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At least 811 records · Page 45Linked to original sources

PubMed1999

Th1 T cell responses to HIV-1 Gag protein delivered by a Listeria monocytogenes vaccine are similar to those induced by endogenous listerial antigens.

Listeria monocytogenes is a facultative intracellular bacterium that lives and grows in the cytoplasm of the host cell. The hallmark of a listerial infection is a cell-mediated immune response to its own secreted virulence factors. Thus, L. monocytogenes vaccines engineered to secrete HIV proteins may be ideal vectors for boosting cellular immune responses against HIV. Using strains of L. monocytogenes that stably express and secrete HIV Gag (Lm-Gag) to deliver this Ag to the immune system, we have previously shown strong MHC class I-restricted cytotoxic T cell responses to this protein. In this study, we examine MHC class II-restricted T cell responses to HIV-Gag delivered by Lm-Gag. We demonstrate the induction of CD4+ T cells that are HIV-Gag specific and identify three epitopes in two strains of mice, BALB/c (H-2d) and C57BL/6 (H-2b), two of which are both H-2d and H-2b restricted, but are not immunodominant for both haplotypes. In addition, we show that the CD4+ T cells induced are of the Th1 phenotype that produce IFN-gamma at levels similar to CD4+ T cells induced to endogenous listerial Ags. These studies suggest that chromosomally modified strains of L. monocytogenes may be useful as vaccine vectors for the induction of Th1 T cell responses against HIV.

Amino Acid Sequence↗

PubMed2000

Pretransplant tumor antigen-specific immunization of allogeneic bone marrow transplant donors enhances graft-versus-tumor activity without exacerbation of graft-versus-host disease.

Allogeneic bone marrow transplantation (BMT) causes a beneficial graft-versus-tumor (GVT) immune response that is often associated with graft-versus-host disease (GVHD). There is substantial interest in developing therapeutic strategies that augment GVT without GVHD. We have demonstrated recently that immunization of BMT donors with cellular tumor vaccines leads to curative GVT but induces unacceptable GVHD because of the presence of recipient minor histocompatibility antigens (mHAgs) in whole-cell tumor vaccines. This study tested the hypothesis that immunization of BMT donors against a defined tumor-specific antigen with a vaccine not containing recipient mHAgs would help to separate the two responses by enhancing GVT activity without exacerbating GVHD, even when cellular vaccines were used after BMT. Recipient strain C57BL/6 fibrosarcoma cells engineered to express the well-characterized model tumor antigen, influenza nucleoprotein (NP), were used in these studies. C3H.SW donors were immunized against NP prior to BMT, and cytolytic T cells were transferred along with bone marrow into irradiated H-2-matched, mHAg-mismatched C57BL/6 recipients with established micrometastatic 205-NP tumors. Donor immunization led to a significant increase in GVT activity, as measured by reduction in tumor growth and enhanced survival. However, deaths in recipients of tumor antigen-specific immune BMT ultimately occurred because of the growth of antigen-loss variants; such tumor growth did not occur in animals receiving BMT from donors treated with whole-cell vaccines. Donor immunization did not lead to an exacerbation of GVHD, even when BMT recipients received additional immunization after BMT with a 205-NP "whole" tumor cell vaccine (which was shown to induce fatal GVHD when used for donor immunization). In conclusion, immunization of allogeneic BMT donors against a tumor-specific antigen significantly enhances GVT activity without an associated exacerbation of GVHD.

Animals↗

PubMed2000

[Musculoskeletal tissue engineering with resorbable polymers].

Musculoskeletal tissues can present congenital or acquired defects as a result of disease, accidental trauma or iatrogenous causes. This loss of bony substance is traditionally treated by the replacement of bony tissue (grafts or flaps), or by synthetic materials. Each of these methods of treatment, however, entails its specific disadvantages, limitations and complications. The recent approach for treatment of musculoskeletal defects has been the development of the growing of neotissues derived from autogenous cells, and artificial biodegradable matrixes. This method assumed the name "tissue engineering" in the late 1980s. Tissue Engineering, or TE, has employed advances made in the area of cellular culture, intercellular matrix biology, and also, in the area of biomaterial science. TE is an multi-disciplinary approach. Musculoskeletal TE, although in its preliminary stages, should allow access to treatments of the future.

