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Heiko Zimmermann - One of the best experts on this subject based on the ideXlab platform.
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towards a xeno free and fully chemically defined cryopreservation medium for maintaining viability recovery and antigen specific functionality of pbmc during long term storage
Journal of Immunological Methods, 2012Co-Authors: J C Schulz, Anja Germann, Beatrice Kempkamke, Heiko Zimmermann, Hagen Von Briesen, Angela S MazzottaAbstract:Abstract Analysis of cryopreserved peripheral mononuclear cells (PBMC) is Important for evaluating new vaccines in immune based therapies and in pathogenesis studies. To ensure comparable assay results from different laboratories and points of time, collaborative research in multicenter trials needs reliable and reproducible cryopreservation protocols that maintain cell viability and functionality. Current cryomedia consist largely of fetal bovine serum (FBS), a natural mix of growth factors, cytokines, and undefined compounds. Standardized procedures are not possible, as FBS can affect the antigen-specific T-cell response, the most Important parameter in functionality assays. Also, worldwide sample exchange is complicated by the strict Import Restrictions on FBS, because of transfection risk. After establishing a serum-free cryopreservation protocol that maintains cell viability, recovery and antigen-specific T-cell response of PBMC comparably to FBS-based cryomedia (Germann et al., 2011), the aim of this study was the complete avoidance of animal proteins and products in combination with efficient cryopreservation. As long-term stability of the cryopreservation process is crucial for retrospective evaluation of samples at different points of time, PBMC were analyzed after storage for maximal four weeks and again after approximately six months. The cryopreservation efficiency of the protein-free and fully chemically defined cryomedium was comparable to FBS-medium after storage for few weeks and several months. Directly after thawing, this medium yielded viabilities over 97% and recovery values over 84%. Also, the specific T-cell functionality was preserved. Additionally, short-term and six month cryopreservation gave comparable results. The fully chemically defined medium presented here will increase standardization and reproducibility of analysis in multicenter-studies or in retrospective evaluation.
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standardized serum free cryomedia maintain peripheral blood mononuclear cell viability recovery and antigen specific t cell response compared to fetal calf serum based medium
Biopreservation and Biobanking, 2011Co-Authors: Anja Germann, J C Schulz, Beatrice Kempkamke, Heiko Zimmermann, Hagen Von BriesenAbstract:The ability to analyze cryopreserved peripheral blood mononuclear cells (PBMCs) from biobanks for antigen-specific T-cell immunity is necessary to evaluate responses to immune-based therapies. Comprehensive studies have demonstrated that the quality of frozen PBMCs is critical and the maintenance of cell viability and functionality by using appropriate cryopreservation techniques is a key to the successful outcome of assays using PBMCs. Different cryomedia additives affect cell viability. The most common additive is fetal calf serum (FCS), although it is widely known that each FCS lot has to be tested before usage to prevent nonspecific stimulation of T-cells. Also, shipping of samples containing FCS is critical because of many Import Restrictions. Often, dimethyl sulfoxide (DMSO) is added as a cryoprotectant. However, DMSO concentration has to be reduced significantly because of its toxic effect on cells at room temperature. Therefore, we have developed freezing approaches to minimize cytotoxicity of cry...
