In-vitro models of stroma-dependent lymphopoiesis

Bone Marrow-Derived Stem Cell Populations Are Differentially Regulated by Thyroid or/and Ovarian Hormone Loss

Bone marrow-derived stem cells (BMDSCs) play an essential role in organ repair and regeneration. The molecular mechanisms by which hormones control BMDSCs proliferation and differentiation are unclear. Our aim in this study was to investigate how a lack of ovarian or/and thyroid hormones affects stem cell number in bone marrow lineage. To examine the effect of thyroid or/and ovarian hormones on the proliferative activity of BMDSCs, we removed the thyroid or/and the ovaries of adult female rats. An absence of ovarian and thyroid hormones was confirmed by Pap staining and Thyroid Stimulating Hormone (TSH) measurement, respectively. To obtain the stem cells from the bone marrow, we punctured the iliac crest, and aspirated and isolated cells by using a density gradient. Specific markers were used by cytometry to identify the different BMDSCs types: endothelial progenitor cells (EPCs), precursor B cells/pro-B cells, and mesenchymal stem cells (MSCs). Interestingly, our results showed that hypothyroidism caused a significant increase in the percentage of EPCs, whereas a lack of ovarian hormones significantly increased the precursor B cells/pro-B cells. Moreover, the removal of both glands led to increased MSCs. In conclusion, both ovarian and thyroid hormones appear to have key and diverse roles in regulating the proliferation of cells populations of the bone marrow.

Immunology of normal pregnancy

Since Medawar's initial contemplations in 1953 on the mechanisms of immune evasion allowing for the survival of the allogeneic conceptus in an immunologically competent mother, physicians and immunologists alike have struggled to understand the immunological paradox of pregnancy. Ultimately, our attempts to define the immunology of normal pregnancy have broadened our appreciation of the myriad mechanisms at play that enable the promotion of implantation and maintenance of pregnancy. In this review, we summarise what is known regarding the immunology of normal pregnancy, with special emphasis on the relation to common disorders of pregnancy.

Bone marrow microenvironmental changes in aged mice compromise V(D)J recombinase activity and B cell generation

B cell generation and immunoglobulin (Ig) diversity in mice is compromised with aging. Our recent work sought to understand mechanism(s) that contribute to reduced B cell production in aged mice. Using in vivo labeling, we found that reduction in marrow pre-B cells reflects increased attrition during passage from the pro-B to pre-B cell pool. Analyses of reciprocal bone marrow (BM) chimeras reveal that the production rates of pre-B cells are controlled primarily by microenvironmental factors, rather than intrinsic events. To understand changes in pro-B cells that could diminish production of pre-B cells, we evaluated rag2 expression and V(D)J recombinase activity in pro-B cells at the single cell level. The percentage of pro-B cells that express rag2 is reduced in aged mice and is correlated with both a loss of V(D)J recombinase activity in pro-B cells and reduced numbers of pre-B cells. Reciprocal BM chimeras revealed that the aged microenvironment also determines rag2 expression and recombinase activity in pro-B cells. These observations suggest that extrinsic factors in the BM that decline with age are largely responsible for less efficient V(D)J recombination in pro-B cells and diminished progression to the pre-B cell stage. These extrinsic factors may include cytokines and chemokines derived from BM stromal cells that are essential to the development of B cell precursors. The changes during aging within the BM hematopoietic microenvironment most likely are linked to the physiology of aging bone. Bone degrades with age (osteoporosis) due to decreased formation of new bone by osteoblasts. Marrow stem cells (MSC) are considered the progenitor of both adipocytes, osteoblasts and hematopoietic stromal cells and a controlled reciprocal regulation exists of osteoblast versus adipocyte differentiation; with age adipocytes increase, and osteoblast decrease. It is possible that stromal cell generation from MSC is compromised during aging. Currently, understanding of BM microenvironmental factors that regulate rag gene expression is very limited. However, as early progenitors differentiate, it is increasing clear that a limited set of transcription factors (e.g. ikaros, PU.1, E2A, EBF, pax5) regulate B-lineage specific genes, and that expression and stability of these factors is responsive to the microenvironment. Current and future work by several groups will strive to understand mechanisms that regulate these factors and how aging impacts these regulatory circuits.