Biocompatible Materials↗

PubMed2005

Allosteric aptamers and aptazymes as probes for screening approaches.

Substantial effort is currently being devoted to engineering allosteric nucleic acids, aptamers and ribozymes for various applications in cellular and molecular biology, biotechnology and diagnostics. These molecular switches alter their different functional activities in response to specific binding molecules, including proteins, nucleic acids and small organic compounds. The interacting molecules trigger a response in the allosteric nucleic acid, which can be used for purposes such as real-time monitoring, high-throughput screening or gene expression control.

Allosteric Regulation↗

PubMedDate not supplied

Perfusion bioreactor for small diameter tissue-engineered arteries.

A scaleable perfusion bioreactor has been developed for tissue engineering of small diameter arterial constructs. This modular bioreactor allows for dynamic sequential seeding of smooth muscle and endothelial cells, biomechanical stimulation of cells during culture, and monitoring of tissue growth and maturation. Bovine aortic smooth muscle and endothelial cells were seeded onto porous tubular poly(glycolic acid) nonwoven scaffolds and cultured in the bioreactor under pulsatile flow conditions for up to 25 days. Cell proliferation was more than 3-fold after 4 days, smooth muscle cells expressed differentiated phenotype after 16 days, and collagen and elastin were distributed throughout the construct after 25 days of culture. In bioreactor experiments in which the construct lumen was seeded with endothelial cells by perfusion after 13 days of smooth muscle cell culture, endothelial cell seeding efficiency was 100%, and a confluent monolayer was observed in the lumen within 48 h. These data demonstrate that this perfusion bioreactor supports sequential seeding of constructs with smooth muscle and endothelial cells. Dynamic culture under pulsatile flow leads to cellular expression of differentiated function and extracellular matrix deposition toward the development of tissue-engineered arterial constructs.

Animals↗

PubMed2007

Induction of directional sprouting angiogenesis by matrix gradients.

The fate of any tissue engineering implant relies upon an adequate oxygen and nutrients supply throughout the cellular construct and, hence, by the ability of the scaffold to induce and guide vascular ingrowth. However, implant vascularization is usually an uncontrolled process that takes several weeks. In this work, we assessed the feasibility of controlling vascular sprout rate and direction within three-dimensional collagen-hyaluronic acid semi-interpenetrated networks by modulating the spatial distribution of the matricellular cues. Results indicated that increasing amount of hyaluronic acid (HA) within the matrix led to a progressive inhibition of sprouting. In HA-rich matrices, the sprout number and the propagation rate showed a 2.7- and 4-fold reduction, respectively, compared to collagen matrices. Furthermore, by creating HA gradients within the collagen network, we were able to direct and enhance the sprouting rate. This study provides an experimental platform for controlling vascularization of engineered tissues.

Animals↗

PubMed1995

Long-term humoral and cellular immunity induced by a single immunization with replication-defective adenovirus recombinant vector.

This study examines the suitability of replication-defective adenovirus vectors for engineering recombinant vaccines. The immunological abilities and limitations of E1-deleted adenoviruses containing the lacZ gene (Ad-beta-gal) were investigated by examining the humoral and cellular immune responses to the beta-galactosidase protein. BALB/c mice (H-2d) were given in a single injection of recombinant adenovirus. The cytotoxic T lymphocyte (CTL) response of spleen cells was evaluated. Recognized target cells were H-2d-derived tumor cells transfected by the lac Z gene, or incubated with the 876-884 beta-galactosidase peptide known to be restricted by the Ld molecule of the major histocompatibility complex. A long-lasting beta-galactosidase-specific cytotoxic T cell response was obtained. By contrast, CTL from mice immunized with the Ld-restricted peptide were less specific for the endogenous epitope presented by the transfectants expressing beta-galactosidase. Ad-beta-gal-immunized mice were also protected against an intra-cerebral challenge with a recombinant vaccinia virus expressing the lac-Z gene. These results suggest that Ad-beta-gal-induced CTL have protective abilities in vivo. The induction of beta-galactosidase-specific T helper lymphocytes and humoral IgG responses were also examined. A proliferative response occurred only late after immunization and the primed T lymphocytes produced interleukin-2, but no interleukin-4. A humoral IgG response to the beta-galactosidase protein was detected 15-30 days after a single immunization and remained stable for 6 months without boosting. Lastly, we followed the evolution of the immune response over the course of successive immunizations. The magnitude and kinetics of the cellular and humoral responses were similar to those obtained after a single immunization. Consistent with these observations, an adenovirus-specific neutralizing antibody response was detected as early as the second immunization. Thus, a single immunization with a replication-defective adenovirus recombinant vector induces long-lasting humoral and cellular immune responses specific to the transgene product.