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standardized serum free cryomedia maintain peripheral blood mononuclear cell viability recovery and antigen specific t cell response compared to fetal calf serum based medium
Biopreservation and Biobanking, 2011Co-Authors: Anja Germann, J C Schulz, Beatrice Kempkamke, Heiko Zimmermann, Hagen Von BriesenAbstract:The ability to analyze cryopreserved peripheral blood mononuclear cells (PBMCs) from biobanks for antigen-specific T-cell immunity is necessary to evaluate responses to immune-based therapies. Comprehensive studies have demonstrated that the quality of frozen PBMCs is critical and the maintenance of cell viability and functionality by using appropriate cryopreservation techniques is a key to the successful outcome of assays using PBMCs. Different cryomedia additives affect cell viability. The most common additive is fetal calf serum (FCS), although it is widely known that each FCS lot has to be tested before usage to prevent nonspecific stimulation of T-cells. Also, shipping of samples containing FCS is critical because of many Import Restrictions. Often, dimethyl sulfoxide (DMSO) is added as a cryoprotectant. However, DMSO concentration has to be reduced significantly because of its toxic effect on cells at room temperature. Therefore, we have developed freezing approaches to minimize cytotoxicity of cryoprotectants and maintain T-cell functionality. We compared different additives to the widely used FCS and found bovine serum albumin fraction V to be an appropriate substitute for the potentially immune-modulating FCS. We also found that DMSO concentration can be reduced by the addition of hydroxyethyl starch. Using our serum-free cryomedia, the PBMC recovery was more than 83% and the PBMC viability was more than 98%. Also, the T-cell functionality measured by enzyme-linked immunospot (ELISpot) was optimal after cryopreservation with our new cryomedia. On the basis of our experimental results, we could finally design 2 different, fully working cryomedia that are standardized, serum free, and manufactured under GMP conditions.
Anja Germann - One of the best experts on this subject based on the ideXlab platform.
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towards a xeno free and fully chemically defined cryopreservation medium for maintaining viability recovery and antigen specific functionality of pbmc during long term storage
Journal of Immunological Methods, 2012Co-Authors: J C Schulz, Anja Germann, Beatrice Kempkamke, Heiko Zimmermann, Hagen Von Briesen, Angela S MazzottaAbstract:Abstract Analysis of cryopreserved peripheral mononuclear cells (PBMC) is Important for evaluating new vaccines in immune based therapies and in pathogenesis studies. To ensure comparable assay results from different laboratories and points of time, collaborative research in multicenter trials needs reliable and reproducible cryopreservation protocols that maintain cell viability and functionality. Current cryomedia consist largely of fetal bovine serum (FBS), a natural mix of growth factors, cytokines, and undefined compounds. Standardized procedures are not possible, as FBS can affect the antigen-specific T-cell response, the most Important parameter in functionality assays. Also, worldwide sample exchange is complicated by the strict Import Restrictions on FBS, because of transfection risk. After establishing a serum-free cryopreservation protocol that maintains cell viability, recovery and antigen-specific T-cell response of PBMC comparably to FBS-based cryomedia (Germann et al., 2011), the aim of this study was the complete avoidance of animal proteins and products in combination with efficient cryopreservation. As long-term stability of the cryopreservation process is crucial for retrospective evaluation of samples at different points of time, PBMC were analyzed after storage for maximal four weeks and again after approximately six months. The cryopreservation efficiency of the protein-free and fully chemically defined cryomedium was comparable to FBS-medium after storage for few weeks and several months. Directly after thawing, this medium yielded viabilities over 97% and recovery values over 84%. Also, the specific T-cell functionality was preserved. Additionally, short-term and six month cryopreservation gave comparable results. The fully chemically defined medium presented here will increase standardization and reproducibility of analysis in multicenter-studies or in retrospective evaluation.
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standardized serum free cryomedia maintain peripheral blood mononuclear cell viability recovery and antigen specific t cell response compared to fetal calf serum based medium
Biopreservation and Biobanking, 2011Co-Authors: Anja Germann, J C Schulz, Beatrice Kempkamke, Heiko Zimmermann, Hagen Von BriesenAbstract:The ability to analyze cryopreserved peripheral blood mononuclear cells (PBMCs) from biobanks for antigen-specific T-cell immunity is necessary to evaluate responses to immune-based therapies. Comprehensive studies have demonstrated that the quality of frozen PBMCs is critical and the maintenance of cell viability and functionality by using appropriate cryopreservation techniques is a key to the successful outcome of assays using PBMCs. Different cryomedia additives affect cell viability. The most common additive is fetal calf serum (FCS), although it is widely known that each FCS lot has to be tested before usage to prevent nonspecific stimulation of T-cells. Also, shipping of samples containing FCS is critical because of many Import Restrictions. Often, dimethyl sulfoxide (DMSO) is added as a cryoprotectant. However, DMSO concentration has to be reduced significantly because of its toxic effect on cells at room temperature. Therefore, we have developed freezing approaches to minimize cytotoxicity of cry...