Involvement of CD44 variant isoform v10 in progenitor cell adhesion and maturation

CD44 has been described repeatedly to be involved in hematopoiesis. Here, we addressed the question of functional activity of CD44 variant isoform v10 (CD44v10) in progenitor cell maturation by in vivo and in vitro blocking studies with a monoclonal antibody and a receptor globulin. We became interested in this question by the observation that CD44v10 is expressed, although at a low level, on a subpopulation of bone marrow cells. Flow cytometry revealed that 15%-20% of hematopoietic cells in the fetal liver and 25%-35% of bone marrow cells in adult mice were CD44v10 positive. The majority of CD44v10+ cells was HSA+/J11d+ and CD43+. CD44v10 was not detected on CD4+, CD8+, IgM+, or IgD+ cells. A CD44v10 receptor globulin did not bind to hematopoietic progenitor cells, but to stromal elements. The CD44v10-CD44v10 ligand interaction had a major impact on the adhesion of progenitor cells to stromal elements. When healthy animals received repeated injections of either anti CD44v10 or the CD44v10 receptor globulin, committed progenitors were mobilized and significantly augmented numbers were recovered in the spleen and the peripheral blood. Furthermore, the CD44v10-CD44v10 ligand interaction, which had no impact on progenitor expansion, influenced progenitor maturation, particularly of the B-cell lineage. Although the nature of the CD44v10 ligand remains to be explored, the supportive role of CD44v10 in progenitor maturation and, importantly, the efficient mobilization of progenitor cells by anti-CD44v10 and a CD44v10 receptor globulin could be of clinical benefit in peripheral blood stem cell transplantation.

Thymus-independent T-cell differentiation in vitro

The generation of large quantities of novel human T-cell clones ex vivo would make a wide range of gene- and immuno-therapies for tumours and viral infections possible. Several techniques have been described to generate, in vitro and in vivo (using xenogenic hosts), mature T cells from fetal-neonatal and adult human CD34+ cells. All these techniques are cumbersome and cannot be easily translated into clinical protocols because they involve co-cultivation of CD34+ cells with thymic fragments from either human or murine fetuses. We report that the mononuclear cells of human cord blood contain a cell population that supports the differentiation of CD34+ cells into CD4+ or CD8+ naive T cells in serum-deprived cultures stimulated with stem cell factor and interleukin 7. CD4+ or CD8+ CD45RA+ TCRalphabeta+ T cells were continuously produced in vitro over a period of 20 d under these conditions. The generation of T cells in these cultures was a dynamic process and clones of T cells expressing new T-cell receptor beta-chain rearrangements were generated over time. These results pave the way for the development of very simple culture conditions for ex-vivo production of naive helper or cytotoxic T cells which could be very useful for gene- and immuno-therapy of human diseases.

Use of explant technology in the study of in vitro immune responses

The establishment of in vitro culture systems provides an accessible means to study events within the immune system. In contrast to either dispersed suspension or two-dimensional monolayer culture, the explantation of tissue fragments under organ culture conditions is, to date, the only method which allows essential three-dimensional cellular interactions to be maintained under conditions which permit controlled experimental manipulation in vitro. Recent modifications of explant technology, particularly within the area of fetal thymic organ culture, now allow the controlled reassociation of defined cellular subsets and manipulation of gene expression, under conditions where the functioning of both lymphoid and stromal cell types closely resembles that in vivo.

Gene transfer into human haematopoietic stem cells

This review of gene transfer to the human haematopoietic system (1) describes the different vectors used to transduce genes into stem cells, emphasizing retroviruses that have already shown their efficiency and innocuousness; (2) analyses which human cells should be targeted to ensure long-lasting engraftment; (3) indicates the different means of infecting these targets ex vivo, underscoring the role of cytokines and stromal cells; (4) recollects the methods used to evaluate transduction efficiency; and (5) gathers the results of clinical trials recently performed using human stem cells. The major conclusions are that good practice can ensure safe gene delivery to human beings and that long-lasting, multilineal precursors can be transduced using retroviral vectors of marker genes or genes of therapeutic interest. However, transduction rates appear to remain relatively low, which should stimulate ongoing research on both vector design and means of ex vivo gene transfer.