Development of a method of thymocyte differentiation of bone marrow-enriched CD34+CD38- cells in postnatal allogeneic cultured thymic epithelia to evaluate immunodeficiency disorders

Modulatory role of thymosin-alpha-1 in normal bone-marrow haematopoiesis and its effect on myelosuppression in T-cell lymphoma bearing mice

In continuation with the earlier and ongoing studies on Thymosin-alpha-1 (Talpha1) exerting its immunomodulatory effects on various components of the immune system including T-cells, NK-cells, blood lymphocytes and macrophages, the role of Talpha1 in normal bone-marrow haematopoiesis has been investigated in the present study. The haematopoietic alterations associated with the growth of murine T-cell lymphoma, Dalton's Lymphoma (DL) and subsequently its restoration by Talpha1 was also investigated. It is observed that the non-adherent bone-marrow cells from normal mice (N-BMCs) exhibited enhanced proliferation on in vitro treatment with Talpha1 (dose range of 1-100 ng/ml) with maximal response at 100 ng/ml of Talpha1. In vitro stimulation with 100 ng/ml of Talpha1 also resulted in increased myeloid colony formation, as manifested by the rise in total number of colonies, frequency of the individual colony types and their size. This response was further upregulated in the presence of various colony stimulating factors (CSFs) like MCSF, GMCSF, GCSF and IL-3. Similarly, in vivo administration of Talpha1 (a single intraperitoneal injection of 10 microg per mouse) to normal mice also resulted in enhanced proliferation and colony formation by BMCs as compared with BMCs obtained from untreated mice. On the contrary, the progressive growth of T-cell lymphoma in mice led to suppressed myelogenesis, with marked reduction in the total colony numbers and their size. The BMCs from DL-bearing mice (DL-BMCs) displayed a preferential lineage-restricted differentiation towards the granulocytic-type colonies with maximum numbers of CFU-Gs and CFU-GMs, followed by CFU-Ms. However, incubation of DL-BMCs with 100 ng/ml of Talpha1, in vitro restored their suppressed proliferation and colony forming ability (CFA) with significantly enhanced total number of colonies and individual colony types, which further increased in the presence of CSFs. In vivo studies with BMCs from DL-bearing mice treated with single intraperitoneal injection of 10 microg Talpha1/mouse also resulted in significant enhancement in their proliferative as well as colony forming ability in comparison to that of untreated DL-mice. The present observations suggest that Talpha1 can positively modulate the haematopoietic functions of normal murine BMCs, in addition to its myelorestorative role in tumour-bearing mice showing suppressed myelopoiesis.

Inhibition of thymopoiesis of CD34+ cell maturation by HIV-1 in an in vitro CD34+ cell and thymic epithelial organ culture model

The mechanisms by which HIV-1 affects thymopoiesis were determined by preincubating CD34+ cells or cultured thymic epithelial (CTE) cells with lymphotropic (T-) and monotropic (M-) strains of HIV-1 in an in vitro CTE organ and CD34+ cell coculture model that allows for analysis of development of thymocytes and mature T cells. When purified CD34+ cells were precultured with either T- or M-tropic strains of HIV-1, thymopoiesis was impaired in a two-week coculture manifested by decreased cell number of thymocytes generated. However, the percentages of thymocyte subpopulations were comparable to control uninfected cocultures. Furthermore, HIV infection of thymocytes was predominantly observed in the CD44+CD3- population. However, in a four-week coculture experiment, HIV infection and depletion of more mature thymocytes were also observed. When CTE cells were preincubated with T- and M-tropic strains of HIV before addition of CD34+ cells, the number of thymocytes and subpopulations of thymocytes at early and later stages of maturation were markedly decreased. Furthermore, CD34+ and CD44+CD3- cells become HIV-infected. In summary, HIV-1 infection inhibited thymocyte maturation at early stages of thymocyte maturation CD44+CD25-CD3-. In addition, HIV also depleted later stages of CD4+ thymocyte subpopulations.

Thymosin-alpha1 stimulates maturation of CD34+ stem cells into CD3+4+ cells in an in vitro thymic epithelia organ coculture model

The effect of thymosin-alpha1 on thymopoiesis is largely unknown. Thymosin is found in the cortical and medullary thymic epithelia, as well as in nurse cells; thus, it is hypothesized that thymosin may affect both early and late stage of thymocyte maturation. In this study, the effect of thymosin-alpha1 on thymopoiesis was determined by coculturing in vitro CD34+ stem cells (SC) with allogeneic cultured thymic epithelia fragments (CTEF) for 1-4 weeks and analyzing T-cell maturation by flow cytometry. Thymosin-alpha1 significantly enhanced the cell number (e.g., proliferation) of mononuclear cells obtained at 2 and 4 weeks of the SC-CTEF cocultures (P < 0.01 and < 0.05, respectively). In particular, thymosin-alpha1 stimulated expression of CD3+ cells at 3 and 4 weeks (P < 0.05). The predominant subpopulation increased by thymosin stimulation was single positive mature CD4+ cells, which was confirmed to occur within the SC-CTEF thymic organ tissue by laser confocal immunofluorescence microscopy. Thymosin stimulation tended to enhance IL-7 synthesis, critical cytokine in the maturation of thymocytes. In summary, this is the first study to demonstrate that thymosin-alpha1 enhanced thymopoiesis of CD34+ stem cells in humans using an in vitro model of differentiation using stem cells and cultured thymic epithelial fragments cocultures. Furthermore, the thymosin significantly increased expression of CD3+4+ T cells.