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standardized serum free cryomedia maintain peripheral blood mononuclear cell viability recovery and antigen specific t cell response compared to fetal calf serum based medium
Biopreservation and Biobanking, 2011Co-Authors: Anja Germann, J C Schulz, Beatrice Kempkamke, Heiko Zimmermann, Hagen Von BriesenAbstract:The ability to analyze cryopreserved peripheral blood mononuclear cells (PBMCs) from biobanks for antigen-specific T-cell immunity is necessary to evaluate responses to immune-based therapies. Comprehensive studies have demonstrated that the quality of frozen PBMCs is critical and the maintenance of cell viability and functionality by using appropriate cryopreservation techniques is a key to the successful outcome of assays using PBMCs. Different cryomedia additives affect cell viability. The most common additive is fetal calf serum (FCS), although it is widely known that each FCS lot has to be tested before usage to prevent nonspecific stimulation of T-cells. Also, shipping of samples containing FCS is critical because of many Import Restrictions. Often, dimethyl sulfoxide (DMSO) is added as a cryoprotectant. However, DMSO concentration has to be reduced significantly because of its toxic effect on cells at room temperature. Therefore, we have developed freezing approaches to minimize cytotoxicity of cryoprotectants and maintain T-cell functionality. We compared different additives to the widely used FCS and found bovine serum albumin fraction V to be an appropriate substitute for the potentially immune-modulating FCS. We also found that DMSO concentration can be reduced by the addition of hydroxyethyl starch. Using our serum-free cryomedia, the PBMC recovery was more than 83% and the PBMC viability was more than 98%. Also, the T-cell functionality measured by enzyme-linked immunospot (ELISpot) was optimal after cryopreservation with our new cryomedia. On the basis of our experimental results, we could finally design 2 different, fully working cryomedia that are standardized, serum free, and manufactured under GMP conditions.
Joachim Zietz - One of the best experts on this subject based on the ideXlab platform.
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distortions in world food markets in the wake of gatt evidence and policy implications
World Development, 1995Co-Authors: Alberto Valdes, Joachim ZietzAbstract:Abstract Although the principle of trade liberalization has gained wide acceptance in recent years, many policy makers in developing countries, especially in Latin America, are exploring temporary Import Restrictions in the form of additional tariff protection to insulate domestic farmers from the impact of depressed prices until the Uruguay Round accord leads to higher world market prices for agricultural products. The paper argues that there is little reason to believe that current world market prices will rise substantially in real terms, even with the Uruguay Round accord fully implemented. This finding suggests that additional tariff protection would not make economic sense.
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distortions in world food markets in the wake of gatt evidence and policy implications
Reports, 1994Co-Authors: Alberto Valdes, Joachim ZietzAbstract:Ahead of the Uruguay Round accord of the General Agreement on Tariffs and Trade (GATT) in December of 1993, numerous developing countries, especially in Latin America, embarked on a process of unilateral trade liberalization. During the late 1980s and early 1990s, bound tariffs were instituted, export taxes removed, and quantitative Restrictions replaced with tariffs. Although the principle of tariffication is now widely accepted, many policymakers in these countries are exploring temporary Import Restrictions in agriculture with the argument that this sector is a special case because of the major distortions in world food prices. Protection is considered in the form of additional tariff protection on Importables, such as cereals in the case of Colombia and Chile. In some cases, pressure exists to revert to levels of protection in effect prior to trade policy reforms. The demand for protection has arisen as a result of a decline in internal real farm prices over the last few years. This decline can be traced mainly to two circumstances: an appreciation of the real exchange rate following a surge in net capital inflows and a global