CD90 Marks a Mesenchymal Program in Human Thymic Epithelial Cells In Vitro and In Vivo

Abstract

Thymic epithelium is critical for the structural integrity of the thymus and for T cell development. Within the fully formed thymus, large numbers of hematopoietic cells shape the thymic epithelium into a scaffold-like structure which bears little similarity to classical epithelial layers, such as those observed in the skin, intestine or pancreas. Here, we show that human thymic epithelial cells (TECs) possess an epithelial identity that also incorporates the expression of mesenchymal cell associated genes, whose expression levels vary between medullary and cortical TECs (m/cTECs). Using pluripotent stem cell (PSC) differentiation systems, we identified a unique population of cells that co-expressed the master TEC transcription factor FOXN1, as well as the epithelial associated marker EPCAM and the mesenchymal associated gene CD90. Using the same serum free culture conditions, we also observed co-expression of EPCAM and CD90 on cultured TECs derived from neonatal human thymus in vitro. Single cell RNA-sequencing revealed these cultured TECs possessed an immature mTEC phenotype and expressed epithelial and mesenchymal associated genes, such as EPCAM, CLDN4, CD90 and COL1A1. Importantly, flow cytometry and single cell RNA-sequencing analysis further confirmed the presence of an EPCAM+CD90+ population in the CD45- fraction of neonatal human thymic stromal cells in vivo. Using the human thymus cell atlas, we found that cTECs displayed more pronounced mesenchymal characteristics than mTECs during embryonic development. Collectively, these results suggest human TECs possess a hybrid gene expression program comprising both epithelial and mesenchymal elements, and provide a basis for the further exploration of thymus development from primary tissues and from the in vitro differentiation of PSCs.

Human pluripotent stem cell-derived macrophages host Mycobacterium abscessus infection

“…In distinction to previous methods that often include multiple myeloid growth factors, such as interleukin (IL) 1, IL3, IL6, granulocyte-macrophage colony stimulating factor (GM-CSF), and tissue necrosis factor ( Lyadova et al., 2021 ), we found that using M-CSF as the sole myeloid factor was sufficient to efficiently induce functional macrophages from the endothelial cell stage onward, and it maintained hPSC-macrophages over a prolonged period of in vitro culture ( Figure S2 ). An optimized version of the basal medium free of albumin also enabled the derivation of endodermal cell lineages from hPSCs and primary human tissue ( Sun et al., 2022 ), potentially facilitating co-culture studies. Our streamlined differentiation protocol efficiently generated macrophages that resembled those created with more complex methods (as reviewed in Lyadova et al., 2021 ), forming a robust platform upon which to undertake functional studies.…”

Biomedical Application of Decellularized Scaffolds

“…Thymic regeneration is an effective way to restore the body's adaptive immune system in order to rebuild an extensive library of T cells (Figure 2). 215,216 Cochlea mainly has the functions of sound transmission and sensory function. More and more people suffer from sensorineural hearing loss (SNHL) due to the aging of the population, long-term exposure to noise, genetics, diseases, drugs, trauma, and other factors.…”

“…Thymic regeneration is an effective way to restore the body’s adaptive immune system in order to rebuild an extensive library of T cells (Figure ). , Tajima et al decellularized the thymus by freeze–thaw cycles and scale. Studies have shown that decellularized thymic scaffolds can effectively promote the homing of bone marrow-derived lymphocyte progenitor cells and support the development of multiple functional T cells …”

Mesenchymal stem cells reverse thymus aging by reprogramming the DNA methylation of thymic epithelial cells

“…The thymus is the main lymphoid organ and is composed of thymic cells and thymic stromal cells. Thymic stromal cells include thymic epithelial cells (TECs), fibroblasts, dendritic cells and endothelial cells [ 1 , 2 ]. TECs are composed of cortical TECs (cTECs) and medullary TECs (mTECs).…”