Generation of Thymic Epithelial Cell Progenitors by Mouse Embryonic Stem Cells

Abstract

Thymopoiesisis regulated by the thymic microenvironment, of which epithelial cells are the major components. Both cortical and medullary thymic epithelial cells (TECs) have been shown to arise from a common progenitor cell. Here we show for the first time that mouse embryonic stem cells (mESCs) can be selectively induced in vitro to differentiate into cells that have the phenotype of thymic epithelial progenitors (TEPs). When placed in vivo, these mESC-derived TEPs self-renew, develop into TECs, and reconstitute the normal thymic architecture. Functionally, these ESC-derived TEPs enhanced thymocyte regeneration after bone marrow transplantation and increased the number of functional naive splenic T cells. In addition to providing a model to study the molecular events underlying thymic epithelial cell development, the ability to selectively induce the development of TEPs in vitro from mESCs has important implications regarding the prevention and/or treatment of primary and secondary T-cell immunodeficiencies.

Rejuvenation of the Thymic Microenvironment by ESC-derived Thymic Epithelial Progenitors

“…In controls, transplantation of CD4 -CD8 -CD45 + immature thymocytes and/or mESC-derived EpCAM1 -cells could not form normal thymic architecture in vivo. Further analysis showed that all stages of T cells were generated in the EpCAM1 + , but not in the EpCAM1 -cell grafts (Lai & Jin, 2009). These data suggest that the mESC-derived EpCAM1 + cells can form normal thymic architecture that supports T-cell development in vivo.…”

“…We have investigated whether mouse ESCs can be selectively induced to generate TEPs in vitro. By using both threedimension embryoid body formation and two-dimension monolayer culture systems in the presence of four growth factors [fibroblast growth factor (FGF)-7, FGF-10, bone morphogenetic protein 4 and epithelial growth factor], we have shown for the first time, that murine ESCs (mESCs) can be selectively induced to differentiate into TEPs (Lai & Jin, 2009). Under these culture conditions, EpCAM1+ cells can be generated from mESCs (Lai & Jin, 2009).…”

“…By using both threedimension embryoid body formation and two-dimension monolayer culture systems in the presence of four growth factors [fibroblast growth factor (FGF)-7, FGF-10, bone morphogenetic protein 4 and epithelial growth factor], we have shown for the first time, that murine ESCs (mESCs) can be selectively induced to differentiate into TEPs (Lai & Jin, 2009). Under these culture conditions, EpCAM1+ cells can be generated from mESCs (Lai & Jin, 2009). Importantly, most of the mESC-derived EpCAM1 + cells co-expressed K5 and K8, a phenotype of TEPs (Gordon et al, 2004;Bleul., 2006;Rossi et al, 2006).…”

“…We found that discrete K8 + K5 -cortical and K8 -K5 + medullary epithelial areas were present in the grafts. Some of the cells co-expressed K8 and K5, suggesting they were residual, or self-replicating, TEPs (Lai & Jin, 2009). In controls, transplantation of CD4 -CD8 -CD45 + immature thymocytes and/or mESC-derived EpCAM1 -cells could not form normal thymic architecture in vivo.…”

“…To further confirm that the mESC-derived TEPs can give rise to both cTECs and mTECs in vivo, we injected a single EGFP + EpCAM1 + cell into irradiated thymic fragments that were then implanted under the kidney capsule of syngeneic mice. We examined the grafts six weeks later and found that EGFP + EpCAM1 + -derived cells were comprised of K5 + K8 + TEPs, K5 -K8 + cTECs, and K5 + K8 -mTECs (Lai & Jin, 2009). These results further suggest the mESCderived TEPs are able to differentiate into both types of TECs and to self-renew in vivo.…”