decline in world prices (Valdes 1993). Only the exchange rate appreciation can be related to a country's ongoing policy reforms. The decline in world food prices, by contrast, is part of a persistent secular trend toward lower real prices. Advocates of agricultural protection in Latin American countries, however, argue that the current decline in world food prices is mainly the result of protectionist policies of industrialized countries. Local farmers cannot be left alone to compete against the treasuries of rich industrial nations; they must be protected from artificially low world prices. This argument for protection receives its economic logic from the widespread belief among policymakers that world prices will turn sharply upware once the Uruguay Round accord (December 1993) of the GATT is fully implemented. The GATT accord will compel industrial countries to lower their rates of protection to farmers and to eliminate export subsidies over time. Protection is therefore only temporarily needed until food prices rise. Are the advocates of protection right? Are prices in world food markets only temporarily depressed? To find out, this paper assembles and evaluates the available evidence on trends in world food prices and on policy-induced price distortions. In addition, recent work on the likely effects of the Uruguay Round is surveyed. From this evidence, it appears that world food prices cannot reasonably be expected to change significantly in the future. To the extent that prices do change, they are likely to continue downward in real terms. Positive price changes will be limited to a few highly protected commodities, such as beef, dairy products, and to some extent sugar. If world food prices do not trend upward in the near future, however, then there is little economic logic behind schemes for protecting domestic farmers from low price Imports. In effect, such protection would only postpone adjustment and unambiguously lower economic welfare of urban consumers, an outcome to be seriously debated before policies of protection are put in place. To avoid the pressure for protection, policymakers may instead want to emphasize measures to enhance productitivity and reduce costs. It may also be useful to develop risk-diffusing instruments to manage price risks and to improve the administrative capacity to apply safeguards and countervailing duties.
Michael S. Michael - One of the best experts on this subject based on the ideXlab platform.
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Quantitative Import Restrictions and Optimal Capital Taxes Under a System of Tax Credits
Review of International Economics, 1998Co-Authors: Michael S. Michael, Panos HatzipanayotouAbstract:This paper examines the optimal capital tax policy under quantitative Import constraints, and international capital tax credits. For a small capital-Importing country, the optimal capital tax equals the foreign tax under a quota, and equals or exceeds the foreign tax under a VER. For a small capital-exporting country, the optimal policy towards capital is a zero tax under a quota, and a tax or a subsidy under a VER. Also examined are the welfare effects of capital taxes and trade liberalization, and the joint setting of the two policies, when both instruments are available to the government.
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Import Restrictions, capital taxes, and welfare
The Canadian Journal of Economics, 1993Co-Authors: Panos Hatzipanayotou, Michael S. MichaelAbstract:This paper develops a two-good, small-country, general-equilibrium model with trade Restrictions (i.e., a tariff, an Import quota, or a voluntary export restraint (VER)), inter- national capital mobility, and taxes on the rate of return to capital. Within this context it examines the price and welfare effects of capital taxes, the second-best policy towards capital in the presence of such trade Restrictions, and the welfare implications of trade liberalization in the presence of capital taxes. The analysis demonstrates, among other things, that (i) the optimal policy towards capital is a zero tax when Imports are quota constrained, and is a tax under a tariff and a subsidy under a VER when the Imported good is capital intensive; and that (ii) an asymmetry exists between trade and capital movements liberalization under the various trade regimes.
J C Schulz - One of the best experts on this subject based on the ideXlab platform.
