolongation was associated with a marked reduction in the number of developing 1B2+ thymocytes (clonal deletion), which occurred primarily at the CD4+ CD8+ stage of thymocyte development, as well as a reduction in the number of mature CD8+ 1B2+ 2C T cells in peripheral lymphoid tissue. In addition, CD8+ 1B2+ 2C T cells that survive deletion have decreased CD8 expression levels and a significantly reduced in vitro proliferative response to specific alloantigen (clonal anergy). Exogenous recombinant interleukin 2 restores the capacity of 2C T cells to respond in vitro to alloantigen. Experiments involving separation of cells by fluorescence-activated cell sorter indicate that there is a precise correlation between the reduction in CD8 expression and anergy induction. Collectively, these data indicate that IT antigen injection can induce antigen-specific systemic tolerance by both clonal deletion and clonal anergy.

Adoptive Transfer↗
PubMed2006

Amphotericin B and caspofungin resistance in Candida glabrata isolates recovered from a critically ill patient.

BACKGROUND: Consecutive Candida glabrata isolates recovered from a patient in an intensive care unit were resistant to amphotericin B (minimum inhibitory concentration, up to 32 mu g/mL; determined by Etest [AB Biodisk]). Analyses at the national reference laboratory showed that some isolates were also resistant to azoles and caspofungin. In this study, 4 isolates were studied thoroughly using susceptibility assays and a mouse model and to determine clonality. METHODS: Different broth microdilution tests, Etests, and time-kill studies for antifungals were performed in different media. Three of the 4 isolates were examined in an in vivo experiment, in which mice were challenged intravenously with 1 of 3 isolates and treated daily with amphotericin B, caspofungin, or saline. For the clonality studies, arbitrarily primed polymerase chain reaction (PCR) was performed with the 4 isolates, 8 isolates obtained from nonrelated patients, and a reference strain. RESULTS: The murine model indicated that 1 isolate was resistant to amphotericin B, 1 had intermediate susceptibility, and 1 was fully susceptible. Two of the 3 isolates were resistant to caspofungin. Microdilution methods did not reliably differentiate between amphotericin B-susceptible and -resistant isolates. All assays identified caspofungin-susceptible and -resistant isolates. Arbitrarily primed PCR showed that the 4 isolates probably were of clonal origin. CONCLUSIONS: We have documented the emergence of amphotericin B-resistant and caspofungin-resistant C. glabrata isolates during treatment of a critically ill liver transplant recipient. Only the Etest predicted amphotericin B resistance in the isolates. We recommend that important fungal strains recovered from patients who are receiving antifungal therapy should be tested for susceptibility to the antifungal drug used, because resistance can be present initially or may occur during treatment.

Aged↗