Adenoviridae↗

PubMed2006

Biomaterials for the treatment of myocardial infarction.

For nearly a decade, researchers have investigated the possibility of cell transplantation for cardiac repair. More recently, the emerging fields of tissue engineering and biomaterials have begun to provide potential treatments. Tissue engineering approaches are designed to repair lost or damaged tissue through the use of growth factors, cellular transplantation, and biomaterial scaffolds. There are currently 3 biomaterial approaches for the treatment of myocardial infarction (MI). The first involves polymeric left ventricular restraints in the prevention of heart failure. The second utilizes in vitro engineered cardiac tissue, which is subsequently implanted in vivo. The final approach entails injecting cells and/or a scaffold into the myocardium to create in situ engineered cardiac tissue. This review gives an overview of the current progress in the growing field of biomaterials for the treatment of MI.

Biocompatible Materials↗

PubMed2003

Acellular scaffold implantation--no alternative to tissue engineering.

OBJECTIVE: Degradation mechanisms of cardiovascular bioprostheses may play an important role in bioartificial implants. The fate of acellular implanted and cellular cardiovascular scaffolds was examined in an in vivo model. METHODS: Decellularized or native ovine carotid artery (CA, n=42) and aorta (AO, n=42) were implanted subcutaneously into rats for 2, 4 and 8 weeks. Immunohistochemical methods were used to monitor repopulation. Desmin-vimentin, CD31-, CD4- and CD18-antibodies for myocytes, endothelium, and inflammatory cell-infiltration, respectively. Calcification was detected by von-Kossa staining. Cell density was quantified by DNA-isolation. RESULTS: Acellular AO and CA matrices showed progressive calcification. Cellular AO and CA matrices trigger a strong inflammatory reaction which subsides after two weeks. CA scaffolds are revascularized progressively, whereas AO biocomposites degenerate. Calcification is less pronounced in cellular AO scaffolds and lacking in CA. CONCLUSION: Acellular bioartificial implants demonstrate degradation mechanisms similar to currently applied cardiovascular bioprostheses. Cellularized viable implants are promising clinical alternatives.

Animals↗

PubMed2003

Distributed sensor networks: a cellular nonlinear network perspective.

Large-scale networks of integrated wireless sensors become increasingly tractable. Advances in hardware technology and engineering design have led to dramatic reductions in size, power consumption, and cost for digital circuitry, and wireless communications. Networking, self-organization, and distributed operation are crucial ingredients to harness the sensing, computing, and computational capabilities of the nodes into a complete system. This article shows that those networks can be considered as cellular nonlinear networks (CNNs), and that their analysis and design may greatly benefit from the rich theoretical results available for CNNs.

Microcomputers↗

PubMed1994

Metabolic stability of mRNA in yeast--a potential target for modulating productivity?

Attempts to improve the production of (heterologous) proteins in yeast cells have, to date, focused almost exclusively on increasing the transcriptional yield of the heterologous gene by raising the number of gene copies per cell, and/or putting the gene under the control of a strong homologous promoter. However, the cellular level of translatable mRNA is a function of the rate at which it is produced and the rate at which it is removed--or at least inactivated--by nucleolytic degradation. Recently, considerable progress has been made in unravelling the mechanism of mRNA decay in yeast cells and in identifying both the cis-acting stability determinants and the trans-acting factors involved in this process. This knowledge can be used as the basis for rational engineering of a given transcript to modulate its metabolic stability, and thus its cellular level.