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towards a xeno free and fully chemically defined cryopreservation medium for maintaining viability recovery and antigen specific functionality of pbmc during long term storage
Journal of Immunological Methods, 2012Co-Authors: J C Schulz, Anja Germann, Beatrice Kempkamke, Heiko Zimmermann, Hagen Von Briesen, Angela S MazzottaAbstract:Abstract Analysis of cryopreserved peripheral mononuclear cells (PBMC) is Important for evaluating new vaccines in immune based therapies and in pathogenesis studies. To ensure comparable assay results from different laboratories and points of time, collaborative research in multicenter trials needs reliable and reproducible cryopreservation protocols that maintain cell viability and functionality. Current cryomedia consist largely of fetal bovine serum (FBS), a natural mix of growth factors, cytokines, and undefined compounds. Standardized procedures are not possible, as FBS can affect the antigen-specific T-cell response, the most Important parameter in functionality assays. Also, worldwide sample exchange is complicated by the strict Import Restrictions on FBS, because of transfection risk. After establishing a serum-free cryopreservation protocol that maintains cell viability, recovery and antigen-specific T-cell response of PBMC comparably to FBS-based cryomedia (Germann et al., 2011), the aim of this study was the complete avoidance of animal proteins and products in combination with efficient cryopreservation. As long-term stability of the cryopreservation process is crucial for retrospective evaluation of samples at different points of time, PBMC were analyzed after storage for maximal four weeks and again after approximately six months. The cryopreservation efficiency of the protein-free and fully chemically defined cryomedium was comparable to FBS-medium after storage for few weeks and several months. Directly after thawing, this medium yielded viabilities over 97% and recovery values over 84%. Also, the specific T-cell functionality was preserved. Additionally, short-term and six month cryopreservation gave comparable results. The fully chemically defined medium presented here will increase standardization and reproducibility of analysis in multicenter-studies or in retrospective evaluation.
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standardized serum free cryomedia maintain peripheral blood mononuclear cell viability recovery and antigen specific t cell response compared to fetal calf serum based medium
Biopreservation and Biobanking, 2011Co-Authors: Anja Germann, J C Schulz, Beatrice Kempkamke, Heiko Zimmermann, Hagen Von BriesenAbstract:The ability to analyze cryopreserved peripheral blood mononuclear cells (PBMCs) from biobanks for antigen-specific T-cell immunity is necessary to evaluate responses to immune-based therapies. Comprehensive studies have demonstrated that the quality of frozen PBMCs is critical and the maintenance of cell viability and functionality by using appropriate cryopreservation techniques is a key to the successful outcome of assays using PBMCs. Different cryomedia additives affect cell viability. The most common additive is fetal calf serum (FCS), although it is widely known that each FCS lot has to be tested before usage to prevent nonspecific stimulation of T-cells. Also, shipping of samples containing FCS is critical because of many Import Restrictions. Often, dimethyl sulfoxide (DMSO) is added as a cryoprotectant. However, DMSO concentration has to be reduced significantly because of its toxic effect on cells at room temperature. Therefore, we have developed freezing approaches to minimize cytotoxicity of cry...
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standardized serum free cryomedia maintain peripheral blood mononuclear cell viability recovery and antigen specific t cell response compared to fetal calf serum based medium
Biopreservation and Biobanking, 2011Co-Authors: Anja Germann, J C Schulz, Beatrice Kempkamke, Heiko Zimmermann, Hagen Von BriesenAbstract:The ability to analyze cryopreserved peripheral blood mononuclear cells (PBMCs) from biobanks for antigen-specific T-cell immunity is necessary to evaluate responses to immune-based therapies. Comprehensive studies have demonstrated that the quality of frozen PBMCs is critical and the maintenance of cell viability and functionality by using appropriate cryopreservation techniques is a key to the successful outcome of assays using PBMCs. Different cryomedia additives affect cell viability. The most common additive is fetal calf serum (FCS), although it is widely known that each FCS lot has to be tested before usage to prevent nonspecific stimulation of T-cells. Also, shipping of samples containing FCS is critical because of many Import Restrictions. Often, dimethyl sulfoxide (DMSO) is added as a cryoprotectant. However, DMSO concentration has to be reduced significantly because of its toxic effect on cells at room temperature. Therefore, we have developed freezing approaches to minimize cytotoxicity of cryoprotectants and maintain T-cell functionality. We compared different additives to the widely used FCS and found bovine serum albumin fraction V to be an appropriate substitute for the potentially immune-modulating FCS. We also found that DMSO concentration can be reduced by the addition of hydroxyethyl starch. Using our serum-free cryomedia, the PBMC recovery was more than 83% and the PBMC viability was more than 98%. Also, the T-cell functionality measured by enzyme-linked immunospot (ELISpot) was optimal after cryopreservation with our new cryomedia. On the basis of our experimental results, we could finally design 2 different, fully working cryomedia that are standardized, serum free, and manufactured under GMP conditions.
