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Introduction: In-vitro models of lymphocyte differentiation
seminars in IMMUNOLOGY,
Introduction:
Vol 7, 1995: p129
In-vitro models of lymphocyte
differentiation
Ana Cumano
The rapid progress in culture conditions allowing B-cell differentiation, contrasts with the absence of liquid culture systems that effectively support Tcell lymphopoiesis. The requirement for different signals delivered by different stromal cells might be evoked to explain the failure of thymic stromal cell lines to sustain Tcell lymphopoiesis. Particular three dimensional constraints for this development have been evoked and fetal thymic organ cultures remain the most effective system to provide the conditions for T-cell differentiation in vitro from hematopoietic cells. In this issue Anderson and collaborators review the latest advances in Tcell differentiation in organ culture. Finally, new culture conditions are being estab lished by Nishikawa and collaborators where defined proteins are being used to support B-cell develop ment, in serum-free conditions. This paper well illustrates some of the limitations of in-vitro systems for primary cell differentiation; cells growing under different conditions will express different genes and surface molecules. Our knowledge of the microenvironment in primary hematopoietic organs and local concentrations of interleukins is limited and it is possible that some soluble factors that are commonly used in vitro are not the molecules responsible for the observed effects in viva or that they are present at different concentrations. This situation might create artifacts in cell surface molecules and gene expression, difficult to control to this point. The last contribution to this volume from Nakano describes exciting advances in in-vitro conditions for Cell differentiation from embryonic stem cells that could welI become a promising well-controlled differentiation system in the future.
THE LAST 10 years saw a considerable
progress in the establishment of culture systems that support in-vitro lymphocyte growth and differentiation. Murine B-cell development is now possible, in culture, starting from a multipotent hematopoietic cell all the way to the stage of mature B lymphocytes that can differentiate into immunoglobulin-secreting plasma cells, as discussed by Godin et al. The environmental influences surrounding these precursors that apparently expand without differentiation, before fetal liver hematopoiesis, will provide an interesting insight on ligand interaction required for self-renewability. The establishment of stromal cell-free cultures defined the growth factor requirements for B-cell development from uncommitted precursors, before responsiveness to interleukin 7 is acquired, as discussed by Kee and Paige. At this stage, commitment into the B-lineage occurs and it is now possible to determine the influence of interleukin-receptor interactions in this process. Committed B-cell precursors express B-cell specific molecules, h5 and V-pre-B that together with the productively rearranged immunoglobulin heavy-chain constitute the pre-B cell receptor. The role of this molecule is still controversial but its presence is fundamental in the differentiation process. In vivo regulation of B-cell development from the beginning of immunoglobulin gene rearrangement until the mature B-cell stage is reviewed by Melchers and collaborators. Interestingly, human B-cell lymphopoiesis in vitro has been more difficult to obtain despite the fact that the same growth factors that act in mouse cells have been isolated in man; Ptault describes some of the approaches used to study lymphopoiesis, in the human system.
Institut Pasteur 28 Rue du Lh Roux, 75724 Pa*, France 01995 Academic Pms Ltd
Cedex 15,
129
Introduction:
Vol 7, 1995: p129
In-vitro models of lymphocyte
differentiation
Ana Cumano
The rapid progress in culture conditions allowing B-cell differentiation, contrasts with the absence of liquid culture systems that effectively support Tcell lymphopoiesis. The requirement for different signals delivered by different stromal cells might be evoked to explain the failure of thymic stromal cell lines to sustain Tcell lymphopoiesis. Particular three dimensional constraints for this development have been evoked and fetal thymic organ cultures remain the most effective system to provide the conditions for T-cell differentiation in vitro from hematopoietic cells. In this issue Anderson and collaborators review the latest advances in Tcell differentiation in organ culture. Finally, new culture conditions are being estab lished by Nishikawa and collaborators where defined proteins are being used to support B-cell develop ment, in serum-free conditions. This paper well illustrates some of the limitations of in-vitro systems for primary cell differentiation; cells growing under different conditions will express different genes and surface molecules. Our knowledge of the microenvironment in primary hematopoietic organs and local concentrations of interleukins is limited and it is possible that some soluble factors that are commonly used in vitro are not the molecules responsible for the observed effects in viva or that they are present at different concentrations. This situation might create artifacts in cell surface molecules and gene expression, difficult to control to this point. The last contribution to this volume from Nakano describes exciting advances in in-vitro conditions for Cell differentiation from embryonic stem cells that could welI become a promising well-controlled differentiation system in the future.
THE LAST 10 years saw a considerable
progress in the establishment of culture systems that support in-vitro lymphocyte growth and differentiation. Murine B-cell development is now possible, in culture, starting from a multipotent hematopoietic cell all the way to the stage of mature B lymphocytes that can differentiate into immunoglobulin-secreting plasma cells, as discussed by Godin et al. The environmental influences surrounding these precursors that apparently expand without differentiation, before fetal liver hematopoiesis, will provide an interesting insight on ligand interaction required for self-renewability. The establishment of stromal cell-free cultures defined the growth factor requirements for B-cell development from uncommitted precursors, before responsiveness to interleukin 7 is acquired, as discussed by Kee and Paige. At this stage, commitment into the B-lineage occurs and it is now possible to determine the influence of interleukin-receptor interactions in this process. Committed B-cell precursors express B-cell specific molecules, h5 and V-pre-B that together with the productively rearranged immunoglobulin heavy-chain constitute the pre-B cell receptor. The role of this molecule is still controversial but its presence is fundamental in the differentiation process. In vivo regulation of B-cell development from the beginning of immunoglobulin gene rearrangement until the mature B-cell stage is reviewed by Melchers and collaborators. Interestingly, human B-cell lymphopoiesis in vitro has been more difficult to obtain despite the fact that the same growth factors that act in mouse cells have been isolated in man; Ptault describes some of the approaches used to study lymphopoiesis, in the human system.
Institut Pasteur 28 Rue du Lh Roux, 75724 Pa*, France 01995 Academic Pms Ltd
Cedex 15,
129