Biotechnology↗

PubMed2003

Structure-guided protein engineering modulates helix bundle exchangeable apolipoprotein properties.

Apolipoprotein (apo) E plays a major role in lipid metabolism by mediating cellular uptake of lipoprotein particles through interaction with members of the low density lipoprotein (LDL) receptor family. The primary region of apoE responsible for receptor binding has been limited to a cluster of basic amino acids between residues 134 and 150, located in the fourth helix of the N-terminal domain globular helix bundle structure. To investigate structural and functional requirements of this "receptor binding region" we engineered an apolipoprotein chimera wherein residues 131-151 of human apoE were substituted for residues 146-166 (helix 5) of Manduca sexta apolipophorin III (apoLp-III). Recombinant hybrid apolipoprotein was expressed in Escherichia coli, isolated, and characterized. Hybrid apolipoprotein and apoE3-N-terminal, but not apoLp-III, bound to heparin-Sepharose. Far UV circular dichroism spectroscopy revealed the presence of predominantly alpha-helix secondary structure, and stability studies revealed a urea denaturation midpoint of 1.05 m, similar to wild-type apoLp-III. Hybrid apolipoprotein-induced dimyristoylphosphatidylcholine (DMPC) bilayer vesicle solubilization activity was significantly enhanced compared with either parent protein, consistent with detection of solvent-exposed hydrophobic regions on the protein in fluorescent dye binding experiments. Unlike wild-type apoLp-III.DMPC complexes, disc particles bearing the hybrid apolipoprotein competed with 125ILDL for binding to the LDL receptor on cultured human skin fibroblasts. We conclude that a hybrid apolipoprotein containing a key receptor recognition element of apoE preserves the structural integrity of the parent protein while conferring a new biological activity, illustrating the potential of helix swapping to introduce desirable biological properties into unrelated or engineered apolipoproteins.

Animals↗

PubMed2003

Space Biology Group: basic research, biotechnology, tissue engineering, and instrument development.

At the beginning of space flight, the investigations were oriented essentially toward the health of the astronauts. But in the last three decades space biology has evolved from "try-and-see" experiments to sophisticated basic and applied research with well-based hypotheses as well as studies on the use of low gravity in biological applications. In 1977 the Space Biology Group of the Swiss Federal Institute of Technology, Zurich, began its activities in space research. A summary of the experiments performed to date, from basic research on the human immune system to the development of sophisticated instruments for biotechnology and medical application, is presented here.

Aerospace Medicine↗

PubMed2005

The fibroblast response to tubes exhibiting internal nanotopography.

The use of three-dimensional scaffolds in cell and tissue engineering is widespread; however, the use of such scaffolds, which bear additional cellular cues such as nanotopography, is as yet in its infancy. This paper details the novel fabrication of nylon tubes bearing nanotopography via polymer demixing, and reports that the topography greatly influenced fibroblast adhesion, spreading, morphology and cytoskeletal organisation. The use of such frameworks that convey both the correct mechanical support for tissue formation and stimulate cells through topographical cues may pave the way for future production of intelligent materials and scaffolds.

Biocompatible Materials↗

PubMed2004

Recent progress of vascular graft engineering in Japan.

The development of a small-diameter vascular graft has long been awaited. This review covers research activities, achievements and progress on vascular engineering in Japan, which was conducted over the last decade. The article includes recently developed experimental scaffolds, biologically active artificial extracellular matrices (ECMs) or non-fouling synthetic coatings, cell sourcing including the autologous vascular cell type, endothelial progenitor cells and genetically-engineered, temporary endothelial-like cells. The discussions were presented from biomechanical, biomaterial, cellular and tissue aspects. Once the mechano-biological and biologically active extracellular milieus are established in a designed vascular graft, the functional, structural and mechanical tissue morphogenesis and adaptation of implanted vascular grafts may proceed with implantation duration, and the spatio-temporal tissue modulations at cytokine, cellular, ECM levels under physiological stress proceed to regenerate vascular tissue architecture. The ultimate solution to a small-diameter vascular graft should be realized by optimal combinations of these factors.

Animals↗

PubMed2006

Fabrication methods of an engineered microenvironment for analysis of cell-biomaterial interactions.

Success in tissue engineering requires an understanding of how cells integrate the signals presented from the microenvironment created by biomaterial scaffolds to alter their responses. Besides the presence of chemical stimuli, there is growing evidence that the spatial organization of cells and tissue within a 3-dimensional (3-D) extracellular matrix (ECM) context is a critical element in controlling cellular function. Therefore, in order to direct cells toward a desirable tissue structure, it is necessary to engineer biomaterials to have spatiotemporal control of the presentation of regulatory signals. Given that, micro-patterning techniques have profited by combining micro-fabrication technology with the chemical conjugation of biologically active molecules to provide new culture systems where cells can be cultured within a specific geometry. The micro-engineered environments have been developed as 2- and 3-D structures, which have proven greatly useful as versatile platforms to study cell, biomaterial, and ECM interactions on both macroscopic and microscopic levels. The main focus of this review is a brief summary of the use of micro-engineered substrates in the analysis of cell-biomaterial interactions with the aim to provide an introductory overview of practical applications available in the literature. In particular, topics regarding (1) the soft-lithography technique to prepare micro-patterned substrates for the spatial control of cell adhesion, (2) biomaterials stiffness-dependent cellular responses, and (3) the microarray techniques for analysis of cell/biomaterials interactions are discussed.

Animals↗

PubMed1999

Parameters affecting cellular adhesion to polylactide films.

Absorbable biomaterials have been recently incorporated into the field of tissue engineering. Little work has been performed, even with the clinically acceptable absorbables, concerning their tissue promoting capability or lack, thereof. Furthermore, the relative attractions of cells to these implants may be largely disguised by the presence of serum. This research involved the development of an adhesion assay to compare the adhesion behavior of two cell types to two different polylactides in a serum free environment. The results showed that the attachment behavior depends not only on the cell or the polymer but a combination of the two.

Animals↗

PubMedDate not supplied

Long-term intermittent compressive stimulation improves the composition and mechanical properties of tissue-engineered cartilage.

Tissue engineering of articular cartilage is a promising alternative for cartilage repair. However, it has been difficult to develop tissue in vitro that mimicks native cartilage. Cartilaginous tissue formed in vitro does not accumulate enough extracellular matrix, is deficient in collagen, and possesses only a fraction of the mechanical properties of native cartilage. In this study, we investigated whether long-term intermittent compressive stimulation would improve the quality of the generated tissue. Chondrocyte cultures were established on the surface of porous calcium polyphosphate substrates and allowed to form cartilaginous tissue. In vitro-formed tissues were subjected to different stimulation protocols for 1 week. The optimal mechanical stimulation parameters identified in this short-term study were then applied to the cultures for up to 4 weeks. Mechanical stimulation applied at a 5% compressive amplitude at a frequency of 1 Hz for 400 cycles every second day resulted in the greatest increase in collagen synthesis (37 +/- 9% over control) while not significantly affecting proteoglycan synthesis (2 +/- 8% over control). This condition, applied to the chondrocyte cultures for 4 weeks, resulted in a significant increase in the amount of tissue that formed (stimulated, 2.4 +/- 0.2 mg dry wt; unstimulated, 1.61 +/- 0.08 mg dry wt). Stimulated tissues contained approximately 40% more collagen (stimulated, 590 +/- 58 microg; unstimulated, 420 +/- 42 microg), and 30% more proteoglycans (stimulated, 393 +/- 34 microg; unstimulated, 302 +/- 32 microg) as well as displaying a 2- to 3-fold increase in compressive mechanical properties (maximal equilibrium stress: stimulated, 10 +/- 1 kPa; unstimulated, 5 +/- 1 kPa; maximal equilibrium modulus: stimulated, 80 +/- 23 kPa; unstimulated, 24 +/- 6 kPa). The results of this study demonstrate that intermittent mechanical stimulation can increase collagen synthesis and, when applied over a 4-week period, can accelerate extracellular matrix accumulation as well as improve the material properties of the developed tissue. Interestingly, only short periods of mechanical stimulation (6 min every second day) were needed to affect the quality of cartilaginous tissue formed in vitro.

Adaptation, Physiological↗